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New homogeneous iron abundances of double-mode Cepheids from high-resolution echelle spectroscopy
Aims.We define the relationship between the double-mode pulsation ofCepheids and metallicity in a more accurate way, determine the empiricalmetallicities of double-mode Cepheids from homogeneous, high-resolutionspectroscopic data, and study of the period-ratio - metallicitydependence. Methods: The high S/N echelle spectra obtained with theFEROS spectrograph were analyzed using a self-developed IRAF script, andthe iron abundances were determined by comparing with synthetic spectraassuming LTE. Results: Accurate [Fe/H] values of 17 galactic beatCepheids were determined. All these stars have solar or slightlysubsolar metallicity. Their period ratio (P1 / P_0) showsstrong correlation with their derived [Fe/H] values. The correspondingperiod ratio - metallicity relation has been evaluated.Based on observations taken with the ESO 2.2-m telescope at La Silla,Chile (Proposal 073.D-0072) and the 1.82 m telescope at David DunlapObservatory, Canada.
| Cepheid parallaxes and the Hubble constant
Revised Hipparcos parallaxes for classical Cepheids are analysedtogether with 10 Hubble Space Telescope (HST)-based parallaxes. In areddening-free V, I relation we find that the coefficient of logP is thesame within the uncertainties in our Galaxy as in the Large MagellanicCloud (LMC), contrary to some previous suggestions. Cepheids in theinner region of NGC4258 with near solar metallicities confirm thisresult. We obtain a zero-point for the reddening-free relation and applyit to the Cepheids in galaxies used by Sandage et al. to calibrate theabsolute magnitudes of Type Ia supernova (SNIa) and to derive the Hubbleconstant. We revise their result for H0 from 62 to 70 +/-5kms-1Mpc-1. The Freedman et al. value is revisedfrom 72 to 76 +/- 8kms-1Mpc-1. These results areinsensitive to Cepheid metallicity corrections. The Cepheids in theinner region of NGC4258 yield a modulus of 29.22 +/- 0.03 (int.)compared with a maser-based modulus of 29.29 +/- 0.15. Distance modulifor the LMC, uncorrected for any metallicity effects, are 18.52 +/- 0.03from a reddening-free relation in V, I; 18.47 +/- 0.03 from aperiod-luminosity relation at K; 18.45 +/- 0.04 from aperiod-luminosity-colour relation in J, K. Adopting a metallicitycorrection in V, I from Macri et al. leads to a true LMC modulus of18.39 +/- 0.05.
| 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.
| Coordinates and Identifications of Harvard Variables
Coordinates and identifications are presented for 726 Harvard Variablestars and suspected variables, discovered or studied by D. Hoffleit andannounced in Harvard Bulletins 874, 884, 887, 901, and 902; plus 141others, previously known, lying in the same fields.
| Photoelectric Observations of Southern Cepheids in 2001
A total of 2097 photometric observations in the BVIc systemare presented for 117 Cepheids located in the southern hemisphere. Themain purpose of the photometry is to provide new epochs of maximumbrightness for studying Cepheid period changes, as well as to establishcurrent light elements for the Cepheids.
| 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
| 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.
| The carbon Cepheid RT Trianguli Australis: additional evidence of triple-α and CNO cycling
We have used echelle spectra of resolving power 35000 to derive chemicalabundances and the 12C/13C ratio in the 1.9-dcarbon Cepheid RT TrA and the Cepheid U TrA, employed as a comparisonstar. We confirm that RT TrA is very metal-rich with [Fe/H]=+0.4. Inaddition, C and N are substantially in excess, and a small deficiency inO is present. We interpret these anomalies as resulting from theappearance on the stellar surface of material enriched in 12Cby the 3-α process, followed by CNO cycling to convert12C to 13C and 14N. In addition, some16O has been processed to 14N. The partialprocessing of 16O to 14N indicates thatsubstantial 17O may be present. Proton capture seems to haveenhanced 23Na from the Ne isotopes.
| 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 shape and scale of Galactic rotation from Cepheid kinematics
A catalog of Cepheid variables is used to probe the kinematics of theGalactic disk. Radial velocities are measured for eight distant Cepheidstoward l = 300 deg; these new Cepheids provide a particularly goodconstraint on the distance to the Galactic center, R0. We model the diskwith both an axisymmetric rotation curve and one with a weak ellipticalcomponent, and find evidence for an ellipticity of 0.043 +/- 0.016 nearthe sun. Using these models, we derive R0 = 7.66 +/- 0.32 kpc andv(circ) = 237 +/- 12 km/s. The distance to the Galactic center agreeswell with recent determinations from the distribution of RR Lyraevariables and disfavors most models with large ellipticities at thesolar orbit.
| 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.
| Derivation of the Galactic rotation curve using space velocities
We present rotation curves of the Galaxy based on the space-velocitiesof 197 OB stars and 144 classical cepheids, respectively, which rangeover a galactocentric distance interval of about 6 to 12kpc. Nosignificant differences between these rotation curves and rotationcurves based solely on radial velocities assuming circular rotation arefound. We derive an angular velocity of the LSR of{OMEGA}_0_=5.5+/-0.4mas/a (OB stars) and {OMEGA}_0_=5.4+/-0.5mas/a(cepheids), which is in agreement with the IAU 1985 value of{OMEGA}_0_=5.5mas/a. If we correct for probable rotations of the FK5system, the corresponding angular velocities are {OMEGA}_0_=6.0mas/a (OBstars) and {OMEGA}_0_=6.2mas/a (cepheids). These values agree betterwith the value of {OMEGA}_0_=6.4mas/a derived from the VLA measurementof the proper motion of SgrA^*^.
| Photometric Parameters for Short-Period Cepheids
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.1313E&db_key=AST
| 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.
| Photoelectric Observations of Southern Cepheids in 1995
Not Available
| Photoelectric Ubvri/c Photometry of Southern Cepheids
Not Available
| Chemical composition of selected double-mode Cepheids and the P_1_/P_0_ - [Fe/H] relation.
We present the results of the detailed spectroscopic investigation ofthree double-mode Cepheids: EW Sct, VX Pup and BQ Ser. The abundanceanalysis has shown: (1) Carbon is deficient (the abundance normalized tothe iron content with respect to the solar value). (2) This carbondeficiency is accompanied by nitrogen overabundance and normal oxygencontent. (3) α - and iron group elements with little exceptionshow solar ratio [M/Fe]. (4) The heavy elements in EW Sct areunderabundant. (5) Normal iron abundance for EW Sct ([Fe/H]=-0.08) andmetal deficiency for VX Pup ([Fe/H]=-0.39) and BQ Ser ([Fe/H]=-0.36)strongly support the existence of a P_1_/P_0_-metallicity relation, asfirst discussed in work of Andrievsky et al. (1993).
| Nonlinear properties of double-mode pulsators
The generalized Fourier phase difference between the components of amultiperiodic oscillation is presented, and it is applied to thedouble-mode Cepheid light curve parameters. It is shown that thegeneralized phase difference of the combination frequency terms can giveuseful information on the nonlinear characteristics of the pulsation andon the possible presence of resonances between pulsation modes as in thecase of the classical phase differences used for single-mode pulsators.Furthermore, it is shown the utility of the qualitative interpretationof the main characteristics of the Fourier phases in the framework ofthe nonlinear adiabatic treatment of double-mode pulsation on theanalogy of single-mode pulsation.
| Opacity, metallicity, and Cepheid period ratios in the galaxy and Magellanic Clouds
Linear pulsation calculations are employed to reproduce the bump Cepheidresonance (P2/P0 = 0.5 at P0approximately equal to 10 days) and to model, individually, theP1/P0 period ratios for the dozen known Galacticbeat Cepheids. Convection is ignored. The results point to a range ofmetallicity among the Cepheids, perhaps as large as 0.01 approximatelyless than Z approximately less than 0.02, with no evidence for any starexceeding Z = 0.02. We find masses and luminosities which range from Mapproximately less than 4 solar mass, log(base 10) approximately lessthan 3.0 at P0 approximately equal to 3 days to Mapproximately less than 6 solar mass, log(base 10) L approximatelygreater than 3.5 at P0 approximately equal to 10 days.Similar parameters are indicated for the P0 approximatelyequal to 10 days Cepheids in the LMC and SMC, provided that theresonance for these stars occurs at a slightly longer period,P0 days, as has been suggested in the literature. Ourcalculations were performed mainly using OPAL opacities, but also withnew opacities from the Opacity project (OP). Only small differences werefound between the OPAL results and those from OP. Finally, somesuggestions are made for possible future work, including evolution andpulsation calculations, and more precise observations of Cepheids in theMagellanic Clouds.
| New radial velocities for classical cepheids. Local galactic rotation revisited
New centre-of-mass radial velocities are calculated for 107 classicalcepheids from CORAVEL observations. We generally determine thesevelocities from four to six measurements carefully spaced in phase, byfitting a "typical" radial velocity curve or the mirror image of thelight curve. A decomposition in Fourier series is used for stars withmore than 10 measurements. Distances are then computed through aperiod-luminosity-colour relation for 278 classical cepheids with knownradial velocity, and an axisymmetric galactic rotation model is appliedto the sample, using a generalised non-linear least square method withuncertainties on both the velocities and the distances. The bestresults, with a rotation curve modelled as a third order polynomial,are: Rsun_=8.09 +/-0.30 kpc, A=15.92 +/-0.34 km/s/kpc, 2ARsun_=257 +/-7 km/s, A2=d^2theta(R)/d R^2^=-3.38+/-0.38 km/s/kpc^2^, A3=d^3theta(R)/d R^3^=1.99 +/-0.62km/s/kpc^3^, u_0_=9.32 +/-0.80 km/s, v_0_=11.18 +/-0.65 km/s. The effectof modifying the distance scale of cepheids, the absorption coefficientor the fitting procedure algorithm are examined. It appears that theproduct 2 A Rsun_ is very robust towards these changes. Theextended sample of classical cepheids with known radial velocitypresented in this paper seems to imply a higher value for A thananterior studies. The radial velocity residuals show a systematic k-termof about 2 km/s. New evidence from cluster cepheids excludes anintrinsic cause for this shift, and a dynamical cause is proposed from acomparison with a N-body simulation of the Galaxy. The simulation showsthat a systematic bias of this magnitude is typical. The structure ofthe local residual velocity field is examined in some detail.
| An Investigation of the Double-Mode Cepheid Tu-Cassiopeiae - Part One - Atmospheric Parameters and Chemical Composition
Abstract image available at:http://adsabs.harvard.edu/abs/1993MNRAS.265..257A
| Color indices of double-mode Cepheids
Separate light curves of both oscillations are constructed for all thedouble-mode Cepheids. Analysis of 4600 photoelectric UBVRI observationsshows that the shape of the curves changes with a period equal to theperiod of the other oscillation. Data on amplitude variations of colorindices confirm an earlier conclusion that divided the group ofdouble-mode Cepheids into two subgroups.
| Amplitudes of light curves of double-mode Cepheids
Maximum and minimum amplitudes of both oscillations of all the 14 knowndouble-mode Cepheids (DMCs) are determined in B, V, R, and I filters.Mathematical and graphical relations between amplitudes, betweenamplitudes and periods, and between amplitudes and wavelength are given.Application of the method of principal components showed that the DMCgroup can be separated into two subgroups: long-period DMCs andshort-period DMCs, which are probably associated genetically withs-Cepheids and single-mode classical Cepheids, respectively.
| A catalogue of Fe/H determinations - 1991 edition
A revised version of the catalog of Fe/H determinations published by G.Cayrel et al. (1985) is presented. The catalog contains 3252 Fe/Hdeterminations for 1676 stars. The literature is complete up to December1990. The catalog includes only Fe/H determinations obtained from highresolution spectroscopic observations based on detailed spectroscopicanalyses, most of them carried out with model atmospheres. The catalogcontains a good number of Fe/H determinations for stars from open andglobular clusters and for some supergiants in the Magellanic Clouds.
| Light curves of double-mode Cepheids
Elements of the light variation of all known double-mode Cepheids arespecified on the basis of an analysis of about 4600 photoelectric UBVRIobservations. The separate light curves for each oscillation for all thedouble-mode Cepheids are obtained. The light curves for each oscillationof the double-mode Cepheids show significant systematic changes duringthe period of the other oscillation.
| A magnitude-limited survey of Cepheid companions in the ultraviolet
Results of a magnitude-limited survey of classic Cepheids brighter than8th mag carried out to search for hot main-sequence companions arepresented. Spectra of 76 stars obtained with the IUE satellite in the2000-3200-A region were compared with the spectra of nonvariablesupergiants and also the single Cepheid Delta Cep to search for excessflux at 2500 A from possible companions. Photometric companions werefound for 21 percent of the sample. When the Cepheids known to be binaryfrom either orbital motion or spectra in the 1200-2000-A region areincluded, the percentage of companions rises to 29 percent. If astatistical correction from stars with orbital motion is included, 34percent have companions. This percentage is compared with that found byAbt et al. (1990) for B2-B5 main-sequence stars. If only systems withperiods longer than a year and separations not more than 30 arcsec areconsidered, only 18 percent of the B stars will become Cepheids withcompanions.
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| Takýmyýldýz: | Guney Ucgeni |
| Sað Açýklýk: | 16h07m19.00s |
| Yükselim: | -62°54'38.0" |
| Görünürdeki Parlaklýk: | 7.955 |
| Uzaklýk: | 763.359 parsek |
| özdevim Sað Açýklýk: | -2.1 |
| özdevim Yükselim: | -2.9 |
| B-T magnitude: | 8.736 |
| V-T magnitude: | 8.02 |
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