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Resolving the compact dusty discs around binary post-AGB stars using N-band interferometry
We present the first mid-IR long baseline interferometric observationsof the circumstellar matter around binary post-AGB stars. Two objects,SX Cen and HD 52961, were observedusing the VLTI/MIDI instrument during Science Demonstration Time. Bothobjects are known binaries for which a stable circumbinary disc isproposed to explain the SED characteristics. This is corroborated by ourN-band spectrum showing a crystallinity fraction of more than 50% forboth objects, pointing to a stable environment where dust processing canoccur. Surprisingly, the dust surrounding SX Cen is not resolved in theinterferometric observations providing an upper limit of 11 mas (or 18AU at the distance of this object) on the diameter of the dust emission.This confirms the very compact nature of its circumstellar environment.The dust emission around HD 52961 originates from avery small but resolved region, estimated to be ~35 mas at 8 μm and~55 mas at 13 μm. These results confirm the disc interpretation ofthe SED of both stars. In HD 52961, the dust is nothomogeneous in its chemical composition: the crystallinity is clearlyconcentrated in the hotter inner region. Whether this is a result of theformation process of the disc, or due to annealing during the longstorage time in the disc is not clear.
| High angular resolution N-band observation of the silicate carbon star IRAS08002-3803 with the VLTI/MIDI instrument . Dusty environment spatially resolved
We present the results of N-band spectro-interferometric observations ofthe silicate carbon star IRAS08002-3803 with the MID-infraredInterferometric instrument (MIDI) at the Very Large TelescopeInterferometer (VLTI) of the European Southern Observatory (ESO). Theobservations were carried out using two unit telescopes (UT2 and UT3)with projected baseline lengths ranging from 39 to 47 m. Ourobservations of IRAS08002-3803 have spatially resolved the dustyenvironment of a silicate carbon star for the first time and revealed anunexpected wavelength dependence of the angular size in the N band: theuniform-disk diameter is found to be constant and 36 mas (72Rstar) between 8 and 10 μm, while it steeply increaseslongward of 10 μm to reach 53 mas (106 Rstar) at 13μm. Model calculations with our Monte Carlo radiative transfer codeshow that neither spherical shell models nor axisymmetric disk modelsconsisting of silicate grains alone can simultaneously explain theobserved wavelength dependence of the visibility and the spectral energydistribution (SED). We propose that the circumstellar environment ofIRAS08002-3803 may consist of two grain species coexisting in the disk:silicate and a second grain species, for which we consider amorphouscarbon, large silicate grains, and metallic iron grains. Comparison ofthe observed visibilities and SED with our models shows that such diskmodels can fairly - though not entirely satisfactorily - reproduce theobserved SED and N-band visibilities. Our MIDI observations and theradiative transfer calculations lend support to the picture whereoxygen-rich material around IRAS08002-3803 is stored in a circumbinarydisk surrounding the carbon-rich primary star and its putativelow-luminosity companion.
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| 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).
| Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
| 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.
| IRAS catalogues and atlases - Atlas of low-resolution spectra
Plots of all 5425 spectra in the IRAS catalogue of low-resolutionspectra are presented. The catalogue contains the average spectra ofmost IRAS poiont sources with 12 micron flux densities above 10 Jy.
| Radial velocities of southern stars obtained with the photoelectric scanner CORAVEL. III - 790 late-type bright stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1985A&AS...59...15A&db_key=AST
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