Stripped helium stars in UV

Abstract

The model of Galactic population of stripped helium stars, the remnants of $5\lesssim M/M_{\odot }\lesssim 24$ primary components of close binaries after RLOF is presented. These stars emit in the UV range of the spectrum and may be observed by detectors aboard planned "Spektr-UV" (WSO-UV) space telescope. For the current star formation rate in the Galaxy 2${\mathrm{M}}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}$, the estimate of the number of 1 to 7 $M_{\odot }$ objects with $T_{\mathrm{eff}}\gtrsim$25,000\,K ranges from 14700 to 28500. The number of 2 to 7 $M_{\odot }$ objects is 3200 to 5500. The main evolutionary factor influencing the estimate is possible formation of common envelopes and merger of components in them. Detection of candidate stripped helium stars by UV-excess is hampered by the dominance of main-sequence companions to stripped helium stars in the combined spectra of binaries. This effect of observational selection may reduce the number of candidate stripped helium stars potentially detectable by photometry to $\lesssim 1000$.

7 pages, 4 figures. Submitted to the refereed proceedings of the conference "Ultraviolet Universe - 2026", Moscow, June 24-26, 2026. Institute of Astronomy Scientific reports, v.11, No.4, 2026