September 2, 2003
Tom Greene
NASA Ames Research Center
"The Astrophysics of Protostars via IR Spectroscopy"
Little is known about the embryonic stellar cores of accreting low-mass protostars. Their high extinctions(Av >= 40 mag) make them impossible
to study via optical spectroscopy with even the largest telescopes. However, recent observational studies using moderate (R ~ 1000) and
high-resolution (R ~ 20000) infraredspectroscopic data are revealing the first astrophysical insights into these objects. We have found that
these very young stellar cores have temperatures, radii, and surface gravities which are similar to somewhat older T Tauri stars. However,
protostars have much higher continuum veilings, indicating very high massaccretion rates. Interestingly, their spectra are dominated by
stellar-like absorption features, and only a fewluminous objects show absorption lines which form in circumstellar disks. Protostars also
appear to be rotatingmuch more quickly than T Tauri stars, so they must lose about half of their angular momenta in only about 100,000 yr.
It is plausible that this can be done via magnetic coupling between protostars and their disks. These first glimpses into the astrophysics of
protostars will also lead to the first ever H-R diagrams which show the true zero-points of stellar evolution.
September 9, 2003
Terry Herter
Cornell University
"Frontier Science Enabled by a Giant Segmented Mirror Telescope"
The GSMT-SWG (Science Working Group) was chartered by the National Science Foundation to "advise the NSF Division of Astronomical
Sciences on a strategy for guiding federal investment in a Giant Segmented Mirror Telescope". This group has worked over the past year getting
inputs from experts in science and technology in the community and from four principal private telescope design groups (CELT, Hawaii, LAT, Magellan 20), and has delivered a report to the NSF. This report focuses on (1) the forefront astrophysical problems likely to emerge over the next decade,
(2) the science potential enabled by next generation telescopes, (3) design options that can achieve that potential, and (4) technologies that must be advanced or developed in order to realize viable telescopes at acceptable cost. Some highlights of this report will be presented.
September 16, 2003
David Spergel
Princeton University
"First Year Results from WMAP: Implications for Cosmology & Inflation"
The Wilkinson Microwave Anisotropy Probe (WMAP) has made an accurate full-sky measurement of the microwave background temperature and polarization fluctuations. I will review how these measurements probe both the physics of the very early universe and the basic properties of the
universe today. The WMAP measurements rigorously test our standard cosmological model and provide an accurate determination of basic
comological parameters (the curvature of the universe, its matter density and composition). When combined with other astronomical measurements,
the WMAP measurements contrain the properties of the dark energy and the mass of the neutrino. The observations also directly probe the physics of
inflation. I will conclude by discussing prospects for future CMB experiments.
September 23, 2003
Xiaohui Fan
University of Arizona
"Probing the Cosmic Evolution with the Highest Redshift Quasars"
I will present studies of the highest redshift quasars discovered from the data taken with the Sloan Digital Sky Survey. These most distant quasars
provide one of the best probes to the high redshift universe. I will present results on the evolution of their luminosity function, their possible
connections to high redshift star formation, and the ionization state of the IGM at z > 6 revealed by the quasar absorption lines. I will discuss
how to use these objects to probe the end of the reionization epoch.
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September 30, 2003
James Graham
UC Berkeley
"Star Formation in Super Star Clusters"
Stars do not form in isolation, but in clusters that span a broad spectrum of masses. These clusters are thought to be the building blocks of galaxies.
Thus, understanding cluster evolution, specifically their dissolution by internal and external forces, is one of the keys to understanding the origin of
stellar populations within galaxies. The discovery that star formation in starburst galaxies is concentrated in numerous, bright, compact knots of stars
therefore ranks amongst the most important made by HST. Dubbed super star clusters (SSCs), these parsec-sized associations probably formed in a
manner approximating an idealized instantaneous burst of star formation. Imaging with HST/NICMOS and high resolution infrared spectroscopy at the
Keck Observatory of individual SSCs yields masses (10^4 - 10^7 solar masses) and sizes (a few pc) reminiscent of globular clusters, leading to the
suggestion that the most massive SSCs may be their progenitors.
October 7, 2003
Doug Richstone
University of Michigan
"Things Invisible to See: Supermassive Black Holes and the Evolution of Galaxies"
Stars do not form in isolation, but in clusters that span a broad spectrum of masses. These clusters are thought to be the building blocks of galaxies.
Thus, understanding cluster evolution, specifically their dissolution by internal and external forces, is one of the keys to understanding the origin of
stellar populations within galaxies. The discovery that star formation in starburst galaxies is concentrated in numerous, bright, compact knots of stars
therefore ranks amongst the most important made by HST. Dubbed super star clusters (SSCs), these parsec-sized associations probably formed in a
manner approximating an idealized instantaneous burst of star formation. Imaging with HST/NICMOS and high resolution infrared spectroscopy at the
Keck Observatory of individual SSCs yields masses (10^4 - 10^7 solar masses) and sizes (a few pc) reminiscent of globular clusters, leading to the
suggestion that the most massive SSCs may be their progenitors.
October 14, 2003
Ray Jayawardhana
University of Michigan
"Exploring Young Brown Dwarfs"
Brown dwarfs, which straddle the mass range between stars and planets, appear to be common both in the field and in star-forming regions.
Their ubiquity makes the question of their origin an important one, both for our understanding of brown dwarfs themselves as well as for theories
on the formation of stars and planets. I will present new results from a multi-faceted observational program that provide valuable clues to the formation
and early evolution of sub-stellar objects. In particular, based on measurements of disk frequency in the infrared and accretion signatures in the optical,
I will discuss whether young brown dwarfs undergo a T Tauri-like phase and if so how long that phase lasts. I will also show that surface gravities and
effective temperatures of very low mass objects can be well determined from a multi-feature analysis of high-resolution spectra in comparison with the
latest synthetic spectra. Their masses and radii can then be derived by combining observed photometry with synthetic fluxes, inferred gravities and known
cluster distances. Two of our Upper Scorpius targets appear to be isolated planetary mass objects (`planemos'), with masses ~6 Jupiters. Our results,
together with recent detections in other young clusters (by other groups), suggest that such objects may not be rare and raise questions about their
origin.
October 21, 2003
John Kormendy
University of Texas at Austin
"Scaling Laws for Dark Matter Halos in Late-type and Dwarf Spheroidal Galaxies"
We study the systematic properties of dark matter (DM) halos in late-type and dwarf spheroidal (dSph) galaxies using published decompositions of
rotation curves V(r) into visible- and dark-matter contributions. Rotation curve decomposition becomes impossible fainter than absolute magnitude
M_B ~ -14, where V becomes comparable to the velocity dispersion of the gas. To increase the luminosity range further, we include virial central
densities of dSph galaxies, which are physically related to spiral and irregular galaxies. Combining these data, we find that DM halos satisfy well
defined scaling laws analogous to the "fundamental plane" relations for elliptical galaxies. Halos in less luminous galaxies have higher central densities
rho_0, smaller core radii, and smaller central velocity dispersions. Scaling laws provide new and detailed constraints on the nature of DM and on galaxy
formation and evolution. Implications include:
1 -- A single, continuous physical sequence of increasing mass extends from the lowest-luminosity galaxies known, i. e., dSph galaxies with M_B ~ -7.6, to
the highest-luminosity Sc galaxies, which have M_B ~ -22.4.
2 -- The high DM densities in dSph galaxies are normal for such tiny galaxies. Since virialized density depends on collapse redshift z_coll, rho_0 is
proportional to (1 + z_coll)**3, the smallest dwarfs formed at least Delta z_coll ~ 7 earlier than the biggest spirals.
3 -- The high DM densities of dSphs implies that they are real galaxies formed from primordial density fluctuations. They are not tidal fragments. Tidal
dwarfs cannot retain even the low DM densities of their giant-galaxy progenitors. In contrast, dSphs have higher DM densities than do giant-galaxy
progenitors.
4 -- The fact that, as luminosity decreases, dwarf galaxies become much more numerous and also more nearly dominated by DM raises the possibility
that there exists a large population of objects that are completely dark. Such objects are a canonical prediction of cold DM theory. If they exist, empty
halos are likely to be small and dense -- that is, darker versions of Draco and UMi.
5 -- The slopes of the DM parameter correlations provide a measure on galactic mass scales of the slope n of the power spectrum, |delta_k|**2
proportional to k**n, of primordial density fluctuations. We derive n = -1.9 +- 0.2. This is consistent with the theory of cold DM.
October 28, 2003
Joshua Bloom
Harvard-Smithsonian CfA
"Cosmological Gamma-ray Bursts: Perspectives and Prospects"
The rapid progress toward an understanding of the progenitors of gamma-ray bursts has forged the exciting possibility of using the bursts as probes
of the universe. While the application of the apparent standardizable energy of the bursts to measure fundamental cosmological parameters has
generated considerable interest, I show that their cosmographic utility is limited. One promising avenue is in the probative value of GRBs for the study
of metals and dust in distant galaxies. I will discuss an initiative, ramping up for the new Swift satellite, to capitalize on the complementarity of GRBs
to quasars as well as my automated survey of burst afterglows at infrared wavelengths.
November 4, 2003
Josh Klein
University of Texas Dept. of Physics
"Unraveling the Solar Neutrino Problem at the Sudbury Neutrino Observatory"
Thirty years ago, Ray Davis and his colleagues hoped to learn something new about the Sun by observing its neutrinos---particles which interact so
weakly that they travel from the solar core to the Earth undisturbed by any of the intervening matter. What Davis found was a surprise: while he
could see the neutrinos, there were far fewer of them than predicted by models of solar energy production. While this was ostensibly a `setback' for
solar astronomy, it was a great opportunity for particle physics, because it raised the possibility that the apparent deficit was the result of new
properties of neutrinos, and that the studies of the Sun could elucidate those properties. Six experiments followed Davis's, and all saw a neutrino
deficit and found---even more suggestively---that the deficit was energy-dependent. The most natural explanation for all the results was that the
electron-flavor neutrinos produced by the Sun were changing into another (unobserved) flavor before reaching the detectors on Earth. The Sudbury Neutrino Observatory (SNO) was designed to determine whether this hypothesis was correct, by directly comparing exclusive measurements of the
flux of electron neutrinos with the inclusive measurement of the flux of all neutrino flavors. SNO's recent results in fact do show a significant difference
between these two measurements, providing direct evidence that neutrinos from the Sun do change flavor. In addition to causing us to re-think our
fundamental ideas about neutrinos, these results allow us to re-start the project Ray Davis began: using neutrinos to understand the Sun.
November 18, 2003
Paolo Padoan
NASA Jet Propulsion Laboratory
"Supersonic MHD Turbulence and the Problem of Star Formation"
This talk presents an approach to the problem of star formation based on the study of supersonic MHD turbulence. I will present recent results on
the statistical properties of supersonic MHD turbulence, such as the energy spectrum, the velocity structure functions and the PDF of density. I also
review methods of comparison between numerical experiments and observational data (radiative transfer of molecular emission lines and thermal
dust emission). Based on such comparison, the interstellar medium may be used as a laboratory for supersonic turbulence. I will then address the issue
of magnetic support of clouds against gravity and discuss the idea that the mass distribution of stars may be understood as a consequence of supersonic
turbulence.
December 2, 2003
Harriet Dinerstein, Neal Evans, Amy Forestell, Claudia Knez
University of Texas at Austin
"Women in Astronomy, 2003"
On June 27-28, a meeting was held in Pasadena on "Women in Astronomy II: Ten Years After", under sponsorship from CalTech, NASA, AURA, AAS
and others - see website at http://www.aas.org/%7Ecswa/WIA2003.html.
(Ten Years After" refers to a meeting held at the Space Telescope Science Institute in 1992 - http://www.aas.org/%7Ecswa/bc.html.)
The fraction of astronomy graduate students who are women has risen to 30% nationally and an actual majority of AAS members in the age range
18-23 years are female, yet this influx of women has not yet translated into proportional participation at higher levels. The four of us who attended the
Pasadena conference will summarize what we heard there, and suggest stratagies to address the outstanding issues and to improve the position of UT
in this area.
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