On the MBM 12 Young Association

I present a comprehensive study of the MBM12 young association (MBM12A). Bycombining infrared (IR) photometry from the Two-Micron All-Sky Survey (2MASS)survey with new optical imaging and spectroscopy, I have performed a census ofthe MBM12A membership that is complete to 0.03 Msun (H~15) for a 1.75deg X1.4deg field encompassing the MBM12 cloud. I find five new members with massesof 0.1-0.4 Msun and a few additional candidates that have not been observedspectroscopically. From an analysis of optical and IR photometry for stars inthe direction of MBM12, I identify M dwarfs in the foreground and background ofthe cloud. By comparing the magnitudes of these stars to those of local fielddwarfs, I arrive at a distance modulus 7.2+/-0.5 (275 pc) to the MBM12 cloud;it is not the nearest molecular cloud and is not inside the local bubble of hotionized gas as had been implied by previous distance estimates of 50-100 pc. Ihave also used Li strengths and H-R diagrams to constrain the absolute andrelative ages of MBM12A and other young populations; these data indicate agesof 2 +3/-1 Myr for MBM12A and 10 Myr for the TW Hya and Eta Cha associations.MBM12A may be a slightly evolved version of the aggregates of young starswithin the Taurus dark clouds (~1 Myr) near the age of the IC 348 cluster (~2Myr).