Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
Lithium abundances and rotational behavior for bright giant stars
Aims.We study the links possibly existing between the lithium content ofbright giant stars and their rotational velocity. Methods: .Weperformed a spectral analysis of 145 bright giant stars (luminosityclass II) spanning the spectral range from F3 to K5. All these starshave homogeneous rotational velocity measurements available in theliterature. Results: .For all the stars of the sample, we provideconsistent lithium abundances (A_Li), effective temperatures (T_eff),projected rotational velocity (v sin i), mean metallicity ([Fe/H]),stellar mass, and an indication of the stellar multiplicity. The gradualdecrease in lithium abundance with T_eff is confirmed for bright giantstars, and it points to a dilution factor that is at least assignificant as in giant stars. From the F to K spectral types, the A_Lispans at least three orders of magnitude, reflecting the effects ofstellar mass and evolution on dilution. Conclusions: .We find thatthe behavior of A_Li as a function of v sin i in bright giant starspresents the same trend as is observed in giants and subgiants: starswith high A_Li are moderate or fast rotators, while stars with low A_Lishow a wide range of v sin i values.
| 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
| 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 catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| DDO photometry of E-region stars and equatorial standards - II
This paper deals with the observations of 72 of McClure's equatorialstandard stars, made with the same photometer and DDO filters as wereused for the E-region stars in Cousins' Paper I in order to standardizethe observations. These observations were reduced in the natural systemand later transformed into McClure's system. Zero-point ties between theequatorial and E-region stars were also needed to standardize the lattersystem. With the exception of C(38-41), our photometry agrees as wellwith McClure's standard system as his own observations do, but both showsome small, apparently systematic, differences which are almostinevitable with a system like the DDO unless the response functions arevery well matched. Comparisons with 17 of Dean's measurements ofE-region stars show good agreement (~2 mmag) for the averagedzero-points, but there are small colour differences affecting C(35-38)and C(38-41) because of differences between the filters and thereduction procedures. This paper also deals with several problems in theDDO photometry that have implications for precision photometry ingeneral.
| The photoelectric astrolabe catalogue of Yunnan Observatory (YPAC).
The positions of 53 FK5, 70 FK5 Extension and 486 GC stars are given forthe equator and equinox J2000.0 and for the mean observation epoch ofeach star. They are determined with the photoelectric astrolabe ofYunnan Observatory. The internal mean errors in right ascension anddeclination are +/- 0.046" and +/- 0.059", respectively. The meanobservation epoch is 1989.51.
| Hybrid stars and the reality of "dividing lines" among G to K bright giants and supergiants.
We present results of pointed ROSAT PSPC observations of 15 hybridstars/candidates, which have been analyzed in a homogenous way. 7 ofthese stars were observed in X-rays for the first time. 12 out of 15hybrid stars have been detected as X-ray sources, some of them close tothe detection limit. We conclude that essentially all hybrid stars asdefined by the simultaneous presence of transition region line emissionand cool stellar winds are X-ray sources if exposed sufficiently deep.The X-ray luminosities of hybrid stars cover a range between 2x10^27^and ~10^30^erg/s. Their X-ray surface fluxes can be as low as =~20erg/cm^2^/s and thus considerably lower than those of normal luminosityclass (LC) III giants. X-ray spectra of hybrid stars tend to be harderthan that of normal LC III giants, moreover, the X-ray brightest starshave the hardest spectra. We find that for K II giants the normalizedX-ray flux versus C IV flux obeys a power law with an exponent a=2.9,steeper than among normal giants (1.5). Hybrid K II stars are X-rayunderluminous by a factor of 5 to 20 compared to LC III giants at thesame level of normalized CIV flux f_CIV_/f_bol_; hybrid G supergiantsare even more X-ray deficient. We reanalyze the CaII wind dividing lineand find it vertical at B-V=1.45 for LC III giants. It is nearlyhorizontal between B-V=1.45 and 1.0 (at M_bol_=~-2...-3), and not welldefined for supergiants with B-V<1.0. We therefore suggest thatpossibly all LC II and Ib G and K giants are hybrid stars and that the"dividing line" concept in its simplest form is not valid for G/K giantsbrighter than M_bol_=~-2. Hybrid stars are supposed to be evolvedintermediate mass stars and their coronal activity may in principle bedetermined by the individual history of each star.
| 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.
| Evolved GK stars near the Sun. 2: The young disk population
From a sample of nearly 2000 GK giants a group of young disk stars withwell determined space motions has been selected. The zero point of theluminosity calibrations, both from the ultraviolet flux (modifiedStroemgren system) and that in the region of 4200 to 4900 A (DDOsystem), show a discontinuity of about a half magnitude at the border ofthe young disk and old disk domains. The population separation is basedon the space velocity components, which are also an age discriminant,with the population interface near 2 x 109 yr, based onmodels with convective overshoot at the core. This age corresponds togiant masses near 1.7 solar mass, near the critical mass separating theyoung stars that do not burn helium in degenerate cores from older starsthat do. Ten percent of both populations show CN anomalies in that thederived value of P(Fe/H) from CN (Cm) and fromFe(M1) differ by more than 0.1 dex and the weak and strong CNstars occur equally in the old disk but the weak CN stars predominate inthe young disk. Peculiar stars, where flux distortions affect theluminosity calibrations, are of the CH+(Ba II) and CH-(weak G band)variety and represent less than 1% of the stars in both populations. Theyoung disk giants are restricted to ages greater than about109 yr, because younger stars are bright giants orsupergiants (luminosity class 2 or 1), and younger than about 2 x109 yr, because the old disk-young disk boundary occurs near1.7 solar mass. The distribution of heavy element abundances, P(Fe/H),for young disk giants is both more limited in range (+/- 0.4 dex) and isskewed toward higher abundances, compared with the nearly normaldistribution for old disk giants. The distribution of (U,V) velocityvectors gives (U,V,W) and their dispersions = (+17.6 +/- 18.4, -14.8 +/-8.4, -6.9 +/- 13.0) and (+3.6 +/- 38.4, -20.7 +/- 27.5, -6.7 +/-17.3)km/s for young and old disk giants, respectively.
| A CaII and MgII luminosity/emission-width data base.
The so-called Wilson-Bappu relationship (hereinafter W-B) is anempirical linear relation established in 1957. Formally simple, thisrelation links two observable parameters of a star: the CaII K line coreemission width with the absolute magnitude of the star havingchromospheric activity. Other Luminosity/Emission-width relationshipswere established on the basis of other chromospheric lines like MgII(2795.5A and 2802.7A) and Lyα (1215.9A). All these resonance linesare used as a diagnostic of physical properties of stellarchromospheres. We have reanalysed all the available data connected withthe CaII K and the MgII k line widths in the literature from 1957 untiltoday to be able to prepare a database containing all the essentialinformation needed to study and to understand empirical stellar activityrelationships.
| Spectral classifications in the near infrared of stars with composite spectra. I. The study of MK standards.
Up to now the spectral classifications of the cool components ofcomposite spectra obtained in the 3800-4800A wavelength region have beenvery disparate. These disparities are due to the fact that the spectraof the evolved cool component are strongly veiled by that of the hotterdwarf component, which makes a classification very difficult. We proposeto study these systems in the near infrared (8380-8780A). In thisspectral domain the magnitude difference between the spectra of thecomponents is in general sufficiently large so that one observespractically only the spectrum of the cool component. In this first paperwe provide, for a sample of MK standards, the relations between theequivalent width (Wlambda_ ) of certain lines and thespectral classifications. For the cool G, K and M type stars, the linesconsidered are those of the calcium triplet (Ca II 8498, 8542 and 8662),of iron (Fe I 8621 and 8688), of titanium (Ti I 8426 and 8435) and ofthe blend λ8468. The use of certain line intensity ratiospermits, after eliminating partially the luminosity effects, a firstapproach to the spectral type. For the hotter stars of types O, B, A andF we study the behavior of the hydrogen lines (P12 and P14), the calciumlines (Ca II 8498 and 8542) as well as those of the oxygen (O I 8446).The latter line presents a very characteristic profile for stars of lowrotation and therefore in Am stars, which are frequently found among thecomposite spectrum binaries. Among the cooler stars of our sample, only6% present real anomalies with respect to the MK classifications. Thisresult is very encouraging for undertaking the classification of asample of composite spectra. The spectra were taken at the Observatoirede Haute-Provence (OHP) with the CARELEC spectrograph at the 193 cmtelescope, with a dispersion of 33 A/mm.
| Photometry of F-K type bright giants and supergiants. I - Intermediate band and H-Beta observations
Over 1500 observations of 560 bright giants and supergiants of types F-Kare presented and compared to the observations by Gray and Olsen (1991).The present results include intermediate-band which is slightlydifferent from the Stromgren data by Gray and Olsen due to a differentwidth for the v filter. A systematic difference in m(1) - M(1) withdecreasing temperature is noted in the two H-Beta data sets, and thecorrelations are defined.
| A critical appraisal of published values of (Fe/H) for K II-IV stars
'Primary' (Fe/H) averages are presented for 373 evolved K stars ofluminosity classes II-IV and (Fe/H) values beween -0.9 and +0.21 dex.The data define a 'consensus' zero point with a precision of + or -0.018 dex and have rms errors per datum which are typically 0.08-0.16dex. The primary data base makes recalibration possible for the large(Fe/H) catalogs of Hansen and Kjaergaard (1971) and Brown et al. (1989).A set of (Fe/H) standard stars and a new DDO calibration are given whichhave rms of 0.07 dex or less for the standard star data. For normal Kgiants, CN-based values of (Fe/H) turn out to be more precise than manyhigh-dispersion results. Some zero-point errors in the latter are alsofound and new examples of continuum-placement problems appear. Thushigh-dispersion results are not invariably superior to photometricmetallicities. A review of high-dispersion and related work onsupermetallicity in K III-IV star is also given.
| CA II H and K measurements made at Mount Wilson Observatory, 1966-1983
Summaries are presented of the photoelectric measurements of stellar CaII H and K line intensity made at Mount Wilson Observatory during theyears 1966-1983. These results are derived from 65,263 individualobservations of 1296 stars. For each star, for each observing season,the maximum, minimum, mean, and variation of the instrumental H and Kindex 'S' are given, as well as a measurement of the accuracy ofobservation. A total of 3110 seasonal summaries are reported. Factorswhich affect the ability to detect stellar activity variations andaccurately measure their amplitudes, such as the accuracy of the H and Kmeasurements and scattered light contamination, are discussed. Relationsare given which facilitate intercomparison of 'S' values with residualintensities derived from ordinary spectrophotometry, and for convertingmeasurements to absolute fluxes.
| Groups of stars with common motion in the Galaxy - Groups of red supergiants of the luminosity classes I and II
Not Available
| High-resolution spectroscopic survey of 671 GK giants. I - Stellar atmosphere parameters and abundances
A high-resolution spectroscopic survey of 671 G and K field giants isdescribed. Broad-band Johnson colors have been calibrated againstrecent, accurate effective temperature, T(eff), measurements for starsin the range 3900-6000 K. A table of polynomial coefficients for 10color-T(eff) relations is presented. Stellar atmosphere parameters,including T(eff), log g, Fe/H, and microturbulent velocity, are computedfor each star, using the high-resolution spectra and various publishedphotometric catalogs. For each star, elemental abundances for a varietyof species have been computed using a LTE spectrum synthesis program andthe adopted atmosphere parameters.
| Mass-losing M supergiants in the solar neighborhood
A list of the 21 mass-losing red supergiants (20 M type, one G type; Lgreater than 100,000 solar luminosities) within 2.5 kpc of the sun iscompiled. These supergiants are highly evolved descendants ofmain-sequence stars with initial masses larger than 20 solar masses. Thesurface density is between about 1 and 2/sq kpc. As found previously,these stars are much less concentrated toward the Galactic center thanW-R stars, which are also highly evolved massive stars. Although withconsiderable uncertainty, it is estimated that the mass return by the Msupergiants is somewhere between 0.00001 and 0.00003 solar mass/sq kpcyr. In the hemisphere facing the Galactic center there is much less massloss from M supergiants than from W-R stars, but, in the anticenterdirection, the M supergiants return more mass than do the W-R stars. Theduration of the M supergiant phase appears to be between 200,000 and400,000 yr. During this phase, a star of initially at least 20 solarmasses returns perhaps 3-10 solar masses into the interstellar medium.
| Large and Kinematically Unbiased Samples of G- and K-Type Stars. III. Evolved Young Disk Stars in the Bright Star Sample
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1989PASP..101...54E&db_key=AST
| Large and kinematically unbiased samples of G- and K-type stars. II - Observations of evolved stars in the Bright Star sample. III - Evolved young disk stars in the Bright Star sample
Four color and RI observations were obtained for a large sample ofG-type and K-type stars in the Bright Star Catalogue. Data are firstpresented for 110 evolved stars. Photometry of evolved young diskpopulation stars have then been calibrated for luminosity, reddening,and metallicity on the basis of results for members of the Hyades andSirius superclusters. New DDO results are given for 120 stars.
| A list of MK standard stars
Not Available
| Energy Distribution in the Stellar Spectra of Different Spectral Types and Luminosities - Part Five - Normal Stars
Not Available
| Red horizontal-branch stars in the galactic disk
A quantitative, three-dimensional spectral classification systemdeveloped by Rose (1984), which uses 2.5-A resolution spectra in theblue, has been used to identify a class of red horizontal branch (RHB)stars in the Galactic disk that are similar to those in the 'metal rich'globular cluster M 71. The RHB are denoted as evolved stars by their SrII 4077 line, and are distinguished from post-main sequence starsevolving through the same region of the HR diagram on the basis of theunique appearance of their CN 3883 and 4216 A bands. The RHB starsconsitute at least 5 percent of the entire giant branch population ofthe disk.
| UBV Photometry of Equatorial Stars
Not Available
| 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.
| The reddening, metal abundance, and luminosity of high-luminosity G-type stars
The abundance parameters of the sample of 100 G-type bright giants andsupergiants whose photometry is presently discussed indicate Fe/H valuesof between about + 0.6 dex and the solar value, using a preliminarycalibration of the photometric indices. The few long period Cepheidsthat are not heavily blanketed F-type stars give reddening values thatare in agreement with current results from other methods of analysis.Supergiants show no clear gradients in the galactic distribution ofabundances, and those nearest the sun range from an Fe/H of about + 0.3dex, for members of the Pleiades Group, to near solar abundance. A smallsample of Large Magellanic Cloud supergiants shows nearly the same rangein metal abundance as the galactic stars, and gives a modulus for thisCloud of 18.3 + or - 0.20 mag.
| Magnetic structure in cool stars. VI - CA II H and K fluxes from evolved stars
Quantitative measurements of the Ca II H and K flux of 335 evolved starsare presented and discussed. The results show that there is a largespread in the fluxes from stars with (B-V) less than 0.95 while the CaII H and K flux of single stars with (B-V) greater than 0.95 correlateswith color with little spread. Short-period binaries show a relativelyhigh Ca II H and K flux indicating that high fluxes result from rapidrotation independent of spectral type. The data are consistent with thehypothesis that the emission depends on dynamo action in the convectiveenvelope, the dynamo efficiency decreasing with decreasing rotationrate. The evolution of the emission is discussed as a function ofstellar mass. It is shown that stars which leave the main sequence withrelatively low or high rotational velocities show relatively low or highemission values, respectively. The flux lasts up to higher (B-V) valuesfor progressively higher masses.
| A photoelectric measurement of magnesium for late-type stars
A photoelectric index of MgH + Mg b for late-type stars has been createdby the addition of one filter bandpass to the DDO system. Measurementsshow that this index has good sensitivity to surface gravity for Kstars, and suggest that it can differentiate metal-poor halo giants fromdisk stars. From this index, involving measurement through two filtersalone, it appears that membership can be determined for stars on thegiant branch of globular clusters. It is possible that the index couldbe used, after calibration with cluster giants, to determine ages ofgiant stars in the field.
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Единорог |
| Прямое восхождение: | 06h27m13.80s |
| Склонение: | +00°17'57.0" |
| Видимая звёздная величина: | 5.2 |
| Расстояние: | 291.545 парсек |
| Собственное движение RA: | 1.3 |
| Собственное движение Dec: | -10 |
| B-T magnitude: | 6.708 |
| V-T magnitude: | 5.318 |
Каталоги и обозначения:
|
INHABITED SKY
