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Register a new userThe peculiar fast-rotating star 51 Oph probed by VEGA/CHARA
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Narges Jamialahamdi
Publication date
2017
fields
Physics
and research's language is
English
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Stellar rotation is a key in our understanding of both mass-loss and evolution of intermediate and massive stars. It can lead to anisotropic mass-loss in the form of radiative wind or an excretion disk. We wished to spatially resolve the photosphere and gaseous environment of 51 Oph, a peculiar star with a very high vsin(i) of 267km s$^{-1}$ and an evolutionary status that remains unsettled. It has been classified by different authors as a Herbig, a $beta$ Pic, or a classical Be star. We used the VEGA visible beam combiner installed on the CHARA array that reaches a submilliarcsecond resolution. Observation were centered on the H$alpha$ emission line. We derived, for the first time, the extension and flattening of 51 Oph photosphere. We found a major axis of $theta_{{mathrm{eq}}}$=8.08$pm$0.70$R_odot$ and a minor axis of $theta_{{mathrm{pol}}}$=5.66$pm$0.23$R_odot$ . This high photosphere distortion shows that the star is rotating close to its critical velocity. Finally, using spectro-interferometric measurements in the H$ alpha$ line, we constrained the circumstellar environment geometry and kinematics and showed that the emission is produced in a 5.2$pm$2R$_{*}$ disk in Keplerian rotation. From the visible point of view, 51 Oph presents all the features of a classical Be star: near critical-rotation and double-peaked H$alpha $ line in emission produced in a gaseous disk in Keplerian rotation. However, this does not explain the presence of dust as seen in the mid-infrared and millimeter spectra, and the evolutionary status of 51 Oph remains unsettled.
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The Vega planetary system hosts the archetype of extrasolar Kuiper belts, and is rich in dust from the sub-au region out to 100s of au, suggesting intense dynamical activity. We present ALMA mm observations that detect and resolve the outer dust belt from the star for the first time. The interferometric visibilities show that the belt can be fit by a Gaussian model or by power-law models with a steep inner edge (at 60-80 au). The belt is very broad, extending out to at least 150-200 au. We strongly detect the star and set a stringent upper limit to warm dust emission previously detected in the infrared. We discuss three scenarios that could explain the architecture of Vegas planetary system, including the new {ALMA} constraints: no outer planets, a chain of low-mass planets, and a single giant planet. The planet-less scenario is only feasible if the outer belt was born with the observed sharp inner edge. If instead the inner edge is currently being truncated by a planet, then the planet must be $gtrsim$6 M$_{oplus}$ and at $lesssim71$ au to have cleared its chaotic zone within the system age. In the planet chain scenario, outward planet migration and inward scattering of planetesimals could produce the hot and warm dust observed in the inner regions of the system. In the single giant planet scenario, an asteroid belt could be responsible for the warm dust, and mean motion resonances with the planet could put asteroids on star-grazing orbits, producing the hot dust.
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