K-band spectroscopy of Be-star X-ray binaries

We present the results of our long-term monitoring of BD +53• 2790, the optical counterpart to the X-ray source 4U 2206+54. Unlike previous studies that classify the source as a Be/X-ray binary, we find that its optical and infrared properties differ from those of typical Be stars: the variability of the V/R ratio is not cyclical; there are variations in the shape and strength of the Hα emission line on timescales less than 1 day; and no correlation between the EW and the IR magnitudes or colors is seen. Our observations suggest that BD +53• 2790 is very likely a peculiar O9.5V star. In spite of exhaustive searches we cannot find any significant modulation in any emission line parameter or optical/infrared magnitudes. Spectroscopy of the source extending from the optical to the K-band confirms the peculiarity of the spectrum: not only are the He lines stronger than expected for an O9.5V star but also there is no clear pattern of variability. The possibility that BD +53• 2790 is an early-type analogue to He-strong stars (like θ 1 Ori C) is discussed.

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“…6. Unlike the OB components of several Be/X-ray binaries observed by Everall et al (1993;see also Everall 1995), BD +53…”

Section: Bd+53mentioning

confidence: 84%

“…The instrumental configuration consisted of the long focal station (300 mm) camera and the 75 lines mm −1 grating, which gives a nominal velocity resolution of 445 km s −1 at 2 µm (λ/∆λ ≈ 700). The data were reduced according to the procedure outlined by Everall et al (1993).…”

Section: Infrared Spectroscopymentioning

confidence: 99%

Multiwavelength monitoring of BD +53°2790, the optical counterpart to 4U 2206+54

Blay

Negueruela

Reig

et al. 2006

A&A

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“…The line uxes, equivalent widths, and full widths at half maximum of these lines are listed in Table 2. For comparison, in Figure 1 is also shown the combined K-band spectra of two late Oe and two early Be high mass X-ray binaries observed by Everall et al (1993) with the same instruments that we used for our observations of GRS 1915+105. The de-reddened spectra of GRS 1915+105 are strikingly similar to the combined spectrum of the four Oe-Be X-ray binaries observed by Everall et al (1993), in the slope of the continuum, as well as in the relative strength of the emission lines.…”

Section: Resultsmentioning

confidence: 99%

“…For comparison, in Figure 1 is also shown the combined K-band spectra of two late Oe and two early Be high mass X-ray binaries observed by Everall et al (1993) with the same instruments that we used for our observations of GRS 1915+105. The de-reddened spectra of GRS 1915+105 are strikingly similar to the combined spectrum of the four Oe-Be X-ray binaries observed by Everall et al (1993), in the slope of the continuum, as well as in the relative strength of the emission lines. The inspection of the K-band spectra of a sample of eight high mass X-ray binaries by Hanson, Conti & Rieke (1996) shows that the spectra of GRS 1915+105 are similar to the four high mass X-ray binaries classi ed as late Oe or early Be, and di erent from the four high mass X-ray binaries with other spectral classi cation (e.g.…”

Section: Resultsmentioning

confidence: 99%

“…At these epochs the source was detected in the 20-100 keV energy band by BATSE on the COMPTON Observatory (Harmon et al 1996). We compare the spectra of GRS 1915+105 with the available K band spectra of high mass stars and high mass X-ray binaries obtained by Everall et al (1993) and Hanson, Conti & Rieke (1996). Finally, we discuss the possible reasons for the apparent absence of Doppler-shifted \moving" lines arising from the jets of GRS 1915+105.…”

Section: Introductionmentioning

confidence: 96%

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