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Публикации по объекту
Predicting accurate stellar angular diameters by the near-infrared surface brightness technique
I report on the capabilities of the near-infrared (near-IR) surfacebrightness technique to predict reliable stellar angular diameters asaccurate as <~2 per cent using standard broad-band Johnson photometryin the colour range -0.1 <= (V-K)O<= 3.7 includingstars of A, F, G, K spectral type. This empirical approach is fast toapply and leads to estimated photometric diameters in very goodagreement with recent high-precision interferometric diametermeasurements available for non-variable dwarfs and giants, as well asfor Cepheid variables. Then I compare semi-empirical diameters predictedby model-dependent photometric and spectrophotometric (SP) methods withnear-IR surface brightness diameters adopted as empirical referencecalibrators. The overall agreement between all these methods is withinapproximately +/-5 per cent, confirming previous works. However, on thesame scale of accuracy, there is also evidence for systematic shiftspresumably as a result of an incorrect representation of the stellareffective temperature in the model-dependent results. I also comparemeasurements of spectroscopic radii with near-IR surface brightnessradii of Cepheids with known distances. Spectroscopic radii are found tobe affected by a scatter as significant as >~9 per cent, which is atleast three times greater than the formal error currently claimed by thespectroscopic technique. In contrast, pulsation radii predicted by theperiod-radius (PR) relation according to the Cepheid period result aresignificantly less dispersed, indicating a quite small scatter as aresult of the finite width of the Cepheid instability strip, as expectedfrom pulsation theory. The resulting low level of noise stronglyconfirms our previous claims that the pulsation parallaxes are the mostaccurate empirical distances presently available for Galactic andextragalactic Cepheids.
| Analysis of the Na, Mg, Al, and Si Abundances in the Atmospheres of Red Giants of Different Spectral Subgroups
We analyze the Na, Mg, Al, and Si abundances in the atmospheres of morethan 40 stars, includingred giants of different spectral subgroups(normal red giants, mild and classical barium stars) and severalsupergiants. All these elements exhibit abundance excesses, with theoverabundance increasing with the star’s luminosity. Thedependence of the overabundances for each of these elements on theluminosity (or log g) is the same for all the spectral subgroups,testifying to a common origin: they are all products of hydrogen burningin the NeNa and MgAl cycles that have been dredged up from the stellarinteriors to the outer atmospheric layers by convection that graduallydevelops during the star’s evolution from the main sequence to thered-giant stage. The sodium abundances derived for several stars arelower than for other stars with similar atmospheric parameters. The agesand kinematic characteristics of these two groups of stars suggest thatthey probably belong to different stellar generations.
| 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
| Improved Baade-Wesselink surface brightness relations
Recent, and older accurate, data on (limb-darkened) angular diameters iscompiled for 221 stars, as well as BVRIJK[12][25] magnitudes for thoseobjects, when available. Nine stars (all M-giants or supergiants)showing excess in the [12-25] colour are excluded from the analysis asthis may indicate the presence of dust influencing the optical andnear-infrared colours as well. Based on this large sample,Baade-Wesselink surface brightness (SB) relations are presented fordwarfs, giants, supergiants and dwarfs in the optical and near-infrared.M-giants are found to follow different SB relations from non-M-giants,in particular in V versus V-R. The preferred relation for non-M-giantsis compared to the earlier relation by Fouqué and Gieren (basedon 10 stars) and Nordgren et al. (based on 57 stars). Increasing thesample size does not lead to a lower rms value. It is shown that theresiduals do not correlate with metallicity at a significant level. Thefinally adopted observed angular diameters are compared to thosepredicted by Cohen et al. for 45 stars in common, and there isreasonable overall, and good agreement when θ < 6 mas.Finally, I comment on the common practice in the literature to average,and then fix, the zero-point of the V versus V-K, V versus V-R and Kversus J-K relations, and then rederive the slopes. Such a commonzero-point at zero colour is not expected from model atmospheres for theV-R colour and depends on gravity. Relations derived in this way may bebiased.
| Determination of fundamental characteristics for stars of the F, G, and K spectral types. The surface gravities and metallicity parameters.
Not Available
| Analysis of Atmospheric Abundances in Classical Barium Stars
We present our analysis of elemental abundances in the atmospheres of 16classical barium stars derived from high-resolution spectra and modelatmospheres. Comparison of the results with analogous data for moderatebarium stars and normal red giants shows that the abundance patterns forelements before the iron peak are the same for all three groups of redgiants, testifying to a similar origin. For binary systems, we confirmthe influence of the orbital period and, hence, the componentseparation, on the overabundance of s-process elements. The amount ofenrichment in s-process elements is also influenced by mass,metallicity, and evolutionary phase. Any of these parameters can beimportant in individual objects.
| Synthetic Lick Indices and Detection of α-enhanced Stars. II. F, G, and K Stars in the -1.0 < [Fe/H] < +0.50 Range
We present an analysis of 402 F, G, and K solar neighborhood stars, withaccurate estimates of [Fe/H] in the range -1.0 to +0.5 dex, aimed at thedetection of α-enhanced stars and at the investigation of theirkinematical properties. The analysis is based on the comparison of 571sets of spectral indices in the Lick/IDS system, coming from fourdifferent observational data sets, with synthetic indices computed withsolar-scaled abundances and with α-element enhancement. We useselected combinations of indices to single out α-enhanced starswithout requiring previous knowledge of their main atmosphericparameters. By applying this approach to the total data set, we obtain alist of 60 bona fide α-enhanced stars and of 146 stars withsolar-scaled abundances. The properties of the detected α-enhancedand solar-scaled abundance stars with respect to their [Fe/H] values andkinematics are presented. A clear kinematic distinction betweensolar-scaled and α-enhanced stars was found, although a one-to-onecorrespondence to ``thin disk'' and ``thick disk'' components cannot besupported with the present data.
| Angular Diameters of Stars from the Mark III Optical Interferometer
Observations of 85 stars were obtained at wavelengths between 451 and800 nm with the Mark III Stellar Interferometer on Mount Wilson, nearPasadena, California. Angular diameters were determined by fitting auniform-disk model to the visibility amplitude versus projected baselinelength. Half the angular diameters determined at 800 nm have formalerrors smaller than 1%. Limb-darkened angular diameters, effectivetemperatures, and surface brightnesses were determined for these stars,and relationships between these parameters are presented. Scatter inthese relationships is larger than would be expected from themeasurement uncertainties. We argue that this scatter is not due to anunderestimate of the angular diameter errors; whether it is due tophotometric errors or is intrinsic to the relationship is unresolved.The agreement with other observations of the same stars at the samewavelengths is good; the width of the difference distribution iscomparable to that estimated from the error bars, but the wings of thedistribution are larger than Gaussian. Comparison with infraredmeasurements is more problematic; in disagreement with models, coolerstars appear systematically smaller in the near-infrared than expected,warmer stars larger.
| 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.
| Absolute spectrophotometry of late-type stars.
Not Available
| A Comparative Analysis of Chemical Abundances in the Atmospheres of Red Giants of Different Age Groups
We analyze previously published chemical abundances in the atmospheresof red giants. Excess abundances are observed not only for Na, but alsofor Al and Si, with the overabundances increasing with the stars’luminosity. The observed anomalies provide evidence that, in addition tothe CNO hydrogen-burning cycle, the Mg-Al and Ne-Na cycles operate inthe interiors of main-sequence stars; their products are brought to thestellar atmospheres by convection after the transition to the red-giantphase. The abundance anomalies for s-process elements, also observed inthe atmospheres of field stars, testify to the presence of a substantialnumber of neutrons. The s-process abundance anomalies are absent fromgiants of the young Hyades cluster.
| 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
| 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
| Composite spectraPaper 10: the equal-mass binary HR 2030 (K0IIb+B8IV)
We separate the spectra of the individual components of HR 2030, asixth-magnitude composite-spectrum binary system, and show that theyhave types close to K0IIb and B8IV, and masses that are equal to withinthe precision of the measurements (mass ratio=1.00+/-0.03). The orbitappears to have a very small eccentricity, although reasons are givenfor believing that such eccentricity is spurious; it has a period of 66dand an inclination estimated at 30° to the line of sight. Ourphotometric model of the system confirms the luminosity types derivedfrom the spectra and indicates an interstellar absorption of 0.4mag, inaccord with the observed strength of the interstellar K line. We derivethe physical parameters (Teff, Mbol, R, L) of thecomponents, and calculate that the mass of each star is close to4.0Msolar. We further show that the hot component(R=5.9+/-0.6Rsolar) has already evolved to a positionsignificantly above the zero-age main sequence (ZAMS), and we proposethat the primary (R=41+/-5Rsolar) is making its first ascentof the red-giant branch. From comparisons with evolutionary tracks, wededuce that the age of the binary (since its arrival at the ZAMS) is inthe range 1-2×108yr. While we suspect that thecomponents are sufficiently close for some tidal distortion to occur,the effects are not discernible in our data owing to the rather loworbital inclination. The system shows Sii in emission as a result ofirradiation of the primary by the hot secondary, but in the opticalspectrum we see little other clear evidence of interaction between thecomponents even though the object has a relatively short period and is astrong X-ray source. On the other hand, Hipparcos photometry suggeststhe existence of a major non-uniformity of the surface of the primarystar.
| Ultraviolet Emission Lines in BA and Non-BA Giants
With the Hubble Space Telescope (HST) and the Goddard High ResolutionSpectrograph we have observed four barium and three weak barium stars inthe ultraviolet spectral region, together with two nonpeculiar giantstandard stars. An additional suspected Ba star was observed with HSTand the Space Telescope Imaging Spectrograph. In the H-R diagram, threeof the observed Ba stars lie on the same evolutionary tracks as theHyades giants. Using International Ultraviolet Explorer (IUE) spectra ofpreviously studied giants together with our HST spectra, we investigatewhether the chromospheric and transition layer emission-line spectra ofthe Ba stars are different from those of nonpeculiar giants and fromthose of giants with peculiar carbon and/or nitrogen abundances. Exceptfor the Ba star HD 46407 and the suspected Ba star HD 65699, the Ba starand mild Ba star emission-line fluxes are, for a given effectivetemperature and for a given luminosity, lower than those for thenonpeculiar giants observed with IUE. In comparison with theHST-observed standard stars, the C IV λ1550-to-C II λ1335line flux ratios are smaller, but not necessarily so in comparison withall IUE-observed nonpeculiar giants. However, the C IV-to-C II line fluxratios for the Ba stars decrease with increasing carbon abundances. Thisshows that the energy balance in the lower transition layer isinfluenced by the carbon abundance. The temperature gradient appears tobe smaller in the C II line-emitting region. There does not seem to be adifference in chromospheric electron densities for the Ba and non-Bastars, though this result is rather uncertain. Based on observationswith the NASA/ESA Hubble Space Telescope obtained at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy, Inc., under NASA contract NAS 5-26555.
| Do All BA II Stars Have White Dwarf Companions?
With the Hubble Space Telescope (HST) and the Goddard High ResolutionSpectrograph (GHRS) we have observed four barium stars, three mildbarium stars, and one weak G-band star in the ultraviolet spectralregion. One barium star was observed with HST and the Space TelescopeImaging Spectrograph (STIS). The aim was to check the hypothesis thatall these peculiar stars have white dwarf (WD) companions, which attheir asymptotic giant branch phase transferred mass with peculiarelement abundances to the present barium and CH peculiar stars. Assumingthat the ultraviolet continua of the cool giants, including the bariumstars, are generated in their chromospheres and that the relationsbetween the continua and the emission lines created in the chromospheresand transition layers are similar in field giants and barium stars, wefound that, indeed, most of our target barium and weak barium starsappear to have excess flux in the UV when compared to standard giantstars. For most of the stars the excess flux can be attributed to WDcompanions with temperatures between 10,000 and 12,000 K, if the WD massis about 0.6 Msolar. Cooling times for the WDs were derivedfrom their effective temperatures and model calculations by M. Wood. Thecalculated cooling times are longer than the lifetimes of the bariumstars on the giant branch. For our target stars the mass transfertherefore happened while they were still on the main sequence. For twoof the mild barium stars and one or perhaps two barium stars the derivedcooling times for the WD companions come out to be longer than the totalevolutionary times of the barium stars as calculated by Schaller et al.If our derivations are correct (the error bars are rather large) theneither evolutionary models with larger convective overshoot have to beused for the barium stars or the cooling times of the white dwarfs haveto be revised downward. Possibly an additional (as yet unknown) coolingmechanism has to be considered? The weak G-band star HD 165634, whichhas a carbon underabundance of about a factor of 10, also appears tohave a WD companion. We discuss the implications of this very low carbonabundance. Based on observations with the NASA/ESA Hubble SpaceTelescope obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy.Incorporated, under NASA contract NAS5-26555.
| Magnitudes absolues des étoiles standards MK des types G à M à partir des parallaxes Hipparcos. The absolute magnitudes of the G to M type MK standards from the Hipparcos parallaxes
We analyse a sample of about 500 MK standards of cool spectral types (Gto M) for to compare the visual absolute magnitudes obtained from bothHipparcos data and Schmidt-Kaler calibrations. Our purpose is tovalidate our spectroscopic work \cite[(Ginestet et al. 1997, 1999)]{G97}on stars with composite spectra with the help of Hipparcos data.Contrary to what is claimed in other papers, the absolute magnitudedomain devoted to the giant stars does not overlap the domain of dwarfs.We find that the discrepancies between absolute magnitudes fromHipparcos data and absolute magnitudes deduced from Schmidt-Kalercalibrations increase with the relative error sigma (pi )/pi on theparallaxes. So, for sigma (pi )/pi <= 0.05 only 3% of the starspresent a discrepancy of one luminosity class, while this percentagereaches 54% for 0.25 < sigma (pi )/pi <= 0.50. Curiously, theluminosity of the giants seems to increase with the distance of thestars, whereas the supergiants of the sample appear underluminous atleast for d < 600 pc! We point out a list of 14 MK standards whoseluminosity classes may be erroneous and need a new spectralclassification, in the near infrared. The case of composite-spectrumbinaries is also discussed. Most of these are too distant for accurateparallaxes even with Hipparcos: only sixteen stars have sigma (pi )/pi<= 0.10; for these, we give new spectral classifications in agreementwith both our classifications in the near infrared of the coolcomponents and Hipparcos data. Finally, for stars having high-precisionparallaxes (sigma (pi )/pi <= 5%) there is no serious problem forSchmidt-Kaler calibrations whith respect to Hipparcos data. The datacorresponding to parallaxes of lower precisions should be used withcaution and only for statistical analyses.
| Rotation and lithium in single giant stars
In the present work, we study the link between rotation and lithiumabundance in giant stars of luminosity class III, on the basis of alarge sample of 309 single stars of spectral type F, G and K. We havefound a trend for a link between the discontinuity in rotation at thespectral type G0III and the behavior of lithium abundances around thesame spectral type. The present work also shows that giant starspresenting the highest lithium contents, typically stars earlier thanG0III, are those with the highest rotation rates, pointing for adependence of lithium content on rotation, as observed for otherluminosity classes. Giant stars later than G0III present, as a rule, thelowest rotation rates and lithium contents. A large spread of about fivemagnitudes in lithium abundance is observed for the slow rotators.Finally, single giant stars with masses 1.5 < M/Msun<=2.5 show a clearest trend for a correlation between rotational velocityand lithium abundance. Based on observations collected at theObservatoire de Haute -- Provence (France) and at the European SouthernObservatory, La Silla (Chile). Table 2 is only available electronicallywith the On-Line publication athttp://link.springer.de/link/service/00230/
| Fundamental properties of the open cluster NGC 2355
NGC 2355 is an old open cluster in the outer part of the galactic disk(l=203fdg4 , b=+11fdg8 ) which has been little studied until now. Thispaper presents the first astrometric and spectroscopic investigation ofthis cluster. We have measured precise absolute proper motions from oldCarte du Ciel plates, POSS-I plates and recent CCD observations obtainedwith the Bordeaux meridian circle. The proper motion data reveal 38highly probable cluster members down to Blim = 15 mag within7' of the cluster center. We have also obtained ELODIE high resolutionspectra for 24 stars. Seventeen of them are confirmed to be members ofthe cluster on the basis of radial velocity. Eight of them are fastrotating turnoff stars for which the projected rotational velocity hasbeen determined. The spectroscopic observations have also providedestimates of the physical parameters Teff, log g, {[Fe/H]},MV of the 24 target stars. Two stragglers have beenidentified in the cluster. Combining our astrometric and spectroscopicresults with previous UBV photometry and recent JHK_s photometry fromthe 2MASS survey we have derived the fundamental properties of thecluster: metallicity, age, distance, size, spatial velocity and orbit.Based on observations made on the 193cm telescope at the Haute-ProvenceObservatory, France, and on plate digitisation at the Centre d'Analysedes Images, Paris. This publication makes use of data products from theTwo Micron All Sky Survey, which is a joint project of the University ofMassachusetts and the Infrared Processing and Analysis Center, funded bythe National Aeronautics and Space Administration and the NationalScience Foundation.
| A new abundance analysis of the super-metal-rich K2 giant, mu Leonis
Spectra of the super-metal-rich K2 giant, mu Leonis, have been recordedat high resolution (lambda /Delta lambda =~ 105) and withsignal/noise =~ 200, in selected regions between 5250 and 8810 Ä.An LTE model atmospheres analysis of these spectra, with particularattention to blending by CN molecular lines, suggests that the wings ofstrong lines and the full profiles of intermediate strength lines areconsistent with the following atmospheric parameters and logarithmicabundances, relative to the Sun: T_eff = 4540+/- 50 K, log g = 2.2+/-0.1 dex, Microturbulence, xi = 1.2+/- 0.1 km s-1,Macroturbulence/rotation, zeta = 2.9+/- 0.2 km s-1, [Fe/H] =+0.29+/- 0.03 dex ~(relative to epsilon (Fe)sun = 7.50),[Ca/H] = +0.32+/- 0.05 dex ~(relative to epsilon (Ca)sun =6.36), [Mg/H] = +0.32+/- 0.05 dex ~(relative to epsilon(Mg)sun = 7.58). In view of the continuing controversy overthe extent to which mu Leo is metal rich, we provide a critical reviewof other recent metallicity determinations and compare the presentresults with our own analyses, undertaken using essentially identicalmethods, of the spectra of other late-type giant stars in the solarneighbourhood.
| Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over more than twocenturies and summarized in the FK5. Part I of the FK6 (abbreviatedFK6(I)) contains 878 basic fundamental stars with direct solutions. Suchdirect solutions are appropriate for single stars or for objects whichcan be treated like single stars. From the 878 stars in Part I, we haveselected 340 objects as "astrometrically excellent stars", since theirinstantaneous proper motions and 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,199 of the stars in Part I 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(I) proper motion in the single-star mode is 0.35 mas/year. This isabout a factor of two better than the typical HIPPARCOS errors for thesestars of 0.67 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(I) proper motions have atypical mean error of 0.50 mas/year, which is by a factor of more than 4better than the corresponding error for the HIPPARCOS values of 2.21mas/year (cosmic errors included).
| Non-LTE analysis of the atmospheric sodium abundances of peculiar disk stars
High-resolution CCD spectra are used to determine the sodium abundancesin the atmospheres of 12 peculiar disk stars with sodium excesses,taking into account deviations from local thermodynamic equilibrium. Insome cases, the non-LTE corrections reach 0.2 dex, and it is necessaryto calculate them in each individual case. On average, however, themagnitude of these corrections does not exceed 0.1 dex, and the sodiumexcesses for most of the stars are not eliminated by taking thesecorrections into account.
| 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.
| A catalog of rotational and radial velocities for evolved stars
Rotational and radial velocities have been measured for about 2000evolved stars of luminosity classes IV, III, II and Ib covering thespectral region F, G and K. The survey was carried out with the CORAVELspectrometer. The precision for the radial velocities is better than0.30 km s-1, whereas for the rotational velocity measurementsthe uncertainties are typically 1.0 km s-1 for subgiants andgiants and 2.0 km s-1 for class II giants and Ib supergiants.These data will add constraints to studies of the rotational behaviourof evolved stars as well as solid informations concerning the presenceof external rotational brakes, tidal interactions in evolved binarysystems and on the link between rotation, chemical abundance and stellaractivity. In this paper we present the rotational velocity v sin i andthe mean radial velocity for the stars of luminosity classes IV, III andII. Based on observations collected at the Haute--Provence Observatory,Saint--Michel, France and at the European Southern Observatory, LaSilla, Chile. Table \ref{tab5} also available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Catalogs of temperatures and [Fe/H] averages for evolved G and K stars
A catalog of mean values of [Fe/H] for evolved G and K stars isdescribed. The zero point for the catalog entries has been establishedby using differential analyses. Literature sources for those entries areincluded in the catalog. The mean values are given with rms errors andnumbers of degrees of freedom, and a simple example of the use of thesestatistical data is given. For a number of the stars with entries in thecatalog, temperatures have been determined. A separate catalogcontaining those data is briefly described. Catalog only available atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| A comparative high-resolution spectroscopic study of the Hyades giants gamma Tauri and epsilon Tauri
Spectra of the Hyades K0 giants gamma Tau and epsilon Tau in the regions5852-5864 Ä,and 6145-6176 Ä,have been recorded at highresolution and with signal/noise in the range 150-250. A criticalcomparison reveals that, although nearly all lines in the observedregions have a similar depth, lines of epsilon Tau are broader by about10% than those of gamma Tau. An LTE analysis indicates that slightlyhigher turbulent broadening in epsilon Tau can account for the observeddifferences in line-width. Study of two particularly temperaturesensitive features confirms earlier observations that the effectivetemperature of epsilon Tau is less than that of gamma Tau and determinesthe temperature difference to be 80 +/- 20 K.
| Stellar atmospheric parameters for the giant stars MU Pegasi and lambda Pegasi
Profiles of the strong lines Ca II 8542 Angstroms, and Mg I 8806Angstroms, together with regions containing Ca I, Fe I and Fe II linesin the spectra of the G8 giant stars mu Peg and lambda Peg have beenrecorded at high resolution and with signal/noise >= 100. The wingsof the strong lines and the full profiles of intermediate strength linesare consistent with an LTE analysis based on the following sets ofatmospheric parameters: star name star name mu Peg lambda Peg T_eff (K)5000 \pm 50 4800 \pm 50 \log g (g in cm s^{-2}) 2.6 \pm 0.1 1.7 \pm 0.1[M/H] -0.1 \pm 0.05 -0.1 \pm 0.05 Microturbulence, \xi(km s^{-1}) 1.4\pm 0.1 1.8 \pm 0.2 Macroturbulence, \zeta(km s^{-1}) 3.00 \pm 0.13 7.6\pm 0.5$ These results, together with Hipparcos parallaxes and recentlypublished photometry, lead to estimates of luminosity, mass and radius.Inferred angular diameters are consistent with a well establishedempirical relationship but disagree with direct measurements by aninterferometric technique.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| 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.
| CA II K Emission Line Asymmetries Among Red Giants
In the spectra of red giants the chromospheric emission feature found inthe core of the Ca II K line often exhibits an asymmetric profile. Thisasymmetry can be documented by a parameter V/R which is classified as> 1, 1, or < 1 if the violet wing of the emission profile is ofgreater, equal, or lower intensity than the redward wing. A literaturesearch has been conducted to compile a V/R dataset which builds on thelarge survey of bright field giants made by Wilson (1976). Among starsof luminosity classes II-III-IV the majority of those with V/R > 1are found to be bluer than B-V =1.3, while those with V/R < 1 aremostly redder than this colour. Stars with nearly symmetric profiles,V/R≈ 1, are found throughout the colour range 0.8 < B-V < 1.5.There is no sharp transition line separating stars of V/R > 1 and< 1 in the colour-magnitude diagram, but rather a `transition zone'centered at B-V ≈ 1.3. The center of this zone coincides closely witha `coronal dividing line' identified by Haish, Schmitt and Rosso (1991)as the red envelope in the H-R diagram of giants detected in soft x-rayemission by ROSAT. It is suggested that both the transition to a Ca II Kemission asymmetry of V/R < 1 and the drop in soft x-ray activityacross the coronal dividing line are related to changes in the dynamicalstate of the chromospheres of red giants. By contrast, the onset ofphotometric variability due to pulsation occurs among stars of early-Mspectral type, that are redward of the mid-point of the Ca II V/R`transition zone', suggesting that the chromospheric motions whichproduce an asymmetry of V/R < 1 are established prior to the onset ofpulsation.
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Пегас |
| Прямое восхождение: | 22h46m31.90s |
| Склонение: | +23°33'56.0" |
| Видимая звёздная величина: | 3.95 |
| Расстояние: | 121.065 парсек |
| Собственное движение RA: | 0 |
| Собственное движение Dec: | 0 |
| B-T magnitude: | 5.325 |
| V-T magnitude: | 4.068 |
Каталоги и обозначения:
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