Spitzer and HHT Observations of the Earliest Stages of Star Formation

Abstract

We use Spitzer Space Telescop and Heinrich Hertz Telescope(HHT) observations to study the earliest stages of low--mass starformation. Using spatially resolved absorption features, termedshadows, we study the cold cloud cores where stars form.We study Barnard 335, a prototypical isolated Bok globule with anembedded Class 0 protostar. We discover an 8 micron shadow in theinner regions of the core; using this feature we measure the densecore structure and mass. Using HHT observations we detect a rotatingstructure, a flattened molecular core, with a diameter~ 10,000 AU. The flattened molecular core is likely to be thesame structure as that generating the 8 micron shadow, and isexpected from theoretical simulations. This structure has not beenrobustly detected in previous observations although there have beensome prior indications of its presence.We study dense starless core structure through longer wavelengthobservations of shadows; we present Spitzer observations of 8 micron,24 micron, and 70 micron\ shadows of 14 cores in total. Combined withHHT observations of 12CO 2--1 and 13CO 2--1, we derive core sizes,masses, study core structure, and investigate the collapse status ofeach core. Our study of starless core CB190 reveals that the core islikely to be stable against collapse if magnetic pressure is presentat a reasonable level in the core. Our study of the 70 micron shadowassociated with the starless core L429 reveals that this object isvery likely to be collapsing. Finally, we study a sample of 12starless cores selected to have prominent 24 micron shadows. We findthat about 2/3 of these sources are likely to be collapsing.Additionally, we find indications that 1/2 of the cores revealed to becollapse candidates show indications of having 70 micron shadows. Weconclude that all cores dense enough to produce 70 micron shadows arecollapse candidates, and that the presence of a shadow at 24 micronis an indicator that the core is likely (60% probability)to be collapsing.