Jonathan Foster's Homepage

Astronomy compels the soul to look upwards and leads us from this world to another.

      ~ Plato, The Republic

My Research: Dark Clouds and Bright Young Stars

Me at Keck HQ

I am currently a YCAA Prize Postdoctoral Fellow at Yale, working on understanding how stars form. My research studies the connections between the formation of the most massive stars and the formation of smaller stars (like our own sun). I am currently studying the low-mass population of high-mass star forming regions and working on the IN-SYNC and RAMPS surveys.

Previously I was a Post-Doctoral research associate with Jim Jackson working on Infrared-Dark Clouds (IRDCs), the Malt90 Survey and various other topics in high-mass star formation. IRDCs are dense clouds seen in extinction against the diffuse light of galaxy and are great places to look for the early stages of high-mass star formation.

As a Ph.D. student I worked as part of the COMPLETE Survey of Star forming clouds with my advisor, Alyssa Goodman. The COMPLETE survey focused on the Perseus, Ophiuchus, and Serpens molecular clouds, where low- to intermediate-mass star formation is happening.

My research page contains little snapshots focusing on my recent research topics and publications. On this website you can also find my full publications list, my Curriculum Vitae, my contact information, and some notes about setting up astronomy software on a Mac

Distributed Low-Mass Star Formation

Using adaptive optics on the Keck telescopes, we have conducted a very sensitive search for low-mass protostars in filamentary infrared dark cloud (IRDC). We were able to identify young stars both statistically as an excess of red sources (see above, left) and individually through their extended emission from outflows or reflection nebulosity (see above, right). Low-mass stars are forming throughout the cloud, not just in the dense knots where high-mass stars form. There is also some evidence that high-mass stars form in the more gravitationally bound portions of the filament. For the latter analysis we mapped out how bound the filamenent was in slices along its length (see below). The full paper is here.

Grain Growth in Molecular Clouds

This beautiful image is a small slice of a 1 degree optical image we took of the Perseus molecular cloud. We combined the optical colors of background stars with the near-infrared colors from the UKIDSS survey to measure how the extinction law slope changes as a function of column density. We used a hierarchical Bayesian model to infer the properties of each individual star simultaneously with inferring the properties of the full population. We found that the extinction law changes from its value in the diffuse ISM to its value in dense clouds over a range of 2 to 10 magnitudes of visual extinction. Y ou can read the full paper