내용
사진
사진 업로드
DSS Images Other Images
관련 글
Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderliche Sterne e.V.
Not Available
| Phase-dependent Variation of the Fundamental Parameters of Cepheids. III. Periods between 3 and 6 Days
We present the results of a detailed multiphase spectroscopic analysisof six classical Cepheids with pulsation periods between 3 and 6 days.For each star we have derived phased values of effective temperature,surface gravity, microturbulent velocity, and elemental abundances. Weshow that the elemental abundance results for these Cepheids areconsistent for all pulsational phases.
| Mean Angular Diameters and Angular Diameter Amplitudes of Bright Cepheids
We predict mean angular diameters and amplitudes of angular diametervariations for all monoperiodic PopulationI Cepheids brighter than=8.0 mag. The catalog is intended to aid selecting mostpromising Cepheid targets for future interferometric observations.
| Improvement of the CORS method for Cepheids radii determination based on Strömgren photometry
In this paper we present a modified version of the CORS method based ona new calibration of the Surface Brightness function in theStrömgren photometric system. The method has been tested by meansof synthetic light and radial velocity curves derived from nonlinearpulsation models. Detailed simulations have been performed to take intoaccount the quality of real observed curves as well as possible shiftsbetween photometric and radial velocity data. The method has been thenapplied to a sample of Galactic Cepheids with Strömgren photometryand radial velocity data to derive the radii and a new PR relation. As aresult we find log R = (1.19 ± 0.09) + (0.74 ± 0.11) logP (rms = 0.07). The comparison between our result and previous estimatesin the literature is satisfactory. Better results are expected from theadoption of improved model atmosphere grids.
| A new Period-Radius relation for Galactic Classical Cepheids
We discuss a new Period-Radius (PR) relation for Galactic ClassicalCepheids, obtained by means of a new version of the CORS method whichhas been modified in order to be run with the Strömgren photometricsystem. The major change consists in the calibration of the SurfaceBrightness as a function of the two ``reddening free'' colourindexes [c1] and [m1], by means of the model atmospheres by Castelli etal. (1997). In this contribution we first briefly discuss somenumerical experiments performed on the basis of synthetic Cepheid lightcurves to test the accuracy of the method, and then report thePeriod-Radius relation for Classical Cepheids obtained by applying thethe new method to a sample of Galactic Cepheids.
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderlichen Serne e.V.
Not Available
| Sodium enrichment of the stellar atmospheres. II. Galactic Cepheids
The present paper is a continuation of our study of the sodium abundancein supergiant atmospheres (Andrievsky et al. 2002a). We present theresults on the NLTE abundance determination in Cepheids, and the derivedrelation between the sodium overabundance and their masses.
| Using Cepheids to determine the galactic abundance gradient. I. The solar neighbourhood
A number of studies of abundance gradients in the galactic disk havebeen performed in recent years. The results obtained are ratherdisparate: from no detectable gradient to a rather significant slope ofabout -0.1 dex kpc-1. The present study concerns theabundance gradient based on the spectroscopic analysis of a sample ofclassical Cepheids. These stars enable one to obtain reliable abundancesof a variety of chemical elements. Additionally, they have welldetermined distances which allow an accurate determination of abundancedistributions in the galactic disc. Using 236 high resolution spectra of77 galactic Cepheids, the radial elemental distribution in the galacticdisc between galactocentric distances in the range 6-11 kpc has beeninvestigated. Gradients for 25 chemical elements (from carbon togadolinium) are derived. The following results were obtained in thisstudy. Almost all investigated elements show rather flat abundancedistributions in the middle part of galactic disc. Typical values foriron-group elements lie within an interval from ~-0.02 to ~-0.04 dexkpc-1 (in particular, for iron we obtainedd[Fe/H]/dRG =-0.029 dex kpc-1). Similar gradientswere also obtained for O, Mg, Al, Si, and Ca. For sulphur we have founda steeper gradient (-0.05 dex kpc-1). For elements from Zr toGd we obtained (within the error bars) a near to zero gradient value.This result is reported for the first time. Those elements whoseabundance is not expected to be altered during the early stellarevolution (e.g. the iron-group elements) show at the solargalactocentric distance [El/H] values which are essentially solar.Therefore, there is no apparent reason to consider our Sun as ametal-rich star. The gradient values obtained in the present studyindicate that the radial abundance distribution within 6-11 kpc is quitehomogeneous, and this result favors a galactic model including a barstructure which may induce radial flows in the disc, and thus may beresponsible for abundance homogenization. Based on spectra collected atMcDonald - USA, SAORAS - Russia, KPNO - USA, CTIO - Chile, MSO -Australia, OHP - France. Full Table 1 is only available in electronicform at http://www.edpsciences.org Table A1 (Appendix) is only, andTable 2 also, available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/32
| Uber die Eruptivendatenbank und einer zukunftige Datenbank aller BAV Beobachtungen.
Not Available
| Cepheiden: was wird beobachtet - was nicht ?
Not Available
| 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
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veraenderliche Sterne e.V.
Not Available
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| An Inquest of Non-Linear Pulsations in BQ Serpens and VX Puppis
We present analysis of two double mode Cepheid variable stars, BQSerpens and VX Puppis. Observations were obtained using Johnson UVBRIphotometry with the Four College Consortium's (FCCAPT) AutomaticPhotometric Telescope. Performing Fourier exapansion, we have refinedthe fundamental frequency of pulsation for BQ Serpens to be 0.2341 c/dand the first overtone to 0.3320 c/d. For VX Puppis, the fundamentalfrequency and first overtone are 0.3320 c/d and 0.4674 c/d,respectively. Decomposing the variation to both the fundamental andfirst overtone exposes non-linear coupling terms. Here, we calculate thedistribution of energy among these various modes of interaction based onPardo and Poretti's analysis of the double mode Cepheid TU CAS. Thisresearch is funded by NSF Grants #AST86-16362,\ #AST91-15114,#AST95-28906, and #AST-0071260 to the College of Charleston
| Masses for Galactic Beat Cepheids
Accurate mass determinations for Cepheids may be used to determine thedegree of excess mixing in the interiors of their main-sequenceprogenitors: the larger the excess mixing, the larger the luminosity ofthe Cepheid of a given mass, or the smaller the mass of a Cepheid withgiven luminosity. Dynamical masses determined recently for a few Cepheidbinaries indicate excess mixing somewhat stronger than thatcorresponding to the convective overshoot models by Schaller et al. BeatCepheids can be used similarly to test main-sequence mixing in stellarinteriors. The period ratios for beat Cepheids depend on luminosity,Teff, heavy element abundance, and mass. By comparingpulsational models and the observationally derived luminosity,Teff, metallicities, and period ratios it is possible toobtain masses for these stars, the so-called beat masses. With the oldopacities masses much smaller than the evolutionary masses wereobtained. With the new OPAL opacities a beat mass close to the dynamicalmass was obtained for the binary beat Cepheid Y Carinae, showing that itis now possible to obtain reliable beat masses. In this paper, wedetermine beat masses for seven Galactic beat Cepheids for whichphotometric and spectroscopic data are available. We find an averagemass around 4.2+/-0.3 Msolar for these stars, though theactual error limits for each star may be larger mainly because ofuncertainties in E(B-V) and the heavy element abundances. (As derivedspectroscopically, beat Cepheids are in general metal-poor, with-0.4<~[Fe/H]<~0.0). The relation between the derived beat massesand the luminosities again indicates excess mixing that is somewhatlarger than that corresponding to the models by Schaller et al.
| The intermediate-band approach to the surface-brightness method for Cepheid radii and distance determination
The surface-brightness parameter Fν is calibrated in termsof the Strömgren intermediate-band colour b-y. The relationFν-(b-y)o valid for Cepheids is calibratedusing accurate near-infrared radii and distances for selected Cepheids.We have obtained uvby photometry for non-Cepheid giant and supergiantstars with known angular diameters and compared the slope and zero-pointof their Fν-(b-y)o relation with the Cepheidcalibration. We found that the two calibrations are significantlydifferent. The theoretical models lie in between the two calibrations.It is remarked that Fν-colour relations derived fromnon-Cepheids and involving blue colours (e.g. B-V or b-y) are notapplicable to Cepheids, while those involving redder colours (e.g. V-R,V-K or V-J) also produce good radii for Cepheids. Selected Cepheids ascalibrators lead to the accurate relationFν=3.898(+/-0.003)-0.378(+/-0.006)(b-y)o, whichallowed the calculation of radii and distances for a sample of 59Galactic Cepheids. The uncertainties in the zero-point and slope of theabove relation are similar to those obtained from near-infrared colours,and determine the accuracies in radii and distance calculations. Whileinfrared light and colour curves for Cepheids may be superior inprecision, the intermediate-band b-y colour allows the recovery of meanradii with an accuracy comparable to those obtained from the infraredsolutions. The derived distances are consistent within the uncertaintieswith those predicted by a widely accepted period-luminosityrelationship. Likewise, the resulting period-radius relation from theintermediate-band approach is in better agreement with infrared versionsthan with optical versions of this law. It is highlighted that theintermediate-band calibration of the surface-brightness method in thiswork is of comparable accuracy to the near-infrared calibrations. Thepresent results stress the virtues of uvby in determining the physicalparameters of supergiant stars of intermediate temperature.
| A photometric and spectroscopic study of the brightest northern Cepheids - III. A high-resolution view of Cepheid atmospheres
We present new high-resolution spectroscopic observations(λ/Δλ~40000) of 18 bright northern Cepheids carriedout at the David Dunlap Observatory in 1997. The measurements mainlyextend those presented in Paper I of this series, adding three morestars (AW Per, SV Vul, T Mon). The spectra were obtained in theyellow-red spectral region in the interval of 5900 and 6660Å,including strong lines of sodium D and Hα. New radial velocitiesdetermined with the cross-correlation technique and the bisectortechnique are presented. The new data are compared with those recentlypublished by several groups. We found systematic differences between thespectroscopic and CORAVEL-type measurements as large as1-3kms-1 in certain phases. We performed Baade-Wesselinkanalysis for CK Cam discovered by the Hipparcos satellite. The resultingradius is 31+/-1Rsolar, which is in very good agreement withrecent period-radius relation by Gieren, Moffett & Barnes III. It isshown that the systematic velocity differences do not affect theBaade-Wesselink radius more than 1per cent for CK Cam. Observationalpieces of evidence of possible velocity gradient affecting theindividual line profiles are studied. The full-width at half minimum(FWHM) of the metallic lines, similarly to the velocity differences,shows a very characteristic phase dependence, illustrating the effect ofglobal compression in the atmosphere. The smallest line widths alwaysoccur around the maximal radius, while the largest FWHM is associatedwith velocity reversal before the minimal radius. Three first overtonepulsators do not follow the general trend: the largest FWHM in SU Casand SZ Tau occurs after the smallest radius, during the expansion, whilein V1334 Cyg there are only barely visible FWHM variations. Thepossibility of a bright yellow companion of V1334 Cyg is brieflydiscussed. The observed line-profile asymmetries exceed the valuespredicted with a simple projection effect by a factor of 2-3. This couldbe associated with the velocity gradient, which is also supported by thedifferences between individual line velocities of different excitationpotentials.
| 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
| I- and JHK-band photometry of classical Cepheids in the HIPPARCOS catalog
By correlating the \cite[Fernie et al. (1995)]{F95} electronic databaseon Cepheids with the ``resolved variable catalog'' of the hipparcosmission and the simbad catalog one finds that there are 280 Cepheids inthe hipparcos catalog. By removing W Vir stars (Type ii Cepheids),double-mode Cepheids, Cepheids with an unreliable solution in thehipparcos catalog, and stars without photometry, it turns out that thereare 248 classical Cepheids left, of which 32 are classified asfirst-overtone pulsators. For these stars the literature was searchedfor I-band and near-infrared data. Intensity-mean I-band photometry onthe Cousins system is derived for 189 stars, and intensity-mean JHK dataon the Carter system is presented for 69 stars.
| The Radial Velocity of Double-mode Cepheid BD -10 4669
We present the first radial velocity measurements of the recentlydiscovered double-mode Cepheid BD
| A photometric and spectroscopic study of the brightest northern Cepheids - I. Observations
We present simultaneous UBVuvby photometry for the 18 brightest northernCepheids carried out between 1995 and 1997. Additionally, two fainterstars have been observed in the Johnson system only. The wholephotometric data base contains about 3500 individual data points for 20stars. The accuracy has been carefully tested with different methods. Aserious systematic difference has been found between the present dataset and the Stromgren photometry available in the literature, which hasprobably been caused by the peculiar filter set used in the earlierstudy. As an extension to the photometry, we took high-resolutionoptical spectra at David Dunlap Observatory in the red spectral region(lambda/Deltalambda~ 40000, in the interval of 6200and6600Angstromsincluding Hα). The spectroscopic programme contained 12stars from the photometric programme, the newly discovered brightclassical Cepheid CK Cam and two double-mode Cepheids (TU Cas and COAur). New radial velocities obtained with the cross-correlationtechnique are presented. We found significant velocity differencesbetween two cross-correlated spectral regions (6188-6220and 6405-6435Angstroms) as large as 0.8-1.2 km s^-1, which show very characteristicphase dependence in certain Cepheids. Finally, recent period variationsare briefly discussed in terms of phase jumps and duplicity.
| UVBY beta Photometric Data and Fourier Coefficients for Galactic Population I and Population II Cepheids
Photometric data in the uvby beta system are presented for a sample of98 Population I Cepheids and seven W Virginis or Population II Cepheids.The importance of the Fourier decomposition technique in the study ofthe structure of pulsating stars is stressed. Mean values and Fourierdecomposition coefficients for the V, b - y, m1, and c1 variations arecalculated. Also, mean values of H beta are provided. New times ofmaximum V light are reported for the majority of the stars in thesample. Significant shifts of the light and color curves were found insome Cepheids; these are explained by their period variations. Thesestars are highlighted in the text.
| A catalog of Cepheid radial velocities measured in 1995-1998 with the correlation spectrometer.
Not Available
| Classification of Population II Stars in the Vilnius Photometric System. II. Results
The results of photometric classification of 848 true and suspectedPopulation II stars, some of which were found to belong to Population I,are presented. The stars were classified using a new calibrationdescribed in Paper I (Bartkevicius & Lazauskaite 1996). We combinethese results with our results from Paper I and discuss in greaterdetail the following groups of stars: UU Herculis-type stars and otherhigh-galactic-latitude supergiants, field red horizontal-branch stars,metal-deficient visual binaries, metal-deficient subgiants, stars fromthe Catalogue of Metal-deficient F--M Stars Classified Photometrically(MDPH; Bartkevicius 1993) and stars from one of the HIPPARCOS programs(Bartkevicius 1994a). It is confirmed that high galactic latitudesupergiants from the Bartaya (1979) catalog are giants or even dwarfs.Some stars, identified by Rose (1985) and Tautvaisiene (1996a) as fieldRHB stars, appear to be ordinary giants according to our classification.Some of the visual binaries studied can be considered as physical pairs.Quite a large fraction of stars from the MDPH catalog are found to havesolar metallicity. A number of new possible UU Herculis-type stars, RHBstars and metal-deficient subgiants are identified.
| Galactic kinematics of Cepheids from HIPPARCOS proper motions
The Hipparcos proper motions of 220 Galactic Cepheids, together withrelevant ground-based photometry, have been analyzed. The effects ofGalactic rotation are very clearly seen. Mean values of the Oortconstants, A = 14.82 +/- 0.84 km/s kpc, and B = -12.37 +/- 0.64 km/skpc, and of the angular velocity of circular rotation at the sun, 27.19+/- 0.87 km/s kpc, are derived. A comparison of the value of A withvalues derived from recent radial velocity solutions confirms, withinthe errors, the zero-points of the period-luminosity andperiod-luminosity-color relations derived directly from the Hipparcostrigonometrical parallaxes of the same stars. The proper motion resultssuggest that the Galactic rotation curve is declining slowly at thesolar distance from the Galactic Center (-2.4 +/- 1.2 km/s kpc). Thecomponent of the solar motion towards the North Galactic Pole is foundto be +7.61 +/- 0.64 km/s. Based on the increased distance scale deducedin the present paper, the distance to the Galactic Center derived in aprevious radial velocity study is increased to 8.5 +/- 0.5 kpc.
| Evolutionary and Pulsational Constraints for Super--Metal-rich Stars with Z = 0.04
We investigate the evolutionary behavior of stellar structures withmetallicity Z = 0.04 in order to disclose theoretical expectations forboth evolutionary and pulsational behaviors of super-metal-rich (SMR)objects, which are found in the solar neighborhood, in the Galacticbulge, and in elliptical galaxies. A suitable set of stellar models ispresented for the given metallicity value but for two alternativeassumptions about the amount of original He, namely, Y = 0.34 and Y =0.37. Theoretical isochrones for H-burning evolutionary phases arepresented for ages ranging from 18 to less than 1 Gyr. The evolutionarybehavior of He-burning structures is discussed for suitable assumptionsabout the mass of the progenitors and the amount of mass loss. For bothquoted assumptions of original He abundance, we confirm that at metalcontents larger than the solar value the luminosity of the horizontalbranch (HB) at the RR Lyrae gap increases as the metal contentincreases, a direct consequence of the expected simultaneous increase oforiginal He. We find that, at the exhaustion of central helium, SMRstars definitely undergo the gravonuclear instabilities previously foundin some He-burning structures with solar metallicity. On the basis ofsuch an evolutionary scenario, we investigate the expected pulsationalbehavior of He-burning SMR stars for suitable assumptions on thepulsators' evolutionary parameters. Linear blue boundaries forpulsational instability in the fundamental and in the first-overtonemodes are derived, and their dependence on stellar mass and chemicalcomposition is investigated. Nonlinear, nonlocal, and time-dependentconvective models are discussed, the modal stability is investigated forthe first two modes, and the theoretical predictions about the perioddistribution inside the instability strip and the shape of both lightand velocity curves are presented. Full-amplitude, nonlinear envelopemodels show that the range of effective temperatures in which SMR RRLyrae variables present a stable limit cycle is smaller than that ofpulsators characterized by lower metal abundances. In fact, the width ofthe instability strip at the zero-age horizontal branch luminosity leveldecreases from 1400 to 1100 K. Also taking into account the peculiarnarrow mass range characterizing SMR pulsators, we estimate that thesetwo factors alone cause a decrease in the occurrence of RR Lyraepulsators by a factor of 7 compared with metal-poor, globularcluster-like stellar populations. We find that canonical analyticalrelations connecting the nonlinear periods of metal-poor variables totheir luminosity, mass, and effective temperature cannot be safelyextrapolated to the range of SMR pulsators. We show that gravonuclearinstabilities largely increase the lifetimes of stars crossing theinstability strip at luminosity levels higher than the HB luminosity,thus increasing the expected occurrence of luminous low-mass variables.We show that both periods and light curves of different groups of typeII Cepheids with periods shorter than 6 days, presented by Diethelm, canbe all reproduced by suitable variations in the effective temperature orin the luminosity level of our SMR post-HB models, supporting evidenceof a substantial homogeneity of these variables. On the basis of bothevolutionary and pulsation findings, we finally predict the rate ofperiod change for a typical type II, metal-rich, field Cepheid acrossthe instability strip and discuss an observational test for validatingthe present theoretical scenarios. In an appendix, we discuss in detailthe physics of gravonuclear instabilities, which appear as asurprisingly exact confirmation of the theoretical predictions given bySchwarzschild & Harm as early as 1965.
| 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
| The galactic double-mode Cepheids. II. Properties of the generalized phase differences.
By considering the least-squares fits of the double-mode Cepheid lightcurves discussed in Paper I we defined their properties by their Fourierparameters and generalized phase differences G_i,j_. When plotting thelatter quantities as a function of the order, the second order terms areconfined in the region just below 3π/2; the third order terms haveπ/2
| The galactic double-mode Cepheids. I. Frequency analysis of the light curves and comparison with single-mode Cepheids.
We submitted the available photometric V data of all the known galacticDouble Mode Cepheids (DMCs) to a careful frequency analysis with the aimof detecting in each case the importance of the harmonics and of thecross coupling terms. For each object, starting from different datasubsets, we progressively built a homogenous set of data, checking theconsistency of the results step by step. It was demonstrated that eachstar displays a different content, showing that no a priori fit can beapplied. Up to 4 harmonics were found for the fundamental radial mode(F); in every case, 2 harmonics were found for the first overtone radialmode (1O). We also proceeded to a preliminar analysis of the Fourierparameters of the DMC light curves and we found a very close similaritybetween i) the light curves of the classical Cepheids and those of theF-mode of the DMCs; ii) the light curves of the s-Cepheids and those ofthe 1O-mode of the DMCs. The analysis of DMC light curves offers thepossibility of unifying the light curves of classical and s-Cepheids.The case of the unique DMC CO Aur is also discussed.
| Radial Velocity Curves and First Calculations of the Radii for Four Double-mode Cepheids
Not Available
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
