Wednesday, July 4, 2007 - 3:15pm
Dr. Martina Wiedner (Universität Köln):
Abstract. To date, astronomical observations in the far-infrared / THz frequency regime have been rare; observations with high spectral and spatial resolution are even rarer. This is due to the poor transmission of the terrestrial atmosphere at THz frequencies, as well as to the technological difficulties of building THz receivers. The scarcity of these observations is troubling, because many astronomical phenomena can best be studied in the THz regime. In order to explore the THz frequency regime, we have built a heterodyne receiver for 1.25 - 1.53 THz (195 - 240 microns). It is an experimental receiver for testing the technical possibilities and focusing on observations of Galactic star-forming regions. The receiver's name, CONDOR (CO N+ Deuterium Observations Receiver), comes from the three species that we are most interested in observing: CO, whose high-J rotational transitions (J= 11-10, 12-11 and 13-12) trace hot (several 100K) molecular gas in massive star forming regions; N+ (at 205 microns), which was the third strongest Galactic emission line observed by COBE, and is predominately emitted by the Warm Ionized Medium (WIM); H2D+, which is the only non-depleting tracer for cold (< 20K) molecular gas. The receiver was built by our SFB Nachwuchsgruppe (junior research group) at Cologne, and it (sur)passed all technical requirements. In November 2005, we installed the instrument on APEX (Atacama Pathfinder EXperiment), the best ground-based telescope for THz astronomy currently available. The observing run at APEX demonstrated that CONDOR is fully functional and affirmed that ground-based THz astronomy is feasible. As for scientific results, we observed CO J=13-12 emission from three sites of star formation in Orion: the FIR4 core (Wiedner et al. 2006), the KL nebul (Volgenau in prep.), and NGC2024 (Emprechtinger in prep.). The CO 13-12 lines at FIR4 were as narrow as lower-J CO lines (~5 km/s), suggesting that the gas in the core is heated directly (to several 100K) by radiation from the embedded protostars, rather than by shocks. At Orion KL, the spatial (~4" main beam) and spectral (<1.1 km/s) resolution of CONDOR on APEX allow us to model the spike, hot core, and plateau components independently, allowing to us to model the physical conditions of the different areas individually. We are looking forward to reconfiguring our instrument for deployment as the low-frequency channel of GREAT (German REciever for Astronomy at THz) on the airborne observatory SOFIA (Stratospheric Observatory For Infrared Astronomy).