Dr. Melissa Enoch, Caltech

"Starless cores and deeply embedded protostars with Spitzer and Bolocam: a
census of the youngest objects in Perseus, Serpens, and Ophiuchus"

Abstract:
We have completed an unbiased census of prestellar cores and deeply
embedded protostars in Perseus, Serpens, and Ophiuchus,  by combining
large-scale 1.1 mm surveys and Spitzer c2d maps.  I will discuss the
properties of the youngest objects in each cloud, and implications for
the core formation process, the origin of the stellar initial mass
function (IMF), and protostellar evolution.
The shape of the combined starless core mass distribution is consistent
with recent measurements of the IMF, supporting the idea that stellar
masses are directly linked to the core formation process.  These dense
starless cores have a lifetime similar to that of the entire embedded
protostellar phase, 2-5x10^5 yr, or only a few free-fall timescales.
Perseus and Serpens contain similar numbers of Class 0 and Class I
protostars, suggesting a relatively long Class 0 lifetime of 1-2x10^5 yr,
in marked contrast to the very small number of Class 0 sources found in
Ophiuchus. Comparing protostellar sources to evolutionary models using the
bolometric temperature-luminosity diagram, we find a population of low
luminosity Class I sources that are inconsistent with a constant or
monotonically decreasing mass accretion rate.  This result argues strongly
for episodic accretion during the Class I phase, with approximately 25% of
sources in a quiescent state.