Program: GN-2016A-Q-63

The environment where stars form has long been a mystery as stars are deeply hidden by thick layers of dust and gas within a molecular cloud. It is not completely understood how grains condense and grow to eventually form larger bodies and even planets. Thus it is vital to study how the dust and gas in these regions are distributed, and how ices are involved in potentially helping grains grow. For my thesis I intend to probe these properties by observing six molecular clouds at different evolutionary stages: two quiescent, two that are currently collapsing, and two that already have star-forming cores. To begin, we will make extinction maps to trace the column densities of the gas and dust which will provide us with an understanding of how dust fragments to form a star and how that changes during the formation process. In previous studies, measurements of background stars are used to calculate column densities and build an extinction map but the assumption is made that the background stars are all toward the galactic bulge and that a single spectral type can be used. Unfortunately this introduces an extinction measurement error around 0.2 magnitudes which is large when considering low extinction regions (A_V < 2). Measuring extinction out in these regions will allow us to measure the amount of dust surrounding the star (thus protecting it from outside turbulence) and whether that changes over time and how much is needed to protect the inner core. We can also combine measurements from lower to higher density regions to formulate an extinction law toward molecular clouds with a wide range of wavelengths. To eliminate the errors on the extinction measurements in low-density regions, we propose to take spectra of background stars in z filter using 18 hours on GMOS to identify the exact spectral type of the stars and use this to build precise extinction maps of our six clouds. Mapping extinction requires a solid knowledge of the extinction law. In molecular clouds the extinction law at infrared wavelengths is complicated by the presence of ice features such as H2O (3.1 μm), CO (4.67 μm), and CO2 (4.27 μm). We propose to use 9.75 hours on Gemini GNIRS to take spectra of 8 infrared bright background stars to measure the H2O and CO ice features (CO2 is not possible from the ground). By combining these measurements with Spitzer data on the same targets we can measure the extinction law for molecular clouds in the L and M band. These observations are also imperative for upcoming JWST GTO observations on NIRCam in which I am currently involved in the planning of, and I will eventually become part of the NIRCam analysis team for molecular cloud studies. Once we identify sources with ice features, further follow-up with JWST’s NIRCam (with grism mode) or NIRSPec can identify CO2 for the same stars and build on this sample by observing fainter sources. Additionally, MIRI (Mid-Infrared Imager) will be capable of measuring the 10 μm silicate feature. Combining information of the silicate and ice features will help us distinguish between grain coagulation and ice deposition which could lead to understanding how grain growth occurs to form larger bodies. The NIRCam team is now in the phase of detailed planning of the GTO observations, and this planning has to be completed at the end of 2016, so there is some urgency in getting ground-based preparatory observations done.