目录
图像
上传图像
DSS Images Other Images
相关文章
UV flux distributions of γ Doradus stars
Context: It seems that the recently identified class of pulsating stars,the γ Dor type-variables, includes objects with different metalabundances and a large percentage of binaries. Aims: We looked forindicators of metal abundance peculiarities and stellar binarity in asample of 40 confirmed γ Dor stars. Methods: Absolute magnitudesfrom Hipparcos parallaxes and UV magnitudes, from the S2/S68 experimenton board the TD1 satellite, are retrieved from databases and comparedwith predicted values. A set of non variable normal stars is used tocheck the consistency of this analysis and also serve as referencestars. Results: Twenty-nine stars of the γ Dor star sample,which is 73% of it, are discovered having abnormal UV fluxes constantlyshowing UV flux excesses compared to those computed with the atmosphericparameters (Teff , log g, and metallicity) determined fromcalibration of the uvbyβ indices. The reason for this UV excess offlux at 196.5 nm and at 236.5 nm, which was previously known only for HD209295, cannot be ascribed to binarity alone. An extra source of UV fluxor less UV absorption - yet unknown - must be present.Tables 1-3 are 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/472/241
| HD 71636, A Newly Discovered Eclipsing Binary
Our differential BV photometric observations, acquired with an automatedtelescope at Fairborn Observatory, show that HD 71636 is an eclipsingbinary. From follow-up red-wavelength spectroscopic observations weclassify the primary and secondary as an F2 dwarf and an F5 dwarf,respectively. The system has a period of 5.01329 days and a circularorbit. We used the Wilson-Devinney program to simultaneously solve ourBV light curves and radial velocities and determined a number offundamental properties of the system. Comparison with evolutionarytracks indicates that both stars are well ensconced on the mainsequence. The age of the system is about 1.2 billion years.
| The 78th Name-List of Variable Stars
We present the next regular Name-List of variable stars containinginformation on 1706 variable stars recently designated in the system ofthe General Catalogue of Variable Stars.
| Analysis of MERCATOR data - Part II: variable A & F stars
For a few decades, a large international community is working at thedevelopment of stellar seismology, intending to open a new window on thestructure and evolution of stars, with the necessary paralleldevelopment of new observational techniques, modeling tools and methodsfor diagnostics and interpretation. This new window is associated withnew observables, characterizing the oscillations (frequencies,amplitudes, line profiles,...) which are sensitive to the stellarinterior and thus very complementary with surface observables,associated to astrometry, spectropolarimetry or interferometry.
| Eleven New γ Doradus Stars
We present new high-dispersion spectroscopic and precise photometricobservations to identify 11 new γ Doradus variables. Seven ofthese new γ Doradus stars appear to be single, three are primariesof single-lined binaries, and one has two distant visual companions;none are double-lined or close visual binaries. Several of the starsshow spectroscopic line-profile and low-amplitude radial velocityvariability indicative of pulsation. All 11 stars are photometricallyvariable with amplitudes between 8 and 93 mmag in Johnson B and periodsbetween 0.398 and 2.454 days. One star is monoperiodic; the rest havebetween two and five independent periods. The variability at all periodsapproximates a sinusoid, although three of the stars exhibitcycle-to-cycle variation in the level of maximum brightness, similar tothe Blazhko effect observed in some RR Lyrae stars. We provide a newtabulation of all 54 γ Doradus stars confirmed to date and listsome of their properties. All are dwarfs or subgiants and lie within awell-defined region of the H-R diagram that overlaps the cool edge ofthe δ Scuti instability strip. Four of the new γ Doradusvariables from this paper also lie within the δ Scuti instabilitystrip but do not exhibit the additional higher frequency variabilitytypical of δ Scuti stars. The variability type of several of thesestars given in the General Catalog of Variable Stars and in SIMBADshould now be revised.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| 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.
| Evidence of the gamma Doradus nature for a group of candidates
We present in this paper new uvbybeta photometry of eight starssuspected to be gamma Doradus variables according to Handler & Kaye(\cite{handler00}). The new observational material has been analyzed andpreviously published data re-analyzed by means of an objective periodsearch technique, based on the least-squares algorithm, called Multifre(Bossi & Nuñez \cite{bossi}). We found evidence for theinclusion of seven of these stars in the list of recognized gammaDoradus variables.
| 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.
|
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:
|
INHABITED SKY
