Berkeley Astronomy Department Colloquium

Fall 2008

All colloquiua held in 2 Leconte at 4 pm with exception of Nov 13 colloquium to be held in McCone.  Colloquium tea is served at 3:30 in Campbell Hall 6th floor lounge.

Aug 28
1 Minute Talks
Sep 4
Bill Hubbard (Arizona)
Joint w/EPS
Gravity Waves in Pluto's Sub-microbar Atmosphere

An Arizona-MIT team observing on the MMT on Mt. Hopkins recorded a grazing occultation of a star by Pluto on 2007 March 18 at unprecedented signal-to-noise.  Data taken simultaneously at 1.6 micrometers (H band) and in the red end of the visible band (about 0.8 micrometers) show large-scale, nearly limb-aligned density fluctuations in Pluto’s atmosphere over a pressure range of ~0.1-0.7 microbars (0.01 to 0.07 Pa; radius range of 1500 to 1350 km). The features are fully resolved and, importantly, achromatic. The data are good enough to show a spectral cutoff moving up in wavenumber with decreasing altitude in Pluto’s atmosphere. We apply scintillation theory to the data.  We find that the cutoff agrees with the theory for dissipation of gravity waves by diffusion of heat and momentum.  Except for much lower characteristic frequencies, Pluto's high atmosphere resembles the Earth's in some respects.
Jim Truran (Chicago)

Nucleosynthesis of Iron and the Energetics and Luminosities of Type Ia Supernovae

The synthesis of iron in an “equilibrium” process in supernova explosions was emphasized in early work by Hoyle and B2FH. These authors anticipated a peak centered on 56Fe. We now understand that mass A=56 is produced in both Type Ia and Type II supernovae in the form of 56Ni, the decay of which – through 56Co to 56Fe - is reflected in the light curves. The level of 56Ni production, and therefore also the brightness of the SNe Ia event at maximum, is also dependent upon the degree of neutronization. We review the underlying energetics of such explosive events and the associated production of intermediate mass and iron-peak nuclei, in the context of current models for SNe Ia. The implications both for Galactic nucleosynthesis and for the light curves and peak luminosities of Type Ia supernovae in diverse stellar populations are then discussed.  
Mark Krumholz (UCSC) From Massive Cores to Massive Stars

The similarity between the mass and spatial distributions of pre-stellar gas cores in star-forming clouds and young stars in clusters provides strong circumstantial evidence that these gas cores are the direct progenitors of individual stars. I describe a physical model for the evolution of massive cores into stars, starting with the intial phases of collapse and fragmentation, through disk formation and fragmentation, the later phases of stellar feedback, and finally interaction of the newly formed stars with their environments. This model shows that a direct mapping from cores to stars is the natural physical outcome of massive core evolution, and thereby allows us to explain many of the properties of young star clusters as direct imprints of their gas-phase progenitors.

Abi Saha (NOAO)
A stellar photometry survey in the Outer Extremities of the Magellanic Clouds

    I will describe a new survey of selected regions in the outer extremities of the Magellanic Cloud system, using multi-band photometry of selected fields that are 7 to 15 kpc from either cloud, and some extending even farther along and near the HI gas streams.  The resulting CMDs reach 2 to 3 mag below the turn-off for the oldest stars in the Clouds, and are very well suited for deciphering ages and chemical abundances.  Main sequence stars below the turn-off are also unbiassed and sensitive tracers of stars associated with the Clouds: they not only probe the extended structure, but also of tenuous features such a stellar halo, stars associated with  the gas streams, and possible structural relics of the interaction between the two Clouds and with the Galaxy.  This is an ongoing survey: I will show some early results that we have found surprising.
Oct 2
Bill Holzapfel (UCB)
The South Pole Telescope: A new probe of cluster cosmology

The South Pole Telescope (SPT) is a 10-meter diameter telescope, with a 960 element millimeter-wavelength bolometric receiver, which is nearing the end of its second season of observation the South Pole. The SPT has been optimized for observations of the Sunyaev-Zel'dovich (SZ) effect in galaxy clusters, which is the inverse Compton scattering of the Cosmic Microwave Background (CMB) by hot intra-cluster gas. With this instrument, we are surveying the southern sky to create a mass limited catalog of galaxy clusters out to the epoch of their formation which can be used to place new constraints on cosmological parameters such as the dark matter density and dark energy equation of state. This program of observations will also produce significant detections of the kinetic SZ effect and weak gravitational lensing of the CMB, a large multi-band millimeter-wavelength point source catalog, and images of the SZ effect in known galaxy clusters with unprecedented sensitivity.  In this talk, I will discuss the science goals of the experiment, the design, construction, and deployment of the SPT, progress of the observations, and conclude by showing some preliminary results.
Dan Marrone (Chicago)
Sunyaev-Zel'dovich Effect Science with the SZA and CARMA

Observations of galaxy clusters through the Sunyaev-Zel'dovich effect have matured rapidly, proceeding in a period of a few years from samples of tens of objects to surveys designed to constrain dark energy with thousands of new cluster detections. Nevertheless, very little observational work has been done to understand the effects of astrophysics and the systematics of the SZ effect in clusters. We are presently using the Sunyaev-Zel'dovich Array, an interferometer optimized for cluster SZ observations, to characterize the SZ signal in known clusters with particular focus on the crucial SZ-mass relationship. Through the Local Cluster Substructure Survey (LoCuSS) we are able to study many tens of clusters via SZ and X-ray imaging, weak and strong gravitational lensing maps, and many other tracers. I will present a few results from the SZA and LoCuSS, including our first examination of the scaling between the SZ signal and gravitational lensing mass. Because gravitational lensing masses are derived without the assumption of hydrostatic equilibrium, as must be done to obtain cluster masses from SZ and X-ray data, this scaling provides an estimate of the non-thermal support in galaxy clusters. I will also discuss our ongoing observational program and the new capabilities enabled by the merging of the SZA and CARMA. The significant sensitivity increase that CARMA provides will allow us to make detailed images of cluster cores, where simulations have difficulty reproducing observational details and where the most important SZ systematics will likely reside.
Alison Coil (UCSD)
Clustering, Quenching, and Feedback: Galaxies and AGN at z=1

Roughly half of the red elliptical galaxies observed today have formed since z=1.  I will present galaxy clustering results from the DEEP2 Redshift Survey that strongly constrain the mechanism responsible for the quenching or cessation of star formation in these galaxies.  I will show where this quenching is occurring on large scales and how it can not be due primarily to cluster-specific physics.  I will also present results on the clustering of optically-bright quasars and X-ray selected AGN and show how AGN accretion correlates with the star formation activity in galaxies at z=1.  I will also show new results on the prevalence of outflowing galactic winds at z=1 and discuss their role in quenching star formation.  Finally, I will present a new wide-area prism survey that will allow further studies of galaxy evolution to z=1 with the largest faint galaxy survey to date.
Sushil Atreya (Michigan)
Joint w/EPS
Titan:  Saturn's Earth-like Moon

Saturn's large satellite, Titan, is unique for having an earth-like atmosphere of nitrogen, a
cycle of methane similar to the hydrological cycle on earth, clouds, rain, channel
networks and river basins presumably sculpted by the rain of methane and ethane,
somewhat similar to the geological features on the earth. In its primordial past, Titan also
possessed the conditions – presence of (liquid) water, ammonia and methane, a warm
environment and energy – necessary for the formation of prebiotic, perhaps even
biogenic, species. Using evidence from Cassini-Huygens Mission and ground-based
telescopes, I will discuss in this lecture the factors that have contributed to the above
unique nature of Titan in the solar system.
de Pater
Sterl Phinney (Caltech)
Electromagnetic Counterparts of Gravitational Wave Sources

Measurement of gravitational waves from high frequency sources by LIGO, and low frequency sources by LISA holds astounding promise for precision tests of strong field general relativity, and precision measurement of properties of compact objects (e.g. mass, spin, radii, distance) hitherto only guessed at from electromagnetic observation.  But when both gravitational wave and electromagnetic observations are both available for a source, the richness of possibility becomes overwhelming. We will review the rich possibilities for LIGO + electromagnetic measurement of neutron star-neutron star and neutron star-black hole binaries, accretion-induced collapse and perhaps supernovae, and for LISA + electromagnetic measurement of Galactic white dwarf binaries, extragalactic tidal disruption of compact objects by supermassive black holes, and cosmological mergers of supermassive binary black holes. We will emphasise (1) the unique impact such combined measurements can have, and (2) how the electromagnetic follow-up should be structured.
Nov 6
Michael Fall (IAS)
Life Cycles of Star Clusters

This colloquium will present a new, comprehensive picture of the
life cycles of star clusters, from their formation in molecular
clouds to their dissolution in the field (unclustered) stellar
population. Our picture is motivated by recent observational
studies (mostly with HST) of clusters of different masses and
ages in several nearby galaxies of different types (dwarf, giant,
interacting, quiescent). Underlying the apparent diversity and
complexity of these cluster systems, we find some fascinating
regularities. These in turn lead us to a quantitative description
of the cluster systems in terms of a simple empirical rule (with
some new theoretical backup) and a simple dynamical model, which
are the main focus of this colloquium. Our new picture revises
several cherished beliefs in this field. We suspect it describes,
at least approximately, the life cycles of most if not all star
clusters (open, globular, proto-, super, etc) in most if not all
Kevin McKeegan (UCLA)
Joint w/EPS
in McCone
The oxygen isotopic composition of captured solar wind: first results
from the Genesis mission

Oxygen is the major constituent of rocky planets and the third most abundant element comprising the Sun, yet the solar oxygen isotopic composition has remained essentially unknown.  One reason is that the usual appeal to primitive meteorites does not work because oxygen is isotopically distinct in all different classes of meteorites.  The cause of this premier “isotopic anomaly” (first discovered in 1973) has been variously ascribed to nucleosynthetic input, e.g. from a nearby supernova, or to exotic isotope-selective chemistry in the solar nebula, e.g. based on molecular symmetry or UV photolysis.  Knowledge of the average starting composition of the solar system, which is preserved in the Sun, would provide a baseline from which one could interpret the oxygen isotopic compositions of planetary materials.  To this end, NASA flew the Genesis Mission to capture samples of the solar wind (SW) in ultra-pure target materials and return them to Earth for laboratory analysis.  At UCLA, we have designed and constructed a hybrid secondary ion and accelerator mass spectrometer (SIMS/AMS), called the “MegaSIMS”, specifically to tackle the unique analytical challenges posed by the Genesis samples: dilute elemental concentrations, limited sample material, and close proximity of likely surface contamination to the implanted solar wind ions.  Three years after the crash-landing of the sample return capsule in the Utah desert, we have succeeded in making oxygen isotopic measurements on SW captured in a SiC target from the Genesis SW concentrator.  Our preliminary data indicate that the Earth and meteorites are grossly isotopically anomalous.  Implications for planetary science will be discussed.
Maxim Markevitch (CfA)
Hydrodynamics of galaxy clusters from Chandra and numeric

As a consequence of Chandra X-ray observations of galaxy
clusters, they can no longer be thought of as spherically
symmetric, isothermal beta-model gas clouds in hyrdostatic
equilibrium. We have discovered bow shocks and "cold
fronts" in merging clusters, as well as sloshing of cool,
dense gas at the centers of clusters previously considered
completely relaxed. I will show lots of striking X-ray
images along with results from our attempts at reproducing
the above phenomena in numeric simulations, and discuss what
we can learn about cluster physics from these data.
Dec 4
Asantha Cooray (UCI)
Missing IR Background: Spitzer and CIBER

The DIRBE extragalactic background light measurements at near-IR
wavelengths is factor of a few or more higher than the integrated
background produced by known star and galaxy counts in existing
surveys. The missing light has been ascribed to reionizing sources and
claims have been made for a large surface density of high redshift
sources based on clustering of fluctuations in deep Spitzer images. I
will show results from our studies with NICMOS and IRAC that question
these claims and show that the missing light cannot be associated with
the first-light galaxies. This still requires an unknown source to
explain most of DIRBE light. To address this, we discuss an attempt to
remeasure the IR background light with a sounding rocket experiment,
CIBER. In the remaining time, I will briefly discuss plans for
cosmological studies with Herschel in the wide-field Herschel-ATLAS