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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.
| Photoelectric Observations of Southern Cepheids in 2001
A total of 2097 photometric observations in the BVIc systemare presented for 117 Cepheids located in the southern hemisphere. Themain purpose of the photometry is to provide new epochs of maximumbrightness for studying Cepheid period changes, as well as to establishcurrent light elements for the Cepheids.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| 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.
| I- and JHK-band photometry of classical Cepheids in the HIPPARCOS catalog
By correlating the \cite[Fernie et al. (1995)]{F95} electronic databaseon Cepheids with the ``resolved variable catalog'' of the hipparcosmission and the simbad catalog one finds that there are 280 Cepheids inthe hipparcos catalog. By removing W Vir stars (Type ii Cepheids),double-mode Cepheids, Cepheids with an unreliable solution in thehipparcos catalog, and stars without photometry, it turns out that thereare 248 classical Cepheids left, of which 32 are classified asfirst-overtone pulsators. For these stars the literature was searchedfor I-band and near-infrared data. Intensity-mean I-band photometry onthe Cousins system is derived for 189 stars, and intensity-mean JHK dataon the Carter system is presented for 69 stars.
| The shape and scale of Galactic rotation from Cepheid kinematics
A catalog of Cepheid variables is used to probe the kinematics of theGalactic disk. Radial velocities are measured for eight distant Cepheidstoward l = 300 deg; these new Cepheids provide a particularly goodconstraint on the distance to the Galactic center, R0. We model the diskwith both an axisymmetric rotation curve and one with a weak ellipticalcomponent, and find evidence for an ellipticity of 0.043 +/- 0.016 nearthe sun. Using these models, we derive R0 = 7.66 +/- 0.32 kpc andv(circ) = 237 +/- 12 km/s. The distance to the Galactic center agreeswell with recent determinations from the distribution of RR Lyraevariables and disfavors most models with large ellipticities at thesolar orbit.
| Derivation of the Galactic rotation curve using space velocities
We present rotation curves of the Galaxy based on the space-velocitiesof 197 OB stars and 144 classical cepheids, respectively, which rangeover a galactocentric distance interval of about 6 to 12kpc. Nosignificant differences between these rotation curves and rotationcurves based solely on radial velocities assuming circular rotation arefound. We derive an angular velocity of the LSR of{OMEGA}_0_=5.5+/-0.4mas/a (OB stars) and {OMEGA}_0_=5.4+/-0.5mas/a(cepheids), which is in agreement with the IAU 1985 value of{OMEGA}_0_=5.5mas/a. If we correct for probable rotations of the FK5system, the corresponding angular velocities are {OMEGA}_0_=6.0mas/a (OBstars) and {OMEGA}_0_=6.2mas/a (cepheids). These values agree betterwith the value of {OMEGA}_0_=6.4mas/a derived from the VLA measurementof the proper motion of SgrA^*^.
| Parameters of the JHK light curves of classical Cepheids and the interstellar-extinction LAW.
Not Available
| The radii of Galactic Cepheids
Optical photometry, infrared photometry and radial velocity data havebeen combined to derive Baade-Wesselink radii of 49 Galactic Cepheids.Of the many possible magnitude-colour combinations four are studied indetail, namely (V, B-V), (V, V-I_C), (K, J-K) and (K, V-K). Afundamental assumption in any form of the Baade-Wesselink technique isthat the surface brightness variations can be represented by changes inthe colour index. The sensitivity of the surface brightness-colour indexrelation to variations in gravity and microturbulence is examined frommodel atmosphere calculations. It is shown that the use of infraredphotometry in calculating Cepheid radii minimizes the effects of suchvariations, and that both random and systematic errors in Cepheid radiicalculated using optical photometry are much larger. The effects ofvarying microturbulence on radii determined using optical photometryappear to be even more severe than the effects of variations in surfacegravity, but both can cause serious systematic errors. The large numberof stars enables a detailed consideration of the factors systematicallyaffecting Baade-Wesselink radii. It is demonstrated that the limitingfactor in most of the radii derived from the observations we have usedis the accuracy with which the radius displacement curve can be definedfrom the radial velocity observations. The non-linear effects indetermining the radius are significant, and a new method by Balona isused to determine the non-linear maximum likelihood radii. This methodappears to be statistically correct, and supersedes the flawednon-linear correction algorithm used by Coulson et al. Comparisons withradii determined by least squares (including the surface brightnessmethod) show that the expected error-dependent systematic errors inleast-squares radii are indeed present. We demonstrate that thesystematic errors in radii calculated using V-I_C and V-R_J photometryappear to be virtually identical. The most accurate period-radiusrelation is derived from the combination of the (K, J-K) and (K, V-K)radius solutions:log R=1.821+0.751(log P-1) +/-0.008+/-0.026.Thisrelation differs significantly from many of the earlier determinationsof the period-radius relation based on various optical magnitude-colourcombinations. The slope is somewhat steeper than in Fernie's meanpre-OPAL theoretical relation, and the zero-point gives radii 12 percent smaller at log P=1. This deviation is in the expected sense, sincepre-OPAL studies predicted Cepheid luminosities greater than thoseobserved.
| New radial velocities for classical cepheids. Local galactic rotation revisited
New centre-of-mass radial velocities are calculated for 107 classicalcepheids from CORAVEL observations. We generally determine thesevelocities from four to six measurements carefully spaced in phase, byfitting a "typical" radial velocity curve or the mirror image of thelight curve. A decomposition in Fourier series is used for stars withmore than 10 measurements. Distances are then computed through aperiod-luminosity-colour relation for 278 classical cepheids with knownradial velocity, and an axisymmetric galactic rotation model is appliedto the sample, using a generalised non-linear least square method withuncertainties on both the velocities and the distances. The bestresults, with a rotation curve modelled as a third order polynomial,are: Rsun_=8.09 +/-0.30 kpc, A=15.92 +/-0.34 km/s/kpc, 2ARsun_=257 +/-7 km/s, A2=d^2theta(R)/d R^2^=-3.38+/-0.38 km/s/kpc^2^, A3=d^3theta(R)/d R^3^=1.99 +/-0.62km/s/kpc^3^, u_0_=9.32 +/-0.80 km/s, v_0_=11.18 +/-0.65 km/s. The effectof modifying the distance scale of cepheids, the absorption coefficientor the fitting procedure algorithm are examined. It appears that theproduct 2 A Rsun_ is very robust towards these changes. Theextended sample of classical cepheids with known radial velocitypresented in this paper seems to imply a higher value for A thananterior studies. The radial velocity residuals show a systematic k-termof about 2 km/s. New evidence from cluster cepheids excludes anintrinsic cause for this shift, and a dynamical cause is proposed from acomparison with a N-body simulation of the Galaxy. The simulation showsthat a systematic bias of this magnitude is typical. The structure ofthe local residual velocity field is examined in some detail.
| Cepheid Period / Luminosity Relations in K H J and V
Abstract image available at:http://adsabs.harvard.edu/abs/1994MNRAS.266..441L
| The Cepheid Period-Luminosity Relation from Independent Distances of 100 Galactic Variables
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993ApJ...418..135G&db_key=AST
| Visual and Infrared Extinction from Cepheid Observations
Accurate visual and infrared photometry of Cepheids in the Galaxy andthe Magellanic Clouds is used to determine the visual and infraredextinction laws. The infrared reddening law is derived for the standardsystem defined by Carter. Two different techniques are used to determinethe value of R = A_V_/E(B - V). Both give consistent results with aweighted mean of R_0_ = 3.06 +/- 0.09 at (B - V)_0_ = 0, given theassumption that A_V_/E(V - K) = 1.1 (Whittet & van Breda). Thederived infrared colour excess ratios are E(H-K)/E(B-V) = 0.171+/-0.007and E(J-H)/E(B-V) = 0.314+/-0.020 for (B-V)_0_ = 0 in the limit E(B-V)goes to zero, implying that E(J-H)/E(H-K)= 1.83 +/- 0.14. The infraredextinction coefficients derived are A_J_/E(B-V) = 0.764, A_H_/E(B-V) =0.450 and A_K_/E(B-V) = 0.279.
| Light-curve systematics of Cepheids in the infrared
Fourier decomposition of infrared light curves has been carried out for51 Galactic Cepheids. The systematic variation of the Fourier parameterswith period is determined. The P2/P sub 0 resonance near P =10 d dominates the trend in light-curve shape, and amplitude plays asecondary role. These relations provide the basis for any futureinvestigation of light-curve shape in the infrared where the lightvariation is dominated by the radius variation of the star.
| JHKL observations of galactic Cepheids
For 51 galactic Cepheids an average of 31 JHK observations per star havebeen obtained, sufficiently well distributed in phase to permit Fourierfitting and the determination of mean magnitudes and colors whoseaccuracy (about +/- 0.01 mag) is primarily determined by the internalconsistency of the standard system developed by Carter (1990). Limited Ldata have been obtained for 42 of these stars.
| A magnitude-limited survey of Cepheid companions in the ultraviolet
Results of a magnitude-limited survey of classic Cepheids brighter than8th mag carried out to search for hot main-sequence companions arepresented. Spectra of 76 stars obtained with the IUE satellite in the2000-3200-A region were compared with the spectra of nonvariablesupergiants and also the single Cepheid Delta Cep to search for excessflux at 2500 A from possible companions. Photometric companions werefound for 21 percent of the sample. When the Cepheids known to be binaryfrom either orbital motion or spectra in the 1200-2000-A region areincluded, the percentage of companions rises to 29 percent. If astatistical correction from stars with orbital motion is included, 34percent have companions. This percentage is compared with that found byAbt et al. (1990) for B2-B5 main-sequence stars. If only systems withperiods longer than a year and separations not more than 30 arcsec areconsidered, only 18 percent of the B stars will become Cepheids withcompanions.
| The calibration of the Stromgren photometric system for A, F and early G supergiants. I - The observational data
An empirical calibration of the Stromgren uvby-beta photometric systemfor the A, F, and early G supergiants is being derived. This paperexplains the observational program and the photometric reductiontechniques used and presents a catalog of new Stromgren photometry forover 600 A, F, and G supergiants.
| The structure of the Cepheid instability strip
About 100 classical Cepheids having color excesses on a homogeneoussystem with standard errors of 0.02 or less mag are used with theFeast-Walker period-luminosity-color relation to study the distributionof such stars in the instability strip. It is found that mean (B-V)magis a better indicator of mean effective temperature than is mean B(i) -mean V(i)(i). The blue edge of the color-magnitude distribution isconsistent with the theoretical blue edge for Y = 0.28 and Z = 0.02.Although the highest amplitude stars are found near the center of theperiod-color array, high- and low-amplitude stars can intermingle, andboth kinds are to be found near the edges of the distribution. The sameis true on the C-M array. Finally, it is pointed out that the Cepheidsdo not populate the instability strip uniformly if the red edge is takento be parallel to the theoretical blue edge. Rather, the localinstability region runs as a parallelogram in the C-M array from thetheoretical blue edge upward and to the red.
| Color Excesses on a Uniform Scale for 328 Cepheids
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990ApJS...72..153F&db_key=AST
| Towards a reconciliation of Cepheid masses
A new set of homogeneous Wesselink masses for 101 classical Cepheids isderived, as well as new evolution and pulsation masses for a subset of52 stars with known luminosities. A detailed comparison and discussionof the different mass determinations shows that, within theuncertainties inherent in each of the methods, there is satisfactoryagreement over the entire range of Cepheid pulsation periods. Inparticular, there is very good agreement among the evolution andWesselink masses. Theoretical masses of Cepheids as defined by Cox showreasonable agreement with the evolution masses.
| The radii of 27 southern galactic Cepheids
Photometric and radial velocity data for 27 Cepheids with P greater than9 d are analyzed and the results combined with those for 21shorter-period stars observed in an identical manner. The data areexamined for evidence of binary companions and the radii of these starsare determined as well as a period-radius relation for Cepheids.
| The period-radius relation for classical Cepheids from the visual surface brightness technique
Surface brightnesses have been obtained for 52 southern Cepheids and 63northern Cepheids using the (V-R) color index. A period-radius relation(in the period range of 3-45 days) of log R = 1.108 + or - 0.743 log Pis obtained, with uncertainties of + or - 0.023 in the zero point andslope. The influence of unresolved binaries and possible overtonepulsators on this relation is considered. The present period-radiusrelation is shown to be consistent with current determinations ofdistances and effective temperature scales for classical Cepheids. Noevidence is found to support the contention that all shorter periodCepheids are overtone pulsators.
| Period changes of bright southern Cepheids
O-C diagrams have been constructed for 44 bright southern Cepheids,mainly for studying the effects of duplicity on the pulsation period.Because the light-time effect in the O-C diagrams of binary Cepheids hasto be accompanied with properly phased variations in the gamma-velocity,the radial velocities of the programme stars have been studied, as well.Light-time effect is found or suspected in eleven cases (V946 Aql, AXCir, AG Cru, BG Cru, BF Oph, AP Pup, AT Pup, Y Sgr, AP Sgr, R TrA and VVel), and a preliminary value of the orbital period is suggested for 14Cepheid binaries (V946 Aql, AX Cir, AG Cru, Y Oph, BF Oph, AP Pup, ATPup, U Sgr, Y Sgr, AP Sgr, BB Sgr, RV Sco, R TrA and V Vel). Thephenomenon of the phase jump (i.e. the return of the pulsation period toan earlier value) is present in the O-C diagram of eight binaries (UAql, YZ Car, KN Cen, S Mus, S Nor, Y Oph, U Sgr and V350 Sgr).
| A cluster analysis of cepheids
The galactic distribution of 300 cepheids is considered. It is shownthat about half of them enter groups with characteristic dimensions ofseveral hundred parsecs. Due to their proximity, the cepheids in eachtaxon have similar radial velocity and period values. If the period of acepheid is associated with age, the results indicate that the clustercontains stars of approximately the same age.
| The Galactic Cepheid period-luminosity relation from the visual surface brightness method
The distances of 52 southern hemisphere Galactic Cepheids covering aperiod range of 3 to 40 days are determined using the visual surfacebrightness method (VSBM). Absolute magnitudes of these stars arecalculated, and a period-luminosity relation of small dispersion isobtained which is based on twice as many Cepheids as any formercalibration. Essential agreement is found between the surface brightnessand the ZAMS-fitting distance scale of Caldwell and Coulson (1987).Cepheid absolute magnitudes based on Stro["!mgren photometry of opencluster B stars are on average 0.2 mag fainter than these scales.Advantages and drawbacks of the present version of the VSBM arediscussed, and it is concluded that its present degree of refinement isadequate to determine the Cepheid luminosity zero point to better than0.2 mag. The slope of the visual surface brightness-color relation validfor Cepheids has now been established to a high degree of confidence.
| Precise Fourier Decomposition Parameters for Classical Cepheids
Abstract image available at:http://adsabs.harvard.edu/abs/1988A&A...196..159A
| Milky Way rotation and the distance to the galactic center from Cepheid variables
The compiled photometry, reddenings, and radial velocities of GalacticCepheids are fit with an axisymmetric Galactic rotation model. R(0) =7.8 + or - 0.7 kpc and 2AR(0) = 228 + or - 19 km/s are derived. The LMCdistance modulus is 18.45 on the same absolute calibration. ObservedCepheid gamma velocities appear on average to be 30 + or - 1 km/s morenegative than the true corresponding center-of-mass velocities. Thetrend of increasing blueness toward larger Galactocentric radiusconfirms the radial metallicity gradient found spectroscopically.
| Intermediate-band and H-beta observations of short-period Cepheids
Intermediate-band and H-beta observations along with light and colorcurves for short-period Cepheids are presented. Although mainlysouthern, a few northern variables are included. Two of the variablesare briefly discussed.
| Photometry and radial velocities of 27 southern galactic Cepheids
Some 950 radial velocities and about 1100 UBV(RI)cphotometric measures of 27 Galactic Cepheids with R 9d are presented.Pulsation periods are redetermined and light and color curves areproduced by aligning the older photometry with new data using suitablezero-point adjustments. The new radial velocities prove to be of a muchhigher quality than the rather limited amount of similar data availablefrom the literature, and so only the new data have been used in theproduction of the velocity curves. Parametric representations of thesecurves are presented in preparation for analysis in a future paper.
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Observation and Astrometry data
| Constellation: | Λύκος |
| Right ascension: | 15h24m38.34s |
| Declination: | -52°51'13.9" |
| Apparent magnitude: | 7.684 |
| Distance: | 377.358 parsecs |
| Proper motion RA: | -2.2 |
| Proper motion Dec: | -1.3 |
| B-T magnitude: | 9.193 |
| V-T magnitude: | 7.809 |
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