Searching for X-ray emission from AGB stars

TL;DR

This study searches archival X-ray data for AGB stars to detect magnetic activity-related emissions, identifying two new sources and emphasizing the need for further targeted observations to understand magnetic fields around these evolved stars.

Contribution

It provides the first systematic search for X-ray emission from AGB stars using multiple archives, discovering new sources and highlighting the importance of targeted follow-up observations.

Findings

Two new X-ray sources detected: T Dra and R UMa.

Most detections are questionable, requiring further validation.

Spectral analysis suggests coronal activity or binary interactions as emission sources.

Abstract

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. The aim of this work is to search the archival data for AGB stars that are intrinsic X-ray emitters. We have searched the ROSAT, CXO, and XMM archives for serendipitous X-ray observations of a sample of ~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. 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. 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.