List of Past Astronomy Colloquia : 01-Sep-2000 to 31-Dec-2000

Date:   Wednesday 6-Sep-00
Speaker:   Dr. Bruce Margon (University of Washington)
Title:  "The Universe in Ten Terabytes: Initial Results from the Sloan Digital Sky Survey"

The Sloan Digital Sky Survey (SDSS) is a multi-institutional project to create a huge digital imaging and spectroscopic data bank of 25 percent of the sky in the optical and near-infrared. The imaging atlas is in five specially-chosen colors, reaching a sensitivity 50 times fainter than past similar work. This data base of 10 TB length is automatically analyzed as it is acquired, to catalog the properties of 200 million stellar images, galaxies, and color-selected quasar candidates. The images are used to autonomously select targets for the spectroscopic survey, which will include more than one million spectra of galaxies, previously unknown quasars,and very unusual stars. SDSS will impact virtually every field of astronomy, from Earth-crossing asteroids to the most distant quasars. The multi-color, precision calibrated imaging archive will be a world resource for many decades. Numerous interesting results are found in the first few percent of the data, including new discoveries of very rare objects that overwhelm all past known examples, from the closest planet/brown dwarf transition objects, to virtually all of the most distant known quasars.

Date:   Wednesday 13-Sep-00
Speaker:   Drs. Kenneth Johnston & P. Kenneth Seidelmann (U.S. Naval Observatory)
Title:  "Full-Sky Astrometric Mapping Explorer (FAME)"


FAME is a space astrometry mission that offers the unique opportunity to measure the positions, proper motions, parallaxes, and photometry of 40,000,000 stars brighter than V=15th magnitude to unprecedented accuracy. The astrometric accuracy will range between 50 and 500 microarcseconds, dependent on the magnitude. The instrument will rotate in a scanning survey pattern similar to the Hipparcos project. The spacecraft will be geosynchronous with the precession primarily driven by solar radiation pressure.

The resulting data will provide a definitive calibration of absolute luminosities of solar neighborhood stars, provide a definitive determination of the frequency of solar-type stars orbited by brown dwarfs and giant planets, provide proper motions and distances for individual stars in star-forming regions, assess the abundance of dark matter in the galactic disk, and become an astrometric and photometric catalog. This mission is a complement to, and source of input data, for the Space Interferometry Mission (SIM).

Date:   Wednesday 20-Sep-00
Speaker:   Steven Beckwith (Space Telescope Science Institute)
Title:  "The Hubble Deep Field and its Legacy"

The Hubble Deep Fields penetrated large distances to the time when galaxies were being assembled. The images reveal an era in which galaxies were smaller and less regular than today, suggesting that we are close to seeing the 'edge' of light in the early universe, the time before galaxies and stars existed. The scientific followup provides a strong motivation for the Next Generation Space Telescope and indicates that we can witness the era in which the first objects formed after the Big Bang. The HDFs were unusual in their use of national resources. The success of large projects on the Hubble Space Telescope heralds a change of culture in astronomy similar to that of particle physics in which the big problems will be addressed by applying enormous resources, rather than the individual investigations that have characterized astronomical research in the past.

Date:   Wednesday 27-Sep-00
Speaker:   Dr. Eric Becklin (University of California at Los Angeles)
Title:  "Imaging of High Mass Planets and Brown Dwarfs around Main Sequence Stars"

We have used the NICMOS camera on the Hubble Space Telescope, the NIRC camera on the Keck I telescope and the NIRSPEC camera with AO on Keck II to search for high mass planets (HMP) orbiting young nearby stars. If present cooling models are correct, we should be able to image objects whose mass is only a few Jupiter masses. Results of the search to date are discussed, including the discovery of two brown dwarfs and one very interesting HMP candidate. Future prospects with the cryo-cooler on NICMOS, SIRTF and SOFIA are also discussed.

Date:   Wednesday 4-Oct-00
Speaker:   Dr. Megan Urry (Space Telescope Science Institute)
Title:  "The Physics of X-Ray Jets"

The very first discovery made with the Chandra X-ray observatory was of a previously unknown kiloparsec-scale X-ray jet in the luminous quasar PKS0637-752. Similar emission from resolved jets has now been seen from half a dozen other active galaxies, including the famous quasar 3C273. The X-ray, optical, and radio properties of these jets can be explained if the jet velocity is still relativistic thousands of light years from the active nucleus. The magnetic field can then be in equipartition with the electrons, the Doppler beaming factors agree with estimates from superluminal motion on smaller (parsec) scales, and the synchrotron cooling times are long enough that the de-projected jet length is explained without particle reacceleration.

Date:   Wednesday 11-Oct-00
Speaker:   Dr. Sally Oey (Space Telescope Science Institute)
Title:  "Consequences of massive star feedback in normal star-forming galaxies"

Populations of massive stars are a principal driver of galaxy evolution. The three dominant effects are: 1. Ionizing radiation, 2. Mechanical feedback, and 3. Chemical enrichment. I will present a self-consistent semi-analytic investigation of the global consequences of these three mechanisms on the interstellar medium of star-forming galaxies, including implications for their evolution.

Suggested reading for the gung-ho:

Reviews by Massey; Skillman; Leitherer in _Stellar Astrophysics for the Local Group_, eds. Aparicio, Herrero, & Sanchez 1996 Kennicutt, Edgar, & Hodge 1989, ApJ, 337, 761

My web page:

Date:   Wednesday 18-Oct-00
Title:  Maryland Astronomers Meeting

Date:   Wednesday 25-Oct-00
Speaker:   Dr. Chung-Pei Ma (University of Pennsylvania)
Title:  "A New Perspective on Cosmological Structure Formation"

Modern cosmology is founded on an understanding of how gravity affects the distribution of matter in the universe. The currently accepted paradigm is that gravitational instabilities amplify small ripples imprinted in matter and radiation in the early universe, and these fluctuations eventually evolve into the observed web of cosmic structures. I will review this paradigm and describe recent developments in our understanding of the nonlinear clustering properties of galaxies and dark matter. I will also discuss the implications for upcoming cosmic microwave background measurements.

Date:   Wednesday 1-Nov-00
Speaker:   Dr. Bruce Draine (Princeton University)
Title:  "Infrared and Microwave Emission from Ultrasmall Interstellar Dust Grains"

The infrared emission spectrum of interstellar clouds requires the existence of a population of ultrasmall dust grains, so small that single-photon heating can produce vibrational temperatures as high as 500 K. These grains, consisting of only 30 -- 1000 atoms, must be sufficiently numerous to account for approximately 20% of the total absorption of starlight in diffuse interstellar clouds.

In addition to being vibrationally excited by starlight, these ultrasmall grains will be rotationally excited by a number of processes, resulting in rotational electric dipole emission in the 10-100 GHz region. This microwave emission appears to have already been detected by CMB experiments.

We have developed a carbon-silicate grain model which includes this substantial population of ultrasmall grains, and is consistent with the observed extinction law as well as abundance constraints. The vibrational and rotational excitation of the grains in this model has been calculated. The composition and size distribution of the ultrasmall grains are strongly constrained by the observed microwave emission together with the observed infrared emssion spectrum, including the "PAH" features.

Other consequences of this grain model will be discussed, including photoelectric heating of the interstellar medium, and recombination of gas phase ions.

Background reading:

Draine, B.T., and Lazarian, A. 1999, "Microwave Emission from Galactic Dust Grains" in "Microwave Foregrounds", ed. A. de Oliveira-Costa & M. Tegmark, ASP Conf. Series, 181, 133,

Weingartner, J.C., and Draine, B.T. 2001, "Dust Grain Size Distributions and Extinction in the Milky Way, LMC, and SMC", submitted to ApJ,

Weingartner, J.C., and Draine, B.T. 2001, "Photoelectric Emission from Interstellar Dust: Grain Charging and Gas Heating", submitted to ApJ,

My web page:

Date:   Wednesday 8-Nov-00
Speaker:   Dr. David Neufeld (Johns Hopkins University)
Title:  "The Submillimeter Wave Astronomy Satellite"

Abstract: Since its launch by NASA in December 1998, the Submillimeter Wave Astronomy Satellite (SWAS) has been working perfectly, producing a wealth of data that probe the chemistry of interstellar molecular clouds and its relation to star-formation. SWAS observations toward several dozen interstellar gas clouds, three evolved stars, and several solar system objects have led to the widespread detection of water vapor, a molecule that had previously been proposed as a potentially important reservoir of oxygen and a potentially dominant coolant of dense molecular clouds. In addition, large scale maps of submillimeter emissions from CI and 13CO have been obtained for several photodissociation regions, and stringent upper limits placed upon the abundance of interstellar O2. The implication of these data for our understanding of the chemistry and thermal balance in molecular clouds and circumstellar envelopes will be discussed.

Date:   Wednesday 15-Nov-00
Speaker:   Megan Donahue (Space Telescope Science Institute)
Title:  "Distant Cluster Hunting: The Past and the Promise"

Abstract: I will review the topic of the evolution of clusters of galaxies. I will highlight and discuss in detail recent results from X-ray satellites and their implications for cosmological parameters. Clusters of galaxies have been counted and catalogued since the middle of the 20th century. Clusters were the first systems to have significant evidence for the presence of dark matter. How are clusters used for studies today? I will review what we think we know about clusters, and what new views the most recent space-based observations of clusters seem to be providing us.

Date:   Wednesday 22-Nov-00
Title:  Thanksgiving

Date:   Wednesday 29-Nov-00
Speaker:   Virginia Trimble (U Maryland/UC Irvine)
Title:  "Astrophysics Faces the Millenium"

[Our previously scheduled speaker, Tony Tyson, "Testing cosmology with gravitational lensing," has cancelled due to illness. Virginia Trimble has graciously offered to take his place. Her abstract follows.]

A thousand years ago, a synthesis of Aristotelian philosophy and medieval church doctrine gave Western Europe a universe that was immaculate, unchanging, single-centered, immediately perceptible, immutable, subject to random ominous celestial events, compact, and much else that we now find strange. Much of modern astronomy can be looked at as the gradual overthrowing of these constraints, and many modern problems can be seen as natural progressions away from them. Probably they all can (but not in 50 minutes). The talk will explore a handful of past triumphs, current puzzles, and potential future advances on relatively long time scales. There will be pretty pictures to look at when you get tired of the words.

[For completeness, Tony Tyson's original abstract follows.]

Dark mass-energy may be "seen" directly via its coherent gravitational lens distortion of the forest of high redshift galaxies. Tomographic inversion of these cosmic mirages in deep wide-field imaging surveys enables a unique view of our universe: images of mountains of dark matter and their development over time provide clues to the process of structure formation in the universe. The mass overdensity spectrum and "cosmic shear" correlations as a function of look-back time, when combined with microwave background anisotropy probes of the early universe, will soon lead to precision cosmology and test our fundamental assumptions. The current Deep Lens Survey, preliminary results, and plans for the Large-aperture Synoptic Survey Telescope will be reviewed.

Date:   Wednesday 6-Dec-00
Speaker:   Dr. Seppo Laine (Space Telescope Science Institute)
Title:  "Properties of nuclear bars in Seyfert and non-Seyfert galaxies"

Bars at kiloparsec scales have been studied extensively and have proved to be responsible for gas inflows, resonance rings, flat abundance gradients and perhaps even for driving the morphological evolution of disk galaxies. In contrast, little is known about their smaller-scale counterparts, the so-called nuclear bars. I will discuss the fraction and properties of nuclear bars in Seyfert galaxies and in less active galaxies ("non-Seyferts"). Our samples were chosen from existing archival HST NICMOS imaging data. We have expanded the radial coverage of the galaxies using available ground-based optical and near-infrared images. Since our work is still ongoing, I present only preliminary results.

Date:   Wednesday 13-Dec-00
Speaker:   Dr. Debbie Elmegreen (Vassar College)
Title:  "Effects of Grazing Encounters in Spiral Galaxies"

Abstract: Three galaxy pairs that have undergone recent grazing collisions have been examined in order to study the effects of close encounters on galaxy morphology, gas distribution, and star formation. Each pair contains a galaxy that has long symmetric tidal arms, a misalignment between the kinematic and photometric axes, warped disks, high gas velocity dispersion, and massive HI clouds. Results of HST optical, ground-based NIR and Halpha, VLA 21 cm emission and radio continuum, and Onsala CO observations will be presented, along with N-body and SPH simulations which reproduce the details of the encounters. Each galaxy pair is at a different stage of closest approach, which allows an evolutionary history to be deduced. Starbursts, super star clusters, and possible tidal dwarf galaxies may result from such encounters.

Suggested reading: Elmegreen et al., 2000, "HST Observations of the Interacting Galaxies NGC 2207 and IC 2163," Astronomical Journal, August issue.

Kaufman et al., 1999, "The Interacting Galaxies NGC 5394/5395: A Post- Ocular Galaxy and its Ring/Spiral Companion," Astronomical Journal, 118, 1577.

Kaufman et al., 1997, "Observations of the Ocular Galaxy NGC 2535 and its Starburst Companion NGC 2536," Astronomical Journal, 114, 2323


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