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The polar wind of the fast rotating Be star Achernar. VINCI/VLTI interferometric observations of an elongated polar envelope
Context: .Be stars show evidence of mass loss and circumstellarenvelopes (CSE) from UV resonance lines, near-IR excesses, and thepresence of episodic hydrogen emission lines. The geometry of theseenvelopes is still uncertain, although it is often assumed that they areformed by a disk around the stellar equator and a hot polar wind.Aims: .We probe the close environment of the fast rotating Be starAchernar at angular scales of a few milliarcseconds (mas) in theinfrared, in order to constrain the geometry of a possible polar CSE. Methods: .We obtained long-baseline interferometric observations ofAchernar with the VINCI/VLTI beam combiner in the H and K bands, usingvarious telescope configurations and baseline lengths with a wideazimuthal coverage. Results: .The observed visibility measurementsalong the polar direction are significantly lower than the visibilityfunction of the photosphere of the star alone, in particular at lowspatial frequencies. This points to the presence of an asymmetricdiffuse CSE elongated along the polar direction of the star. To ourdata, we fit a simple model consisting of two components: a 2Delliptical Gaussian superimposed on a uniform ellipse representing thedistorted photosphere of the fast rotating star. Conclusions: .Weclearly detected a CSE elongated along the polar axis of the star, aswell as rotational flattening of the stellar photosphere. For theuniform-ellipse photosphere we derive a major axis of θ_eq = 2.13± 0.05 mas and a minor axis of θ_pol = 1.51 ± 0.02mas. The relative near-IR flux measured for the CSE compared to thestellar photosphere is f = 4.7 ± 0.3%. Its angular dimensions areloosely constrained by the available data at ρ_eq = 2.7 ± 1.3mas and ρ_pol = 17.6 ± 4.9 mas. This CSE could be linked tofree-free emission from the radiative pressure driven wind originatingfrom the hot polar caps of the star.
| Gravitational-darkening of Altair from interferometry
Interferometric observations have revealed that the rapid rotator Altairis a flattened star with a non-centrally symmetric intensitydistribution. In this work we perform for the first time a physicallyconsistent analysis of all interferometric data available so far,corresponding to three different interferometers operating in severalspectral bands. These observations include new data (squaredvisibilities in the H and K bands from VLTI-VINCI) as well as previouslypublished data (squared visibilities in the K band from PTI and squaredvisibilities, triple amplitudes, and closure phases in the visiblebetween 520 nm and 850 nm from NPOI). To analyze these data we perform aχ2 minimization using an interferometry-oriented modelfor fast rotators, which includes Roche approximation, limb-darkening,and von Zeipel-like gravity-darkening. Thanks to the richinterferometric data set available and to this physical model, the mainuniqueness problems were avoided. As a result, we show that theobservations can only be explained if Altair has a gravity-darkeningcompatible with the expected value for hot stars, i.e., the von Zeipeleffect (T_eff∝ g0.25).
| VLTI/VINCI diameter constraints on the evolutionary status of δ Eri, ξ Hya, η Boo
Using VLTI/VINCI angular diameter measurements, we constrain theevolutionary status of three asteroseismic targets: the stars δEri, ξ Hya, η Boo. Our predictions of the mean large frequencyspacing of these stars are in agreement with published observationalestimations. Looking without success for a companion of δ Eri, wedoubt its classification as an RS CVn star.
| First results from the ESO VLTI calibrators program
The ESO Very Large Telescope Interferometer (VLTI) is one of the leadinginterferometric facilities. It is equipped with several 8.2 and 1.8 mtelescopes, a large number of baselines up to 200 m, and with severalsubsystems designed to enable high quality measurements and to improvesignificantly the limits of sensitivities currently available tolong-baseline interferometry. The full scientific potential of the VLTIcan be exploited only if a consistent set of good quality calibrators isavailable. For this, a large number of observations of potentialcalibrators have been obtained during the commissioning phase of theVLTI. These data are publicly available. We briefly describe theinterferometer, the VINCI instrument used for the observations, the dataflow from acquisition to processed results, and we present and commenton the volume of observations gathered and scrutinized. The result is alist of 191 calibrator candidates, for which a total of 12 066observations can be deemed of satisfactory quality. We present a generalstatistical analysis of this sample, using as a starting point theangular diameters previously available in the literature. We derive thegeneral characteristics of the VLTI transfer function, and its trendwith time in the period 2001 through mid-2004. A second paper will bedevoted to a detailed investigation of a selected sample, aimed atestablishing a VLTI-based homogeneous system of calibrators.
| 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
| VLTI near-IR interferometric observations of Vega-like stars. Radius and age of α PsA, β Leo, β Pic, ɛ Eri and τ Cet
We report in this paper the direct interferometric measurement of theangular diameter of five nearby Vega-like stars: α PsA, βLeo, β Pic, ɛ Eri and τ Cet. The near-infrared (K and Hbands) observations were conducted at the VLTI during the commissioningperiod with the VINCI instrument and three different baselines rangingfrom 66 m to 140 m. The five stellar photospheres are resolved and wederive their angular diameters with a 1 to 2% accuracy, except forβ Pic (14%). We discuss the detectability and the influence of apossible small amount of warm circumstellar dust on our measurements. Inaddition, we have used the stellar evolution code CESAM (Morel\cite{m97}) to compare the computed fundamental parameters to theobserved values (linear diameter, luminosity, temperature and chemicalabundance). As a result of the simulation, the age of the stars isinferred and found to be in good agreement with previous estimates fromvarious other methods.
| First observations with an H-band integrated optics beam combiner at the VLTI
This paper reports results obtained with the Very Large TelescopeInterferometer Commissioning Instrument (VLTI-VINCI) where the fiberinterferometric coupler MONA was temporarily replaced by an integratedoptics beam combiner (IONIC). The two-beam combiner operating in the Hatmospheric band was tested at Paranal during two weeks in July 2002.Fringes were recorded on several stars with the siderostats and the UnitTelescopes (UT). We demonstrate that integrated optics allows beamcombination with a high interferometric efficiency, stability andspatial filtering. The instrumental visibility of VLTI+IONIC is betterthan 85%, which is just 5% under the visibility of the IONIC devicealone. During this run, the flux injection in the IONIC combiner was notoptimized since we used the K-band MONA optics. However, we obtainfringes with the 35 cm siderostats on a star of magnitude mH=2.47(κ2 Scl). It allows us to extrapolate a magnitudearound mH6 with 8 m telescopes without adaptive optics and in thesame poor injection conditions.Based on observations collected at the European Southern Observatory,Paranal, Chile (public commissioning data).
| Cepheid distances from infrared long-baseline interferometry. I. VINCI/VLTI observations of seven Galactic Cepheids
We report the angular diameter measurements of seven classical Cepheids,X Sgr, η Aql, W Sgr, ζ Gem, β Dor, Y Oph and ℓ Carthat we have obtained with the VINCI instrument, installed at ESO's VLTInterferometer (VLTI). We also present reprocessed archive data obtainedwith the FLUOR/IOTA instrument on ζ Gem, in order to improve thephase coverage of our observations. We obtain average limb darkenedangular diameter values of /line{θLD}[X Sgr] = 1.471± 0.033 mas, /line{θLD[η Aql] = 1.839± 0.028 mas, /line{θLD}[W Sgr] = 1.312 ±0.029 mas, /line{θLD}[β Dor] = 1.891 ±0.024 mas, /line{θLD}[ζ Gem] =1.747 ±0.061 mas, /line{θLD}[Y Oph] = 1.437 ± 0.040mas, and /line{θLD}[ℓ Car] = 2.988 ± 0.012mas. For four of these stars, η Aql, W Sgr, β Dor, and ℓCar, we detect the pulsational variation of their angular diameter. Thisenables us to compute directly their distances, using a modified versionof the Baade-Wesselink method: d[η Aql] =276+55-38 pc, d[W Sgr] =379+216-130 pc, d[β Dor] =345+175-80 pc, d[ℓ Car] =603+24-19 pc. The stated error bars arestatistical in nature. Applying a hybrid method, that makes use of theGieren et al. (\cite{gieren98}) Period-Radius relation to estimate thelinear diameters, we obtain the following distances (statistical andsystematic error bars are mentioned): d[X Sgr] = 324 ± 7 ±17 pc, d[η Aql] = 264 ± 4 ± 14 pc, d[W Sgr] = 386± 9 ± 21 pc, d[β Dor] = 326 ± 4 ± 19pc, d[ζ Gem] = 360 ± 13 ± 22 pc, d[Y Oph] = 648± 17 ± 47 pc, d[ℓ Car] = 542 ± 2 ± 49pc.Tables 3 to 10 are only available in electronic form athttp://www.edpsciences.org
| Tests of stellar model atmospheres by optical interferometry. VLTI/VINCI limb-darkening measurements of the M4 giant ψ Phe
We present K-band interferometric measurements of the limb-darkened (LD)intensity profile of the M 4 giant star ψ Phoenicis obtained withthe Very Large Telescope Interferometer (VLTI) and its commissioninginstrument VINCI. High-precision squared visibility amplitudes in thesecond lobe of the visibility function were obtained employing two 8.2 mUnit Telescopes (UTs). This took place one month after light from UTswas first combined for interferometric fringes. In addition, we sampledthe visibility function at small spatial frequencies using the 40 cmtest siderostats. Our measurement constrains the diameter of the star aswell as its center-to-limb intensity variation (CLV). We construct aspherical hydrostatic PHOENIX model atmosphere based onspectrophotometric data from the literature and compare its CLVprediction with our interferometric measurement. We compare as well CLVpredictions by plane-parallel hydrostatic PHOENIX, ATLAS 9, and ATLAS 12models. We find that the Rosseland angular diameter as predicted bycomparison of the spherical PHOENIX model with spectrophotometry is ingood agreement with our interferometric diameter measurement. The shapeof our measured visibility function in the second lobe is consistentwith all considered PHOENIX and ATLAS model predictions, and issignificantly different to uniform disk (UD) and fully darkened disk(FDD) models. We derive high-precision fundamental parameters for ψPhe, namely a Rosseland angular diameter of 8.13 ± 0.2 mas, withthe Hipparcos parallax corresponding to a Rosseland linear radius R of86 ± 3 Rȯ, and an effective temperature of 3550± 50 K, with R corresponding to a luminosity of \logL/Lȯ=3.02 ± 0.06. Together with evolutionarymodels, these values are consistent with a mass of 1.3 ± 0.2Mȯ, and a surface gravity of \log g = 0.68 ±0.11.Based on public data released from the European Southern ObservatoryVLTI obtained from the ESO/ST-ECF Science Archive Facility. The VLTI wasoperated with the commissioning instrument VINCI and the MONA beamcombiner.
| The spinning-top Be star Achernar from VLTI-VINCI
We report here the first observations of a rapidly rotating Be star,alpha Eridani, using Earth-rotation synthesis on the Very LargeTelescope (VLT) Interferometer. Our measures correspond to a 2a/2b =1.56+/-0.05 apparent oblate star, 2a and 2b being the equivalent uniformdisc angular diameters in the equatorial and polar direction.Considering the presence of a circumstellar envelope (CSE) we argue thatour measurement corresponds to a truly distorted star since alphaEridani exhibited negligible Hα emission during theinterferometric observations. In this framework we conclude that thecommonly adopted Roche approximation (uniform rotation and centrallycondensed mass) should not apply to alpha Eridani. This result opensnew perspectives to basic astrophysical problems, such as rotationallyenhanced mass loss and internal angular momentum distribution. Inaddition to its intimate relation with magnetism and pulsation, rapidrotation thus provides a key to the Be phenomenon: one of theoutstanding non-resolved problems in stellar physics.
| A catalogue of calibrator stars for long baseline stellar interferometry
Long baseline stellar interferometry shares with other techniques theneed for calibrator stars in order to correct for instrumental andatmospheric effects. We present a catalogue of 374 stars carefullyselected to be used for that purpose in the near infrared. Owing toseveral convergent criteria with the work of Cohen et al.(\cite{cohen99}), this catalogue is in essence a subset of theirself-consistent all-sky network of spectro-photometric calibrator stars.For every star, we provide the angular limb-darkened diameter, uniformdisc angular diameters in the J, H and K bands, the Johnson photometryand other useful parameters. Most stars are type III giants withspectral types K or M0, magnitudes V=3-7 and K=0-3. Their angularlimb-darkened diameters range from 1 to 3 mas with a median uncertaintyas low as 1.2%. The median distance from a given point on the sky to theclosest reference is 5.2degr , whereas this distance never exceeds16.4degr for any celestial location. The catalogue is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/183
| CHARM: A Catalog of High Angular Resolution Measurements
The Catalog of High Angular Resolution Measurements (CHARM) includesmost of the measurements obtained by the techniques of lunaroccultations and long-baseline interferometry at visual and infraredwavelengths, which have appeared in the literature or have otherwisebeen made public until mid-2001. A total of 2432 measurements of 1625sources are included, along with extensive auxiliary information. Inparticular, visual and infrared photometry is included for almost allthe sources. This has been partly extracted from currently availablecatalogs, and partly obtained specifically for CHARM. The main aim is toprovide a compilation of sources which could be used as calibrators orfor science verification purposes by the new generation of largeground-based facilities such as the ESO Very Large Interferometer andthe Keck Interferometer. The Catalog is available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/386/492, and from theauthors on CD-Rom.
| 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).
| Spectral Irradiance Calibration in the Infrared. X. A Self-Consistent Radiometric All-Sky Network of Absolutely Calibrated Stellar Spectra
We start from our six absolutely calibrated continuous stellar spectrafrom 1.2 to 35 μm for K0, K1.5, K3, K5, and M0 giants. These wereconstructed as far as possible from actual observed spectral fragmentstaken from the ground, the Kuiper Airborne Observatory, and the IRAS LowResolution Spectrometer, and all have a common calibration pedigree.From these we spawn 422 calibrated ``spectral templates'' for stars withspectral types in the ranges G9.5-K3.5 III and K4.5-M0.5 III. Wenormalize each template by photometry for the individual stars usingpublished and/or newly secured near- and mid-infrared photometryobtained through fully characterized, absolutely calibrated,combinations of filter passband, detector radiance response, and meanterrestrial atmospheric transmission. These templates continue ourongoing effort to provide an all-sky network of absolutely calibrated,spectrally continuous, stellar standards for general infrared usage, allwith a common, traceable calibration heritage. The wavelength coverageis ideal for calibration of many existing and proposed ground-based,airborne, and satellite sensors, particularly low- tomoderate-resolution spectrometers. We analyze the statistics of probableuncertainties, in the normalization of these templates to actualphotometry, that quantify the confidence with which we can assert thatthese templates truly represent the individual stars. Each calibratedtemplate provides an angular diameter for that star. These radiometricangular diameters compare very favorably with those directly observedacross the range from 1.6 to 21 mas.
| 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.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| The position corrections of 1400 stars observed with PA II in San Juan.
Not Available
| Second astrolabe catalogue of Santiago.
Positions for 350 FK5 and 164 FK5 Extension stars as determined with theDanjon astrolabe of Santiago and differences astrolabe-catalogue aregiven for Equinox J2000.0 and for the mean observation epoch of eachstar. The average mean error in alpha is +/-0.005s and +/-0.07" indelta. The mean epoch of observation of the catalogue is J1979.96.
| Improved Mean Positions and Proper Motions for the 995 FK4 Sup Stars not Included in the FK5 Extension
Not Available
| A list of MK standard stars
Not Available
| The Perkins catalog of revised MK types for the cooler stars
A catalog is presented listing the spectral types of the G, K, M, and Sstars that have been classified at the Perkins Observatory in therevised MK system. Extensive comparisons have been made to ensureconsistency between the MK spectral types of stars in the Northern andSouthern Hemispheres. Different classification spectrograms have beengradually improved in spite of some inherent limitations. In thecatalog, the full subclasses used are the following: G0, G5, G8, K0, K1,K2, K3, K4, K5, M0, M1, M2, M3, M4, M5, M6, M7, and M8. Theirregularities are the price paid for keeping the general scheme of theoriginal Henry Draper classification.
| 1988 Revised MK Spectral Standards for Stars GO and Later
Not Available
| 1985 revised MK spectral standards : stars GO and later
Not Available
| Astrometric constants for 18 Pup, BD +44 1847, Lal 26325,G 137-8 and selected reference stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978AJ.....83..305R&db_key=AST
| A Luminosity Index for Bright K0-K5 Stars
Not Available
| Narrow-Band and Broad-Band Photometry of Red Stars. III. Southern Giants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970ApJ...161..199E&db_key=AST
| BVRI Photoelectric Photometry for 275 Stars located between -25° y -50° Fotometría Fotoeléctrica en BVRI para 275 estrellas comprendidas en su mayoría entre -25° y -50°
BYRI photometry in Johnson's system was done for 275 stars the mayority ofwhich are comprised between -25° and -50°. Due to systematicvariations in V magnitude in R. A. of the order of 0.2 magnitude it wasdecided to use in the present work V magnitudes of the Catalogue of theRoyal Observatory, Cape of Good Hope, South Africa. The colours presentedhere, should permit to have an homogeneous R and I Systems of photometryfor both the Northern and Southern sky, complete to the fifth magnitude, anup to -50° in declination
| Stellar groups, VI. Space motions of the dwarf A-type and giant M-type stars in the solar neighbourhood
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1960MNRAS.120..448E&db_key=AST
| Lichtelektrische Flächenphotometrie der Magellanschen Wolken. I. Die Kleine Magellansche Wolke. Mit 4 Textabbildungen
Not Available
| Summary of the parallaxes of 130 stars.
Not Available
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Pozíciós és asztrometriai adatok
| Csillagkép: | Főnix |
| Rektaszcenzió: | 02h01m42.40s |
| Deklináció: | -44°42'49.0" |
| Vizuális fényesség: | 5.14 |
| Távolság: | 114.155 parszek |
| RA sajátmozgás: | -32.1 |
| Dec sajátmozgás: | -48.5 |
| B-T magnitude: | 7.088 |
| V-T magnitude: | 5.313 |
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INHABITED SKY
