UC Berkeley Astronomy Colloquium Series

Fall 2010

Colloquiua are Thursdays @ 4pm.

Organizer:  Geoff Bower (gbower@astro.berkeley.edu)

26 August
1 minute colloquium

2 September
Christian Ott (Caltech)
Black Hole Formation in Failing Core-Collapse Supernovae

The cores of massive stars collapse to protoneutron stars, forming, at core bounce, a hydrodynamic shock that initially travels outward in mass and radius, but soon stalls, needing revival by the supernova mechanism. If the latter lacks efficacy, the protoneutron star may reach its maximum mass before an explosion is launched, leading to a second stage of gravitational collapse resulting in the formation of a black hole. Under special, yet to be determined conditions, a black hole -- accretion torus system may form in such failing supernovae and act as the engine of a long gamma-ray burst. I present results from new 1.5D (spherical symmetry plus rotation) simulations that show the systematics of black hole formation with progenitor mass, metallicty, rotation, and nuclear EOS, and lead to new theoretical constraints on the birth spin of black holes. I go on to present the first 3D simulations of black hole forming core collapse events that track the evolution from the onset of collapse, through the protoneutron star phase and protoneutron star collapse to multiple tens of milliseconds after the appearance of the black hole horizon.
9 September
Jaymie Matthews (UBC)
Rewriting the textbooks:
Finding convection where you least expect it

Since all of us were astronomy students, we've known that main
sequence stars with spectral types earlier than about F0 (masses
greater than about 2 solar masses) show no evidence for granulation,
and hence no surface convection zones. That's what the textbooks
have said for decades, but those sections may need to be revised.

I present evidence for granulation in two delta Scuti stars of
spectral type A2: HD 174936 and HD 50844. Recent analyses of CoRoT
satellite photometry revealed up to about 1000 frequencies in the
photometry of each of these stars. The frequencies were interpreted
as individual pulsation modes. If true, there would have to be large
numbers of non-radial modes of very high degree which should suffer
cancellation effects in disk-integrated photometry and not be
detectable (even with high space-based precision). The pulsational
interpretation of all the frequencies in HD 174936 and HD 50844
depends on the assumption of white (frequency independent) noise.

Our independent analyses of the data provide an alternative: most
of the peaks in the Fourier spectra are the signature of non-white
granulation background noise, and less than about 100 of the
frequencies are actual stellar p-modes in each star. We find
granulation time scales which are consistent with scaling relations
that describe cooler stars with known surface convection, including
MOST space telescope observations of the cool supergiant Betelgeuse.

The stars know what they're doing, even when we don't.

16 September
Phil Hopkins (UCB)
How do Massive Black Holes Get their Gas (and Get Rid of It)?

Recent observations of tight correlations between supermassive black hole masses and the properties of their host galaxies demonstrate that black holes and bulges are co- eval, and have motivated theoretical models in which feedback from AGN activity regulates the black hole and host galaxy evolution. I will review the state of models and observations regarding quasar and AGN fueling and feedback, using new multi-scale simulations that can probe from galaxy scales down to the accretion disk. Combining simulations, analytic models, and recent observations, answers to a number of questions are starting to take shape: How to AGN get triggered? How long do they live? Are there relics in the local Universe -- perhaps even in M31 and the Milky Way -- that provide unique information on the epoch of black hole growth? Is feedback necessary/sufficient to regulate BH growth? What effects does that feedback have on the host galaxy? And how does this interact with the dynamics of stellar evolution and other sources of feedback in the ISM?

23 September
Greg Laughlin (UCSC)
Inferring the Physical Properties of Extrasolar Planets

Of order 500 extrasolar planets have now been cataloged. In this talk, I will give an overview of current progress that is being made in characterizing their physical properties. Using a variety of observational techniques and inferences, it is now possible to probe planetary compositions, interior structures, weather variability, and global energy budgets. I will place particular focus on the remarkable and diverse insights that can be gained when one has access to the particularly auspicious situation of a transiting planet in a multiple-planet system orbiting a bright parent star.
30 September
Mark Reid (CfA)
Measuring the Cosmos

Over 2000 years ago, Hipparcus measured the distance to the Moon by triangulation 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 18th centuries attempted to measure stellar parallax, not only to determine the scale of the cosmos but also to test Heliocentric cosmologies. While these efforts failed, along the way they lead to many discoveries, including atmospheric refraction, precession, and aberration of light. It was not until the 19th century 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 and the compact object at the center of the Milky Way. Using the Very Long Baseline Array we now can achieve positional accuracy approaching 10 micro-arcseconds! These measurements address fundamental problems in Galactic dynamics, evidence for supermassive black holes, and the mass of the dark matter halo of the Milky Way.
7 October
David Ballantyne (Georgia Tech) Connecting Star Formation, Galaxy Evolution and the X-ray Background

As we now know, the growth of galaxies and their central black holes is connected through some unknown mechanism. The cosmic X-ray background encodes within it the entire history of accretion onto supermassive massive black holes and so provides an unique view of the role of AGN in the assembly of galaxies. This talk presents results of recent work that is attempting to exploit the information contained in the X-ray background (and ancillary multiwavelength studies) to construct a testable scenario for the evolution of AGN and their host galaxies.
14 October
Rob Simcoe (MIT)
Early Galaxy Formation and the Chemical Enrichment of Intergalactic Matter

Heavy elements have been detected in tenuous intergalactic gas at
essentially all observed redshifts.  This suggests that nascent
galaxies expelled some fraction of their interstellar material
starting very early in the history of the universe.  The physical
process that distributed these metals may also govern many aspects of
the galaxy formation process itself.  I will review the status of
intergalactic chemical abundance measurements and describe new efforts
to push these techniques beyond redshift 6, using the newly commissioned
FIRE infrared spectrometer at the Magellan telescopes.  At these epochs, we may
begin to witness nucleosynthetic byproducts from the generation of galaxies that
reionized the universe.

21 October
Nick Schneider (Colorado) --- Joint w/EPS

Plumes on Enceladus: The Ocean Debate

The discovery of water vapour and ice particles erupting from Saturn's moon Enceladus fuelled speculation that an internal ocean was the source. Alternatively, the source might be ice warmed, melted or crushed by tectonic motions. If a long-lived ocean is present and in contact with a rocky core, dissolved sodium chloride is predicted to be present at the few percent level. Here we report a ground-based spectroscopic search for atomic sodium near Enceladus that places an upper limit on the mixing ratio in the vapour plumes orders of magnitude below the expected ocean salinity. The low sodium content of escaping vapour, together with the small fraction of salt-bearing particles, argues against a situation in which a near-surface geyser is fuelled by a salty ocean through cracks in the crust1. The lack of observable sodium in the vapour is consis- tent with a wide variety of alternative eruption sources, including a deep ocean, a freshwater reservoir, or ice. I will highlight the differences between these models, and describe their strengths and weaknesses in terms of matching observations, breadth of physics incorporated and geophysical plausibility. I will also discuss the broader implications of each scenario, including their astrobiogical potential.

28 October
Meredith Hughes (Berkeley)

Millimeter-Wavelength Observations of Circumstellar Disks, and What They
Can Tell Us about Planets

Our understanding of the properties of young planetary systems is
intimately linked to our knowledge of the structure and evolution of disks
around young stars.  I will describe how we are using high-resolution
observations at millimeter wavelengths to constrain the physical mechanisms
driving the dissipation of gas and dust from circumstellar disks, as well
as the architectures of the planetary systems they leave behind.  I will
focus on observations of the later stages of disk evolution.  The
"transitional" objects intermediate between primordial gas-rich disks and
tenuous, dusty debris disks provide a window into the properties of the
youngest (Myr-old) planetary systems.  The debris disks themselves can
point the way to otherwise undetectable plants far from the star, and
provide unique dynamical constraints on the masses of directly-imaged
planets.  I will include a discussion of how next-generation instruments
like ALMA are poised to revolutionize the field within the next few years.

4 November
Tony Wong (UIUC)
The Molecular Cloud Population of the Large Magellanic Cloud

With the Magellanic Mopra Assessment (MAGMA), we have recently completed a
CO imaging survey of the brightest giant molecular clouds (GMCs) in the
Large Magellanic Cloud (LMC).  In this talk I will review our limited
understanding of GMC evolution, in particular their formation and
destruction mechanisms, and describe our progress in deepening that
understanding using CO surveys of the LMC.  The inferred properties of LMC
GMCs depend a great deal on the analysis technique, but like their Galactic
cousins, they appear to be much more elongated than is commonly believed,
and are the predominant sites for massive star formation.  The velocity
gradients across GMCs are similar to those found in the surrounding atomic
gas and do not appear indicative of rotation.  The locations of GMCs
vis-a-vis young stellar objects may shed light on the longstanding issue of
their lifetimes, although current inferences are limited by the
incompleteness of YSO catalogs.

18 November
Keivan Stassun (Vanderbilt)
Empirical Constraints on the Formation and Evolution of Low-Mass Stars and Brown Dwarfs: A Data-Intensive Approach

Recent and ongoing large surveys, both from the ground and from space, are enabling new data-intensive approaches to a variety of problems in stellar astrophysics. This talk describes three such projects, each serving as a vignette of a different but complementary mode of data-intensive research into low-mass star formation and evolution. The X10000 Project takes a panchromatic, time-domain approach to study the structures of young stellar coronae in order to understand the role of extreme coronal mass ejections in the angular momentum evolution of young stars. SLoWPoKES takes an ensemble, data-mining approach to extract from the Sloan Digital Sky Survey the largest sample of wide low-mass binaries ever assembled, which can be used to constrain binary formation theory and for refining the fundamental mass-age-activity-rotation-metallicity relations for low-mass stars. The EB Factory project takes a time-domain, data-mining approach to identify rare, but astrophysically very interesting, case studies from among the large numbers of eclipsing binaries being harvested by surveys for transiting exoplanets. We will highlight recent discoveries from this work, and will draw these results together to elucidate the physical interrelationships between stellar rotation, magnetic field generation, and stellar structure during the star-formation process.
2 December
Rogier Windhorst (ASU)
How will the James Webb Space Telescope measure First Light, Reionization, and Galaxy Assembly in the post WFC3 era?

We review how the 6.5 meter James Webb Space Telescope (JWST) can measure First Light, Reionization, Galaxy Assembly, building on lessons learned from the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3). We show what combination of area, depth, and wavelength coverage are needed for JWST to detect a sufficient number of First Light objects, and to measure their evolving luminosity function (LF). In detail, JWST will map the epoch of First light through Pop III star dominated objects at redshifts z=8--20, and its transition to the first Pop II stars in dwarf galaxies at z<9. JWST will measure the evolution of the steep faint-end of the dwarf galaxy LF at z=6--12, which likely provided the UV-flux needed to start and finish Hydrogen reionization.

We will discuss: 1) what deep JWST images will look like compared to the Hubble UltraDeep Field (HUDF), given JWST's expected PSF performance; (2) simulations of what nearby galaxies observed in the restframe UV--optical by HST would look like to JWST at very high redshifts; (3) quantitative methods to determine structural parameters of faint galaxies in deep JWST images as a function of cosmic epoch to delineate the progress of galaxy assembly; (4) to what extent JWST's short-wavelength performance --- which needed to be relaxed in the 2005 redefinition of the telescope --- will affect JWST's ability to accurately determine faint galaxy parameters; and (5) if ultradeep JWST images will run into the instrumental and natural confusion limits. A new generation of algorithms may be needed to automatically detect, measure and classify objects in very crowded, ultradeep JWST fields.

This work was funded by NASA JWST Interdisciplinary Scientist grant NAG5-12460 from GSFC, and grant HST/DD-11359 from STScI, operated by AURA for NASA under contract NAS 5-26555.
9 December
Jean-Luc Margot (UCLA) - Joint w/EPS

Solar System Binaries and Triples: Properties, Origin, and Evolution

Previous Colloquiua

Spring 2010
Fall 2009
Spring 2009
Fall 2008
Spring 2008