2022A&A...661A..44S


Query : 2022A&A...661A..44S

2022A&A...661A..44S - Astronomy and Astrophysics, volume 661A, 44-44 (2022/5-1)

A first eROSITA view of ultracool dwarfs.

STELZER B., KLUTSCH A., COFFARO M., MAGAUDDA E. and SALVATO M.

Abstract (from CDS):

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 Spektrum-Roentgen-Gamma mission. 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 extracted all X-ray sources from the catalog of the first survey, eRASS1, that have a UCD or candidate within three times their positional uncertainty. Then we examined all Gaia objects in the vicinity of these 96 X-ray sources and we associated them to the most plausible counterpart on the basis of their spatial separation to the X-ray position and their multiwavelength properties. This way we find 40 UCDs that have a secure identification with an X-ray source (that is bonafide 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. Twenty-one of the bonafide and plausible X-ray emitting UCDs have a spectroscopic confirmation, while the others have been selected based on Gaia photometry and we computed 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 verified the hypothesis that these high values are due to flaring activity through an analysis of the eRASS1 light curve. X-ray spectra could be analyzed for the two brightest objects in terms of count rate, both showing an emission-measure weighted plasma temperature of <kT> = 0.75 keV. 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.

Abstract Copyright: © ESO 2022

Journal keyword(s): X-rays: stars - stars: activity - stars: coronae - stars: flare - brown dwarfs

VizieR on-line data: <Available at CDS (J/A+A/661/A44): table1.dat table2.dat>

Status at CDS : Tables of objects will be appraised for possible ingestion in SIMBAD.

Simbad objects: 22

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Number of rows : 22
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 2MASS J02192210-3925225 ** 02 19 22.1103954432 -39 25 22.539937296   18.5   15.5 13.42 M6+L4 18 0
2 FBS 0444-113B PM* 04 46 51.6818367888 -11 16 47.509528008           M6 1 0
3 FBS 0444-113 ** 04 46 51.72816 -11 16 47.5932     12.252 11.928   M3.0V 20 0
4 FBS 0444-113A PM* 04 46 51.7832900592 -11 16 47.654712588           M5e 1 0
5 BD+13 1727 PM* 07 39 44.1030809064 +13 04 56.489967912       9.1   K5 6 0
6 CD-37 4268 * 08 07 29.8538920824 -37 54 27.428496696   10.59 9.96     ~ 2 0
7 SCR J0850-0318 PM* 08 50 08.6136909696 -03 18 26.192908008   12.49 11.661 11.214 9.77 M1 6 0
8 Gaia EDR3 5762038930728469888 PM* 08 50 09.1207084704 -03 18 30.506899968           ~ 2 0
9 TYC 8573-3247-1 * 08 52 44.8427710416 -55 17 00.640657248   11.35 10.86     ~ 2 0
10 LP 666-9 LM* 08 53 36.1604798120 -03 29 32.197505547     18.959 16.781 14.487 M9Ve 238 0
11 TWA 22 LXB 10 17 26.8927745040 -53 54 26.387425044   15.69 13.96 13.72   M5 77 0
12 Gaia EDR3 3754497583659096320 PM* 10 39 58.4387887272 -12 03 57.611156616           ~ 2 0
13 BD-03 3000 PM* 10 49 59.7159972936 -04 15 47.720887812   10.62 9.74     ~ 2 0
14 Gaia EDR3 3777108250009273856 PM* 10 50 00.1495903224 -04 16 07.323605184           ~ 2 0
15 NAME TW Hya Association As* 11 01.9 -34 42           ~ 889 0
16 NAME Cha 1 MoC 11 06 48 -77 18.0           ~ 1070 1
17 CHXX 16 LM* 11 10 22.2523149192 -76 25 13.841167332         16.58 ~ 29 0
18 SDSS J123337.60+073132.7 QSO 12 33 37.6078017744 +07 31 32.766273516   20.07 19.61     ~ 17 0
19 Gaia EDR3 3902395843353397248 PM* 12 33 37.8947158728 +07 31 37.927996068           ~ 2 0
20 TYC 8662-1667-1 * 13 33 17.7485762760 -53 51 13.030125012   12.21 11.25     ~ 5 0
21 NAME beta Pic Moving Group MGr 14 30 -42.0           ~ 675 0
22 CD-68 1857 PM* 17 43 27.5200462752 -68 56 15.817683444   9.26 8.70     ~ 10 0

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2022.08.09-15:46:25

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