University of Wisconsin

Space Astronomy Laboratory



ISM Program:
Guest Investigator Project to observe Polarization in the Large Magellanic Cloud

GI Astronomers: Geoffrey Clayton, James Green

The Large Magellanic Cloud (LMC) is a satellite galaxy of our own Milky Way Galaxy, about 150,000 light years away from us. We have indications that it has a smaller amount of heavy elements than ours. Studies of interstellar dust, which may carry a sizable fraction of the interstellar heavy elements in a galaxy, will be important in comparative studies of the evolution of the LMC and the Galaxy.

Geoff Clayton (now at LSU) and Jim Green (U of Colorado) proposed obtaining WUPPE and HUT observations of stars in the LMC as a Guest Investigator project to study the interstellar medium in the LMC.

For this program WUPPE obtained polarimetry of two stars which are reddened and have significant polarization in visible light:

Sanduleak-69 239 (abbreviated Sk-69 239; the designation is in a catalog of LMC stars by Nick Sanduleak = no. 239 in the -69 degree declination zone) is a tenth magnitude star. It has been shown to be polarized in the optical by about three percent.

Sk-69 270 is an eleventh magnitude star in the Large Magellanic Cloud. It has been shown to be polarized in the optical by about three percent. This star, since it is hotter than SK-69 239, is slightly brighter in the ultraviolet.

WUPPE and HUT spectra were obtained of two unreddened stars, Sk-67 78 and Sk-67 90, and HUT spectra were obtained of unreddened Sk-69 83 and reddened Sk-66 19.

Their conclusions appear in a paper written with some other members of the HUT and WUPPE teams in ApJ 460, 313, 1996. Regarding interstellar polarization in the LMC, they find that the wavelength dependence is similar to that seen in stars in our own Galaxy.

Besides these, WUPPE obtained some observations of other LMC stars.