- ID:
- ivo://CDS.VizieR/J/ApJ/325/798
- Title:
- Einstein survey of stars in the Hyades
- Short Name:
- J/ApJ/325/798
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The paper reports the results of an extensive X-ray study of the Hyades region and improves on previous studies by using refined X-ray source detection algorithms and the complete set of Einstein Observatory IPC exposures covering the Hyades cluster region (a total of 63 1 x 1 deg images). Maximum likelihood integral X-ray luminosity functions were computed for the Hyades stars for given color index (B-V) ranges. The present results agree substantially with a previous survey about the ubiquity of the stellar activity in the Hyades cluster, especially among solar-type stars. The result of Stern et al. (1981ApJ...249..647S) that stellar X-ray emission is dependent on stellar age is confirmed.
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- ID:
- ivo://CDS.VizieR/J/ApJ/351/492
- Title:
- X-ray emission in the Ursa Major stream.
- Short Name:
- J/ApJ/351/492
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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.
- ID:
- ivo://CDS.VizieR/J/ApJ/348/557
- Title:
- X-ray studies of stars in the Pleiades
- Short Name:
- J/ApJ/348/557
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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.
