Potential Sites in Changthang Ladakh for Submillimeter Astronomy

Abstract

The attenuation by atmospheric water vapor and other constituents makes it difficult to observe celestial sources in the submillimeter waveband using ground-based telescopes. High-altitude, cold, dry sites provide significant reduction in the. attenuation. Observatories at the summit of Mauna Kea in Hawaii islands, and higher sites in Chilean Andes have proved these advantages, and additional sites are being characterized in Dome C (Antarctica), Ladakb (India), Tibet and Xinjiang (China). The Indian Institute of Astrophysics (IIA), Bangalore, has set up Indian Astronomical Observatory (IAO) at Hanle (latitude: 32O 46'46" N; longitude: 7g057'51 " E; 4500 mabove md), in Changthang Ladakh, initially with the 2-m aperture opticalinfrared Himalayan Chandra Telescope (HCT). The telescope operates as a National Facility and is operated remotely from Bangalore using a dedicated satellitebased communication link. The observatory has provided infrastructural support for the development of further national and international facilities for research in astronomy and astrophysics, geodynamics and geornagnetics, as also atmospheric studies. Characterization of Hanle and nearby higher altitude regions for submillimeter and far-infared astronomy is being carried out by IIA in collaboration with the Raman Research Institute (RRI), Bangalore, the University of Tokyo and the Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA. A 220 G Hz radiometer has been operating at Hanle for over 3 years and the results show that the site is at least as good as Mauna Kea. Some infrastructure is developed at Polakongka La (5000 m above msl). Higher peaks are available near both these locations. We present here information on the geographical locations of our sites in Ladakh, site characterization experiments in progress, and results on weather parameters, atmospheric water vapor and 220 GHz opacities.