Shkolnik et al. 2010

Searching for Young M Dwarfs with GALEX

purpose: use NUV and FUV emission to identify M dwarfs with ages < 300 Myr

**none of these stars match up with DEBRIS targets but suggests a method for estimating age

Abstract

• FUV and NUV emission is in excess for spectral types >K5 and younger than 300 Myr
• search is for M stars in TW Hydra association (TWA)
• search should be sensitive down to M4-M5

Introduction

• indicators of youth = chromospheric activity, strong X-ray emission 
• as yet, there are not as many M3-M7 stars as there should be in TWA
• may be a result of insufficient observations
• they came up with a selection method to find these missing stars

Selection of Young Stars Using GALEX

• M dwarfs are 10-300 times less luminous than solar-type stars
• GALEX flux for M dwarfs
• transition region C IV and continuum flux (FUV)
• Mg II, Fe II, Al II, C III, and continuum flux (NUV)
• both NUV and FUV have coronal lines
• young M dwarfs can be detected to further distances and later spectral types with GALEX

Sample Selection of TWA Candidates

•  Took data from HST (optical), 2MASS (JHK), and GSC2.3, then cross-calibrated with GALEX
• Made color cuts in color-magnitude diagrams
• ended up with a list of 38 target stars

Spectroscopic Confirmation

•   first examined low res spectra looking for H alpha emission lines
• indicative of young low mass stars

Spectral Types

• spectra are dominated by TiO molecular bands (temperature)
• spectral subclass is calculated using TiO band strength 

Identifying the Young Stars

• diagnostics of age:
• Strong fractional NUV and FUV flux 
• low g
• Li depletion
• Accretion/H alpha emission

Conclusions:

• after further velocity studyies to determine membership, only two new M-type stars in TWA were found.
• it remains possible that the M stars in question (~10 Myr) have depleted all their lithium and did not make the initial filter.