Jan 20

"Chemical Evolution from Pre-Stellar Cores to Circumstellar Disks"
Ruud Visser, Leiden Observatory, Netherlands

The chemical composition of a molecular cloud changes dramatically as it collapses to form a low-mass protostar and circumstellar disk. Spherical models have always been used to model this chemical evolution, but they cannot describe the disk. I will present the first model that follows the entire chemical evolution from a pre-stellar core to a circumstellar disk in two dimensions. The model enables us to compute where the material accretes onto the disk (close to the star or far out) and how this affects the abundances of various key species. I will compare the model results to observational data. I will also discuss several applications of the model, such as the chemical origin of cometary material and the crystalline fraction of circumstellar silicate dust.

Feb 10

"Surveying the Submillimeter Universe with CCAT (Cerro Chajnantor Atacama Telescope)"
Jonas Zmuidzinas, California Institute of Technology

As first predicted by Frank Low and Wallace Tucker in 1969, and confirmed observationally only in the mid-1990s, the universe shines quite brightly at submillimeter wavelengths, with an energy density about equal to that at optical and near-infrared wavelengths. This spectral region is still quite poorly explored, mainly due to technological limitations, but the situation is changing quickly as submillimeter-wavelength detector array technology continues to advance at a very rapid, Moore's-law pace. In the future, submillimeter cameras will move from the present kilopixel-scale to the megapixel scale, and broadband multi-object spectrometers capable of targeting tens to hundreds of objects simultaneously will become feasible. CCAT is a proposed 25 m submillimeter telescope that is specifically being designed to exploit these emerging capabilities. Located on a very high mountaintop site in Chile, CCAT will survey the submillimeter universe with unprecedented breadth, depth, and angular resolution.

Feb 24

"Discovering and Understanding the Most Luminous Galaxies"
Andrew Blain, California Institute of Technology

The most extreme end of the galaxy luminosity function is revealed most clearly in far-infrared light. By seeking the far-infrared properties of galaxies when star formation and galaxy evolution were at their most intense, their true total power output can be revealed, along with information about the astrophysics in the gas from which stars form and supermassive blackholes grow. I will describe multi-wavelength observations of some of the most extreme galaxies at redshifts 2-3, and highlight some opportunities with ALMA, and NASA's recently launched WISE MIDEX mission, that of 24th February should have imaged more than 20% of the sky from 3.3-23 microns.

Mar 03

"Disk Evolution and Dissipation at an Age of a few Myr"
Elise Furlan, Jet Propulsion Laboratory; Beatrice M. Tinsley Visiting Scholar

Protoplanetary disks are known to disperse within a few million years of their formation, but the details are still not well understood. The Spitzer Space Telescope allows sensitive and thorough studies of the infrared emission from these protoplanetary disks and thus of the composition and distribution of their dust. I present an analysis of Spitzer IRS spectra of disks in nearby, 1-3 Myr-old star-forming regions which display various evidence of disk evolution, like dust settling and gap or hole formation. These disks suggest that different disk dissipation mechanisms are at work; among them, planet formation is the most likely agent in the creation of gaps, implying that disk evolution is often dynamic.

Mar 17

"Simulating Reionization"
Andreas Pawlik, University of Texas at Austin

Reionization is the transformation of the neutral gas that once filled intergalactic space into the ionized plasma that we observe today. Much about reionization is still unknown. New telescopes like MWA and LOFAR will soon take deep low-frequency radio observations and open a new window onto this cosmic epoch. The advent of these and other new telescopes, like JWST, implies an urgent need for detailed simulations of reionization. Simulating reionization is a demanding numerical task that requires the radiation-hydrodynamical modeling of large representative volumes of the Universe at high resolution.TRAPHIC is a radiative transfer method designed for application in this computationally challenging regime for use with smoothed particle hydrodynamics simulations. In this talk I will explain how TRAPHIC works and illustrate how it improves upon state-of-the-art radiative transfer methods. I will also present first results from radiative transfer hydrodynamical simulations of both large-scale structure formation and the assembly of individual galaxies.

Mar 24

"When the Stars Align: Microlensed Main-Sequence Stars and a New View of the Galactic Bulge"
Jennifer Johnson, Ohio State University, Beatrice M. Tinsley Visiting Scholar

The Galactic bulge is our nearest spheroid, but even here spectroscopic studies have been limited to the bright giants. However, gravitational microlensing will occasionally magnify a main-sequence star in the bulge by a large factor, making high-resolution, high S/N spectroscopic observations possible. These observations revealed some of the most metal-rich stars in teh bulge, as well as providing abundances of new elements, such as C, N, Cu and Zn. In addition, ages are measured for dwarfs near the turnoff, providing the first age-metallicity relation for bulge stars. I will discuss our ongoing VLT porgram to observe these events and the new insights on the formation and evolution of the bulge we are gaining.

Apr 14

"The Role of Gas in the Evolution of Disk Galaxies"
Alyson Brooks, Caltech, Beatrice M. Tinsley Visiting Scholar

A realistic model for the formation of galaxy disks depends on a proper treatment of the gas in galaxies. Historically, cosmological simulations of disk galaxy formation have suffered from a lack of resolution and a physically motivated feedback prescription. Recent computational progress has allowed for unprecedented resolution, which in turn allows for a more realistic treatment of feedback. These advances have led to a new examination of gas accretion, evolution, and loss in the formation of galaxy disks. Here I highlight the role that gas inflows, the regulation of gas by feedback, and gas outflows play in achieving simulated disk galaxies that better match observational results as a function of redshift.

Apr 21

"Exoplanets and their Odd Orbital Orientations"
Joshua Winn, MIT, Beatrice M. Tinsley Visiting Scholar

In the Solar system, the planets follow orbits that are aligned with the Sun's equatorial plane to within 10 degrees. What about planets around other stars? Recently we have measured the orbital orientations (relative to their parent stars' equators) of about 20 different exoplanets, using a technique first theorized in the 19th century. Many systems have good alignment, as in the Solar system -- but there are a few surprises. I will discuss these results and their implications for theories of planet formation and migration.