J/A+A/661/A44 A first eROSITA view of ultracool dwarfs (Stelzer+, 2022)
A first eROSITA view of ultracool dwarfs.
Stelzer B., Klutsch A., Coffaro M., Magaudda E., Salvato M.
<Astron. Astrophys. 661, A44 (2022)>
=2022A&A...661A..44S 2022A&A...661A..44S (SIMBAD/NED BibCode)
ADC_Keywords: X-ray sources ; Stars, flare ; Stars, late-type
Keywords: X-rays: stars - stars: activity - stars: coronae - stars: flare -
brown dwarfs
Abstract:
We present the first X-ray detections of ultracool dwarfs (UCDs) from
the first all-sky survey of the extended ROentgen Survey with an
Imaging Telescope Array (eROSITA) onboard the Russian-German
Spektrum-Roentgen-Gamma mission, SRG. We use three publicly available
input catalogs of spectroscopically confirmed UCDs and Gaia-selected
UCD candidates that together comprise nearly 20000 objects. In a
careful source identification procedure we first extract all X-ray
sources from the catalog of the first survey, eRASS1, that have an UCD
or candidate within three times their positional uncertainty. Then we
examine all Gaia objects in the vicinity of these 96 X-ray sources. We
associate the most plausible counterpart on the basis of their spatial
separation to the X-ray position and their multi-wavelength
properties. This way we find 40 UCDs that have a secure identification
with an X-ray source (i.e. bona-fide UCD X-ray emitters) and 18
plausible UCD X-ray emitters for which we consider it likely that the
X-ray source has its origin in the UCD. Twentyone of the bona-fide and
plausible X-ray emitting UCDs have a spectroscopic confirmation, while
the others have been selected based on Gaia photometry and we compute
spectral types from the G-J color. The spectral types of the X-ray
emitting UCDs and candidates range between M5 and M9. The distances of
the eRASS1 UCDs range from 3.5 to 190 pc. The spectroscopically
confirmed UCDs at the high end of the distance distribution are known
to be members of nearby star forming regions. The majority of the UCDs
from the eRASS1 sample show a ratio of X-ray to bolometric luminosity
well above the canonical saturation limit of log(Lx/Lbol)~-3. For
the two most extreme outliers we have verified the hypothesis that
these high values are due to flaring activity through an analysis of
the eRASS1 lightcurve. X-ray spectra could be analysed for the two
brightest objects in terms of count rate, showing both an
emission-measure weighted plasma temperature of <kT≥0.75keV. These
observations demonstrate the potential of eROSITA for advancing our
knowledge on the faint coronal X-ray emission from UCDs by building
statistical samples for which the average X-ray brightness, flares and
coronal temperatures can be derived.
Description:
table 1 summarize the basic X-ray parameters from eRASS1cat for the
UCDs from Gagne and UCD candidates from Reyle (2018, Cat.
J/A+A/619/L8) that are within 3 times the uncertainty of the X-ray
position.
table 2 reports the multi-wavelength properties of the UCDs and UCD
candidates identified as bona-fide or plausible counterparts to an
eRASS1 X-ray source.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 114 96 Basic X-ray parameters from the eRASS1 catalog
for our sample of the UCDs and UCD candidates
table2.dat 178 58 Multi-wavelength properties of the UCDs and UCD
candidates identified as bona-fide or plausible
counterparts to an eRASS1 X-ray source
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
I/347 : Distances to 1.33 billion stars in Gaia DR2 (Bailer-Jones+ 2018)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+, 2003)
II/328 : AllWISE Data Release (Cutri+, 2013)
J/A+A/619/L8 : New ultra-cool and brown dwarf candidates in Gaia DR2
(Reyle+, 2018)
J/A+A/661/A1 : The eFEDS X-ray catalogs (V7.4) (Brunner+, 2022)
J/A+A/661/A2 : Galaxy clusters and groups in eFEDS (Liu+, 2022)
J/A+A/661/A3 : eFEDS counterparts to point-like sources (Salvato+, 2022)
J/A+A/661/A4 : eFEDS optical cluster and group catalog (Klein+, 2022)
J/A+A/661/A5 : The eFEDS AGN catalog (Liu+, 2022)
J/A+A/661/A7 : X-ray properties of eFEDS clusters and groups (Bahar+, 2022)
J/A+A/661/A8 : eFEDS catalogue of variable X-ray sources (Boller+, 2022)
J/A+A/661/A10 : eFEDS galaxy clusters and groups in disguise (Bulbul+, 2022)
J/A+A/661/A23 : Exoplanet X-ray irradiation & evaporation rates (Foster+, 2022)
J/A+A/661/A24 : Corona-chromosphere connection (Fuhrmeister+, 2022)
J/A+A/661/A29 : First eROSITA study of nearby M dwarfs (Magaudda+, 2022)
J/A+A/661/A34 : eta Cha cluster eROSITA X-ray scan (Robrade+, 2022)
J/A+A/661/A35 : eROSITA study of 47 Tuc globular cluster (Saeedi+, 2022)
J/A+A/661/A38 : SRG/ART-XC 1st year all-sky X-ray survey (Pavlinsky+, 2022)
J/A+A/661/A44 : A first eROSITA view of ultracool dwarfs (Stelzer+, 2022)
https://jgagneastro.com/list-of-m6-m9-dwarfs : The online database of
"M6-M9 dwarfs" maintained by J. Gagne
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- GaiaDR2 Gaia DR2 (Cat. I/345) designation (source_id)
21- 39 F19.15 deg RAdeg Right ascension of the boresight corrected
eRASS1 positions (J2000) (ra_corr)
41- 60 F20.16 deg DEdeg Declination of the boresight corrected
eRASS1 positions (J2000) (dec_corr)
62- 66 F5.2 arcsec ePos Error on the eRASS1 positions (delta_radec)
68- 72 F5.2 arcsec SepOX Separation between the proper motion corrected
optical positions and the X-ray positions
(sep_ox)
74- 78 F5.3 ct/s Rate Broad band (0.2-5.0 keV) source count rates
(rate)
80- 84 F5.3 ct/s e_Rate Error on the broad band (0.2-5.0keV) source
count rates (err_rate)
86- 91 F6.1 --- DetML Maximum likelihood for the X-ray detection in
the broad band (col. DETLIKE0 from
eRASS1cat) (detml)
93 A1 --- funiqucd Flag for UCDs being the unique Gaia
counterparts to the eRASS1 source
(flaguniqucd)
95 A1 --- fcpm Flag for common proper motion pairs involving
an UCD or UCD candidate (flag_cpm)
97 A1 --- fxdata Flag for objects with archival X-ray
detections (flag_xdata)
99 A1 --- fbfucd Flag for UCDs considered as 'bona-fide'
counterparts to the eRASS1 sources
(flagbonafide_ucd)
101 A1 --- fplucd Flag for UCDs considered as 'plausible'
counterparts to the eRASS1 sources
(flagplausibleucd)
103-114 A12 --- iCat Original input catalog (iCat) (1)
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Note (1): Original input catalog as follows:
GagneM = refers to the spectroscopically confirmed UCDs,
https://jgagneastro.com/list-of-m6-m9-dwarfs
Reyle (2018) = refers to the Gaia-selected UCD candidates,
Reyle et al., 2018, Cat. J/A+A/619/L8
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- GaiaDR2 Gaia DR2 (Cat. I/345) designation of the
UCD (source_id)
21- 29 F9.6 mag Gmag G-band magnitude from the Gaia DR2 catalog
(Gmag)
31- 36 F6.3 mag Jmag J-band magnitude from the 2MASS
(Cat. II/246) catalog (Jmag)
38- 43 F6.3 mag W1mag ?=- W1-band magnitude from the AllWISE
(Cat. II/328) catalog (W1mag)
45- 51 A7 --- SpTypeopt Spectroscopic spectral type in visual
bandpass (spt_opt) (1)
53- 60 A8 --- SpTypeph Photometric spectral type from the G-J
color index (spt_photo) (2)
62- 79 F18.14 pc Dist Distance from Bailer-Jones et al.
(2018, Cat. I/347) (dist)
81 A1 --- --- [-]
82-102 F21.19 pc e_Dist Lower error on the distance estimated by
Bailer-Jones et al. (2018) (elo_dist)
104-124 F21.19 pc E_Dist Upper error on the distance estimated by
Bailer-Jones et al. (2018) (eup_dist)
126-143 F18.15 [10-6W] logLX log of Lx for the eROSITA band 1+2
(LogLx) (3)
145-163 F19.16 [-] logLX/Lbol log of the ratio between the eROSITA LX and
Lbol from Filippazzo et al.
(2015ApJ...810..158F 2015ApJ...810..158F) (LogLxLbol)
165 A1 --- fyoung Flag for young star (flag_young) (4)
167-171 A5 --- ryoung Reference on young star (ref_young)
173 A1 --- fbinary Flag for binary system (flag_binary) (4)
175-178 A4 --- rbinary Reference on binary system (ref_binary)
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Note (1): The spectral types come from the online database of "M6-M9 dwarfs"
maintained by J. Gagne: https://jgagneastro.com/list-of-m6-m9-dwarfs.
Note (2): We make use of the "Stellar Color/Teff" table maintained by
E. Mamajek:
http://www.pas.rochester.edu/~emamajek/EEM_dwarf_UBVIJHK_colors_Teff.txt
Note (3): log of Lx for the eROSITA band 1+2 calculated with the Bailer-Jones
et al. (2018, Cat. I/347) distance and the rate-to-flux conversion factor for
this energy band estimated as in Magaudda et al. (submitted) (LogLx).
Note (4): References as follows:
1 = Washington Double Star Catalog (2001AJ....122.3466M 2001AJ....122.3466M, Cat. B/wds)
2 = Carpenter et al. (2002AJ....124.1001C 2002AJ....124.1001C)
3 = Song et al. (2003ApJ...599..342S 2003ApJ...599..342S)
4 = Bonnefoy et al. (2009A&A...506..799B 2009A&A...506..799B)
5 = Shkolnik et al. (2009ApJ...699..649S 2009ApJ...699..649S, Cat. J/ApJ/699/649)
6 = Shkolnik et al. (2012ApJ...758...56S 2012ApJ...758...56S, Cat. J/ApJ/758/56)
7 = Kraus et al. (2014AJ....147..146K 2014AJ....147..146K)
8 = Artigau et al. (2015ApJ...806..254A 2015ApJ...806..254A)
9 = Gagne et al. (2015ApJS..219...33G 2015ApJS..219...33G)
10 = Gagne et al. (2015ApJ...798...73G 2015ApJ...798...73G)
11 = Gagne et al. (2018ApJ...862..138G 2018ApJ...862..138G)
12 = Luhman et al. (2018AJ....156...76L 2018AJ....156...76L)
13 = Winters et al. (2019AJ....157..216W 2019AJ....157..216W)
14 = Luhman et al. (2020AJ....160...44L 2020AJ....160...44L)
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Acknowledgements:
Alexis Klutsch, alexis.klutsch(at)astro.uni-tuebingen.de
References:
The Early Data Release of eROSITA and Mikhail Pavlinsky ART-XC on the
SRG mission, 2022, A&A, 661, A1-A46
(End) Alexis Klutsch, Beate Stelzer [IAAT], Patricia Vannier [CDS] 08-Jul-2021