J/A+A/664/A105 Stellar content of the ROSAT all-sky survey (Freund+, 2022)
The stellar content of the ROSAT all-sky survey.
Freund S., Czesla S., Robrade J., Schneider P.C., Schmitt J.H.M.M.
<Astron. Astrophys. 664, A105 (2022)>
=2022A&A...664A.105F 2022A&A...664A.105F (SIMBAD/NED BibCode)
ADC_Keywords: X-ray sources ; Cross identifications ; Stars, late-type
Keywords: X-ray: stars - stars: activity - stars: coronae - stars: late-type -
methods: statistical
Abstract:
We present and apply a method to identify the stellar content of the
ROSAT all-sky survey (RASS).
We performed a crossmatch between the RASS sources and stellar
candidates selected from Gaia Early Data Release 3 (EDR3) and
estimated stellar probabilities for every RASS source from the
geometric properties of the match and additional properties, namely
the X-ray to G-band flux ratio and the counterpart distances.
A comparison with preliminary detections from the first eROSITA
all-sky survey (eRASS1) show that the positional offsets of the RASS
sources are larger than expected from the uncertainties given in the
RASS catalog. From the RASS sources with reliable positional
uncertainties, we identify 28630 (24.9%) sources as stellar; this is
the largest sample of stellar X-ray sources to date. Directly from the
stellar probabilities, we estimate the completeness and reliability of
the sample to be about 93% and confirm this value by comparing it to
the identification of randomly shifted RASS sources, preliminary
stellar eRASS1 identifications, and results from a previous
identification of RASS sources. Our stellar RASS sources contain
sources of all spectral types and luminosity classes. According to
their position in the color-magnitude diagram, many stellar RASS
sources are young stars with ages of a few 107yr or binaries. When
plotting the X-ray to bolometric flux ratio as a function of the
color, the onset of convection and the saturation limit are clearly
visible. We note that later-type stars reach continuously higher
FX/Fbol values, which is probably due to more frequent flaring.
The color distribution of the stellar RASS sources clearly differs
from the unrelated background sources. We present the
three-dimensional distribution of the stellar RASS sources that shows
a clear increase in the source density near known stellar clusters.
Description:
We present the stellar content of the ROSAT all-sky survey (RASS),
which was identified by a crossmatch between the RASS sources and
eligible stellar counterparts from Gaia EDR3. The main catalog
contains counterparts to the 115000 RASS sources with the best
positional accuracy. The identifications to the remaining sources are
listed in the supplementary catalog, but for these sources our
identification procedure is less reliable. The catalogs contain the
names of the RASS sources and the stellar matches (Gaia source ID or
Tycho2 ID if the source is not available in Gaia EDR3), the corrected
positional uncertainties of the RASS sources, the angular separations
between the RASS sources and the stellar identifications, the proper
motion corrected Gaia positions at the RASS observation time, and
basic properties. Sources located more than 1.5mag below the main
sequence are flagged as a subdwarf and are probably the correct
identification but the X-ray emission is not produced by a solar-like
corona. Furthermore, we provide stellar (p_stellar) and matching
probabilities (p_ij) to the RASS sources and the individual
counterparts. These probabilities are estimated with a Bayesian
framework that is based on a training set of sources with a good
geometric match. In the training catalog, the counterparts with high
geometric probabilities (pgeo>0.9) are specified and sources that
are unlikely to be coronal emitters are flagged. Note that we adopted
only the unflagged sources for our training set. The main and
supplementary catalogs contain all stellar counterparts with a
matching probability pij>0.1 to the RASS sources with a stellar
probability pstellar>0.2. RASS sources with multiple counterparts
have several entries in the catalog. For the discussion of the
properties of the stellar RASS sources, we adopted the counterparts
with pstellar>0.51 and pij>0.5 of the main catalog that are not
flagged as a subdwarf.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
main.dat 138 36285 Stellar counterparts to high quality RASS sources
(table B1)
suppl.dat 138 4410 Stellar counterparts to low quality RASS sources
(table B1)
train.dat 136 846 Training set sources (table B2)
--------------------------------------------------------------------------------
See also:
I/259 : The Tycho2 Catalogue (Hog+, 2000)
I/350 : Gaia EDR3 catalog (Gaia Collaboration, 2020)
J/A+A/588/A103 : Second ROSAT all-sky survey (2RXS) source catalog
(Boller+, 2016)
Byte-by-byte Description of file: main.dat suppl.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 21 A21 --- 2RXS ID of RASS source
23- 44 A22 --- Match Source ID of Gaia EDR3 or Tycho2 counterpart
46- 51 F6.2 arcsec ePos Positional uncertainty of RASS
53- 58 F6.2 arcsec Sep Angular separation between RASS source and
counterpart
60- 65 F6.4 --- pstellar [0.2/1.0] Stellar probability
67- 72 F6.4 --- pij [0.1/1.0] Probability of the individual match
74- 83 F10.6 deg RAdeg Right ascension at RASS observation time,
J2000
85- 95 F11.6 deg DEdeg Declination at RASS observation time, J2000
97-104 E8.3 mW/m2 FX Stellar X-ray flux
106-110 F5.2 --- HR [-1.0/1.0]? Hardness ratio
112-117 F6.2 mag Gmag Magnitude in Gaia's G-band
119-124 F6.2 mag BP-RP Gaia's BP-RP color
126-132 F7.2 mas plx Parallax
134-138 A5 --- subdwarf [True False] Source located more than
1.5mag below main sequence
--------------------------------------------------------------------------------
Byte-by-byte Description of file: train.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 21 A21 --- 2RXS ID of RASS source
23- 44 A22 --- Match Source ID of Gaia EDR3 or Tycho2 counterpart
46- 51 F6.2 arcsec ePos Positional uncertainty of RASS
53- 58 F6.2 arcsec Sep Angular separation between RASS
source and counterpart
60- 65 F6.4 --- pgeo [0.9/1.0] Geometric stellar probability
67- 72 F6.4 --- pijgeo [0.9/1.0] Geometric probability of the
individual match
74- 83 F10.6 deg RAdeg Right ascension at RASS observation time,
J2000
85- 95 F11.6 deg DEdeg Declination at RASS observation time, J2000
97-104 E8.3 mW/m2 FX Stellar X-ray flux
106-110 F5.2 --- HR [-1.0/1.0]? Hardness ratio
112-117 F6.2 mag Gmag Magnitude in Gaia's G-band
119-124 F6.2 mag BP-RP Gaia's BP-RP color
126-132 F7.2 mas plx Parallax
134-136 A3 --- flag [FLM ] Flag for unreliable coronal X-ray
emitters (1)
--------------------------------------------------------------------------------
Note (1): Flag as follows:
F = High X-ray to G-band flux ratio
L = High X-ray luminosity
M = Located below main sequence
--------------------------------------------------------------------------------
Acknowledgements:
Sebastian Freund, Sebastian.Freund(at)uni-hamburg.de
(End) Patricia Vannier [CDS] 07-Jun-2022