A Spectroscopic Survey of the Youngest Field Stars in the Solar Neighborhood. II. The optically faint sample

TL;DR

This study extends spectroscopic observations of young, optically faint field stars in the solar neighborhood, providing detailed stellar parameters, binary identification, and age estimates using high-resolution spectra and Gaia data.

Contribution

It offers new spectroscopic data and analysis for faint young stars, including binary detection and age determination, expanding previous surveys to fainter magnitudes.

Findings

Over 35% of targets are binaries or multiples.

60% of stars are younger than the UMa cluster.

42 very young stars identified near the Pleiades lithium boundary.

Abstract

Star formation in the solar neighborhood is mainly traced by young stars in open clusters, associations and in the field, which can be identified by their X-ray emission. The determination of stellar parameters for the counterparts of X-ray sources is crucial for their study. This work extends the spectroscopic study of the RasTyc sample, based on TYCHO and RASS catalogs, to stars fainter than V=9.5 mag. We acquired 625 high-resolution spectra for 443 targets with four different instruments in the Northern hemisphere. The radial and rotational velocity (vsini) of our targets are measured by means of the cross-correlation technique, which is also helpful to discover binaries and multiple systems. We use the code ROTFIT for determining the atmospheric parameters and vsini of the single stars and SB1 systems. For these objects, we also measured the equivalent widths of the H$\alpha$ and LiI-6708\AA\ lines, which enables us to derive their chromospheric activity level and lithium abundance. We make use of Gaia DR1 parallaxes and proper motions for locating the targets in the HR diagram and for computing the space velocity components of the youngest objects. We find a remarkable fraction (>35%) of binaries and multiple systems. Our sample is mostly (60%) composed of stars younger than the members of the UMa cluster. We identify 42 very young stars, which lie above or very close to the Pleiades upper envelope of the lithium abundance. A significant fraction (12%) of giants/subgiants stars is also present in our sample. Some of them are also lithium rich (A(Li)>1.4).