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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.
| 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
| 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.
| The Cepheid period-luminosity zero-point from HIPPARCOS trigonometrical parallaxes
Hipparcos trigonometrical parallaxes of Cepheid variables are used toderive a zero-point for the period-luminosity (PL) relation. Adopting aslope from the Large Magellanic Cloud (LMC), the relation is found to be=-2.81 log P-1.43. The standard error of the zero-point is0.10 mag. Together with metallicity corrections this corresponds to adistance modulus of 18.70+/-0.10 for the LMC and 24.77+/-0.11 for M31.Some implications of these results are discussed. Estimates of theHubble constant (H_0) that are based on Cepheid observations togetherwith an adopted LMC distance modulus of 18.50 will on average now needto be decreased by ~10 per cent. However, metallicity corrections, whichhave frequently been ignored, will result in the actual percentagechange varying with the sample of galaxies studied. Calibration of RRLyrae absolute magnitudes using the LMC and M31 Cepheid distancesimplies an age for the oldest Galactic globular clusters of ~11 Gyr. Theparallax data show that the period of Polaris corresponds to firstovertone pulsation.
| A search for evolutionary changes in the periods of low-amplitude Cepheids.
Not Available
| 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^*^.
| A comparison between observations and nonlinear models of first overtone mode Cepheids.
Light and radial velocity curves of observed first overtone modeCepheids have been compared with the curves of nonlinear modelsconstructed using the new opacities. The study confirms that thecharacteristics of the curves depend on the resonance P_1_/P_4_=2between the first and the fourth overtone mode. However, discrepanciesand systematic differences between theory and observations are stillpresent. It is shown that the diagrams of amplitude ratios R_21_ andphase difference φ_21_ of light curves versus the period aresensitive to the T_e_ of the models. Interesting properties of the phaselag between light and radial velocity curve are also discussed.
| The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
| New method to recognize s-Cepheids
A new method of delineating sinusoidal or s-Cepheids is presented. Themethos uses the values of (V) (the mean intensity), V - Bar (the averagemagnitude), and Vmean (the value of the mean magnitude).Fourier coefficient data from galactic Cepheids is used to derive theseterms in the V band and the differences between the various terms showsystematic trends with increasing period. The Cepheids can be easilygrouped into 3 divisions-short period s-Cepheids, intermediate periodCepheids (P less than 9 days), and long period Cepheids (P greater than9 days). Cepheids previously designated as s-Cepheids by others arecompared to those found using the method outlined here. The method isalso applied to Cepheids in the Small Magellanic Cloud to examine itssuitability as a pulsation mode discriminator.
| Photoelectric Observations of Southern Cepheids in 1995
Not Available
| Photoelectric Ubvri/c Photometry of Southern Cepheids
Not Available
| 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.
| The Study of Period Variability in Small-Amplitude Cepheids in Centaurus Crux Cygnus Gemini Vulpecula Lyra Monoceros Norma and Ophiuchus
Not Available
| A scanned CCD search for Cepheids and other variables in Crux and Centaurus
The results of a photometric survey for variable stars in a 9.4 squaredegree region along the galactic plane in Crux and Centaurus arepresented. A total of 300,308 stars were observed at seven epochs over42 days; 224,524 of these stars were detected at multiple epochs andwere tested for possible variations in brightness that exceedobservational error. About 2422 stars are identified as variable at aformal confidence level of 99 percent; 270 of the new variables brighterthan I = 14.0 are classified as long period variables. A list of 242likely short period variables with rms amplitudes of less than 0.060 magis given. From this list, 37 Cepheid candidates were selected afterinspection of their light curves.
| 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
| Absolute and relative amplitudes of variations in radius of classical Cepheids
An analysis of observations of the absolute Delta R and relative DeltaR/R amplitudes of variations in radius of 85 galactic classical Cepheidshas yielded four empirical relations. Results are presented forlong-period, short-period, and s Cepheids. For a given group ofvariables, it is shown that Delta R and Delta R/R values increase withboth pulsation period (P) values and with P(Delta V) values (where DeltaV is the amplitude of light variations).
| 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.
| Structural properties of the light curves of s-Cepheids
Fourier decomposition of light curves of short period Cepheids ands-Cepheids has been performed in order to investigate the properties ofs-Cepheid light curves, compare them with those of classical Cepheidsand detect suspected overtone pulsators. In general, the low orderamplitude ratio and phase difference of s-Cepheid light curves aredifferent from those of classical Cepheids. In particular, thedistribution of phase difference values against the period indicates thepossible presence of two different trends separated by a discontinuitynear 3 days. This property has been interpreted tentatively as theeffect of a new type of resonance between pulsation modes. Among thestars taken into account in the present work, only IR Cep is a suspectedovertone pulsator.
| The importance of colour-colour loops in the determination of the physical parameters of pulsating variables
Attention is drawn to the importance of studying the surface brightnessof pulsating stars as a function of two colors, in order to disentanglethe contributions of temperature and gravity variations to the observedcurve from that due to the simultaneous variation of the emittingsurface of the star. The area of the observed color-color loops obtainedwith different colors is compared with the area delta B of thesurface-brightness color loop, inferred from calibrations. The existenceof the color-color loops and the dependence of the loop area on thepulsation period, very similar to that of delta B, is easily explained,under the assumption of quasi-static approximation, by the existence ofa loop in the plane of effective temperature and effective gravity, thearea of which varies with the period. The consistency and adequacy ofthe whole picture on which the CORS method (used to determine the radiusof classical Cepheids) is based are strongly supported by theexperimental evidence.
| Observational determination of pulsation modes and photometric masses of Cepheid variables
An attempt is made to characterize the pulsation modes and crossingnumbers of Cepheids analytically, based on observational data. Theobservations cover 66 Cepheids and their mean and maximum Wesselinkradii, the log P - log R relationship, and the mass-luminosity ratio.The inherent inaccuracies of current data weight the actual values withprobabilities. Calculation of instabilities among the Cepheids are foundto require at least three variables, e.g., luminosity, period, radius,etc. Five stars have been identified as first overtone pulsators: BGCru, BF Oph, V 482 Sco, Y Sgr, and U Aql. It is concluded that the trackof stellar evolution of normal stars must be modified when analyzingpulsating stars in the instability region, except for calculations basedon the luminosity-effective temperature relationship.
| The Catalogue of Distances and Light Absorption for Cepheids
Not Available
| Cepheid radii and masses by means of VBLUW photometry
Caccin et al. (1981) have illustrated a new method for the determinationof the radii of pulsating variables. The current investigation utilizesthe new method for a more precise determination of the radii ofclassical cepheids. The radius of a radially pulsating star can beobtained by solving a certain implicit equation. The equation is solvedfor thirty cepheids considered by Pel (1976) in connection with hisVBLUW observations. Attention is given to aspects of radiusdeterminations, and masses and luminosities. It is believed that a fullagreement of luminosities based on data obtained with the aid of the newmethod and theoretical luminosities has to be reached by means of afully hydrodynamical treatment of the cepheid atmosphere, instead ofintroducing inhomogeneous models.
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Центавр |
| Прямое восхождение: | 11h53m33.54s |
| Склонение: | -62°51'07.9" |
| Видимая звёздная величина: | 10.119 |
| Собственное движение RA: | -4 |
| Собственное движение Dec: | 1.4 |
| B-T magnitude: | 11.206 |
| V-T magnitude: | 10.209 |
Каталоги и обозначения:
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