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P.M. McGehee (LANL and NMSU)
Multi-epoch imaging of the Orion equatorial region by the Sloan Digital Sky Survey has revealed that significant variability in the blue continuum persists into the mid-M spectral types indicating that magnetospheric accretion processes occur below the substellar boundary in the Orion OB1b association. We investigate the strength of the continuum veiling by comparing the reddening-invariant colors of the most highly variable stars against those of main sequence M dwarfs. A gradual decrease in the g band veiling is seen for the coolest and less massive members. We find that the near-IR excess attributed to circumstellar disk thermal emission drops rapidly for spectral types later than M4. This is likely due to the decrease in contrast between the disk and the cooler stellar photosphere. Since accretion signatures, which require a substantial stellar magnetic field and the presence of a circumstellar disk, are seen here as late as spectral type M6 (0.04 solar masses for an age of 2 Myr) we surmise that brown dwarfs and low mass stars share a common mode of formation.
Funding for the Sloan Digital Sky Survey (SDSS) has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Aeronautics and Space Administration, the National Science Foundation, the U.S. Department of Energy, the Japanese Monbukagakusho, and the Max Planck Society.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.