JULY 14 - 18, 2008

MONDAY, JULY 14

12 noon: Solar, Stellar, and Planetary Sciences Division Seminar. "Evidence for a Turnover in the Low Mass IMF: Analysis from an Ensemble of Young Clusters," Michael R. Meyer, Steward Observatory, University of Arizona. Pratt Conference Room.

Abstract: Astronomers have known for almost a decade that sub-stellar objects do not contribute significantly to the dynamical mass of normal stellar populations (e.g. Reid et al. 1999). Yet until recently there remained considerable debate whether brown dwarfs might outnumber stars (e.g. Allen et al. 2005). We set out to explore, in a quantitative way, whether we could rule out the hypothesis that the slope of the initial mass function continued to rise into the brown dwarf regime using an ensemble of results from seven deep surveys of various young star clusters. We first demonstrate that the ratios of stars to brown dwarfs are consistent with a single underlying IMF. With this assumption, we then combine the ratios of stars to brown dwarfs from each cluster in order to constrain the shape of the low mass IMF, finding it to be consistent with the log-normal form of Chabrier (2005). This analysis indicates, with high confidence (P > 99.99%), that the sub-stellar IMF turns over (dN/dM M^(-alpha), alpha < 0). More information can be found at http://xxx.lanl.gov/abs/0807.1354.

THURSDAY, JULY 17

4:00 pm: Summer Colloquium Series. "Accretion Disks and the Microquasar GRS 1915+105," Joseph Neilsen, CfA. Preceded by refreshments at 3:30 pm. Phillips Auditorium.

Abstract: X-ray binaries are often highly prized for the information they give us about their enigmatic engines, black holes and neutron stars. But accretion onto these compact objects is a fascinating and dynamic process in and of itself and can be studied with high-resolution X-ray spectroscopy. I will discuss LMC X-4, a neutron star binary in which the accretion disk is warped, tilted out of the orbital plane, and precessing around the neutron star. I will also discuss GRS 1915+105, a black hole binary which is well known for its relativistic jets and its bizarre variability.

FRIDAY, JULY 18

12:30 pm: Radio and Geoastronomy Division Lunch Talk. "HI observations of Superthin Galaxies," Dr. Juan Uson, NRAO. Room M-340, 160 Concord Avenue.

Abstract: Superthin galaxies are bulgeless, late-type spiral galaxies seen edge-on. HI synthesis observations probe the kinematic structure of their interstellar medium. I shall present the results of high-sensitivity VLA observations of UGC7321, IC2233, UGC3697 and UGC10043 done in collaboration with Lynn Matthews (CfA). Two of these galaxies are rather isolated while the other two are the dominant members of small groups. We have detected a pattern of corrugations in IC 2233, the first such detection in neutral Hydrogen in an external galaxy. UGC 3697, the Integral Sign galaxy shows a spectacular S-shaped bend that has been triggered by the passage of an intruder through its disk. UGC 10043, not quite a superthin galaxy, has presented us with an unexpected, rich interaction with a previously unknown companion which is reminiscent of the M51 system (the Whirlpool galaxy) seen from the side. These results have required the development (in collaboration with Bill Cotton) of an algorithm to correct the VLA beam-squint. This in turn has presented us with the pieces of a VLA pipeline. Ill discuss this development briefly and (time-permitting) I shall include a live demonstration of the squint-correcting algorithm.

THURSDAY, JULY 24

4:00 pm: Summer Colloquium Series. "The Lives of Galaxies" Dr. Sukanya Chakrabarti, CfA. Preceded by refreshments at 3:30 pm. Phillips Auditorium.

Abstract: I will talk about the dynamical evolution of galaxies broadly - from quiescently evolving spirals to the more dramatic lives of ULIRGs. I will also talk about recent methods that have been developed to observe simulated galaxies to correlate their photometric time evolution with their dynamical evolution, to develop diagnostics of galaxy evolution. Finally, I will touch on some recent observations of high redshift galaxies that are difficult to explain.

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