Protoplanetary Disks in the Nearest Star-Forming Cloud: Mid-Infrared Imaging and Optical Spectroscopy of MBM 12 Members

The recent identification of several groups of young stars within 100 parsecs of the Sun has generated widespread interest. Given their proximity and possible age differences, these systems are ideally suited for detailed studies of star and planet formation. Here we report on the first investigation of protoplanetary disks in one such group, the high-latitude cloud MBM 12 at a distance of $sim$65 pc. We present mid-infrared observations of the eight candidate pre-main-sequence (PMS) members and the two main-sequence (MS) stars in the same line-of-sight which may or may not be associated with the group. We have also derived H$alpha$ and Li line widths from medium-resolution optical spectra. We report the discovery of significant mid-infrared excess from six PMS stars --LkH$alpha$ 262, LkH$alpha$ 263, LkH$alpha$ 264, E02553+2018, RXJ0258.3+1947 and S18 --presumably due to optically thick circumstellar disks. Our flux measurements for the other two PMS stars and the two MS stars are consistent with photospheric emission, allowing us to rule out dusty inner disks. The disks we have found in MBM 12 represent the nearest known sample of very young protoplanetary systems, and thus are prime targets for high-resolution imaging at infrared and millimeter wavelengths.Comment: 10 pages including one figure, to appear in The Astrophysical Journal Letter