Ultraviolet-Selected Field and Pre-Main-Sequence Stars Towards Taurus and Upper Scorpius

TL;DR

This study uses GALEX ultraviolet data combined with infrared surveys to identify and confirm young stars in Taurus and Upper Scorpius, demonstrating the effectiveness of UV observations in detecting dispersed young stellar populations.

Contribution

It introduces a method for identifying young stars via ultraviolet excess and confirms several new members, highlighting the potential of GALEX data for wide-area stellar population studies.

Findings

Identification of new young star members in Taurus and Upper Scorpius.

Demonstration of GALEX's capability to find dispersed young stellar populations.

Discovery of a large population of UV excess stars without optical activity indicators.

Abstract

We have carried out a Galaxy Evolution Explorer (GALEX) Cycle 1 guest investigator program covering 56 square degrees near the Taurus T association and 12 square degrees along the northern edge of the Upper Scorpius OB association. We combined photometry in the GALEX FUV and NUV bands with data from the Two Micron All Sky Survey to identify candidate young (<100 Myr old) stars as those with an ultraviolet excess relative to older main sequence stars. Follow-up spectroscopy of a partial sample of these candidates suggest 5 new members of Taurus, with 8-20 expected from additional observations, and 5 new members of Upper Scorpius, with 3-6 expected from additional observations. These candidate new members appear to represent a distributed, non-clustered population in either region, although our sample statistics are as of yet too poor to constrain the nature or extent of this population. Rather, our study demonstrates the ability of GALEX observations to identify young stellar populations distributed over a wide area of the sky. We also highlight the necessity of a better understanding of the Galactic ultraviolet source population to support similar investigations. In particular, we report a large population of stars with an ultraviolet excess but no optical indicators of stellar activity or accretion, and briefly argue against several interpretations of these sources.