Volume 626, June 2019
|Number of page(s)||7|
|Published online||06 June 2019|
Follow-up observations of X-ray emitting hot subdwarf stars: the compact He-poor sdO star Feige 34⋆
INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica – Milano, Via A. Corti 12, 20133 Milano, Italy
2 IUSS-Istituto Universitario di Studi Superiori, piazza della Vittoria 15, 27100 Pavia, Italy
3 Istituto Nazionale di Fisica Nucleare, Sezione di Pavia, Via A. Bassi 6, 27100 Pavia, Italy
Accepted: 15 April 2019
We report on results obtained with the XMM-Newton observation of Feige 34 carried out in April 2018. This is the first spectroscopic X-ray observation of a compact and helium-poor hot subdwarf star. The source was detected at a flux level fX = 3.4 × 10−14 erg cm−2 s−1 in the energy range 0.2–3 keV, which implies an X-ray-to-bolometric flux ratio fX/fbol ≃ 10−6.5. The source spectrum can be described with the sum of two thermal-plasma components with subsolar abundances at temperatures of ≃0.3 and 1.1 keV. These properties are similar to what is observed in early-type main-sequence stars, where the X-ray emission is attributed to turbulence and shocks in the stellar wind. Therefore, the same phenomenon could explain the X-ray properties of Feige 34. However, it is not possible to reproduce the observed spectrum with a thermal-plasma model if the elemental abundances are fixed at the values obtained from the optical and UV spectroscopy. Moreover, we show that the X-ray luminosity and spectrum are consistent with those expected from a young main-sequence star of late spectral type. Therefore, we discuss the possibility that the observed X-ray emission is due to the companion star of M0 spectral type, whose presence is suggested by the IR excess in the spectral energy distribution of Feige 34.
Key words: stars: early-type / subdwarfs / stars: individual: Feige 34 / X-rays: stars
© ESO 2019
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.