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Rate of Period Change as a Diagnostic of Cepheid Properties
The rate of period change P˙ for a Cepheid is shown to be aparameter that is capable of indicating the instability-strip crossingmode for individual objects and, in conjunction with light amplitude,the likely location of the object within the instability strip. Theobserved rates of period change in over 200 Milky Way Cepheids aredemonstrated to be in general agreement with predictions from stellarevolutionary models, although the sample also displays features that areinconsistent with some published models and indicative of the importanceof additional factors not fully incorporated in models to date.
| Cepheid distances from interferometry .
Long baseline interferometry is now able to resolve the pulsationalchange of the angular diameter of a significant number of Cepheids inthe solar neighborhood. This allows the application of a new version ofthe Baade-Wesselink (BW) method to measure their distance, for which wedo not need to estimate the star's temperature. Using angular diametermeasurements from the VLT Interferometer, we derived the distances tofour nearby Cepheids. For three additional stars, we obtained averagevalues of their angular diameters. Based on these new measurements andalready existing data, we derived calibrations of the Period-Luminosityand Period-Radius relations. We also obtained reliable surfacebrightness-color relations, that can be employed for the infraredsurface brightness version of the BW method.
| High resolution spectroscopy for Cepheids distance determination. I. Line asymmetry
Context: .The ratio of pulsation to radial velocity (the projectionfactor) is currently limiting the accuracy of the Baade-Wesselinkmethod, and in particular of its interferometric version recentlyapplied to several nearby Cepheids. Aims: .This work aims atestablishing a link between the line asymmetry evolution over theCepheids' pulsation cycles and their projection factor, with the finalobjective to improve the accuracy of the Baade-Wesselink method fordistance determinations. Methods: .We present HARPS high spectralresolution observations (R=120 000) of nine galactic Cepheids:R Tra, S Cru, YSgr, β Dor, ζGem, Y Oph, RZ Vel,ℓ Car and RS Pup, having agood period sampling (P=3.39d to P=41.52d). We fit spectral lineprofiles by an asymmetric bi-Gaussian to derive radial velocity,Full-Width at Half-Maximum in the line (FWHM) and line asymmetry for allstars. We then extract correlations curves between radial velocity andasymmetry. A geometric model providing synthetic spectral lines,including limb-darkening, a constant FWHM (hereafter σ_C) and therotation velocity is used to interpret these correlations curves.Results: .For all stars, comparison between observations and modellingis satisfactory, and we were able to determine the projected rotationvelocities and σC for all stars. We also find acorrelation between the rotation velocity (V_rot sin i) and the periodof the star: V_rot sin i= (-11.5 ± 0.9) log (P) + (19.8 ±1.0) [ km s-1] . Moreover, we observe a systematic shift inobservational asymmetry curves (noted γ_O), related to the periodof the star, which is not explained by our static model:γ_O=(-10.7 ± 0.1) log (P) + (9.7 ± 0.2) [in %]. Forlong-period Cepheids, in which velocity gradients, compression or shockwaves seem to be large compared to short- or medium-period Cepheids weobserve indeed a greater systematic shift in asymmetry curves.Conclusions: .This new way of studying line asymmetry seems to be verypromising for a better understanding of Cepheids atmosphere and todetermine, for each star, a dynamic projection factor.
| Extended envelopes around Galactic Cepheids. I. ℓ Carinae from near and mid-infrared interferometry with the VLTI
We present the results of long-baseline interferometric observations ofthe bright southern Cepheid ℓ Carinae in the infrared N (8-13 μm)and K (2.0-2.4 μm) bands, using the MIDI and VINCI instruments of theVLT Interferometer. We resolve in the N band a large circumstellarenvelope (CSE) that we model with a Gaussian of 3 Rstar(≈500 Rȯ ≈ 2-3 AU) half width at half maximum. Thesignature of this envelope is also detected in our K band data as adeviation from a single limb darkened disk visibility function. Thesuperimposition of a Gaussian CSE on the limb darkened disk model of theCepheid star results in a significantly better fit of our VINCI data.The extracted CSE parameters in the K band are a half width at halfmaximum of 2 Rstar, comparable to the N band model, and atotal brightness of 4% of the stellar photosphere. A possibility is thatthis CSE is linked to the relatively large mass loss rate of ℓ Car.Though its physical nature cannot be determined from our data, wediscuss an analogy with the molecular envelopes of RV Tauri, redsupergiants and Miras.
| Mean JHK Magnitudes of Fundamental-Mode Cepheids from Single-Epoch Observations
We present an empirical method for converting single-point near-infraredJ, H, and K measurements of fundamental-mode Cepheids to meanmagnitudes, using complete light curves in V or I bands. The algorithmis based on the template light curves in the near-infrared bandpasses.The mean uncertainty of the method is estimated to about 0.03 mag, whichis smaller than the uncertainties obtained in other approaches to theproblem in the literature.
| The Period Changes of Polaris
The evolutionary changes in pulsation period for the Cepheid Polaris arereinvestigated using archival observational material (radial velocities,photometry, and eye observations) over the interval 1844 to the present,including new photometry for the star obtained in 2003-2004. The star'spulsation period increased at a rate of 4.5 s yr-1 duringthat interval, with the exception of a brief hiatus between 1963 and1966, when it suddenly decreased, possibly as a result of a briefreduction in average stellar radius amounting to -0.055%. At roughly thesame time, the pulsation amplitude of Polaris underwent a marked change.Prior to 1963 the V amplitude was in excess of about 0.1 mag, possiblydecreasing at a rate of 0.019 mag century-1. Following thehiatus of 1963-1966, the pulsation amplitude underwent a sharp declineand now appears to be erratic on a cycle-to-cycle basis, always smallerthan 0.05 mag. The rapid rate of period increase for Polaris isconsistent with a first crossing of the Cepheid instability strip, whilethe hiatus of 1963-1966 and sudden decrease in pulsation amplitudethereafter suggest that the star may have left the instability strip forfirst crossers at that time, leaving it near the center of theinstability strip for Cepheids in higher crossing modes.
| A spectroscopic study of bright southern Cepheids - a high-resolution view of Cepheid atmospheres
We present high-resolution spectroscopic observations andspecies-by-species radial velocities of a number of southern Cepheids.The stars (BP Cir, V350 Sgr, AX Cir, V636 Sco, W Sgr, S Mus, β Dor,TT Aql, Y Oph, YZ Car, SW Vel, X Pup, T Mon and l Car) were observed aspart of a long-term programme at Mt John University Observatory. Radialvelocities were determined with the line bisector technique, and have aprecision of ~300 ms-1. Velocity differences as large as 30kms-1 were found for Hα and CaII when referenced to themetallic line velocity curves, but more subtle variations (of 1-2kms-1) were also detected in many other species. Pulsationalphase anticorrelations are found between lines of SiII and BaII,confirming the propagation time delay between line-forming layersproducing these two species. We find that the amplitude and phasedifferences between the various species increase with period.
| Predicting accurate stellar angular diameters by the near-infrared surface brightness technique
I report on the capabilities of the near-infrared (near-IR) surfacebrightness technique to predict reliable stellar angular diameters asaccurate as <~2 per cent using standard broad-band Johnson photometryin the colour range -0.1 <= (V-K)O<= 3.7 includingstars of A, F, G, K spectral type. This empirical approach is fast toapply and leads to estimated photometric diameters in very goodagreement with recent high-precision interferometric diametermeasurements available for non-variable dwarfs and giants, as well asfor Cepheid variables. Then I compare semi-empirical diameters predictedby model-dependent photometric and spectrophotometric (SP) methods withnear-IR surface brightness diameters adopted as empirical referencecalibrators. The overall agreement between all these methods is withinapproximately +/-5 per cent, confirming previous works. However, on thesame scale of accuracy, there is also evidence for systematic shiftspresumably as a result of an incorrect representation of the stellareffective temperature in the model-dependent results. I also comparemeasurements of spectroscopic radii with near-IR surface brightnessradii of Cepheids with known distances. Spectroscopic radii are found tobe affected by a scatter as significant as >~9 per cent, which is atleast three times greater than the formal error currently claimed by thespectroscopic technique. In contrast, pulsation radii predicted by theperiod-radius (PR) relation according to the Cepheid period result aresignificantly less dispersed, indicating a quite small scatter as aresult of the finite width of the Cepheid instability strip, as expectedfrom pulsation theory. The resulting low level of noise stronglyconfirms our previous claims that the pulsation parallaxes are the mostaccurate empirical distances presently available for Galactic andextragalactic Cepheids.
| Zur Beobachtung und Auswertung von Cepheiden-Lichtkurven.
Not Available
| Welchen Lichtwechsel kann ein Beobachter bei Cepheiden erwarten?
Not Available
| Infrared Surface Brightness Distances to Cepheids: A Comparison of Bayesian and Linear-Bisector Calculations
We have compared the results of Bayesian statistical calculations andlinear-bisector calculations for obtaining Cepheid distances and radiiby the infrared surface brightness method. We analyzed a set of 38Cepheids using a Bayesian Markov Chain Monte Carlo method that had beenrecently studied with a linear-bisector method. The distances obtainedby the two techniques agree to 1.5%+/-0.6%, with the Bayesian distancesbeing larger. The radii agree to 1.1%+/-0.7%, with the Bayesiandeterminations again being larger. We interpret this result asdemonstrating that the two methods yield the same distances and radii.This implies that the short distance to the Large Magellanic Cloud foundin recent linear-bisector studies of Cepheids is not caused bydeficiencies in the mathematical treatment. However, the computeduncertainties in distance and radius for our data set are larger in theBayesian calculation by factors of 1.4-6.7. We give reasons to favor theBayesian computations of the uncertainties. The larger uncertainties canhave a significant impact on interpretation of Cepheid distances andradii obtained from the infrared surface brightness method.
| Direct Distances to Cepheids in the Large Magellanic Cloud: Evidence for a Universal Slope of the Period-Luminosity Relation up to Solar Abundance
We have applied the infrared surface brightness (ISB) technique toderive distances to 13 Cepheid variables in the LMC that span a periodrange from 3 to 42 days. From the absolute magnitudes of the variablescalculated from these distances, we find that the LMC Cepheids definetight period-luminosity (PL) relations in the V, I, W, J, and K bandsthat agree exceedingly well with the corresponding Galactic PL relationsderived from the same technique and are significantly steeper than theLMC PL relations in these bands observed by the OGLE-II Project in V, I,and W and by Persson and coworkers in J and K. We find that the LMCCepheid distance moduli we derive, after correcting them for the tilt ofthe LMC bar, depend significantly on the period of the stars, in thesense that the shortest period Cepheids have distance moduli near 18.3,whereas the longest period Cepheids are found to lie near 18.6. Sincesuch a period dependence of the tilt-corrected LMC distance modulishould not exist, there must be a systematic, period-dependent error inthe ISB technique not discovered in previous work. We identify as themost likely culprit the p-factor, which is used to convert the observedCepheid radial velocities into their pulsational velocities. Bydemanding (1) a zero slope on the distance modulus versus period diagramand (2) a zero mean difference between the ISB and ZAMS fitting distancemoduli of a sample of well-established Galactic cluster Cepheids, wefind that p=1.58(+/-0.02)-0.15(+/-0.05)logP, with the p-factor dependingmore strongly on Cepheid period (and thus luminosity) than indicated bypast theoretical calculations. When we recalculate the distances of theLMC Cepheids with the revised p-factor law suggested by our data, we notonly obtain consistent distance moduli for all stars but also decreasethe slopes in the various LMC PL relations (and particularly in thereddening-independent K and W bands) to values that are consistent withthe values observed by OGLE-II and Persson and coworkers. From our 13Cepheids, we determine the LMC distance modulus to be 18.56+/-0.04 mag,with an additional estimated systematic uncertainty of ~0.1 mag. Usingthe same corrected p-factor law to redetermine the distances of theGalactic Cepheids, the new Galactic PL relations are also foundconsistent with the observed optical and near-infrared PL relations inthe LMC. Our main conclusion from the ISB analysis of the LMC Cepheidsample is that, within current uncertainties, there seems to be nosignificant difference between the slopes of the PL relations in theMilky Way and LMC. With literature data on more metal-poor systems, itseems now possible to conclude that the slope of the Cepheid PL relationis independent of metallicity in the broad range in [Fe/H] from -1.0 dexto solar abundance, within a small uncertainty. The new evidence fromthe first ISB analysis of a sizable sample of LMC Cepheids suggests thatthe previous, steeper Galactic PL relations obtained from this techniquewere caused by an underestimation of the period dependence in themodel-based p-factor law used in the previous work. We emphasize,however, that our current results must be substantiated by newtheoretical models capable of explaining the steeper period dependenceof the p-factor law, and we will also need data on more LMC fieldCepheids to rule out remaining concerns about the validity of ourcurrent interpretation.
| 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.
| 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
| Cepheid pulsations resolved by the VLTI.
Not Available
| 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.
| Cepheidenbeobachtung in der BAV: Ruckblick und Ausblick.
Not Available
| Phase-dependent Variation of the Fundamental Parameters of Cepheids. I. Periods from 6 to 10 Days
We present the results of a detailed multiphase spectroscopic analysisof 10 classical Cepheids with pulsation periods between 6 and 10 days.For each star, we have derived phased values of effective temperature,surface gravity, microturbulent velocity, and elemental abundances. Weshow that the elemental abundance results for intermediate-periodCepheids are consistent for all pulsational phases.
| Cepheid distances from infrared long-baseline interferometry. III. Calibration of the surface brightness-color relations
The recent VINCI/VLTI observations presented in Paper I have nearlydoubled the total number of available angular diameter measurements ofCepheids. Taking advantage of the significantly larger color rangecovered by these observations, we derive in the present paper highprecision calibrations of the surface brightness-color relations usingexclusively Cepheid observations. These empirical laws make it possibleto determine the distance to Cepheids through a Baade-Wesselink typetechnique. The least dispersed relations are based on visible-infraredcolors, for instance FV(V-K) = -0.1336 ± 0.0008 (V-K)+ 3.9530 ± 0.0006}. The convergence of the Cepheid (this work)and dwarf star (Kervella et al. \cite{kervella04c}) visible-infraredsurface brightness-color relations is strikingly good. The astrophysicaldispersion of these relations appears to be very small, and below thepresent detection sensitivity.Table \ref{table_measurements1} is only available in electronic form athttp://www.edpsciences.org
| Cepheid distances from infrared long-baseline interferometry. II. Calibration of the period-radius and period-luminosity relations
Using our interferometric angular diameter measurements of sevenclassical Cepheids reported in Kervella et al. (\cite{kervella04},A&A, 416, 941 - Paper I), complemented by previously existingmeasurements, we derive new calibrations of the Cepheid period-radius(P-R) and period-luminosity (P-L) relations. We obtain a P-R relation oflog R = [0.767 ± 0.009] log P + [1.091 ± 0.011], only 1σ away from the relation obtained by Gieren et al.(\cite{gieren98}, ApJ, 496, 17). We therefore confirm their P-R relationat a level of Δ(log R) = ± 0.02. We also derive an originalcalibration of the P-L relation, assuming the slopes derived by Gierenet al. (\cite{gieren98}) from LMC Cepheids, αK = -3.267± 0.042 and αV = -2.769 ± 0.073. With aP-L relation of the form Mλ =αλ (log P - 1) + βλ, weobtain log P = 1 reference points of βK = -5.904± 0.063 and βV = -4.209 ± 0.075. Ourcalibration in the V band is statistically identical to the geometricalresult of Lanoix et al. (\cite{lanoix99}, MNRAS, 308, 969).
| Improvement of the CORS method for Cepheids radii determination based on Strömgren photometry
In this paper we present a modified version of the CORS method based ona new calibration of the Surface Brightness function in theStrömgren photometric system. The method has been tested by meansof synthetic light and radial velocity curves derived from nonlinearpulsation models. Detailed simulations have been performed to take intoaccount the quality of real observed curves as well as possible shiftsbetween photometric and radial velocity data. The method has been thenapplied to a sample of Galactic Cepheids with Strömgren photometryand radial velocity data to derive the radii and a new PR relation. As aresult we find log R = (1.19 ± 0.09) + (0.74 ± 0.11) logP (rms = 0.07). The comparison between our result and previous estimatesin the literature is satisfactory. Better results are expected from theadoption of improved model atmosphere grids.
| 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.
| Cepheid distances from infrared long-baseline interferometry. I. VINCI/VLTI observations of seven Galactic Cepheids
We report the angular diameter measurements of seven classical Cepheids,X Sgr, η Aql, W Sgr, ζ Gem, β Dor, Y Oph and ℓ Carthat we have obtained with the VINCI instrument, installed at ESO's VLTInterferometer (VLTI). We also present reprocessed archive data obtainedwith the FLUOR/IOTA instrument on ζ Gem, in order to improve thephase coverage of our observations. We obtain average limb darkenedangular diameter values of /line{θLD}[X Sgr] = 1.471± 0.033 mas, /line{θLD[η Aql] = 1.839± 0.028 mas, /line{θLD}[W Sgr] = 1.312 ±0.029 mas, /line{θLD}[β Dor] = 1.891 ±0.024 mas, /line{θLD}[ζ Gem] =1.747 ±0.061 mas, /line{θLD}[Y Oph] = 1.437 ± 0.040mas, and /line{θLD}[ℓ Car] = 2.988 ± 0.012mas. For four of these stars, η Aql, W Sgr, β Dor, and ℓCar, we detect the pulsational variation of their angular diameter. Thisenables us to compute directly their distances, using a modified versionof the Baade-Wesselink method: d[η Aql] =276+55-38 pc, d[W Sgr] =379+216-130 pc, d[β Dor] =345+175-80 pc, d[ℓ Car] =603+24-19 pc. The stated error bars arestatistical in nature. Applying a hybrid method, that makes use of theGieren et al. (\cite{gieren98}) Period-Radius relation to estimate thelinear diameters, we obtain the following distances (statistical andsystematic error bars are mentioned): d[X Sgr] = 324 ± 7 ±17 pc, d[η Aql] = 264 ± 4 ± 14 pc, d[W Sgr] = 386± 9 ± 21 pc, d[β Dor] = 326 ± 4 ± 19pc, d[ζ Gem] = 360 ± 13 ± 22 pc, d[Y Oph] = 648± 17 ± 47 pc, d[ℓ Car] = 542 ± 2 ± 49pc.Tables 3 to 10 are only available in electronic form athttp://www.edpsciences.org
| J - K DENIS photometry of a VLTI-selected sample of bright southern stars
We present a photometric survey of bright southern stars carried outusing the DENIS instrument equipped with attenuating filters. Theobservations were carried out not using the survey mode of DENIS, butwith individual target pointings. This project was stimulated by theneed to obtain near-infrared photometry of stars to be used in earlycommissioning observations of the ESO Very Large TelescopeInterferometer, and in particular to establish a network of brightcalibrator sources.We stress that near-infrared photometry is peculiarly lacking for manybright stars. These stars are saturated in 2MASS as well as in regularDENIS observations. The only other observations available for brightinfrared stars are those of the Two Micron Sky Survey dating from overthirty years ago. These were restricted to declinations above≈-30°, and thus cover only about half of the sky accessible fromthe VLTI site.We note that the final 2MASS data release includes photometry of brightstars, obtained by means of point-spread function fitting. However, thismethod only achieves about 30% accuracy, which is not sufficient formost applications.In this work, we present photometry for over 600 stars, each with atleast one and up to eight measurements, in the J and K filters. Typicalaccuracy is at the level of 0\fm05 and 0\fm04 in the J and K_s bands,respectively.Based on observations collected at the European Southern Observatory, LaSilla.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/413/1037
| Cepheid Variables in the AAVSO International Database
There are 205,500 visual observations for 148 Cepheids as well as 182photoelectric observations for 7 Cepheids in the AAVSO InternationalDatabase. These data were reduced with Hertzprung's method and 2,010times of maximum brightness were obtained. O-C diagrams for 21well-observed Cepheids are presented and results obtained are comparedwith existing data.
| Beobachtungsegebnisse Bundesdeutsche Arbeitsgemainschaft fur Veranderliche Sterne e.V.
Not Available
| Sodium enrichment of the stellar atmospheres. II. Galactic Cepheids
The present paper is a continuation of our study of the sodium abundancein supergiant atmospheres (Andrievsky et al. 2002a). We present theresults on the NLTE abundance determination in Cepheids, and the derivedrelation between the sodium overabundance and their masses.
| 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.
| Cepheiden: was wird beobachtet - was nicht ?
Not Available
| 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.
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