Query : 2022A&A...661A..29M

2022A&A...661A..29M - Astronomy and Astrophysics, volume 661A, 29-29 (2022/5-1)

First eROSITA study of nearby M dwarfs and the rotation-activity relation in combination with TESS.


Abstract (from CDS):

We present the first results with the ROentgen Survey with an Imaging Telescope Array (eROSITA) on board the Russian Spektrum-Roentgen-Gamma mission, and we combine the new X-ray data with observations with the Transiting Exoplanet Survey Satellite (TESS). We used theSUPERBLINK proper motion catalog of nearby M dwarfs as input sample to search for eROSITA and TESS data. We extracted Gaia DR2 data for the full M dwarf catalog, which comprises ∼9000 stars, and we calculated the stellar parameters from empirical relations with optical/IR colors. Then we cross-matched this catalog with the eROSITA Final Equatorial Depth Survey (eFEDS) and the first eROSITA all-sky survey (eRASS1). After a meticulous source identification in which we associated the closest Gaia source with the eROSITA X-ray detections, our sample of M dwarfs is defined by 687 stars with SpT = K5..M7 (673 from eRASS1 and 14 from eFEDS). While for eRASSl we used the data from the source catalog provided by the eROSITA_DE consortium, for the much smaller eFEDS sample, we performed the data extraction, and we analyzed the X-ray spectra and light curves. This unprecedented data base for X-ray emitting M dwarfs allowed us to place a quantitative constraint on the mass dependence of the X-ray luminosity, and to determine the change in the activity level with respect to pre-main-sequence stars. TESS observations are available for 489 of 687 X-ray detected M dwarfs. By applying standard period search methods, we were able to determine the rotation period for 180 X-ray detected M dwarfs. This is about one-forth of the X-ray sample. With the joint eROSITA and TESS sample, and combining it with our compilation of historical X-ray and rotation data for M dwarfs, we examined the mass dependence of the saturated regime of the rotation-activity relation. A first comparison of eROSITA hardness ratios and spectra shows that 65% of the X-ray detected M dwarfs have coronal temperatures of ∼0.5 keV. We performed a statistical investigation of the long-term X-ray variability of M dwarfs by comparing the eROSITA measurements to those obtained ∼30 yr earlier during the ROSAT all-sky survey (RASS). Evidence for X-ray flares is found in various parts of our analysis: directly from an inspection of the eFEDS light curves, in the relation between RASS and eRASSl X-ray luminosities, and in a subset of stars that displays hotter X-ray emission than the bulk of the sample according to the hardness ratios. Finally, we point out the need to obtain X-ray spectroscopy for more M dwarfs to study the coronal temperature-luminosity relation, which is not well constrained by our eFEDS results.

Abstract Copyright: © ESO 2022

Journal keyword(s): stars: low-mass - stars: activity - stars: rotation - stars: magnetic field - X-rays: stars

VizieR on-line data: <Available at CDS (J/A+A/661/A29): table2.dat table3.dat table5.dat>

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

Simbad objects: 9

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Number of rows : 9
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
1 NAME Orion Nebula Cluster OpC 05 35.0 -05 29           ~ 2160 1
2 V* YZ CMi Er* 07 44 40.1723046464 +03 33 08.875227574 13.761 12.831 11.225 9.958 8.263 M4.0Ve 831 0
3 PM J09034-0023 PM* 09 03 27.6188356968 -00 23 30.038909820     13.533 13.242   M3e 6 0
4 L 678-39 PM* 09 36 01.6372169407 -21 39 38.877606712 13.647 12.48 10.906 9.858 8.577 M2.5V 127 0
5 BD+20 2465 Er* 10 19 36.2808181226 +19 52 12.010446571   10.82 9.52 9.19   dM3 1232 0
6 NAME Proxima Centauri Er* 14 29 42.9461331854 -62 40 46.164680672 14.21 12.95 11.13 9.45 7.41 M5.5Ve 1144 0
7 SCR J1845-6357 LM* 18 45 05.2532493080 -63 57 47.450109578     17.40 14.99 12.46 M8.5V 63 1
8 V* AU Mic LM* 20 45 09.5324974119 -31 20 27.237889841   10.05 8.627 9.078 6.593 M1VeBa1 1012 0
9 V* EV Lac Er* 22 46 49.7312610268 +44 20 02.374381562   11.85 10.26 9.89   M4.0Ve 853 2

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