The X-ray activity-rotation-age relation of M dwarfs and its mass dependence
Abstract
The activity of the Sun and solar-like stars is driven by an αΩ-dynamo, according to which the combination of differential rotation and convective motions of the outer atmospheric envelope continuously regenerates the magnetic field that manifests itself in the form of powerful optical, UV, and X-ray radiation. The study of the X-ray activity-rotation-age relation therefore probes both the stellar dynamo and spin evolution. Moreover, how the X-ray emission varies with stellar age is of great importance for planetary atmospheres and yields information about how stellar X-rays affect their evolution. M dwarfs are also known to be magnetically active, but the physical mechanism is poorly understood. In this talk, I present the largest uniform sample of M dwarfs (302 stars) consisting of observations taken with XMM-Newton, Chandra, and K2 combined with X-ray and rotation data from the literature. With the use of spin models we compared the evolution of the predicted rotation periods (Prot) with our results on the empirical Lx- Prot relation to provide an estimate for the age decay of X-ray luminosity and we compare it to the few stars with known age and X-ray emission. Later, new X-ray data from eROSITA and rotation periods extracted from TESS light curves doubled our sample of M dwarfs, allowing us to put a quantitative constraint on the mass dependence of the X-ray emission, and to determine the drop in activity level with respect to pre-main sequence stars. Finally, we quantified the X-ray variability of this large sample by comparing the Lx from eROSITA and ROSAT measurements and we examined the sensitivity improvements with eROSITA. In particular, eROSITA is able to detect faint M dwarfs that are visible by ROSAT only during flaring emission and it is also sensitive for slower rotating M dwarfs in the unsaturated regime of the Lx- Prot relation (Prot ≥ 10 d) that is inaccessible to TESS.
- Publication:
-
The 21st Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun
- Pub Date:
- December 2022
- DOI:
- 10.5281/zenodo.7521560
- Bibcode:
- 2022csss.confE.101M
- Keywords:
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- stars: low mass; stars: activity; stars:rotation; stars:magnetic field; X-ray:stars;
- Zenodo community cs21