A MULTIWAVELENGTH CAMPAIGN ON γ CASSIOPEIAE. III. THE CASE FOR MAGNETICALLY CONTROLLED CIRCUMSTELLAR KINFMATICS

摘要

In two previous papers, we have discussed simultaneous Rossi X-Ray Timing Explorer (RXTE) and Hubble Space Telescope GHRS observations made of γ Cas (BO.5e) over a full day on 1996 March 14-15. The light curves generated from these data show features that anticorrelate and led us to con- clude that the star has multiple surface activity centers that rotate into view every rotational cycle of 1.123 days. In a second paper we found that dips in the UV continuum (UVC) light curve are probably caused by the passage of cool, co-orbiting clouds that are suspended above surface X-ray-active centers. In this paper we use difference spectra from our >21 hr GHRS time series to investigate ≤ 2 spectral variations within the photospheric Si iv 1394-1403 A lines as well as smaller variations from features in neighboring wavelengths at 13821386 and 1404-1417 A. Several difficulties arise in interpreting these variations as signatures of surface inhomogeneities, so we have studied both types of variations in the context of the kinematics of occulting circumstellar (CS) structures. By means of model-atmospheres codes and up-to-date line lists, we computed a grid of cloud opacity for various temperatures in our spectral range. Using these synthetic spectra, we are able to identify features as optically thick absorp- tions due to Fe II, Cr II, and C I lines from "cool" (T < 10,000 K) plasma, of Si IV, Si III, S IV, and Ni II lines from " warm" plasma (～10,000-18,000 K), and of Si IV and Fe V lines from hot plasma ( ≥ 30,000 K). The variations of the cool- and hot-plasma lines are in pha