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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
| 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
| J - K DENIS photometry of a VLTI-selected sample of bright southern stars
We present a photometric survey of bright southern stars carried outusing the DENIS instrument equipped with attenuating filters. Theobservations were carried out not using the survey mode of DENIS, butwith individual target pointings. This project was stimulated by theneed to obtain near-infrared photometry of stars to be used in earlycommissioning observations of the ESO Very Large TelescopeInterferometer, and in particular to establish a network of brightcalibrator sources.We stress that near-infrared photometry is peculiarly lacking for manybright stars. These stars are saturated in 2MASS as well as in regularDENIS observations. The only other observations available for brightinfrared stars are those of the Two Micron Sky Survey dating from overthirty years ago. These were restricted to declinations above≈-30°, and thus cover only about half of the sky accessible fromthe VLTI site.We note that the final 2MASS data release includes photometry of brightstars, obtained by means of point-spread function fitting. However, thismethod only achieves about 30% accuracy, which is not sufficient formost applications.In this work, we present photometry for over 600 stars, each with atleast one and up to eight measurements, in the J and K filters. Typicalaccuracy is at the level of 0\fm05 and 0\fm04 in the J and K_s bands,respectively.Based on observations collected at the European Southern Observatory, LaSilla.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/413/1037
| 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
| 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.
| X-ray and optical monitoring of the peculiar source 4U 1700+24/V934 Her
We report on ASCA and BeppoSAX X-ray broad band observations of thegalactic low-luminosity X-ray source 4U 1700+24 performed on 1995 and1998, respectively, and on (quasi-)simultaneous ground observations ofits optical counterpart, V934 Her, from the Loiano 1.5-meter telescope.In order to better understand the nature of the source we also analyzepublic archival ROSAT and RXTE data as well as the RXTE ASM light curveof 4U 1700+24; we also re-analyze a 1985 EXOSAT pointing. The opticalspectra are typical of a M2 III star; this allows us to determine arevised distance to the object of ~ 400 pc. While these spectra do notshow either any spectral change between the two epochs or any peculiarfeature apart from those observed in normal red giants, thespectroscopic measurements carried out in X-rays reveal a complex andlong-term variable spectrum, with a clear soft excess. The X-rayspectral properties of the source are best described by a thermalComptonization spectrum plus a soft energy (<1 keV) excess, which canbe modeled in the form of a blackbody emission with kT_BB ~ 1 keV; thelatter component is not detected at the lowest source flux levels. Theratio between the two components varies substantially with the sourceflux. The X-ray emission from the object appears to become harder as itsluminosity increases: indeed, the RXTE data acquired during an outburstoccurred in October-November 1997 display a hard tail, detected up to100 keV and modeled with a comptonizing cloud which is hotter and lessopaque than that seen in the low intensity state. Apart from erraticshot-noise variability on timescales of tens to thousands of seconds, nosignificant properties (such as pulsations or QPOs) are found from thetiming analysis of the X-ray light curves extracted from theobservations presented here. With the new distance determination, the2-10 keV X-ray luminosity range spanned in the considered observationslies between ~ 2x1032 and ~ 1x1034 ergs-1. All this information, combined with the findings byother authors, allows us to suggest that the scenario which bestdescribes the object consists of a wide binary system in which a neutronstar accretes matter from the wind of a M-type giant star. Implicationsof such a model are discussed. Partly based on observations collected atthe Bologna Astronomical Observatory in Loiano, Italy.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable 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/qcar?J/A+A/367/521
| On the Variability of K5-M Stars
I investigate the Hipparcos Satellite photometry of K5-M stars to seethe pattern of activity of these stars. A few stars for which furtherstudy is desirable are identified.
| Photometric Separation of Stellar Properties Using SDSS Filters
Using synthetic photometry of Kurucz model spectra, we explore thecolors of stars as a function of temperature, metallicity, and surfacegravity with Sloan Digital Sky Survey (SDSS) filters, u'g'r'i'z'. Thesynthetic colors show qualitative agreement with the few publishedobservations in these filters. We find that the locus of synthetic starsis basically two-dimensional for 4500 < T < 8000 K, whichprecludes simultaneous color separation of the three basic stellarcharacteristics we consider. Colors including u' contain the mostinformation about normal stellar properties; measurements in this filterare also important for selecting white dwarfs. We identify two differentsubsets of the locus in which the loci separate by either metallicity orsurface gravity. For 0.5 < g' - r' < 0.8 (corresponding roughly toG stars), the locus separates by metallicity; for photometric error of afew percent, we estimate metallicity to within ~0.5 dex in this range.In the range -0.15 < g' - r' < 0.00 (corresponding roughly to Astars), the locus shows separation by surface gravity. In both cases, weshow that it is advantageous to use more than two colors whendetermining stellar properties by color. Strategic observations in SDSSfilters are required to resolve the source of a ~5% discrepancy betweensynthetic colors of Gunn-Stryker stars, Kurucz models, and externaldeterminations of the metallicities and surface gravities. The syntheticstar colors can be used to investigate the properties of any normal starand to construct analytic expressions for the photometric prediction ofstellar properties in special cases.
| 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.
| Radii and Effective Temperatures for K and M Giants and Supergiants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.1705D&db_key=AST
| 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.
| Theoretical colours and isochrones for some Hubble Space Telescope colour systems. II
A grid of synthetic surface brightness magnitudes for 14 bandpasses ofthe Hubble Space Telescope Faint Object Camera is presented, as well asa grid of UBV, uvby, and Faint Object Camera surface brightnessmagnitudes derived from the Gunn-Stryker spectrophotometric atlas. Thesynthetic colors are used to examine the transformations between theground-based Johnson UBV and Stromgren uvby systems and the Faint ObjectCamera UBV and uvby. Two new four-color systems, similar to theStromgren system, are proposed for the determination of abundance,temperature, and surface gravity. The synthetic colors are also used tocalculate color-magnitude isochrones from the list of theoretical tracksprovided by VandenBerg and Bell (1990). It is shown that by using theappropriate filters it is possible to minimize the dependence of thiscolor difference on metallicity. The effects of interstellar reddeningon various Faint Object Camera colors are analyzed as well as theobservational requirements for obtaining data of a given signal-to-noisefor each of the 14 bandpasses.
| Third list of corrections to the identifications of IRAS sources in Astron. & Astrophys Suppl. 65, 607 and Astron. J. 98, 931
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.
| Lunar occultations of IRAS point sources, 1991-2000
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1989ApJS...69..651C&db_key=AST
| Energy Distribution in the Stellar Spectra of Different Spectral Types and Luminosities - Part Five - Normal Stars
Not Available
| A Catalog of Stellar Angular Diameters Measured by Lunar Occultation
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987AJ.....94..751W&db_key=AST
| 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.
| The Wolf 630 moving group of stars
An analysis is made of the probability of collective membership of thestars assigned by Eggen to the Wolf 630 moving group. This probabilityis estimated from the scatter of points in the color-absolute magnitudediagram when compared to the intrinsic scatter observed for M67.Particular attention is paid to the random errors for all the observedand deduced stellar parameters. Results show that either theobservational errors must be about 2.4 times larger than given in theproper motion and radial velocity source catalogues, or the intrinsicscatter in the color-magnitude diagram for the Wolf 630 group must bemuch larger than for M67, or many of the stars considered cannot bemembers.
| Stellar spectrophotometric atlas, wavelengths from 3130 to 10800 A
Over the course of the past 10 years, a large body of homogeneousspectrophotometric data on relatively bright stars has been gathered toserve as a library with which to synthesize galaxy spectra in populationstudies. As the data might be generally useful, they are presented inthree tables. One hundred seventy-five (175) stars were selected, mostfrom the Navy photometric catalog. Covered are complete ranges ofspectral type and luminosity class. Normalized spectral energydistributions of these stars in pictorial form are provided along withtables of calculated colors, scan line and continuum indices, and someinformation on the relation of the scan colors to real photometricsystems.
| Angular diameters by the lunar occultation technique. V - 26 late-type stars
Near-infrared occultation observations have yielded 37 new angulardiameter measurements for 26 late-type stars. The list includes threecarbon stars and five giants in the range M4-M8. A multichannelphotometer has been tested successfully on five events.
| Photoelectric observations of lunar occultations. XII
Occultation observations of 414 events observed between 6 July 1979 and4 September 1980 with the 0.76-m telescope of McDonald Observatory arereported. Timings and data on double stars are given. Angular diameterinformation in six cases is included. The stars concerned with their runnumbers are: SAO 161754 (5270); 94027 (Alpha Tau) (5319, 5381, 5454);159370 (Gamma Lib) (5325, 5571); 162413 (43 Sgr) (5332); 97472 (3 Cnc)(5414); and 93955 (Theta Tau) (5445).
| Old disk subdwarfs
Measurements of CaH and TiO band strengths are presented for M dwarfs ofthe old disk population which lie below the main sequence. Their bandstrengths imply a composition intermediate between that of halosubdwarfs and that of disk dwarfs.
| A sample of old-disk-population red giants.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976PASP...88..426E&db_key=AST
| Narrow-and broad-band photometry of red stars. VI. Luminosities and temperatures for old disk-population red stars of high luminosity
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971ApJ...165..317E&db_key=AST
| Stellar Groups in the Old Disk Population
Not Available
| Three-color photometry of the components in 228 wide double and multiple systems.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1963AJ.....68..483E&db_key=AST
| Radial Velocities of 360 Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1952ApJ...115..157W&db_key=AST
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Datos observacionales y astrométricos
| Constelación: | Libra |
| Ascensión Recta: | 15h57m05.21s |
| Declinación: | -16°02'03.9" |
| Magnitud Aparente: | 6.575 |
| Distancia: | 252.525 parsecs |
| Movimiento Propio en Ascensión Recta: | 8.2 |
| Movimiento Propio en Declinación: | -34.5 |
| B-T magnitude: | 8.918 |
| V-T magnitude: | 6.769 |
Catálogos y designaciones:
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