Bolometric Temperature and Its Applications to Young Stars in Taurus and Ophiuchus

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Session 44 -- Young Stars, T Tauri Stars, Herbig Haro Objects
Display presentation, Wednesday, 1, 1994, 9:20-6:30

[44.13] Bolometric Temperature and Its Applications to Young Stars in Taurus and Ophiuchus

H. Chen, P. C. Myers (CfA), E. F. Ladd (IfA, U. of Hawaii), D. O. S. Wood (NRAO)

Bolometric temperature ($T_{bol}$) is defined as the temperature of a blackbody having the same mean frequency as the observed continuum spectrum. It measures the redness (or youth) of young stellar objects (YSOs). We calculated $T_{bol}$ and bolometric luminosity ($L_{bol}$) of all the known YSOs in Taurus, Ophiuchus core, and Ophiuchus off-core regions. Most of the YSOs we studied are aggregated into small groups of a few tens of sources. These groups contain both ``cold'' sources ($T_{bol} =40-1000 K$, including deeply embedded sources and protostar candidates) and ``hot'' sources ($T_{bol}=1000-5000 K$, including classical T Tauri stars and weak-line T Tauri stars). The cold sources are more aggregated and are closer to the peak of gas and dust emission than the hot sources. These results are consistent with the suggestion that young stars can continuously form within dense cores. We compared $T_{bol}$ of YSOs with their age inferred from star formation models, and found a reasonably good correlation. The correlation can be explained in terms of dust envelope and circumstellar material dissipation during the early stages of stellar evolution. $T_{bol}$ shows a monotonic increase during the course of star formation and early evolution, and could be an excellent evolution indicator of YSOs. Sources in the three regions are also different in their distribution in the log-log plot of $T_{bol}$ vs. $L_{bol}$. The fraction of the cold sources in Ophiuchus core is higher than that of Taurus sources, and is much higher than that of Ophiuchus off-core sources. The YSOs in Ophiuchus core are also more luminous. We explain these differences as the differences in star formation history and possibly in mass distribution.

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