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Wind accretion in the massive X-ray binary 4U 2206+54: abnormally slow wind and a moderately eccentric orbit

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Wind accretion in the massive X-ray binary 4U 2206+54: abnormally slow wind and a moderately eccentric orbit

dc.contributor.author	Ribó, M.
dc.contributor.author	Negueruela, I.
dc.contributor.author	Blay Serrano, Pedro Jose
dc.contributor.author	Torrejón, J. M.
dc.contributor.author	Reig Torres, Pablo
dc.date.accessioned	2010-06-29T10:30:50Z
dc.date.available	2010-06-29T10:30:50Z
dc.date.issued	2006
dc.identifier.citation	RIBÓ, M. ; Negueruela, I. ; Blay Serrano, Pedro Jose ; Torrejón, J.M. ; Reig Torres, Pablo, 2006, Wind accretion in the massive X-ray binary 4U 2206+54: abnormally slow wind and a moderately eccentric orbit, Astronomy and Astrophysics, vol. 449, no. 2, p. 687–698	en
dc.identifier.uri	http://hdl.handle.net/10550/13990
dc.description.abstract	Massive X-ray binaries are usually classified by the properties of the donor star in classical, supergiant and Be X-ray binaries, the main difference being the mass transfer mechanism between the two components. The massive X-ray binary 4U 2206+54 does not fit in any of these groups, and deserves a detailed study to understand how the transfer of matter and the accretion on to the compact object take place. To this end we study an IUE spectrum of the donor and obtain a wind terminal velocity (v(sub)∞) of ∼350 km s−1, which is abnormally slow for its spectral type. We also analyse here more than 9 years of available RXTE/ASM data. We study the long-term X-ray variability of the source and find it to be similar to that observed in the wind-fed supergiant system Vela X-1, reinforcing the idea that 4U 2206+54 is also a wind-fed system. We find a quasi-period decreasing from ∼270 to ∼130 d, noticed in previous works but never studied in detail. We discuss possible scenarios for its origin and conclude that long-term quasi-periodic variations in the mass-loss rate of the primary are probably driving such variability in the measured X-ray flux. We obtain an improved orbital period of Porb = 9.5591 ± 0.0007 d with maximum X-ray flux at MJD 51856.6 ± 0.1. Our study of the orbital X-ray variability in the context of wind accretion suggests a moderate eccentricity around 0.15 for this binary system. Moreover, the low value of v∞ solves the long-standing problem of the relatively high X-ray luminosity for the unevolved nature of the donor, BD +53◦2790, which is probably an O9.5V star. We note that changes in v∞ and/or the mass-loss rate of the primary alone cannot explain the different patterns displayed by the orbital X-ray variability. We finally emphasize that 4U 2206+54, together with LS 5039, could be part of a new population of wind-fed HMXBs with main sequence donors, the natural progenitors of supergiant X-ray binaries.	en
dc.language.iso	en	en
dc.subject	X-rays binaries ; X-rays individuals ; 4U 2206+54 ; Individual stars ; BD +53◦2790 ; Winds ; Outflows Emission-line ; Be	en
dc.title	Wind accretion in the massive X-ray binary 4U 2206+54: abnormally slow wind and a moderately eccentric orbit	en
dc.type	journal article	es_ES
dc.subject.unesco	UNESCO::ASTRONOMÍA Y ASTROFÍSICA	en
dc.subject.unesco	UNESCO::ASTRONOMÍA Y ASTROFÍSICA::Cosmología y cosmogonia	en
dc.identifier.doi	10.1051/0004-6361:20054206	en
dc.identifier.idgrec	027124	en
dc.type.hasVersion	VoR	es_ES
dc.identifier.url	http://www.aanda.org/articles/aa/pdf/2006/14/aa4206-05.pdf	en