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Estimation of the galactic spiral pattern speed from Cepheids
To study the peculiarities of the Galactic spiral density wave, we haveanalyzed the space velocities of Galactic Cepheids with propermotionsfrom the Hipparcos catalog and line-of-sight velocities from varioussources. First, based on the entire sample of 185 stars and taking R0 = 8 kpc, we have found the components of the peculiar solarvelocity ( u &sun;, v &sun;) = (7.6, 11.6)± (0.8, 1.1) km s-1, the angular velocity of Galacticrotation ?0 = 27.5 ± 0.5 km s-1kpc-1 and its derivatives ?'0 = -4.12± 0.10 km s-1 kpc-2 and??0 = 0.85 ± 0.07 km s-1kpc-3, the amplitudes of the velocity perturbations in thespiral density wave f R = -6.8 ± 0.7 and f ? = 3.3 ± 0.5 km s-1, the pitch angle ofa two-armed spiral pattern ( m = 2) i = -4.6° ± 0.1°(which corresponds to a wavelength ? = 2.0 ± 0.1 kpc), andthe phase of the Sun in the spiral density wave ?&sun; =-193° ± 5°. The phase ?&sun; has beenfound to change noticeably with the mean age of the sample. Havinganalyzed these phase shifts, we have determined the mean value of theangular velocity difference ? p - ?, whichdepends significantly on the calibrations used to estimate theindividual ages of Cepheids. When estimating the ages of Cepheids basedon Efremov's calibration, we have found |? p -?0| = 10 ± 1stat ±3syst km s-1 kpc-1. The ratio of theradial component of the gravitational force produced by the spiral armsto the total gravitational force of the Galaxy has been estimated to bef r0 = 0.04 ± 0.01.
| 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.
| 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
| 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.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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
| Photometry and radial velocities of cepheids and other variable stars in the Galaxy and the LMC
UBVRIc and radial velocity measurements are presented for Galactic andLMC Cepheids, and for several variables of other type. The photometrycomprises 168 objects with 1790 phases, and the speedometry 15 objectswith 97 phases.
| 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.
| The shape and scale of Galactic rotation from Cepheid kinematics
A catalog of Cepheid variables is used to probe the kinematics of theGalactic disk. Radial velocities are measured for eight distant Cepheidstoward l = 300 deg; these new Cepheids provide a particularly goodconstraint on the distance to the Galactic center, R0. We model the diskwith both an axisymmetric rotation curve and one with a weak ellipticalcomponent, and find evidence for an ellipticity of 0.043 +/- 0.016 nearthe sun. Using these models, we derive R0 = 7.66 +/- 0.32 kpc andv(circ) = 237 +/- 12 km/s. The distance to the Galactic center agreeswell with recent determinations from the distribution of RR Lyraevariables and disfavors most models with large ellipticities at thesolar orbit.
| Galactic kinematics of Cepheids from HIPPARCOS proper motions
The Hipparcos proper motions of 220 Galactic Cepheids, together withrelevant ground-based photometry, have been analyzed. The effects ofGalactic rotation are very clearly seen. Mean values of the Oortconstants, A = 14.82 +/- 0.84 km/s kpc, and B = -12.37 +/- 0.64 km/skpc, and of the angular velocity of circular rotation at the sun, 27.19+/- 0.87 km/s kpc, are derived. A comparison of the value of A withvalues derived from recent radial velocity solutions confirms, withinthe errors, the zero-points of the period-luminosity andperiod-luminosity-color relations derived directly from the Hipparcostrigonometrical parallaxes of the same stars. The proper motion resultssuggest that the Galactic rotation curve is declining slowly at thesolar distance from the Galactic Center (-2.4 +/- 1.2 km/s kpc). Thecomponent of the solar motion towards the North Galactic Pole is foundto be +7.61 +/- 0.64 km/s. Based on the increased distance scale deducedin the present paper, the distance to the Galactic Center derived in aprevious radial velocity study is increased to 8.5 +/- 0.5 kpc.
| Rotation curve of the system of classical Cepheids and the distance to the galactic center
Not Available
| New radial velocities for 96 faint southern Cepheids
96 faint classical Cepheids have been measured, each a small number oftimes (4 to 7 times), in radial velocity, in order to calculate theircentre-of-mass radial velocity accurately enough for an analysis of thelocal galactic rotation. This paper contains the raw radial velocitydata. The analysis and results are presented in a joint paper in theMain Section of this journal (Pont et al. 1994).
| 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.
| Gamma velocities of 58 faint Milky Way Cepheids
Using new radial velocity measurements of 47 faint southern hemisphereGalactic Cepheids, together with additional velocity data from Metzgeret al. (1991), gamma velocities are found for 58 low galactic latitudeCepheids. The gamma velocity is determined by using the period of aCepheid to generate a 'typical' velocity curve, then fitting the curveto the velocity measurements using two free parameters, the gammavelocity, and the phase. The velocity curve is generated using a secondorder Fourier series with coefficients determined from the period. Forthe Cepheids with observations that sample the velocity curve over avariety of pulsation phases, gamma velocities are determined to betterthan 1.0 km/s. Good agreement between these gamma velocities andpreviously published values where they exist.
| The separation of S-Cepheids from classical Cepheids and a new definition of the class
Fourier decomposition has been applied to a sample of 184 classical andS-Cepheids with P less than 8 d and a careful evaluation of errors inthe determination of the parameters has been made. The S-Cepheids starsare redefined by the authors as Population I Cepheids that do not followthe Hertzsprung progression, but have a progression of their own. In thephi(21)-P plane, the S- and classical Cepheids are characterized by twosequences well separated for P less than 5.5 d. In the period range Pbetween 3d and 5.5 d, two different progressions are also present in thephi(31)-P plane while a discriminating value R(21) = 0.20 can be seen inthe R(21)-P plane. The first overtone pulsation seems to be wellestablished for S-Cepheids with P less then 3.2 d; it is probable forall the stars of the redefined subclass. A discontinuity is clearlyvisible at about 3 d in the S-Cepheid sequence in the phi(21)-P plane;it is interpreted as a resonance effect. An apparent decrease in thenumber of stars is present in the classical sequence for P less than 3d.
| 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
| 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).
| Classical Cepheids - Their distances and space distribution
A simplified method of calculating classical Cepheid distances isproposed. It is based on photometric data, without the use of thereddenings. By means of results obtained in this way the followingproblems are discussed: Cepheid double and more numerous aggregates andproperties of the cluster and association Cepheid.
| 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.
| The catalogue of light curves parameters, distances and space coordinates of classical Cepheids.
Not Available
| The Catalogue of Distances and Light Absorption for Cepheids
Not Available
| Intrinsic colours and physical properties of Cepheids
Reddening-free colors and VBLUW color excesses are determined for 170Southern Hemisphere galactic Cepheids. The Cepheid colors are correctedfor interstellar reddening, the VBLUW color excesses are compared withcolor excesses obtained in other studies of Cepheids, and physicalproperties are derived by comparing the reddening-free colors withtheoretical colors previously computed from a grid of model-atmospherefluxes. The cyclic behavior of temperature, gravity, luminosity, andradius is calculated along with the equilibrium values of thesequantities for 98 Cepheids with periods shorter than 11 days. It isfound that at least 25% of the Cepheids studied show evidence of abinary companion and that the computed velocity curves are in reasonableagreement with observed radial-velocity curves. It is concluded that theuse of hydrostatic-equilibrium model atmospheres is not too unrealisticfor the continuum colors of Cepheids.
| A method for constructing envelopes and the period-amplitude relationof cepheids.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977A&A....61..827E&db_key=AST
| The frequency of Cepheids with companions: a photoelectric approach.
Abstract image available at:http://adsabs.harvard.edu/abs/1977MNRAS.178..505M
| Photoelectric observations of cepheids in the galactic centre region.
Abstract image available at:http://adsabs.harvard.edu/abs/1976MNRAS.175..129W
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| קבוצת-כוכבים: | סרגל |
| התרוממות ימנית: | 16h05m09.97s |
| סירוב: | -53°55'09.9" |
| גודל גלוי: | 10.095 |
| תנועה נכונה: | 3.4 |
| תנועה נכונה: | -8.6 |
| B-T magnitude: | 11.187 |
| V-T magnitude: | 10.186 |
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