Space Astronomy Laboratory
ASTRO - 2
OBJECT: P CYGNI (P-Cyg)
Other names: HD193237
ID # 2133
UW Astronomer: Karen Bjorkman
P Cygni is found in the constellation of Cygnus, a large prominent constellation in the summer sky. The Milky Way passes through the center of Cygnus. For most northern latitudes, it passes through the zenith.
P Cygni has remained in a semi-quiescent phase for over 100 years, without undergoing any major evolution. However, recent ground-based and space-based (International Ultraviolet Explorer satellite) observations indicate that this star has ejected material. This is certainly the most interesting time to observe such a star. Spectropolarimetry should allow us to determine in what form the mass is ejected: is it ejected uniformly in the form of a shell, is it ejected in so-called "plumes", or is it ejected in the form of "blobs" of materials? We will be testing models proposed by University of Wisconsin scientists Cassinelli, Nordsieck, and Murison.
This star was observed on Astro-1, and has a large database of PBO observations showing extreme variability on short timescales (1-10 days). For Astro-2, we observed it 3 times during the mission: once in the second day of the mission, once about 5 days later, and another about 4 days after that. This will provide good information about UV polarization variability over (approximately) 5-day and 10-day timescales.
Since this star should have substantial interstellar polarization, the WUPPE observations have been analyzed along with other stars in the WUPPE interstellar medium polarization program before studying any possible variations. See our paper in AJ 112, 2726 1996.