FUNA Lunch Talk:

Mike Freed, Tim Pennucci, and Diane Leigh

Northern Arizona University, Columbia University, UVa, and NRAO

Probably "Saturn's Satellites at True Opposition", "A 350 MHz Drift-Scan Survey for Pulsars with the GBT", and "Investigating the Physical and Chemical Environments of Hot Cores in the Interstellar Medium".

August 17

12:10PM, Note unusual location: Room 311 , NRAO, Edgemont Road


Freed: On 14 January 2005, in a rare cosmic alignment, the Earth passed directly between Saturn and the Sun. Viewed from Saturn's moons, this resulted in a transit of the Earth across the center of the solar disk. From the Earth, this event, which will not occur again until 2049, provided the opportunity to observe the saturnian satellites at "true" opposition. A world-wide space- and ground-based campaign using 9 telescopes at 7 observatories from Italy to the Western US and HST acquired ~40GB of imaging data in the visible and near-infrared. These data include the satellites' "opposition effect", the dramatic increase in their brightness that occurs as the solar phase angle (between the Earth-Sun-satellite) decreases toward zero. The amplitude and width of the opposition effect reveal surface particle properties (such as porosity, grain size, and grain size distribution) that contain important clues to the thermal and weathering history of the satellites. A subset of this remarkable data set was analyzed to extract the opposition effect of Saturn's satellites thereby revealing the physical properties of their surface microstructure.

Pennucci: Due to necessary track repairs, the Green Bank Telescope has been approximately fixed in azimuthal angle since late April allowing for a blind pulsar drift scan survey. The survey is centered around 350 MHz and covers 50 MHz in bandwidth utilizing the pulsar-specific SPIGOT back end. Prior simulations predicted that the survey should detect about 5 normal pulsars per observing day and a millisecond pulsar every 2-3 observing days, the latter type being the primary interest of the survey. However, recently uncovered complications with the receiver may have decreased the anticipated detection rate by a factor of two in the already processed data. Millisecond pulsars are of particular interest because of their numerous applications in studying the interstellar medium, gravitational waves, general relativity, nuclear physics and so forth. The pulsar searching package PRESTO is used to comb the data using both periodicity and single pulse searches. No new pulsars are confirmed thus far, however a significant discrepancy with a published dispersion measure of the known three second pulsar J1503+2111 was found as well as a possibly worrisome bias in candidate selection. Though the recent efforts scouring the processed data have yielded only possible candidates, it is (sort of) comforting to know that only about 12.5 hours of the data out of ~60 observing days have been processed and looked at.

Leigh: As the number of detections of large interstellar and circumstellar molecules continues to grow, it is quite obvious that observations are clearly outpacing the predictions of the chemical models. Also, most of the 147 interstellar molecules have been identified from their rotational emission spectra in hot core regions, where the gas and dust around a newly formed star have been heated sufficiently to release grain surface species and drive a complex network of grain surface and gas phase chemistry. Over the last several years, the primary instrument used in detecting these large molecular species has been the NRAO Green Bank Telescope. Yet despite ongoing additions to the list of detected hot core molecules, very little is understood about the formation mechanisms for those species already detected. Recent chemical modelling work has made it apparent that the physical parameters of a hot core will greatly influence the resultant chemical evolution. This is not a surprising result, and the two hot core regions that have been examined in enough detail to provide sufficient physical constraints for these models are Orion and Sagittarius B2(N). Archival GBT, VLA and BIMA array data of hot cores including Orion and Sagittarius B2(N), were examined to further investigate the physical and chemical environments of these very interesting regions, and extending the list of molecules and transitions for which we have observational constraints for both the physical environment and the complex chemistry, allowing us to investigate the correlations between the physical and chemical evolution of a hot core.