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Temporal variations of the outer atmosphere and the dust shell of the carbon-rich Mira variable V Ophiuchi probed with VLTI/MIDI
Aims.We present the first multi-epoch N-band spectro-interferometricobservations of the carbon-rich Mira variable V Ophusing MIDI at the ESO's Very Large Telescope Interferometer. Our aim isto study temporal variations of physical properties of the outeratmosphere and the circumstellar dust shell based onspectrally-dispersed N-band visibilities over the C2H2 (+HCN) featuresand the dust emission. Methods: Our MIDI observations werecarried out at three different phases 0.18, 0.49, and 0.65, with threedifferent baselines (projected baseline lengths of 42-124 m) using four8.2 m Unit Telescopes (UT2-UT4, UT1-UT4, and UT2-UT3 baselineconfigurations). Results: The wavelength dependence of theuniform-disk diameters obtained at all epochs is characterized by aroughly constant region between 8 and 10 μm with a slight dipcentered at 9.5 μm and a gradual increase longward of 10 μm.These N-band angular sizes are significantly larger than the estimatedphotospheric size of V Oph. The angular sizes observed at differentepochs reveal that the object appears smaller at phase 0.49 (minimumlight) with uniform-disk diameters of 5-12 mas than at phases 0.18 (12-20 mas) and 0.65 ( 9-15 mas). We interpret these results with a modelconsisting of optically thick C2H2 layers and an optically thin dustshell. Our modeling suggests that the C2H2 layers around V Oph are moreextended ( 1.7-1.8 Rstar) at phases 0.18 and 0.65 than atphase 0.49 ( 1.4 Rstar) and that the C2H2 column densitiesappear to be the smallest at phase 0.49. We also find that the dustshell consists of amorphous carbon and SiC with an inner radius of 2.5Rstar, and the total optical depths of τV ≈0.6-0.9 (τ11.3 μm ≈ 0.003 and 0.004 for amorphouscarbon and SiC, respectively) found at phases 0.18 and 0.65 are higherthan the value obtained at phase 0.49, τV ≈ 0.3(τ11.3 μm ≈ 0.001 and 0.002 for amorphous carbonand SiC, respectively). Conclusions: Our MIDI observations andmodeling indicate that carbon-rich Miras also have extended layers ofpolyatomic molecules as previously confirmed in oxygen-rich Miras. Thetemporal variation of the N-band angular size is largely governed by thevariations of the opacity and the geometrical extension of the C2H2layers and the dust shell, and consequently, this masks the sizevariation of the photosphere. Also, the observed weakness of themid-infrared C2H2 absorption in carbon-rich Miras can be explained bythe emission from the extended C2H2 layers and the dust shell.Based on observations made with the Very Large Telescope Interferometerof the European Southern Observatory. Program ID: 075.D-0607. Table 4 isonly available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/466/1099
| A compact dusty disk around the Herbig Ae star HR 5999 resolved with VLTI / MIDI
Aims.We have used mid-infrared long-baseline interferometry to resolvethe circumstellar material around the Herbig Ae star HR 5999, providingthe first direct measurement of its angular size, and to deriveconstraints on the spatial distribution of the dust. Methods:.MIDI at the VLTI was used to obtain a set of ten spectrally dispersed(8-13 μm) interferometric measurements of HR 5999 at differentprojected baseline lengths and position angles. To derive constraints onthe geometrical distribution of the dust, we compared ourinterferometric measurements to 2D, frequency-dependent radiationtransfer simulations of circumstellar disks and envelopes. Results: .The derived visibility values between 0.5 and 0.9 show thatthe mid-infrared emission from HR 5999 is clearly resolved. Thecharacteristic size of the emission region depends on the projectedbaseline length and position angle, and it ranges between 5-15milliarcsec (Gauss FWHM), corresponding to remarkably small physicalsizes of 1-3 AU. For disk models with radial power-law densitydistributions, the relatively weak but very extended emission from outerdisk regions ( 3 AU) leads to model visibilities that aresignificantly lower than the observed visibilities, making these modelsinconsistent with the MIDI data. Disk models in which the density istruncated at outer radii of 2 - 3 AU, on the other hand, provide goodagreement with the data. Conclusions: .A satisfactory fit to theobserved MIDI visibilities of HR 5999 is found with a model of ageometrically thin disk that is truncated at 2.6 AU and seen under aninclination angle of 58degr (i.e. closer to an edge-on view than to aface-on view). Neither models of a geometrically thin disk seen nearlyedge-on, nor models of spherical dust shells can achieve agreementbetween the observed and predicted visibilities. The reason why the diskis so compact remains unclear; we speculate that it has been truncatedby a close binary companion.
| 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
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/397/997
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| 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.
| 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.
| Régions H II de l'hémisphère austral
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970A&AS....3....1G&db_key=AST
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