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Galactic Cepheids. II. Lithium
We report on the discovery of two lithium Cepheids in the Galaxy, basedon observations made with the echelle spectrograph of the Apache PointObservatory. We have used high-resolution, high signal-to-noise ratiospectra to determine abundances of chemical elements in 16 classicalCepheids. Only two of our program stars show a lithium line, RX Aur andYZ Aur (RX Aur has been also classified by us as a new nonradialpulsator). For the others, including the stars with [N/C]<0.2, Li isdepleted up to logN(Li)<1.0. Hence, it appears that mixing depletesLi before stars enter the instability strip. According to stellarmodels, the main mixing event takes place when Teff dropsbelow 4000 K, which is outside the red edge of the instability strip;i.e., after stars have crossed the instability strip for the first time.
| A catalog of rotational and radial velocities for evolved stars. II. Ib supergiant stars
Rotational velocity vsin i and mean radial velocity are presented for asample of 231 Ib supergiant stars covering the spectral region F, G andK. This work is the second part of the large survey carried out with theCORAVEL spectrometer to establish the behavior of the rotation for starsevolving off the main sequence (De Medeiros & Mayor 1999). Thesedata will add constraints to the study of the rotational behavior inevolved stars, as well as solid information concerning tidalinteractions in binary systems and on the link between rotation,chemical abundance and activity in stars of intermediate masses. Basedon observations collected at the Haute-Provence Observatory,Saint-Michel, France and at the European Southern Observatory, La Silla,Chile Table 1 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/395/97
| The Lithium-rich supergiant HD172365
The F-type supergiant HD172365 was discovered by Luck (1982) to be ahigh Li abundance star. We find that the lithium abundance in this staris log A(Li) = 2.9 from a careful spectroscopic study. This value islarger than the abundance derived by Luck. We discuss the properties ofthis supergiant and tentatively conclude that HD172365 may, in fact, bea post-blue straggler star with a mass ~ 2 times greater than the"turn-off point" mass for the open cluster IC 4756, of which HD172365 isa member. The star is formed by a merger of a close binary system. Thisconclusion is supported by, for example, its large projected rotationalvelocity, solar carbon abundance and high lithium content.
| Colour excesses of F-G supergiants and Cepheids from Geneva photometry.
A reddening scale for F-G supergiants and Cepheids is presented.Supergiants with low reddenings or in clusters form the basis of thecalibration. In this sense, it is entirely empirical. The data have beenobtained in the Geneva photometric system. Comparisons with otherreddening scales show no disagreement. The only problem is with Fernie'sscale for Cepheids (1990), where a systematic trend exists. Its originis not clear. It is suggested to extend the number of supergiants withindependently obtained colour excesses in order to test the existence ofa possible luminosity dependence of the calibration. A period-colourrelation for Cepheids is deduced, on the basis of the present reddeningcorrections. It gives strong support for V473 Lyr being a secondovertone pulsator.
| 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.
| Supergiants and the Galactic metallicity gradient. II - Spectroscopic abundances for 64 distant F- to M-type supergiants
The metallicity gradient in the Galactic disk from in situ stars withvisual magnitude ranging from 6 to 10 is analyzed. Atmosphericparameters and detailed chemical abundances for 64 Population Isupergiants of spectral types F through M and luminosity classes Iathrough II have been determined. The derived Fe/H ratios ranging from-0.5 to + 0.7 show a mean value of +0.13 with an estimated uncertaintyof + or - 0.2. A subset of 25 supergiants fainter than 7th magnitudelying in the direction of the Galactic center shows a Fe/H mean of +0.18+ or - 0.04, while a similar sample of 15 faint supergiants lying in thedirection of the Galactic anticenter shows a lower Fe/H mean of +0.07 +or - 0.06. For a sample of bright supergiants analyzed by Luck andLambert (1985), the mean abundance pattern for all 64 stars showed thefollowing: deficient C and O along with enhancement of N, indicatingmixing of CNO-cycled material to the stellar surfaces; an apparent Srenhancement attributed to departures from LTE; and an essentially solarpattern of other chemical elements.
| Carbon, nitrogen, and oxygen in two lithium-rich supergiants
An analysis deriving CNO abundances for two lithium-rich supergiants (HR7008 and HD 174104) is presented. Lithium abundances are rederived usinghigh-resolution, high signal-to-noise ratio Reticon data. It is foundthat these stars do not have CNO abundances typical of othersupergiants, that is, processed through the CN cycle, nor do they havethe CNO content which would be expected if they were unprocessed stars.In HR 7008, Sigma CNO is enhanced relative to iron; whereas, in HD174104 Sigma CNO is deficient relative to iron. There is no knownscenario in stellar evolution which can explain these objects.
| Nineteen new spectroscopic binaries and the rate of binary stars among F-M supergiants
Nineteen spectroscopic binaries (SBs) have been discovered in radialvelocity measurements made with the CORAVEL spectrophotometer on 181northern F-M supergiants. The rate of detected SBs among northern F-Msupergiants is 21 percent, without any dependence on spectral orluminosity class. The study of the binary F-M supergiants with knownorbital elements indicates that all the systems with a period smallerthan the critical value P(circ) have a nearly circular orbit. The valueof P(circ) depends on the luminosity class, being 400-600 d for class Iband 2000-7000 d for class Ia. This circularization of the orbits may bedue to the transfer of angular momentum during the phase of binary massexchange.
| New UBVRI photometry for 900 supergiants
A description is presented of the results obtained in connection with asystematic program of supergiant photometry on the Johnson UBVRI system.During the eight years after the start of the program, almost 1000 starshave been observed, about 400 three or more times each. The originalselection of stars used the spectral type catalog of Jaschek et al.(1964) to choose supergiants. Since observations were possible from bothChile and Canada, no declination limits were imposed, and no particularselection criteria were imposed other than to eliminate carbon stars.These are so red as to require enormous extrapolations of thetransformation equations.
| Supergiants and the galactic metallicity gradient. I - 27 late-type supergiants in the inner-arm regions
From an analysis of high-dispersion Kitt Peak echelle data, atmosphericparameters and chemical abundances have been derived for 27 supergiantsof spectral type F through M. Since the stars studied lie within about 1kpc of the sun, their abundances will form the local reference point forextensions of this study to larger distances. The derived Fe/H abundanceratios range from minus 0.6 to plus 0.1 dex, show a mean value of -0.15dex, and have an internal uncertainty of plus or minus 0.2 dex.
| Two lithium-rich supergiants
Two extraordinary stars of type F and G are identified. These stars, HR7008 and HD 174104, have strong lithium doublets. A detailed analysisshows each to have the cosmic abundance of lithium. It is argued thatthey are unmixed stars on the redward approach to the first giantbranch.
| Photometric data for 139 supergiants.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972AJ.....77..150F&db_key=AST
| The space distribution and kinematics of supergiants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970AJ.....75..602H&db_key=AST
| Color Excesses from Six-Color Photometry of Supergiant Stars
Not Available
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Pozíciós és asztrometriai adatok
| Csillagkép: | Lant |
| Rektaszcenzió: | 18h47m44.16s |
| Deklináció: | +28°43'12.5" |
| Vizuális fényesség: | 8.36 |
| Távolság: | 2941.176 parszek |
| RA sajátmozgás: | -3 |
| Dec sajátmozgás: | -6.1 |
| B-T magnitude: | 9.232 |
| V-T magnitude: | 8.432 |
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