Observing CMB polarisation through ice

Ice crystal clouds in the upper troposphere can generate polarisation signals at the uK level. This signal can seriously affect very sensitive ground based searches for E- and B-mode of Cosmic Microwave Background polarisation. In this paper we estimate this effect within the ClOVER experiment observing bands (97, 150 and 220 GHz) for the selected observing site (Llano de Chajnantor, Atacama desert, Chile). The results show that the polarisation signal from the clouds can be of the order of or even bigger than the CMB expected polarisation. Climatological data suggest that this signal is fairly constant over the whole year in Antarctica. On the other hand the stronger seasonal variability in Atacama allows for a 50% of clean observations during the dry season.Comment: 7 Pages, 4 figure

The effect of a radome on submillimeter site testing measurements

We evaluate the effect that radome transparency has on atmospheric opacity measurements performed by the skydip technique. We show that, except at rather high opacities, it is not sufficient to ignore losses in the radome (or “window”) during the data analysis and then subtract them off from the derived atmospheric opacity. Perhaps surprisingly, unless radome transparency is correctly modelled, the atmosphere will appear to have a minimum opacity that is many times greater that the radome losses. Our conclusion is that some previous site studies may have significantly underestimated the quality of the best submillimeter sites, and that the difference between these sites and poorer sites may be much greater that currently believed. We also show that part of the residual 857 GHz opacity at the best sites, currently ascribed to “dry-air opacity”, can in fact be just an artefact caused by not properly modelling the radome during the data analysis

Astrophysics at Dome C

This paper summarises presentations made at the Third International Workshop on Astrophysics at Dome C, held in Hobart, Tasmania, on 28--29 June 2001. It also includes sensitivity estimates for proposed Antarctic telescopes, as well as the parameter space such telescopes might cover if used for galaxy number count studies in the thermal IR.

Atmospheric site testing in Antarctica and observations with submillimetre and millimetre telescopes

This dissertation covers, through seven peer-reviewed publications, a number of observations conducted in two different continents, Antarctica and Australia, spanning from the near-infrared to submillimeter and millimeter wavelengths. The work begins in 2001 with a fundamental contribution to the development of SUMMIT, a sky-brightness monitoring instrument operating at 350 μm. This rugged, low power and low maintenance instrument was designed for astronomical site testing and allowed the measurement of atmospheric precipitable water vapour at very dry sites. It was successfully operating at two locations in Antarctica—South Pole and Dome C—making the first measurements of submillimeter sky opacity at the latter one, and demonstrating the site’s outstanding potential for submillimeter astronomy. Improvements and corrections to the skydip observing strategy and to the data reduction algorithms are described.NISM (Near-Infrared Sky Monitor) is an instrument operated with the same observing strategy as SUMMIT—skydips—but in the Kdark window at 2.4 μm. The instrument was installed at the South Pole Station in 2001, and showed good performance in the subsequent winter, confirming that the sky brightness at the site is more than an order of magnitude lower than excellent astronomical sites such as Mauna Kea.The work highlights results from exploiting the submillimeter windows at the South Pole, where I operated without interruption, for the entire year of 2003, SPARO (Submillimeter Polarimeter for Antarctic Remote Observations) a 9-pixel, 450 μm polarimeter installed at the focal plane of Viper, a 2 m submillimeter telescope. Most of the winter was dedicated to measure the magnetic fields in four Giant Molecular Clouds (GMCs). These observations demonstrated that in these regions the magnetic field direction was preserved through the GMC formation process, and that the magnetic energy density was comparable to the turbulent energy density, imposing important constraints on GMC evolution models.The work concludes with results from several observation campaigns from 2004 at the Mopra millimetre telescope, including mapping of 13CO, measurements of glycine and propylene oxides in different GMCs, and a survey of 83 methanol masers in massive star-forming regions