HST Time Series of gamma Cas GHRS Observations ("GHRS_GAMMACAS")

GHRS_GAMMACAS is an ultraviolet grayscale timeseries of difference spectra for gamma Cas in the neighborhood of the SiIV resonance lines.

The spectral data were recorded for over 21 hours while gamma Cas was in HST's continuous viewing zone on 1996 March 14-15 using the GHRS 2 arcsecond Large Science Aperture (LSA). The observations covered 1045 out of a total of 1280 minutes. The data were obtained at a cadence of one spectrum per second in the ACCUM mode (8100 counts per second per pixel) with the G160M grating and were later rebinned to 1 spectrum per minute. The ACCUM mode permitted only a modest resolution (30 km/s) but provided the ability to integrate fluxes unobstructed by an aperture and construct a pseudo-continuum light curve from 'non-line pixels'. The spectral range covers approximately 1382--1417 Angstroms.

Several instrumental effects had to be removed to obtain the final spectra. These effects included included fixed pattern noise artifacts from the detector, differential spacecraft velocities, and shifts of the spectrum in both detector coordinates caused by changes in the Geomagnetic field (so-called 'GIMP') as the spacecraft traced its orbit. Photometric variations 140 pixels to the red of the Si IV line complex were removed and are presented as a separate data file. Finally, a maximum-spectrum template was obtained from the spectra by submtracting the maximum flux at each pixel from each spectrum of the time series. The data shown are from difference spectra from that template in units of continuum = 1. The spectra were taken as part of a simultaneous campaign with the RXTE satellite and contemporaneously with IUE and optical observations two months earlier.