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Constraints on the winds of hot subdwarf stars from X-ray observations of two sdB binaries with compact companions: CD-30 degrees 11223 and PG 1232-136

Mereghetti S, La Palombara N, Esposito P, Gastaldello F, Tiengo A, Heber U, Geier S, Wilms J (2014)

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Publication Status: Published

Publication Type: Journal article

Publication year: 2014

Journal

Publisher: OXFORD UNIV PRESS

Book Volume: 441

Pages Range: 2684-2690

Journal Issue: 3

DOI: 10.1093/mnras/stu773

Abstract

Little observational data are available on the weak stellar winds of hot subdwarf stars of B spectral type (sdB). Close binary systems composed of an sdB star and a compact object (white dwarf, neutron star or black hole) could be detected as accretion-powered X-ray sources. The study of their X-ray emission can probe the properties of line-driven winds of sdB stars that cannot be derived directly from spectroscopy because of the low luminosity of these stars. Here we report on the first sensitive X-ray observations of two sdB binaries with compact companions. CD -30A degrees A 11223 is the sdB binary with the shortest known orbital period (1.2 h) and its companion is certainly a white dwarf. PG 1232-136 is an sdB binary considered the best candidate to host a black hole companion. We observed these stars with XMM-Newton in 2013 August for 50 ks and in 2009 July for 36 ks, respectively. None of them was detected and we derived luminosity upper limits of similar to 1.5 x 10(29) erg s(-1) for CD -30A degrees A 11223 and similar to 5 x 10(29) erg s(-1) for PG 1232-136. The corresponding mass-loss rate for PG 1232-136 is poorly constrained, owing to the unknown efficiency for black hole accretion. On the other hand, in the case of CD -30A degrees A 11223 we could derive, under reasonable assumptions, an upper limit of similar to 3 x 10(-13) M-aS (TM) yr(-1) on the wind mass-loss rate from the sdB star. This is one of the few observational constraints on the weak winds expected in this class of low-mass hot stars. We also report the results on the X-ray emission from a cluster of galaxies serendipitously discovered in the field of CD -30 degrees 11223.

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How to cite

APA:

Mereghetti, S., La Palombara, N., Esposito, P., Gastaldello, F., Tiengo, A., Heber, U.,... Wilms, J. (2014). Constraints on the winds of hot subdwarf stars from X-ray observations of two sdB binaries with compact companions: CD-30 degrees 11223 and PG 1232-136. Monthly Notices of the Royal Astronomical Society, 441(3), 2684-2690. https://dx.doi.org/10.1093/mnras/stu773

MLA:

Mereghetti, Sandro, et al. "Constraints on the winds of hot subdwarf stars from X-ray observations of two sdB binaries with compact companions: CD-30 degrees 11223 and PG 1232-136." Monthly Notices of the Royal Astronomical Society 441.3 (2014): 2684-2690.

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