The Volans-Carina association An X-ray Bridge Between Younger and Older Stellar Populations

Abstract

Nearby young moving groups (NYMGs) provide benchmarks for studying the evolution of magnetic activity and planetary environments at early ages. The Volans-Carina association (VCA), as a pre-main sequence association at a distance of ~90 pc, occupies a sparsely sampled region of parameter space between younger nearby associations and older distant open clusters. We have re-evaluated the membership probabilities of the VCA catalog presented in Gagne et al. (2018a) with BANYAN as well as updated kinematics from Gaia DR3. Stellar parameters were derived from multi-wavelength spectral energy distributions, with the obtained bolometric luminosity and effective temperature being used in combination with pre-main sequence evolutionary models to obtain an isochronal age of the association. We joined data from the SRG (Spectrum Roentgen Gamma)/eROSITA and ROSAT all-sky surveys with a dedicated XMM-Newton Large Programme to construct a comprehensive X-ray catalog. Our updated census of the VCA comprises 29 highly probable members, 30 candidate members, and four uncertain objects. Isochronal analysis of the association yields an age of 80+-20 Myr, consistent with previous estimates. We detect X-ray emission from 56 objects, reaching ~90% completeness, one of the most complete X-ray censuses achieved for a NYMG. Low-mass members and candidates (<0.6 Msolar) have X-ray to bolometric luminosity ratios around the canonical saturation limit (Lx/Lbol~10^-3). X-ray luminosity functions show the VCA to be consistent with the similarly aged Pleiades (in the F5 to M3 range) and significantly more active than the older Hyades (in the F5 to K4 range). The combination of an updated membership census and a nearly complete X-ray census establishes the VCA as a particularly robust calibration point for studies of the early evolution of coronal X-ray activity.