A SEARCH FOR PROTOPLANETARY DISKS AROUND NAKED T-TAURI STARS

We apply and extend a method of modeling circumstellar emission from c ircumstellar disks to an x-ray selected sample of stars in the Taurus- Auriga association. We model these stars from 0.36 to 60 mu m using a three-zone model: a photosphere with starspots and an optically thick passive disk. Our objective is to make a conservative estimate of the number of these stars possessing disks. To accomplish this, we demonst rate that small near-infrared excesses do not necessarily imply the ex istence of an optically thin disk. Of the 39 x-ray selected stars in o ur sample, only 2 have an infrared excess attributable to an optically thick disk. Four have thin or cleared disks. We found near-IR flux ex cesses in 9 stars which can be explained by cool starspots. For all of the others, we can exclude any optically thick active or passive flat disk. We estimate the dissipation time scales of circumstellar disks to be less than about 100 000 years. (C) 1996 American Astronomical So ciety.