X-raying the Sco-Cen OB association: The low-mass stellar population revealed by eROSITA

Abstract

We present the results of the first X-ray all-sky survey (eRASS1) performed by the eROSITA instrument on board the Spectrum-Roentgen-Gamma (SRG) observatory of the Sco-Cen OB association. Bona fide Sco-Cen member stars are young and are therefore expected to emit X-rays at the saturation level. The sensitivity limit of eRASS1 makes these stars detectable down to about a tenth of a solar mass. By cross-correlating the eRASS1 source catalog with the Gaia EDR3 catalog, we arrive at a complete identification of the stellar (i.e., coronal) source content of eROSITA\ in the Sco-Cen association, and in particular obtain for the first time a 3D view of the detected stellar X-ray sources. Focusing on the low-mass population and placing the optical counterparts identified in this way in a color-magnitude diagram, we can isolate the young stars out of the detected X-ray sources and obtain age estimates of the various Sco-Cen populations. A joint analysis of the 2D and 3D space motions, the latter being available only for a smaller subset of the detected stellar X-ray sources, reveals that the space motions of the selected population show a high degree of parallelism, but there is also an additional population of young, X-ray emitting and essentially cospatial stars that appears to be more diffuse in velocity space. Its nature is currently unclear. We argue that with our procedures, an identification of almost the whole stellar content of the Sco-Cen association will become possible once the final Gaia and eROSITA catalogs are available by the end of this decade. We furthermore call into question any source population classification scheme that relies on purely kinematic selection criteria.

arXiv comment17 pages, 16 figures. To appear on A&A, Special Issue: The Early Data Release of eROSITA and Mikhail Pavlinsky ART-XC on the SRG Mission

References in corpus (27)

• The Gaia mission
• PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code
• Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-Main Sequence Stars
• A Hipparcos census of the nearby OB associations
• The eROSITA X-ray telescope on SRG
• The stellar activity-rotation relationship and the evolution of stellar dynamos
• The GALAH Survey: Scientific Motivation
• Gaia Data Release 2: first stellar parameters from Apsis
• eROSITA Science Book: Mapping the Structure of the Energetic Universe
• The Star-formation History and Accretion-Disk Fraction Among the K-Type Members of the Scorpius-Centaurus OB Association
• On the origin of the O and B-type stars with high velocities II Runaway stars and pulsars ejected from the nearby young stellar groups
• The eROSITA Final Equatorial Depth Survey (eFEDS): The X-ray catalog
• The Spatial Distribution of Star Formation in the Solar Neighbourhood: Do all stars form in clusters?
• The stellar and sub-stellar IMF of simple and composite populations
• Stellar Winds on the Main-Sequence II: the Evolution of Rotation and Winds
• Multi-Dimensional Bayesian Membership Analysis of the Sco OB2 moving Group
• Refining the Census of the Upper Scorpius Association with Gaia
• On the kinematic evolution of young local associations and the Sco-Cen complex
• The stellar population of Sco OB2 revealed by Gaia DR2 data
• New Pre-main-Sequence Stars in the Upper Scorpius Subgroup of Sco-Cen
• Theoretical values of convective turnover times and Rossby numbers for solar-like, pre-main sequence stars
• Revised Geometric Estimates of the North Galactic Pole and the Sun's Height Above the Galactic Midplane
• A kinematic study and membership analysis of the Lupus star-forming region
• Accurate age determinations of several nearby open clusters containing magnetic Ap stars
• A new compact young moving group around V1062 Sco
• The eROSITA Final Equatorial-Depth Survey (eFEDS). The stellar counterparts of eROSITA sources identified by machine learning and Bayesian algorithms
• Beyond the Coronal Graveyard

Cited by in corpus (5)

• The SRG/eROSITA all-sky survey: First X-ray catalogues and data release of the western Galactic hemisphere
• The star formation history of the Sco-Cen association. Coherent star formation patterns in space and time
• Significance Mode Analysis (SigMA) for hierarchical structures. An application to the Sco-Cen OB association
• Toward the fabric of the Milky Way I. The density of disk streams from a local $250^3$ pc${}^3$ volume
• Star Forming Regions