UC Berkeley Astronomy Colloquium Series

Fall 2009

Colloquiua are Thursdays @ 4pm.

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

August 27
Mike Boylan-Kolchin (MPA)
Simulating the formation of structure in the Universe

Numerical simulations of structure formation have become essential 
tools for studying cosmology and galaxy formation.  I will describe 
some of the newest, highest resolution cosmological simulations and 
discuss how they are influencing our understanding of the formation 
and evolution of dark matter halos.  I will also focus on the Milky 
Way as a testing ground for models of cosmology and galaxy formation.  
The wealth of available and forthcoming observational data will 
provide strong constraints on both luminous and dark matter in the 
Galaxy.  I will discuss how combining this data with the latest 
generation of numerical simulations is advancing our knowledge of how 
galaxies form.

September 3
1 Minute Colloquium
September 10
John Johnson (Caltech)
The Golden Age of Exoplanet Spin-Orbit Measurements

The angular momentum of the Solar System planets is remarkably well aligned with the spin axis of the Sun. This arrangement supports the hypothesis that the planets and the Sun formed from the same spinning disk of gas and dust. Until very recently, measurement of the spin-orbit alignment of exoplanets had revealed that planets around other stars, most in very close-in orbits, also have well-aligned spin and orbit axes. However, our recent measurements from this past year have revealed that there may be a second class of exoplanets that inhabit very tilted orbits, and that some may even have retrograde configurations. I'll show how spin-orbit measurements are made, and discuss how the distribution of observed spin-orbit angles informs, and challenges, theories of planet migration.
September 17
Pasquale Blasi (Arcetri)
Particle Acceleration in Supernova Explosions and the Origin of Cosmic Rays

The Galaxy is permeated by Cosmic Rays, a gas of charged particles whose energy spectrum extends from 10^8 eV to about 10^20 eV. Their origin is still matter of much debate but in the last few years we have moved some crucial steps forward toward understanding how these particles are accelerated, the primary candidate sources being supernova remnants. I will describe these recent developments focusing on non linear particle acceleration at collisionless shocks and the important connection between the microphysics of particle scattering and the overall appearance of supernova remnants in radio, X-rays and gamma rays. I will also discuss some implications of the emerging picture that could provide a clue to the origin of the highest energy part of the cosmic ray spectrum, believed to be of extragalactic origin.

September 24
Dave Jewitt (UCLA)

We now know that primordial ice exists in at least three distinct Solar system
reservoirs;  the Oort cloud, the Kuiper belt and the asteroid main-belt. Continuing
efforts to determine the nature of the ice and its distribution are important for several
scientific reasons.  First, the mere existence of the ice sets a limit to the degree of
thermal processing of the objects in which it is found, and therefore constrains
geophysical models of thermal evolution of ice rich bodies.  Second, water ice, if
in the amorphous form, can trap other volatiles from the protoplanetary disk
of the Sun at high abundance.  Their subsequent release upon crystallization can
perhaps explain the anomalous activity observed in many comets and is a
source of energy, since crystallization is exothermic.  Third, water and other
volatiles on the terrestrial planets seem likely to have been delivered, in part, from
the ice reservoirs. The comets and ice-rich asteroids therefore may hold the key to
understanding the origin of the oceans and atmosphere.

In this talk, I will aim to provide a broad overview of our current knowledge
(and lack of knowledge) of the primordial ice reservoirs. I will emphasize
links to the formation epoch and draw connections for those interested in the origin of
the oceans and the atmosphere and in the thermal evolution of asteroids and
comets. I will try to do this in a way interesting to astronomers, Earth scientists
and atmospheric scientists alike.

de Pater
October 1
Moshe Elitzur (UKy)
The AGN Torus --- a Paradigm Change

The variety of observations of Active Galactic Nuclei (AGN) show that
the nuclear activity is powered by a central massive black hole that
drives radio emitting jets and ionizes surrounding line-emitting clouds.
This central engine is surrounded by an obscuring torus, comprised of
optically thick dusty clouds in a rotating configuration. The torus
dynamical origin, and especially its vertical support, present a serious

We have recently developed the formalism for radiative transfer in
clumpy media, and in this talk I show that past problems with modeling
the AGN infrared emission find a natural explanation in clumpy torus
models. Furthermore, the clumpy model may also provide the answer for
the torus dynamical origin and solidify the case for a paradigm shift:
the torus is apparently just the dusty region of wind outflow from the
AGN accretion disk in which the clouds are optically thick.
October 8
Chris Fassnacht (UC Davis)
Galaxy Halos and Subhalos at Moderate Redshifts

Current simulations of galaxy formation make predictions 
about how mass will be distributed in galaxy halos.  Using the 
technique of gravitational lensing, it is becoming possible to 
measure details of mass distributions in galaxies beyond the local 
Universe and, thus, to compare observations directly to simulations 
for samples of cosmologically distant objects.  I will describe 
results from two ongoing projects that take advantage of high-
resolution space- and ground-based imaging.  The first combines 
strong and weak gravitational lensing to quantify the relative 
contributions of the dark and luminous matter in galaxies on scales 
from 10 kpc to nearly 1 Mpc.  The second focuses on detecting the CDM 
subhalos predicted by simulations, via both direct imaging and 
gravitational lens modeling.
October 15
Eve Ostriker (UMD)
The Large-Scale Regulation of Star Formation in Disk Galaxies

Star formation in disk galaxies takes place in cold, dense clouds
containing millions of solar masses of molecular gas.  These clouds
are very dynamic, forming out of diffuse interstellar gas, undergoing
local collapse to produce clusters of stars, and then dispersing due
to energetic feedback from star formation.  Recent numerical
simulations have shown how self-gravitating ISM compression results in
strings of HII regions that light up spiral arms, and creates interarm
structures seen in high-resolution HST and Spitzer images of grand
design spirals.  Simulations including a multiphase ISM have been able
to reproduce observed relationships between large-scale gas properties
and star formation rates in nearby disk galaxies, and have
demonstrated how feedback-driven turbulence and environment (including
the rotation rate and the stellar disk's gravity) are crucial in
setting these rates on ~kpc scales.  These results help to explain why
observed molecular-to-atomic mass ratios and star formation rates
correlate with the mean midplane pressure.  In addition, they suggest
that empirical Kennicutt-Schmidt relations between star formation rate
and gas surface density arise in part as a result of long-term
galactic evolution toward Toomre parameters near unity.  In discussing
these recent results, I will also highlight the importance of
resolving disks' vertical structure in numerical models, in order to
obtain reliable measures of the star formation rate.
October 22
Laurent Loinard (UNAM)
The space distribution of nearby star-formation

Using the excellent astrometry capabilities of
the Very Long Baseline Array, we have measured the
trigonometric parallax (and the proper motions) of a
number of young stars in several nearby star-forming
regions with an accuracy better than a few percents.
This represents an improvement by one to two orders
of magnitude over previous determinations. In particular,
we have found that the distance to the core of Ophiuchus
is 120 +/- 4.5 pc, and we have confirmed that the mean
distance to Taurus is 140 pc. Our data also allows us to
obtain a rough determination of the 3D structure of the
regions under study. In the case of Taurus, we have
shown that the total extent of the complex along the line
of sight is about 30 pc, the eastern portion being on the
far side and the region around L1495 on the near side.
In this talk, after presenting the results themselves, I will
describe several new constraints for the formation and
early evolution of stars that these data provide, focusing
in particular on pre-main sequence evolutionary models.
I will end my talk by mentioning preliminary results in
other regions (particularly Serpens and Cepheus), as
well as longer-terms prospects.
October 29
Paul Ho (CfA/ASIAA)
Preparing for ALMA First Science

The Submillimeter Array has been in operations on Mauna Kea since 2004. 
Many interesting and important results have been obtained in that time
including planetary studies, dusty circumstellar disks, extremely collimated
molecular outflows, circumnuclear disks in nearby galaxies, magnetic fields
via dust polarization studies, and dark submillimeter galaxies at high red
shifts.  These studies are paving the say for the first science projects to
be attempted on ALMA, currently under construction in that Atacama Desert.
I will show some of our latest results.   
November 5
Lincoln Greenhill (CfA)
Moving Images of Accretion and Outflow in High-Mass Star Formation

The details of how massive stars form are poorly understood.  Testing
the viability of disk-mediated accretion, and identifying the processes
that extract angular momentum benefit from direct measurement
of the dynamics of gas at small radii, where outflows are launched and
collimated.  Using the VLBA and VLA, and for the first time, we have
 traced gas structures and tracked 3-D motions within them, 10-1000 AU from a high-mass YSO.  We resolve an edge-on disk about 50 AU across and measure its rotation.  We also resolve a wide-angle outflow that collimates at radii beyond 100 AU. The implied dynamical mass is about 8 Msun. Close to the disk, curved streamlines suggest that magnetic fields may play a role in launching the outflow.  The YSO is quite highly embedded, without known emission up to 20 um.  This is consistent with the inferred edge-on disk orientation and high column density. I will discuss possible origins for this disk
November 12
Mate Adamkovics (UCB)
Using tropospheric methane and stratospheric aerosol to monitor  
circulation on Titan.

The largest moon of Saturn is completely covered by aerosol hazes,
complicating the remote study of the lower atmosphere, where an exotic
meteorological cycle takes place. Recent advances in IR
instrumentation, adaptive optics, and the Cassini/Huygens mission have
produced many, sometimes difficult to reconcile, views of this
environment. I will present measurements from ground-based VLT/SINFONI
and Keck/OSIRIS instruments, as well as the Cassini/VIMS spacecraft,
while explaining the techniques and methodologies used to interpret
these observations. Views of changing global-scale hazes, cloud
evolution, and indications of precipitation will be discussed in the
context of global circulation models and possible long-term changes to
the climate on Titan.
November 19
Norm Sleep (Stanford)
The interaction of photosynthesis with the crust and mantle and the
effect of the moon-forming impact on the current Earth

Photosynthesis evolved before 3.8 billion years ago. Rocks of that
age include metamorphosed black shales with pyrite showing that
sulfur based and iron based photosynthesis existed. A complete carbon
cycle existed on land and at sea.  The land biota needed FeO to dump
oxygen. A consortium with efficient weathering evolved to obtain the
FeO from exposed rocks. Weathering in turn led to wide-spread
continents with Fe-poor sediments and Fe-poor granites. The presence
of these rock types provided selective pressure to vent oxygen
directly and the advent of cyanobacteria. The mantle as well as the
crust sequesters biological information. The Earth became habitable
after the moon-forming impact once its interior was cold enough for
carbonate to subduct in very C-rich domains in the upper oceanic
crust. This process continues today causing mantle carbon to exist
within highly concentrated domains. The chemical and isotopic
character of these domains survives subduction and even partial
melting of kimberlites and their freezing within the lithosphere. The
build up of oxygen in the Earth's atmosphere is evident in U/Th of
zircons in kimberlites. Subduction of carbonate 4.26 billion years
ago and its emplacement with the continental lithosphere at 3.6
billion years ago is indicated by study of a 1.48 suite of alkalic
rocks in India.
December 3
Maryam Modjaz (UCB)
Elucidating the SN-GRB Connection from the SN Perspective

Massive stars die violently. Long-duration gamma-ray bursts (GRBs) and
Type Ib/c Supernovae (SN Ib/c) are two of nature's magnificent explosions
that can be seen over cosmological distances, and both are products of
collapsing massive stars. However, we still do not fully understand the
exact conditions that produce each kind of stellar explosion. While GRBs
emit relativistic jets, SN Ib/c are core-collapse SN whose massive
progenitors have been stripped of their hydrogen and helium envelopes.

I will present a number of observational venues that probe the progenitor
environments of SN with and without GRBs, the metallicities at their sites
and their explosion geometries. Specifically, I will discuss SN 2008D,
which was discovered serendipitously in January 2008 with the NASA Swift
satellite via its X-ray emission and has generated great interest by
astronomers (12 papers and counting). I will discuss the significance of
this SN, whether it harbored a jet, and its implications for the SN-GRB
connection. I will conclude with the most promising venues of upcoming
research that can clarify how massive stars die.


Previous Colloquiua

Spring 2009
Fall 2008
Spring 2008