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University of Wyoming

University of Wyoming Physics & Astronomy Colloquium Series

Fridays -- 4:10 PM -- Prowse Room 234

Pre-Colloquium tea served at 3:45 in the Cinnamon Room, PS 237

Spring 2006 Schedule

Jan 27 Peter Conti (U. Colorado)
Radio Selected GHII Regions in our Galaxy: A Biased Sample of Rich O-type Star Clusters

Nearly all of the Giant HII regions in our Galaxy have been found by centimeter wavelength surveys of the galactic plane. These objects provide the energy for the ionization of the interstellar environment in the Galaxy and outline its spiral arm structure. Few objects are seen at optical wavelengths due to the extinction of the intervening dust but many can be studied at near IR wavelengths where the extinction is much smaller. We have been obtaining NIR imaging and spectroscopy of the radio selected GHII regions of our Galaxy, some 54 in all. Although nearly a third are not yet visible with available NIR photometry (but are found in the MIR), the rest are seen to be associated with clusters containing O-type stars. I shall describe observations of the stellar constituents and indicate how spectroscopic distances may be obtained, which will eventually shed light on galactic structure. Most of the clusters contain very young O-type stars, still embedded in their birth material. Thus the radio selected GHII region samples only the very youngest clusters, in contrast to optically detected GHII regions in other galaxies where, on average the objects are older. Remarkably, most of the rich O-star clusters in our Galaxy are as yet undetected.

Mar 24 Lynne Hillenbrand (Caltech)
From Protostars to Planets: Evolution of Circumstellar Material from Myr to Gyr Time Scales

Apr 7 Horace Smith (Michigan State University)
Tracing the Assembly of the Galaxy: RR Lyrae Stars in Globular Clusters

RR Lyrae variable stars are found among the old stellar populations of the Milky Way galaxy. In 1939 Dutch astronomer P. Th. Oosterhoff discovered that globular clusters could be divided into two groups based upon the properties of their RR Lyrae stars. Recent observations have suggested a more complicated pattern than the original two Oosterhoff groups, but have also raised the possibility that RR Lyrae stars can be used to identify particular events associated with the formation of the galactic halo. This possibility, and recent advances in the study of RR Lyrae stars in globular clusters, will be presented.

Apr 14 Jeremy Darling (U. Colorado)
Tunneling, Masing, and Dasing Insights into Galaxy and Black Hole Evolution, Cosmology, and Fundamental Physics

The quantum structure of simple molecules can produce pathological behavior in common natural settings, providing astronomers with useful astrophysical probes.

The most striking pathology is molecular maser emission, which can exhibit brightness temperatures in excess of 10^15 K. The extreme brightness temperatures and small scales of molecular masers make them excellent probes of distance scales, the ionized interstellar medium, and gas kinematics in starbursts and around massive black holes. "Umbrella" inversion tunneling in ammonia can also mase, and in absorption provides a natural molecular gas thermometer.

Molecules can conversely be coaxed into stimulated absorption. For example, OH produces "conjugate" lines: one line is a maser and the conjugate line forms an anti-maser; the net energy budget is null. These lines indicate the molecular gas density and provide precise determinations of the value of physical constants at arbitrary redshift. Formaldehyde (H2CO) can produce the ultimate "anti-maser" in which line excitation temperatures are cooled below the local cosmic microwave background (CMB) temperature. Because the CMB (by definition) covers the sky and lies behind every galaxy, H2CO absorption can be detected at arbitrary redshift and does not rely on the fortuitous alignment of foreground molecular clouds with background flat- or inverted-spectrum radio sources. Moreover, H2CO is a "Swiss Army Knife" molecule for gastrophysics, providing measurements of molecular gas density, total molecular gas mass, astrochemistry pathways, and line excitation, rotation, and kinetic temperatures. Formaldehyde will be a molecule of choice for ALMA and EVLA observations of dense molecular gas from present day to the early universe.

Apr 21 Jane Charlton (Penn St.)
Star Forming Pockets Apart from Galaxies: The Mystery of Weak MgII Absorbers

In the vast space between luminous galaxies there are numerous regions in which stars have formed, which have metals as abundant as they are in the vicinity of the Sun. These metal-rich pockets have been discovered by the shadows that they cast in the spectra of quasars. They are numerous, covering about the same area of the sky in total as luminous galaxies do. Yet, their nature is still unknown, since we must study them only through their shadows. I will present a summary of the properties of these objects and their evolution over time. Then I will place them in the context of the cosmic web of gas that interweaves between groups and clusters of galaxies. Possible connections to dwarf galaxies and to high velocity clouds, such as those surrounding the Milky Way Galaxy, will be discussed.

May 9 Ann Hornschemeier (NASA Goddard)
X-ray Emission from Normal and Starburst Galaxies Outside the Local Universe

This talk will cover progress in the last several years in unraveling the nature of normal and starburst galaxies detected in deep X-ray surveys. The utility of broad-band X-ray emission as a Star Formation (SF) indicator, especially as compared to other multiwavelength measurements, will be reviewed. The normal galaxy X-ray Luminosity Function in deep field and cluster surveys has also recently been measured, and the talk will include discussion of what this tells us about the binary populations in galaxies. New analysis of data from the "other" XMM-Newton instrument, the Optical Monitor (OM) will also be presented. The OM is a UV instrument whose shortest wavelength filter overlaps the GALEX NUV filter. The OM has surveyed a large area of the nearby Coma cluster at ~2" angular resolution and our work indicates that OM data may be used to characterize the SF history of cluster galaxies. The talk will close with a brief discussion of distant normal galaxy science with future X-ray observatories such as as the upcoming Constellation-X mission.

Previous colloquia series: Fall 2002 Spring 2003 Fall 2003
Spring 2004 Fall 2004
Spring 2005
Fall 2005
Contact for program information: Daniel Dale (ddale @