The Revolution Revolution: magnetic morphology driven spin-down (1804.01986)
C. Garraffo, J. J. Drake, A. Dotter, J. Choi, D. J. Burke, S. P. Moschou, J. D. Alvarado-Gomez, V. L. Kashyap, O. Cohen
April 5, 2018 astro-ph.SR
Observations of young open clusters show a bimodal distribution of rotation periods that has been difficult to explain with existing stellar spin-down models. Detailed MHD stellar wind simulations have demonstrated that surface magnetic field morphology has a strong influence on wind-driven angular momentum loss. Observations suggest that faster rotating stars store a larger fraction of their magnetic flux in higher-order multipolar components of the magnetic field. In this work, we present a new model for stellar spin-down that, for the first time, accounts for the stellar surface magnetic field configuration. We show how a magnetic complexity that evolves from complex toward simple configurations as a star spins down can explain the salient features of stellar rotation evolution, including the bimodal distribution of both slow and fast rotators seen in young open clusters.
A and F stars as probes of outer Galactic disc kinematics (1801.01043)
A. Harris, J. E. Drew, H. J. Farnhill, M. Monguió, M. Gebran, N. J. Wright, J. J. Drake, S. E. Sale
Jan. 3, 2018 astro-ph.GA, astro-ph.SR
Previous studies of the rotation law in the outer Galactic disc have mainly used gas tracers or clump giants. Here, we explore A and F stars as alternatives: these provide a much denser sampling in the outer disc than gas tracers and have experienced significantly less velocity scattering than older clump giants. This first investigation confirms the suitability of A stars in this role. Our work is based on spectroscopy of $\sim$ 1300 photometrically-selected stars in the red calcium-triplet region, chosen to mitigate against the effects of interstellar extinction. The stars are located in two low Galactic latitude sightlines, at longitudes $\ell = 118^{\circ}$, sampling strong Galactic rotation shear, and $\ell = 178^{\circ}$, near the Anticentre. With the use of Markov Chain Monte Carlo parameter fitting, stellar parameters and radial velocities are measured, and distances computed. The obtained trend of radial velocity with distance is inconsistent with existing flat or slowly rising rotation laws from gas tracers (Brand & Blitz 1993; Reid et al. 2014). Instead, our results fit in with those obtained by Huang et al. (2016) from disc clump giants that favoured rising circular speeds. An alternative interpretation in terms of spiral arm perturbation is not straight forward. We assess the role that undetected binaries in the sample and distance error may have in introducing bias, and show that the former is a minor factor. The random errors in our trend of circular velocity are within $\pm 5$ km s$^{-1}$.
A Comprehensive Library of X-ray Pulsars in the Small Magellanic Cloud: Time Evolution of their Luminosities and Spin Periods (1703.05196)
J. Yang, S. G. T. Laycock, D. M. Christodoulou, S. Fingerman, M. J. Coe, J. J. Drake
March 15, 2017 astro-ph.HE
We have collected and analyzed the complete archive of {\itshape XMM-Newton\} (116), {\itshape Chandra\} (151), and {\itshape RXTE\} (952) observations of the Small Magellanic Cloud (SMC), spanning 1997-2014. The resulting observational library provides a comprehensive view of the physical, temporal and statistical properties of the SMC pulsar population across the luminosity range of $L_X= 10^{31.2}$--$10^{38}$~erg~s$^{-1}$. From a sample of 67 pulsars we report $\sim$1654 individual pulsar detections, yielding $\sim$1260 pulse period measurements. Our pipeline generates a suite of products for each pulsar detection: spin period, flux, event list, high time-resolution light-curve, pulse-profile, periodogram, and spectrum. Combining all three satellites, we generated complete histories of the spin periods, pulse amplitudes, pulsed fractions and X-ray luminosities. Some pulsars show variations in pulse period due to the combination of orbital motion and accretion torques. Long-term spin-up/down trends are seen in 12/11 pulsars respectively, pointing to sustained transfer of mass and angular momentum to the neutron star on decadal timescales. Of the sample 30 pulsars have relatively very small spin period derivative and may be close to equilibrium spin. The distributions of pulse-detection and flux as functions of spin-period provide interesting findings: mapping boundaries of accretion-driven X-ray luminosity, and showing that fast pulsars ($P<$10 s) are rarely detected, which yet are more prone to giant outbursts. Accompanying this paper is an initial public release of the library so that it can be used by other researchers. We intend the library to be useful in driving improved models of neutron star magnetospheres and accretion physics.
A multi-observatory database of X-ray pulsars in the Magellanic Clouds (1703.04708)
J. Yang, S. G. T. Laycock, J. J. Drake, M. J. Coe, S. Fingerman, J. Hong, V. Antoniou, A. Zezas
Using hundreds of XMM-Newton and Chandra archival observations and nearly a thousand RXTE observations, we have generated a comprehensive library of the known pulsars in the Small and Large Magellanic Clouds (SMC, LMC). The pulsars are detected multiple times across the full parameter spaces of X-ray luminosity ($L_X= 10^{31-38}$~erg/s) and spin period ( P$<$1s -- P$>$1000s) and the library enables time-domain studies at a range of energy scales. The high time-resolution and sensitivity of the EPIC cameras are complemented by the angular resolution of Chandra and the regular monitoring of RXTE. Our processing %$\sim$15 year pipeline uses the latest calibration files and software to generate a suite of useful products for each pulsar detection: event lists, high time-resolution light curves, periodograms, spectra, and complete histories of $\dot{P}$, the pulsed fraction, etc., in the broad (0.2-12 keV), soft (0.2-2 keV), and hard (2-12 keV) energy bands. After combining the observations from these telescopes, we found that 28 pulsars show long-term spin up and 25 long-term spin down. We also used the faintest and brightest sources to map out the lower and upper boundaries of accretion-powered X-ray emission: the propeller line and the Eddington line, respectively. We are in the process of comparing the observed pulse profiles to geometric models of X-ray emission in order to constrain the physical parameters of the pulsars. Finally we are preparing a public release of the library so that it can be used by others in the astronomical community.
Origin of asymmetries in X-ray emission lines from the blast wave of the 2014 outburst of nova V745 Sco (1610.05692)
S. Orlando, J. J. Drake, M. Miceli
The symbiotic nova V745 Sco was observed in outburst on 2014 February 6. Its observations by the Chandra X-ray Observatory at days 16 and 17 have revealed a spectrum characterized by asymmetric and blue-shifted emission lines. Here we investigate the origin of these asymmetries through three-dimensional hydrodynamic simulations describing the outburst during the first 20 days of evolution. The model takes into account thermal conduction and radiative cooling and assumes a blast wave propagates through an equatorial density enhancement. From the simulations, we synthesize the X-ray emission and derive the spectra as they would be observed with Chandra. We find that both the blast wave and the ejecta distribution are efficiently collimated in polar directions due to the presence of the equatorial density enhancement. The majority of the X-ray emission originates from the interaction of the blast with the equatorial density enhancement and is concentrated on the equatorial plane as a ring-like structure. Our "best-fit" model requires a mass of ejecta in the outburst $M_{ej} \approx 3\times 10^{-7}\,M_{\odot}$ and an explosion energy $E_b \approx 3 \times 10^{43}$ erg and reproduces the distribution of emission measure vs temperature and the evolution of shock velocity and temperature inferred from the observations. The model predicts asymmetric and blue-shifted line profiles similar to those observed and explains their origin as due to substantial X-ray absorption of red-shifted emission by ejecta material. The comparison of predicted and observed Ne and O spectral line ratios reveals no signs of strong Ne enhancement and suggests the progenitor is a CO white dwarf.
Optical, UV, and X-Ray Evidence for a 7-Year Stellar Cycle in Proxima Centauri (1610.03447)
B. J. Wargelin, S. H. Saar, G. Pojmański, J. J. Drake, V. L. Kashyap
Oct. 11, 2016 astro-ph.SR
Stars of stellar type later than about M3.5 are believed to be fully convective and therefore unable to support magnetic dynamos like the one that produces the 11-year solar cycle. Because of their intrinsic faintness, very few late M stars have undergone long-term monitoring to test this prediction, which is critical to our understanding of magnetic field generation in such stars. Magnetic activity is also of interest as the driver of UV and X-ray radiation, as well as energetic particles and stellar winds, that affect the atmospheres of close-in planets that lie within habitable zones, such as the recently discovered Proxima b. We report here on several years of optical, UV, and X-ray observations of Proxima Centauri (GJ 551; dM5.5e): 15 years of ASAS photometry in the V band (1085 nights) and 3 years in the I band (196 nights), 4 years of Swift XRT and UVOT observations (more than 120 exposures), and 9 sets of X-ray observations from other X-ray missions (ASCA, XMM-Newton, and three Chandra instruments) spanning 22 years. We confirm previous reports of an 83-day rotational period and find strong evidence for a 7-year stellar cycle, along with indications of differential rotation at about the solar level. X-ray/UV intensity is anti-correlated with optical V-band brightness for both rotational and cyclical variations. From comparison with other stars observed to have X-ray cycles we deduce a simple empirical relationship between X-ray cyclic modulation and Rossby number, and we also present Swift UV grism spectra covering 2300-6000 {\AA}.
Simulating the environment around planet-hosting stars - II. Stellar winds and inner astrospheres (1607.08405)
J. D. Alvarado-Gómez, G. A. J. Hussain, O. Cohen, J. J. Drake, C. Garraffo, J. Grunhut, T. I. Gombosi
July 28, 2016 astro-ph.SR
We present the results of a comprehensive numerical simulation of the environment around three exoplanet-host stars (HD 1237, HD 22049, and HD 147513). Our simulations consider one of the latest models currently used for space weather studies in the Heliosphere. Large-scale magnetic field maps, recovered with two implementations of the tomographic technique of Zeeman-Doppler imaging, serve to drive steady-state solutions in each system. This paper contains the description of the stellar wind and inner astrosphere, while the coronal structure was previously discussed in Alvarado-G\'omez et al. (2016). The analysis includes the magneto-hydrodynamical properties of the stellar wind, the associated mass and angular momentum loss rates, as well as the topology of the astrospheric current sheet in each system. A systematic comparison among the considered cases is performed, including two reference solar simulations covering activity minimum and maximum. For HD 1237, we investigate the interactions between the structure of the developed stellar wind, and a possible magnetosphere around the Jupiter-mass planet in this system. We find that the process of particle injection into the planetary atmosphere is dominated by the density distribution rather than velocity profile of the stellar wind. In this context, we predict a maximum exoplanetary radio emission of 12 mJy at 40 MHz in this system, assuming the crossing of a high-density streamer during periastron passage. Furthermore, in combination with the analysis performed in Alvarado-G\'omez et al. (2016), we obtain for the first time a fully simulated mass loss-activity relation, which is compared and discussed in the context of the relation based on astrospheric detections proposed by Wood et al. (2005a). Finally, we provide a characterisation of the 3D properties of the stellar wind of these systems, at the inner edges of their habitable zones.
Photoevaporation and close encounters: how the environment around Cygnus OB2 affects the evolution of protoplanetary disks (1605.01773)
M. G. Guarcello, J. J. Drake, N. J. Wright, J. F. Albacete-Colombo, C. Clarke, B. Ercolano, E. Flaccomio, V. Kashyap, G. Micela, T. Naylor, N. Schneider, S. Sciortino, J. S. Vink
May 5, 2016 astro-ph.GA, astro-ph.SR
In our Galaxy, star formation occurs in a variety of environments, with a large fraction of stars formed in clusters hosting massive stars. OB stars have an important feedback on the evolution of protoplanetary disks around nearby young stars and likely on the process of planet formation occurring in them. The nearby massive association Cygnus OB2 is an outstanding laboratory to study this feedback. It is the closest massive association to our Sun, and hosts hundreds of massive stars and thousands of low mass members. In this paper, we analyze the spatial variation of the disk fraction in Cygnus OB2 and we study its correlation with the local values of Far and Extreme ultraviolet radiation fields and the local stellar surface density. We present definitive evidence that disks are more rapidly dissipated in the regions of the association characterized by intense local UV field and large stellar density. In particular, the FUV radiation dominates disks dissipation timescales in the proximity (i.e. within 0.5 pc) of the O stars. In the rest of the association, EUV photons potentially induce a significant mass loss from the irradiated disks across the entire association, but the efficiency of this process is reduced at increasing distances from the massive stars due to absorption by the intervening intracluster material. We find that disk dissipation due to close stellar encounters is negligible in Cygnus OB2, and likely to have affected 1% or fewer of the stellar population. Disk dissipation is instead dominated by photoevaporation. We also compare our results to what has been found in other young clusters with different massive populations, concluding that massive associations like Cygnus OB2 are potentially hostile to protoplanetary disks, but that the environments where disks can safely evolve in planetary systems are likely quite common in our Galaxy.
Physical parameters of IPHAS-selected classical Be stars. (I. Determination procedure and evaluation of the results.) (1604.05935)
L. Gkouvelis, J. Fabregat, J. Zorec, D. Steeghs, J. E. Drew, R. Raddi, N. J. Wright, J. J. Drake
April 20, 2016 astro-ph.SR
We present a semi-automatic procedure to obtain fundamental physical parameters and distances of classical Be (CBe) stars, based on the Barbier-Chalonge-Divan (BCD) spectrophotometric system. Our aim is to apply this procedure to a large sample of CBe stars detected by the IPHAS photometric survey, to determine their fundamental physical parameters and to explore their suitability as galactic structure tracers. In this paper we describe the methodology used and the validation of the procedure by comparing our results with those obtained from different independent astrophysical techniques for subsamples of stars in common with other studies. We also present a test case study of the galactic structure in the direction of the Perseus Galactic Arm, in order to compare our results with others recently obtained with different techniques and the same sample of stars. We did not find any significant clustering of stars at the expected positions of the Perseus and Outer Galactic Arms, in agreement with previous studies in the same area that we used for verification.
The statistical uncertainties on X-ray flux and spectral parameters from Chandra ACIS-I observations of faint sources: Application to the Cygnus OB2 Association (1603.08372)
J. F. Albacete-Colombo, E. Flaccomio, J. J. Drake, N. J. Wright, M. Guarcello, V. Kashyap
March 28, 2016 astro-ph.IM, astro-ph.HE
We investigate the uncertainties of fitted X-ray model parameters and fluxes for relatively faint Chandra ACIS-I source spectra. Monte-Carlo (MC) simulations are employed to construct a large set of 150,000 fake X-ray spectra in the low photon count statistics regime (from 20 to 350 net counts) using the XSPEC spectral model fitting package. The simulations employed both absorbed thermal (APEC) and non-thermal (power-law) models, in concert with the Chandra ACIS-I instrument response and interstellar absorption. Simulated X-ray spectra were fit assuming a wide set of different input parameters and C-statistic minimization criteria to avoid numerical artifacts in the accepted solutions. Results provide an error estimate for each parameter (absorption, NH, plasma temperature, kT, or power-law slope, Gamma, and flux, and for different background contamination levels. The distributions of these errors are studied as a function of the 1 sigma quantiles and we show how these correlate with different model parameters, net counts in the spectra and relative background level. Maps of uncertainty in terms of the 1 sigma quantiles for parameters and flux are computed as a function of spectrum net counts. We find very good agreement between our estimated X-ray spectral parameter and flux uncertainties and those recovered from spectral fitting for a subset of the X-ray sources detected in the Chandra Cygnus OB2 Legacy Survey diagnosed to be Association members and that have between 20 and 350 net counts. Our method can provide uncertainties for spectral parameters whenever formal X-ray spectral fits cannot be well-constrained, or are unavailable, and predictions useful for computing Chandra ACIS-I exposure times for observation planning.
Simulating the Environment Around Planet-Hosting Stars - I. Coronal Structure (1601.04443)
Jan. 18, 2016 astro-ph.SR
We present the results of a detailed numerical simulation of the circumstellar environment around three exoplanet-hosting stars. A state-of-the-art global magnetohydrodynamic (MHD) model is considered, including Alfv\'en wave dissipation as a self-consistent coronal heating mechanism. This paper contains the description of the numerical set-up, evaluation procedure, and the simulated coronal structure of each system (HD 1237, HD 22049 and HD 147513). The simulations are driven by surface magnetic field maps, recovered with the observational technique of Zeeman Doppler Imaging (ZDI). A detailed comparison of the simulations is performed, where two different implementations of this mapping routine are used to generate the surface field distributions. Quantitative and qualitative descriptions of the coronae of these systems are presented, including synthetic high-energy emission maps in the Extreme Ultra-Violet (EUV) and Soft X-rays (SXR) ranges. Using the simulation results, we are able to recover similar trends as in previous observational studies, including the relation between the magnetic flux and the coronal X-ray emission. Furthermore, for HD 1237 we estimate the rotational modulation of the high-energy emission due to the various coronal features developed in the simulation. We obtain variations, during a single stellar rotation cycle, up to 15\% for the EUV and SXR ranges. The results presented here will be used, in a follow-up paper, to self-consistently simulate the stellar winds and inner astrospheres of these systems.
Classical T Tauri stars with VPHAS$+$: I: H$\alpha$ and $u$-band accretion rates in the Lagoon Nebula M8 (1507.06786)
V. M. Kalari, J. S. Vink, J. E. Drew, G. Barentsen, J. J. Drake, J. Eislöffel, E. L. Martín, Q. A. Parker, Y. C. Unruh, N. A. Walton, N. J. Wright
July 24, 2015 astro-ph.SR, astro-ph.IM
We estimate the accretion rates of 235 Classical T Tauri star (CTTS) candidates in the Lagoon Nebula using $ugri$H$\alpha$ photometry from the VPHAS+ survey. Our sample consists of stars displaying H$\alpha$-excess, the intensity of which is used to derive accretion rates. For a subset of 87 stars, the intensity of the $u$-band excess is also used to estimate accretion rates. We find the mean variation in accretion rates measured using H$\alpha$ and $u$-band intensities to be $\sim$ 0.17 dex, agreeing with previous estimates (0.04-0.4 dex) but for a much larger sample. The spatial distribution of CTTS align with the location of protostars and molecular gas suggesting that they retain an imprint of the natal gas fragmentation process. Strong accretors are concentrated spatially, while weak accretors are more distributed. Our results do not support the sequential star forming processes suggested in the literature.
Activity and Magnetic Field Structure of the Sun-Like Planet Hosting Star HD 1237 (1507.04117)
J. D. Alvarado-Gómez, G. A. J. Hussain, J. Grunhut, R. Fares, J.-F. Donati, E. Alecian, O. Kochukhov, M. Oksala, J. Morin, S. Redfield, O. Cohen, J. J. Drake, M. Jardine, S. Matt, P. Petit, F. M. Walter
July 15, 2015 astro-ph.SR, astro-ph.EP
We analyse the magnetic activity characteristics of the planet hosting Sun-like star, HD 1237, using HARPS spectro-polarimetric time-series data. We find evidence of rotational modulation of the magnetic longitudinal field measurements consistent with our ZDI analysis, with a period of 7 days. We investigate the effect of customising the LSD mask to the line depths of the observed spectrum and find that it has a minimal effect on shape of the extracted Stokes V profile but does result in a small increase in the S/N ($\sim$ 7%). We find that using a Milne-Eddington solution to describe the local line profile provides a better fit to the LSD profiles in this slowly rotating star, which also impacts the recovered ZDI field distribution. We also introduce a fit-stopping criterion based on the information content (entropy) of the ZDI maps solution set. The recovered magnetic field maps show a strong (+90 G) ring-like azimuthal field distribution and a complex radial field dominating at mid latitudes ($\sim$45 degrees). Similar magnetic field maps are recovered from data acquired five months apart. Future work will investigate how this surface magnetic field distribution impacts the coronal magnetic field and extended environment around this planet-hosting star.
X-ray Fading and Expansion in the "Miniature Supernova Remnant" of GK Persei (1503.03181)
D. Takei, J. J. Drake, H. Yamaguchi, P. Slane, Y. Uchiyama, S. Katsuda
We report on a second epoch of Chandra X-ray imaging spectroscopy of the spatially-resolved old nova remnant GK Persei. An ACIS-S3 observation of 97.4 ks was conducted in November 2013 after a lapse of 13.8 years from the last visit in 2000. The X-ray emitting nebula appeared more faint and patchy compared with the first epoch. The flux decline was particularly evident in fainter regions and the mean decline was 30-40 % in the 0.5-1.2 keV energy band. A typical expansion of the brightest part of the remnant was 1.9 arcsec, which corresponds to an expansion rate of 0.14 arcsec yr^{-1}. The soft X-ray spectra extracted from both the 2000 and 2013 data can be explained by a non-equilibrium ionization collisional plasma model convolved with interstellar absorption, though do not allow us to constrain the origin of the flux evolution. The plasma temperature has not significantly evolved since the 2000 epoch and we conclude that the fading of the X-ray emission is due largely to expansion. This implies that recent expansion has been into a lower density medium, a scenario that is qualitatively consistent with the structure of the circumstellar environment photographed soon after the initial explosion more than a century ago. Fainter areas are fading more quickly than brighter areas, indicating that they are fainter because of a lower ambient medium density and consequently more rapid expansion.
Optical and infrared counterparts of the X-ray sources detected in the Chandra Cygnus OB2 Legacy Survey (1501.03761)
M. G. Guarcello, J. J. Drake, N. J. Wright, T. Naylor, E. Flaccomio, V. L. Kashyap, D. Garcia-Alvarez
The young massive OB association Cygnus OB2, in the Cygnus X complex, is the closest (1400 pc) star forming region to the Sun hosting thousands of young low mass stars and up to 1000 OB stars, among which are some of the most massive stars known in our Galaxy. This region holds great importance for several fields of modern astrophysics, such as the study of the physical properties of massive and young low-mass stars and the feedback provided by massive stars on star and planet formation process. Cygnus OB2 has been recently observed with Chandra/ACIS-I as part of the 1.08Msec Chandra Cygnus OB2 Legacy Project. This survey detected 7924 X-ray sources in a square degree area centered on Cyg OB2. Since a proper classification and study of the observed X-ray sources also requires the analysis of their optical and infrared counterparts, we combined a large and deep set of optical and infrared catalogs available for this region with our new X-ray catalog. In this paper we describe the matching procedure and present the combined catalog containing 5703 sources. We also briefly discuss the nature of the X-ray sources with optical and infrared counterparts using their position in the color-magnitude and color-color diagrams.
A deep catalogue of classical Be stars in the direction of the Perseus Arm: spectral types and interstellar reddenings (1410.1533)
R. Raddi, J. E. Drew, D. Steeghs, N. J. Wright, J. J. Drake, G. Barentsen, J. Fabregat, S. E. Sale
Oct. 6, 2014 astro-ph.SR
We present a catalogue of 247 photometrically and spectroscopically confirmed fainter classical Be stars (13 < r < 16) in the direction of the Perseus Arm of the Milky Way (-1 < b < +4, 120 < l < 140). The catalogue consists of 181 IPHAS-selected new classical Be stars, in addition to 66 objects that were studied by Raddi et al. (2013) more closely, and 3 stars identified as classical Be stars in earlier work. This study more than doubles the number known in the region. Photometry spanning 0.6 to 5 micron, spectral types, and interstellar reddenings are given for each object. The spectral types were determined from low-resolution spectra (lambda / Delta-lambda ~ 800-2000), to a precision of 1-3 subtypes. The interstellar reddenings are derived from the (r - i) colour, using a method that corrects for circumstellar disc emission. The colour excesses obtained range from E(B-V) = 0.3 up to 1.6 - a distribution that modestly extends the range reported in the literature for Perseus-Arm open clusters. For around half the sample, the reddenings obtained are compatible with measures of the total sightline Galactic extinction. Many of these are likely to lie well beyond the Perseus Arm.
Accretion and outflow in the proplyd-like objects near Cygnus OB2 (1409.1017)
M. G. Guarcello, J. J. Drake, N. J. Wright, D. Garcìa-Alvarez, K. E. Kraemer
Sept. 3, 2014 astro-ph.SR
Cygnus OB2 is the most massive association within 2kpc from the Sun, hosting hundreds of massive stars, thousands of young low mass members, and some sights of active star formation in the surrounding cloud. Recently, 10 photoevaporating proplyd-like objects with tadpole-shaped morphology were discovered in the outskirts of the OB association, approximately 6-14pc away from its center. The classification of these objects is ambiguous, being either evaporating residuals of the parental cloud which are hosting a protostar inside, or disk-bearing stars with an evaporating disk, such as the evaporating proplyds observed in the Trapezium Cluster in Orion. In this paper we present a study based on low resolution optical spectroscopic observations made with the Optical System for Imaging and low Resolution Integrated Spectroscopy (OSIRIS), mounted on the 10.4m Gran Telescopio CANARIAS (GTC), of two of these protostars. The spectrum of one of the objects shows evidence of accretion but not of outflows. In the latter object, the spectra show several emission lines indicating the presence of an actively accreting disk with outflow. We present estimates of the mass loss rate and the accretion rate from the disk, showing that the former exceeds the latter as observed in other known objects with evaporating disks. We also show evidence of a strong variability in the integrated flux observed in these objects, as well as in the accretion and outflow diagnostics.
The Second Data Release of the INT Photometric H-Alpha Survey of the Northern Galactic Plane (IPHAS DR2) (1406.4862)
Geert Barentsen, H. J. Farnhill, J. E. Drew, E. A. González-Solares, R. Greimel, M. J. Irwin, B. Miszalski, C. Ruhland, P. Groot, A. Mampaso, S. E. Sale, A. A. Henden, A. Aungwerojwit, M. J. Barlow, P. J. Carter, R. L. M. Corradi, J. J. Drake, J. Eislöffel, J. Fabregat, B. T. Gänsicke, N. P. Gentile Fusillo, S. Greiss, A. S. Hales, S. Hodgkin, L. Huckvale, J. Irwin, R. King, C. Knigge, T. Kupfer, E. Lagadec, D. J. Lennon, J. R. Lewis, M. Mohr-Smith, R. A. H. Morris, T. Naylor, Q. A. Parker, S. Phillipps, S. Pyrzas, R. Raddi, G. H. A. Roelofs, P. Rodríguez-Gil, L. Sabin, S. Scaringi, D. Steeghs, J. Suso, R. Tata, Y. C. Unruh, J. van Roestel, K. Viironen, J. S. Vink, N. A. Walton, N. J. Wright, A. A. Zijlstra
Aug. 12, 2014 astro-ph.SR, astro-ph.IM
The INT/WFC Photometric H-Alpha Survey of the Northern Galactic Plane (IPHAS) is a 1800 square degrees imaging survey covering Galactic latitudes |b| < 5 deg and longitudes l = 30 to 215 deg in the r, i and H-alpha filters using the Wide Field Camera (WFC) on the 2.5-metre Isaac Newton Telescope (INT) in La Palma. We present the first quality-controlled and globally-calibrated source catalogue derived from the survey, providing single-epoch photometry for 219 million unique sources across 92% of the footprint. The observations were carried out between 2003 and 2012 at a median seeing of 1.1 arcsec (sampled at 0.33 arcsec/pixel) and to a mean 5\sigma-depth of 21.2 (r), 20.0 (i) and 20.3 (H-alpha) in the Vega magnitude system. We explain the data reduction and quality control procedures, describe and test the global re-calibration, and detail the construction of the new catalogue. We show that the new calibration is accurate to 0.03 mag (rms) and recommend a series of quality criteria to select the most reliable data from the catalogue. Finally, we demonstrate the ability of the catalogue's unique (r-Halpha, r-i) diagram to (1) characterise stellar populations and extinction regimes towards different Galactic sightlines and (2) select H-alpha emission-line objects. IPHAS is the first survey to offer comprehensive CCD photometry of point sources across the Galactic Plane at visible wavelengths, providing the much-needed counterpart to recent infrared surveys.
The corona of HD 189733 and its X-ray activity (1403.1029)
I. Pillitteri, S. J. Wolk, J. Lopez-Santiago, H. M. Guenther, S. Sciortino, O. Cohen, V. Kashyap, J. J. Drake
March 5, 2014 astro-ph.SR
Abridged. Here we report on the X-ray activity of the primary star, HD189733 A, using a new XMM-Newton observation and a comparison with the previous X-ray observations. The spectrum in the quiescent intervals is described by two temperatures at 0.2 keV and 0.7 keV, while during the flares a third component at 0.9 keV is detected. We obtain estimates of the electron density in the range $n_e = 1.6 - 13 \times 10^{10}$ cm$^{-3}$ and thus the corona of HD189733 A appears denser than the solar one. {For the third time, we observe a large flare that occurred just after the eclipse of the planet. Together with the flares observed in 2009 and 2011, the events are restricted to a small planetary phase range of $\phi = 0.55-0.65$. Although we do not find conclusive evidence of a significant excess of flares after the secondary transits, we suggest that the planet might trigger such flares when it passes close to locally high magnetic field of the underlying star at particular combinations of stellar rotational phases and orbital planetary phases. For the most recent flares, a wavelet analysis of the light curve suggests a loop of length of four stellar radii at the location of the bright flare, and a local magnetic field of order of 40-100 G, in agreement with the global field measured in other studies. The loop size suggests an interaction of magnetic nature between planet and star, separated by only $\sim8 R_*$. We also detect the stellar companion (HD 189733 B, $\sim12"$ from the primary star) in this XMM observation. Its very low X-ray luminosity ($L_X = 3.4\times 10^{26}$ erg s$^{-1}$) confirms the old age of this star and of the binary system. The high activity of the primary star is best explained by a transfer of angular momentum from the planet to the star.
Chasing the Identification of ASCA Galactic Objects (ChIcAGO) - An X-ray Survey of Unidentified Sources in the Galactic Plane I: Source Sample and Initial Results (1403.0404)
G. E. Anderson, B. M. Gaensler, D. L. Kaplan, P. O. Slane, M. P. Muno, B. Posselt, J. Hong, S. S. Murray, D. T. H. Steeghs, C. L. Brogan, J. J. Drake, S. A. Farrell, R. A. Benjamin, D. Chakrabarty, J. E. Drew, J. P. Finley, J. E. Grindlay, T. J. W. Lazio, J. C. Lee, J. C. Mauerhan, M. H. van Kerkwijk
March 3, 2014 astro-ph.HE
We present the Chasing the Identification of ASCA Galactic Objects (ChIcAGO) survey, which is designed to identify the unknown X-ray sources discovered during the ASCA Galactic Plane Survey (AGPS). Little is known about most of the AGPS sources, especially those that emit primarily in hard X-rays (2-10 keV) within the F_x ~ 10^-13 to 10^-11 erg cm^-2 s^-1 X-ray flux range. In ChIcAGO, the subarcsecond localization capabilities of Chandra have been combined with a detailed multi-wavelength follow-up program, with the ultimate goal of classifying the >100 unidentified sources in the AGPS. Overall to date, 93 unidentified AGPS sources have been observed with Chandra as part of the ChIcAGO survey. A total of 253 X-ray point sources have been detected in these Chandra observations within 3' of the original ASCA positions. We have identified infrared and optical counterparts to the majority of these sources, using both new observations and catalogs from existing Galactic plane surveys. X-ray and infrared population statistics for the X-ray point sources detected in the Chandra observations reveal that the primary populations of Galactic plane X-ray sources that emit in the F_x ~ 10^-13 to 10^-11 erg cm^-2 s^-1 flux range are active stellar coronae, massive stars with strong stellar winds that are possibly in colliding-wind binaries, X-ray binaries, and magnetars. There is also a fifth population that is still unidentified but, based on its X-ray and infrared properties, likely comprise partly of Galactic sources and partly of active galactic nuclei.
The VST Photometric Halpha Survey of the Southern Galactic Plane and Bulge (VPHAS+) (1402.7024)
J. E. Drew, E. Gonzalez-Solares, R. Greimel, M. J. Irwin, A. Kupcu Yoldas, J. Lewis, G. Barentsen, J. Eisloeffel, H. J. Farnhill, W. E. Martin, J. R. Walsh, N. A. Walton, M. Mohr-Smith, R. Raddi, S. E. Sale, N. J. Wright, P. Groot, M. J. Barlow, R. L. M. Corradi, J. J. Drake, J. Fabregat, D. J. Frew, B. T. Gaensicke, C. Knigge, A. Mampaso, R. A. H. Morris, T. Naylor, Q. A. Parker, S. Phillipps, C. Ruhland, D. Steeghs, Y.C. Unruh, J. S. Vink, R. Wesson, A. A. Zijlstra
March 2, 2014 astro-ph.GA
The VST Photometric Halpha Survey of the Southern Galactic Plane and Bulge (VPHAS+) is surveying the southern Milky Way in u, g, r, i and Halpha at 1 arcsec angular resolution. Its footprint spans the Galactic latitude range -5 < b < +5 at all longitudes south of the celestial equator. Extensions around the Galactic Centre to Galactic latitudes +/-10 bring in much of the Galactic Bulge. This ESO public survey, begun on 28th December 2011, reaches down to 20th magnitude (10-sigma) and will provide single-epoch digital optical photometry for around 300 million stars. The observing strategy and data pipelining is described, and an appraisal of the segmented narrowband Halpha filter in use is presented. Using model atmospheres and library spectra, we compute main-sequence (u - g), (g - r), (r - i) and (r - Halpha) stellar colours in the Vega system. We report on a preliminary validation of the photometry using test data obtained from two pointings overlapping the Sloan Digital Sky Survey. An example of the (u - g, g - r) and (r - Halpha, r - i) diagrams for a full VPHAS+ survey field is given. Attention is drawn to the opportunities for studies of compact nebulae and nebular morphologies that arise from the image quality being achieved. The value of the u band as the means to identify planetary-nebula central stars is demonstrated by the discovery of the central star of NGC 2899 in survey data. Thanks to its excellent imaging performance, the VST/OmegaCam combination used by this survey is a perfect vehicle for automated searches for reddened early-type stars, and will allow the discovery and analysis of compact binaries, white dwarfs and transient sources.
X-ray Development of the Classical Nova V2672 Ophiuchi with Suzaku (1311.5969)
D. Takei, M. Tsujimoto, J. J. Drake, S. Kitamoto
We report the Suzaku detection of a rapid flare-like X-ray flux amplification early in the development of the classical nova V2672 Ophiuchi. Two target-of-opportunity ~25 ks X-ray observations were made 12 and 22 days after the outburst. The flux amplification was found in the latter half of day 12. Time-sliced spectra are characterized by a growing supersoft excess with edge-like structures and a relatively stable optically-thin thermal component with Ka emission lines from highly ionized Si. The observed spectral evolution is consistent with a model that has a time development of circumstellar absorption, for which we obtain the decline rate of ~10-40 % in a time scale of 0.2 d on day 12. Such a rapid drop of absorption and short-term flux variability on day 12 suggest inhomogeneous ejecta with dense blobs/holes in the line of sight. Then on day 22 the fluxes of both supersoft and thin-thermal plasma components become significantly fainter. Based on the serendipitous results we discuss the nature of this source in the context of both short- and long-term X-ray behavior.
The protoplanetary disks in the nearby massive star forming region Cygnus OB2 (1306.5757)
M. G. Guarcello, J. J. Drake, N. J. Wright, J. E. Drew, R. A. Gutermuth, J. L. Hora, T. Naylor, T. Aldcroft, A. Fruscione, D. Garcia-Alvarez, V. L. Kashyap, R. King
June 24, 2013 astro-ph.SR
The formation of stars in massive clusters is one of the main modes of the star formation process. However, the study of massive star forming regions is hampered by their typically large distances to the Sun. One exception to this is the massive star forming region Cygnus OB2 in the Cygnus X region, at the distance of about 1400 pc. Cygnus OB2 hosts very rich populations of massive and low-mass stars, being the best target in our Galaxy to study the formation of stars, circumstellar disks, and planets in presence of massive stars. In this paper we combine a wide and deep set of photometric data, from the r band to 24 micron, in order to select the disk bearing population of stars in Cygnus OB2 and identify the class I, class II, and stars with transition and pre-transition disks. We selected 1843 sources with infrared excesses in an area of 1 degree x 1 degree centered on Cyg OB2 in several evolutionary stages: 8.4% class I, 13.1% flat-spectrum sources, 72.9% class II, 2.3% pre-transition disks, and 3.3% transition disks. The spatial distribution of these sources shows a central cluster surrounded by a annular overdensity and some clumps of recent star formation in the outer region. Several candidate subclusters are identified, both along the overdensity and in the rest of the association.
X-ray Eclipse Diagnosis of the Evolving Mass Loss in the Recurrent Nova U Scorpii 2010 (1303.5766)
D. Takei, J. J. Drake, M. Tsujimoto, J.-U. Ness, J. P. Osborne, S. Starrfield, S. Kitamoto
We report the Suzaku detection of the earliest X-ray eclipse seen in the recurrent nova U Scorpii 2010. A target-of-opportunity observation 15 days after the outburst found a 27+/-5% dimming in the 0.2-1.0 keV energy band at the predicted center of an eclipse. In comparison with the X-ray eclipse depths seen at two later epochs by XMM-Newton, the source region shrank by about 10-20% between days 15 and 35 after the outburst. The X-ray eclipses appear to be deeper than or similar to contemporaneous optical eclipses, suggesting the X-ray and optical source region extents are comparable on day 15. We raise the possibility of the energy dependency in the photon escape regions, and that this would be a result of the supersoft X-ray opacity being higher than the Thomson scattering optical opacity at the photosphere due to bound-free transitions in abundant metals that are not fully ionized. Assuming a spherically symmetric explosion model, we constrain the mass-loss rate as a function of time. For a ratio of actual to Thomson opacity of 10-100 in supersoft X-rays, we find a total ejecta mass of about 10^{-7}-10^{-6} M_{\odot}.
First results of an H-alpha based search of classical Be stars in the Perseus Arm and beyond (1301.1298)
R. Raddi, J. E. Drew, J. Fabregat, D. Steeghs, N. J. Wright, S. E. Sale, H. J. Farnhill, M. J. Barlow, R. Greimel, L. Sabin, R. M. L. Corradi, J. J. Drake
We investigate a region of the Galactic plane, between 120 <= l <= 140 and -1 <= b <= +4, and uncover a population of moderately reddened (E(B-V) \sim 1) classical Be stars within and beyond the Perseus and Outer Arms. 370 candidate emission line stars (13 <= r <= 16) selected from the INT Photometric H-alpha Survey of the Northern Galactic plane (IPHAS) have been followed up spectroscopically. A subset of these, 67 stars with properties consistent with those of classical Be stars, have been observed at sufficient spectral resolution (Delta_lambda \sim 2 - 4 Angstrom) at blue wavelengths to narrow down their spectral types. We determine these to a precision estimated to be +/- 1 sub-type and then we measure reddenings via SED fitting with reference to appropriate model atmospheres. Corrections for contribution to colour excess from circumstellar discs are made using an established scaling to H-alpha emission equivalent width. Spectroscopic parallaxes are obtained after luminosity class has been constrained via estimates of distances to neighbouring A/F stars with similar reddenings. Overwhelmingly, the stars in the sample are confirmed as luminous classical Be stars at heliocentric distances ranging from 2 kpc up to \sim 12 kpc. However, the errors are presently too large to enable the cumulative distribution function with respect to distance to distinguish between models placing the stars exclusively in spiral arms, or in a smooth exponentially-declining distribution.