List of Past Astronomy Colloquia : 01-Sep-2002 to 31-Dec-2002

Date:   Wednesday 11-Sep-2002
Speaker:   Sara Seager (DTM)
Title:  "Characterizing Extrasolar Planets"

There are 100 known extrasolar giant planets orbiting single sun-like stars. Characterizing the planet atmospheres is difficult because the planet-star contrast is many orders of magnitude and the planet-star systems cannot be spatially resolved with existing instruments. Nevertheless, extrasolar planet atmosphere observations are being attempted in the combined light of the planet-star system for the class of "close-in" planets---seven times closer to their parent stars than Mercury is to our sun---that are hot thermally and potentially bright in reflected light. The first observational success was the detection of neutral sodium in the atmosphere of the transiting CEGP HD209458b, and this has provided the first constraint on model atmospheres. I will present theoretical atmospheric signatures and existing observational constraints for the CEGPs. I will also discuss the search for Earth-like planets and new studies of Earth as an extrasolar planet. I will conclude with what current and future observations will tell us about extrasolar planets.

Date:   Wednesday 18-Sep-2002
Speaker:   Stacy McGaugh (Maryland)
Title:  "Gravity and Dark Matter"

Date:   Wednesday 25-Sep-2002
Speaker:   Greg Bothun (Oregon)
Title:  "The z=0 Baryon Dilemma"

Detailed studies of the D/H ratio as well as the acoustic spectrum of the Microwave Background have lead to strong constraints on the baryon abundance of the Universe. These studies suggest that Omega_baryon is 4% of the closure density. However, current inventories of the possible baryonic respositories can only account for 10% of this expected number. The other 90%, therefore, seems to be playing a clever game of hide and seek, avoiding detection. This talk will focus on where the missing baryons are likely to be residing, techniques for detecting that population, and finally, the possibility that all of the mass in the Universe is just baryonic.

Date:   Wednesday 2-Oct-2002
Speaker:   Larry Nittler (DTM)
Title:  "Meteoritic Stardust and the Evolution of the Galaxy"

Date:   Wednesday 9-Oct-2002
Speaker:   No Colloquium
Title:  October Conference

Date:   Wednesday 16-Oct-2002
Speaker:   Neil Gehrels (Goddard)
Title:  "Gamma Ray Burst Discoveries and the Upcoming Swift Mission"

Date:   Wednesday 23-Oct-2002
Speaker:   Brent Tully (IfA)
Title:  "Structure in the Universe: From Big to Small"

We will look at the properties of the distribution of galaxies on three scales. First the distribution of the most massive collapsed structures will be considered, as delineated by a catalog of 2,000 Abell clusters extending to +/-0.14c. Then we will give attention to an all-sky catalog of 30,000 galaxies within a cube centered on the Galaxy extending to +/-8,000 km/s. Then our attention will focus on the region within 5 Mpc already containing 360 cataloged galaxies.

There is the big question of the relationship between the light of galaxies and the underlying mass distribution. It will be argued that there are large variations in mass to light with environment. Intermediate mass regimes associated with groups of spiral galaxies manifest the most light per mass. There is much less light associated with mass in the regimes of larger and smaller structures.

Date:   Wednesday 30-Oct-2002
Speaker:   Alycia Weinberger (DTM)
Title:  "Nearby Stellar Associations as Proto-planetary Disk Laboratories"

Date:   Wednesday 6-Nov-2002
Speaker:   Karl Glazebrook (JHU)
Title:  "The Gemini Deep Deep Survey: first results"

The aim of the GDDS is to bridge the redshift gap bwteen z=1, where the current Hubble sequence of ellipticals and spirals is extant and z>2 where the only field galaxies with spectroscopic redshifts we know about are blue, star-forming and of fragmented morphology. To do this we need to secure redshifts of the oldest, reddest galaxies (candidate ellipticals) at z>1. Using the 'nod & shuffle' facility on the GMOS spectrograph which we developed and recently commissioned on Gemini North we have done precisely this. Our first field is an ultra-deep 14 hour Gemini exposure in 0.5" seeing on a MOS field of 77 galaxies reaching I=24.5 and z=1.5, including galaxies with the restframe UV spectra of red, old stellar populatons. I give a report on results from our first field and future GDDS plans.

Date:   Wednesday 13-Nov-2002
Speaker:   Sean Carroll (Chicago)
Title:  "Dark Energy and the Preposterous Universe"

A variety of observations have led cosmologists to conclude that the universe is dominated by a mysterious form of "dark energy" (in addition to the well-established "dark matter", which now seems prosaic by comparison). This dark energy could be vacuum energy (a cosmological constant), or something dynamical and slowly evolving. All of the possibilities are very exciting, and future observations have promise for distinguishing between them. I will give an overview of the theoretical proposals for dark energy and the observational constraints which any model must satisfy.

Date:   Wednesday 20-Nov-2002
Speaker:   Jeremy Heyl (CfA)
Title:  "The Secret Life of Neutron Stars"

Neutron stars were discovered nearly thirty-five years ago, but until the last decade, for the most part those studied followed two metabolic strategies; they either derived energy from rotation (radio pulsars) or accretion (X-ray binaries). The Soft-Gamma Repeaters provided a hint that the neutron-star menagerie might be more diverse. Over the past decade ROSAT, and in much greater detail over the past few years, Chandra, XMM and RXTE have established new sections in the neutron-star zoo. I will discuss an important and possibly common manifestation of young neutron stars in the wild: thermally or magnetically powered neutron stars, also known as anomalous X-ray puslars and soft-gamma repeaters.

Without a companion, neutron stars fade away in the X-rays a few million years after the supernova. However, in symbiosis with a low-mass star, an accreting neutron star can remain active for several billion years. I will tell the story of how old neutron stars get their stripes, which show up as Type-I burst oscillations, and speculate whether some shiver to keep warm, using gravitational-radiation reaction to heat their interiors.

Date:   Wednesday 27-Nov-2002
Speaker:   No Colloquium
Title:  Thanksgiving Break

Date:   Wednesday 4-Dec-2002
Speaker:   Arthur Kosowsky (Rutgers)
Title:  "The Atacama Cosmology Telescope"

The coming release of MAP data will likely close one chapter in the study of the cosmic microwave background anisotropies and open another. I will describe the kinds of questions future microwave background experiments will probe. One such experiment is the Atacama Cosmology Telescope (ACT), a proposed collaboration between Princeton, Penn, Rutgers, Goddard, and several other partners. ACT's aim is to make a map of the microwave background at roughly micro-Kelvin sensitivity and arcminute angular resolution. The types of technological advances and design considerations making such an experiment possible will be described. ACT will observe the Sunyaev-Zeldovich effect and gravitational lensing of the microwave background, along with other signals from non-linear structures. The eventual cosmological impact of such an experiment will be discussed.

Date:   Wednesday 11-Dec-2002
Speaker:   David Helfand (Columbia)
Title:  "Contemplating Original Spin"

Neutron stars are born in the last few seconds of the life of a massive star. The instantaneous release of 1046 Joules of gravitational energy which accompanies each such birth violently disrupts the remainder of the parent star, distributing to interstellar space the nucleosynthetic products of the star's life and synthesizing all of the elements from Nickel to Uranium. Folklore suggests that the remnant core spins roughly 100 times per second, and supports a magnetic field of 1012 G; the Crab Nebula and its central pulsar are characterized as prototypical remnants of this process. This talk refutes that folklore. Through targeted observations of supernova remnants with the Chandra and XMM X-ray Observatories and radio studies with the VLA, we are finding an extraordinarily wide range of initial neutron star spin rates, magnetic field strengths, and velocities. These results hold important implications for models of supernova collapse and the chemical evolution of the Galaxy.

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