Fundamental properties of pre-main sequence stars in young, southern star forming regions: Metallicities the weak-lined T-Tauri stars

Abstract

Aims. The primary motivation for this project is to search for metal-rich star forming regions, in which, stars of super-solar metallicity will be created, as hopefully, will be extra-solar planets orbiting them! The two aims of this project are: 1) to show that our sample stars are young, lithium rich, magnetically active and non-accreting kinematic members of their respective regions. 2) To measure the metallicity for such members. Methods. The FEROS échelle spectrograph together with ESO's 2.2 m telescope, was used to obtain high resolution (R = 32 000) spectra for each of our weak-lined T-Tauri target stars. The wavelength range of the spectra is ≃4000-8000 Å. Results. We find (pre-main sequence) model-dependent isochronal ages of the Lupus, Chamaeleon and CrA targets to be 9.1 ± 2.1 Myr, 4.5 ± 1.6 Myr and 9.0 ± 3.9 Myr respectively. The majority of the stars have Li i 6707.8 Å equivalent widths similar to, or above those of, their similar mass Pleiades counterparts, confirming their youthfulness. Most stars are kinematic members, either single or binary, of their regions. We find a mean radial velocity for objects in the Lupus cloud to be RV = +2.6 ± 1.8 km s−1, for the Chamaeleon i & ii clouds, RV = +12.8 ± 3.6 km s−1 whereas for the CrA cloud, we find RV = −1.1 ± 0.5 km s−1. All stars are coronally and chromospherically active, exhibiting X-ray and Hα emission levels marginally less, approximately equal or superior to that of their older IC 2602/2391 and/or Pleiades counterparts. All bar three of the targets show little or no signature of accretion from a circumstellar environment, according to their positions in a J − K/H − K diagram. For the higher quality spectra, we have performed an iron-line metallicity analysis for five (5) stars in Chamaeleon, four (4) stars in Lupus and three (3) stars in the CrA star forming regions. These results show that all three regions are slightly metal-poor, with marginally sub-solar metallicities, with I([Fe/H]) = −0.11 ± 0.14, −0.10 ± 0.04 and −0.04 ± 0.05 respectively. Conclusions. A sample of stars in several nearby, young star-forming regions has been established, the majority of which is young, lithium rich, magnetically active and are non-accreting kinematic members of their respective clouds. Within the errors, each region is essentially of solar metallicity.