Resolving the circumstellar environment of the B[e] star V921 Scorpii in the near-infrared with VLTI/AMBER ^⋆

¹ Max Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: akreplin@mpifr-bonn.mpg.de
² Department of Astronomy, University of Michigan, 500 Church St., Ann Arbor, MI 48109-1090, USA
³ Deutsches Zentrum für Luft- und Raumfahrt, Königswinterer Strasse 522-524, 53227 Bonn, Germany

Received: 21 March 2011
Accepted: 20 October 2011

Abstract

Aims. We study the AU-scale circumstellar environment of the unclassified B[e] star V921 Sco in the near-infrared. For interpreting the observations, we employ temperature-gradient disk models.

Methods. Using the near-infrared beam combiner instrument AMBER, we recorded spectrally dispersed (spectral resolution R = 35) interferograms in the H and K bands. To obtain an improved calibration of the visibilities, we developed a method that is able to equalize the histograms of the optical path difference of target and calibrator. We fit temperature-gradient disk models to the visibilities and spectral energy distribution (SED) to analyze the circumstellar dust geometry.

Results. We derived a geometric ring-fit radius of 2.10 ± 0.16 mas in the K band. If we adopt the distance of 1150 ± 150 pc reported elsewhere, we obtain a ring-fit radius of 2.4 AU, which is slightly smaller than the 3.5 AU dust sublimation radius predicted by the size-luminosity relation. The fitted H-band radius of 1.61 ± 0.23 mas (1.85 AU) is found to be more compact than the K-band radius. The best-fit temperature-gradient disk model has an inner disk radius of  ~1.45 AU, an inner-edge disk temperature T₀ = 1533 K, and a temperature-gradient exponent q = 0.46 suggesting a flared disk geometry.

Conclusions. The distance and luminosity of V921 Sco are not well known. If we assume a distance of 1150 ± 150 pc, we derive a ring-fit radius of  ~2.4 AU, which is approximately consistent with the computed temperature-gradient disk model with inner and outer ring radii of 1.45 and 8.5 AU, respectively. If the inner radius of V921 Sco is more compact than the sublimation radius, this compact observed size can be explained by emitting material (e.g., a gaseous disk) inside the dust sublimation radius, as suggested for several other B[e] stars.