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Публикации по объекту
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.
| 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
| The Distance Scale for Classical Cepheid Variables
New radii, derived from a modified version of the Baade-Wesselink (BW)method that is tied to published KHG narrowband spectrophotometry, arepresented for 13 bright Cepheids. The data yield a best-fittingperiod-radius relation given bylog=1.071(+/-0.025)+0.747(+/-0.028)logP0. In combination with other high-quality radiusestimates recently published by Laney & Stobie, the new data yield aperiod-radius relation described bylog=1.064(+/-0.0006)+0.750(+/-0.006)logP0, which simplifies to ~P3/4.The relationship is used to test the scale of Cepheid luminositiesinferred from cluster zero-age main-sequence (ZAMS) fitting, for whichwe present an updated list of calibrating Cepheids located in stellargroups. The cluster ZAMS-fitting distance scale tied to a Pleiadesdistance modulus of 5.56 is found to agree closely with the distancescale defined by Hipparcos parallaxes of cluster Cepheids and alsoyields Cepheid luminosities that are a good match to those inferred fromthe period-radius relation. The mean difference between absolute visualmagnitudes based on cluster ZAMS fitting,C, and those inferred for 23 clusterCepheids from radius and effective temperature estimates,BW, in the sense of C-BW is+0.019+/-0.029 s.e. There is no evidence to indicate the need for amajor revision to the Cepheid cluster distance scale. The absolutemagnitude differences are examined using available [Fe/H] data for thecluster Cepheid sample to test the metallicity dependence of theperiod-luminosity relation. Large scatter and a small range ofmetallicities hinder a reliable estimate of the exact relationship,although the data are fairly consistent with predictions from stellarevolutionary models. The derived dependence isΔMV(C-BW)=+0.06(+/-0.03)-0.43(+/-0.54)[ Fe/H].
| 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.
| 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.
| Speckle Interferometry of New and Problem HIPPARCOS Binaries
The ESA Hipparcos satellite made measurements of over 12,000 doublestars and discovered 3406 new systems. In addition to these, 4706entries in the Hipparcos Catalogue correspond to double star solutionsthat did not provide the classical parameters of separation and positionangle (rho,theta) but were the so-called problem stars, flagged ``G,''``O,'' ``V,'' or ``X'' (field H59 of the main catalog). An additionalsubset of 6981 entries were treated as single objects but classified byHipparcos as ``suspected nonsingle'' (flag ``S'' in field H61), thusyielding a total of 11,687 ``problem stars.'' Of the many ground-basedtechniques for the study of double stars, probably the one with thegreatest potential for exploration of these new and problem Hipparcosbinaries is speckle interferometry. Results are presented from aninspection of 848 new and problem Hipparcos binaries, using botharchival and new speckle observations obtained with the USNO and CHARAspeckle cameras.
| 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.
| 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^*^.
| Colour excesses of F-G supergiants and Cepheids from Geneva photometry.
A reddening scale for F-G supergiants and Cepheids is presented.Supergiants with low reddenings or in clusters form the basis of thecalibration. In this sense, it is entirely empirical. The data have beenobtained in the Geneva photometric system. Comparisons with otherreddening scales show no disagreement. The only problem is with Fernie'sscale for Cepheids (1990), where a systematic trend exists. Its originis not clear. It is suggested to extend the number of supergiants withindependently obtained colour excesses in order to test the existence ofa possible luminosity dependence of the calibration. A period-colourrelation for Cepheids is deduced, on the basis of the present reddeningcorrections. It gives strong support for V473 Lyr being a secondovertone pulsator.
| Parameters of the JHK light curves of classical Cepheids and the interstellar-extinction LAW.
Not Available
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Rotation Curve of the System of Classical Cepheids and the Distance to the Galactic Center
Not Available
| Fundamental parameters of Cepheids. I. Photometric data in the Geneva system.
Photometric data in the Geneva system for 26 Cepheid stars are given,representing 869 individual measurements. After a short explanation onthe analysis, the choice of the period and the quality of the fit of thelight curve are discussed. The data and the fitted light- and colourcurves are given, as well as the Fourier coefficients of the best fitfor each star.
| 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.
| On Cepheids at maximum and minimum light
It has been known for many decades that the spectral type of Cepheids atlight maximum is constant with period. We use hydrodynamic pulsationmodels to explain this result in terms of the outward reach of thehydrogen ionization front. On the other hand, we show that, at minimumlight, the Cepheid photospheric temperature is mainly a function ofamplitude. A number of observed Cepheids have published temperaturesthat seem too hot at both maximum and minimum. We attribute this to anoverestimation of the reddening for these stars. A list is given.
| 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.
| Cepheid Measures at Auckland Observatory
Not Available
| 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.
| 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
| Reddenings of Cepheids from G-band spectrophotometry
Measurements of the strength of the G-band (CH) of galactic Cepheidshave been used to construct a relation between G-band strength and (B-V)color. The zero-point of the relation is fixed from stars in clustersand associations whose reddenings are believed to be known, enablingreddenings to be derived for individual Cepheids. These reddenings arein agreement with those derived previously by similar methods butsystematically different from those derived from two-color diagrams.This difference is attributed to the luminosity dependence of the G-bandin these stars.
| Stromgren and H-beta photometry of stars earlier than G0 in the Southern Coalsack direction
Four-color and H-beta photometry have been obtained for 236 starsearlier than G0 in order to study the color excess distribution in theSouthern Coalsack direction. The beta histogram of the stars reveals arelative absence of stars in the range of A4 to A9. The (b-y)distribution for B-type stars suggests the existence of three differenttypes of stars located at different distances.
| 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.
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Наблюдательные данные и астрометрия
| Созвездие: | Южный Крест |
| Прямое восхождение: | 12h23m37.69s |
| Склонение: | -61°37'44.9" |
| Видимая звёздная величина: | 6.915 |
| Расстояние: | 507.614 парсек |
| Собственное движение RA: | -10.3 |
| Собственное движение Dec: | -3.7 |
| B-T magnitude: | 7.987 |
| V-T magnitude: | 7.004 |
Каталоги и обозначения:
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