# Refutation of K2-256b and Rejection of 130 Unconfirmed Transiting Planet
Candidates with Gaia DR3 NSS

Thomas W. Tarrants11affiliation: Corresponding Email<EMAIL_ADDRESS>Elvis O. Mendes22affiliation: Corresponding Email:
<EMAIL_ADDRESS>
###### Abstract

Much of the exoplanet discovery efforts over the next several years are
largely tasked with finding candidates for the upcoming Ariel mission. This is
a role that TESS is well-suited for. Radial velocity follow-up is needed to
confirm the planetary nature of these systems, as many of its planet
candidates turn out to be eclipsing binary systems with small stellar
secondaries. Focused Doppler follow-up to obtain these radial velocities is
expensive. The Gaia mission’s radial velocity measurements on its target stars
are not adequately precise for a general search for orbiting planetary
companions. While the RV data has yielded thousands of spectroscopic binary
systems, only an extreme minority of these reach into the planetary-mass
regime. Nonetheless, they do detect eclipsing binary systems that can
masquerade as transiting hot Jupiters. In this work, we compare the Gaia DR3
Non-Single Stars catalogue to the current planet candidate list from TESS and
determine several of these candidate planetary systems are actually eclipsing
binaries. We find $\sim 130$ eclipsing binaries among the TOI and EPIC lists
that do not appear to be in the literature, including the previously
statistically validated planet K2-256 b. This work illustrates the usefulness
of Gaia to exoplanet validation efforts and will help guide follow-up efforts
for discovering new transiting planets for the Ariel mission by avoiding
misdirecting valuable telescope time.

###### Subject headings:

planetary systems - planets and satellites: atmospheres - techniques:
spectroscopic - methods: data analysis

††slugcomment: Draft Version; not for circulation

##  I. Introduction

With the advent of space-based transit surveys like Kepler and TESS, the
floodgates have been opened: thousands of candidate transiting planets have
been identified, allowing for extrasolar planets to be understood at the
population level. Nevertheless, important to maintaining a high-fidelity
sample of extrasolar planets is excluding astrophysical false-positives –
eclipsing binary stars that produce transits that appear to mimic those of
extrasolar giant planets.

Many more candidate planets have been identified than can pursued with follow-
up ground-based Doppler detection, and many of the smaller planet candidates
identified by these missions are inaccessible to Doppler detection without a
lengthy and intensive dedication of telescope time. There is simply not enough
high-precision spectrometers to go around.

This problem is compounded by non-negligible false-positive rates. Santerne et
al. (2012) used SOPHIE radial velocity data to estimate a false positive rate
of $34.8\pm 6.5$ percent for hot Jupiters from Kepler. Concerns over the need
to identify genuine planets from false positives encouraged the development of
statistical validation techniques where false positive scenarios were ruled
out to sufficiently high levels of confidence that a candidate planet without
a Doppler detection could be argued to be "validated" with false positive
probabilities below a sought threshold (Morton, 2012), typically on the order
of $10^{-3}$.

Celestia111
Website: https://celestiaproject.space/
Discord: https://discord.gg/gYagY6W2Gv is a free, flexible, editable 3D Space
Simulator that allows users to view solar and extrasolar planetary objects,
moons, comets, etc. There is a community of content creators for it that add
extrasolar planets as they’re discovered, various eclipsing binaries, and
other phenomena of interest. It was noticed by this community that some of the
new TESS planet candidates were overlapping with known eclipsing binary stars,
especially from the EBLM project (Triaud et al., 2017). This motivated an
attempt to identify more systems out of a desire to help exclude candidate
planets that were clearly astrophysical false positives.

The Gaia DR3 NSS SB1 catalogue (Gaia Collaboration, 2023) contains over a
hundred thousand spectroscopic binaries, many of which are no-doubt
transiting. Combining this catalogue with the TESS list of transiting planet
candidates regularly updated at the Exoplanet Follow-up Observing Project
(ExoFOP) website provides a way of constraining the nature of these candidate
planets and in many cases determining whether if they can be attributed to
astrophysical sources, such as eclipsing binaries. For thoroughness, we also
performed the same check on the list of planets and planet candidates
identified by the Kepler-K2 mission. We found over 130 matches between Gaia
SB1 systems and planet candidates where the Gaia system could be positively
matched to the source of the transits identified by these two missions,
including most interestingly a planet that had been statistically validated at
K2-256.

##  II. Methodology

Two .csv files, one containing the TESS Object of Interest (TOI) list which
was downloaded from the ExoFOP, and the other containing a list of Kepler-K2
candidates from the NASA Exoplanet Archive. The Gaia DR3 NSS SB1 list was then
downloaded from VizieR. The TESS pixel size is 21 arcseconds, but given the
potential for contamination from nearby background eclipsing binaries
contributing flux within the TESS PSF of a given candidate transiting planet
system, we searched for Gaia NSS SB1 targets within $\sim$5 times this radius
limit (250 arcseconds). A search box around the TESS target was defined by
$\alpha_{\text{G}}-(\alpha_{\text{T}}/\cos{\delta_{\text{T}}})<0.1$ and
$\delta_{\text{G}}-\delta_{\text{T}}<0.1$, where the subscripts G and T denote
the coordinates for the Gaia and TESS systems, respectively and the
$\cos{\delta_{\text{T}}}$ accommodates the geometric distortion that arises
from a two-dimensional coordinate system projected onto a spherical sky,
resulting in "pinching" toward the celestial poles. We used the same radius
for the search for matches for Kepler-K2 systems for consistency. Any Gaia
systems within this box were taken as a candidate match to the TESS system.
This search therefore includes many systems that do not have the same Gaia DR3
identifier as the TIC system presented, allowing us to identify nearby
eclipsing binary blends.

###  II.1. Candidates with Known Periods

We accept as a match a Gaia SB1 solution whose period is within a factor of
$10^{-3}$ of the sought period (or a factor of two of the sought period, as
eclipsing binaries can often appear to have a photometric period half the
radial velocity period), or if the Gaia DR3 source ID matches that of the star
with the transiting planet candidate. If a match is found, there are two ways
forward:

a) The Gaia DR3 NSS SB1 period matches the period of the transiting planet
candidate. In this case, we can safely ascertain that the system detected in
transit is an eclipsing binary that has produced the radial velocity
variations that led to its detection by Gaia.

b) The Gaia DR3 NSS SB1 period does not match the period of the transiting
planet candidate. In this case, multiple possibilities present themselves.

It could be that the system is, for example, an eclipsing binary with
approximately equal-brightness stellar components. For circular orbits this
can produce a transit period that is half the true period, and consequently
half the period reported with radial velocity. For eccentric orbits, it’s
possible that an eclipse and a transit occur in the same observation window
with a ratio only related to the true period via the orbital eccentricity and
longitude of periapsis. In this case, the true period and the reported period
from transits could have a non-trivial ratio.

One conceivable scenario is that an unresolved quadruple system - where the
dimmer component is in an edge-on configuration, could be producing transits
detected by Kepler-K2 or TESS, but the brighter pair is what is being picked
up by Gaia DR3 NSS as a spectroscopic binary.

It’s also possible that the reported radial velocity solution is an alias of
the true period, complicating the situation further.

With these caveats in mind, it’s quite possible that one may not be able to
associate a transit period with a Gaia DR3 NSS SB1 period, and this may not be
taken as the ability to rule out an eclipsing binary nature for the system in
question.

As a result, we only claim to rule out planetary nature around a subset of
matches between Gaia DR3 NSS SB1 systems and transiting planet candidates. In
all other cases, we claim no further constraints on their nature.

###  II.2. Single-Transit Candidates

In situations where there is a Gaia SB1 solution for a star with a candidate
single-transit planet, and knowing that there are mismatches between the SB1
period and the TESS or Kepler period for some systems, we cannot, therefore,
determine that the transit event can be explained by an eclipse in the system
as reported by Gaia DR3. This is despite it appearing intuitively to be the
case if the Gaia period is longer than the TESS observation baseline. From
here the only clear path forward is to calculate the predicted transit times
from the Gaia SB1 solution and compare these to the single TESS-reported
transit time. For completeness, this exercise is also done for systems with
known orbital periods, however in such cases it may be much less constraining.

For single-transit systems where we do find a transit time match, we cannot
neglect the possibility that the period given by the Gaia DR3 NSS SB1 solution
is still incorrect - perhaps an integer ratio alias of the true period. This
doesn’t change the results of the present work, however. We seek not to fully
characterize the orbits of these eclipsing binaries, but simply to identify
them among the list of transiting planet candidates.

The need to evaluate single-transit systems is a much more common problem for
TESS systems than for Kepler-K2 systems, owing to the latter’s much longer
observation baseline.

###  II.3. Transit Time Predictions

We must calculate the predicted transit times for Gaia DR3 NSS spectroscopic
binaries to better evaluate whether or not they are responsible for the
detection of a candidate planet in the TESS data.

We first calculate the true anomaly as $f=\pi/2-\omega$, where $\omega$ is the
longitude of periapsis. The eccentric anomaly $E$ is then related to the
eccentricity $e$ via

$E=2\arctan\left(\sqrt{\frac{1-e}{1+e}}\,\tan{\frac{f}{2}}\right)$

The time since periapsis passage is calculated from the orbital period $P$ via

$T_{e}=\frac{P}{2\pi}(E-e\sin{E})$

The time of conjunction $T_{\text{conj}}$ is simply $T_{\text{Peri}}+T_{e}$.
Whether or not this conjunction corresponds to a transit in an edge-on orbit
is what TESS will determine, and is what we’re especially interested in here.

We can also calculate the time of secondary eclipse by calculating the true
anomaly as $f=3\pi/2-\omega$. This might be relevant where only the secondary
eclipse of a long-period eclipsing binary was detected in the TESS
observations.

There are situations where a Gaia DR3 NSS SB1 system identifier corresponds to
a transiting planet candidate system and has the same orbital period, however
the calculated conjunction time may be inconsistent with the transit time
reported by TESS or Kepler. Given the potential issues with the Gaia DR3 NSS
SB1 fitting, this appears to us to be indicative of possible poor fitting of
the radial velocity. In situations where the eccentricity is low, the
longitude of periapsis may be poorly constrained, which necessarily leads to
high levels of uncertainty on the estimated transit time. The propagation of
the error on the transit time from the Gaia SB1 solution may become such a
large fraction of the period of the orbit that a match between it and the
transit time reported by Kepler-K2 or TESS may be non-constraining.
Furthermore if the fitted period is an alias of the true period, then the
transit window could easily not correspond to a true transit detection of the
companion.

As a result, while the conjunction epoch matching with the transit time is
potentially a powerful indicator of the nature of the system, it is our least
reliable test.

In some cases, the predicted transit time from the Gaia DR3 NSS SB1 solution
falls $\sim$half an orbital period away from the transit time identified by
TESS or K2. It’s possible that this indicates that the detected transit is in
fact a secondary eclipse in a system that is inclined and eccentric such that
no primary eclipses occur. Given the limited information we have to work with,
we don’t attempt to assess this in each case.

We find particularly poor matching for systems with low orbital periods from
transit. This is likely due to the rather wide sampling of the system’s radial
velocity from Gaia, resulting in rather severe sample aliasing. As an
illustration of this issue, the known eclipsing binary EPIC 202971774 (Adams
et al., 2016) is reported in Gaia DR3 NSS SB1 as having a radial velocity
period of $658.2135\pm 48.9873$ days, however it’s period from Kepler is
$\sim$0.2359 days.

##  III. Discussion of Specific Systems

###  III.1. EPIC 201257461

The NASA Exoplanet Archive lists this system with a 50.278 day orbit, matching
the Gaia SB1 solution. However, Armstrong, D. J. et al. (2015) analyzed this
system and reported a period of approximately half that value ($\sim$25.160
days). The given transit time is predicted transit time from the Gaia SB1
solution is $\sim$25-days off (and extrapolating the errors backward, the
uncertainty on T${}_{\text{Transit}}$ from the Gaia SB1 solution is only 3.7
percent of the 50-day orbital period, about 4.1 days). Because the stars
appear to be a G+M binary, and because no primary or secondary eclipse would
occur at the time of the Gaia $T_{\text{conj}}$ for a period of 50 days, we
reject the 50-day period given at the NASA Exoplanet Archive in favor of that
of Armstrong, D. J. et al. (2015). Substituting the Gaia SB1 period for the
latter, we find that the Gaia prediction is a good match for the observed
transit time.

###  III.2. EPIC 211808055

The NASA Exoplanet Archive lists this system as having a planet candidate in a
3.382 day orbit. Our Gaia DR3 NSS SB1 coordinate search returned a system at
Gaia DR3 659288410630096000, with a period of $6.76224\pm 0.00068$ days. This
is exactly half (period ratio $0.5001\pm 0.0001$) of the period of the planet
candidate. However, Gaia DR3 659288410630096000 is actually EPIC 211807843,
identified by Kruse et al. (2019) as an eclipsing binary in a 6.7642 day
period. These are not the same star, yet the extraordinary coincidence of the
orbital periods is difficult to ignore. The transit epochs given by the NASA
Exoplanet Archive for EPIC 211808055 and by Kruse et al. (2019) for EPIC
211807843 also match. Therefore, we consider this system to be a blend, and
rule out the planetary nature of EPIC 211808055’s planet candidate.

###  III.3. EPIC 211839430 and EPIC 211839462

EPIC 211839430 and EPIC 211839462 correspond to BD+18 2050A and BD+18 2050B,
respectively. They have the same 2.6128 day orbital period in the NASA
Exoplanet Archive and essentially the same transit time. Neither of them
correspond to the Gaia NSS SB1 source system returned by our coordinate
search. Nonetheless, the secondary component was identified by Pepper et al.
(2008) as an eclipsing binary with a 5.2301 day period. We consider both of
these planet candidates to be clearly non-planetary in nature. The planet
candidate for EPIC 211839430 doesn’t exist, and is blended with the eclipsing
binary EPIC 211839462 with twice the period. Unfortunately Gaia DR3 did not
spectroscopically detect this eclipsing binary.

###  III.4. EPIC 211972627

This system is a known spectroscopic binary from Mermilliod et al. (2009) and
listed in the Ninth Spectroscopic Binary Catalogue (Pourbaix et al., 2004) as
SBC9 3451. Gaia DR3 recovers this spectroscopic binary and the NSS SB1 list
for this star has parameters consistent with SB9. This system appears to be a
76.7 day binary G+M binary in the Praesepe. The NASA Exoplanet archive reports
this system as having an $\sim$earth-sized planet in a $\sim$1.1 day orbit.
This would be a rather interesting discovery if it could be confirmed. Notes
in the Observation Logs for this system on the ExoFOP suggest it appears that
the transit signal is likely to be electronic crosstalk contamination from the
eclipsing binary S Cnc.

###  III.5. EPIC 212024647 and EPIC 212024672

EPIC 212024647 is a clear case of an eclipsing binary. It corresponds to Gaia
DR3 663154156074506752, which Gaia DR3 NSS lists as a spectroscopic binary
with a period ratio within $10^{-4}$ of unity. We notice that the nearby
system EPIC 212024672 has again the same orbital period, as well as the same
transit time reported by K2 for EPIC 212024647. Therefore, equipped with the
new understanding of EPIC 212024647 as an eclipsing binary, we reject the
planetary nature of both systems, with the latter being a blend with the
former.

###  III.6. EPIC 220209578

EPIC 220209578 is reported to have a candidate transiting planet in a
$8.9045\pm 0.0002$ day orbit. There is a brighter star to the North-West, Gaia
DR3 2534988933319166976, which is identified by Gaia DR3 NSS has a
spectroscopic binary in a $17.68055\pm 0.02328$ day orbit (for a period ratio
of $\sim 0.5036$. This looks like a blend with an eclipsing binary with twice
the reported period, and it was identified as TOI-844 by TESS at the $8.9$ day
period. Eclipsing binaries often appear to have half their true orbital period
in light curves as secondary eclipses can sometimes appear similar to primary
eclipses. A complicating factor here, though, is that preliminary
spectroscopic follow-up work performed by the ExoFOP’s TFOPWG finds a centroid
offset not on the Gaia-identified spectroscopic binary, but rather on EPIC
220209578 itself. The nature of this confusion is unclear – are both systems
eclipsing binaries with a coincidental 1:2 ratio periods? – but the weight of
the evidence strongly suggests that the transit-like events identified by
Kepler-K2 on EPIC 220209578 are an astrophysical false positive and not a
genuine planet.

###  III.7. EPIC 228968232 (K2-256)

One of the most interesting and important findings of this work centers around
EPIC 228968232. The system was statistically validated by Livingston et al.
(2018) as having a $2.63^{+0.25}_{-0.21}$ earth-radius planet in a
$5.52011^{0.0024}_{0.0029}$ day orbit. This work earned the system a
designation of K2-256. Our Gaia DR3 NSS SB1 coordinate search returned a
candidate match on the star Gaia DR3 3693923014184650496 (TYC 4941-622-1).
This star lies to the south-west at a distance of $\sim$78.51” from K2-256 and
is significantly brighter (V$\sim$10.46 compared to V$\sim$14.94). Gaia DR3
NSS SB1 lists this as a spectroscopic binary with a period of $5.1872\pm
0.00018$ days, highly consistent with the orbital period of K2-256 b (period
ratio $1.0003\pm 0.0004$). Our epoch matching finds somewhat reasonable
agreement as well. The transit mid-time reported at the NASA Exoplanet Archive
is 2457586.5247, while our calculated transit mid-time from the Gaia DR3 SB1
solution that comes nearest this time is $2457585.47068\pm 0.6908$. This is
off by about a day, though consistent to within 2$\sigma$.

K2-256 b’s confirmation was arrived at by statistical validation. This
eclipsing binary may have been stealthy enough to have evaded the even-odd
test performed by Livingston et al. (2018). Indeed other statistically
validated exoplanets from Kepler-K2 have been determined to be blends with
nearby eclipsing binaries. Shporer et al. (2017) determined that the
statistically validated planets at K2-51, K2-67 and K2-76 were eclipsing
binaries with low-mass stars, and Cabrera et al. (2017) showed that the
statistically validated planets at K2-78, K2-82 and K2-92 were actually caused
by nearby contaminating eclipsing binaries. The latter of these very much
mirrors our proposed situation for K2-256. Consequently, we suggest that
K2-256 b does not exist, and that this joins K2-78, K2-82 and K2-92 in being
caused by an eclipsing binary blend.

Given the significance of such a claim, we wanted to verify that TYC
4941-622-1 is indeed an eclipsing binary with the reported period in Gaia DR3
NSS SB1. We viewed the Kepler-K2 photometry for the star in the MAST (Mikulski
Archive for Space Telescopes) Portal and discovered a clear, classical
eclipsing binary phase curve at the period of K2-256 b. While the primary
eclipse was identified in the Kepler-K2 data for K2-256, the secondary eclipse
appears to have been too faint in the blend scenario, allowing K2-256 to have
survived an even-odd test. Altogether this gives us the confidence we need to
argue that K2-256 b is not a real planet.

Figure 1.— The Kepler-K2 Light Curve of the spectroscopic binary TYC
4941-622-1 phased to the period of the nearby ($\sim$78.51”) exoplanet system
K2-256.

###  III.8. TOI-289

TOI-289 is a single-transit event detected by TESS. Gaia DR3 NSS SB1 lists the
system as being a spectroscopic binary with a $224.706\pm 0.906$ days. The
predicted transit time (JD $2458367.0396\pm 3.406$) does not match the
observed transit time from TESS (JD $2458326.64586$), but the predicted
secondary eclipse time (JD $2458318.7491\pm 3.1553$) is a rather close match.
The difference is $\sim 7.897$ days, or about 4 percent of the orbital period.
Interpreting the transit detection by TESS as the secondary eclipse of a long-
period eclipsing binary explains the rather large transit depth, suggestive of
a $\sim 1.4\,R\text{J}$ object. These radii, while more consistent with the
inflated hot Jupiter population, are not consistent with the radii for giant
transiting planets at orbital periods sufficiently long to make TOI-289.01 a
single-transit object.

TOI-289 was the subject of investigation by Holl et al. (2023) who provided
updated orbital parameters based on the Gaia data. They provided a revised and
more precise orbital period and eccentricity for this system. Using their
orbital parameters and re-calculating the eclipse time, we find a new
prediction of JD $2458320.7856\pm 5.6759$, bringing this into consistency with
the TESS observed transit time. This confirms the system as an eclipsing
binary. We report these more precise parameters in place of the default Gaia
DR3 NSS SB1 parameters in this work.

###  III.9. TOI-2473

The ExoFOP website lists TOI-2473 as having a candidate transiting planet with
a 1.2312-day orbit, as well as a second candidate with a 6.48369-day orbit.
Our Gaia DR3 NSS SB1 coordinate matching brought our attention to the
unrelated foreground star 2MASS J04573259+1025178, which is reported to be a
spectroscopic binary in a $6.48369\pm 0.00077$ day orbit. The similarity with
the second planet candidate is hard to ignore and we suggest that this second
candidate is the result of a nearby eclipsing binary blend. Unfortunately
we’re unable to achieve meaningful constraints from a match of the transit
window from the Gaia orbit solution to the transit time observed by TESS
because the uncertainty in the transit window is two-thirds the orbital
period. We are unable to comment on the nature of the 1.2312-day planet
candidate around TOI-2473.

###  III.10. TOI-2482

TOI-2482 was matched to a Gaia DR3 NSS SB1 entry of Gaia DR3
3173374317940622976. The Gaia period is $7.6680\pm 0.00326$ days, compared to
the TESS period of $14.9316\pm 0.0002$ days. With a ratio of $1.9473\pm
0.0008$, this is close to a factor of two, but not close enough for us to
consider it conclusively an eclipsing binary with either of the reported
periods. The uncertainty on the transit window from the SB1 orbit solution is
also much too large to attempt epoch-matching. The radial velocity semi-
amplitude given by Gaia of $K_{\text{RV}}=1.314\pm 0.188\,\text{km s}^{-1}$,
which at the TESS period corresponds to a mass of $\sim 13\,M_{\text{J}}$, and
at the Gaia period corresponds to a mass of $\sim 10.5\,M_{\text{J}}$. This
possible low (perhaps planetary) mass has prompted us to comment on this
system.

The given radius from TESS ($\sim 1.5\,R_{\oplus}$) is much too small for
either mass. This could be caused by a grazing transit in a high-impact
parameter orbit or contamination from another star. The TESS-reported transit
duration of $\sim 4.729$ hours also appears to make the shorter Gaia period
difficult to explain for this late-K/early-M dwarf star. An inspection of the
TESS light curve data shows one transit each in two TESS Sectors: Sector 5 and
Sector 32. It’s true period may be one of any number of candidate periods
(half, 1/4th, etc the time between the two transits) and the Gaia period must
be wrong.

We cannot, therefore, determine the nature of this system, and we leave it as
a tempting target for future work given it’s (relatively) low $K_{\text{RV}}$.

###  III.11. TOI-4330

TOI-4330 is reported by TESS as a $17R_{\text{J}}$ planet candidate in a
3.3513 day orbit. The star corresponds to the star HD 129051, a K-type giant
reported to have a stellar companion by Mugrauer et al. (2023). Neither the
TICv8.2 radius of $8.7R_{\odot}$ nor the Gaia DR3 radius of $8.3R_{\odot}$
appear to support the claim of a transiting planet in such a short period.

Our coordinate search returned a result at TYC 7304-483-1, which Gaia DR3 NSS
SB1 lists as having a $K=54.1\pm 2.6$ km s-1 signal in a $3.36662\pm 0.00034$
day orbit. This is close, but not quite equal to, the TESS period (period
ratio of $0.9955\pm 0.0001$). We examined the TESS light curve for TYC
7304-483-1 and found eclipses at $\sim 3.6$ days, but given the highly blended
nature of the system, we remain unable to comment on its nature.

###  III.12. TOI-951 and TOI-953

TOI-951 and TOI-953 are the B and A components, respectively, of the visual
binary system ADS 3266. Our Gaia DR3 NSS SB1 search produced the latter of
these two as a match with TOI-953. The Gaia source is reported as a
spectroscopic binary with a period equal to that of the TESS photometric
period. The eclipsing binary nature of the star was also noted by Schanche et
al. (2019).

The same Gaia source was also returned in our coordinate search for TOI-951,
which also has the same periods as TOI-953. TOI-951, therefore, appears to be
a blend with the TOI-953 eclipsing binary. Cosnequently, we reject the
planetary nature of both candidate systems.

##  IV. Conclusions

Searching for Gaia DR3 NSS SB1 systems in the vicinity of known transiting
planet candidates, we find numerous examples of situations where the candidate
transiting planet can be established to be an eclipsing binary star, as well
as some cases where a nearby eclipsing binary with the same orbital period can
be determined to be blended with the candidate planetary system, in both
events leading to a "false positive."

Of particular note, we identify TYC 4941-622-1 as an eclipsing binary from the
Gaia DR3 NSS combined with Kepler light curve data, and note that it has the
same period and ephemeris to the nearby ($\sim$78.51”) statistically validated
transiting planet K2-256 b. This makes it almost certainly the case that
K2-256 b is not a genuine planet, and reinforces an already-noted concerns
about eclipsing binaries surviving statistical validation techniques. The flux
of TYC 4941-622-1 affected the Kepler data for K2-256 only slightly, such that
only the primary eclipses were detected in the K2-256 b light curve. As a
result, K2-256 b passed the even-odd test that would have rejected most
eclipsing binary systems.

We find a higher eclipsing binary identification rate with TESS planet
candidates than we do for Kepler-K2 planet candidates. This is likely because
the TESS target systems are on average much brighter, and consequently more
easily detected by Gaia in the event that they are indeed eclipsing binaries.

Numerous systems in Gaia DR3 NSS SB1 correspond to known transiting planet
candidates but the spectroscopic solution from Gaia does not match the
photometric period from TESS. While the Gaia period is probably wrong, we
suggest that these systems are nevertheless likely to be eclipsing binaries –
something massive must be producing the radial velocity variability identified
by Gaia.

Overall we find that Gaia DR3 NSS is a powerful tool for constraining the true
nature of transiting planet candidates. While Gaia’s radial velocity precision
is essentially inadequate to the task of detecting planetary mass objects, it
can detect eclipsing binaries. A planet candidate system appearing in the Gaia
DR3 NSS SB1 list should be considered an immediate warning, but SB1 stars in
the surrounding area should also be investigated to help identify eclipsing
binary blends that can occur at a variety of distances from the candidate
planetary system.

##  V. Acknowledgements

This research has made use of the Exoplanet Follow-up Observation Program
(ExoFOP; DOI: 10.26134/ExoFOP5) website, which is operated by the California
Institute of Technology, under contract with the National Aeronautics and
Space Administration under the Exoplanet Exploration Program.

Table 1Gaia DR3 NSS SB1 Coordinate Matches with Kepler-K2 Candidate Systems

EPIC ID | Gaia DR3 ID | Identifier? | Period? | Epoch? | Nature | Note
---|---|---|---|---|---|---
EPIC 201160662 | 3599805123787755648 | Yes | Yes | ? | EB | Kruse et al. (2019)
EPIC 201257461 | 3601830428502237312 | Yes | Yes | Yes | EB | Armstrong, D. J. et al. (2015)
EPIC 201516974 | 3798898062211776256 | Yes | Yes | No | EB | New EB
EPIC 202088212 | 3368700905049734784 | Yes | No | No | ? |
EPIC 202971774 | 6045243267437785856 | Yes | No | No | EB | Adams et al. (2016)
EPIC 203485624 | 6048670406520239104 | Yes | Yes | ? | EB | Drake et al. (2017)
EPIC 203942067 | 6049731027225353344 | Yes | No | ? | EB | Kruse et al. (2019)
EPIC 204546592 | 6243506654403685504 | Yes | No | ? | ? |
EPIC 211002562 | 61904742323780992 | Yes | No | ? | ? |
EPIC 211093684 | 66747816167123712 | Yes | Yes | ? | EB | V1283 Tau
EPIC 211342524 | 600099122725424768 | Yes | Yes | Yes | EB | New EB
EPIC 211408138 | 604911410242410752 | Yes | Yes | Yes | EB | HV Cnc
EPIC 211418290 | 601790961883658112 | Yes | Yes | Yes? | EB | New EB
EPIC 211424769 | 602552128870918144 | Yes | Yes | Yes | EB | New EB
EPIC 211452175 | 604460473035451904 | Yes | Yes | Yes | EB | New EB
EPIC 211642307 | 655332195994611584 | Yes | No | No | ? |
EPIC 211705654 | 610081416995398656 | Yes | No | No | ? |
EPIC 211710534 | 610074785565868032 | Yes | Yes | ? | EB | Kruse et al. (2019)
EPIC 211808055 | 659288410630096000 | No | Yes | Yes? | Blend | See discussion
EPIC 211830293 | 611323517241144576 | Yes | Yes | Yes | EB | New EB
EPIC 211839430 | 659847065615319936 | No | No | No | EB | Pepper et al. (2008)
EPIC 211839462 | 659847065615319936 | No | No | No | EB | Pepper et al. (2008)
EPIC 211886472 | 635409251456055168 | Yes | No | No | EB | New EB
EPIC 211972627 | 661302887731820416 | Yes | No | No | Blend? | See discussion
EPIC 212024647 | 663154156074506752 | Yes | Yes | ? | EB | New EB
EPIC 212024672 | 663154156074506752 | No | Yes | ? | Blend | See discussion
EPIC 212033577 | 637075282154501760 | Yes | Yes | Yes | EB | New EB
EPIC 212039539 | 665412587317415296 | Yes | Yes | ? | EB | New EB
EPIC 212069706 | 685756434352272896 | No | No | ? | EB | Adams et al. (2016)
EPIC 212117087 | 665841018894658688 | Yes | Yes | ? | EB | Yu et al. (2018)
EPIC 212772313 | 3631703609673030784 | Yes | No | No | ? |
EPIC 214912104 | 6769386779452266240 | No | Yes | Yes? | Blend |
EPIC 220209578 | 2534988933319166976 | No | Yes | ? | Blend? | See discussion
EPIC 220477223 | 2576503365647719296 | Yes | Yes | Yes | EB | Kruse et al. (2019)
EPIC 228729473 | 3579529686991039360 | Yes | Yes | Yes? | EB | New EB
EPIC 228968232 | 3693923014184650496 | No | Yes | Yes | Blend | K2-256 - See discussion
EPIC 247281516 | 3408649117423934208 | Yes | Yes | Yes? | EB | New EB
EPIC 247724061 | 146833837950817408 | Yes | No | No | ? |
EPIC 248740905 | 3876036185948161792 | Yes | Yes | Yes | EB | New EB
EPIC 249239123 | 6238897432936164736 | Yes | Yes | ? | EB | New EB
EPIC 251292838 | 630850328354376320 | Yes | Yes | No? | EB | New EB
EPIC 251330444 | 635898431051113216 | Yes | Yes | ? | EB | Yu et al. (2018)
EPIC 251380988 | 687194870439222656 | Yes | No | No | ? |

Note. — Matches between Gaia DR3 NSS SB1 and Kepler K2 candidate systems.
Systems identified by this work are marked as ’New EB.’ Systems where there
was no apparent association, either ID, period or epoch, are clearly field
SB1s and have not been included here.

Table 2Gaia DR3 NSS SB1 Coordinate Matches with TESS Object of Interest (TOI)
Systems

TESS ID | Matched Gaia DR3 ID | Identifier? | Period? | Epoch? | Nature | Note
---|---|---|---|---|---|---
TOI-121 | 6571502449115103232 | Yes | Yes | Yes | EB | Triaud et al. (2017)
TOI-148 | 6594248591617970560 | Yes | Yes | ? | EB | Grieves et al. (2021)
TOI-156 | 4720986721294105216 | Yes | Yes | Yes | EB | New EB
TOI-158 | 6508105536369837312 | Yes | No | ? | ? |
TOI-162 | 6804708139515008640 | Yes | Yes | ? | EB | New EB
TOI-184 | 5270358663889956480 | Yes | Yes | ? | EB | New EB
TOI-185 | 4955371367334610048 | Yes | Yes | ? | Pl | Hellier et al. (2009)
TOI-222 | 6531037981670835584 | Yes | ? | No | ? |
TOI-236 | 2434381179836445952 | Yes | Yes | ? | EB | Triaud et al. (2017)
TOI-276 | 4769981165586553728 | Yes | Yes | ? | EB | Triaud et al. (2017)
TOI-289 | 4919562197762515456 | Yes | ? | No | EB | See discussion
TOI-383 | 5280337144228825472 | No | No | ? | Blend | Grieves et al. (2021)
TOI-416 | 3262082160152897408 | Yes | Yes | No? | EB | New EB
TOI-425 | 2988427421239442432 | Yes | Yes | ? | EB | New EB
TOI-446 | 4824755364549309824 | Yes | Yes | ? | EB | Psaridi et al. (2022)
TOI-459 | 4676885550423032064 | Yes | Yes | Yes | EB | New EB
TOI-478 | 2919669912574582912 | Yes | Yes | ? | EB | Psaridi et al. (2022)
TOI-484 | 3220802537980446848 | No | Yes | ? | Blend | New EB
TOI-503 | 650254479499119232 | Yes | Yes | ? | EB | Šubjak et al. (2020)
TOI-586 | 5538255324833781888 | Yes | Yes | Yes | EB | New EB
TOI-592 | 5695996352497664512 | Yes | No | ? | ? |
TOI-604 | 5596318442261247232 | Yes | No | ? | ? |
TOI-646 | 4641589646622686720 | Yes | Yes | ? | EB | New EB
TOI-665 | 5417424326998593408 | Yes | Yes | Yes | EB | New EB
TOI-668 | 5416752486737577984 | Yes | Yes | ? | EB | New EB
TOI-691 | 5569479810090831104 | Yes | Yes | ? | ? |
TOI-707 | 4779298186602189440 | Yes | Yes | No? | EB | EBLM J0418-53
TOI-746 | 5280337144228825472 | Yes | Yes | ? | EB | Grieves et al. (2021)
TOI-759 | 5395959695358663296 | Yes | Yes | ? | EB | New EB
TOI-764 | 5385762893242980992 | Yes | Yes | ? | EB | Psaridi et al. (2022)
TOI-768 | 6194034953338162816 | Yes | No | ? | ? |
TOI-827 | 5210891547437609856 | Yes | No | ? | ? |
TOI-838 | 6161800502228330240 | Yes | Yes | Yes | EB | New EB
TOI-844 | 2534988933319166976 | Yes | No | ? | ? |
TOI-846 | 4916461712411594112 | Yes | Yes | Yes | EB | New EB
TOI-901 | 5925532800797072128 | Yes | Yes | ? | EB | New EB
TOI-924 | 4769649280577737728 | Yes | Yes | ? | EB | New EB
TOI-948 | 2961066353557939456 | Yes | Yes | ? | EB | New EB
TOI-951 | 3285409673726608768 | No | Yes | ? | Blend | See discussion
TOI-953 | 3285409673726608768 | Yes | Yes | ? | EB | See discussion
TOI-996 | 5714269239318650880 | Yes | Yes | ? | EB | New EB
TOI-1018 | 5505717481529404416 | Yes | Yes | ? | EB | New EB
TOI-1035 | 251077357420917376 | Yes | No | No | ? |
TOI-1059 | 5911682531996474624 | Yes | Yes | Yes | EB | New EB
TOI-1072 | 4649937757389347456 | Yes | Yes | Yes | EB | New EB
TOI-1111 | 6445176465824182272 | Yes | Yes | Yes? | EB | New EB
TOI-1115 | 6650192366014887424 | Yes | Yes | ? | EB | New EB
TOI-1119 | 6660655834058823680 | Yes | Yes | Yes | EB | New EB
TOI-1140 | 1421127098253596288 | Yes | Yes | Yes? | EB | New EB
TOI-1141 | 1710280239538684928 | Yes | Yes | Yes | EB | New EB
TOI-1153 | 1726947014749701504 | Yes | Yes | No? | EB | New EB
TOI-1186 | 1635325672880724864 | Yes | Yes | Yes | EB | New EB
TOI-1251 | 2160710158704303360 | Yes | Yes | ? | EB | New EB
TOI-1270 | 2289068176923197952 | Yes | Yes | No | EB | New EB
TOI-1338 | 5494443978353833088 | Yes | No | No | EB | Triaud et al. (2017)
TOI-1341 | 2236532858514382336 | Yes | Yes | Yes | EB | Schanche et al. (2019)
TOI-1371 | 1898569131896247680 | Yes | Yes | Yes? | EB | Schanche et al. (2019)
TOI-1393 | 2004338572785772800 | Yes | No | No | ? |
TOI-1455 | 2246355002042750976 | Yes | Yes | ? | EB | New EB
TOI-1461 | 320523552351605632 | Yes | Yes | ? | EB | Schanche et al. (2019)
TOI-1514 | 2209081592227687680 | Yes | No | ? | ? |
TOI-1553 | 348551718652896000 | Yes | Yes | Yes | EB | New EB
TOI-1567 | 443040655569966208 | Yes | ? | Yes | EB | New EB
TOI-1572 | 352678495029040000 | Yes | 2x | Yes | EB | New EB
TOI-1591 | 462926457230782208 | Yes | ? | Yes | EB | New EB
TOI-1608 | 125548289270234880 | Yes | Yes | ? | EB | V687 Per
TOI-1645 | 345093337969643392 | Yes | Yes | ? | EB | Schanche et al. (2019)
TOI-1656 | 275228582433787904 | Yes | ? | No | ? |
TOI-1677 | 473104258412065408 | Yes | No | No | ? |
TOI-1698 | 957955110633719552 | Yes | 2x | Yes | EB | New EB
TOI-1711 | 932236090550183296 | Yes | 2x | Yes | EB | Maxted (2023)
TOI-1712 | 917823348536224768 | Yes | Yes | ? | EB | Schanche et al. (2019)
TOI-1786 | 1039196547341014016 | Yes | Yes | ? | EB | New EB
TOI-1787 | 802616348383896448 | Yes | Yes | ? | EB | New EB
TOI-1788 | 751544445585226496 | Yes | Yes | Yes | EB | New EB
TOI-1822 | 764958758026610560 | Yes | Yes | Yes? | EB | New EB
TOI-1834 | 1468504126582376448 | Yes | No | ? | ? |
TOI-1856 | 1602005522755589760 | Yes | 2x | No | EB | New EB
TOI-1888 | 5254794943714396800 | No | Yes | Yes? | Blend | New EB
TOI-1897 | 548075249022607744 | Yes | Yes | No | EB | New EB
TOI-1951 | 5199893510584259968 | Yes | Yes | Yes | EB | New EB
TOI-1952 | 5199213874958918784 | Yes | No | ? | ? |
TOI-1974 | 5235114127904811648 | Yes | Yes | ? | EB | New EB
TOI-1991 | 5348534425968598400 | Yes | Yes | ? | EB | New EB
TOI-1996 | 5377428178491618944 | Yes | 2x | ? | EB | New EB
TOI-2008 | 5096613016130459136 | Yes | ? | Yes | EB | New EB
TOI-2028 | 2204963130906718592 | Yes | No | No | ? |
TOI-2038 | 2295415623189777024 | Yes | Yes | ? | EB | New EB
TOI-2065 | 3961485079994112896 | Yes | ? | No | EB | Collins et al. (2018)
TOI-2121 | 1342147666203453312 | Yes | No | ? | ? |
TOI-2157 | 4570820611494681984 | Yes | Yes | Yes | EB | New EB
TOI-2159 | 1363495509089066880 | Yes | Yes | Yes | EB | Schanche et al. (2019)
TOI-2218 | 5285592504869495296 | Yes | No | ? | ? |
TOI-2335 | 4852751438852929920 | Yes | No | ? | ? |
TOI-2349 | 5689821044216119296 | Yes | Yes | Yes? | EB | New EB
TOI-2360 | 4671762272913404160 | Yes | Yes | No | EB | New EB
TOI-2366 | 3023791185522078592 | Yes | Yes | Yes | EB | New EB
TOI-2413 | 6825245573613327616 | Yes | Yes | Yes | EB | New EB
TOI-2442 | 4884422424614580352 | Yes | Yes | Yes | EB | New EB
TOI-2469 | 3173208463482530176 | Yes | Yes | ? | EB | New EB
TOI-2473 | 3291551648758101248 | No | Yes | ? | Blend | See discussion
TOI-2482 | 3173374317940622976 | Yes | 2x? | ? | ? | See discussion
TOI-2489 | 6567569977058424448 | Yes | No | ? | ? |
TOI-2490 | 4818818585874648320 | Yes | No | ? | ? |
TOI-2492 | 3321419774751152128 | Yes | Yes | ? | EB | New EB
TOI-2521 | 3005862518856922752 | Yes | No | ? | ? |
TOI-2533 | 1259922196651254272 | Yes | Yes | ? | EB | New EB
TOI-2543 | 579084083968560256 | Yes | No | ? | EB | Psaridi et al. (2022)
TOI-2544 | 5320246568758675328 | Yes | 2x | Yes | EB | New EB
TOI-2546 | 3147890181029001984 | Yes | No | ? | ? |
TOI-2555 | 5697796768432105216 | Yes | Yes | Yes | EB | New EB
TOI-2598 | 3026047834355902464 | Yes | Yes | Yes | EB | New EB
TOI-2606 | 5301643549272386560 | Yes | Yes | ? | EB | New EB
TOI-2611 | 6404469659144989056 | Yes | No | ? | ? |
TOI-2614 | 4635190862611016448 | Yes | No | ? | ? |
TOI-2664 | 3855170410190523008 | Yes | Yes | ? | EB | New EB
TOI-2674 | 3544898334892093952 | Yes | No | ? | ? |
TOI-2819 | 3166138805578006016 | Yes | Yes | ? | EB | New EB
TOI-3006 | 5310692633056834432 | Yes | Yes | Yes | EB | New EB
TOI-3010 | 5299710470390857728 | Yes | Yes | Yes? | EB | New EB
TOI-3148 | 5202007248674569728 | Yes | Yes | ? | EB | New EB
TOI-3155 | 5869945139392446336 | Yes | Yes | ? | EB | New EB
TOI-3191 | 5851691833256275200 | Yes | Yes | ? | EB | New EB
TOI-3241 | 6070306974290936960 | Yes | Yes | ? | EB | New EB
TOI-3243 | 5872390109623076992 | Yes | No | ? | ? |
TOI-3260 | 4639398560466507904 | Yes | Yes | Yes? | EB | New EB
TOI-3298 | 6419210296144773504 | Yes | Yes | ? | EB | New EB
TOI-3501 | 3486043573401367168 | Yes | Yes | ? | EB | New EB
TOI-3502 | 5343051878733534592 | Yes | Yes | ? | EB | New EB
TOI-3542 | 2057752233480414848 | Yes | Yes | ? | EB | New EB
TOI-3697 | 409061893681183232 | Yes | No | ? | ? |
TOI-3756 | 189461074831319680 | Yes | Yes | ? | EB | New EB
TOI-3796 | 1087913090069066496 | Yes | Yes | ? | EB | New EB
TOI-3904 | 1512692949146107520 | Yes | Yes | No? | EB | New EB
TOI-3995 | 420954215752408192 | Yes | Yes | ? | EB | New EB
TOI-4226 | 5614312912124661632 | Yes | No | ? | ? |
TOI-4245 | 5516850925816335744 | Yes | No | ? | ? |
TOI-4330 | 6215224775792959232 | No | No | ? | ? | See discussion
TOI-4331 | 6005773858021162624 | Yes | No | ? | ? |
TOI-4338 | 6063252821253530752 | Yes | Yes | Yes | EB | New EB
TOI-4400 | 6463801879263478144 | Yes | Yes | ? | EB | New EB
TOI-4420 | 5808849641863958528 | No | Yes | ? | EB | Blend
TOI-4462 | 4605954852723545088 | Yes | Yes | ? | EB | New EB
TOI-4657 | 2395520590619923328 | Yes | Yes | ? | EB | New EB
TOI-4771 | 3087689411148553472 | Yes | No | ? | ? |
TOI-4792 | 577614689757449728 | Yes | Yes | Yes? | EB | New EB
TOI-4807 | 5587000905841875456 | Yes | Yes | ? | EB | New EB
TOI-4973 | 5230545317792027776 | Yes | Yes | No | EB | New EB
TOI-5103 | 600788374781198720 | Yes | 2x | Yes? | EB | New EB
TOI-5149 | 2167586710592820096 | Yes | Yes | Yes | EB | New EB
TOI-5156 | 3278323493085459456 | Yes | Yes | No | EB | New EB
TOI-5197 | 1130631384551617024 | Yes | Yes | ? | EB | New EB
TOI-5200 | 2148571309814936576 | Yes | Yes | No | EB | New EB
TOI-5307 | 2581395161599229952 | Yes | Yes | Yes | EB | New EB
TOI-5372 | 109773424146717568 | Yes | Yes | ? | EB | New EB
TOI-5379 | 983011056484954496 | Yes | Yes | ? | EB | New EB
TOI-5394 | 623779716969345920 | Yes | Yes | Yes | EB | New EB
TOI-5427 | 3341401062125577088 | Yes | Yes | ? | EB | Schmidt et al. (2023)
TOI-5475 | 3429797609407986176 | Yes | Yes | Yes? | EB | New EB
TOI-5547 | 674670853180191360 | Yes | Yes | Yes? | EB | New EB
TOI-5677 | 3643353863081886336 | Yes | Yes | ? | EB | New EB
TOI-5746 | 1018729069670619520 | Yes | ? | Yes | EB | New EB
TOI-5761 | 548058859427458688 | Yes | Yes | No? | EB | New EB
TOI-5811 | 1814257343328666624 | Yes | No | ? | ? |
TOI-5860 | 1802021977935667200 | Yes | Yes | ? | EB | New EB
TOI-5882 | 1869489729418662528 | Yes | Yes | ? | EB | New EB
TOI-6066 | 1117014688955305984 | Yes | No | ? | ? |
TOI-6096 | 3845758148275527936 | Yes | No | ? | ? |
TOI-6106 | 5696528202583814400 | Yes | No | ? | ? |
TOI-6111 | 2070280099026014336 | Yes | Yes | Yes | EB | New EB
TOI-6117 | 2838654459861938944 | Yes | Yes | ? | EB | New EB
TOI-6133 | 1928695681777800960 | Yes | Yes | ? | EB | New EB
TOI-6151 | 2167122162624970624 | Yes | No | ? | ? |
TOI-6207 | 2871631592420978432 | Yes | Yes | ? | EB | New EB
TOI-6210 | 1980382761343741952 | Yes | No | ? | ? |
TOI-6218 | 392652614647892736 | Yes | Yes | ? | EB | New EB
TOI-6242 | 2859788722613818112 | Yes | Yes | ? | EN | New EB
TOI-6549 | 4768885261731108480 | Yes | No | ? | ? |
TOI-6566 | 6197199790185469184 | Yes | No | ? | ? |
TOI-6568 | 6057181524220247680 | Yes | Yes | Yes? | EB | New EB
TOI-6611 | 5795018365391402368 | Yes | Yes | ? | EB | New EB

Note. — Matches between Gaia DR3 NSS SB1 and TESS candidate systems. Systems
identified by this work are marked as ’New EB’

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