Subscribe to: iCal

Astronomy Colloquia at Caltech for 2009-2010

Colloquia are held every Wednesday during the academic year at 4pm in the Cahill Hameetman auditorium. Tea and cookies are served at 3:45 pm in the Ahmanson library located on the 1st floor of Cahill.

Date

Speaker

Talk Title

SEPTEMBER

30

Rachel Akeson Caltech Host: Schuyler van Dyk

Infrared Interferometry and the Evolution of Circumstellar Disks Abstract: After a brief review of the current state of infrared interferometry, particularly the Keck Interferometer, I will focus on observations of circumstellar disks around young and main sequence stars. Infrared interferometry is unique in its ability to make direct, milli-arcsecond scale measurements of the physical properties of the central regions of these disks. These measurements have placed strong constraints on the inner disk regions of T Tauri and Herbig stars. More recently, this technique has also been applied to the so-called transitions disks and the debris disks around main sequence stars.

OCTOBER

7	Pavel Kroupa AIfA Host: Sterl Phinney	The satellite galaxies of the Milky Way and Andromeda Abstract: The satellite galaxies of the Milky Way, and to a less-significant amount, those of Andromeda, are distributed anisotropically about their hosts. The MW system appears to be a disk-like feature which is rotating. These and other features of the satellite galaxy population indicate that many of the satellites may be ancient tidal-dwarf galaxies. If true this would have major implications for fundamental physics.
14	John Carpenter Caltech	Structure and Evolution of Protoplanetary Disks Abstract: The properties and evolution of circumstellar disks around young (< 10 Myr) stars provide an indirect means to investigate the formation of planetary systems. I present recent results from the Spitzer Space Telescope that probe the evolution of disks in this time period, including the dissipation of gas-rich primordial disks and the formation of debris systems. In addition, I will present sub-arcsecond resolution CARMA images of the dust emission in a sample of primordial disks in the Taurus-Auriga and Ophiuchus molecular clouds.
21	Eliot Quataert UC Berkeley Host: Sterl Phinney	The Birth of Neutron Stars and Black Holes in Gamma-ray Bursts Abstract: Gamma-ray bursts (GRBs) have long been among the most enigmatic of astrophysical transients. Observations during the past decade have led to a revolution in our understanding of long-duration GRBs, associating these events with the core-collapse of massive stars. However, only in the past few years have the host galaxies of short-duration GRBs been established, confirming that these arise from a separate progenitor population; the leading model for such events is the merger of two compact objects (e.g., a neutron star and a black hole) although alternative possibilities remain viable (e.g., the accretion induced collapse of a white dwarf to a neutron star). In this talk, I will describe theoretical models for both long and short-duration bursts, emphasizing several outstanding problems. Short GRBs are particularly interesting since compact object mergers are the primary target for km-scale gravitational wave observatories such as Advanced LIGO. I will describe possible electromagnetic counterparts to these gravitational wave sources.
28	Reinhard Genzel MPE Host: Sterl Phinney	Spatially resolved dynamics of z~2forming galaxies Abstract: I report on two major programs of studying the kinematics, star formation and cold gas properties of z~2 massive star forming galaxies (z2SFGs) with spatially resolved spectroscopy. With the adaptive optics assisted, integral field spectrometer SINFONI on the ESO VLT we have studied about 90 z2SFGs and find compelling evidence for large, turbulent rotating disk galaxies in ~50% of the larger objects that we spatially resolve well. It appears plausible that these z2SFGs may be driven by continuous, rapid accretion of gas from their dark matter halos, and that their evolution is strongly influenced by internal, secular evolution. In a new program on the IRAM Plateau de Bure millimeter interferometer we have also detected for the first time CO 3-2 line emission in a sample of these z2SFGs (as well as in matched z~1.2 counterparts). We find that the z~1-2 SFGs are gas rich and that their star formation properties are fully compatible with a standard Kennicutt-Schmidt star formation relation. I will discuss the impact of these new observations on our understanding of galaxy evolution in the early Universe.

NOVEMBER

4	Andy Gould Ohio State University Host: Judy Cohen	Microlensing: Measuring the Galactic Distribution of Planets. Abstract: Microlensing has discovered 13 planets, including the first "cold Neptunes", the first Sun/Jupiter/Saturn analog, the least massive planet, and the heaviest planet orbiting an M dwarf. A great strength of microlensing is that it does not depend on photons from the host star, and so probes classes of planets not accessible to other techniques. Originally, this was also considered a great weakness: since the host cannot be seen, we generally did not expect to be able to determine its mass and distance. I show that masses and distances have nevertheless been measured for the majority of planets discovered to date. In particular, we can determine which are in the Galactic disk vs the Galactic bulge. I report a very surprising initial result from this observed distribution of distances.
11	Mark Reid Harvard-Smithsonian Center for Astrophysics Host: Nick Scoville	Measuring the Cosmos Abstract: Over 2000 years ago, Hipparcus measured the parallax of the Moon from two locations across the Mediterranean Sea. However, determining distances to stars proved much more difficult. Many of the best scientists of the 16th through 19th centuries attempted to measure stellar parallax, not only to determine the scale of the cosmos but also to test the Heliocentric cosmology. It was not until 1838 that Bessel measured the first stellar parallax. Distance measurement in astronomy remained a difficult problem even into the early 20th century, when the nature of galaxies ("spiral nebulae") was still debated. While we now know the distances of galaxies at the edge of the Universe, we have only just begun to measure distances accurately throughout the Milky Way. I will present new results on parallaxes and motions of star forming regions with near micro-arcsecond accuracy using the VLBA. These measurements address fundamental issues, including the spiral structure, size, and mass of the Milky Way.
18	Željko Ivezić University of Washington Host: Judy Cohen	Mapping the Milky Way: from SDSS and 2MASS to LSST and Gaia Abstract: The formation of galaxies like the Milky Way was long thought to be a steady process that created a smooth distribution of stars. Instead, recent discoveries of complex substructure in the distribution of the Milky Way's stars have deeply shaken this standard view. I will discuss how the unprecedentedly accurate and robust data from modern sky surveys, such as Sloan Digital Sky Survey and 2MASS, have enabled some of these discoveries, and will speculate what further progress can be expected from the upcoming next-generation surveys, such as Gaia and Large Synoptic Survey Telescope.
25	Nov 25 –no colloquium

DECEMBER

2

Wendy Freedman Carnegie Host: Judy Cohen

The Carnegie Supernova and Hubble Projects Abstract: I will discuss two ongoing projects: The Carnegie Supernovae Project (CSP), a long-term program using Type Ia supernovae to place constraints on the equation of state for dark energy; and The Carnegie Hubble Project (CHP), a new Spitzer Exploration Program aimed at measuring the Hubble constant to an accuracy of 2%. As part of the CSP, we have been extensively monitoring Type Ia supernovae, obtaining multi-wavelength (uBVgriYJHK) observations at low redshifts (z<0.08), and measuring the first I-band Hubble diagram out to redshifts of 0.7. The CHP is extending the entire extragalactic distance scale calibration into the mid-infrared. Based on a geometric parallax calibration of Cepheids from the Hubble Space Telescope (and in future, from GAIA), and with negligible reddening in the mid-infrared, this program will re-measure the Cepheid distances to nearby galaxies, calibrating Type Ia supernovae and other methods well out into the Hubble flow. I will discuss how this improved accuracy in the Hubble constant, in combination with new experiments like Planck, provides strong constraints on other cosmological parameters.

JANUARY

6
13	Jonathan Tan University of Florida Host: Jessica Lu
20
27	William J. Borucki Host: Schuyler van Dyck

FEBRUARY

3
10
17	John Grunsfeld NASA/Johnson Space Center Host: Lynne Hillenbrand	(12th Annual Greenstein Lecturer)
24

MARCH

3

APRIL

7

14

21

28

MAY

5

12

19

26

JUNE

2

Information for Speakers

• How to get to the Caltech
• Campus Map
• Visitor parking information
• Reimbursement form

Previous Astronomy Colloquia:
1997
1998
1999
2000
2001
2002
2003
2004

2005

2006

2007

2008

2009

Updated: 11/16/09 gma