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Physics & Astronomy Colloquium
Thursdays, 3:30 p.m.
Call us at: (323) 343-2100
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Winter Quarter 2012 Schedule

King Hall C3102
Note -NEW LOCATION this quarter
Refreshments - 3:15 p.m., Colloquium - 3:30 p.m


Dr. Neal Turner
Jet Propulsion Laboratory, California Institute of Technology

"A Hot Gap around Jupiter's Orbit in the Solar Nebula"

ABSTRACT: The Sun grew by accreting material from an orbiting disk of gas and dust, the Solar nebula, in which the planets also formed.  Our star was ten times more luminous during the first few hundred thousand years of its existence, due in part to the gravitational energy released by the accreting material.  If Jupiter was already near its present mass, as in scenarios where the planet formed through a gravitational instability, then the planet's tides opened an optically-thin gap in the surrounding nebula.  I will show using Monte Carlo radiative transfer calculations that sunlight absorbed by the nebula and re-radiated into the gap raised temperatures well above the sublimation threshold for water ice, with potentially drastic consequences for the icy bodies in Jupiter's feeding zone.  Bodies up to a meter in size were vaporized within a single orbit if the planet was near its present location during this early epoch.  Dust particles lost their ice mantles, and bigger bodies lost some or all of their volatiles, depending on their size.  The loss of ices is a problem when using ice-trapping to explain Jupiter's enrichment in the noble gases by factors of several compared with the Sun.  The enrichments might be achieved by either forming the planet much further from the star, or capturing icy bodies at later epochs after the luminosity declined.  More generally, the results demonstrate that the Sun's luminosity is a factor worth accounting for in any model of the formation of icy Solar system bodies.  More is at .


No Colloquium


Dr. Andrea Isella
Department of Astronomy, California Institute of Technology

"Probing the Origins of Solar Systems with Millimeter-wave Interferometry"

ABSTRACT: It is generally accepted that circumstellar disks around pre-main sequence stars are the birth-places of planets. Nevertheless, it is still uncertain how, when and where planet formation occurs within the disks. During the talk I will discuss how we can use millimeter-wave interferometry to address these questions, focusing, in particular, on the derivation of the radial distribution of the circumstellar material and of the dust properties. I will present the most recent results achieved with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) and discuss what we will be able to achieve with ALMA in the next future.


Dr. Wilson Liu
Infrared Processing and Analysis Center
California Institute of Technology

" Star Formation and Debris Disks with the WISE All-Sky Survey"

ABSTRACT: In December 2009, NASA launched the Wide-Field Infrared Survey Explorer, a mission to map the entire sky at four mid-infrared wavelengths. Over the next year, WISE completed its mission objectives, and the data has already led to numerous discoveries and scientific achievements. I will present highlights from the mission and early science and give a preview of the upcoming All-Sky Data Release. I will also present my own research, which involves the investigation of star forming regions as well as debris disks (which are exosolar analogs to our Solar System's Kuiper Belt). Specifically, I will discuss the characteristics of two young star clusters in Circinus and Auriga, and what can be learned from mid-infrared imaging. I will also describe our ongoing project to identify solar neighborhood debris disks and discuss how they will help identify targets for future exosolar planet observations.




Dr. Luisa Rebull
Spitzer Science Center, IPAC, California Institute of Technology

"Looking for New Young Stars in Taurus"

ABSTRACT: The Taurus Molecular Cloud is the closest active star-forming region, and as such, subtends a large solid angle on the sky -- in excess of 250 square degrees. The search for legitimate Taurus members to date has been limited by sky coverage as well as the challenge of distinguishing members from field interlopers. With the advent of facilities that can cover large areas of sky in the infrared, we can attempt to find more Taurus members. We use infrared excess, assumed to be due to a circumstellar disk, to identify candidate members. We conducted a large (44 sq. deg.) survey with the Spitzer Space Telescope, a pointed observatory. Based on our experience with that region, we were well-primed to take advantage of the Wide-field Infrared Survey Explorer (WISE) data -- WISE recently observed the entire sky. We took advantage of the opportunity to search for young stellar object (YSO) candidate Taurus members from a ~260 square degree region designed to encompass previously-identified Taurus members. We use near- and mid-infrared colors to select objects with apparent infrared excesses and incorporate other catalogs of ancillary data to identify a set of rediscovered Taurus YSOs with infrared excesses (taken to be due to circumstellar disks), a set of rejected YSO candidates (largely galaxies), and a set of 94 surviving candidate new YSO-like Taurus members. There is likely to be contamination lingering in this candidate list, and follow-up spectra are warranted.


Professor Bryan Penprase
Pomona College

"Element Formation in the Early Universe - Reading the History of Star Formation in the Absorption Lines of Quasars"

ABSTRACT: In order to study the early universe, astronomers have to use the very few photons available to them from the faint early galaxies, or instead can use the abundant light of very distant quasars to "light up" the space in front of them. By making use of these quasars as "lighthouses" it is possible to detect traces of star-forming gas clouds too faint to see otherwise, and within the absorption from these clouds are clues to the formation of the first elements in the universe. Our program is using a sample of quasars to detect the first nuclei of C, N, and O in the early universe to get clues about the nature of the first stars that produced these elements, which eventually became part of our planet and our bodies (we are star stuff after all!). By observing the absorption of primordial C, N, O, and other elements such as Fe and Al it is possible to constrain the masses of the first stars that produced all of the elements in the periodic table heavier than Helium.


Dr. Ann Marie Cody
Department of Astronomy, California Institute of Technology

"Twinkle, Twinkle Little Star: High Precision Photometry
Sheds Light on Young Stars and Brown Dwarfs"



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