Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003aas...203.4805a&link_type=abstract
American Astronomical Society Meeting 203, #48.05; Bulletin of the American Astronomical Society, Vol. 36, p.580
Astronomy and Astrophysics
Astronomy
Scientific paper
``Hybrid chromosphere'' stars show evidence of cool winds together with hot emission lines like C 4 λ 1548 (T ˜ 105 K), originally thought to be mutually exclusive in ``noncoronal'' giants and supergiants to the red of the Linsky-Haisch coronal dividing line near K1 III. Several surveys of such stars by the Roentgensatellit (ROSAT ) reported numerous X-ray detections and concluded that the hybrids as a class are legitimate coronal sources, in some cases strong. However, several of the detected sources were displaced from the predicted stellar positions, calling into question the identifications. I have reexamined the issue, using the U.S. Naval Observatory A2 Catalog to astrometrically register deep pointings by the ROSAT Position Sensitive Proportional Counter (PSPC) and High-Resolution Imager (HRI) to ˜few arcsecond accuracy. At least two of the previously proposed detections of key hybrid stars---γ Draconis (K5 III) and β Aquarii (G0 Ib)---must be rejected on the basis of lack of positional coincidence. (Together with HR 4289 [K5 III] whose identification originally was challenged by Huensch, Reimers, & Schmitt [1996, A&A, 313, 755], who found that the ˜ 30'' displaced X-ray source coincided with a faint, previously unknown galaxy.) Given that many of the original survey sample were not even detected by ROSAT in the first place, and that several of the secure detections plausibly can be attributed to low-mass active MS companions, the conclusion is that hybrid stars generally are very weak coronal sources, at best. The hybrids possibly fall into the same category as the ``noncoronal'' red giants like α Boo (K1 III) and α Tau (K5 III) whose hot-line emitting regions appear to be buried deep in their X-ray opaque chromospheres.
[-3mm]
This work was supported by grant NAG5-13058 from NASA to the University of Colorado. The study made extensive use of the ROSAT public archive at the HEASARC of NASA's Goddard Space Flight Center, and the USNO-A2 astrometric catalog, as accessed from the Catalogue Server of the ESO/ST-ECF Archive.
No associations
LandOfFree
Hybrid-Star Coronal X-ray Sources does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Hybrid-Star Coronal X-ray Sources, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hybrid-Star Coronal X-ray Sources will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1420139