Pre-Colloquium tea served at 3:45 in the Prowse Room
|September 12|| Atomic and Ionized Hydrogen Gas at the Disk-Halo Interface in Spiral
Rene Walterbos (New Mexico State University)
Observations over the past two decades have provided ample evidence for thick layers of HI and diffuse ionized gas extending sometimes far above the midplane of galaxies into their halos. A few nearby galaxies, including the Milky Way also show evidence for a distribution of HI clouds and filaments further into the halo. Some of these features may be explained by galactic fountains, a cyclical process of gas outflow and inflow driven by star formation in the disk. Accretion of gas from the IGM and from tidal interactions is also called for to explain some of the larger scale phenomena. The kinematic signature of the gas at the disk-halo interface may provide information on the origin of the gas. I will describe some recent results on the kinematics of HI from deep observations with the WSRT and VLA radio telescopes of a sample of nearby disk galaxies, as part of the HALOGAS project, and from deep multi-slit spectroscopy of ionized gas in edge-on galaxies with the ARC 3.5m telescope. A general result is a decrease in rotational velocity of gas with height above the disk. The sense of the lag is as predicted by galactic fountain models, though its magnitude is far larger than simple models would predict. In general, few galaxies show strong evidence for accretion of cool gas, and the bulk of IGM inflow predicted to exist remains as of yet undetected.
|September 19|| Title, TBA
Paul Butler (Carnegie Institute of Washington)
Modern science began with Copernicus speculating that the Earth is a planet and that all the planets orbit the Sun. Bruno followed up by speculating that the Sun is a star, that other stars have planets, and other planets are inhabited by life. For this and other heresies, Bruno was burned at the stake in a public square in Rome in 1600. Astronomy and extrasolar planets were a really hot field at the time. Over the past 20 years more than a thousand extrasolar planets have been found, first from ground-based precision Doppler and photometric transit surveys, and more recently by the Kepler space mission. We have concentrated on building precise Doppler systems to survey the nearest stars. Our systems at Lick, Keck, AAT, and Magellan have found hundreds of planets, including 5 of the first six planets, the first saturn-mass planet, the first neptune-mass planet, the first terrestrial mass planet, and the first multiple planet system. We are currently focusing our attention on new custom built "R4" echelle spectrometers designed for Iodine cells, which are yielding 1 m/s precision. These spectrometers have a footprint about the size of a ping pong table, allowing for temperature stabilization, yet deliver higher resolution and dispersion than the much larger classic echelle spectometers, such as the Lick Hamilton, the AAT UCLES, and the Keck HIRES. The two working examples, PFS on Magellan, and the Levy spectrometer on the 2.4-m APF, cost about US$2M each. They do not use fibers or scrambling, and have throughput of 20 to 30%, a factor of 2 to 4 better than classic echelles. These spectrometers will lead to the discovery of many terrestrial mass and potentially habitable planets over the next decade.
|October 17|| WIRO OPEN HOUSE, NO ASTRO COLLOQUIUM
||November 28|| THANKSGIVING, NO COLLOQUIUM
|March 20|| SPRING BREAK, NO COLLOQUIUM
||April 3|| EASTER, NO COLLOQUIUM