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 stellar poplation which includes data for 56 objects. The sources for this study were largely selected from a K < 10 mag limited sample in order to reduce the bias of the previous IRAS-selected survey of the cloud. This sample was supplemented with fainter sources that are very red as well as sources that also have radio-continuum emission. The K < 10 sources are found to have spectral energy distributions predominantly similar to those of reddened T Tauri stars (Class II), while the other sources are mostly either embedded (Class I) or else have little or no circumstellar material (Class III). We develop an empirical technique for estimating the bolometric luminosities of Class II sources from their near-IR data and use it to estimate the luminosities of our newly-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 luminosity segregation between spectral energy distribution classes is reinforced; we find an excess of Class I sources at intermediate (approximately 10 L.) luminosities. Comparisons with Taurus-Auriga YSOs suggest that these high Class I luminosities may be entirely attributable to a higher 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 comparable to that of the Taurus-Auriga clouds. We estimate the masses of the Class II and III cloud population by comparing source luminosities to pre-main-sequence stellar models and find the mean Class II mass to be 1.0 M..