Contents
Images
Upload your image
DSS Images Other Images
Related articles
Baade-Wesselink distances to Galactic and Magellanic Cloud Cepheids and the effect of metallicity
Context. The metallicity dependence of the Cepheid period-luminosity(PL) relation is of importance in establishing the extragalacticdistance scale. Aims: The aim of this paper is to investigate themetallicity dependence of the PL relation in V and K, based on a sampleof 128 Galactic, 36 Large Magellanic Cloud (LMC), and 6 Small MagellanicCloud (SMC) Cepheids with individual Baade-Wesselink (BW) distances(some of the stars also have an Hubble Space Telescope (HST) based andHipparcos parallax or are in clusters) and individually determinedmetallicities from high-resolution spectroscopy. Methods:Literature values of the V-band, K-band, and radial velocity data werecollected for the sample of Cepheids. Based on a (V - K)surface-brightness relation and a projection factor, distances werederived from a BW analysis. Results: The p-relation finallyadopted is 1.50-0.24log P. The slope of this relation is based on thecondition that the distance to the LMC does not depend on period or (V -K) colour and that the slope of the PL relation based on the BWdistances agrees with that based on apparent magnitude. The zero pointof the relation is tight to the Cepheids with HST and revised Hipparcosparallaxes as well as to Cepheids in clusters. The slope of the Galacticand LMC K-band relation formally agrees within the errors, and combiningall Cepheids (including the SMC) results in a negligible metallicitydependence and a relation of MK = (-2.50 ± 0.08) +(-3.06 ± 0.06)log P. A similar conclusion is found for thereddening-free Wesenheit relation (W(VK) = K - 0.13(V - K)), withMWVK = (-2.68 ± 0.08) + (-3.12 ± 0.06)log P. Inthe V-band the situation is more complex. The slope of the LMC and theGalactic PL relation differ at the 3σ level. Combining the samplenevertheless results in a metallicity term significant at the 2σlevel: MV = (-1.55 ± 0.09) + (-2.33 ± 0.07)logP + (+0.23 ± 0.11)[Fe/H]. Taking only the Galactic Cepheids, themetallicity term is no longer significant, namely ( + 0.17 ±0.25). Compared to the recent works by Storm et al. (2011a, A&A,534, A94; 2011b, A&A, 534, A95), there is both agreement anddisagreement. A similar dependence of the p-factor on period is found,but the zero point found here implies a shorter distance scale. Thedistance modulus (DM) to the LMC and SMC found here are 18.29 ±0.02 and 18.73 ± 0.06 (statistical error on the mean),respectively. Systematic differences in reddening could have an effectof order +0.05 in DM. The details of the comparison of BW-baseddistances and Cepheids with HST and revised Hipparcos parallaxes alsoplay a role. The method used by Storm et al. would lead to larger DM of18.37 and 18.81 for the LMC and SMC, respectively. The LMC DM is shorterthan the currently accepted value, which is in the range 18.42 to 18.55,and it is speculated that the p-factor may depend on metallicity. Thisis not predicted by theoretical investigations, but these sameinvestigations do not predict a steep dependence on period either,indicating that additional theoretical work is warranted.Tables 1-6, 10, and Appendix A are available in electronic form at http://www.aanda.org
| Galactic restrictions on iron production by various types of supernovae
We propose a statistical method for decomposition of contributions toiron production from various sources: Type II supernovae and thesubpopulations of Type Ia supernovae, prompt (their progenitors areshort-lived stars with ages lower than ˜100 Myr) and tardy (theirprogenitors are long-lived stars with ages >100 Myr). To do that, wedevelop a theory of oxygen and iron synthesis that takes into accountthe influence of the spiral arms on the amount of the above elementssynthesized by both Type II supernovae and prompt Type Ia supernovae. Inthe framework of the theory, we processed statistically the new, moreprecise, observational data on Cepheid abundances, which, as is wellknown, demonstrate non-trivial radial distributions of oxygen and ironin the Galactic disc with bends in the gradients. In our opinion, suchfine structure in the distribution of elements along the Galactic discenables one to decompose the amount of iron unambiguously into threecomponents produced by the above three sources. In addition, by means ofour statistical methods we solve this task without any preliminarysuppositions about the ratios between the proportions of ironsynthesized by the above sources.The total mass supplied to the Galactic disc during its life by alltypes of supernovae is ˜(4.0 ± 0.4) × 107M&sun;, while the mass of iron occurring in the presentinterstellar medium (ISM) is ˜(1.20 ± 0.05) ×107 M&sun;, i.e. about two thirds of iron iscontained in stars and stellar remnants.The relative proportion of iron synthesized by tardy type Ia supernovaefor the lifetime of the Galaxy is ˜35 per cent (in the present ISMthis portion is ˜50 per cent). Correspondingly, the totalproportion of iron supplied to the disc by Type II supernovae and promptType Ia supernovae is ˜65 per cent (in the present ISM thisproportion is ˜50 per cent). The above result depends slightly onthe adopted mass of oxygen and iron synthesized during one supernovaexplosion and the shape (bimodal or smooth) of the so-called delay-timedistribution function.The proportions of iron mass distributed between short-lived supernovaeare usually as follows: depending on the ejected masses of oxygen oriron during one Type II supernova event, the relative proportion of ironsupplied to the Galactic disc for its age varies in the range 12-32 percent (in the present ISM 9-25 per cent); the proportion supplied byprompt Type Ia supernovae to the Galactic disc is 33-53 per cent (in theISM 26-42 per cent).Our method also confirms that the bend in the observed slope of theoxygen radial distribution and the minimum in [O/Fe] at ˜7 kpcform in the vicinity of the location of the corotation resonance.
| The Distribution of the Elements in the Galactic Disk. II. Azimuthal and Radial Variation in Abundances from Cepheids
This paper reports on the spectroscopic investigation of 101 Cepheids inthe Carina region. These Cepheids extend previous samples by about 35%in number and increase the amount of the Galactic disk coverageespecially in the direction of l ? 270°. The new Cepheids do notadd much information to the radial gradient, but provide a substantialincrease in azimuthal coverage. We find no azimuthal dependence inabundance over an 80° angle from the Galactic center in an annulusof 1 kpc depth centered on the Sun. A simple linear fit to the Cepheiddata yields a gradient d[Fe/H]/dRG = -0.055 ± 0.003dex kpc-1 which is somewhat shallower than found from ourprevious, smaller Cepheid sample.
| Random forest automated supervised classification of Hipparcos periodic variable stars
We present an evaluation of the performance of an automatedclassification of the Hipparcos periodic variable stars into 26 types.The sub-sample with the most reliable variability types available in theliterature is used to train supervised algorithms to characterize thetype dependencies on a number of attributes. The most useful attributesevaluated with the random forest methodology include, in decreasingorder of importance, the period, the amplitude, the V-I colour index,the absolute magnitude, the residual around the folded light-curvemodel, the magnitude distribution skewness and the amplitude of thesecond harmonic of the Fourier series model relative to that of thefundamental frequency. Random forests and a multi-stage scheme involvingBayesian network and Gaussian mixture methods lead to statisticallyequivalent results. In standard 10-fold cross-validation (CV)experiments, the rate of correct classification is between 90 and 100per cent, depending on the variability type. The main mis-classificationcases, up to a rate of about 10 per cent, arise due to confusion betweenSPB and ACV blue variables and between eclipsing binaries, ellipsoidalvariables and other variability types. Our training set and thepredicted types for the other Hipparcos periodic stars are availableonline.
| Near-infrared (JHK) Photometry of 131 Northern Galactic Classical Cepheids
Near-infrared photometric measurements for 131 Northern GalacticCepheids are presented. The Cepheid light curves are sampled with anaverage of 22 measurements per star fully covering the phase of eachCepheid. The J, H, and K light curves for each Cepheid were uniformlyinterpolated to find the intensity mean magnitudes within each band. Theresults are consistent within ±1% for 26 stars in common withprevious studies. This paper is the first in a projected series of twopapers which will provide additional fundamental data for Cepheids inthe Galaxy, namely, NIR photometry and line-of-sight extinction. In thecourse of this project, 93 additional variables were fortuitouslyobserved within the Cepheid program fields, 82 of which have previouslynot been identified.
| Bayesian inference of stellar parameters and interstellar extinction using parallaxes and multiband photometry
Astrometric surveys provide the opportunity to measure the absolutemagnitudes of large numbers of stars, but only if the individualline-of-sight extinctions are known. Unfortunately, extinction is highlydegenerate with stellar effective temperature when estimated frombroad-band optical/infrared photometry. To address this problem, Iintroduce a Bayesian method for estimating the intrinsic parameters of astar and its line-of-sight extinction. It uses both photometry andparallaxes in a self-consistent manner in order to provide anon-parametric posterior probability distribution over the parameters.The method makes explicit use of domain knowledge by employing theHertzsprung-Russell Diagram (HRD) to constrain solutions and to ensurethat they respect stellar physics. I first demonstrate this method byusing it to estimate effective temperature and extinction from BVJHKdata for a set of artificially reddened Hipparcos stars, for whichaccurate effective temperatures have been estimated from high-resolutionspectroscopy. Using just the four colours, we see the expected strongdegeneracy (positive correlation) between the temperature andextinction. Introducing the parallax, apparent magnitude and the HRDreduces this degeneracy and improves both the precision (reduces theerror bars) and the accuracy of the parameter estimates, the latter byabout 35 per cent. The resulting accuracy is about 200 K in temperatureand 0.2 mag in extinction. I then apply the method to estimate theseparameters and absolute magnitudes for some 47 000 F, G, K Hipparcosstars which have been cross-matched with Two-Micron All-Sky Survey(2MASS). The method can easily be extended to incorporate the estimationof other parameters, in particular metallicity and surface gravity,making it particularly suitable for the analysis of the 109stars from Gaia.
| uvby-beta Photoelectric Photometry of Cepheid Stars
We present time-series uvby-beta photometry of 41 classical Cepheidstars. A brief discussion of a comparison between the present data andprevious photometric observations is included.
| Observational studies of Cepheid amplitudes. I. Period-amplitude relationships for Galactic Cepheids and interrelation of amplitudes
Context: The dependence of amplitude on the pulsation period differsfrom other Cepheid-related relationships. Aims: We attempt torevise the period-amplitude (P-A) relationship of Galactic Cepheidsbased on multi-colour photometric and radial velocity data. Reliable P-Agraphs for Galactic Cepheids constructed for the U, B, V, R_C, andIC photometric bands and pulsational radial velocityvariations facilitate investigations of previously poorly studiedinterrelations between observable amplitudes. The effects of bothbinarity and metallicity on the observed amplitude, and the dichotomybetween short- and long-period Cepheids can both be studied. Methods: A homogeneous data set was created that contains basicphysical and phenomenological properties of 369 Galactic Cepheids.Pulsation periods were revised and amplitudes were determined by theFourier method. P-A graphs were constructed and an upper envelope to thedata points was determined in each graph. Correlations between variousamplitudes and amplitude-related parameters were searched for, usingCepheids without known companions. Results: Large amplitudeCepheids with companions exhibit smaller photometric amplitudes onaverage than solitary ones, as expected, while s-Cepheids pulsate withan arbitrary (although small) amplitude. The ratio of the observedradial velocity to blue photometric amplitudes, AV_RAD/A_B,is not as good an indicator of the pulsation mode as predictedtheoretically. This may be caused by an incorrect mode assignment to anumber of small amplitude Cepheids, which are not necessarily firstovertone pulsators. The dependence of the pulsation amplitudes onwavelength is used to identify duplicity of Cepheids. More than twentystars previously classified as solitary Cepheids are now suspected tohave a companion. The ratio of photometric amplitudes observed invarious bands confirms the existence of a dichotomy among normalamplitude Cepheids. The limiting period separating short- andlong-period Cepheids is 10.47 days. Conclusions:Interdependences of pulsational amplitudes, the period dependence of theamplitude parameters, and the dichotomy have to be taken into account asconstraints in modelling the structure and pulsation of Cepheids.Studies of the P-L relationship must comply with the break at 10.47°instead of the currently used “convenient” value of 10 days.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/504/959
| Galactic abundance gradients from Cepheids. On the iron abundance gradient around 10-12 kpc
Context: Classical Cepheids are excellent tracers of intermediate-massstars, since their distances can be estimated with very high accuracy.In particular, they can be adopted to trace the chemical evolution ofthe Galactic disk. Aims: Homogeneous iron abundance measurements for 33Galactic Cepheids located in the outer disk together with accuratedistance determinations based on near-infrared photometry are adopted toconstrain the Galactic iron gradient beyond 10 kpc. Methods: Ironabundances were determined using high resolution Cepheid spectracollected with three different observational instruments: ESPaDOnS@CFHT,Narval@TBL and FEROS@2.2m ESO/MPG telescope. Cepheid distances wereestimated using near-infrared (J,H,K-band) period-luminosity relationsand data from SAAO and the 2MASS catalog. Results: The least squaressolution over the entire data set indicates that the iron gradient inthe Galactic disk presents a slope of -0.052±0.003 textrm {dexkpc}-1 in the 5-17 kpc range. However, the change of the ironabundance across the disk seems to be better described by a linearregime inside the solar circle and a flattening of the gradient towardthe outer disk (beyond 10 kpc). In the latter region the iron gradientpresents a shallower slope, i.e. -0.012±0.014 textrm {dexkpc}-1. In the outer disk (10-12 kpc) we also found thatCepheids present an increase in the spread in iron abundance. Currentevidence indicates that the spread in metallicity depends on theGalactocentric longitude. Finally, current data do not support thehypothesis of a discontinuity in the iron gradient at Galactocentricdistances of 10-12 kpc. Conclusions: The occurrence of a spread in ironabundance as a function of the Galactocentric longitude indicates thatlinear radial gradients should be cautiously treated to constrain thechemical evolution across the disk.
| Reddenings of FGK supergiants and classical Cepheids from spectroscopic data
Accurate and homogeneous atmospheric parameters(Teff,logg,Vt, [Fe/H]) are derived for 74 FGKnon-variable supergiants from high-resolution, high signal-to-noiseratio, echelle spectra. Extremely high precision for the inferredeffective temperatures (10-40K) is achieved by using the line-depthratio method. The new data are combined with atmospheric values for 164classical Cepheids, observed at 675 different pulsation phases, takenfrom our previously published studies. The derived values are correlatedwith unreddened B - V colours compiled from the literature for theinvestigated stars in order to obtain an empirical relationship of theform (B - V)0 = 57.984 -10.3587(logTeff)2 +1.67572(logTeff)3 - 3.356logg +0.0321Vt + 0.2615[Fe/H] + 0.8833(logg)(logTeff).The expression is used to estimate colour excesses E(B - V) forindividual supergiants and classical Cepheids, with a precision of+/-0.05 mag for supergiants and Cepheids with n = 1-2 spectra, reaching+/-0.025mag for Cepheids with n > 2 spectra, matching uncertaintiesfor the most sophisticated photometric techniques. The reddening scaleis also a close match to the system of space reddenings for Cepheids.The application range is for spectral types F0-K0 and luminosity classesI and II.
| Photoelectric observations of Cepheids in UBV(RI)c (Berdnikov, 2008)
This catalog gathers the observation of 894 Cepheids made between 1986to 2004.Observations are listed in alphabetical order of the constellations. Thestandard deviation for every magnitude and color is 0.01mag.This version supersedes the 1997 edition (Cat. )(3 data files).
| 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.
| Conventional and new directions in studying Cepheids
In the first part of this paper, traditional methods of studyingCepheids are summarized, mentioning Detre's contribution to this field.Then the new directions of Cepheid related research are reviewed with anemphasis on the problems concerning the period-luminosity relationship.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 30 maximum times of cepheids
I report new visual maximum times of classical cepheids and oneW-Virginis (CWA-) variable, based on observations of the years 2004until 2006.
| The Distribution of the Elements in the Galactic Disk
This paper reports on the spectroscopic investigation of 54 Cepheids,deriving parameters and abundances. These Cepheids extend previoussamples by about 35% in number and increase the amount of the Galacticdisk coverage, especially in the direction of l~120deg. Wefind that there exists in the Galactic disk at that longitude and at asolar distance of about 3-4 kpc a region that has enhanced abundances,~+0.2, with respect to the local region. A simple linearfit to all Cepheid data now extant yields a gradientd[Fe/H]/dRG=-0.068+/-0.003 dex kpc-1. Afterconsideration of the spatial abundance inhomogeneities in the sample, weconclude that the best current estimate of the overall gradient isd[Fe/H]/dRG=-0.06 dex kpc-1.
| Elemental Abundance Ratios in Stars of the Outer Galactic Disk. III. Cepheids
We present metallicities, [Fe/H], and elemental abundance ratios,[X/Fe], for a sample of 24 Cepheids in the outer Galactic disk based onhigh-resolution echelle spectra. The sample members have galactocentricdistances covering 12 kpc<=RGC<=17.2 kpc, making themthe most distant Galactic Cepheids upon which detailed abundanceanalyses have been performed. We find subsolar ratios of [Fe/H] andoverabundances of [α/Fe], [La/Fe], and [Eu/Fe] in the programstars. All abundance ratios exhibit a dispersion that exceeds themeasurement uncertainties. As seen in our previous studies of old openclusters and field giants, enhanced ratios of [α/Fe] and [Eu/Fe]reveal that recent star formation has taken place in the outer disk withType II supernovae preferentially contributing ejecta to theinterstellar medium and with Type Ia supernovae playing only a minorrole. The enhancements for La suggest that asymptotic giant branch starshave contributed to the chemical evolution of the outer Galactic disk.Some of the young Cepheids are more metal-poor than the older openclusters and field stars at comparable galactocentric distances. Thisdemonstrates that the outer disk is not the end result of the isolatedevolution of an ensemble of gas and stars. We showed previously that theolder open clusters and field stars reached a basement metallicity atabout 10-11 kpc. The younger Cepheids reach the same metallicity but atlarger galactocentric distances, roughly 14 kpc. This suggests that theGalactic disk has been growing with time, as predicted from numericalsimulations. The outer disk Cepheids appear to exhibit a bimodaldistribution for [Fe/H] and [α/Fe]. Most of the Cepheids continuethe trends with galactocentric distance exhibited by S. M. Andrievsky'slarger Cepheid sample, and we refer to these stars as the ``GalacticCepheids.'' A minority of the Cepheids show considerably lower [Fe/H]and higher [α/Fe], and we refer to these stars as the ``MergerCepheids.'' One signature of a merger event would be compositiondifferences between the Galactic and Merger Cepheids. The Cepheidssatisfy this requirement, and we speculate that the distinctcompositions suggest that the Merger Cepheids may have formed under theinfluence of significant merger or accretion events. The short lifetimesof the Cepheids reveal that the merger event may be ongoing, with theMonoceros Ring and Canis Major galaxy being possible merger candidates.This paper makes use of observations obtained at the National OpticalAstronomy Observatory, which is operated by the Association ofUniversities for Research in Astronomy (AURA), Inc., under contract fromthe National Science Foundation. We also employ data products from theTwo Micron All Sky Survey, which is a joint project of the University ofMassachusetts and the Infrared Processing and Analysis Center,California Institute of Technology, funded by the National Aeronauticsand Space Administration and the National Science Foundation.
| Galactic Cepheids. II. Lithium
We report on the discovery of two lithium Cepheids in the Galaxy, basedon observations made with the echelle spectrograph of the Apache PointObservatory. We have used high-resolution, high signal-to-noise ratiospectra to determine abundances of chemical elements in 16 classicalCepheids. Only two of our program stars show a lithium line, RX Aur andYZ Aur (RX Aur has been also classified by us as a new nonradialpulsator). For the others, including the stars with [N/C]<0.2, Li isdepleted up to logN(Li)<1.0. Hence, it appears that mixing depletesLi before stars enter the instability strip. According to stellarmodels, the main mixing event takes place when Teff dropsbelow 4000 K, which is outside the red edge of the instability strip;i.e., after stars have crossed the instability strip for the first time.
| Galactic Cepheids. I. Elemental Abundances and Their Implementation for Stellar and Galactic Evolution
We have added data for 16 distant Cepheids observed with the echellespectrograph of the Apache Point 3.5 m telescope to improve thecorrelations of abundance parameters with pulsation period and distancefrom the Galactic center (RG ). While we see no importanttrends with pulsation period, some important ratios are closely relatedto the evolution of stars through the instability strip. The mostinteresting is the N/C ratio, which is predicted to be enhanced by afactor of 4 when an evolving supergiant cools to Teff=4000 Kand the outer convection zone reaches the depth at which CN processinghas converted C to N. We find a Gaussian distribution around a value of[N/C]=0.6, just as predicted. The ratio of about 30:1 mixed to unmixedstars can be taken as the ratio of evolutionary time spent on the blueloop to the time spent on the first crossing through the instabilitystrip. According to stellar models, the main mixing event takes placewhen Teff drops below 4000 K, which is outside the red edgeof the instability strip; i.e., after stars have crossed the instabilitystrip for the first time. We have confirmed previously knowncorrelations of [Fe/H] with RG. We find that [Fe/H] shows agradient of -0.06 Kpc-1. The only other significant gradientis that of [Eu/Fe], which increases with RG, thereby showingan increasing ratio of SN II/SN Ia in the outer Galaxy.
| New Period-Luminosity and Period-Color relations of classical Cepheids: I. Cepheids in the Galaxy
321 Galactic fundamental-mode Cepheids with good B, V, and (in mostcases) I photometry by Berdnikov et al. (\cite{Berdnikov:etal:00}) andwith homogenized color excesses E(B-V) based on Fernie et al.(\cite{Fernie:etal:95}) are used to determine their period-color (P-C)relation in the range 0.4~ 1.4). The latter effect is enhanced by asuggestive break of the P-L relation of LMC and SMC at log P = 1.0towards still shallower values as shown in a forthcoming paper.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/404/423
| Using Cepheids to determine the galactic abundance gradient. III. First results for the outer disc
As a continuation of our previous work, which concerned the radialabundance distribution in the galactic disc over the distances 4-10 kpcthis paper presents the first results on the metallicity in the outerdisc (RG > 10 kpc). Based on high-resolution spectraobtained for 19 distant Cepheids we sampled galactocentric distancesfrom 10 to 12 kpc. Combined with the results of our previous work on theinner and middle parts of the galactic disc, the present data enable oneto study the structure of the radial abundance distribution over a largebaseline. In particular, we find indications of a discontinuity in theradial abundance distribution for iron as well as a number of the otherelements. The discontinuity is seen at a galactocentric distanceRG = 10 kpc. This finding supports the results reportedearlier by Twarog et al. (\cite{twaet97}). Based on spectra collected atESO - La Silla, Chile. Table A1 is only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/392/491
| 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
| Metallicity effects on classical Cepheids: Velocity curve morphology of outer disc Cepheids
We present new radial velocity data for eleven classical Cepheidssituated in the outer parts of the Galactic disc. The resultant velocitycurves for these metal-deficient Cepheids are decomposed in Fourierparameters, and compared to solar-metallicity Cepheid data, in order tostudy the effect of metallicity on the pulsation properties. Up to P =~8 days, the phi 21 phase shift is found to follow veryclosely the corresponding sequence for solar-metallicity Cepheids,indicating the absence of metallicity effects on phi 21 forlow periods. However, metal-deficient Cepheids show a slightly largerA1 amplitude and R21 amplitude ratio for P<5days. At P>12 days, there is some evidence that the phi 21phase shift is significantly larger for metal-deficient Cepheids than atsolar metallicity. A posteriori, this effect is also detected inphotometric data for outer disc and LMC Cepheids in the 12-20 day periodrange. In good qualitative agreement with the predictions of theoreticalpulsation models, we therefore see some indication of a metallicitydependence of the P2/P0 resonance properties. Thelargest effects on velocity curve shape are expected in the crucial 8-12day period range - around the P2/P0 resonance forfundamental-mode Cepheids - that is not covered by our data. Possibletargets for future measurements are suggested to fill this gap, and toimprove the quantitative determination of metallicity effects on thestructural properties of Cepheid velocity curves. Based on observationscollected at the European Southern Observatory (La Silla, Chile) and atthe Observatoire de Haute-Provence (France).
| 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.
| Galactic Cepheids. Catalogue of light-curve parameters and distances
We report a new version of the catalogue of distances and light-curveparameters for Galactic classical Cepheids. The catalogue listsamplitudes, magnitudes at maximum light, and intensity means for 455stars in BVRI filters of the Johnson system and (RI)_C filters of theCron-Cousins system. The distances are based on our new multicolour setof PL relations and on our Cepheid-based solution for interstellarextinction law parameters and are referred to an LMC distance modulus of18.25. The catalogue is only available in electronic form at the CDS viaanonymous ftp (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Multi-colour PL-relations of Cepheids in the bt HIPPARCOS catalogue and the distance to the LMC
We analyse a sample of 236 Cepheids from the hipparcos catalog, usingthe method of ``reduced parallaxes'' in V, I, K and the reddening-free``Wesenheit-index''. We compare our sample to those considered by Feast& Catchpole (1997) and Lanoix et al. (1999), and argue that oursample is the most carefully selected one with respect to completeness,the flagging of overtone pulsators, and the removal of Cepheids that mayinfluence the analyses for various reasons (double-mode Cepheids,unreliable hipparcos solutions, possible contaminated photometry due tobinary companions). From numerical simulations, and confirmed by theobserved parallax distribution, we derive a (vertical) scale height ofCepheids of 70 pc, as expected for a population of 3-10 Msunstars. This has consequences for Malmquist- and Lutz-Kelker (Lutz &Kelker 1973, Oudmaijer et al. 1998) type corrections which are smallerfor a disk population than for a spherical population. The V and I datasuggest that the slope of the Galactic PL-relations may be shallowerthan that observed for LMC Cepheids, either for the whole period range,or that there is a break at short periods (near log P_0 ~ 0.7-0.8). Westress the importance of two systematic effects which influence thedistance to the LMC: the slopes of the Galactic PL-relations andmetallicity corrections. In order to assess the influence of thesevarious effects, we present 27 distance moduli (DM) to the LMC. Theseare based on three different colours (V,I,K), three different slopes(the slope observed for Cepheids in the LMC, a shallower slope predictedfrom one set of theoretical models, and a steeper slope as derived forGalactic Cepheids from the surface-brightness technique), and threedifferent metallicity corrections (no correction as predicted by one setof theoretical models, one implying larger DM as predicted by anotherset of theoretical models, and one implying shorter DM based onempirical evidence). We derive DM between 18.45 +/- 0.18 and 18.86 +/-0.12. The DM based on K are shorter than those based on V and I andrange from 18.45 +/- 0.18 to 18.62 +/- 0.19, but the DM in K could besystematically too low by about 0.1 magnitude because of a bias due tothe fact that NIR photometry is available only for a limited number ofstars. From the Wesenheit-index we derive a DM of 18.60 +/- 0.11,assuming the observed slope of LMC Cepheids and no metallicitycorrection, for want of more information. The DM to the LMC based on theparallax data can be summarised as follows. Based on the PL-relation inV and I, and the Wesenheit-index, the DM is 18.60 ± 0.11(± 0.08 slope)(^{+0.08}_{-0.15} ;metallicity), which is ourcurrent best estimate. Based on the PL-relation in K the DM is ;;;;18.52 +/- 0.18 (± 0.03 ;slope) (± 0.06 ;metallicity)(^{+0.10}_{-0} ;sampling ;bias). The random error is mostly due to thegiven accuracy of the hipparcos parallaxes and the number of Cepheids inthe respective samples. The terms between parentheses indicate thepossible systematic uncertainties due to the slope of the GalacticPL-relations, the metallicity corrections, and in the K-band, due to thelimited number of stars. Recent work by Sandage et al. (1999) indicatesthat the effect of metallicity towards shorter distances may be smallerin V and I than indicated here. From this, we point out the importanceof obtaining NIR photometry for more (closeby) Cepheids, as for themoment NIR photometry is only available for 27% of the total sample.This would eliminate the possible bias due to the limited number ofstars, and would reduce the random error estimate from 0.18 to about0.10 mag. Furthermore, the sensitivity of the DM to reddening,metallicity correction and slope are smallest in the K-band. Based ondata from the ESA HP astrometry satellite.
| Direct calibration of the Cepheid period-luminosity relation
After the first release of Hipparcos data, Feast & Catchpole gave anew value for the zero-point of the visual Cepheid period-luminosityrelation, based on trigonometric parallaxes. Because of the largeuncertainties on these parallaxes, the way in which individualmeasurements are weighted is of crucial importance. We thereforeconclude that the choice of the best weighting system can be aided by aMonte Carlo simulation. On the basis of such a simulation, it is shownthat (i) a cut-off in π or in σ_ππ introduces a strongbias; (ii) the zero-point is more stable when only the brightestCepheids are used; and (iii) the Feast & Catchpole weighting givesthe best zero-point and the lowest dispersion. After correction, theadopted visual period-luminosity relation is=-2.77logP-1.44+/-0.05. Moreover, we extend this study to thephotometric I band (Cousins) and obtain=-3.05logP-1.81+/-0.09.
| 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.
| A catalog of Cepheid radial velocities measured in 1995-1998 with the correlation spectrometer
We present a catalog of 2444 original radial-velocity measurements for108 Cepheids based on the 1995-1998 observations with the correlationspectrometer. Detailed radial-velocity curves are given for 12 Cepheidsfor the first time.
| New spectroscopic binaries among classical Cepheids. II.
Radial velocity measurements of classical Cepheids obtained by theCORAVEL and ELODIE spectrographs have been analysed. The comparison withearlier radial velocity data resulted in the discovery of eight newspectroscopic binaries (in the 9.7'-12.4' interval of meanV-brightness). An updated value of the pulsation period is alsodetermined for the new SB-Cepheids.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | ぎょしゃ座 |
| Right ascension: | 05h15m21.98s |
| Declination: | +40°04'40.9" |
| Apparent magnitude: | 10.254 |
| Proper motion RA: | -1.4 |
| Proper motion Dec: | 1.3 |
| B-T magnitude: | 12.262 |
| V-T magnitude: | 10.42 |
Catalogs and designations:
|
