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AMBER is the first near infrared focal instrument of the VLTI. It combines three telescopes and produces spectrally resolved interferometric measures. This paper discusses some preliminary results of the first scientific observations of AMBER with three Unit Telescopes at medium (1500) and high (12000) spectral resolution. We derive a first set of constraints on the structure of the circumstellar material around the Wolf Rayet Gamma2 Velorum and the LBV Eta Carinae.
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While the search for exoplanets around main sequence stars more massive than the Sun have found relatively few such objects, surveys performed around giant stars have led to the discovery of more than 30 new exoplanets. The interest in studying planet hosting giant stars resides in the possibility of investigating planet formation around stars more massive than the Sun. Masses of isolated giant stars up to now were only estimated from evolutionary tracks, which led to different results depending on the physics considered. To calibrate the theory, it is therefore important to measure a large number of giant star diameters and masses as much as possible independent of physical models. We aim in the determination of diameters and effective temperatures of 5 giant stars, one of which is known to host a planet. AMBER/VLTI observations with the ATs were executed in low resolution mode on 5 giant stars. In order to measure high accurate calibrated squared visibilities, a calibrator-star-calibrator observational sequence was performed. We measured the uniform disk and limb-darkened angular diameters of 4 giant stars. The effective temperatures were also derived by combining the bolometric luminosities and the interferometric diameters. Lower effective temperatures were found when compared to spectroscopic measurements. The giant star HD12438 was found to have an unknown companion star at an angular separation of ~ 12 mas. Radial velocity measurements present in the literature confirm the presence of a companion with a very long orbital period (P ~ 11.4 years).}
Massive stars deeply influence their surroundings by their luminosity and the injection of kinetic energy. So far, they have mostly been studied with spatially unresolved observations, although evidence of geometrical complexity of their wind are numerous. Interferometry can provide spatially resolved observations of massive stars and their immediate vicinity. Specific geometries (disks, jets, latitude-dependent winds) can be probed by this technique. The first observation of a Wolf-Rayet (WR) star (gamma^2 Vel) with the AMBER/VLTI instrument yielded to a re-evaluation of its distance and an improved characterization of the stellar components, from a very limited data-set. This motivated our team to increase the number of WR targets observed with AMBER. We present here new preliminary results that encompass several spectral types, ranging from early WN to evolved dusty WC. We present unpublished data on WR79a, a massive star probably at the boundary between the O and Wolf- Rayet type, evidencing some Wolf-Rayet broad emission lines from an optically thin wind. We also present new data obtained on gamma^2 Vel that can be compared to the up-to-date interferometry-based orbital parameters from North et al. (2007). We discuss the presence of a wind-wind collision zone in the system and provide preliminary analysis suggesting the presence of such a structure in the data. Then, we present data obtained on 2 dusty Wolf-Rayet stars: WR48a-b and WR118, the latter exhibiting some clues of a pinwheel-like structure from the visibility variations.
Context. The putative tori surrounding the accretion disks of active galactic nuclei (AGNs) play a fundamental role in the unification scheme of AGNs. Infrared long-baseline interferometry allows us to study the inner dust distribution in AGNs with unprecedented spatial resolution over a wide infrared wavelength range. Aims. Near- and mid-infrared interferometry is used to investigate the milli-arcsecond-scale dust distribution in the type 1.5 Seyfert nucleus of NGC 3783. Methods. We observed NGC 3783 with the VLTI/AMBER instrument in the K-band and compared our observations with models. Results. From the K-band observations, we derive a ring-fit torus radius of 0.74 +/- 0.23 mas or 0.16 +/- 0.05 pc. We compare this size with infrared interferometric observations of other AGNs and UV/optical-infrared reverberation measurements. For the interpretation of our observations, we simultaneously model our near- and mid-infrared visibilities and the SED with a temperature/density-gradient model including an additional inner hot 1400 K ring component.
Aims. We study the enigmatic B[e] star MWC 300 to investigate its disk and binary with milli-arcsecond-scale angular resolution. Methods. We observed MWC 300 with the VLTI/AMBER instrument in the H and K bands and compared these observations with temperature-gradient models to derive model parameters. Results. The measured low visibility values, wavelength dependence of the visibilities, and wavelength dependence of the closure phase directly suggest that MWC 300 consists of a resolved disk and a close binary. We present a model consisting of a binary and a temperature-gradient disk that is able to reproduce the visibilities, closure phases, and spectral energy distribution. This model allows us to constrain the projected binary separation (~4.4 mas or ~7.9 AU), the flux ratio of the binary components (~2.2), the disk temperature power-law index, and other parameters.
The rapidly rotating primary component of Regulus A system has been observed, for the first time, using the technique of differential interferometry at high spectral resolution. The observations have been performed across the Br$_gamma$ spectral line with the VLTI/AMBER focal instrument in high spectral resolution mode (R $approx$ 12000) at $approx$ 80-130m (projected on the sky) Auxiliary Telescopes triplet baseline configurations. We confirm, within the uncertainties, the results previously obtained using the techniques of classical long-baseline interferometry, although the question of anomalous gravity darkening remains open for the future study.
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