Nov 5

"Embedded Protostellar Disks Around (sub-) Solar Stars: The Dark Ages of Disk Evolution and the Planet Formation Perspective"
Eduard Vorobyov, St. Mary's UNiversity, Nova Scotia, Canada

(Sub-)solar-type stars form via gravitational collapse of rotating molecular hydrogen cores and planets emerge in gaseous and dusty disks that form around stars during the collapse. I will discuss the earliest stages of the evolution of star+disk systems when they are deeply embedded in parent cloud cores. Embedded disks are difficult to probe with modern telescopes due to obscuration of light, yet this phase may be crucial for the subsequent evolution. To study these elusive phases of disk evolution, I employ numerical hydrodynamic simulations that start from a starless cloud core and terminate when the core has accreted onto a forming star+disk system. I show that the path along which a star+disk object moves is largely determined by the initial properties of the parent cloud core. Objects formed from low-angular-momentum and low-mass cores proceed along a rather calm path showing a low-amplitude accretion (and luminosity) variability caused by mild disk instability. On the contrary, objects formed from high-angular-momentum and high-mass cores exhibit high- amplitude variability, disk pulsations, and disk fragmentation. Most of the forming fragments are quickly driven into the disk inner regions and (likely) onto the star, triggering intense luminosity outbursts. If dust sedimentation in the fragments is fast enough, some of them may survive the rapid inward migration and form icy giants or even terrestrial planet cores on close orbits. A small fraction of the fragments may form gas giants and settle on wide orbits around the central star, resembling in appearance the Fomalhaut b or HR 8977 planetary systems.

Nov 12

PhD Defense Presentation: "Physical Properties of Star-Froming Regions Across the Galaxy"
Miranda Dunham, University of Texas at Austin

The Bolocam Galactic Plane Survey (BGPS) has surveyed the northern Galactic plane at 1.1 mm and detected 8,358 sources. The BGPS catalog is large enough to characterize the properties of massive star formation in a statistically significant way. In this dissertation, I have conducted a survey of NH3 lines toward 771 BGPS sources located throughout the Galactic plane. The NH3 and 1.1 mm continuum observations together have allowed for complete characterization of the physical properties of these sources.

I detected the NH3(1,1) line toward 408 BGPS sources in the inner Galaxy, allowing for determination of their kinematic distances. At distances less than roughly 1 kpc, the BGPS detects predominately cores which will form a single star or small multiple system, while at distances between 1 and 7 kpc the BGPS detects predominately clumps which will form entire stellar clusters. At distances greater than 7 kpc, the BGPS detects the large scale clouds which contain clumps and cores.

I have correlated the BGPS catalog with mid-IR catalogs of massive young stellar objects (MYSOs), and found that 49% of the BGPS sources contain signs of active star formation. The masses, densities, H2 and NH3 column densities, gas kinetic temperatures, and NH3 velocity dispersions are higher in BGPS sources with associated mid-IR sources.

I have also studied the physical properties of the BGPS sources as a function of Galactocentric radius, Rg. I find that the mean radius and mass decrease with increasing Rg but peak within the 5 kpc molecular ring where the gas kinetic temperature reaches a minimum. The fraction of BGPS sources with associated mid-IR sources decreases by 10% within the molecular ring. I postulate that these trends can be explained by an ambient gas density which decreases with Rg, but peaks within the molecular ring. Similarly, the NH3 column density and abundance decrease by almost an order of magnitude from the inner to outer Galaxy.