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The discovery of 13s X-ray pulsations from the hydrogen depleted subdwarf O6 star binary HD49798

G. L. Israel·L. Stella·L. Angelini·N. E. White·T. R. Kallman·P. Giommi·A. Treves
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Abstract

We discovered strong 13s X-ray pulsations in the public Rosat PSPC light curve of HD49798, a 1.55d single-component spectroscopic binary containing a hydrogen depleted subdwarf O6 star. We find no evidence for period changes during the about 4hr Rosat pointing. The source X-ray spectrum is extremely soft, with an unabsorbed 0.1-2keV luminosity of a few times 10^32 erg s^-1 (distance of 650pc). A higher luminosity might be hidden in the EUV. Our results imply that the unseen companion is an accreting degenerate star, a white dwarf or, more likely, a neutron star. In either case HD49798 corresponds to a previously unobserved evolutionary stage of a massive binary system, after common envelope and spiral-in.

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G. L. Israel, L. Stella, L. Angelini, N. E. White, T. R. Kallman, P. Giommi, A. Treves. 1996-10-17. The discovery of 13s X-ray pulsations from the hydrogen depleted subdwarf O6 star binary HD49798. https://doi.org/10.1086/310418

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