First ground-based 200-um observing with THUMPER on JCMT - sky characterisation and planet maps

Details First ground-based 200-um observing with THUMPER on JCMT - sky characterisation and planet maps First ground-based 200-um observing with THUMPER on JCMT - sky characterisation and planet maps

2005-09-22

arxiv.org/abs/astro-ph/0509674v1

Mon.Not.Roy.Astron.Soc.364:843-848,2005

Astronomy and Astrophysics

Astrophysics

7 pages, 8 figures, accepted by MNRAS

Scientific paper

10.1111/j.1365-2966.2005.09625.x

We present observations that were carried out with the Two HUndred Micron PhotometER (THUMPER) mounted on the James Clerk Maxwell Telescope (JCMT) in Hawaii, at a wavelength of 200 um (frequency 1.5 THz). The observations utilise a small atmospheric window that opens up at this wavelength under very dry conditions at high-altitude observing sites. The atmosphere was calibrated using the sky-dipping method and a relation was established between the optical depth, tau, at 1.5 THz and that at 225 GHz: tau_1.5THz = (95 +/- 10)*tau_225GHz. Mars and Jupiter were mapped from the ground at this wavelength for the first time, and the system characteristics measured. A noise equivalent flux density (NEFD) of ~65 +/- 10 Jy (1 sigma 1 second) was measured for the THUMPER-JCMT combination, consistent with predictions based upon our laboratory measurements. The main-beam resolution of 14 arcsec was confirmed and an extended error-beam detected at roughly two-thirds of the magnitude of the main beam. Measurements of the Sun allow us to estimate that the fraction of the power in the main beam is ~15%, consistent with predictions based on modelling the dish surface accuracy. It is therefore shown that the sky over Mauna Kea is suitable for astronomy at this wavelength under the best conditions. However, higher or drier sites should have a larger number of useable nights per year.

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