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تسجيل مستخدم جديدThe binary Be star {delta} Sco at high spectral and spatial resolution: Disk geometry and kinematics before the 2011 periastron
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Anthony Meilland
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Classical Be stars are hot non-supergiant stars surrounded by a gaseous circumstellar disk that is responsible for the observed IR-excess and emission lines. The influence of binarity on these phenomena remains controversial. delta Sco is a binary system whose primary suddently began to exhibit the Be phenomenon at the last periastron in 2000. We want to constrain the geometry and kinematics of its circumstellar environment. We observed the star between 2007 and 2010 using spectrally-resolved interferometry with the VLTI/AMBER and CHARA/VEGA instruments. We found orbital elements that are compatible with previous estimates. The next periastron should take place around July 5, 2011 (+- 4,days). We resolved the circumstellar disk in the HAlpha (FWHM = 4.8+-1.5mas), BrGamma (FWHM = 2.9 0.,mas), and the 2.06$ mu$m HeI (FWHM = 2.4+-0.3mas) lines as well as in the K band continuum (FWHM ~2.4mas). The disk kinematics are dominated by the rotation, with a disk expansion velocity on the order of 0.2km/s. The rotation law within the disk is compatible with Keplerian rotation. As the star probably rotates at about 70% of its critical velocity the ejection of matter doesnt seems to be dominated by rotation. However, the disk geometry and kinematics are similar to that of the previously studied quasi-critically rotating Be stars, namely Alpha Ara, Psi Per and 48 Per.
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Classical Be stars are hot non-supergiant stars surrounded by a gaseous circumstellar disk that is responsible for the observed infrared (IR) excess and emission lines. The influence of binarity on these phenomena remains controversial. We followed t
he evolution of the environment surrounding the binary Be star $delta$ Scorpii one year before and one year after the 2011 periastron to check for any evidence of a strong interaction between its companion and the primary circumstellar disk. We used the VLTI/AMBER spectro-interferometric instrument operating in the K band in high (12000) spectral resolution to obtain information on both the disk geometry and kinematics. Observations were carried out in two emission lines: Br$gamma$ (2.172,$mu$m) and $ion{He}{i}$ (2.056,$mu$m). We detected some important changes in $delta$ Scorpiis circumstellar disk geometry between the first observation made in April 2010 and the new observation made in June 2012. During the last two years the disk has grown at a mean velocity of 0.2,km,s$^{-1}$. This is compatible with the expansion velocity previously found during the 2001-2007 period. The disk was also found to be asymmetric at both epochs, but with a different morphology in 2010 and 2012. Considering the available spectroscopic data showing that the main changes in the emission-line profiles occurred quickly during the periastron, it is probable that the differences between the 2010 and 2012 disk geometry seen in our interferometric data stem from a disk perturbation caused by the companion tidal effects. However, taking into account that no significant changes have occurred in the disk since the end of the 2011 observing season, it is difficult to understand how this induced inhomogeneity has been frozen in the disk for such a long period.
We describe the results of the world-wide observing campaign of the highly eccentric Be binary system delta Scorpii 2011 periastron passage which involved professional and amateur astronomers. Our spectroscopic observations provided a precise measure
ment of the system orbital period at 10.8092+/- 0.0005 years. Fitting of the He II 4686A line radial velocity curve determined the periastron passage time on 2011 July 3, UT 9:20 with a 0.9--day uncertainty. Both these results are in a very good agreement with recent findings from interferometry. We also derived new evolutionary masses of the binary components (13 and 8.2 Msun) and a new distance of 136 pc from the Sun, consistent with the HIPPARCOS parallax. The radial velocity and profile variations observed in the H_alpha line near the 2011 periastron reflected the interaction of the secondary component and the circumstellar disk around the primary component. Using these data, we estimated a disk radius of 150 Rsun. Our analysis of the radial velocity variations measured during the periastron passage time in 2000 and 2011 along with those measured during the 20th century, the high eccentricity of the system, and the presence of a bow shock-like structure around it suggest that delta Sco might be a runaway triple system. The third component should be external to the known binary and move on an elliptical orbit that is tilted by at least 40 degree with respect to the binary orbital plane for such a system to be stable and responsible for the observed long-term radial velocity variations.
The rapidly rotating Be star phi Persei was spun up by mass and angular momentum transfer from a now stripped-down, hot subdwarf companion. Here we present the first high angular resolution images of phi Persei made possible by new capabilities in lo
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We present optical and NIR spectroscopic observations of U Sco 2010 outburst. From the analysis of lines profiles we identify a broad and a narrow component and show that the latter originates from the reforming accretion disk. We show that the accre
tion resumes shortly after the outburst, on day +8, roughly when the super-soft (SSS) X-ray phase starts. Consequently U Sco SSS phase is fueled (in part or fully) by accretion and should not be used to estimate $m_{mathrm{rem}}$, the mass of accreted material which has not been ejected during the outburst. In addition, most of the He emission lines, and the HeII lies in particular, form in the accretion flow/disk within the binary and are optically thick, thus preventing an accurate abundance determination. A late spectrum taken in quiescence and during eclipse shows CaII H&K, the G-band and MgI b absorption from the secondary star. However, no other significant secondary star features have been observed at longer wavelengths and in the NIR band.
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