Kepler, Microlensing, and Direct Imaging: New Constraints on Exoplanet Formation Theories

Alan Boss

(DTM, Carnegie Institution

Tuesday, January 24, 2012

Abstract

Doppler and ground-based transit searches have discovered over 700 exoplanet candidates to date. These discoveries have generally supported the core accretion mechanism for giant planet formation. However, more recent discoveries have raised questions about the core accretion mechanism as the sole mechanism for exoplanet formation. NASA's Kepler space telescope has now detected 2326 exoplanet candidates, with many of these candidates occupying an oasis in discovery space that was predicted to be a desert on the basis of population synthesis models based solely on core accretion. Similarly, ground-based microlensing surveys, as well as direct imaging detections, have demonstrated the existence of significant numbers of giant planets on orbits wide enough to be difficult to explain purely by core accretion. These new constraints on planet formation theories suggest that future population synthesis models need to consider hybrid formation mechanisms, where at least some of the giant planets are formed by the disk instability mechanism, coupled with the formation of rocky planets, hot and cold super-Earths, and some giant planets by the traditional core accretion mechanism.

Making the Milky Way: Fresh News on the Continuing Saga

Jay Lockman

NRAO

Tuesday, January 31, 2012

Abstract

The first part of the talk is about the Green Bank 100-meter diameter radio telescope, its dramatic origin in the collapse of the 300-foot telescope, and its unique capabilities. Some of its recent scientific programs include the search for gravitational radiation, study of Mercury's molten core, discovery of new organic molecules in interstellar space, and topics in the growth and evolution of galaxies.

The second part of the talk will expand on the evolution of galaxies, with a focus on the Milky Way's continual need for fresh gas. Recently we have discovered that there is a large cloud in the process of merging with the Milky Way whose main body contains several million solar masses of Hydrogen. It will hit the disk in a few tens of Myr. This unique object gives us information on the evolution of the Galaxy, the structure of its gaseous halo, and the existence of dark matter halos, but its origin is still quite uncertain.

The Formation of Brown Dwarfs and Wide Planetary Companions

Kevin Luhman

Pennsylvania State University

Tuesday, February 7, 2012

Abstract

Brown dwarfs have been discovered at progressively lower masses in recent years, reaching well into the mass regime of giant planets. Meanwhile, high-contrast imaging is beginning to uncover planetary-mass companions in very large orbits around stars and brown dwarfs. It is difficult for theories of star and planet formation to explain the existence of both free-floating brown dwarfs and wide planetary companions. I will review recent observational and theoretical progress in understanding the origin of these objects. I will begin by describing the latest measurements of various properties of brown dwarfs, including their initial mass function, binarity, circumstellar environment (disks, accretion, envelopes), and spatial and velocity distributions at birth, and I will compare these data to the predictions of theories for the formation of brown dwarfs. I will then describe the observed properties of wide planetary-mass companions and the resulting constraints on their formation.

Dual Supermassive Black Holes as a New Observational Tracer of Galaxy Evolution

Julie Comerford

University of Texas

Tuesday, February 14, 2012

Abstract

Dual supermassive black holes (SMBHs) with kpc-scale separations are an expected consequence of galaxy mergers, yet surprisingly few dual SMBHs have been observed to date. I will describe the first systematic search for dual SMBHs. This search employs a combination of large spectroscopic surveys of galaxies, longslit spectroscopy, and X-ray and radio observations to identify dual SMBHs that power active galactic nuclei. I will present the first batch of dual SMBHs that have been discovered with these techniques. This systematic survey will enable us, for the first time, to assemble a large observational catalog of dual SMBHs, which will provide observational constraints on the galaxy merger rate, SMBH growth via gas accretion during mergers, and SMBH coalescence.

George Sonneborn

GSFC

Tuesday, February 28, 2012

A Discussion of Diversity in Astronomy and Astrophysics

Jarita Holbrook

University of Arizona

Tuesday, March 6, 2012

Abstract

In 2009, I began an NSF funded project to study women and minorityrity astronomers and their practices related to large database driven projects. This social science project uses oral history interviews as the primary means of data collection along with publicly available information about individual scientists and large database driven projects. The majority of the interviews conducted for the project focus on the Infrared Processing and Data Center (IPAC), the Large Synoptic Survey Telescope (LSST), and the Sloan Digital Sky Survey (SDSS). This presentation will review the numbers for diversity within astronomy, the current hypotheses for the lack of diversity and current strategies for increasing diversity. From the NSF project, we have learned about the professional networks, the career paths, mentoring, and the hostile environment experienced by women and minority astrophysicists. Finally, there will be an open discussions of new hypotheses and strategies to increase diversity within astronomy and astrophysics.

Charles Gammie

University of Illinois

Tuesday, March 13, 2012

Karl Gordon

STScI

Tuesday, March 20, 2012

Jason Steffen

Fermilab

Tuesday, March 27, 2012

Constraining the Progenitors of Type Ia Supernovae in the Era of the Expanded Very Large Array

Laura Chomiuk

CfA

Tuesday, April 3, 2012

Abstract

While there is general agreement that Type Ia Supernovae (SNe Ia) signal the destruction of accreting white dwarfs that approach the Chandrasekhar mass, the mode of this accretion and the nature of the binary companion star remain some of the greatest unsolved mysteries in stellar astrophysics. Each possible progenitor scenario is accompanied by theory that makes predictions for the circumbinary medium surrounding the accreting white dwarf, and we might therefore rule out possible progenitor systems by searching for signs of interaction between the SN Ia explosion and surrounding material. Here, we present the strongest constraints to date on such material around SNe Ia, using the unrivalled sensitivity of radio continuum observations from the Expanded Very Large Array (EVLA). However, in detail these deep limits on the density of material surrounding SNe Ia can be difficult to interpret, due to a limited empirical understanding of the environments of local accreting white dwarfs. We therefore also present our intensive EVLA campaign to monitor recent Galactic novae---local laboratories for mass transfer and accretion processes---at radio wavelengths, probing the circumbinary material in these systems with unprecedented detail and sensitivity.

Tom Murphy

University of California San Diego

Tuesday, April 17, 2012

Tess Jaffe

IRAP

Tuesday, April 24, 2012

Fernando Atrio-Barandela

Salamanca

Tuesday, May 1, 2012

Kailash Sahu

STScI

Tuesday, May 8, 2012

Stefan Funk

Stanford University

Tuesday, May 15, 2012