Searching for X-ray emission from AGB stars
Artikel i vetenskaplig tidskrift, 2012

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.

stars: magnetic field

activity

stars: AGB and post-AGB

dust formation

white-dwarfs

evolved stars

X-rays: stars

circumstellar envelopes

mass-loss rates

radio line emission

magnetic

period-luminosity relation

giant-branch stars

planetary-nebulae

Författare

S. Ramstedt

Universität Bonn

R. Montez

Rochester Institute of Technology

J. H. Kastner

Rochester Institute of Technology

Wouter Vlemmings

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 543 Article Number: A147 - A147

Ämneskategorier

Astronomi, astrofysik och kosmologi

Fundament

Grundläggande vetenskaper

DOI

10.1051/0004-6361/201118516