Candidate isolated neutron stars and other stellar x-ray sources from the ROSAT all-sky and Sloan Digital Sky Surveys

Abstract

Thesis (Ph. D.)--University of Washington, 2006.Although extra-solar X-ray sources were first observed almost fifty years ago, the first all-sky imaging X-ray survey was only recently completed. The ROSAT All-Sky Survey (RASS) Bright and Faint Source Catalogs include approximately 124,000 X-ray sources detected in the 0.1--2.4 keV range. However, while X-ray source counterparts are known to range from distant quasars to nearby M dwarfs, the RASS data alone are often insufficient to determine whether an X-ray source is Galactic or extragalactic. As a result, no more than 10% of RASS sources have had their counterparts identified and fully characterized. A major obstacle to identifying more RASS sources was the absence of a large-area optical survey of equivalent sensitivity with which to correlate the RASS catalogs. In the Sloan Digital Sky Survey (SDSS) we now have the needed optical survey; SDSS provides a uniform optical photometry and spectroscopic dataset with which to identify RASS sources. In this thesis, I present results from a campaign to identify and characterize stellar counterparts to RASS sources falling within the SDSS footprint.Of order one-third of the RASS source counterparts are likely to be stars. Most of these are bright stars with coronal X-ray emission, and are not suitable for optical identification based on routine SDSS multi-fiber spectroscopy, which is not designed for m < 15 objects. Instead, I used SDSS imaging photometry, correlations with the Two Micron All Sky Survey and other catalogs, and spectroscopy from the Apache Point Observatory 3.5-m telescope to identify these stellar X-ray counterparts in the SDSS Data Release 1 region. In addition, I describe efforts to identify and characterize other, rarer stellar X-ray sources in the entire SDSS area: cataclysmic variables, white dwarfs, and especially elusive isolated neutron stars, of which only a handful are currently known