Characterization of low-mass pre-main sequence stars in the Southern Cross

Abstract

We report high-resolution spectroscopic observations, as well as high-resolution near infrared (IR) imaging of six stars previously identied in a ROSAT pointed observation in the direction of the B-type star Cru, and classied as low-mass pre-main sequence (PMS) stars. Four of the stars are conrmed to be low-mass PMS stars, associated with the Lower Centaurus-Crux group, while the other two are unrelated to the Sco-Cen association. The conrmed PMS stars are most likely in their post-T Tauri evolutionary phase. Although future deep X-ray observations with high-resolution imagers might detect more new PMS stars, the possibility that the Crux PMS stars are part of a small aggregate, with Crux itself approximately at the center, is rather unlikely, given the high velocity dispersion and the low spatial density of the conrmed PMS stars. Instead, these stars may be part of a moving group in a more disperse and numerous population of low-mass PMS stars, distributed in the Lower Centaurus-Crux subgroup. New PMS binaries and multiple systems were also discovered among the stars in the sample, namely a close visual pair and a hierarchical triple system in which one of the components is a double-lined spectroscopic binary (SB2). The detailed orbital solution is reported for the inner short-period (Porb = 58.3 days) SB2. A preliminary orbital solution for the hierarchical triple system yields a systemic orbital period of about 4.6 years, which makes this object a very suitable target for follow-up observations with the Very-Large Telescope Interferometer (VLTI) in the coming years.