J/A+A/684/A121 SRG/eROSITA all-sky survey coronal content (Freund+, 2024)
The SRG/eROSITA all-sky survey. Identifying the coronal content with HamStar.
Freund S., Czesla S., Predehl P., Robrade J., Salvato M., Schneider P.C.,
Starck H., Wolf J., Schmitt J.H.M.M.
<Astron. Astrophys. 684, A121 (2024)>
=2024A&A...684A.121F 2024A&A...684A.121F (SIMBAD/NED BibCode)
ADC_Keywords: X-ray sources ; Stars, late-type ; Cross identifications
Keywords: methods: statistical - stars: activity - stars: coronae -
stars: late-type - X-ray: stars
Abstract:
The first eROSITA all-sky survey (eRASS1) performed onboard of the
Spectrum-Roentgen-Gamma mission (SRG) provides more than 900000 X-ray
sources in the 0.2-2.3keV band located in the western hemisphere.
We present identifications of the eRASS1 sources obtained using our
HamStar method, which was designed for the identification of coronal
X-ray sources.
HamStar is a Bayesian framework that estimates coronal probabilities
for each eRASS1 source based on a cross-match with optical
counterparts from Gaia DR3. It considers geometric properties, such as
the angular separation and positional uncertainty, as well as
additional properties namely the fractional X-ray flux, color, and
distance.
We identify 138800 coronal eRASS1 sources and estimate a completeness
and reliability of about 91.5% for this sample, which we confirmed
with Chandra detections. This is the largest available sample of
coronal X-ray emitters and we find nearly five times as many coronal
sources as in the ROSAT all-sky survey. The coronal eRASS1 sources are
made up sources of all spectral types and the onset of convection and
the saturation limit are clearly visible. As opposed to previous
samples, rare source types are also well populated. About 10% of the
coronal eRASS1 sources have a correlated secondary counterpart, which
is a wide binary companion or belongs to the same stellar cluster. We
also identify 6700 known unresolved binaries, and an excess of fast
binary periods below 10d. Furthermore, the binary sequence is clearly
visible in a color-magnitude diagram. When combining the coronal
eRASS1 sources with rotation modulations from Gaia DR3, we find 3700
X-ray sources with known rotation periods, which is the largest sample
of this kind. We fitted the rotation-activity relation and convection
turnover times for our flux limited sample. We do not detect the
low-amplitude fast rotators discovered in the Gaia DR3 sample in
X-rays.
Description:
We present the coronal identifications of the main eRASS1 catalog
obtained with the HamStar method. HamStar performs a crossmatch of the
eRASS1 sources with eligible coronal counterparts from Gaia DR3 and
Tycho2 restricted to sources brighter than G=19mag and with a
parallax over error >3. For each eRASS1 source, a coronal probability
(pcoronal) is estimated and for every counterpart, a matching
probability (p_ij) is derived by a Bayesian framework. It considers
geometric properties of the match in addition to astrophysical
properties, i.e., the fractional X-ray flux, color, and distance of
the counterpart. The catalog of likely identifications contains 149
300 counterparts to 139 700 eRASS1 sources with pcoronal>0.53 and
p_ij>0.1. This sample is expected to be complete and reliable to
about 91.5% and its properties are discussed in Freund the paper. The
catalog of possible identifications contains further 23900
counterparts to 23000 eRASS1 sources with 0.53>pcoronal>0.2 and
p_ij>0.1. We expect most of these counterparts to be spurious
associations but this sample still contains some correct coronal X-ray
sources. Although the HamStar method is optimized for coronal
identifications, some sources have properties more typical for
extragalactic or accreting objects and we flagged these sources
(CORONAL≡0). Furthermore, we flagged sources affected by optical
loading (FLAG_OPT) or with a different best counterpart obtained by
the NWAY algorithm (NWAY_DIFFCTP). These identifications should be
interpreted with care.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
like_ctp.dat 209 149311 Likely coronal identifications of the eRASS1
main sources
pos_ctp.dat 209 23900 Possible but less likely coronal identifications
of the eRASS1 main sources
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
I/259 : The Tycho-2 Catalogue (Hog+ 2000)
J/A+A/482/A34 : SRG/eROSITA all-sky survey catalogs (eRASS1) (Merloni+, 2024)
Byte-by-byte Description of file: like_ctp.dat pos_ctp.dat
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Bytes Format Units Label Explanations
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1- 23 A23 --- ERO IAU name of the eRASS1 source (ERO_IAUNAME)
25- 34 F10.2 d MJD [58828.93/59011.42] Epoch of the observation
of the eRASS1 source (ERO_MJD)
36- 40 F5.2 arcsec ePos Positional uncertainty of the eRASS1 source
(EROPOSERR)
42 I1 --- CtpRank [1/4] Rank of the counterpart that increase
for less likely alternative counterparts
(CTP_RANK)
44- 65 I22 --- CtpId Identifier of the counterpart (CTP_ID) (1)
67- 72 F6.2 arcsec CtpSep Proper motion corrected angular separation
between eRASS1 source and counterpart
(CTP_SEP) (2)
74- 79 F6.4 --- p-coronal [0/1] Probability of the eRASS1 source to be
coronal (p_coronal)
81- 86 F6.4 --- p-ij [0/1] Probability of the counterpart to be
associated to the eRASS1 source (p_ij)
88- 97 F10.6 deg RAdeg Proper motion corrected right ascension of the
counterpart adopting the observation time of
the eRASS1 source as provided by ERO_MJD,
J2000 (RAdeg)
99-108 F10.6 deg DEdeg Proper motion corrected declination of the
counterpart adopting the observation time of
the eRASS1 source as provided by ERO_MJD,
J2000 (DEdeg)
110-117 E8.3 mW/m2 FX X-ray flux in the 0.2-2.3keV band assuming a
coronal spectrum (Fx)
119-124 F6.2 mag Gmag G band magnitude of the counterpart (Gmag)
126-130 F5.2 mag BP-RP BP-RP color of the counterpart (BP-RP)
132-137 F6.2 mas plx Parallax of the counterpart (plx)
139-178 A40 --- SName Name of the Simbad identification if available
(SIMBAD_NAME)
180-199 A20 --- SOType Classification in the Simbad database
if available (SIMBAD_OTYPE)
201 I1 --- TrainSet [0/1] 1 if counterpart to an eRASS:4 training
set source (TRAIN_SET)
203 I1 --- Coronal [0/1] 0 if the properties are untypical for
coronal X-ray emitters (CORONAL)
205 I1 --- OB-Star [0/1] 1 for likely reddened OB stars (OB_STAR)
207 I1 --- FlagOpt [0/1] 1 if the source is affected by optical
loading (FLAG_OPT)
209 I1 --- NWAYDCtp [0/1] 1 if NWAY provides a different best
counterpart (NWAY_DIFFCTP)
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Note (1): source_id if Gaia source, otherwise combination of TYC1, TYC2, TYC3;
for Tycho-2 only sources CTP_ID < 1e10.
Note (2): adopting the observation time of the eRASS1 source as provided by MJD.
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Acknowledgements:
Sebastian Freund, sebastian.freund(at)uni-hamburg.de
Refernces:
Merloni et al., 2024A&A...482A..34M 2024A&A...482A..34M, Cat. J/A+A/482/A34
Predhel et al., 2021A&A...647A...1P 2021A&A...647A...1P
(End) Patricia Vannier [CDS] 31-Jan-2024