VLTI/AMBER spectro-interferometry of the Herbig Be star MWC 297 with spectral resolution 12 000

Abstract

Context. Circumstellar disks and outflows play a fundamental role in star formation. Infrared spectro-interferometry allows the inner accretion-ejection region to be resolved. Aims. We study the disk and Brγ-emitting region of MWC 297 with high spatial and spectral resolution and compare our observations with disk-wind models. Methods. We measured interferometric visibilities, wavelength-differential phases, and closure phases of MWC 297 with a spectral resolution of 12 000. To interpret our MWC 297 observations, we employed disk-wind models. Results. The measured continuum visibilities confirm previous results that the continuum-emitting region of MWC 297 is remarkably compact. We derive a continuum ring-fit radius of ∼2.2 mas (∼0.56 AU at a distance of 250 pc), which is ∼5.4 times smaller than the 3 AU dust sublimation radius expected for silicate grains (in the absence of radiation-shielding material). The strongly wavelengthdependent and asymmetric Brγ-emitting region is more extended (∼2.7 times) than the continuum-emitting region. At the center of the Brγ line, we derive a Gaussian fit radius of ∼6.3 mas HWHM (∼1.6 AU). To interpret the observations, we employ a magnetocentrifugally driven disk-wind model consisting of an accretion disk, which emits the observed continuum radiation, and a disk wind, which emits the Brγ line. The calculated wavelength-dependent model intensity distributions and Brγ line profiles are compared with the observations (i.e., K-band spectrum, visibilities, differential phases, and closure phases). The closest fitting model predicts a continuum-emitting disk with an inner radius of ∼0.3 AU and a disk wind ejection region with an inner radius of ∼0.5 AU (∼17.5 stellar radii). We obtain a disk-wind half-opening angle (the angle between the rotation axis and the innermost streamline of the disk wind) of ∼80 • , which is larger than in T Tau models, and a disk inclination angle of ∼20 • (i.e., almost pole-on). Conclusions. Our observations with a spectral resolution of 12 000 allow us to study the AU-scale environment of MWC 297 in ∼10 different spectral channels across the Brγ emission line. We show that the K-band flux, visibilities, and remarkably strong phases can be explained by the employed magneto-centrifugally driven disk wind model.

Hydrogen lines as a diagnostic tool for studying multicomponent emitting regions in hot young stars: magnetosphere, X-wind, and disk wind

“…The model we developed for the more luminous and massive Herbig Ae/Be stars was described in detail in Grinin & Tambovtseva (2011) and Weigelt et al (2011). In the present paper, we briefly summarize the main properties of the model and the calculation method.…”

“…Several teams have modeled the hydrogen line profiles or interferometric observables of T Tauri stars (TTSs) or Herbig Ae/Be stars (HAEBEs) (e.g., Muzerolle et al 2001;Kurosawa et al 2006Kurosawa et al , 2011Lima et al 2010;Proga et al 1998;Tambovtseva et al 2001;Muzerolle et al 2004;RousseletPerraut et al 2010;Weigelt et al 2011;Lumsden et al 2012). It is difficult to investigate the structure of the emitting region in hot young stars because this region usually consists of several components.…”

“…For this purpose we use the non-LTE solution for hydrogen atoms derived on the basis of the Sobolev approximation (Sobolev 1960) with exact integration over the whole emitting volume (Grinin & Tambovtseva 2011;Weigelt et al 2011 and references therein). In Sect.…”

Interferometric observations of rapidly rotating stars

“…Sufficiently high-resolution dispersion, such as the R ∼ 12,000 available with the VLTI AMBER instrument (Petrov et al 2007), make it possible to examine spectral line profiles in a spatially resolved or even imaged sense. AMBER has already been used for spectro-interferometric observations of the Herbig Be star MWC 297 as this high spectral resolution (Weigelt et al 2011). …”

An interferometric journey around massive stars

“…They showed that, for this object, the Brγ emission was coming from a region larger than the dusty-disk inner rim and that it was expanding, ruling out the possibility of an emission coming from an inner gaseous disk. This object was observed again by Weigelt et al (2011) with a higher spectral resolution and they managed to fully model their observations with a disk-wind model. For an other object, HD 104237, Tatulli et al (2007) found that the extension of the gaseous emission was of the order of the dusty disk inner rim.…”