X-ray variability study of the TW Hya association with the eROSITA All-Sky Surveys

Exploring the X-ray emission from nearby young moving groups (NYMGs) provides key insights into the early evolution of stellar magnetic activity, accretion processes, and the effects of high-energy photons on protoplanetary disks. Young stars (<10 Myr) show strong coronal emission due to robust internal magnetic dynamos, in theory formed through differential rotation and convection, resulting in significant surface magnetic fields. As a consequence, late-type pre-main sequence (pre-MS) stars display X-ray luminosities (Lx) relative to bolometric (Lbol) that lie in the range −4 ~< log(Lx/Lbol) ~< −3. The TW Hydrae Association (TWA) is a nearby group of pre-MS stars with distances between ~30pc and 140 pc. It was first identified due to bright X-ray emission, typical of low-mass pre-MS stars (~0.1–1.5 M⊙), detected with ROSAT (Kastner+97). Since then, TWA has become a key focus for studying coronal activity in very low-mass stars and brown dwarfs. With the advent of the new X-ray all-sky survey instrument eROSITA on board the Russian Spektrum-Roentgen-Gamma mission, we can now conduct comprehensive long-term investigations into the X-ray properties and variability of NYMGs, performing variability studies over a period of two years. In this presentation, I will discuss our ongoing eROSITA X-ray study of the TWA, involving 80 bonafide and candidate members, spanning spectral types from A to late-M and mass ranges from 2 to significantly below one solar mass. Out of 80 stars in the TWA, we detected X-ray emission in all four eRASSs for 63 TWA objects and 17 during at least one surveys. We systematically analyzed their short-term variability within each single eROSITA survey and long-term variability comparing data from the 4 surveys. We also calculated model-dependent X-ray fluxes and coronal temperatures from the brightest detections and X-ray luminosities for all TWA objects detected with eROSITA that we compared with the results from our previous studies of field stars.