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AMBER and MIDI interferometric observations of the post-AGB binary IRAS 08544-4431: the circumbinary disc resolved
Context: For a large group of post-AGB binaries, the presence of astable reservoir of dust is postulated. Although this reservoir willinfluence the final evolution stages of these objects significantly, itsactual geometry and structure remains largely unknown. Aims: Weaim at determining the dust morphology of a member of this group, IRAS08544-4431. Methods: We use the interferometric capabilities ofthe AMBER and MIDI instruments, operating in the K and N-bandrespectively. The high spatial resolution measurements are used inconjunction with the broad band spectral characteristics to determinethe dust geometry, based on self consistent 2D radiative transfermodels. Results: We resolve the object in both K and N.Moreover, using the closure phase capabilities of AMBER, we measure inthe K-band a large asymmetry of the dusty environment. Theinterferometric data are clearly incompatible with a spherical outflow.We model the dusty environment with a passive irradiated dusty discmodel. Although this model is constrained mainly on the basis of thespectral energy distribution, it reproduces simultaneously the amplitudeand closure phase of the visibilities, in both wavelength bands. Conclusions: Our model of a passive, irradiated disc in equilibriumgives an excellent fit to both the K and N-band visibilities and closurephase. The dust around this evolved binary star is indeed locked in acircumbinary disc with a significant scale height. Grain growth,settling, radial mixing and crystallization are efficient in such anenvironment. We conclude that the circumbinary disc of this evolvedobject, is governed by the same physical processes that govern theproto-planetary discs around young stellar objects.Based on observations collected at the EuropeanSouthern Observatory, Chile: ESO.076.D-0274, ESO.078.D-0113.
| A catalog of bright calibrator stars for 200-m baseline near-infrared stellar interferometry
We present in this paper a catalog of reference stars suitable forcalibrating infrared interferometric observations. In the K band,visibilities can be calibrated with a precision of 1% on baselines up to200 meters for the whole sky, and up to 300 meters for some part of thesky. This work, extending to longer baselines a previous catalogcompiled by Bordé et al. (2002, A&A, 393, 183), isparticularl y well adapted to hectometric-class interferometers such asthe Very Large Telescope Interferometer (VLTI, Glindemann et al. 2003,Proc. SPIE, 4838, 89) or the CHARA array (ten Brummelaar et al. 2003,Proc. SPIE, 4838, 69) when one is observing well-resolved, high-surfacebrightness objects (K 8). We use the absolute spectro-photometriccalibration method introduced by Cohen et al. (1999, AJ, 117, 1864) toderive the angular diameters of our new set of 948 G8-M0 calibratorstars extracted from the IRAS, 2MASS and MSX catalogs. Angular stellardiameters range from 0.6 mas to 1.8 mas (median is 1.1 mas) with amedian precision of 1.35%. For both the northern and southernhemispheres, the closest calibrator star is always less than 10°away.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
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