paper

850 SRG/eROSITA X-ray sources associated with Pleiades stars

arXiv:2505.05006

Abstract

Using data from the SRG/eROSITA all-sky X-ray survey and the GAIA-based catalog of 2,209 members of the Pleiades open star cluster, we found 850 X-ray sources associated with the cluster stars. Over 650 of them were detected in X-rays for the first time. At the distance of the Pleiades, the nominal sensitivity of eROSITA corresponds to a luminosity of $L_{X} \sim 1.6 \cdot 1 0^{28}$ erg/s in the 0.3-2.3 keV band. The eROSITA sources associated with Pleiades stars have a total luminosity of $L_{X, t o t} \sim 1.3 \cdot 1 0^{32}$ erg/s , a million times greater than the X-ray luminosity of the quiet Sun. Strong X-ray variability, more than 10 times, was recorded for 27 sources. Most of them are known as eruptive optical variables of the dM class. The value of $R_{X} = l o g (L_{X} / L_{b o l})$ increases with decreasing effective temperature of the star from $R_{X} \approx - 5$ to $R_{X} \approx - 2$ . The distribution of stars over $R_{X}$ is bimodal, with the left peak at $R_{X} \sim - 4.3$ being formed by stars of FGK classes, and the right peak at $R_{X} \sim - 3.1$ being mainly populated by M-stars. The relation between $R_{X}$ and the Rossby number $R o$ depends on the spectral class. For K- and M- stars, at low Rossby numbers $R_{X} \sim - 3$ and depends weakly on $R o$ . At $R o > 0.25$ , a rapid drop in $R_{X}$ is observed for K stars, while in our sample there are no M stars with large Rossby number. Most of F- and G- stars appear to have smaller $R_{X} \sim - 4.5$ , however, our sample size is insufficient for a more detailed characterization of their $R_{X} - R o$ dependence.

16 pages, 12 figures, 3 tables