We present X-ray data from the ROSAT all-sky survey for those sources catalogued in the Einstein Extended Medium Sensitivity Survey (EMSS) (Cat. <VII/152>) which have been identified with Galactic stars. This "second epoch" of X-ray data taken 10yr later, is used to study coronal flux variability for the most active examples of late-type stars. About 72% of the EMSS stars have been redetected by ROSAT. While the F-stars appear to have remained constant, we find evidence for a general decrease in X-ray flux for the M and solar-type stars. This is probably due to the fact that an X-ray-selected sample will preferentially detect stars while flaring. In contradiction to this, the RS CVn binaries have been redetected at higher X-ray flux levels for the sample as a whole.
Results are presented of an extensive X-ray survey of 380 giant and supergiant stars of spectral types from F to M, carried out with the Einstein Observatory. It was found that the observed F giants or subgiants (slightly evolved stars with a mass M less than about 2 solar masses) are X-ray emitters at the same level of main-sequence stars of similar spectral type. The G giants show a range of emission more than 3 orders of magnitude wide; some single G giants exist with X-ray luminosities comparable to RS CVn systems, while some nearby large G giants have upper limits on the X-ray emission below typical solar values. The K giants have an observed X-ray emission level significantly lower than F and F giants. None of the 29 M giants were detected, except for one spectroscopic binary.
This catalog contains sources from EINSTEIN IPC (Imaging Proportional counter aboard the EINSTEIN (HEAO 2) satellite, in orbit between November 1978 and April 1981) detected during pointed observations. Note that a single source may have more than one entry in the catalog.
The Einstein Observatory is the second of NASA's three High Energy Astrophysical Observatories, HEAO-2, renamed Einstein after launch, and was the first fully imaging X-ray telescope put into space. It observed in the energy range 0.2-20keV. It was launched on 12 November 1978, and remained in operation until April 1981. The High Resolution Imager (HRI) is one fo the four instruments aboard the Einstein Observatory, operating in the 0.2-3.0keV energy range, with a spatial resolution of a few arcseconds, and a field of view of 25arcmin. Field and source parameters observed with this instrument are given here.
The X-ray sources from the observations with the Einstein Observatory (HEAO-2) with intensities of 2-sigma above the background are compiled in this catalog. This catalog covers more sky at fainter flux levels than the Einstein Medium Sensitivity Survey. Fields with diffuse emission sources were excluded. Thus data within 10 degrees of the galactic plane as well as fields within the boundaries of the Magellanic Clouds were excluded. The catalog covers 1850 sq. degrees of the sky. The generation of the Einstein Two-Sigma Catalog was described in detail by Moran et al. (1996). Read this article carefully to ensure responsible use of the Catalog. Address any questions to Ed Moran (edhed@igpp.llnl.gov). In particular it should be noted that only 28%, or about 13,000 sources in the 2-sigma catalog are real sources. The authors show that cross-correlations with other catalogs is an effective way to select sources in this catalog that are probably real.
We have used all tha available data from the Einstein Observatory Imaging Proportional Counter (IPC), and a critical compilation of catalogued optical data, to measure the 0.16-3.5 keV X-ray emission from 88 K and 169 M stars of luminosity classes IV, V and VI within 25 pc from the Sun. The IPC detected 54 out of the 88 K stars, 70 out of the 138 M stars with M_v_ less than 13.4 (corresponding approximatively to M5), and 15 out of the 31 fainter M stars. We have identified a subsample of surveyed stars that is statistically representative of the population of K and M stars in the solar neighborhood.
Results of a volume-limited X-ray survey of stars of luminosity classes IV and V in the spectral range F7-G9 observed with the Einstein Observatory are presented. Using survival analysis techniques, the stellar X-ray luminosity function in the 0.15-4.0 keV energy band for both single and multiple sources. It is shown that the difference in X-ray luminosity between these two classes of sources is consistent with the superposition of individual components in multiple-component systems, whose X-ray properties are similar to those of the single-component sources. The X-ray emission of the stars in our sample is well correlated with their chromospheric CA II H-K line emission and with their projected equatorial rotational velocity. Comparison of the X-ray luminosity function constructed for the sample of the dG stars of the local population with the corresponding functions derived elsewhere for the Hyades, the Pleiades, and the Orion Ic open cluster confirms that the level of X-ray emission decreases with stellar age.
Results are reported from a comprehensive survey of X-ray emission from stars known or suspected to be members of the UMa cluster and/or stream. Of the 42 UMa member stars surveyed, 18 were detected as X-ray sources, and spectral analysis was performed for 10 stars with sufficient X-ray counts. Consideration is given to relations between X-ray luminosity, color, and kinematics of the sample stars, and the X-ray spectra of the UMa stars are discussed in the context of the general problem of stellar X-ray temperatures. Also confirmed is the lack of X-ray-emitting A dwarfs among UMa members; among stars of later spectral type there is a rather large dispersion in X-ray luminosity. This dispersion cannot readily be explained by contamination with field star interlopers and appears rather to be a property of the UMa X-ray luminosity distribution function.
This paper summarizes the observations of Galactic supernova remnants with the imaging detectors of the Einstein Observatory. X-ray surface brightness contours of 47 remnants are shown together with gray-scale pictures. Count rates for these remnants have been derived and are listed for the HRI, IPC, and MPC detectors.
Coronal X-ray emission of the Pleiades stars is investigated, and maximum likelihood, integral X-ray luminosity functions are computed for Pleiades members in selected color-index ranges. A detailed search is conducted for long-term variability in the X-ray emission of those stars observed more than once. An overall comparison of the survey results with those of previous surveys confirms the ubiquity of X-ray emission in the Pleiades cluster stars and its higher rate of emission with respect to older stars. It is found that the X-ray emission from dA and early dF stars cannot be proven to be dissimilar to that of Hyades and field stars of the same spectral type. The Pleiades cluster members show a real rise of the X-ray luminosity from dA stars to early dF stars. X-ray emission for the young, solar-like Pleiades stars is about two orders of magnitude more intense than for the nearby solar-like stars.
