| Popis: |
AGB stars are not expected to be X-ray-emitters, yet a small fraction of them, the so-called X-AGBs, show X-ray emission that can be attributed to coronal activity of a companion or accretion onto it. By searching the recently released eROSITA-DE eRASS1 source catalog, we aim to increase the sample of known X-AGBs. So far, 36 X-AGBs have been reported, including 21 previous ROSAT RASS, Chandra and XMM detections and 15 more eROSITA eRASS1 recent detections. We cross-correlated the position of sources in the eROSITA-DE eRASS1 catalog with those of AGB stars to find possible X-ray counterparts. We carefully checked these by comparing X-ray and near-IR $K$ images, disregarding those affected by optical loading, diffuse sources, or unreliable positional associations. Seven high-confidence X-AGBs and another seven possible ones are found. Accounting for previous X-ray detections, the sample of X-AGBs is increased from 36 up to 47, of which eROSITA-DE has so far discovered 26 new X-AGBs, more than doubling the number of known X-AGBs. This demonstrates eROSITA's capability to detect X-AGBs despite the challenge posed by the optical loading caused by their near-IR brightness. The eRASS1 X-AGBs tend to have higher X-ray luminosity than previously detected X-AGBs, suggesting a bias toward brighter sources. A comparison of the X-ray and far-UV luminosity of X-AGBs with those of X-ray-emitter symbiotic stars (X-SySts) revealed an overlap in the X-ray luminosity range $10^{29.5}Comment: 15 pages, 5 figures, to be published in Astronomy & Astrophysics |
