FURTHER MIDINFRARED STUDY OF THE RHO-OPHIUCHI CLOUD YOUNG STELLAR POPULATION - LUMINOSITIES AND MASSES OF PRE-MAIN-SEQUENCE STARS

We present a new mid-infrared photometric study of the rho Oph young s tellar poplation which includes data for 56 objects. The sources for t his study were largely selected from a K < 10 mag limited sample in or der to reduce the bias of the previous IRAS-selected survey of the clo ud. This sample was supplemented with fainter sources that are very re d as well as sources that also have radio-continuum emission. The K < 10 sources are found to have spectral energy distributions predominant ly similar to those of reddened T Tauri stars (Class II), while the ot her sources are mostly either embedded (Class I) or else have little o r no circumstellar material (Class III). We develop an empirical techn ique for estimating the bolometric luminosities of Class II sources fr om their near-IR data and use it to estimate the luminosities of our n ewly-observed Class II young stellar objects (YSOs). Most of the newly identified Class II sources have L almost-equal-to 1 L., and several low-luminosity Class I sources are also found. The suspected luminosit y segregation between spectral energy distribution classes is reinforc ed; we find an excess of Class I sources at intermediate (approximatel y 10 L.) luminosities. Comparisons with Taurus-Auriga YSOs suggest tha t these high Class I luminosities may be entirely attributable to a hi gher mass accretion rate in the rho Oph cloud. We estimate an embedded YSO phase lifetime of approximately (2 +/- 1) x 10(5) yr, which is co mparable to that of the Taurus-Auriga clouds. We estimate the masses o f the Class II and III cloud population by comparing source luminositi es to pre-main-sequence stellar models and find the mean Class II mass to be 1.0 M..