A large Hαline forming region for the massive interacting binaries β Lyrae and υ Sagitarii

Abstract

Aims. This study aims at constraining the properties of two interacting binary systems by measuring their continuum-forming region in the visible and the forming regions of some emission lines, in particular Hα, using optical interferometry. Methods. We have obtained visible medium (R ∼ 1000) spectral resolution interferometric observations of β Lyr and of υ Sgr using the VEGA instrument of the CHARA array. For both systems, visible continuum (520/640 nm) visibilities were estimated and differential interferometry data were obtained in the Hα emission line at several epochs of their orbital period. For β Lyr, dispersed visibilities and phases were also obtained in the Hβ and the HeI 6678 Å lines. Results. As expected, for baselines shorter than 60 m, the system of β Lyr is unresolved in the visible continuum, but the source associated with the Hα, the Hβ and the HeI 6678 Å lines appears to be well resolved at any orbital phase. The differential visibilities through these lines are lower during eclipses, indicating that significant emission originates close to the stars. The Hα line forming region appears to be made up of a compact source located near the orbital plane (possibly linked with the "hot point") and an extended source (i.e. ≥2 mas, i.e. 125 R ) out of the orbital plane (possibly associated to the "jet-like feature"). The υ Sgr continuum visibilities are at a similar level for short (20-25 m) and long (90-110 m) baselines. This is interpreted as the presence of an extended structure surrounding a compact bright source. No binary signal was detected, excluding a flux ratio between the stellar components of the system larger than 0.1 from 500 to 700 nm. The radius of the brightest star is estimated to be 0.33 ± 0.16 mas, i.e. 21 ± 10 R using the latest Hipparcos distance. By contrast, the Hα line forming region is very extended (i.e. ≥6 mas, i.e. 400 R ) and found to be off-center from the brightest star, following the orbital motion of the hidden companion. Conclusions. In both cases, the extension of the Hα line forming region is much larger than the size of the system, which is indicative of a non-conservative evolution. Although a large circumbinary disk surrounds the evolved system υ Sgr, storing a considerable part of the lost material, a substantial part of the Hα, Hβ, and the HeI 6678 Å line emission derives from regions perpendicular to the orbital plane of β Lyr.

A high angular and spectral resolution view into the hidden companion ofεAurigae

“…We note that during 2009, when the redshifted portions of the rotating disk were beginning to occult the blueshifted side of the F star, three of four profiles show V <1 for λ < λ o , with λ o the central wavelength of the line, suggesting that photons from the F star are being scattered by extended hydrogen associated with disk material -which mainly covers the blueshifted hemisphere of the F star during ingress (2009). Phase shifts in three of the four spectra are positive, implying a source offset (Bonneau et al 2011a;Meilland et al 2011) to the south of the F star photocentre, which is consistent with the disk's orbital plane offset as defined by the interferometric imaging. The visibility in the Si II line shows some differential signal with respect to the continuum during 2009, but the amplitudes are minimal, with a small amount of blueshift relative to the line core.…”

“…This gaussian function is used to extract the minimum value of the visibility and the associated radial velocity and to estimate the full width at half maximum (in radial velocity) of the visibility drop. All the differential phase measurements have been oriented in the same way, which means that a positive offset represents an astrometric displacement towards the south in our case (Bonneau et al 2011a;Meilland et al 2011). The uncertainties of the differential interferometric quantities are obtained from a pure photon noise analysis.…”

New distances for a selected set of visual binaries with inconsistent dynamical masses

“…The B5-A0 supergiant status (rather than F2p, given in SIM-BAD) indicates M sp to be about 10 and makes the Malkov et al (2012) M sp estimations (1.35) incorrect. As the hotter, unseen secondary component seems to be more massive (Bonneau et al 2011), the minimum total mass of the system should be at least ≈ 20 which is more consistent with the Malkov et al (2012), M ph =32.1. Yet, Bonneau et al (2011) mention that the separation of the stars may have been much smaller than estimated.…”

“…This massive, single-lined spectroscopic binary contains a bright star and an unseen companion. In their medium spectral resolution interferometric observations, Bonneau et al (2011) found WDS 19217−1557 (= υ Sgr) to be an interactive binary with a non-conservative evolution. The B5-A0 supergiant status (rather than F2p, given in SIM-BAD) indicates M sp to be about 10 and makes the Malkov et al (2012) M sp estimations (1.35) incorrect.…”

An interferometric journey around massive stars

“…On these images two components are seen, one unresolved, the primary, and one elongated, the secondary surrounded by the accretion disk. To go further in this study, and disentangle the stellar and circumstellar emission, the system was also observed in Hα with the CHARA/VEGA instrument (Bonneau et al 2011). The authors found that the emission was coming from a structure larger than the binary separation, most probably a circumbinary disk with possible contributions from polar jets.…”