目录
图像
上传图像
DSS Images Other Images
相关文章
Rotation and Lithium Surface Abundances, Revisited
For giants in the Hertzsprung gap, the relations betweenTeff, vsini, and lithium surface abundances arereinvestigated and compared with the relations found for Hyadesmain-sequence F stars. For the Hyades main-sequence F stars, the vsinidecrease steeply around Teff~6450 K. At the same temperaturethe lithium surface abundances show a narrow, deep dip. For most giantsthere is also a steep decrease of vsini for Teff around 6450K. At this temperature the lithium surface abundances of the giants alsodecrease steeply and remain low for Teff<6400 K. Thechanges in rotation and Li surface abundances occur over a temperatureinterval of less than 300 K, which for a 2 Msolar giantcorresponds to an age interval of about 106 yr. Thesimultaneous steep decreases of rotation velocities and Li surfaceabundances indicate that for the giants these changes are due to thesame cause, which we suggest to be deep mixing. It then seems ratherlikely that for the Hyades main-sequence F5 V stars the decrease ofrotation and Li surface abundance is also caused by deep mixing. Wesuggest that in both cases the changes are related to the merging of thehydrogen and helium convection zones.
| Spectral Classification of the Hot Components of a Large Sample of Stars with Composite Spectra, and Implication for the Absolute Magnitudes of the Cool Supergiant Components.
A sample of 135 stars with composite spectra has been observed in thenear-UV spectral region with the Aurélie spectrograph at theObservatoire de Haute-Provence. Using the spectral classifications ofthe cool components previously determined with near infrared spectra, weobtained reliable spectral types of the hot components of the samplesystems. The hot components were isolated by the subtraction methodusing MK standards as surrogates of the cool components. We also derivedthe visual magnitude differences between the components usingWillstrop's normalized stellar flux ratios. We propose a photometricmodel for each of these systems on the basis of our spectroscopic dataand the Hipparcos data. We bring to light a discrepancy for the Gsupergiant primaries between the visual absolute magnitudes deduced fromHipparcos parallaxes and those tabulated by Schmidt-Kaler for the GIbstars: we propose a scale of Mv-values for these stars incomposite systems. By way of statistics, about 75% of the hot componentsare dwarf or subgiant stars, and 25% should be giants. The distributionin spectral types is as follows: 41% of B-type components, 57% of typeA, and 2% of type F; 68% of the hot components have a spectral type inthe range B7 to A2. The distribution of the ΔMv-valuesshows a maximum near 0.75 mag.
| Speckle Observations of Composite Spectrum Stars with PISCO in 1993-1998
We present speckle interferometry observations of 47 composite spectrumstars obtained between 1993 and 1998 at the Pic du Midi Observatory withthe PISCO speckle camera. 76% of over 150 independent 10 minutesequences of observations led to a companion detection. Binary componentangular separations ranged from 0.05" to 1.2". We also obtained a seriesof 23 measurements of an additional nine close binaries. PISCOobservations confirm, for the first time since their discovery, theduplicity of HD 29104 (L4), HD 83808 (WGT 1Aa), HD 183912 Aa' (BON Ap),and HD 156729 (HR 6436). Discovered as double by Hipparcos, theparticularly difficult to resolve HD 156729 was observed despite thelarge magnitude difference, Δm=4.2, between its two components.Based on observations made with the Télescope Bernard Lyot at Picdu Midi Observatory, France.
| Spectral classifications in the near infrared of stars with composite spectra. III. Study of a sample of 137 objects with the Aurelie spectrograph
We provide spectral classifications for a sample of 137 stars mentionedas having composite spectra. The classifications were carried out on 33Angstroms /mm spectra in the region 8370 - 8870 Angstroms. Of these 137objects, 115 correspond in the infrared to cool stars (G, K or M) ofluminosity classes III, II and I; for 22 stars, we find only hot spectraof types B, A, F or Am, so that they do not fulfil our definition ofcomposite spectra. We detect four new Am stars, and one Am star (HD70826) turns out to be a composite spectrum object. As in Paper II, thecool components of composite spectra show a strong concentration in thevicinity of G8III. Based upon observations carried out at Observatoirede Haute-Provence (OHP).
| Spectral classifications in the near infrared of stars with composite spectra. II. Study of a sample of 180 stars
A sample of 180 supposedly composite-spectrum stars has been studied onthe basis of spectra obtained in the near infrared (8370-8780 Angstroms)at a dispersion of 33 Anstroms/mm. The objective was to study the coolercomponents of the systems. Of our sample, 120 are true compositespectra, 35 are hot spectra of types B, F and 25 are Am stars. We find astrong concentration of the cooler components of the composite spectraaround G8III. In view of the difficulty of classifying compositespectra, because of the super position of an early type dwarf and a latetype giant or supergiant spectrum, we have made several tests to controlthe classification based upon the infrared region. Since all tests gavepositive results, we conclude that our classifications can be consideredas being both reliable and homogeneous. Table \ref{tab1} is alsoavailable electronically at the CDS via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstracts.html} Based upon observationscarried out at Observatoire de Haute-Provence (CNRS).
| 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.
| The lithium content and other properties of F2-G5 giants in the Hertzsprung Gap
As stars of 2-5 solar mass evolve across the Hertzsprung Gap they shouldfirst deplete their surface lithium by convective dilution and then,when convection penetrates deeper, begin to bring CN processed materialto their surfaces. To investigate this process we have observed 52giants, 25 of which have known C/N ratios, for their Li abundances.After eliminating four stars that may actually be dwarfs and includingthe two components of Capella analyzed by Pilachowski and Sowell we havecompared our (Li/Fe) ratios with models of Swenson. For stars showing vsin i greater than 50 km/s we find (Li/Fe) to be unaffected by mixingfor B - V less than 0.7 as predicted. For stars cooler than B - V = 0.7both v sin i and (Li/Fe) drop to smaller values. For the sharp linedstars (v sin i less than 50 km/s) we find a drop in Li between B - V =0.45 and 0.60 which cannot be understood in terms of dilution byconvection. Various possible causes of such an early depletion ordilution of surface Li are discussed including diffusion at the base ofthe convection zone, mass loss possibly enhanced by pulsation, andmagnetic activity as in the magnetic A and B type stars. The models ofRicher & Michaud (1993) with diffusion point toward a satisfactorysolution. A few giants with low v sin i values stand out with muchhigher than expected (Li/Fe) values despite their cool effectivetemperatures. We do not understand why those stars have not depletedtheir lithium as have most giants of similar color. The correlation of(N/C) with (Li/Fe) follows expectations in so far as almost all starswith enhanced (N/C) have depleted their Li as well.
| All-sky Stromgren photometry of speckle binary stars
All-sky Stromgren photometric observations were obtained for 303 specklebinaries. Most stars were in the range of V = 5-8. These data, whencombined with ratios of intensities from the CHARA speckle photometryprogram, will allow the determination of photometric indices for theindividual components of binary stars with separations as small as 0.05arcsec. These photometric indices will complement the stellar massesfrom the speckle interferometry observations to provide a much improvedmass-luminosity relationship.
| Radial-velocity measurements. V - Ground support of the HIPPARCOS satellite observation program
The paper presents data on 1070 radial velocity measurements of starsdistributed in 39 fields measuring 4 deg x 4 deg. The PPO series ofFehrenbach et al. (1987) and Duflot et al. (1990) is continued using theFehrenbach objective prism method.
| Composite spectra. V - Orbital elements for 30 systems
A comprehensive survey of bright composite-spectrum binaries in thenorthern sky has provided so many radial-velocity data that orbits cannow be determined for many objects whose orbits were hitherto unknown orelse insecure or actually erroneous. Elements are given for the orbitsof 30 such objects, thereby more than doubling the number ofcomposite-spectrum binaries with known orbits.
| ICCD speckle observations of binary stars. II - Measurements during 1982-1985 from the Kitt Peak 4 M telescope
This paper represents the continuation of a systematic program of binarystar speckle interferometry initiated at the 4 m telescope on Kitt Peakin late 1975. Between 1975 and 1981, the observations were obtained witha photographic speckle camera, the data from which were reduced byoptical analog methods. In mid-1982, a new speckle camera employing anintensified charge-coupled device as the detector continued the programand necessitated the development of new digital procedures for reducingand analyzing speckle data. The camera and the data-processingtechniques are described herein. This paper presents 2780 newmeasurements of 1012 binary and multiple star systems, including thefirst direct resolution of 64 systems, for the interval 1982 through1985.
| Spectral classification of weak-lined stars discovered photometrically
A random sample of 140 stars of the 800+ members in Olsen's (1984)sample of stars believed to be weak-lined has been observed andclassified independently of knowledge of the stars' photometriccharacteristics. It is found that 97 percent of the proposed weak-lineddwarfs are indeed such; the remainder are composites or normal, moreluminous stars. Deficiencies in the metallic-line types are comparedwith (Fe/H) values and metallic strength indices. These comparisons showthat a metal deficiency of at least a factor of two is needed before thespectra look weak-lined.
| Binary stars unresolved by speckle interferometry. III
The KPNO's 4-m telescope was used in 1975-1981 to determine the epochsof 1164 speckle observations for 469 unresolved, known or suspectedbinary stars. The data, presented in tabular form, encompass visualbinaries with eccentric orbits, occultation binaries, astrometricbinaries, Hyades stars of known or suspected duplicity, and many longperiod spectroscopic binaries.
| Estimation of spectral classifications for bright northern stars with interesting Stromgren indices
The purpose of this investigation is to provide spectroscopic observerswith finding lists of potentially interesting objects. From anunpublished UVBY catalogue of 7026 northern stars (mostly brighter than8.3m) 1094 objects with interesting combinations of UVBY indices havebeen selected. Most stars with post-HD classifications have beenexcluded, as well as late F dwarfs belonging to the intermediatepopulation II. For the 792 remaining stars estimated spectralclassifications are given. The techniques and experience from a previouspaper dealing with southern stars have been utilized here. Among thepredicted spectral classifications are 40 OB stars; 262 Ap, Am, or Fmstars; 16 supergiants of types A to G; 110 bright giants of types A to K(class II); 156 double stars or objects with composite spectra; 26 lateF dwarfs; 91 weak-lined dwarf and giant stars of types F to K, includingearly F-type population II field blue stragglers; and a few possiblefield horizontal branch stars, lambda Bootis-type stars, and late-typehalo giants.
| Stars Brighter than V=6M5 not Listed in the HR Catalogue
Not Available
| Rotational velocities and spectral types for a sample of binary systems.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975A&AS...19...91L&db_key=AST
| Catalog of Indidual Radial Velocities, 0h-12h, Measured by Astronomers of the Mount Wilson Observatory
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970ApJS...19..387A&db_key=AST
| A catalogue of four-color photometry of late F-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74..705P&db_key=AST
| A survey of stars with composite spectra.
Not Available
|
提交文章
相关链接
提交链接
下列团体成员
|
观测天体数据
目录:
|
