내용
사진
사진 업로드
DSS Images Other Images
관련 글
Spectral Classification of Stars in A Supplement to the Bright Star Catalogue
MK spectral types are given for about 584 stars in A Supplement to theBright Star Catalogue. These are compared with Hipparcos parallaxes tocheck the reliability of those classifications. The estimated errors are+/-1.2 subtypes, and 10% of the luminosity classes may be wrong.
| Multi-site, multi-technique survey of γ Doradus candidates. I. Spectroscopic results for 59 stars
We present the first results of a 2-year high-resolution spectroscopycampaign of 59 candidate γ Doradus stars which were mainlydiscovered from the HIPPARCOS astrometric mission. More than 60% of thestars present line profile variations which can be interpreted as due topulsation related to γ Doradus stars. For all stars we alsoderived the projected rotation velocity (up to more than 200 kms-1). The amplitude ratios 2K/Δ m for the mainHIPPARCOS frequency are in the range 35-96 kms-1,mag-1. About 50% of the candidates arepossible members of binary systems, with 20 stars being confirmedγ Doradus. At least 6 stars present composite spectra, and in allbut one case (for which only one spectrum could be obtained), the narrowcomponent shows line profile variations, pointing towards anuncomfortable situation if this narrow component originates from a shellsurrounding the star. This paper is the first of a series concerningmode identification using both photometric and spectroscopic methods forthe confirmed γ Doradus stars of the present sample.Partially based on observations obtained at the Observatoire deHaute-Provence.
| A Dozen New γ Doradus Stars
We use new high-dispersion spectroscopic and precise photometricobservations to identify 12 new γ Doradus stars. Two of the 12systems are double-lined binaries that show obvious velocityvariability. Five other stars have metallic lines with compositeprofiles characterized by a narrow feature near the center of each broadcomponent. Spectrograms of the Hα line indicate that all fivestars are binaries rather than shell stars. The remaining five stars inour sample are probably single. All 12 stars are photometricallyvariable with amplitudes between 6 and 87 mmag in Johnson B and periodsbetween 0.3 and 1.2 days. Four stars are monoperiodic; the rest havebetween two and five independent periods. The variability at all periodsapproximates a sinusoid. Although many of the stars lie within theδ Scuti instability strip, none exhibit the higher frequencyvariability seen in δ Scuti stars. We have increased the sample ofknown γ Doradus stars by 40% and revised the positions of a numberof variables in the H-R diagram by accounting for duplicity. Our list of42 confirmed γ Doradus variables gives some of their properties.All are dwarfs or subgiants and lie within a well-defined region of theH-R diagram that overlaps the cool edge of the δ Scuti instabilitystrip. We compare the observed location of the γ Doradus variableswith a recently published theoretical γ Doradus instability stripand find good agreement.
| Spectroscopy of Early F Stars: γ Doradus Candidates and Possible Metallic Shell Stars
We obtained high-resolution spectroscopic observations of 34 γDoradus candidates. From the red-wavelength spectra, we determinedspectral classes, radial velocities, and projected rotationalvelocities. The spectra of seven late A or early F stars show metalliclines that have composite profiles consisting of a narrow component nearthe center of a broad line, indicating that they may be shell stars orbinaries. Several stars, including HD 152896, HD 173977, HD 175337, andHD 195068/9, show large line profile asymmetries. Two stars, HD 11443(=α Trianguli) and HD 149420, are ellipsoidal variables and notγ Doradus stars. The percentage of binary systems in our samplemay be as high as 74%.
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| The domain of γ Doradus variables in the Hertzsprung-Russell diagram
70 new γ Doradus candidates were identified from Hipparcosphotometry, which represents more than a doubling of the presently knownnumber. Selecting the objects with good evidence for multiperiodicity,it is found that these stars, together with bona fide members of theclass, occupy a well-defined region in a colour-magnitude diagram. Thisdomain corresponds to a range of 7200-7700K on the zero-age mainsequence (ZAMS) and 6900-7500K one magnitude above it, which partlyoverlaps with the instability strip of δ Scuti stars. For thefirst time, γ Doradus stars can be discussed as a group. They canbe found over a significant fraction of the main sequence lifetimes forobjects in the relevant temperature range. An upper limit on the surfacemetallicity of γ Doradus stars is apparent, which may guide thesearch for their pulsation driving mechanism. The importance of possibleobjects exhibiting both γ Doradus and δ Scuti-typepulsations is discussed.
| 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.
| U, V, W velocity components for the old disk using radial velocities of 1295 stars in the three cardinal Galactic directions
New radial velocities are presented for 1295 stars chosen at random nearthe three cardinal Galactic directions of l = 180 deg, b = 0; l = 90deg, b = 0 deg; and b = 90 deg, giving the distribution in U, V, and W,respectively, from the radial velocities alone. The measurements weremade with the coude spectrograph of the Mount Wilson 100 in. Hookerreflector. The purpose of the program is to set limits on the densitynormalization in the solar neighborhood of the old thin disk, the oldthick disk, and the halo. Many more high-velocity stars are present inthe unbiased sample than expected from previous estimates of thenormalization. The data suggest the density ratios in the solarneighborhood to be about 90 percent, 10 percent, and about 0.5 percentfor the thin disk, thick disk, and halo populations, respectively.
| Further Studies of A-Stars and F-Stars in the Region of the North Galactic Pole - Part Four - a Catalogue of Uvbyr Photometry and Derived Quantities
Not Available
| Further Studies of A-Stars and F-Stars in the Region of the North Galactic Pole - Part Three - a Catalogue of Star Names and Positions
Not Available
| Studies of A and F stars in the region of the North galactic pole-II. uvby β photometry
Not Available
| Studies of A and F stars in the region of the North galactic pole-I. Radial velocities and MK Classifications
Not Available
| Photometrie de la comete MRKOS (1957d).
Not Available
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
