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Beta Lyr - eigentlich ein ideales Objekt auch fuer CCD.
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| Hypervelocity Stars. I. The Spectroscopic Survey
We discuss our targeted search for hypervelocity stars (HVSs), starstraveling with velocities so extreme that dynamical ejection from amassive black hole is their only suggested origin. Our survey, nowhalf-complete, has successfully identified a total of four probable HVSsplus a number of other unusual objects. Here we report the two mostrecently discovered HVSs: SDSS J110557.45+093439.5 and possibly SDSSJ113312.12+010824, traveling with Galactic rest-frame velocities atleast +508+/-12 and +418+/-10 km s-1, respectively. The otherlate B-type objects in our survey are consistent with a population ofpost-main-sequence stars or blue stragglers in the Galactic halo, withmean metallicity [Fe/H]Wk=-1.3 and velocitydispersion 108+/-5 km s-1. It is interesting to note that thevelocity distribution shows a tail of objects with large positivevelocities that may be a mix of low-velocity HVSs and high-velocityrunaway stars. Our survey also includes a number of DA white dwarfs withunusually red colors, possibly extremely low mass objects. Two of ourobjects are B supergiants in the Leo A dwarf, providing the firstspectroscopic evidence for star formation in this dwarf galaxy withinthe last ~30 Myr.
| Resolving the Effects of Rotation in Altair with Long-Baseline Interferometry
We report the successful fitting of a Roche model, with a surfacetemperature gradient following the von Zeipel gravity darkening law, toobservations of Altair made with the Navy Prototype OpticalInterferometer. We confirm the claim by Ohishi et al. that Altairdisplays an asymmetric intensity distribution due to rotation, the firstsuch detection in an isolated star. Instrumental effects due to the highvisible flux of this first magnitude star appear to be the limitingfactor in the accuracy of this fit, which nevertheless indicates thatAltair is rotating at 0.90+/-0.02 of its breakup (angular) velocity. Ourresults are consistent with the apparent oblateness found by van Belleet al. and show that the true oblateness is significantly larger owingto an inclination of the rotational axis of ~64° to the line ofsight. Of particular interest, we conclude that instead of beingsubstantially evolved as indicated by its classification, A7 IV-V,Altair is only barely off the zero-age main sequence and represents agood example of the difficulties rotation can introduce in theinterpretation of this part of the HR diagram.
| An Improved Infrared Passband System for Ground-based Photometry: Realization
We describe new simulations and field trials of the new infraredpassband system developed and discussed by Young, Milone, & Stagg,who discussed and illustrated the state of infrared photometry andsuggested ways in which it could be improved. In particular, theypresented a new set of passbands that minimize the dependence of thephotometry on the water vapor bands of the atmospheric windows, whichdefined the edges of many previous infrared passbands, especially whenused at sites and under conditions for which they were not designed. Inthis paper, we present numerical simulations for three atmosphericmodels, demonstrate a measure of the signal-to-noise ratio in the newpassbands for these models, and present observational data obtained at arelatively low-elevation site. The latter demonstrate the utility ofthis system for most astronomical sites where photometry can beperformed, and permit the transformation of observations to this system.Publications of the Rothney Astrophysical Observatory, No. 74.
| Antoine Darquier et la decouverte de la nebuleuse de la Lyre.
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| Infrared Photometry for Five Close Binary Systems
We present the JHKLM photometry for five close (W Ser) binary systemsobtained in the period 1996 2004. Positive phase shifts (with respect ofthe adopted ephemerides) have been found in the orbital infrared lightcurves for three binaries, RX Cas, KX And, and β Lyr; the rates ofincrease in their periods are 3.5 × 10-4, 1.6 ×10-3, and 1.4 × 10-4 days yr-1, respectively. We haveperformed the spectral classification of the components of the binariesunder study and estimated their parameters.
| 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
| The physical properties of normal A stars
Designating a star as of A-type is a result of spectral classification.After separating the peculiar stars from those deemed to be normal usingthe results of a century of stellar astrophysical wisdom, I define thephysical properties of the "normal" stars. The hotter A stars haveatmospheres almost in radiative equilibrium. In the A stars convectivemotions can be found which increase in strength as the temperaturedecreases.
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| The Compact H II Region S88B: Excitation and Extinction
We have undertaken an investigation into the excitation of, and dustextinction to, the massive star formation region S88B. Studying stellarproperties of the wide-field Two Micron All Sky Survey (2MASS) J (1.23μm), H (1.65 μm), and Ks (2.16 μm) images, we havedetermined the extent of, and extinction to, the molecular cloudassociated with the ultracompact H II regions S88B-1 and S88B-2 and witha newly described infrared H II region. Infrared observations ofBrγ and Brα hydrogen recombination lines provide extinctionmaps to the infrared H II region, and 3.3 and 3.4 μm images show thepolycyclic aromatic hydrocarbon (PAH) emission distribution. We alsoreport the detection of an infrared counterpart to S88B-2.
| STELIB: A library of stellar spectra at R ~ 2000
We present STELIB, a new spectroscopic stellar library, available athttp://webast.ast.obs-mip.fr/stelib. STELIB consists of an homogeneouslibrary of 249 stellar spectra in the visible range (3200 to 9500Å), with an intermediate spectral resolution (la 3 Å) andsampling (1 Å). This library includes stars of various spectraltypes and luminosity classes, spanning a relatively wide range inmetallicity. The spectral resolution, wavelength and spectral typecoverage of this library represents a substantial improvement overprevious libraries used in population synthesis models. The overallabsolute photometric uncertainty is 3%.Based on observations collected with the Jacobus Kaptein Telescope,(owned and operated jointly by the Particle Physics and AstronomyResearch Council of the UK, The Nederlandse Organisatie voorWetenschappelijk Onderzoek of The Netherlands and the Instituto deAstrofísica de Canarias of Spain and located in the SpanishObservatorio del Roque de Los Muchachos on La Palma which is operated bythe Instituto de AstrofÃsica de Canarias), the 2.3 mtelescope of the Australian National University at Siding Spring,Australia, and the VLT-UT1 Antu Telescope (ESO).Tables \ref{cat1} to \ref{cat6} and \ref{antab1} to A.7 are onlyavailable in electronic form at http://www.edpsciences.org. The StellarLibrary STELIB library is also available at the CDS, via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/402/433
| The latitude and epoch for the formation of the southern Greek constellations
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| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| The ever challenging emission-line binary beta Lyrae
A brief history of investigations of Lyr, an emission-line binary andone of the first ever discovered Be stars is presented. A rather fastprogress in the understanding of this enigmatic object during the pastfifteen years is then discussed in some detail. The current picture ofbeta Lyr is that it is an eclipsing binary in a stage of mass transferbetween the components. The mass-losing star is a B6-8II object, with amass of about 3 M(sun), which is filling the Roche lobe and sendingmaterial towards its more massive companion at a rate of about 2 ×10-5 M(sun) yr-1. This leads to the observed rapidincrease of the orbital period at a rate of 19 s per year. Themass-gaining star is as early B star with a mass of about 13 M(sun). Itis completely hidden inside an opaque accretion disk, jet-likestructures, perpendicular to the orbital plane and a light-scatteringhalo above the poles of the star. The observed radiation of the diskcorresponds to an effective temperature which is much lower than whatwould correspond to an early B star. The disk shields the radiation ofthe central star in the directions along the orbital plane andredistributes it in the directions perpendicular to it. That is why themass-losing star appears brighter of the two in the optical region ofthe spectrum. At present, rather reliable estimates of all basicproperties of the binary and its components are available. However, inspite of great progress in understanding the system in recent years,some disagreement between the existing models and observed phasevariations still variations still remains, both for continuum and linespectrum, which deserves further effort.
| Multiplicity among chemically peculiar stars. II. Cool magnetic Ap stars
We present new orbits for sixteen Ap spectroscopic binaries, four ofwhich might in fact be Am stars, and give their orbital elements. Fourof them are SB2 systems: HD 5550, HD 22128, HD 56495 and HD 98088. Thetwelve other stars are: HD 9996, HD 12288, HD 40711, HD 54908, HD 65339,HD 73709, HD 105680, HD 138426, HD 184471, HD 188854, HD 200405 and HD216533. Rough estimates of the individual masses of the components of HD65339 (53 Cam) are given, combining our radial velocities with theresults of speckle interferometry and with Hipparcos parallaxes.Considering the mass functions of 74 spectroscopic binaries from thiswork and from the literature, we conclude that the distribution of themass ratio is the same for cool Ap stars and for normal G dwarfs.Therefore, the only differences between binaries with normal stars andthose hosting an Ap star lie in the period distribution: except for thecase of HD 200405, all orbital periods are longer than (or equal to) 3days. A consequence of this peculiar distribution is a deficit of nulleccentricities. There is no indication that the secondary has a specialnature, like e.g. a white dwarf. Based on observations collected at theObservatoire de Haute-Provence (CNRS), France.Tables 1 to 3 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/394/151Appendix B is only available in electronic form athttp://www.edpsciences.org
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| On the effective temperatures and surface gravities of superficially normal main sequence band B and A stars
Effective temperatures and surface gravities for 48 main sequence band Band A stars were found by matching optical region spectrophotometry andHγ profiles with the predictions of ATLAS9 solar composition modelatmospheres. When these values were compared with those found usingStrömgren uvbybeta photometry based on ATLAS6 model atmospheres, wefound a difference (photometry-spectrophotometry) of 25+/- 118 K for 29stars with 8000 K le Teff <= 10 050 K compared to 76 +/-105 K for 14 stars with 10 050 K <= Teff <= 17 000 K.The surface gravity scales are in agreement. These stars aresufficiently hot that their effective temperatures and surface gravitydeterminations are unaffected by discrepancies due to the choice ofMixing-Length or Canuto-Mazzitelli convection theories.
| The ISO-SWS post-helium atlas of near-infrared stellar spectra
We present an atlas of near-infrared spectra (2.36 mu m-4.1 mu m) of ~300 stars at moderate resolution (lambda /delta lambda ~ 1500-2000). Thespectra were recorded using the Short-Wavelength Spectrometer aboard theInfrared Space Observatory (ISO-SWS). The bulk of the observations wereperformed during a dedicated observation campaign after the liquidhelium depletion of the ISO satellite, the so-called post-heliumprogramme. This programme was aimed at extending the MK-classificationto the near-infrared. Therefore the programme covers a large range ofspectral types and luminosity classes. The 2.36 mu m-4.05 mu m region isa valuable spectral probe for both hot and cool stars. H I lines(Bracket, Pfund and Humphreys series), He I and He II lines, atomiclines and molecular lines (CO, H2O, NH, OH, SiO, HCN,C2H2, ...) are sensitive to temperature, gravityand/or the nature of the outer layers of the stellar atmosphere(outflows, hot circumstellar discs, etc.). Another objective of theprogramme was to construct a homogeneous dataset of near-infraredstellar spectra that can be used for population synthesis studies ofgalaxies. At near-infrared wavelengths these objects emit the integratedlight of all stars in the system. In this paper we present the datasetof post-helium spectra completed with observations obtained during thenominal operations of the ISO-SWS. We discuss the calibration of the SWSdata obtained after the liquid helium boil-off and the data reduction.We also give a first qualitative overview of how the spectral featuresin this wavelength range change with spectral type. The dataset isscrutinised in two papers on the quantitative classification ofnear-infrared spectra of early-type stars ({Lenorzer} et al.\cite{lenorzer:2002a}) and late-type stars (Vandenbussche et al., inprep). Based on observations with ISO, an ESA project with instrumentsfunded by ESA Members States (especially the PI countries France,Germany, the Netherlands and the United Kingdom) and with theparticipation of ISAS and NASA. The full atlas is available inelectronic form at www.edpsciences.org Table 1 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?/A+A/390/1033
| 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.
| An atlas of 2.4 to 4.1 mu m ISO/SWS spectra of early-type stars
We present an atlas of spectra of O- and B-type stars, obtained with theShort Wavelength Spectrometer (SWS) during the Post-Helium program ofthe Infrared Space Observatory (ISO). This program is aimed at extendingthe Morgan & Keenan classification scheme into the near-infrared.Later type stars will be discussed in a separate publication. Theobservations consist of 57 SWS Post-Helium spectra from 2.4 to 4.1 μm, supplemented with 10 spectra acquired during the nominal mission witha similar observational setting. For B-type stars, this sample providesample spectral coverage in terms of subtype and luminosity class. ForO-type stars, the ISO sample is coarse and therefore is complementedwith 8 UKIRT Larcmin -band observations. In terms of the presence ofdiagnostic lines, the Larcmin -band is likely the most promising of thenear-infrared atmospheric windows for the study of the physicalproperties of B stars. Specifically, this wavelength interval containsthe Bralpha , Pfgamma , and other Pfund lines which are probes ofspectral type, luminosity class and mass loss. Here, we present simpleempirical methods based on the lines present in the 2.4 to 4.1 mu minterval that allow the determination of i) the spectral type of Bdwarfs and giants to within two subtypes; ii) the luminosity class of Bstars to within two classes; iii) the mass-loss rate of O stars and Bsupergiants to within 0.25 dex. Based on observations with ISO, an ESAproject with instruments funded by ESA Member States (especially the PIcountries: France, Germany, The Netherlands and the UK) and with theparticipation of ISAS and NASA. The appendix 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/384/473
| Der 8X50 Feldstecher ergantzt das Auge.
Not Available
| A Black Hole in the Superluminal Source SAX J1819.3-2525 (V4641 Sgr)
Spectroscopic observations of the fast X-ray transient and superluminaljet source SAX J1819.3-2525 (V4641 Sgr) reveal a best-fitting period ofPspect=2.81678+/-0.00056 days and a semiamplitude ofK2=211.0+/-3.1 km s-1. The optical mass functionis f(M)=2.74+/-0.12 Msolar. We find a photometric period ofPphoto=2.81730+/-0.00001 days using a light curve measuredfrom photographic plates. The folded light curve resembles anellipsoidal light curve with two maxima of roughly equal height and twominima of unequal depth per orbital cycle. The secondary star is a lateB-type star that has evolved off the main sequence. Using a moderateresolution spectrum (R=7000) we measure Teff=10500+/-200 K,logg=3.5+/-0.1, and Vrotsini=123+/-4 km s-1 (1σ errors). Assuming synchronous rotation, our measured value ofthe projected rotational velocity implies a mass ratio ofQ≡M1/M2=1.50+/-0.08 (1 σ). The lack ofX-ray eclipses implies an upper limit to the inclination of i<=70.7d.On the other hand, the large amplitude of the folded light curve (~0.5mag) implies a large inclination (i>~60deg). Using theabove mass function, mass ratio, and inclination range, the mass of thecompact object is in the range 8.73<=M1<=11.70Msolar and the mass of the secondary star is in the range5.49<=M2<=8.14 Msolar (90% confidence). Themass of the compact object is well above the maximum mass of a stableneutron star, and we conclude that V4641 Sgr contains a black hole. TheB-star secondary is by far the most massive, the hottest, and the mostluminous secondary of the dynamically confirmed black hole X-raytransients. We find that the α-process elements nitrogen, oxygen,calcium, magnesium, and titanium may be overabundant in the secondarystar by factors of 2-10 times with respect to the Sun. Finally, assumingE(B-V)=0.32+/-0.10, we find a distance 7.40<=d<=12.31 kpc (90%confidence). This large distance and the high proper motions observedfor the radio counterpart make V4641 Sgr possibly the most superluminalgalactic source known, with an apparent expansion velocity of >~9.5cand a bulk Lorentz factor of Γ>~9.5, assuming that the jetswere ejected during one of the bright X-ray flares observed with theRossi X-ray Timing Explorer. Based on observations collected at theEuropean Southern Observatory, Chile (program 65.H-0360) and the WilliamHerschel Telescope, operated on the island of La Palma by the IsaacNewton Group in the Spanish Observatorio del Roque de los Muchachos ofthe Instituto de Astrofisica de Canarias.
| Elemental abundance analyses with DAO spectrograms. XXV. The superficially normal B and A stars alpha Draconis, tau Herculis, gamma Lyrae, and HR 7926
Elemental abundances analyses of the superfically normal B and A starsalpha Dra (A0 III), tau Her (B5 IV), gamma Lyr (B9 III), and HR 7926 (B8II-III) are performed consistent with previous studies of this seriesusing spectrograms obtained with Reticon and CCD detectors. Comparisonsof the first two analyses with those of the same stars performed earlierin this series which used mostly coadded photographic plates show thegeneral consistency of the derived elemental abundances. A slightincrease in the adopted effective temperature produces a correspondingincrease in the derived abundances. In these stars the He/H ratios arefound to be close to solar. Except for gamma Lyr the metals show for themost part marginally subsolar abundance values. But this star has Al,Ca, Sc, and Sr abundances that are substantially underabundant as wellas other underabundant values. Table 5 is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/371/1078
| 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
| Research Note Hipparcos photometry: The least variable stars
The data known as the Hipparcos Photometry obtained with the Hipparcossatellite have been investigated to find those stars which are leastvariable. Such stars are excellent candidates to serve as standards forphotometric systems. Their spectral types suggest in which parts of theHR diagrams stars are most constant. In some cases these values stronglyindicate that previous ground based studies claiming photometricvariability are incorrect or that the level of stellar activity haschanged. Table 2 is 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/367/297
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| On the Variability of Late B III-V Stars
We investigate the Hipparcos Satellite photometry of luminosity classIII-V B6-B9 stars. Most are relatively non-variable. Candidates forwhich further study is desirable are identified.
| An analysis of the Johnson et al. Catalina UBVRI photometry for second order extinction effects.
Not Available
| Site characterisation for the IUCAA telescope
Not Available
| Stellar Angular Diameters of Late-Type Giants and Supergiants Measured with the Navy Prototype Optical Interferometer
We have measured the angular diameters of 50 F, G, K, and M giant andsupergiant stars using the Navy Prototype Optical Interferometer atwavelengths between 649 and 850 nm and using three baselines withlengths up to 37.5 m. Uniform-disk diameters, obtained from fits to thevisibility amplitude, were transformed to limb-darkened diametersthrough the use of limb-darkening coefficients for plane-parallelstellar atmosphere models. These limb-darkened diameters are comparedwith those measured with the Mark III optical interferometer and withthose computed by the infrared flux method. Sources of random andsystematic error in the observations are discussed.
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Datos observacionales y astrométricos
| Constelación: | Lira |
| Ascensión Recta: | 18h58m56.60s |
| Declinación: | +32°41'22.0" |
| Magnitud Aparente: | 3.24 |
| Distancia: | 194.553 parsecs |
| Movimiento Propio en Ascensión Recta: | -2.8 |
| Movimiento Propio en Declinación: | 1.7 |
| B-T magnitude: | 3.181 |
| V-T magnitude: | 3.217 |
Catálogos y designaciones:
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