Astronomical instrumentation

Abstract:

The results of a search for OH megamaser emission from a sample of 32 galaxies selected from the IRAS Point Source Catalog on the basis of their IR properties are presented. For each galaxy (other than those few already observed elsewhere), an optical redshift is obtained and both OH and H I emission are sought. The search yielded one new OH megamaser galaxy, and H I was detected toward nine objects. There are unlikely to be any OH megamasers in the Southern Hemisphere with flux densities comparable to that of Arp 220 (280 mJy), although there may be a population of weaker megamasers. No special conditions are required to explain the known OH megamasers other than those expected in a cool, dusty, active galaxy.

Abstract:

Spectropolarimetric observations of the BN object at 10 and 20 microns reveal a surprisingly large ratio of 20-to-10-micron polarization in the respective peaks. The results are compared with the predictions of core/mantle grain models based on graphite and ice mixtures with a variety of silicates. Except for a glassy bronzite, in which the wavelength match to the peak in the 20 micron region is very poor, all of these predict substantially smaller amounts of 20-micron polarization than is observed. It seems that either the astronomically important silicates have a particularly strong Si-O bending mode, or that the presence of impurities in ice mantles introduces large 20 micron polarization.

Abstract:

Infrared spectroscopy has allowed the identification of a number of different components of interstellar dust. Refractory species such as silicates and silicon carbide are commonly seen in circumstellar dust, whilst the former also dominate the infrared absorption by interstellar dust. In addition, spectral features from a number of more volatile species condensed on grains have been measured in cold, sheltered regions such as molecular clouds and dense circumstellar outflows from cool evolved stars. In diffuse regions, and particularly in ionization fronts and photodissociation regions close to hot stars, the infrared emission spectrum is dominated by a family of narrow emission features between 3 and 13μm produced by small carbon-rich grains. Recent observations have shown that there are a number of weak bands in addition to the well-known strong features. -from Author