The χFactor: Determining the Strength of Activity in Low Mass Dwarfs

Abstract

We describe a new, distance-independent method for calculating the magnetic activity strength in low mass dwarfs, L_{Hα}/L_{bol}. Using a well-observed sample of nearby stars and cool standards spanning spectral type M0.5 to L0, we compute ``χ'', the ratio between the continuum flux near H-alpha and the bolometric flux, f_{\lambda6560}/f_{bol}. This ratio may be multiplied by the measured equivalent width of the H-alpha emission line to yield L_{Hα}/L_{bol}. We provide χvalues for all objects in our sample, as well as fits to χas a function of color and average values by spectral type. This method was used by West et al.(2004) to examine trends in magnetic activity strength in low mass stars.