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The complex structure of the disk around HD 100546. The inner few astronomical units
Context. Disclosing the structure of disks surrounding Herbig AeBe starsis important to expand our understanding of the formation and earlyevolution of stars and planets. The first astronomical units of thesedisks in particular, because they are hot, dense, and subject to intenseradiation field, hold critical clues to accretion and ejectionprocesses, as well as planet formation in environment different thanwhat prevailed around our own early Sun. Aims: We aim atrevealing the sub-AU disk structure around the 10 Myr old Herbig Be starHD 100546 and at investigating the origin of its near and mid-infraredexcess. Methods: We used new AMBER/VLTI observations to resolvethe K-band emission and to constrain the location and composition of thehot dust in the innermost circumstellar disk. Combining AMBERobservations with photometric and MIDI/VLTI measurements from thelitterature, we revisit the disk geometry using a passive disk modelbased on 3D Monte-Carlo radiative transfer (including full anisotropicscattering). Results: We propose a model that includes a tenuousinner disk made of micron-sized dust grains, a gap, and a massiveoptically thick outer disk, that successfully reproduces theinterferometric data and the SED. We locate the bulk of the K-bandemission at ~0.26 AU. Assuming that this emission originates fromsilicate dust grains at their sublimation temperature of 1500 K, we showthat micron-sized grains are required to enable the dust to survive atsuch a close distance from the star. As a consequence, in our bestmodel, more than 40% of the K-band flux is related to scattering,showing that the direct thermal emission of hot dust is not alwayssufficient to explain the near-infrared excess. In the massive outerdisk, large grains in the mid-plane are responsible for the mm emissionwhile a surface layer of small grains allows the mid and far infraredexcesses to be reproduced. Such vertical structure may be an evidencefor sedimentation. The interferometric observations are consistent witha disk model that includes a gap until ~13 AU from the star and a totaldust mass of ~0.008 lunar mass (~6.1023 g) inside it. Thesevalues together with the derived scale height (~2.5 AU) and temperature(~220 K) at the inner edge of the outer disk (r=13 AU), are consistentwith recent CO observations.Based on observations collected at the VLTI (ESO Paranal, Chile) withprogram 076.C-0851(B).
| A binary engine fuelling HD 87643's complex circumstellar environment. Determined using AMBER/VLTI imaging
Context: The star HD 87643, exhibiting the “B[e]phenomenon”, has one of the most extreme infrared excesses forthis object class. It harbours a large amount of both hot and cold dust,and is surrounded by an extended reflection nebula. Aims: One ofour major goals was to investigate the presence of a companion inHD87643. In addition, the presence of close dusty material was testedthrough a combination of multi-wavelength high spatial resolutionobservations. Methods: We observed HD 87643 with high spatialresolution techniques, using the near-IR AMBER/VLTI interferometer withbaselines ranging from 60 m to 130 m and the mid-IR MIDI/VLTIinterferometer with baselines ranging from 25 m to 65 m. Theseobservations are complemented by NACO/VLT adaptive-optics-correctedimages in the K and L-bands, and ESO-2.2m optical Wide-Field Imagerlarge-scale images in the B, V and R-bands. Results: We reportthe direct detection of a companion to HD 87643 by means of imagesynthesis using the AMBER/VLTI instrument. The presence of the companionis confirmed by the MIDI and NACO data, although with a lowerconfidence. The companion is separated by ~34 mas with a roughlynorth-south orientation. The period must be large (several tens ofyears) and hence the orbital parameters are not determined yet. Binaritywith high eccentricity might be the key to interpreting the extremecharacteristics of this system, namely a dusty circumstellar envelopearound the primary, a compact dust nebulosity around the binary systemand a complex extended nebula suggesting past violent ejections.Based on observations made with the ESO very large telescope at ParanalObservatory under programs 076.D-0575, 077.D-0095, 076.D-0141,380.D-0340, and 280.C-5071, with the ESO 1.52-m and archival ESO data.Appendix is only available in electronic form at http://www.aanda.org
| 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
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| Fifth fundamental catalogue. Part 2: The FK5 extension - new fundamental stars
The mean positions and proper motions for 3117 new fundamental starsessentially in the magnitude range about 4.5 to 9.5 are given in thisFK5 extension. Mean apparent visual magnitude is 7.2 and is on average2.5 magnitudes fainter then the basic FK5 which has a mean magnitude of4.7. (The basic FK5 gives the mean positions and proper motions for theclassical 1535 fundamental stars). The following are discussed: theobservational material, reduction of observations, star selection, andthe system for the FK5 extension. An explanation and description of thecatalog are given. The catalog of 3117 fundamental stars for the equinoxand epoch J2000.0 and B1950.0 is presented. The parallaxes and radialvelocities for 22 extension stars with large forecasting effects aregiven. Catalogs used in the compilation of the FK5 fundamental catalogare listed.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Légy |
| Rektaszcenzió: | 11h40m20.47s |
| Deklináció: | -69°40'18.3" |
| Vizuális fényesség: | 7.294 |
| Távolság: | 316.456 parszek |
| RA sajátmozgás: | -13.1 |
| Dec sajátmozgás: | -19 |
| B-T magnitude: | 8.959 |
| V-T magnitude: | 7.432 |
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