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ROSAT Observations of Symbiotic Stars

Published online by Cambridge University Press:  07 August 2017

K.F. Bickert
Affiliation:
MPI f. extraterrestrische Physik (MPE), Garching, FRG
R.E. Stencel
Affiliation:
Center f. Astron.& Astrophys. (CASA), Boulder, Colorado
R. Luthardt
Affiliation:
Sternwarte Sonneberg, Sonneberg, FRG

Abstract

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The German X-ray astronomy satellite ROSAT (launched 1990 June 1) performed an all-sky survey (from 1990 Jul 30 till 1991 Jan 26) with the Position Sensitive Proportional Counter (2 deg FoV, .1–2.4 keV) covering 96% of the sky. Analysis of bright X-ray sources suggests PSPC positions can be accurately determined to within 30 arcsec, and 1‥2 arcmin for soft weak ones. We have examined the survey data for detections from among a list of 189 symbiotic and symbiotic-like objects compiled by Vaidis (1988) with own extensions, chosen for completeness. For 178 objects, all-sky data was available. Standard Analysis Software System (SASS) and EXtended Standard Analysis Software packages (EXSAS) both use a three-step approach to detect sources. After quality screening, a sliding-window algorithm (LD) locates bright sources. These are excluded in the 2D-spline interpolated smoothed background map. A second sliding window MD runs on the background subtracted event files. All possible sources were then tested by maximum likelihood in the background-subtracted, exposure-corrected image. If LD, MD, or ML did not detected a source at the optical position, an upper limit ML program tried to find enhanced emission. For EXSAS, photon event files contain all photons within 20 arcmin radius around a source. Cut radii, background determination, and other parameters can be iteratively improved.

Type
IV. Planetary Nebulae Connection: Evolution from the AGB
Copyright
Copyright © Kluwer 1993