title:
An exploratory study of the hard X-ray variability properties of PG
  quasars with RXTE

abstract:
  We have monitored with the RXTE PCA the variability pattern of the 2-20 keV
flux in four PG quasars (QSOs) from the Laor et al. (1994) sample. Six
observations of each target at regular intervals of 1 day were performed. The
sample comprises objects with extreme values of Balmer line width (and hence
soft X-ray steepness) and spans about one order of magnitude in luminosity. The
most robust result is that the variability amplitude decreases as energy
increases. Several options for a possible ultimate driver of the soft and hard
X-ray variability, such as the influx rate of Comptonizing relativistic
particles, instabilities in the accretion flow or the number of X-ray active
sites, are consistent with our results.


title:
Evidence for a high accretion rate as the defining parameter of
  Narrow-Line Seyfert 1 galaxies

abstract:
  X-ray spectral features which are unusually strong in many Narrow-Line
Seyfert galaxies are found to be consistent with reflection from strongly
ionized matter, providing further evidence of a high accretion rate in these
objects and offering a unique signature of that key parameter in future
observations.


title: Slim Disk Model for Narrow-Line Seyfert 1 Galaxies

abstract:
  We argue that both the extreme soft X-ray excess and the large-amplitude
variability of Narrow-Line Seyfert 1 galaxies (NLS1s) can be explained in the
framework of the slim disk model. When the disk luminosity approaches the
Eddington luminosity, the disk becomes a slim disk, exhibiting a multi-color
blackbody spectrum with a maximum temperature, T(bb), of about 0.2 (M/1e5 solar
masses)e(-1/4) keV, and size of the X-ray emitting region, r(bb), of about R(S)
(the Schwarzschild radius). Furthermore, magnetic energy can be amplified up to
a level exceeding radiation energy emitted from the disk, causing substantial
variability in X-rays by consecutive magnetic flares.


title: Disk/corona model: The transition to ADAF

abstract:
  We propose a model of the accretion flow onto a black hole consisting of the
accretion disk with an accreting two-temperature corona. The model is based on
assumptions about the radiative and conductive energy exchange between the two
phases and the pressure equilibrium. The complete model is determined by the
mass, the accretion rate, and the viscosity parameter. We present the radial
dependencies of parameters of such a two-phase flow, with advection in the
corona and the disk/corona mass exchange due to evaporation/condensation
included, and we determine the transition radius from a two-phase disk/corona
accretion to a single-phase optically thin flow (ADAF) in the innermost part of
the disk as a function of accretion rate. We identify the NLS1 galaxies with
objects accreting at a rate close to the Eddington accretion rate. The strong
variability of these objects may be related to the limit cycle behaviour
expected in this luminosity range, as the disk, unstable due to the dominance
by the radiation pressure, oscillates between the two stable branches: the
advection-dominated optically thick branch and the evaporation branch.


title: Are Narrow-Line Seyfert 1s Really Strange?

abstract:
  Narrow-Line Seyfert 1s (NLS1s) are generally considered to be strange Active
Galactic Nuclei (AGNs). Surprisingly, this makes them very useful for
constraining models. I discuss what happens when one attempts to qualitatively
fit the NLS1 phenomenon using the stellar wind model for AGN line emission
(e.g., Kazanas 1989). The simplest way of narrowing profile bases of this model
to the widths observed in NLS1s is probably to lower the mass of the
supermassive black hole. In a flux-limited and redshift-limited data set, this
is indeed similar to increasing L/L_Edd. Because the broad line region (BLR) of
the stellar line emission model scales with the tidal radius of the stars, this
model predicts maximal BLR velocities of FWZI proportional (L/L_Edd)^(-1/3).
This implies that the black holes of NLS1s are approximately 3^3=27 times less
massive than those in other Seyfert 1s if the stellar line emission model is
correct. Another consequence of increasing L/L_Edd in this model is that it
results in an increase in the wind edge densities. NLS1 spectra appear to
support this result as well. Even the collateral features of NLS1s, such as the
line asymmetries and continuum properties, appear to be easily explained within
the context of this model. For better or worse, if the stellar wind line
emission is correct, NLS1s are not much stranger than other AGNs.


title: X-Ray Variability of NLS1s and BLS1s

abstract:
  Evenly-sampled hard X-ray monitoring was obtained with RXTE for one NLS1 (Akn
564) and four BLS1s. The variability amplitude of the NLS1 was no larger than
the mean of the BLS1s, and the NLS1 showed stronger variability in the harder
portion of the RXTE band, while the BLS1s were more strongly variable in the
relatively soft part of the band. This contribution discusses possible
explanations for these surprising results, including possible calibration
errors or systematic differences between long and short time scale variability
in NLS1s and BLS1s.


title:
Spectral Energy Distributions of Active Galactic Nuclei from an
  Accretion Disk with Advective Coronal Flow

abstract:
  To explain the broad-band spectral energy distributions (SED) of Seyfert
nuclei and QSOs, we study the emission spectrum emerging from a vertical
disk-corona structure composed of a two-temperature plasma by solving
hydrostatic equilibrium and radiative transfer self-consistently. Our model can
nicely reproduce the soft X-ray excess with alpha (L_frequency proportional to
the frequency to the power of -alpha) of about 1.5 and the hard tail extending
to about 50 keV with alpha about 0.5. The different spectral slopes (alpha
about 1.5 below 2 keV and about 0.5 above) are the results of different
emission mechanisms: unsaturated Comptonization in the former and a combination
of Comptonization, bremsstrahlung, and reflection of the coronal radiation at
the disk-corona boundary in the latter.


title:
How Do We See the Nuclear Region (r < 0.1 pc) of Narrow-Line Seyfert 1
  Galaxies?

abstract:
  We propose two statistical tests to investigate how we see the nuclear region
(r < 0.1 pc) of Narrow-Line Seyfert 1 galaxies (NLS1s). 1) The high-ionization
nuclear emission-line region (HINER) test: Seyfert 1 galaxies (S1s) have
systematically higher flux ratios of [Fe VII] lambda 6087 to [O III] lambda
5007 than Seyfert 2 galaxies (S2s). This is interpreted in that a significant
part of the [Fe VII] lambda 6087 emission arises from the inner walls of dusty
tori that cannot be seen in S2s (Murayama & Taniguchi 1998a,b). 2) The
mid-infrared test: S1s have systematically higher flux ratios of the L band
(3.5 micrometer) to the IRAS 25 micrometer band than S2s. This is also
interpreted in that a significant part of the L band emission arises from the
inner walls of dusty tori, because the tori are optically thick enough to
absorb the L band emission if the tori are viewed nearly edge on (Murayama et
al. 2000). Applying these tests to a sample of NLS1s, we have found that the
NLS1s possibly have nearly the same properties as S1s.


title: Statistical Properties of Narrow-Line Seyfert 1 galaxies

abstract:
  The number of publications considering Narrow-Line Seyfert 1 galaxies has
increased dramatically in recent years. Especially after the launch of the
X-ray missions ROSAT and ASCA, Narrow-Line Seyfert 1s have become very popular.
In these proceedings I will give an overview of how they are distributed over
the electromagnetic spectrum. I will describe what we know about them at radio,
infrared, optical, and X-ray bands, and how they differ and how they are
similar to Broad-Line Seyfert 1s. Finally I will introduce a method to find
them with high probability.


title:
Observational Similarities and Potential Connections Between Luminous
  Ultrasoft NLS1s and BALQSOs

abstract:
  Luminous ultrasoft NLS1s and low-ionization BALQSOs share many properties,
and they both represent important extremes of the active galaxy phenomenon. We
briefly discuss their observational similarities as well as potential physical
connections between them, concentrating on the X-ray point of view. We present
several ways by which potential connections might be further tested.


title: NLS1s and Sy1s: A comparison of ionized X-ray absorber properties

abstract:
  The first results from a systematic study of warm absorbers in NLS1s using
BeppoSAX public archive data are presented here. We confirm ASCA results
showing that a warm absorber, as modeled by two oxygen K-shell absorption
edges, is less frequent in NLS1s than in broad line (BL) Sy1s (about 20 per
cent versus about 50 per cent). However, our study suggests that the ionization
state of NLS1s is not lower than that of BLS1s, as opposed to the ASCA-based
results. The soft excess temperatures of our sample, when fitted with blackbody
emission models, lie within a small range of values (about 0.02-0.15 keV in the
rest frame) with no marked dependence on source luminosity. This is in
agreement with ASCA-based findings for NLS1s and early results from IUE-ROSAT
BL Sy1 observations.


title: X-ray Continuum Slope and X-ray Spectral Features in NLS1 Galaxies

abstract:
  The idea that some of the unusual features in the X-ray spectra of
Narrow-Line Seyfert 1 galaxies (NLS1s) are due to the steep X-ray continuum is
tested by comparing photoionization model calculations with various observed
properties of Seyfert 1 galaxies. A meaningful comparison must involve the
careful use of the right X-ray ionization parameter, designated here U(oxygen).
When this is done, it is found that the strength of the continuum absorption
features is insensitive to the exact slope of the 0.1-50 keV continuum. It is
also shown that the complex of iron L-shell lines near 1 keV can produce strong
absorption and emission features, depending on the gas distribution and line
widths. While this may explain some unusual X-ray features in AGN, the
predicted intensity of the features do not distinguish NLS1 from broader line
sources. Finally, acceleration of highly ionized gas, by X-ray radiation
pressure, is also not sensitive to the exact slope of the X-ray continuum.


title: Variability of NGC 4051 and the Nature of Narrow-Line Seyfert 1 Galaxies

abstract:
  We report on a three-year program of coordinated X-ray and optical monitoring
of the Narrow-Line Seyfert 1 galaxy NGC 4051. The rapid continuum variations
observed in the X-ray spectra are not detected in the optical, although the
X-ray and optical continuum fluxes are correlated on time scales of many weeks
and longer. Variations in the flux of the broad H-beta line are found to lag
behind the optical continuum variations by approximately 6 days (with an
uncertainty of 2-3 days), and combining this with the line width yields a
virial mass estimate of about 1.1e6 solar masses, at the very low end of the
distribution of AGN masses measured by line reverberation. Strong variability
of He II lambda 4686 is also detected, and the response time measured is
similar to that of H-beta, but with a much larger uncertainty. The He II lambda
4686 line is almost five times broader than H-beta, and it is strongly blueward
asymmetric, as are the high-ionization UV lines recorded in archive spectra of
NGC 4051. The data are consistent with the Balmer lines arising in a
low-inclination (nearly face-on) disk-like configuration, and the
high-ionization lines arising in an outflowing wind, of which we observe
preferentially the near side. During the third year of monitoring, both the
X-ray continuum and the He II lambda 4686 line went into extremely low states,
although the optical continuum and the H-beta broad line were both still
present and variable. We suggest that the inner part of the accretion disk may
have gone into an advection-dominated state, yielding little radiation from the
hotter inner disk.


title: Optical, UV, and X-ray Clues to the Nature of Narrow Line AGNs

abstract:
  AGNs with narrow Balmer lines show various extreme properties. In particular,
rapid X-ray variability, steep X-ray spectra, peculiar optical and UV line
ratios, and possibly peculiar line profiles. Since all these phenomena occur
together they are likely to be related to one specific underlying physical
parameter. I review recent evidence, based on HST imaging of low z quasars,
which suggests that the H-beta line width and continuum luminosity of quasars
provide a reasonably accurate estimate of the black hole mass. This implies
that narrow-line AGN have relatively low black hole masses, and thus high
L/L_Edd, as independently suggested based on their steep X-ray spectra. I
present additional evidence suggesting that the X-ray variability and the radio
loudness are primarily driven by the black hole mass. The high mass inflow rate
into the core of narrow-line AGNs may produce a denser and more enriched BLR, a
high column radiation pressure driven outflow, and a smaller illumination angle
for the NLR, as suggested by the observed emission line properties. Narrow-line
AGNs may thus provide important clues for understanding the rich overall
phenomenology of AGNs.


title: FOS Observations of Four NLS1s

abstract:
  Ultraviolet through optical spectroscopy of four NLS1s shows strong
absorption features in the high-ionization UV resonance lines such as C IV, N
V, and Si IV. Mg II is not absorbed. The absorption could originate in the warm
absorber.


title: H-beta Line Width and the UV-X-ray Spectra of Luminous AGN

abstract:
  The width of the broad H-beta emission line is the primary defining
characteristic of the NLS1 class. This parameter is also an important component
of Boroson and Green's optical Eigenvector 1 (EV1), which links steeper soft
X-ray spectra with narrower H-beta emission, stronger H-beta blue wing,
stronger optical Fe II emission, and weaker [O III] lambda 5007. Potentially,
EV1 represents a fundamental physical process linking the dynamics of fueling
and outflow with the accretion rate. We attempted to understand these
relationships by extending the optical spectra into the UV for a sample of 22
QSOs with high quality soft-X-ray spectra, and discovered a whole new set of UV
relationships that suggest that high accretion rates are linked to dense gas
and perhaps nuclear starbursts. While it has been argued that narrow (BLR)
H-beta means low Black Hole mass in luminous NLS1s, the C IV, lambda 1549 and
Ly alpha emission lines are broader, perhaps the result of outflows driven by
their high Eddington accretion rates. We present some new trends of optical-UV
with X-ray spectral energy distributions. Steeper X-ray spectra appear
associated with stronger UV relative to optical continua, but the presence of
strong UV absorption lines is associated with depressed soft X-rays and redder
optical-UV continua.


title: Molecular Gas and Star Formation in the Host Galaxy of I Zw 1

abstract:
  A recent analysis of high angular resolution NIR imaging and spectroscopic
data in conjunction with Plateau de Bure interferometric mm-line observations
indicate the presence of a circum-nuclear starburst ring of about 1.5 arcsec
(1.5 kpc) diameter in I Zw 1. High angular resolution NIR imaging, using the
MPE SHARP camera at the ESO NTT, HST V-band images, as well as NIR spectroscopy
with MPE 3D provide an improved analysis of the star formation activity in the
disk and nucleus of I Zw 1. We present first results from subarcsecond
interferometric imaging in the 12CO(2-1) line using the Plateau de Bure
Interferometer.


title:
The contribution of Narrow-Line Seyfert 1 galaxies to the soft X-ray
  background

abstract:
  The ROSAT Ultradeep HRI survey in the Lockman Hole contains a complete sample
of 91 X-ray sources with fluxes in the 0.5-2 keV band larger than 1.2 times
10e-15 erg cm-2 s-1, where over about 75 per cent of the sources are quasars or
Seyfert galaxies. During the course of our optical identification work, we have
obtained optical spectra of 67 narrow emission line galaxies (NELG), which are
physically not associated with the X-ray sources. We have derived the
equivalent width (EW) and the full width at half maximum (FWHM) for the most
prominent emission lines of 41 quasars and Seyfert galaxies taken from the
ROSAT Deep Survey (RDS), which has a flux limit of 5.5 times 10e-15 erg cm-2
s-1 in the 0.5-2.0 keV band. Furthermore we have obtained the EW and FWHM
values of the field NELGs. Here we present the spectroscopic discrimination
between RDS Seyfert galaxies and field galaxies (NELG). The analysis of the
emission lines has revealed that a single object out of 69 spectroscopically
identified AGN fits the optical criteria of Narrow-Line Seyfert 1 galaxies
(NLS1). This may indicate that NLS1 contribute only marginally to the soft
X-ray background, but we can not exclude a possible larger contribution.


title: Radio Properties of NLS1s

abstract:
  While NLS1s have been studied intensively at X-ray and optical wavelengths,
comparatively little is known about their characteristics in the radio band.
Therefore, we have carried out an investigation of the radio luminosities,
source sizes, spectral index distribution, and variability of a large,
uniformly selected sample of NLS1s. Our results indicate that, in some
respects, the radio properties of NLS1s differ significantly from those of
classical Seyfert galaxies. Radio observations of NLS1s may thus provide
important clues regarding the nature of their nuclear activity.


title: Coronal Line Emission from NLS1s

abstract:
  We discuss the optical coronal line spectra observed for a sample of 19
Narrow-Line Seyfert 1 galaxies. We find no correlation between the coronal line
strength and the soft X-ray power-law index derived from ROSAT PSPC data. There
is a trend for broader coronal lines to have larger equivalent widths. In
addition, a strong trend is found between line width and velocity relative to
the NLR. This trend is interpreted in terms of a decelerating outflow,
originating close to the nucleus.


title:
A Look at What Is (and Isn't) Known About Quasar Broad Line Regions and
  How Narrow-Line Seyfert 1 Galaxies Fit In

abstract:
  The evidence is reviewed that the Broad Line Region (BLR) probably has two
distinct components located at about the same distance from the central black
hole. One component, BLR II, is optically-thick, low-ionization emission at
least some of which arises from a disc and the other, BLR I, is probably
optically-thin emission from a more spherically symmetric halo or atmosphere.
The high Fe II/H-beta ratios seen in Narrow-Line Seyfert 1 galaxies (NLS1s) are
not due to strong Fe II emission, as is commonly thought, but to unusually weak
Balmer emission, probably caused by higher densities. NLS1s probably differ
from non-NLS1s because of the higher density of gas near the black hole. This
produces a higher accretion rate, a denser BLR, and a view of the central
regions that is more face-on.


title: ISOPHOT Observations of Narrow-Line Seyfert 1 Galaxies

abstract:
  Broad infrared spectra (7-200 micrometer) of four NLS1 galaxies, obtained
with the imaging photo-polarimeter (ISOPHOT) on board the Infrared Space
Observatory (ISO), are presented. The infrared luminosities and temperatures,
opacities and sizes of the emitting dust components are derived. A comparison
between the observed infrared spectra and the optical emission line fluxes of a
sample of 16 NLS1 galaxies suggests that these objects suffer different degrees
of dust absorption according to the inclination of the line of sight with
respect to the dust distribution.


title: The Fe II problem in NLS1s

abstract:
  For more than twenty years, strong Fe II emission lines have been observed in
Active Galactic Nuclei and in particular in Narrow Line Seyfert 1 galaxies. A
quick overview of the observations and of the models proposed to interpret the
Fe II spectrum is given. The influence of atomic data and of physical
parameters are discussed, and it is shown that the strengths of the Fe II lines
cannot be explained in the framework of photoionization models. A non-radiative
heating, for instance due to shocks, with an overabundance of iron, can help to
solve the problem. A comparison with other objects emitting intense Fe II lines
favors also the presence of strong outflows and shocks. We suggest some issues
in the context of AGN evolution.


title: Early Results from the Chandra X-ray Observatory

abstract:
  We present some early results on AGN from the Chandra X-ray Observatory,
highlighting high resolution spectroscopy using the High Energy Transmission
Grating Spectrometer (HETGS). The quasar PKS 0637-752 was found to have a very
bright X-ray jet whose shape is remarkably similar to that of the radio jet on
a size scale of 100 kpc, but the X-ray emission is still inexplicably bright.
Two BL Lac objects, PKS 2155-304 and Mrk 421, observed with the spectrometer
were found to have no strong absorption or emission features. Other radio loud
AGN observed with the HETGS show simple power law spectra without obvious
features.


title:
Evidence of Rapid Optical Variability In Selected Narrow-Line Seyfert 1
  Galaxies

abstract:
  We present the first results of a search for the presence of rapid optical
variability in a sample of five Narrow-Line Seyfert 1 galaxies. We find clear
evidence of rapid variability for IRAS 13224-3809 with variations occurring on
time scales of an hour. However, the results are less conclusive for the other
four sources in our sample, Markarian 766, PG 1244+026, PG 1404+226 and
Arakelian 564. While there are several instances among these latter objects
where there is a hint that variability may be present, IRAS 13224-3809 provides
the only conclusive evidence of rapid optical variability detected to date.


title:
X-ray reprocessing in Narrow-Line Seyfert 1 Galaxies: Ton S180 and Ark
  564

abstract:
  We present the results of spectral analysis of the ASCA data for the
Narrow-Line Seyfert 1 galaxy (NLS1) Ton S180 and simultaneous ASCA and RXTE
data modelling for the NLS1 Ark 564. We model both the primary and reflected
continuum as well as the iron K alpha line, the energy of which depends on the
ionization state of the reprocessor. We show that the reprocessing matter is
mildly ionized, and we find the soft to hard luminosity ratio to be about 2.5.
The accretion rate approximately corresponds to the Eddington limit value.


title: BLR velocities in optically and X-ray selected AGN samples

abstract:
  We have analyzed optical spectra of 473 X-ray and 235 optically selected
AGNs, to study their emission line properties. We present results of an
analysis of the H-beta linewidths. We find that the linewidth distribution of
quasars is shifted towards higher velocities (<v>=4300 km s-1) compared to the
distribution of Sy 1s (<v>=3000 km s-1). There are no Narrow Line Quasars, i.e.
there are no AGNs with quasar luminosities and FWHM(H-beta) < 2000 km s-1.
NLSy1s comprise 20-30 per cent of the AGN population at faint absolute
magnitudes (MB>-22), irrespective of the selection method. In the RASS sample
we find Gamma [0.1-2.4 keV] < 3.3. The Gamma vs. FWHM(H-beta) distribution for
Sy 1 galaxies is consistent with previous work. For QSOs the spectral index
also flattens with increasing FWHM(H-beta), but they have larger linewidths
than Seyfert 1s.


title: Coronal lines and the warm X-ray absorber in Seyfert 1 Galaxies

abstract:
  The connection between the coronal lines and the warm absorber is examined
systematically. In an earlier work it was found that the coronal line emitting
plasma and the warm absorber gas share the same density and temperature. If
there is a connection between the warm absorber gas and the forbidden
high-ionization line (FHIL) plasma, one can use the profiles of coronal lines
to derive the kinematics and dynamics of the warm absorber due to the high
spectral resolution available in the optical range. Further support for a
connection is a correlation between the equivalent width of [Fe X] 6375 and the
ROSAT spectral index found for an optically selected sample. For X-ray selected
objects with absorption edges observed by ASCA, we looked for a correlation
between the coronal lines and the warm absorber gas. A direct correlation
cannot be confirmed.


title:
A New Model for the Width of the Broad Emission Lines in AGN: The Role
  of the Accretion Rate

abstract:
  We present a model which relates the Broad Emission Line Regions of AGN to
the accretion mechanism. Based on the Keplerian assumption for the high
velocity clouds of the gas responsible for the production of the Broad Emission
Lines, we identify that gas with an outflowing disk/coronal wind forms a
stabilized Shakura-Sunyaev accretion disk. We show that in the framework of
this picture the observed range of H-beta FWHM from Broad Line to Narrow Line
type 1 AGN, is well reproduced as a function of the accretion rate.


title: The UV spectra of NLS1s - Implications for their broad line regions

abstract:
  We study the UV spectra of NLS1 galaxies and compare them with typical
Seyfert 1 galaxies and quasars. The NLS1 spectra show narrower UV lines as well
as weaker CIV lambda 1549 and CIII] lambda 1909 emission. We show that these
line properties are due to a lower ionization parameter and somewhat higher BLR
cloud densities. These modified conditions can be explained by the hotter big
blue bumps observed in NLS1s, which are in turn due to higher L/L_Edd ratios,
as shown by our accretion disk and corona modeling of the NLS1 continua. We
also present evidence that the Boroson & Green eigenvector 1, which is
correlated with the optical and UV emission-line properties, is not driven by
orientation and hence NLS1s, which have extreme eigenvector 1 values, are not
viewed from an extreme viewing angle.


title: A Structure for Quasars

abstract:
  We propose a simple unifying structure for the inner regions of quasars and
AGN. This empirically derived model links together the BALs, the narrow
UV/X-ray ionized absorbers, the BELR, and the Compton scattering/fluorescing
regions into a single structure. The model also suggests an origin for the
large-scale bi-conical outflows. Some other potential implications of this
structure are discussed.


title: X-ray Fluctuations from the Slim Disk

abstract:
  The responses of perturbations added into the optically thick,
advection-dominated accretion disk (ADAD), what we call the slim disk (SD), are
investigated through numerical simulations. Although it is proposed that the SD
is thermally stable, I find that a perturbation added into the disk is not
rapidly damped and moves through the disk in its free-fall time. After the
perturbation moves, the global structure of the disk does not vary very much.
These facts may account for the substantial variability of the X-ray
luminosities of stellar super-luminal jet sources (SLJSs) and Narrow-Line
Seyfert 1s (NLS1s).


title: Optical Monitoring of NLS1s at the Wise Observatory

abstract:
  We report the preliminary results of a spectrophotometric monitoring program
of Narrow-Line Seyfert 1 galaxies conducted at the Wise Observatory in 1999.
The data we collected will be used to evaluate the line-to-continuum time lag
in an attempt to test the idea that the accretion rate in NLS1s is larger than
in other Seyfert 1 galaxies.


title: Unravelling Active Galactic Nuclei

abstract:
  A complete flat-spectrum radio-loud sample of AGN includes a significant
fraction of Seyfert-like AGN including a NLS1. Analysis of their optical
spectra suggests that the reddest continuum colours are either associated with
AGN in nearby resolved galaxies, or distant quasars showing relatively narrow
permitted emission lines.


title: Discovery of a narrow line Seyfert 1 galaxy

abstract:
  We have discovered a Narrow-Line Seyfert 1 (NLS1) galaxy and identified it
with an ultrasoft X-ray source RX 215319-1514 detected with ROSAT. We present
its X-ray and optical spectral characteristics. Its redshift is found to be
0.0778+-0.0002. Its optical spectrum shows fairly strong Fe II emission lines,
and its X-ray spectrum has an extremely steep power-law index of Gamma
greater/equal 4, making it an extremely interesting example of this class of
AGNs. No low-energy absorption or variability is observed. The soft X-ray
(0.1-2.0 keV) luminosity is estimated to be 3.4-12.5 times 1e43 erg/s,
depending on the spectral model.


title: 1E 0117.2-2837 and the NLR of Narrow-Line Seyfert 1 galaxies

abstract:
  Based on photoionization calculations we present a study of the NLR emission
line ratios of Narrow-line Seyfert 1 (NLS1) galaxies. In particular, we
investigate the influence of different EUV - soft-X-ray spectral shapes (a
giant soft excess, a steep X-ray powerlaw, the presence of a warm absorber) and
NLR cloud properties (density, abundances, distance from the continuum source)
on the predicted optical emission-line ratios like [OIII] and [FeXIV].


title: New NLS1 galaxies detected among RASS galaxies

abstract:
  Six Narrow-Line Seyfert 1 galaxies have been discovered in optical follow-up
spectroscopy of nuclei of galaxies selected for their high X-ray flux in the
ROSAT All Sky Survey. We give X-ray and optical parameters of the sources and
show optical spectra.


title:
The response of the X-ray luminosity to the interaction strength in
  Seyfert 1 & 2 galaxies

abstract:
  We have correlated a sample of 99 Seyfert 1 and 98 Seyfert 2 (Rafanelli et
al., 1995) interacting galaxies with the survey and pointed ROSAT data and have
detected 91 Seyferts 1 and 47 Seyfert 2s in the X-ray band. We have performed
spectral and timing analysis of the X-ray detected sources, and we have
examined the relation of the X-ray luminosity L_X with the interaction strength
Q.


title:
Modelling of the X-ray broad absorption features in Narrow-Line Seyfert
  1s

abstract:
  We investigate the origin of the broad absorption features detected near
1-1.4 keV in several Narrow Line Seyfert 1 galaxies, by modelling the absorbing
medium with various physical parameters, using the ionization code PEGAS. The
observed properties of the X-ray absorption features can be reproduced by
taking into account the peculiar soft X-ray excess which is well fitted by a
blackbody plus an underlying power law. We equally stress that the emission
coming from the absorbing medium (related to the covering factor) has a strong
influence on the resulting X-ray spectrum, in particular on the apparent
position and depth of the absorption features. A non-solar iron abundance may
be required to explain the observed deep absorption. We also investigate the
influence of an additional collisional ionization process (hybrid case) on the
predicted absorption features.


title: The enigmatic soft X-ray NLS1 RX J0134.2-4258

abstract:
  We report the discovery and analysis of the follow-up ROSAT pointed
observation, an ASCA observation and optical and radio observations of the
enigmatic Narrow-Line Seyfert 1 galaxy RX J0134.2-4258. While its spectrum was
one of the softest observed from an AGN during the ROSAT All-Sky Survey, its
spectrum was found to be dramatically harder during a pointed observation
although the count rate remained constant. In the pointed observation we found
that the spectrum is softer when it is fainter, and spectral fitting
demonstrates that it is the hard component that is variable. The ASCA
observation confirms the presence of a hard X-ray power law, the slope of which
is rather flat compared with other NLS1s. Survey and follow-up radio
observations reveal that RX J0134.2-4258 is also unusual in that it is a member
of the rare class of radio-loud NLS1s, and, with R=71, it holds the current
record for the largest radio-to-optical ratio in NLS1s. We discuss possible
scenarios to explain its strange behaviour.


title: The evolution of the galactic morphological types in clusters

abstract:
  The morphological types of galaxies in nine clusters in the redshift range
0.1<z<0.25 are derived from very good seeing images taken at the NOT and the La
Silla Danish telescopes. With the purpose of investigating the evolution of the
fraction of different morphological types with redshift, we compare our results
with the morphological content of nine distant clusters studied by the MORPHS
group, five clusters observed with HST-WFPC2 at redshift z = 0.2-0.3, and
Dressler's (1980) large sample of nearby clusters. After having checked the
reliability of our morphological classification both in an absolute sense and
relative to the MORPHS scheme, we analyze the relative occurrence of
elliptical, S0 and spiral galaxies as a function of the cluster properties and
redshift. We find a large intrinsic scatter in the S0/E ratio, mostly related
to the cluster morphology. In particular, in our cluster sample, clusters with
a high concentration of ellipticals display a low S0/E ratio and, vice-versa,
low concentration clusters have a high S0/E. At the same time, the trend of the
morphological fractions and ratios with redshift clearly points to a
morphological evolution: as the redshift decreases, the S0 population tends to
grow at the expense of the spiral population, whereas the frequency of Es
remains almost constant. We also analyze the morphology-density (MD) relation
in our clusters and find that -similarly to higher redshift clusters- a good MD
relation exists in the high-concentration clusters, while it is absent in the
less concentrated clusters. Finally, the comparison of the MD relation in our
clusters with that of the D97 sample suggests that the transformation of
spirals into S0 galaxies becomes more efficient with decreasing local density.


title: Properties of Warm absorbers in Narrow-Line Seyfert 1 galaxies

abstract:
  We present a study of the X-ray properties of several NLS1 galaxies, focusing
on their warm absorbers. In the first part, we discuss properties of dusty and
dust-free warm absorbers in NLS1s, and study their potential contribution to
high-ionization optical iron lines. In the second part, we summarize our work
on the exceptional spectral variability of the NLS1 galaxy RX J0134.3-4258
(from Gamma about -4.4 in the ROSAT all-sky survey observation, to about -2.2
in our subsequent pointed observation).


title:
The Magnetic Field Sign Reversal and Evolution of Rossby and Alfven
  Waves Induced by Velocity Shear Oscillations on the Sun

abstract:
  The behaviour of the toroidal and meridional components of the solar
large-scale magnetic field and linear Alfven and Rossby waves during solar
activity cycles and bi-annual time periods are theoretically investigated in
this work. We consider the case of periodical velocity shear with bi-annual
oscillation period . The large-scale magnetic field toroidal and meridional
components are obtained as harmonic functions of the time. The sign reversal of
these magnetic field components is studied. The numerical simulations show
that, due to the velocity shear oscillations, the toroidal or meridional
component of the large-scale magnetic field reverses its sign three times in
one of the hemispheres (northern or southern) of the Sun, during the solar
activity cycle 23. According to our results the appearance of velocity shear
oscillations leads to the modulation of the magnetic field 22-year period
oscillations by the bi-annual ones. The presented model is applicable for
investigation of the magnetic field evolution at the base of convection zone as
well as for understanding the magnetic field properties in the upper solar
atmosphere. The excitement of the linear Rossby and Alfven waves in the shear
layer at the base of the convection zone is also considered. The periodical
impulsive growth is characteristic to the energy density of Alfven and Rossby
waves and they propagate as localized in time powerful pulses. Such behavior of
waves well explains mechanisms of the solar flare excitement and activity.


title: WD1953-011 - a magnetic white dwarf with peculiar field structure

abstract:
  We present H-alpha spectra of the magnetic white dwarf star WD1953-011 which
confirm the presence of the broad Zeeman components corresponding to a field
strength of about 500kG found by Maxted & Marsh (1999). We also find that the
line profile is variable over a timescale of a day or less. The core of the
H-alpha line also shows a narrow Zeeman triplet corresponding to a field
strength of of about 100kG which appears to be almost constant in shape. These
observations suggest that the magnetic field on WD1953-011 has a complex
structure and that the star has a rotational period of hours or days which
causes the observed variability of the spectra. We argue that neither an offset
dipole model nor a double-dipole model are sufficient to explain our
observations. Instead, we propose a two component model consisting of a high
field region of magnetic field strength of about 500kG covering about 10% of
the surface area of the star superimposed on an underlying dipolar field of
mean field strength of about 70kG. Radial velocity measurements of the narrow
Zeeman triplet show that the radial velocity is constant to within a few km/s
so this star is unlikely to be a close binary.


title: Studies of the high luminosity quasar, PDS 456

abstract:
  X-ray and multi-wavelength observations of the most luminous known local
(z<0.3) AGN, the recently discovered radio-quiet quasar PDS 456, are presented.
The spectral energy distribution shows that PDS 456 has a bolometric luminosity
of 1e47 erg/s, peaking in the UV. The X-ray spectrum obtained by ASCA and RXTE
shows considerable complexity. The most striking feature observed is a deep,
highly-ionised, iron K edge (8.7 keV, rest-frame), originating via reprocessing
from highly ionised material, possibly the inner accretion disk. PDS 456 was
found to be remarkably variable for its luminosity; in one flare the X-ray flux
doubled in just about 15 ksec. If confirmed this would be an unprecedented
event in a high-luminosity source, with a light-crossing time corresponding to
about 2RS. The implications are that either flaring occurs within the very
central regions, or else that PDS 456 is a super-Eddington or relativistically
beamed system.


title: New Insights Into The Narrow-Line Seyfert 1 Phenomenon

abstract:
  I briefly review the X/UV absorber models and show that the observations of
NLS1s are generally consistent with the models. The covering factor of
absorbers in NLS1s is likely to be high and there is some evidence of
super-solar metallicities. I argue that NLS1s may be active galaxies in the
early stage of their evolution and as such, may be low luminosity, low redshift
analogues of the high redshift quasars. NLS1s may reside in rejuvenated
gas-rich galaxies. I also propose that the high Fe II emission in NLS1s may be
a direct consequence of their large accretion rate and so a collisional
ionization origin of FeII is favored.


title: Eigenvector 1: An Optimal Correlation Space for Active Galactic Nuclei

abstract:
  We identify a correlation space involving optical and UV emission line
parameters as well as the soft X-ray spectral index that provides optimal
discrimination between all principal classes of active galactic nuclei. Most of
the sources in our three high quality data samples show a strong
intercorrelation with narrow line Seyfert 1 (NLSy1) galaxies and steep spectrum
radio galaxies occupying opposite extrema in the space. NLSy1 sources show a
clear continuity with broader line sources indicating that they are not a
disjoint class of AGN as is sometimes suggested. We interpret the principal
intercorrelation in the parameter space as being driven by AGN luminosity to
black hole mass ratio (L/M prop. to the Eddington ratio). Source orientation no
doubt also plays an important role but it is not yet clear whether FWHM H beta
or CIV 1549 line shift is the better indicator. We tentatively identify two RQ
populations: an almost pure RQ population A with FWHM<=4000 and population B
which occupies the same parameter domain as the flat spectrum RL sources. A
possible interpretation sees Pop. A/NLSy1 as lower mass/high accretion rate
sources and Pop. B/RL sources the opposite.


title: LWS spectroscopy of the luminous Blue Compact Galaxy Haro 11

abstract:
  We present far infrared (FIR) spectroscopy of the luminous blue compact
galaxy (BCG) Haro 11 (ESO 350-IG38) obtained with the ISO Long Wavelength
Spectrometer (LWS) in low resolution mode. This metal poor dwarf merger is an
extremely hot IRAS source with a high [CII]158um/CO(1-0) flux ratio. We discuss
the balance between dust and line cooling in the photodissociated regions
(PDR), in particular the role of the [CII] line, and derive the basic
properties of the PDR gas. While samples of other starburst galaxies show a
correlation between the [CII]/FIR flux ratio and the IRAS f60/f100 ratio, Haro
11 deviates significantly from this relationship being brighter in [CII] than
average. We propose that the relationship is caused by an increasing optical
depth with increasing IRAS temperature but that the low metallicity and the
extreme starburst properties of Haro 11 allow the medium to be thin despite its
high f60/f100 ratio, explaining the [CII] excess. This leaves room for a more
optimistic view on the possibilities to detect massive starforming mergers at
high redshifts, using the [CII] line.


title:
Abundance evolution of intermediate mass elements (C to Zn) in the Milky
  Way halo and disk

abstract:
  We present a comprehensive study of the evolution of the abundances of
intermediate mass elements, from C to Zn, in the Milky Way halo and in the
local disk. We use a consistent model to describe the evolution of those two
galactic subsystems. The halo and the disk are assumed to evolve independently,
both starting with gas of primordial composition, and in different ways: strong
outflow is assumed to take place during the $\sim$1 Gyr of the halo formation,
while the disk is built by slowly infalling gas. This description of the
halo+disk evolution can correctly account for the main observational
constraints (at least in the framework of simple models of galactic chemical
evolution). We utilise then metallicity dependant yields to study the evolution
of all elements from C and Zn. Comparing our results to an extensive body of
observational data (including very recent ones), we are able to make a critical
analysis of the successes and shortcomings of current yields of massive stars.
Finally, we discuss qualitatively some possible ways to interpret the recent
data on oxygen vs iron, which suggest that oxygen behaves differently from the
other alpha-elements.


title:
Possible Detection of Gamma Ray Air Showers in Coincidence with BATSE
  Gamma Ray Bursts

abstract:
  Project GRAND presents the results of a search for coincident high-energy
gamma ray events in the direction and at the time of nine Gamma Ray Bursts
(GRBs) detected by BATSE. A gamma ray has a non-negligible hadron production
cross section; for each gamma ray of energy of 100 GeV, there are 0.015 muons
which reach detection level (Fasso & Poirier, 1999). These muons are identified
and their angles are measured in stations of eight planes of proportional wire
chambers (PWCs). A 50 mm steel plate above the bottom pair of planes is used to
distinguish muons from electrons. The mean angular resolution is 0.26 degrees
over a +/- 61 degree range in the XZ and YZ planes. The BATSE GRB catalogue is
examined for bursts which are near zenith for Project GRAND. The geometrical
acceptance is calculated for each of these events. The product is then taken of
the GRB flux and GRAND's geometrical acceptance. The nine sources with the best
combination of detection efficiency and BATSE's intensity are selected to be
examined in the data. The most significant detection of these nine sources is
at a statistical significance of +3.7 sigma; this is also the GRB with the
highest product of GRB flux and geometrical acceptance.


title:
Cosmological Reionization Around the First Stars: Monte Carlo Radiative
  Transfer

abstract:
  We study the evolution of ionization fronts around the first proto-galaxies
by using high resolution numerical cosmological (Lambda+CDM model) simulations
and Monte Carlo radiative transfer methods. We present the numerical scheme in
detail and show the results of test runs from which we conclude that the scheme
is both fast and accurate. As an example of interesting cosmological
application, we study the reionization produced by a stellar source of total
mass M=2 10^8 M_\odot turning on at z=12, located at a node of the cosmic web.
The study includes a Spectral Energy Distribution of a zero-metallicity stellar
population, and two Initial Mass Functions (Salpeter/Larson). The expansion of
the I-front is followed as it breaks out from the galaxy and it is channeled by
the filaments into the voids, assuming, in a 2D representation, a
characteristic butterfly shape. The ionization evolution is very well tracked
by our scheme, as realized by the correct treatment of the channeling and
shadowing effects due to overdensities. We confirm previous claims that both
the shape of the IMF and the ionizing power metallicity dependence are
important to correctly determine the reionization of the universe.


title: A Pressure Anomaly for HII Regions in Irregular Galaxies

abstract:
  The pressures of giant HII regions in 6 dwarf Irregular galaxies are a factor
of ~10 larger than the average pressures of the corresponding galaxy disks,
obtained from the stellar and gaseous column densities. Either the visible HII
regions in these dwarfs are all so young that they are still expanding, or
there is an unexpected source of disk self-gravity that increases the
background pressure. We consider the possibility that the additional
self-gravity comes from disk dark matter, but suggest this is unlikely because
the vertical scale heights inferred for Irregular galaxies are consistent with
the luminous matter alone. Some of the HII region overpressure is probably the
result of local peaks in the gravitational field that come from large gas
concentrations, many of which are observed directly. These peaks also explain
the anomalously low average column density thresholds for star formation that
were found earlier for Irregular galaxies, and they permit the existence of a
cool HI phase as the first step toward dense molecular cores. Many of the HII
regions could also be so strongly over-pressured that they will expand for a
long time. In this case, the observed population would be only 7% of the total,
and the aging HII regions, now too faint to see, should occupy nearly the
entire dwarf galaxy volume. Such prolonged HII region expansion would explain
the origin of the giant HI shells that are seen in these galaxies, and account
for the lack of bright central clusters inside these shells.


title:
Simulated Cluster Archive: A Computational Catalog of X-Ray Clusters in
  a Lambda-CDM Universe

abstract:
  We have simulated the evolution of a large sample of X-ray clusters in a
Lambda-CDM universe at high spatial resolution using adaptive mesh refinement
and placed the results in an online archive for public access. The Simulated
Cluster Archive website http://sca.ncsa.uiuc.edu provides tools for interactive
2D and 3D analysis of gas and dark matter fields, X-ray and SZ imaging, and
data export. We encourage community use and solicit their feedback.


title: HST revisits the proper motion of PSR B0656+14

abstract:
  We report the first successful measurement (with HST/WFPC2) of a significant
proper motion for a V~ 25 object which we had proposed as the optical
counterpart of the radio pulsar PSR B0656+14. The yearly displacement of 43+/-
2 mas is highly significant and, while in agreement with early, rougher, radio
measurements, stands out for its vastly improved accuracy. Together with the
report of a possible optical pulsation (Shearer et al. 1998), we regard this
result as the final proof of the optical identification of PSR B0656+14.


title: Early Starbursts and Magnetic Field Generation in Galaxy Clusters

abstract:
  We propose a mechanism for the early generation of the mean Intracluster
magnetic field in terms of magnetized galactic winds. These winds are the
result of starburst phases of the cluster galaxies, assumed to produce the
predominant population of early type galaxies in mergers of gas-rich
progenitors. After further cluster contraction typical field strengths are
$10^{-7}$ Gauss. This estimate may increase to the level of $10^{-6}$ Gauss if
more extreme galactic parameters, and subsequent shear amplification of the
field are considered. The topology of the field is one of almost unconnected
Wind Bubbles with Parker-type spiral field configurations over scales of the
distance between galaxies. Further cluster accretion, that continues
chaotically in space and time up to the present, will perturb these
"large-scale" mean fields on smaller or at best comparable spatial scales. The
small scale fields in the resulting turbulent fluctuation spectrum should be
able to confine relativistic particles over times longer than the age of the
Universe. The nonthermal particle content of galaxy clusters should therefore
also have a "cosmological" hadronic component generated during the early
starburst phase of the member galaxies. Already by itself it implies a
nonthermal energy fraction of about 10 percent for the Intracluster gas which
should then be detectable by future gamma-ray telescopes.


title: Superconducting Cosmic Strings

abstract:
  These relics from the early universe could be the answer to many
astrophysical conundrums.


title:
On the Correlation Between CO Absorption and Far-Ultraviolet Non-Linear
  Extinction Toward Galactic OB Stars

abstract:
  A sample of 59 sight lines to reddened Galactic OB stars was examined for
correlations of the strength of the CO Fourth Positive (A - X) absorption band
system with the ultraviolet interstellar extinction curve parameters. We used
archival high-dispersion NEWSIPS IUE spectra to measure the CO absorption for
comparison to parametric fits of the extinction curves from the literature. A
strong correlation with the non-linear far-UV curvature term was found with
greater absorption, normalized to E(B-V), being associated with more curvature.
A weaker trend with the linear extinction term was also found. Mechanisms for
enhancing CO in dust environments exhibiting high non-linear curvature are
discussed.


title:
Neutron-Capture Elements in the Early Galaxy: Insights from a Large
  Sample of Metal-Poor Giants

abstract:
  New abundances for neutron-capture (n-capture) elements in a large sample of
metal-poor giants from the Bond survey are presented. The spectra were acquired
with the KPNO 4-m echelle and coude feed spectrographs, and have been analyzed
using LTE fine-analysis techniques with both line analysis and spectral
synthesis. Abundances of eight n-capture elements (Sr, Y, Zr, Ba, La, Nd, Eu,
Dy) in 43 stars have been derived from blue (lambda = 4070--4710, R~20,000, S/N
ratio~100-200) echelle spectra and red (lambda = 6100--6180, R~22,000, S/N
ratio~100-200) coude spectra, and the abundance of Ba only has been derived
from the red spectra for an additional 27 stars. Overall, the abundances show
clear evidence for a large star-to-star dispersion in the heavy element-to-iron
ratios. The new data also confirm that at metallicities [Fe/H] <~ --2.4, the
abundance pattern of the heavy (Z >= 56) n-capture elements in most giants is
well-matched to a scaled Solar System r-process nucleosynthesis pattern. The
onset of the main r-process can be seen at [Fe/H] ~ --2.9. Contributions from
the s-process can first be seen in some stars with metallicities as low as
[Fe/H] ~ --2.75, and are present in most stars with metallicities [Fe/H] >
--2.3. The lighter n-capture elements (Sr-Y-Zr) are enhanced relative to the
heavier r-process element abundances. Their production cannot be attributed
solely to any combination of the Solar System r- and main s-processes, but
requires a mixture of material from the r-process and from an additional
n-capture process which can operate at early Galactic time.


title: Observational Constraints on the Theory of the IMF

abstract:
  Observational constraints on the theory of the IMF are reviewed. These
observations include the new result that star formation is very rapid, usually
going from start to finish in only 1 or 2 dynamical times on a wide range of
scales. This result, combined with the observation that the IMF is independent
of cluster density over a factor of several hundred, implies that protostar
coagulation during orbital motions in a cloud are not important for the IMF:
there is not enough time. The observation that the IMF in individual clusters
is about the same as the IMF in whole galaxies implies that stars of all masses
form randomly in self-gravitating clouds of all masses. There cannot be a
sequence of stellar masses in a cluster, based on stirring or heating for
example, where the largest star that forms keeps increasing until the cloud is
destroyed. The uniformity of the IMF over time and space argues for a process
that is independent of specific properties of molecular clouds. This
uniformity, along with the common observation of young stars in hierarchical
clusters that resemble the structures of interstellar gas, suggests that the
IMF, at least in the power law range, is a by-product of turbulence. Detailed
physical processes may affect the turnover at low mass, but even this may have
a universal character arising from a combination of turbulence-induced
variations in the local cloud properties, and fragmentation in unstable cloud
pieces.


title: Polarization in Sagittarius A*

abstract:
  We summarize the current state of polarization observations of Sagittarius
A*, the compact radio source and supermassive black hole candidate in the
Galactic Center. These observations are providing new tools for understanding
accretion disks, jets and their environments. Linear polarization observations
have shown that Sgr A* is unpolarized at frequencies as high as 86 GHz.
However, recent single-dish observations indicate that Sgr A* may have strong
linear polarization at frequencies higher than 150 GHz. Circular polarization,
which was recently discovered in Sgr A*, is detectable to frequencies as high
as 43 GHz. It is strongly variable on a 10-day timescale, with the degree of
variability increasing with frequency. At low frequencies, fractional circular
polarization is stable over nearly 20 years. We discuss some of the possible
models for the origin of the circular polarization.


title: Three Dimensional Radiative Transfer

abstract:
  Radiative Transfer (RT) effects play a crucial role in the thermal history of
the intergalactic medium. Here I discuss recent advances in the development of
numerical methods that introduce RT to cosmological hydrodynamics. These
methods can also readily be applied to time dependent problems on interstellar
and galactic scales.


title: Resolving the Controversy Over the Core Radius of 47 Tucanae (NGC 104)

abstract:
  This paper investigates the discrepancy between recent measurements of the
density profile of the globular cluster 47 Tuc that have used HST data sets.
Guhathakurta et al. (1992) used pre-refurbishment WFPC1 V-band images to derive
r_c = 23" +/- 2". Calzetti et al. (1993) suggested that the density profile is
a superposition of two King profiles (r_c = 8" and r_c = 25") based on U-band
FOC images. De Marchi et al. (1996) used deep WFPC1 U-band images to derive r_c
= 12" +/- 2". Differences in the adopted cluster centers are not the cause of
the discrepancy. Our independent analysis of the data used by De Marchi et al.
reaches the following conclusions: (1) De Marchi et al.'s r_c ~ 12" value is
spuriously low, a result of radially-varying bias in the star counts in a
magnitude limited sample -- photometric errors and a steeply rising stellar
luminosity function cause more stars to scatter across the limiting magnitude
into the sample than out of it, especially near the cluster center where
crowding effects are most severe. (2) Changing the limiting magnitude to the
main sequence turnoff, away from the steep part of the luminosity function,
partially alleviates the problem and results in r_c = 18". (3) Combining such a
limiting magnitude with accurate photometry derived from PSF fitting, instead
of the less accurate aperture photometry employed by De Marchi et al., results
in a reliable measurement of the density profile which is well fit by r_c = 22"
+/- 2". Archival WFPC2 data are used to derive a star list with a higher degree
of completeness, greater photometric accuracy, and wider areal coverage than
the WFPC1 and FOC data sets; the WFPC2-based density profile supports the above
conclusions, yielding r_c = 24" +/- 1.9".


title:
Gamma-ray bursts from internal shocks in a relativistic wind: an
  hydrodynamical study

abstract:
  The internal shock model for gamma-ray bursts involves shocks taking place in
a relativistic wind with a very inhomogeneous initial distribution of the
Lorentz factor. We have developed a 1D lagrangian hydrocode to follow the
evolution of such a wind and the results we have obtained are compared to those
of a simpler model presented in a recent paper (Daigne & Mochkovitch 1998)
where all pressure waves are suppressed in the wind so that shells with
different velocities only interact by direct collisions. The detailed
hydrodynamical calculation essentially confirms the conclusion of the simple
model: the main temporal and spectral properties of gamma-ray bursts can be
reproduced by internal shocks in a relativistic wind.


title: Dwarf satellite galaxies in the modified dynamics

abstract:
  In the modified dynamics (MOND) the inner workings of dwarf satellites can be
greatly affected by their mother galaxy-over and beyond its tidal effects.
Because of MOND's nonlinearity a system's internal dynamics can be altered by
an external field in which it is immersed (even when this field, by itself, is
constant in space). As a result, the size and velocity dispersion of the
satellite vary as the external field varies along its orbit. A notable outcome
of this is a substantial increase in the dwarf's vulnerability to eventual
tidal disruption-rather higher than Newtonian dynamics (with a dark-matter
halo) would lead us to expect for a satellite with given observed parameters.


title: Multi-wavelength visibility measurements of the red giant R Doradus

abstract:
  We present visibility measurements of the nearby Mira-like star R Doradus
taken over a wide range of wavelengths (650--990 nm). The observations were
made using MAPPIT (Masked APerture-Plane Interference Telescope), an
interferometer operating at the 3.9-m Anglo-Australian Telescope. We used a
slit to mask the telescope aperture and prism to disperse the interference
pattern in wavelength. We observed in R Dor strong decreases in visibility
within the TiO absorption bands. The results are in general agreement with
theory but differ in detail, suggesting that further work is needed to refine
the theoretical models.


title: ISOPHOT observations of 3CR quasars and radio galaxies

abstract:
  In order to check for consistency with the radio-loud AGN unification scheme,
ISOPHOT data obtained for two small sets of intermediate redshift
steep-spectrum 3CR radio galaxies and quasars are being examined. Supplementary
submillimeter and centimeter radio data for the quasars are also taken into
account, in order to assess the magnitude of any beamed nonthermal radiation.
The fact that we find broad-lined objects to be somewhat more luminous in their
far-infrared output than narrow-lined objects, hints at a contradiction to the
unification scheme. However, as the sample objects are not particularly well
matched, the sample size is small, and the FIR radiation may still be partly
anisotropic, this evidence is, at the moment, weak.


title:
Measuring cosmological bulk flows via the kinematic Sunyaev-Zeldovich
  effect in the upcoming cosmic microwave background maps

abstract:
  We propose a new method to measure the possible large-scale bulk flows in the
Universe from the cosmic microwave background (CMB) maps from the upcoming
missions, MAP and Planck. This can be done by studying the statistical
properties of the CMB temperature field at many X-ray cluster positions. At
each cluster position, the CMB temperature fluctuation will be a combination of
the Sunyaev-Zeldovich (SZ) kinematic and thermal components, the cosmological
fluctuations and the instrument noise term. When averaged over many such
clusters the last three will integrate down, whereas the first one will be
dominated by a possible bulk flow component. In particular, we propose to use
all-sky X-ray cluster catalogs that should (or could) be available soon from
X-ray satellites, and then to evaluate the dipole component of the CMB field at
the cluster positions. We show that for the MAP and Planck mission parameters
the dominant contributions to the dipole will be from the terms due to the SZ
kinematic effect produced by the bulk flow (the signal we seek) and the
instrument noise (the noise in our signal). Computing then the expected
signal-to-noise ratio for such measurement, we get that at the 95 % confidence
level the bulk flows on scales >100h^{-1} Mpc can be probed down to the
amplitude of $< 200$ km/sec with the MAP data and down to only 30 km/sec with
the Planck mission.


title: Normal Galaxies in the Infrared

abstract:
  This review addresses what can be learned from infrared observations about
galaxies powered predominantly by star formation. Infrared techniques mostly
probe the interstellar medium of galaxies, yielding physical and chemical
information on the medium out of which stars form, which is in turn affected by
those stars. Methods traditionally used in the study of such normal galaxies at
wavelengths longer than 3 microns are described, and major questions currently
pursued in the field are outlined. The most prominent results from the IRAS
survey are reviewed. Contributions by ISO in the field of broad-band photometry
are then presented, followed by ISO results in spectrospcopy. Normal galaxy
studies not directly concerned with the ISM are quickly reviewed. The outlook
and challenges in pursuing the interpretation of infrared data on the ISM are
discussed.


title:
The response of a turbulent accretion disc to an imposed epicyclic
  shearing motion

abstract:
  We excite an epicyclic motion, whose amplitude depends on the vertical
position, $z$, in a simulation of a turbulent accretion disc. An epicyclic
motion of this kind may be caused by a warping of the disc. By studying how the
epicyclic motion decays we can obtain information about the interaction between
the warp and the disc turbulence. A high amplitude epicyclic motion decays
first by exciting inertial waves through a parametric instability, but its
subsequent exponential damping may be reproduced by a turbulent viscosity. We
estimate the effective viscosity parameter, $\alpha_{\rm v}$, pertaining to
such a vertical shear. We also gain new information on the properties of the
disc turbulence in general, and measure the usual viscosity parameter,
$\alpha_{\rm h}$, pertaining to a horizontal (Keplerian) shear. We find that,
as is often assumed in theoretical studies, $\alpha_{\rm v}$ is approximately
equal to $\alpha_{\rm h}$ and both are much less than unity, for the field
strengths achieved in our local box calculations of turbulence. In view of the
smallness ($\sim 0.01$) of $\alpha_{\rm v}$ and $\alpha_{\rm h}$ we conclude
that for $\beta = p_{\rm gas}/p_{\rm mag} \sim 10$ the timescale for diffusion
or damping of a warp is much shorter than the usual viscous timescale. Finally,
we review the astrophysical implications.


title: Gravitational Lensing by Nearby Clusters of Galaxies

abstract:
  We present an estimation of the expected number of arcs and arclets in a
sample of nearby (z<0.1) clusters of galaxies, that takes into account the
magnitude limit of the objects as well as seeing effects. We show that strong
lensing effects are not common, but also they are not as rare as usually
stated. Indeed, for a given cluster, they present a strong dependence with the
magnitude limit adopted in the analysis and the seeing of the observations. We
also describe the procedures and results of a search for lensing effects in a
sample of 33 clusters spanning the redshift range of 0.014 to 0.076,
representative of the local cluster distribution. This search produced two arc
candidates. The first one is in A3408 (z=0.042), the same arc previously
discovered by Campusano & Hardy (1996), with z=0.073 and associated to the
brightest cluster galaxy. The second candidate is in the cluster A3266
(z=0.059) and is near a bright elliptical outside the cluster center, requiring
the presence of a very massive sub-structure around this galaxy to be produced
by gravitational lensing.


title:
First correlation between compact object and circumstellar disk in the
  Be/X-ray binaries

abstract:
  A remarkable correlation between the H-alpha emission line and the radio
behaviour of LSI+61 303 (V615 Cas, GT 0236+610) over its 4 yr modulation is
discovered. The radio outburst peak is shifted by a quarter of the 4 yr
modulation period (about 400 days) with respect to the equivalent width of the
H-alpha emission line variability. The onset of the LSI+61 303 radio outbursts
varies in phase with the changes of the H-alpha emission line, at least during
the increase of H-alpha equivalent width. This is the first clear correlation
between the emission associated to the compact object and the Be circumstellar
disk in a Be/X-ray binary system.


title:
Was the Whirlpool (M51) a Spiral Galaxy before the Encounter with the
  Companion NGC 5195?

abstract:
  Using the B-I color index in the radial photometry of M51, applied to defined
azimuthal sectors, we reveals asymmetries in the shape of the density pattern
of the galactic arms. The anomalous shape is present only in the side close to
the companion and not in the far side. Two more non-interacting check-spirals
do not show similar behaviour. The anomalous sawtooth-like shape is similar to
that produced by a progressive wave propagating in a preexisting density
pattern. In this hypothesis we have to conclude that the galaxy M51 could be a
spiral galaxy formerly, i.e. before the encounter with the companion.


title: Jets from black hole binaries and Galactic Nuclei

abstract:
  Relativistic outflows are a common phenomenon in accreting black holes.
Despite the enormous differences in scale, stellar-mass black holes in binaries
and supermassive black holes in Galactic Nuclei produce jets with analogous
properties. In both are observed two types of relativistic outflows: 1) steady
compact jets with flat-spectrum, and 2) sporadic extended jets with
steep-spectrum and apparent superluminal motions. Besides, the most common
class of gamma-ray bursts are afterglows from ultra-relativistic jets
associated to the formation of black holes at cosmological distances.


title:
A Catalogue of Galaxies in the HDF-South: Photometry and Structural
  Parameters

abstract:
  We describe the construction of a catalogue of galaxies in the optical field
of the Hubble Deep Field South. The HDF-S observations produced WFPC2 images in
U, B, V, and I, the version 1 data have been made public on 23 November 1999.
The effective field of view is 4.38 arcmin$^2$, and the 5$\sigma$ limiting
magnitudes (in a FWHM aperture) are 28.87, 29.71, 30.19, 29.58 in the U, B, V
and I bands, respectively. We created a catalogue for each pass-band
(I$_{814}$, V$_{606}$, B$_{450}$, U$_{300}$), using simulations to account for
incompleteness and spurious sources contamination. Along with photometry in all
bands, we determined on the I$_{814}$-selected catalogue (I$_{814}<26$)
structural parameters, such as a metric apparent size, derived from the
petrosian radius, an asymmetry index, light concentration indexes and the mean
surface brightness within the petrosian radius.


title: Redshift estimation from low-resolution prism SEDs with an NGST MOS

abstract:
  We discuss the utility of a low resolution prism as a component of a
Multi-Object Spectrometer for NASA's proposed Next Generation Space Telescope
(NGST). Low resolution prism spectroscopy permits simultaneous observation of
the 0.6-5micron wavelength regime at R~50. To such data we can apply the modern
techniques in spectral energy distribution (SED) fitting to determine source
redshifts, sometimes called ``photometric redshifts''. Low resolution prism
observations of galaxy SED's provide a significant advantage over multi-filter
observations for any realistic observing strategy, and we have performed
extensive simulations to quantify it. The advantage of the prism is largest in
the regime of faint (K_AB>30) objects at high redshift (z>4), the primary
discovery space of NGST. Many important objects will be too faint for follow up
at higher spectral resolution, so prism observations are the optimal technique
to study them. Prism observations also reduce the contamination of high
redshift samples by lower redshift interlopers.


title: Decaying Cold Dark Matter Model and Small-Scale Power

abstract:
  The canonical cosmological constant dominated cold dark matter model (LCDM)
may possess too much power on small scales at z=0, manifested as central
over-concentration of dark matter and over-abundance of dwarf galaxies. We
suggest an alternative model, LDCDM, where one half of the cold dark matter
particles decay into relativistic particles by z=0. The model successfully
lowers the concentration of dark matter in dwarf galaxies as well as in large
galaxies like our own at low redshift, while simultaneously retaining the
virtues of the LCDM model. The model solves the problem of over-production of
small dwarf galaxies in the LCDM not by removing them but by identifying them
with failed, "dark" galaxies, where star-formation is quenched due to dark
matter evaporation and consequent halo expansion. A dramatic difference between
the LDCDM model and other proposed variants of the LCDM model is that the
small-scale power at high redshift (z>2) in the LDCDM model is enhanced
compared to the LCDM model.
  A COBE-and-cluster normalized LDCDM model can be constructed with the
following parameters: H0=60km/sec/Mpc, lambda0=0.60, Omega_{0,CDM}=0.234,
Omega_{0,b}=0.044, n=1.0, and sigma8=1.06. A clean test of this model can be
made by measuring the evolution of gas fraction in clusters. The prediction is
that the gas fraction should decrease with redshift and is smaller by 31% at
z=1 than at z=0. X-ray and Sunyaev-Zel'dovich effect observations should
provide such a test.


title: Acceleration time scale in an ultrarelativistic shock

abstract:
  The acceleration mechanism at ultrarelativistic shocks is investigated using
the Monte Carlo simulations. We apply a method of discrete small amplitude
particle momentum scattering to reproduce highly anisotropic conditions at the
shock and carefully describe the acceleration mechanism. The obtained
acceleration times equal $1.0 r_{g}/c$ if the spectral index reach the value of
2.2, independent of physical conditions in the shock. Some other parameters of
the acceleration process are also provided.


title:
High-Resolution Imaging of Molecular Gas and Dust in the Antennae (NGC
  4038/39): Super Giant Molecular Complexes

abstract:
  We present new aperture synthesis CO maps of the Antennae (NGC 4038/39)
obtained with the Caltech Millimeter Array. These sensitive images show
molecular emission associated with the two nuclei and a partial ring of star
formation to the west of NGC 4038, as well as revealing the large extent of the
extra-nuclear region of star formation (the ``overlap region''), which
dominates the CO emission from this system. The largest molecular complexes
have masses of 3-6x10^8 M_sun, typically an order of magnitude larger than the
largest structures seen to date in more quiescent galaxy disks. The extremely
red luminous star clusters identified previously with HST are well-correlated
with the CO emission, which supports the conclusion that they are highly
embedded young objects rather than old globular clusters. There is an excellent
correlation between the CO emission and the 15 micron emission seen with ISO,
particularly for the brightest regions. The most massive complexes in the
overlap region have similar [NeIII]/[NeII] ratios, which implies that all these
regions are forming many massive stars. However, only the brightest
mid-infrared peak shows strong, rising continuum emission longward of 10
microns, indicative of very small dust grains heated to high temperatures by
their proximity to nearby luminous stars. Since these grains are expected to be
removed rapidly from the immediate environment of the massive stars, it is
possible that this region contains very young (< 1 Myr) sites of star
formation. Alternatively, fresh dust grains could be driven into the sphere of
influence of the massive stars, perhaps by the bulk motions of two giant
molecular complexes. The kinematics and morphology of the CO emission in this
region provide some support for this second scenario.


title:
Kinematic Age Estimates for 4 Compact Symmetric Objects from the
  Pearson-Readhead Survey

abstract:
  Based on multi-epoch observations at 15 and 43 GHz with the Very Long
Baseline Array (VLBA) we detect significant angular expansions between the two
hot spots of 4 Compact Symmetric Objects (CSOs). From these relative motions we
derive kinematic ages of between 300 and 1200 years for the radio emission.
These ages lend support to the idea that CSOs are produced in a recent phase of
activity. These observations also allow us to study the evolution of the hot
spots dynamically in individual sources. In all 4 sources the hot spots are
separating along the source axis, but in 1031+567 the tip of one hot spot
appears to be moving almost orthogonally to the source axis. Jet components,
seen in 3 of the 4 sources observed, are found to be moving relativistically
outward from the central engines towards the more slowly moving hot spots.


title: Annihilating Cold Dark Matter

abstract:
  Structure formation with cold dark matter (CDM) predicts halos with a central
density cusp, which are observationally disfavored. If CDM particles have an
annihilation cross section sigma*v ~ 10**(-29) (m/GeV) cm**2, then
annihilations will soften the cusps. We discuss plausible scenarios for
avoiding the early Universe annihilation catastrophe that could result from
such a large cross section. The predicted scaling of core density with halo
mass depends upon the velocity dependence of sigma*v, and s-wave annihilation
leads to a core density nearly independent of halo mass, which seems consistent
with observations.


title:
On Young Neutron Stars as Propellers and Accretors with Conventional
  Magnetic Fields

abstract:
  The similarity of rotation periods of, the anomalous X-ray pulsars (AXPs),
the soft gamma ray repeaters (SGRs) and the dim thermal neutron stars (DTNs)
suggests a common mechanism with an asymptotic spindown phase through the
propeller and early accretion stages. The DTNs are in the propeller stage.
Their luminosities arise from frictional heating in the neutron star. If the
8.4 s rotation period of the DTN RXJ 0720.4-3125 is close to its rotational
equilibrium period, the propeller torque indicates a magnetic field in the
10$^{12}$ Gauss range. The mass inflow rate onto the propeller is of the order
of the AXP accretion rates. The limited range of rotation periods, taken to be
close to equilibrium periods, and magnetic fields in the range 5 E11- 5 E12
Gauss correspond to mass inflow rates 3.2 E14 gm/s < \dot{M} < 4.2 E17 gm/s.
Observed spindown rates of the AXPs and SGRs also fit in with these fields
rather than magnetar fields periods. The source of the mass inflow is a remnant
accretion disk formed as part of the fallback during the supernova explosion.
These classes of sources thus represent the alternative pathways for those
neutron stars that do not become radio pulsars. For the highest mass inflow
rates the propeller action may support enough circumstellar material so that
the optical thickness to electron scattering destroys the X-ray beaming, and
the rotation period is not observable. These are the radio quiet neutron stars
(RQNSs) at the centers of supernova remnants Cas A, Puppis A, RCW 103 and
296.5+10.


title:
Discovery of 0.08 Hz QPO in the power spectrum of black hole candidate
  XTE J1118+480

abstract:
  We found a strong QPO feature at 0.085+/-0.002 Hz in the power spectrum of
X-ray transient XTE J1118+480. The QPO was detected in PCA/RXTE data with an
amplitude close to 10% rms, and the width 0.034+/-0.006 Hz. The shape of the
power spectrum is typical for black hole candidates: almost flat at frequencies
lower than 0.03 Hz, roughly power law with slope ~1.2 from 0.03 to 1 Hz, with a
following steepening to ~1.6 at higher frequencies. The hard energy spectrum
detected up to ~150 keV and the absence of significant X-ray variability at the
high frequencies above 100 Hz strongly support the identification of XTE
J1118+480 as black hole transient.


title: A Search for Environmental Effects on Type Ia Supernovae

abstract:
  We use integrated colors and B and V absolute magnitudes of Type Ia supernova
(SN) host galaxies in order to search for environmental effects on the SN
optical properties. With the new sample of 44 SNe we confirm the conclusion by
Hamuy et al. (1996a) that bright events occur preferentially in young stellar
environments. We find also that the brightest SNe occur in the least luminous
galaxies, a possible indication that metal-poorer neighbourhoods produce the
more luminous events. The interpretation of these results is made difficult,
however, due to the fact that galaxies with younger stellar populations are
also lower in luminosity. In an attempt to remove this ambiguity we use models
for the line strengths in the absorption spectrum of five early-type galaxies,
in order to estimate metallicities and ages of the SN host galaxies. With the
addition of abundance estimates from nebular analysis of the emission spectra
of three spiral galaxies, we find possible further evidence that luminous SNe
are produced in metal-poor neighborhoods. Further spectroscopic observations of
the SN host galaxies will be necessary to test these results and assist in
disentangling the age/metallicity effects on Type Ia SNe.


title: Discovery of a Young Radio Pulsar in a Relativistic Binary Orbit

abstract:
  We report on the discovery of PSR J1141-6545, a radio pulsar in an eccentric,
relativistic 5-hr binary orbit. The pulsar shows no evidence for being
recycled, having pulse period P = 394 ms, characteristic age tau_c = 1.4 x 10^6
yr, and inferred surface magnetic dipole field strength B = 1.3 x 10^12 G. From
the mass function and measured rate of periastron advance, we determine the
total mass in the system to be (2.300 +/- 0.012) solar masses, assuming that
the periastron advance is purely relativistic. Under the same assumption, we
constrain the pulsar's mass to be M_p < 1.348 solar masses and the companion's
mass to be M_c > 0.968 solar masses (both 99% confidence). Given the total
system mass and the distribution of measured neutron star masses, the companion
is probably a massive white dwarf which formed prior to the birth of the
pulsar. Optical observations can test this hypothesis.


title: Spectroscopy of Giant Stars in the Pyxis Globular Cluster

abstract:
  The Pyxis globular cluster is a recently discovered globular cluster that
lies in the outer halo (R_{gc} ~ 40 kpc) of the Milky Way. Pyxis lies along one
of the proposed orbital planes of the Large Magellanic Cloud (LMC), and it has
been proposed to be a detached LMC globular cluster captured by the Milky Way.
We present the first measurement of the radial velocity of the Pyxis globular
cluster based on spectra of six Pyxis giant stars. The mean heliocentric radial
velocity is ~ 36 km/sec, and the corresponding velocity of Pyxis with respect
to a stationary observer at the position of the Sun is ~ -191 km/sec. This
radial velocity is a large enough fraction of the cluster's expected total
space velocity, assuming that it is bound to the Milky Way, that it allows
strict limits to be placed on the range of permissible transverse velocities
that Pyxis could have in the case that it still shares or nearly shares an
orbital pole with the LMC. We can rule out that Pyxis is on a near circular
orbit if it is Magellanic debris, but we cannot rule out an eccentric orbit
associated with the LMC. We have calculated the range of allowed proper motions
for the Pyxis globular cluster that result in the cluster having an orbital
pole within 15 degrees of the present orbital pole of the LMC and that are
consistent with our measured radial velocity, but verification of the tidal
capture hypothesis must await proper motion measurement from the Space
Interferometry Mission or HST. A spectroscopic metallicity estimate of [Fe/H] =
-1.4 +/- 0.1 is determined for Pyxis from several spectra of its brightest
giant; this is consistent with photometric determinations of the cluster
metallicity from isochrone fitting.


title: Magnetic fields around black holes

abstract:
  The electromagnetic field near a rotating black hole is being explored in
educational style here. By employing analytic solutions for electrovacuum
fields, we plot the surfaces of constant flux and we show how the field is
dragged around the black hole by purely geometrical effects of the strong
gravitational field. We visualize the structure of magnetic lines and we also
propose possible astrophysical applications of more realistic situations
involving the presence of plasma: The entangled and twisted field lines result
in reconnection processes which accelerate the particles injected into the
vicinity of the black hole. Such acceleration mechanisms of the electromagnetic
origin are considered as a possible source of high-speed outflows emerging from
numerous nuclei of galaxies where black holes reside.


title: ALFA & 3D: integral field spectroscopy with adaptive optics

abstract:
  One of the most important techniques for astrophysics with adaptive optics is
the ability to do spectroscopy at diffraction limited scales. The extreme
difficulty of positioning a faint target accurately on a very narrow slit can
be avoided by using an integral field unit, which provides the added benefit of
full spatial coverage. During 1998, working with ALFA and the 3D integral field
spectrometer, we demonstrated the validity of this technique by extracting and
distinguishing spectra from binary stars separated by only 0.26". The
combination of ALFA & 3D is also ideally suited to imaging distant galaxies or
the nuclei of nearby ones, as its field of view can be changed between
1.2"x1.2" and 4"x4", depending on the pixel scale chosen. In this contribution
we present new results both on galactic targets, namely young stellar objects,
as well as extra-galactic objects including a Seyfert and a starburst nucleus.


title: Extremely High Energy and Violation of Lorentz Invariance

abstract:
  Extremely high-energy(EHE) cosmic rays might provide a chance to check a
violation of the Lorentz symmetry of spacetime. Some theoretical consideration
is described about why the Lorentz symmetry might break-down in EHE phenomena
in this universe. Some models which introduce the violation of the Lorentz
symmetry will be discussed.


title:
The X-ray spectra of Compton-thick Seyfert 2 galaxies as seen by
  BeppoSAX

abstract:
  Results from BeppoSAX observations of Compton--thick Seyfert 2 galaxies are
summarized and reviewed, and their general properties derived and discussed. In
five out of the seven observed sources, the nucleus is directly visible at high
X-ray energies, where the photons penetrate absorbers with column densities in
the range 1.1-4.3x10^{24} cm-2 (in the other two sources, NGC 1068 and NGC
7674, the nucleus is instead totally obscured at all energies, implying even
larger column densities). In most sources there is unambiguous evidence of a
reflection component from optically thick, cold matter, while in two (or maybe
four) cases there is also evidence of reflection from ionized matter. For the
sources with a measured X-ray luminosity, a comparison with the infrared
luminosity is made; while in two cases (the Circinus galaxy and NGC 4945) the
IR emission appears to be dominated by starburst activity, in the other three
sources (NGC 6240, Mrk 3 and TOL 0109-383) it is likely to be dominated by
reprocessing of the UV and X-ray photons emitted by an AGN.


title:
A method of self-consistent three-dimensional solution of the
  magnetohydrostatic equations using magnetogram data

abstract:
  A technique is proposed for constructing three-dimensional solutions
comlplying with the self-consistent magnetohydrostatic (MHS) equations and with
observations along the line of sight of the magnetic field at the photosphere.
The technique is a generalization of a paper Rudenko, {\tt
arXiv:astro-ph/0004222} to a potential-field approximation. The solution of the
problem under consideration leans a representation of the magnetic field in
terms of a scalar function, with its subsequent harmonic expansion in terms of
a spherical functional basis that satisfies specified boundary conditions. A
numerical realization of the proposed method is expected to permit a real-time
modelling of three-dimensional magnetic field, temperature, pressure and
density distributions.


title:
New type astrophysical solution to the solar neutrino problems and its
  predicitons to the SNO

abstract:
  The anomalously slow rotation of the solar core is just one from a remarkable
lists of fundamental indications showing that the solar core is somehow coupled
to the surface activity cycle. On the other hand, the atmospheric, LSND and
solar neutrino problems are not consistent, therefore one or more of the
neutrino experiments must be attributed - at least in part - to some phenomena
other than neutrino oscillations, or a fourth neutrino is required. We use the
luminosity constraint in a general case not considered yet, taking into account
nuclear reactions occurring in small hot bubbles indicated to be present in the
solar core (Grandpierre, 2000). The dynamic solar model fit the observed
neutrino fluxes within one-and-half sigma even without oscillations. This fit
is shown to be better than the present day MSW and VAC fits. An attracting
perspective is obtained for a simultaneous solution of the neutrino problems
and the solar core-related astrophysical problems. Predictions of the dynamic
solar model are presented for the SNO measurements.


title:
Particle acceleration at ultrarelativistic shocks: an eigenfunction
  method

abstract:
  We extend the eigenfunction method of computing the power-law spectrum of
particles accelerated at a relativistic shock fronts to apply to shocks of
arbitrarily high Lorentz factor. In agreement with the findings of Monte-Carlo
simulations, we find the index of the power-law distribution of accelerated
particles which undergo isotropic diffusion in angle at an ultrarelativistic,
unmagnetized shock is s=4.23 (where s=-d(ln f)/dp with f the Lorentz invariant
phase-space density and p the momentum). This corresponds to a synchrotron
index for uncooled electrons of a=0.62 (taking cooling into account a=1.12),
where a=-d(ln F)/dn, F is the radiation flux and n the frequency. We also
present an approximate analytic expression for the angular distribution of
accelerated particles, which displays the effect of particle trapping by the
shock: compared with the non-relativistic case the angular distribution is
weighted more towards the plane of the shock and away from its normal. We
investigate the sensitivity of our results to the transport properties of the
particles and the presence of a magnetic field. Shocks in which the ratio of
Poynting to kinetic energy flux upstream is not small are less compressive and
lead to larger values of $s$.


title: New Stars on the Block

abstract:
  Groups of young stars located in the solar neighborhood have recently
received a lot of attention. These stars, which are $\lesssim$ 10 million years
old, can provide insights into the birth of stars and planetary systems. For
example, the TW Hydrae Association is just at the age when planets are believed
to form, while MBM12 represents an earlier stage. In this Perspective, I
briefly discuss recent research in this field.


title: beta-model and cooling flows in X-ray clusters of galaxies

abstract:
  The spatial emission from the core of cooling flow clusters of galaxies is
inadequately described by a beta-model(Cavaliere and Fusco-Femiano 1976).
Spectrally, the central region of these clusters are well approximated with a
two-temperature model, where the inner temperature represents the multiphase
status of the core and the outer temperature is a measure of the ambient gas
temperature.Following this observational evidence, I extend the use of the
beta-model to a two-phase gas emission, where the two components coexist within
a boundary radius r_cool and the ambient gas alone fills the volume shell at
radius above r_cool. This simple model still provides an analytic expression
for the total surface brightness profile. Based upon a physically meaningful
model for the X-ray emission, this formula can be used (i) to improve
significantly the modeling of the surface brightness profile of cooling flow
clusters of galaxies when compared to the standard beta-model results, (ii) to
constrain properly the physical characteristics of the intracluster plasma in
the outskirts, like, e.g., the ambient gas temperature.


title: Possible Signature of Low Scale Gravity in Ultra High Enegry Cosmic Rays

abstract:
  We show that the existence of low scale gravity at TeV scale could lead to a
direct production of photons with energies above 10^22 eV due to annihilation
of ultra high energy neutrinos on relic massive neutrinos of the galactic halo.
Air showers initialized in the terrestrial atmosphere by these ultra energetic
photons could be collected in near future by the new generation of cosmic ray
experiments.


title: Doubling the number of Be/X-ray binaries in the SMC

abstract:
  A correlation of X-ray source and Halpha emission-line object catalogues in
the Small Magellanic Cloud (SMC) shows that more than two thirds of the
optically identified Be stars in Be/X-ray binaries are found as emission-line
objects in the catalogues. On the basis of this result we propose up to 25
X-ray sources mainly from recent ROSAT catalogues as new Be/X-ray binaries and
give their likely optical counterparts. Also for the five yet unidentified
X-ray pulsars in the SMC we propose emission-line stars as counterparts. This
more than doubles the number of known high mass X-ray binary systems in this
nearby galaxy. The spatial distribution of the new candidates is similar to
that of the already identified Be/X-ray binaries with a strong concentration
along the SMC main body and some systems in the eastern wing. The new
candidates contribute mainly to the low-luminosity end of the X-ray luminosity
distribution of Be/X-ray binaries. A comparison with the luminosity
distribution in the Milky Way reveals no significant differences at the
high-luminosity end and the large number of low-luminosity systems in the SMC
suggests that many such systems may still be undetected in the Galaxy. The
overall ratio of known Be to OB supergiant X-ray binaries in the SMC is an
order of magnitude larger than in the Galaxy, however, might show spatial
variations. While in the eastern wing the ratio is comparable to that in the
Galaxy no supergiant X-ray binary is currently known in the main body of the
SMC. Possible explanations include a different star formation history over the
last ~15 My.


title:
The Chandra X-ray Observatory Resolves the X-ray Morphology and Spectra
  of a Jet in PKS 0637-752

abstract:
  The core-dominated radio-loud quasar PKS 0637-752 (z = 0.654) was the first
celestial object observed with the Chandra X-ray Observatory, offering the
early surprise of the detection of a remarkable X-ray jet. Several observations
with a variety of detector configurations contribute to a total exposure time
with the Chandra Advanced CCD Imaging Spectrometer (ACIS; Garmire et al. 2000,
in preparation) of about 100ks. A spatial analysis of all the available X-ray
data, making use of Chandra's spatial resolving power of about 0.4 arcsec,
reveals a jet that extends about 10 arcsec to the west of the nucleus. At least
four X-ray knots are resolved along the jet, which contains about 5% of the
overall X-ray luminosity of the source. Previous observations of PKS 0637-752
in the radio band (Tingay et al. 1998) had identified a kpc-scale radio jet
extending to the West of the quasar. The X-ray and radio jets are similar in
shape, intensity distribution, and angular structure out to about 9 arcsec,
after which the X-ray brightness decreases more rapidly and the radio jet turns
abruptly to the north. The X-ray luminosity of the total source is log Lx ~
45.8 erg/s (2 - 10keV), and appears not to have changed since it was observed
with ASCA in November 1996. We present the results of fitting a variety of
emission models to the observed spectral distribution, comment on the
non-existence of emission lines recently reported in the ASCA observations of
PKS 0637-752, and briefly discuss plausible X-ray emission mechanisms.


title:
Testing the photoionization models of powerful radio galaxies: Mixed
  line-emitting media in 3C 321

abstract:
  The photoionization models for the narrow emission line regions of powerful
radio galaxies have yet to be tested in depth. To this end, we present
high-quality long-slit spectroscopy of the powerful double-nucleus radio galaxy
3C 321. The data have good enough spatial resolution to be able to trace the
variation in emission-line properties on kpc scales. Continuum modelling and
subtraction enables the faint emission line fluxes to be measured in several
regions across the emission line nebula. We plot diagnostic line-ratio diagrams
and compare them with the predictions of various photoionization models,
finding that the data is best fit by models which assume a mixture of optically
thin and thick clouds illuminated by a power-law continuum.
  The emission line kinematics, line ratios and deduced physical conditions
show remarkably little variation across the source. We deduce a mean electron
density of 400 +/- 120 cm-3 and a mean temperature of 11500 +/- 1500 K.
Assuming a single population of optically thick line-emitting clouds, we
calculate a mean photoionization parameter of (1.1 +/- 0.5) x 10e-2 and hence a
photoionizing photon luminosity of Q ~ 10e55 -- 10e56 photon/s/sr. This
indicates a central engine as luminous as that of the powerful quasar 3C 273,
yet there is no evidence for such an energetically prolific central engine at
either far-infrared or radio wavelengths. We therefore conclude that the
mixed-media models, which give Q ~ 5 x 10e53 -- 5 x 10e54, represent a more
likely scenario.
  As a by-product of the continuum subtraction we infer that young stellar
populations account for ~ 0.4% of the visible stellar mass in the galaxy, and
that these populations are spatially extended.


title: The Case for an Accelerating Universe from Supernovae

abstract:
  The unexpected faintness of high-redshift Type Ia supernovae (SNe Ia), as
measured by two teams, has been interpreted as evidence that the expansion of
the Universe is accelerating. We review the current challenges to this
interpretation and seek to answer whether the cosmological implications are
compelling. We discuss future observations of SNe Ia which could offer
extraordinary evidence to test acceleration.


title: Hydrodynamical Survey of First Overtone Cepheids

abstract:
  A hydrodynamical survey of the pulsational properties of first overtone
Galactic Cepheids is presented. The goal of this study is to reproduce their
observed light- and radial velocity curves. The comparison between the models
and the observations is made in a quantitative manner on the level of the
Fourier coefficients. Purely radiative models fail to reproduce the observed
features, but convective models give good agreement.
  It is found that the sharp features in the Fourier coefficients are indeed
caused by the P1/P4 = 2 resonance, despite the very large damping of the 4th
overtone. For the adopted mass-luminosity relation the resonance center lies
near a period of 4.2d +/- 0.2 as indicated by the observed radial velocity
data, rather than near 3.2d as the light-curves suggest.


title: IR-TF Relation In The Zone Of Avoidance With 2MASS

abstract:
  Using the Tully-Fisher relation, one can map the peculiar velocity field and
estimate the mass in regions such as the Great Attractor. 2MASS is surveying
the full sky in J, H and K bands and has the great advantage that it allows us
to detect galaxies more uniformly to lower Galactic latitude than optical
surveys. This study shows the feasibility of using 2MASS and the TF relation to
probe large scale structure. We found that (i) we can use axis ratio $b/a$ up
to 0.5; (ii) intrinsic extinction is present (up to 0.5mag at J, 0.1 mag at K);
(iii) the zero-point of the TF relation is independent of the 2MASS magnitude
measurement and is consistent with the HST Key-Project value; (iv) the 2MASS
K-band 20th mag/arcsec$^2$ isophotal aperture magnitude produces the best TF
relation; and (v) there is no type dependence of the residuals