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Публикации по объекту
CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| The metallicity dependence of the Cepheid PL-relation
A sample of 37 Galactic, 10 LMC and 6 SMC cepheids is compiled for whichindividual metallicity estimates exist and BVIK photometry in almost allcases. The Galactic cepheids all have an individual distance estimateavailable. For the MC objects different sources of photometry arecombined to obtain improved periods and mean magnitudes. Amulti-parameter Period-Luminosity relation is fitted to the data whichalso solves for the distance to the LMC and SMC. When all three galaxiesare considered, without metallicity effect, a significant quadratic termin log P is found, as previously observed and also predicted in sometheoretical calculations. For the present sample it is empiricallydetermined that for log P < 1.65 linear PL-relations may be adopted,but this restricts the sample to only 4 LMC and 1 SMC cepheid.Considering the Galactic sample a metallicity effect is found in thezero point in the VIWK PL-relation (-0.6 ± 0.4 or -0.8 ±0.3 mag/dex depending on the in- or exclusion of one object), in thesense that metal-rich cepheids are brighter. The small significance ismostly due to the fact that the Galactic sample spans a narrowmetallicity range. The error is to a significant part due to the errorin the metallicity determinations and not to the error in the fit.Including the 5 MC cepheids broadens the observed metallicity range anda metallity effect of about -0.27 ± 0.08 mag/dex in the zeropoint is found in VIWK, in agreement with some previous empiricalestimates, but now derived using direct metallicity determinations forthe cepheids themselves.
| Period-luminosity relations for Galactic Cepheid variables with independent distance measurements
In this paper, we derive the period-luminosity (PL) relation forGalactic Cepheids with recent independent distance measurements fromopen cluster, Barnes-Evans surface brightness, interferometry and HubbleSpace Telescope astrometry techniques. Our PL relation confirms theresults from recent works, which showed that the Galactic Cepheidsfollow a different PL relation to their Large Magellanic Cloud (LMC)counterparts. Our results also show that the slope of the Galactic PLrelation is inconsistent with the LMC slope with more than 95 per centconfidence level. We apply this Galactic PL relation to find thedistance to NGC 4258. Our result of μo= 29.49 +/- 0.06 mag(random error) agrees at the ~1.4σ level with the geometricaldistance of μgeo= 29.28 +/- 0.15 mag from water masermeasurements.
| 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.
| A Bayesian Analysis of the Cepheid Distance Scale
We develop and describe a Bayesian statistical analysis to solve thesurface brightness equations for Cepheid distances and stellarproperties. Our analysis provides a mathematically rigorous andobjective solution to the problem, including immunity from Lutz-Kelkerbias. We discuss the choice of priors, show the construction of thelikelihood distribution, and give sampling algorithms in a Markov chainMonte Carlo approach for efficiently and completely sampling theposterior probability distribution. Our analysis averages over theprobabilities associated with several models rather than attempting topick the ``best model'' from several possible models. Using a sample of13 Cepheids we demonstrate the method. We discuss diagnostics of theanalysis and the effects of the astrophysical choices going into themodel. We show that we can objectively model the order of Fourierpolynomial fits to the light and velocity data. By comparison withtheoretical models of Bono et al. we find that EU Tau and SZ Tau areovertone pulsators, most likely without convective overshoot. Theperiod-radius and period-luminosity relations we obtain are shown to becompatible with those in the recent literature. Specifically, we findlog()=(0.693+/-0.037)[log(P)-1.2]+(2.042+/-0.047) andv>=-(2.690+/-0.169)[log(P)-1.2]-(4.699+/-0.216).
| Period Changes in Galactic Classical Cepheids. Slow Evolution of Long-Period Cepheids
We compared period changes derived from O-C diagrams for 63 classicalCepheids from our Galaxy with model calculations. We found that forCepheids with log P > 1.0 the observed changes are smaller thanpredicted values, except variable SZ Cas. However some of the firstovertone Cepheids, particularly EU Tau and Polaris, change its periodmuch faster than it follows from theory. Summary of the known data onperiod changes in Cepheids from the Galaxy and from the MagellanicClouds (previous papers) leads to conclusion that none of the 999Cepheids is undergoing the first crossing of the instability strip. Alsothe observed period changes for long-period Cepheids are a few timesslower than predicted by the models. These results imply that muchlarger fraction of helium is burned in the Cepheid stage than it ispredicted by models.
| Fundamental Parameters of Cepheids. V. Additional Photometry and Radial Velocity Data for Southern Cepheids
I present photometric and radial velocity data for Galactic Cepheids,most of them being in the southern hemisphere. There are 1250 Genevaseven-color photometric measurements for 62 Cepheids, the averageuncertainty per measurement is better than 0.01 mag. A total of 832velocity measurements have been obtained with the CORAVEL radialvelocity spectrograph for 46 Cepheids. The average accuracy of theradial velocity data is 0.38 km s-1. There are 33 stars withboth photometry and radial velocity data. I discuss the possiblebinarity or period change that these new data reveal. I also presentreddenings for all Cepheids with photometry. The data are availableelectronically. Based on observations obtained at the European SouthernObservatory, La Silla.
| CHARM: A Catalog of High Angular Resolution Measurements
The Catalog of High Angular Resolution Measurements (CHARM) includesmost of the measurements obtained by the techniques of lunaroccultations and long-baseline interferometry at visual and infraredwavelengths, which have appeared in the literature or have otherwisebeen made public until mid-2001. A total of 2432 measurements of 1625sources are included, along with extensive auxiliary information. Inparticular, visual and infrared photometry is included for almost allthe sources. This has been partly extracted from currently availablecatalogs, and partly obtained specifically for CHARM. The main aim is toprovide a compilation of sources which could be used as calibrators orfor science verification purposes by the new generation of largeground-based facilities such as the ESO Very Large Interferometer andthe Keck Interferometer. The Catalog is 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/386/492, and from theauthors on CD-Rom.
| 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
| 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
| Coordinates and Identifications for Sonneberg variables on MVS 287-291
Not Available
| 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.
| Analyses of the Short-Period Cepheid SU Cassiopeiae
Baade-Wesselink analyses of this important Galactic classical Cepheidprovide new values for the radius, luminosity, distance, and mass andshow SU Cas likely to be pulsating in the first overtone. Application ofa modified Baade-Wesselink technique and the maximum likelihood method,which we have previously applied to δ Scuti-type variables, yieldvalues of R=33.0+/-1.1 Rsolar, L=1536+/-291Lsolar, MV=-3.28-0.19+0.23, r=486+/-52 pc,mass (from the Baade-Wesselink radius), M=6.5+/-0.6 Msolar(assuming first-overtone pulsation), and evolutionary mass,Mev=5.5+/-0.3 Msolar. The results are consistentwith the Hipparcos satellite parallax, 2.31+/-0.58 mas(433+145-87 pc), providing further support forovertone pulsation of SU Cas. In the course of the analyses, amodification to the maximum likelihood method, devised by one of us (W.J. F. W.), is presented as an alternative to the modifications of Laney& Stobie and Coulson, Caldwell, & Gieren. We dedicate this paper toAdriaan J. Wesselink, a dedicated scientist and teacher, and inventor of``the method.''
| 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.
| Structural properties of s-Cepheid velocity curves Constraining the location of the omega_4 = 2omega_1 resonance
The light curves of the first overtone Pop. I Cepheids (s-Cepheids) showa discontinuity in their phi_ {21} vs. {P} diagram, near {P} = 3.2 day.This feature, commonly attributed to the 2:1 resonance between the firstand the fourth overtones (omega_4 ~ 2omega_1 ), is not reproduced by thehydrodynamical models. With the goal of reexamining the resonancehypothesis, we have obtained new CORAVEL radial velocity curves for 14overtone Cepheids. Together with 10 objects of Krzyt et al.( te{krzyt}), the combined sample covers the whole range of overtoneCepheid periods. The velocity Fourier parameters display a strongcharacteristic resonant behavior. In striking contrast to photometricones, they vary smoothly with the pulsation period and show no jump at3.2 day. The existing radiative hydrodynamical models match the velocityparameters very well. The center of the omega_4 = 2omega_1 resonance isestimated to occur at {P}r = 4.58\pm 0.04 day, i.e. at aperiod considerably longer than previously assumed (3.2 day). Weidentify two new members of the s-Cepheid group: MYPup and V440 Per. Based on observationscollected at the European Southern Observatory (La Silla, Chile) and atthe Observatoire de Haute-Provence (France)}
| BA II lines as luminosity indicators: s-Cepheids and non-variable supergiants
Ba II line equivalent widths appear to be well correlated with theabsolute magnitudes for yellow supergiants. Two Ba II lines 5853.6Angstroms and 6141.7 Angstroms were applied for investigation of thepossible relation between their equivalent widths and Mv forsmall-amplitude Cepheids and non-variable supergiants.
| Ba II line as Cepheid luminosity indicator. I
Ba II lines are proposed as luminosity indicators for yellowsupergiants. In particular, it is shown that equivalent width of BaII5853.6 line is well correlated with for sCepheids.
| The effect of artificial viscosity on a hydrodynamic model of Cepheids
The effect of artificial viscosity on a hydrodynamic simulation ofstellar radial pulsation is examined for the purpose of studying thedependence of the modal coupling on the sharpness of the shock front.The model used in our study is a 2.5-d first-overtone pulsator in theCepheid instability strip. By increasing the parameters in the vonNeumann-Richtmyer formula of artificial viscosity, we obtained a lowgrowth rate together with a small pulsation amplitude. The time scalerelated to pulsation mode-switching is also increased.
| A catalog of Cepheid radial velocities measured in 1995-1998 with the correlation spectrometer.
Not Available
| Monitoring the Evolution of Cepheid Variables
Described here are preliminary results of a pilot project to monitorchanges in the ephemerides of northern hemisphere Cepheid's using anSBIG camera attached to the 0.4-m telescope of the campus obversatory atSaint Mary's University. Epochs of maximum light for fifteen Cepheid'shave been derived using published light curves for each variable astemplates, and the results are being used to update the O-C ephemeridesfor the program stars. Results for BB Her are presented here. Periodchanges for Cepheid variables are demonstrated to be an excellent meansof pinpointing their evolutionary status, as well as for investigatingother peculiarities of the class.
| Radii of Low-Amplitude Cepheids and Their Pulsation Mode
Based on the period-radius relation of classical cepheids, it is shownthat both fundamental ard first overtone pulsators occur among thelow-amplitude cepheids
| Radii and Distances of Cepheids. I. Method and Measurement Errors
We develop a formulation of the Baade-Wesselink method which uses theFourier coefficients of the observables. We derive an explicit, analyticexpression to determine the mean radius from each Fourier order. Thesimplicity of this method allows us to derive the uncertainty in themean radius due to measurement errors. Using simulations and a recentdata set we demonstrate that the precision of the radius measurementwith optical magnitudes is in most cases limited by the accuracy of themeasurement of the phase difference between the light and the colorindex curve. In this case it is advantageous to determine the inverseradius, because it has normal errors.
| Fundamental parameters of Cepheids. IV. Radii and luminosities.
A temperature scale for Cepheids is presented, based on Genevaphotometry. It uses new atmosphere models computed at various values ofmicroturbulent velocity. The scale so-obtained is compared to other onesand the importance of microturbulence effects is shown. This calibrationis applied to 20 Cepheids for which the variation of microturbulence isknown. The detailed variations of temperature and gravity are derived.The behavior of the photometric gravity is in very good agreement withthe effective gravity (sum of GM/R^2^ and of the derivative of theradial velocity). Thus static atmosphere models can be used to describethe temperature and gravity variations in Cepheids under the followingconditions: i) the microturbulence has to be taken into account, ii) theeffective gravity must be considered instead of the static gravity, iii)in some cases, a small phase interval around minimum radius does notgive reliable results. The temperature and bolometric corrections arethen used to derive radii and distances via the Baade-Wesselinktechnique. The resulting Period-Radius and Period-Luminosity relationsare discussed. Our results compare very well with similar analysis basedon infra-red (JHK) photometry.
| Cepheid radii and the CORS method revisited.
We have refined the CORS method, introduced in 1980 for the computationof the cepheid radii, in order to extend its applicability to recent andextensive sets of observations. The refinement is based on thecomputation, from observational data only, of one of the terms of thesolving equation, previously based only on precise calibrations ofphotometric colors. A limited number of assumptions, generally acceptedin the literature, is used. New radii are computed for about 70cepheids, and the resulting P-R relation is discussed.
| A search for evolutionary changes in the periods of low-amplitude Cepheids.
Not Available
| The chemical composition of the s-Cepheids. III.
The hypothesis about s-Cepheids' first time crossing of the instabilitystrip is checked by spectroscopic testing. On the basis of CCD spectraanalysis, we have derived the abundances for seven s-Cepheids. Thefollowing results have been obtained: 1) V473 Lyr, IR Cep, UY Mon, BYCas, V636 Cas have solar iron abundance, while V526 Mon and V924 Cygshow moderate iron deficiency. 2) The absolute carbon deficiency(relatively to the solar (C/H) value) found for all program stars(excepting V636 Cas) and a nitrogen overabundance show that theses-Cepheids are not crossing the instability strip for the first time. 3)Similarly to previously investigated Cepheid V1162 Aql, V636 Cas alsodemonstrates rather high carbon content. The plausible explanation ofthis phenomenon is that this star is crossing the instability strip forthe first time. 4) Na and Al are overabundant for all program starswhere these elements were measured. Sodium overabundance takes placealso for two first- time crossing Cepheids. Possibly such anoverabundance arises during the main-sequence phase. 5) α-elementsshow practically solar ratios with respect to Fe. 6) For iron-groupelements the (M/Fe) values are close to the solar ones. 7) s-processelements are perhaps slightly enhanced in the program stars. The resultsof the present paper are discussed together with the results of therecent paper by Andrievsky et al. (1996A&A...305..551A) devoted tos-Cepheids.
| Colour excesses of F-G supergiants and Cepheids from Geneva photometry.
A reddening scale for F-G supergiants and Cepheids is presented.Supergiants with low reddenings or in clusters form the basis of thecalibration. In this sense, it is entirely empirical. The data have beenobtained in the Geneva photometric system. Comparisons with otherreddening scales show no disagreement. The only problem is with Fernie'sscale for Cepheids (1990), where a systematic trend exists. Its originis not clear. It is suggested to extend the number of supergiants withindependently obtained colour excesses in order to test the existence ofa possible luminosity dependence of the calibration. A period-colourrelation for Cepheids is deduced, on the basis of the present reddeningcorrections. It gives strong support for V473 Lyr being a secondovertone pulsator.
| Fundamental parameters of Cepheids. III. Turbulence variations.
Observations of the line broadening during the cycle of pulsation areanalysed for 41 Cepheids. The main components of this line broadeningare the stellar atmospheric turbulence and the velocity fields due topulsation and to axial rotation. The variation of the broadening due topulsation is calculated for each star by using the observed radialvelocity curve. The residual broadening at maximum radius allows to showthat the value of the equatorial rotational velocity is smaller than ~10km/s for the large majority of classical Cepheids. It will be shown thatturbulence is the major effect that can explain the variation of thelines widths during the cycle of pulsation. We show that the behavioursof classical and s-Cepheids are different with respect to turbulence anda new method is proposed to separate these classes. This leads to thediscovery of a few new s-Cepheids. The second overtone Cepheid V473 Lyrdoes not follow the sequence of s-Cepheids, that are highly suspected tobe overtone pulsators. It is also shown that the turbulence is in phasewith the acceleration and, particularly, that the maximum turbulence isattained near minimum radius, where the acceleration is also at itsmaximum.
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Наблюдательные данные и астрометрия
| Созвездие: | Телец |
| Прямое восхождение: | 05h45m40.53s |
| Склонение: | +18°39'24.8" |
| Видимая звёздная величина: | 8.108 |
| Расстояние: | 1162.791 парсек |
| Собственное движение RA: | 0 |
| Собственное движение Dec: | -2.1 |
| B-T magnitude: | 8.909 |
| V-T magnitude: | 8.175 |
Каталоги и обозначения:
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