COMPARISON OF STAR-FORMATION IN 5 NEARBY MOLECULAR CLOUDS

We have calculated bolometric temperature (T-bol) and bolometric lumin osity (L(bol)) for 383 young stellar objects (YSOs) in five molecular clouds within 200 pc in Corona Australis (CrA), Ophiuchus (Oph), Tauru s (Tau), Chamaeleon (Cha), and Lupus (Lup). We used T-bol, L(bol), and bolometric luminosity-temperature (BLT) diagrams to characterize and compare the overall-star-formation activity of the clouds on a self-co nsistent basis. The main results are the following: (1) the YSO popula tions in the clouds can be differentiated by the fraction of their low -T-bol Sources, which increases systematically from Lup and Cha to Tau and to Oph and CrA. This trend is interpreted as increasing current s tar-forming activity in the same order; (2) the clouds with higher col d source fractions also seem to have higher bright source fractions; ( 3) In the BLT diagram, the CrA and Oph sources are more uniformly dist ributed while the Cha and Lup sources are aggregated near the zero-age mainsequence (ZAMS). Tau sources appear to be an intermediate case. T aurus also seems to contain more cold (T-bol < 1000 K) and low-luminos ity (L(bol) < 1 L.) sources than the other complexes; (4) the YSOs sho w a characteristic distribution in the median BLT diagram. This distri bution is qualitatively consistent with the early YSO evolution from a protostar to a pre-main-sequence star and provides a unique observati onal test to star-formation models; (5) for Lup pre-main-sequence star s, the ratio of their T-bol to T-eff increases during their approach t o the ZAMS. This increase can be explained by the disk and envelope di ssipation during the pre-main-sequence evolution; (6) the most active star-forming clouds (Oph and CrA) also have denser molecular cores as measured by (CO)-O-18 J = 1-0 line emission, suggesting that the star formation occurs in the densest parts of the molecular clouds; and (7) we find an anti-correlation between T-bol and (CO)-O-18 emission for the class 0 and I Tau sources (T-bol < 650 K). This shows that T-bol m easures the intrinsic redness of YSOs, rather than their disk-envelope orientation. The disk orientation may have a more important effect on T-bol of the pre-main-sequence stars.