Astronomy Colloquia

January 13, 2010 | 15:30, RI 480 | Host: Arieh Konigl
The Early Stages of Planet Formation: Astrophysics Meets Cosmochemistry
Fred Ciesla, The University of Chicago (Geophysical Sciences)
Protoplanetary disks are dynamic objects through which mass and angular momentum are transported as part of the final stages of pre-main sequence evolution for a star. Chondritic meteorites record a dynamic history for our own solar system as they contain a variety of objects that formed in distinct physical and chemical environments, yet are intimately mixed on fine-scales. To date it remains to be determined whether models of protoplanetary disks can explain the variety of primitive materials found in our own solar system and how they came to be accreted into common meteorite parent bodies. Further, it remains unclear what stages of disk evolution identified by astrophysical models are recorded within meteorites. I will discuss these issues and argue that the earliest stages of solar nebula evolution recorded by meteorites coincide with no later than the first few hundred thousand years of our sun's formation.

January 20, 2010 | 15:30, RI 480 | Host: Richard G. Kron
Understanding the Star Formation Rate
Mark Krumholz, University of California - Lick Observatory
Note: Refreshments served at 3:15 pm
Stars are the engines of the Universe: nuclear reactions within them are the only significant source of non-gravitational power in the cosmos and the source of all heavy elements. However, the process by which stars form remains poorly understood, and one mystery in particular stands out: why is star formation so slow? In many galaxies the bulk of the interstellar medium does not participate in star formation, and in all galaxies even those clouds that are active form stars at a rate of only ~1% of their mass per dynamical time. Any successful theory of cosmic evolution must be able to explain these facts, and be able to predict how the star formation process changes with galactic environment and over cosmological time. In this talk I discuss progress toward a physical theory of star formation capable of meeting these requirements.

February 3, 2010 | 15:30, RI 480 | Host: Richard G. Kron
Waves, Winds and Jets from Coalescing Compact Binaries
Enrico Ramirez-Ruiz, University of California (Lick Observatory)
Note: Refreshments served at 3:15 pm
Merging compact binaries are the one source of gravitational radiation so far identified. Because short-period systems that will merge in less than a Hubble time have already been observed as binary pulsars, they are important both as gravitational wave sources for observatories such as LIGO, but also as progenitors for short gamma-ray bursts. Recent progress in our understanding of these systems is outlined, emphasizing the breadth of the subject and the links with fundamental physics. An effort is made to distinguish between ideas that are already well established and those that still lie on the speculative frontiers. There are, fortunately, several feasible types of observation that could soon clarify the issues.

February 24, 2010 | 15:30, RI 480 | Host: Arieh Konigl
First Science Results from Kepler
William Cochran, McDonald Observatory, The University of Texas at Austin
Note: Refreshments served at 3:15 pm
The Kepler spacecraft, launched in March 2009, is designed to detect potentially habitable Earths around other stars by detecting the transits of these planets across the disks of their parent stars. This requires performing differential photometry to a precision of 20ppm on a sample of 170,000 stars for a period of 3.5 years. We will discuss the on-orbit performance of the Kepler photometer, and then present the first scientific results from Kepler. Five new transiting planets around solar-type stars have been discovered so far, along with several other interesting objects.

March 10, 2010 | 15:30, RI 480 | Host: Arieh Konigl
Insights from the Galactic Planetary Census
Gregory Laughlin, University of California Santa Cruz
Note: Refreshments served at 3:15 pm
The past year has seen enormous advances in our understanding of extrasolar planets. In this talk, I'll focus on some of the most exciting recent highlights. These include (i) the discovery and characterization of remarkable new transiting planets, (ii) a complete upending of the conventional wisdom regarding the statistics of the galactic planetary census, and (iii) a new method for actually looking inside certain transiting planets.

March 17, 2010 | 15:30, RI 480 | Host: Arieh Konigl
Microlensing Planets: A Controlled Scientific Experiment Drawn From Absolute Chaos
Andrew Gould, Ohio State University
Note: Refreshments served at 3:15 pm
Microlensing planet searches have discovered a total of 17 planets, including the first Jupiter-Saturn like system and the only 4 "cold Neptunes" yet detected. The discovery process is almost unbelievably chaotic, with the so-called "high-magnification events" being the most chaotic. I show, nevertheless, that the high-magnification subsample constitutes a "controlled experiment",
which enables rigorous statistical analysis, yielding important new clues to planetary architecture. I also discuss the future potential of microlensing to explore domains of planet parameter space not probed by any other method.

March 31, 2010 | 15:30, RI 480 | Host: Craig Hogan
The North American Nanohertz Observatory of Gravitational Waves (NANOGrav)
Andrea Lommen, Franklin and Marshall College
Note: Refreshments served at 3:15 pm
NANOGrav is a consortium of radio astronomers and gravitational wave physicists whose goal is to detect gravitational waves using an array of millisecond pulsars as clocks. Whereas interferometric gravitational wave experiments use lasers to create the long arms of the detector, NANOGrav uses earth-pulsar pairs. The limits that pulsar timing places on the energy density of gravitational waves in the universe are on the brink of limiting models of galaxy formation and have already placed limits on the tension of cosmic strings. Pulsar timing has traditionally focused on stochastic sources, but most recently I have been investigating the idea of detecting individual gravitational wave bursts wherein there are some interesting advantages. I will also demonstrate how the array can be used to reconstruct the waveform and obtain its direction.