Comparison of Star Formation in Five Nearby Molecular Clouds

We have calculated bolometric temperature ( T bol ) and bolometric luminosity ( L bol ) for 383 young stellar objects (YSOs) in five molecular clouds within 200 pc in Corona Australis (CrA), Ophiuchus (Oph), Taurus (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-consistent basis. The main results are the following: (1) the YSO populations 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 star-forming activity in the same order; (2) the clouds with higher cold source fractions also seem to have higher bright source fractions; (3) In the BLT diagram, the CrA and Oph sources are more uniformly distributed while the Cha and Lup sources are aggregated near the zero-age mainsequence (ZAMS). Tau sources appear to be an intermediate case. Taurus also seems to contain more cold ( T bol < 1000 K) and low-luminosity ( L bol < 1 L ☉ ) sources than the other complexes; (4) the YSOs show a characteristic distribution in the median BLT diagram. This distribution is qualitatively consistent with the early YSO evolution from a protostar to a pre-main-sequence star and provides a unique observational test to star-formation models; (5) for Lup pre-main-sequence stars, the ratio of their T bol to T eff increases during their approach to the ZAMS. This increase can be explained by the disk and envelope dissipation during the pre-main-sequence evolution; (6) the most active star-forming clouds (Oph and CrA) also have denser molecular cores as measured by C 18 O 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 C 18 O emission for the class 0 and I Tau sources ( T bol < 650 K). This shows that T bol measures 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.