K. Nandy

ULTRAVIOLET INTERSTELLAR POLARIZATION OBSERVED WITH THE HUBBLE SPACE TELESCOPE

We have used the Faint Object Spectrograph of the Hubble Space Telescope to observe interstellar linear polarization from 1300 to 3300 A in two stars with well-studied interstellar polarization at visible wavelenths. The wavelength dependence of linear polarization declines smoothly with decreasing wavelength and is devoid of structure associated with the prominent 2175 A absorption bump in the interstellar extinction curve. The data for one star (HD 161056) are consistent with an extrapolation based on the Serkowski formula of a fit to the ground-based polariztion; the other star (HD 7252) shows excess (super-Serkowski) polarization relative to the extrapolation. Out of a total of 10 stars now studied by means of spectropolarimetry in the satellite ultraviolet, including eight obseved with the Wisconsin Ultraviolet Photopolarimeter, five (those of longest lambda (sub max)) show Serkowski behavior, and four others show super-Serkowski behavior; only one (HD 197770) shows evidence for polarization associated with the 2175 A bump. These results place important constraints on the nature of the bump feature.

The Spectrum of HD 51585 in the Blue and in the Ultraviolet

New visible and ultraviolet spectra of the peculiar emission line star HD 51585 are described. Interstellar lines and the λ 2200 feature are rather weak. A colour excess E(B-V) = 0.33 is derived. The extinction curve resembles the one obtained from LMC stars.

Preliminary observations of the Magellanic Clouds with the ultraviolet sky survey telescope

Observations of the Magellanic Clouds have been made with the ultraviolet skysurvey telescope (S2-68) on board the E.S.R.O. satellite TD-1A. From the data so far reduced, the ultraviolet surface brightness has been derived for four wavelength bands centred near 1550, 1950, 2350 and 2740 A Ultraviolet maps of the Large Magellanic Cloud are presented and the flux distributions in each cloud are compared with that expected from a galactic luminosity function.