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Searching for X-ray emission from AGB stars

S. Ramstedt ; R. Montez ; J. Kastner ; Wouter Vlemmings (Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik)
Astronomy & Astrophysics (0004-6361). Vol. 543 (2012), p. Article Number: A147 .
[Artikel, refereegranskad vetenskaplig]

Context. Magnetic fields have been measured around asymptotic giant branch (AGB) stars of all chemical types using maser polarization observations. If present, a large-scale magnetic field would lead to X-ray emission, which should be observable using current X-ray observatories. Aims. The aim is to search the archival data for AGB stars that are intrinsic X-ray emitters. Methods. We have searched the ROSAT, CXO, and XMM-Newton archives for serendipitous X-ray observations of a sample of similar to 500 AGB stars. We specifically searched for the AGB stars detected with GALEX. The data is calibrated, analyzed and the X-ray luminosities and temperatures are estimated as functions of the circumstellar absorption. Results. We identify 13 AGB stars as having either serendipitous or targeted observations in the X-ray data archives, however for a majority of the sources the detailed analysis show that the detections are questionable. Two new sources are detected by ROSAT: T Dra and R UMa. The spectral analysis suggests that the emission associated with these sources could be due to coronal activity or interaction across a binary system. Conclusions. Further observations of the detected sources are necessary to clearly determine the origin of the X-ray emission. Moreover, additional objects should be subject to targeted X-ray observations in order to achieve better constraints for the magnetic fields around AGB stars.

Nyckelord: stars: AGB and post-AGB, stars: magnetic field, X-rays: stars, giant-branch stars, period-luminosity relation, radio line emission, mass-loss rates, circumstellar envelopes, planetary-nebulae, magnetic, activity, dust formation, evolved stars, white-dwarfs

Denna post skapades 2012-09-13. Senast ändrad 2014-09-02.
CPL Pubid: 163296


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Institutioner (Chalmers)

Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik (2010-2017)


Astronomi, astrofysik och kosmologi

Chalmers infrastruktur