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A Multiwavelength Study of 1WGA J1346.5-6255: A New γ Cas Analog Unrelated to the Background Supernova Remnant G309.2-00.6
1WGA J1346.5-6255 is a ROSAT X-ray source found within the radio lobesof the supernova remnant (SNR) G309.2-00.6. It appears to coincide withthe bright and early-type star HD 119682, in the galactic open clusterNGC 5281. Its radio morphology, consisting of two brightened anddistorted arcs of emission on opposite sides of the 1WGA J1346.5-6255source and of a jetlike feature and break in the shell, suggest that1WGA J1346.5-6255/G309.2-00.6 is a young analog of the microquasarpowering the W50 nebula SS 433. This motivated us to study this sourceat X-ray and optical wavelengths. We present new Chandra observations of1WGA J1346.5-6255, archival XMM-Newton observations of G309.2-00.6, andoptical spectroscopic observations of HD 119682, to search for X-rayjets from 1WGA J1346.5-6255, study its association with the SNR, andtest for whether HD 119682 represents its optical counterpart. We findno evidence for jets from 1WGA J1346.5-6255 down to an unabsorbed fluxof 2.6×10-13 ergs cm-2 s (0.5-7.5 keV), werule out its association with G309.2-00.6, and we confirm that HD 119682is its optical counterpart. We derive a distance of 1.2+/-0.3 kpc,consistent with the distance estimate to NGC 5281 (1.3+/-0.3 kpc), andmuch smaller than the distance derived to G309.2-00.6. We discuss thenature of the source, unveil that HD 119682 is a Be star, and suggest itis a new member of the recently proposed group of γ Cas analogs.The Chandra and XMM-Newton X-ray light curves show variability ontimescales of hundreds of seconds, and the presence of a possible periodof ~1500 s that could be the rotational period of an accreting neutronstar or white dwarf in this γ Cas analog.
| New γ Cassiopeiae-like objects: X-ray and optical observations of SAO 49725 and HD 161103
A growing number of early Be stars exhibit X-ray luminosities that areintermediate between those typical of early type stars and those emittedby most Be/X-ray binaries in quiescence. We report on XMM-Newtonobservations of two such Be stars, SAO 49725 andHD 161103, which were originally discovered in asystematic cross-correlation between the ROSAT all-sky survey andSIMBAD. The new observations confirm the X-ray luminosity excess(LX ~ 1032-33 erg s-1) and the hardnessof their X-ray spectra, which are both unusual for normal early typestars. An iron Kα complex is clearly detected in HD161103 in which the H-like, He-like, and fluorescentcomponents are resolved, while strong evidences also exist for thepresence of similar features in SAO 49725. X-rayspectra can be equally well-fitted by a thermal plasma (mekal) with T ~108 K and solar abundances or by a power law + iron linemodel with photon index ~1.5-1.8, both with a soft thermal componentwith T ~ 107 K. The intensity of the fluorescence 6.4 keVline reflects the presence of large amounts of cold material close tothe X-ray sources and strongly argues against accretion onto a companionneutron star in a large orbit. On the other hand, the probable thermalorigin of the X-ray emission, as supported by the ionised iron lines,disagrees with those observed in all known Be/X-ray binaries, in which anon-thermal component is always required. Remarkably, the X-ray featuresare similar to those of white dwarves in several cataclysmic variables.There is no evidence of high frequency pulsations in neither of the twosystems. However, a large oscillation in the light curve of HD161103 with P ~ 3200 s is readily detected. The X-ray lightcurve of SAO 49725 exhibits clear variability by ~80%on time scales as short as ~1000 s. New optical observations provideupdated spectral types (B0.5 III-Ve) and disclose a dense, large, andapparently stable circumstellar disc for both stars. The nature of theexcess X-ray emission is discussed in light of the models proposed forγ Cas, magnetic disc-star interaction, oraccretion onto a compact companion object - whether neutron star orwhite dwarf. These two new objects, added to similar cases discovered inXMM-Newton surveys, point to the emergence of a new class ofγ Cas analogs.
| Kinematics of the Open Cluster System in the Galaxy
Absolute proper motions and radial velocities of 202 open clusters inthe solar neighborhood, which can be used as tracers of the Galacticdisk, are used to investigate the kinematics of the Galaxy in the solarvicinity, including the mean heliocentric velocity components(u1,u2,u3) of the open cluster system,the characteristic velocity dispersions(σ1,σ2,σ3), Oortconstants (A,B) and the large-scale radial motion parameters (C,D) ofthe Galaxy. The results derived from the observational data of propermotions and radial velocities of a subgroup of 117 thin disk young openclusters by means of a maximum likelihood algorithm are:(u1,u2,u3) =(-16.1+/-1.0,-7.9+/-1.4,-10.4+/-1.5) km s-1,(σ1,σ2,σ3) =(17.0+/-0.7,12.2+/-0.9,8.0+/-1.3) km s-1,(A,B) =(14.8+/-1.0,-13.0+/-2.7) km s-1 kpc-1, and (C,D) =(1.5+/-0.7,-1.2+/-1.5) km s-1 k pc-1. A discussionon the results and comparisons with what was obtained by other authorsis given.
| Proper motion determination of open clusters based on the UCAC2 catalogue
We present the kinematics of hundreds of open clusters, based on theUCAC2 Catalogue positions and proper motions. Membership probabilitieswere obtained for the stars in the cluster fields by applying astatistical method uses stellar proper motions. All open clusters withknown distance were investigated, and for 75 clusters this is the firstdetermination of the mean proper motion. The results, including the DSSimages of the cluster's fields with the kinematic members marked, areincorporated in the Open Clusters Catalogue supported on line by ourgroup.
| The Initial Mass Function as given by the fragmentation
The dichotomy between a universal mass function (IMF) and a variable IMFwhich depends on local physical parameters characterises observationaland theoretical stellar astronomy. In this contribution the availabledistributions of probability are briefly reviewed. The physical natureof two of them, gamma variate and lognormal, is then explained once theframework of the fragmentation is introduced. Interpolating techniquesare then applied to the sample of the first 10 pc and to the opencluster NGC 6649: in both cases lognormal distribution produces the bestfit. The three power law function has also been investigated and visualcomparison with an artificially generated sample of 100000 starssuggests that the variations in the spectral index are simply due to thesmall number of stars available in the observational sample. In order toderive the sample of masses, a new formula that allows us to express themass as a function of the absolute magnitude and (B-V) for MAIN V,GIANTS III and SUPERGIANTS I is derived.
| Comparison of the Luminosity Functions of Open Clusters Based on USNO-A1 Data
The luminosity and mass functions of a group of Galactic open clustersare constructed by applying a statistical method to photometric datafrom the USNO-A1 catalog. Despite some limitations, this catalog can beused for statistical analyses in Galactic astronomy. Pairwisecomparisons of the derived cluster luminosity functions are performedfor five age intervals. The differences between the luminosity functionsof the open clusters are not statistically significant in most cases. Itis concluded that the luminosity functions are approximately universalthroughout a large volume in the solar neighborhood. Combined luminosityand mass functions are constructed for six age intervals. The slope ofthe mass spectrum may vary somewhat from cluster to cluster, and themean slope may be somewhat higher than the Salpetervalue.
| Metallicity distribution on the galactic disk
Depending mainly on UBVCCD data, the metallicities of 91 open starclusters nearby the galactic disk have been estimated using Cameron's[A&A 147 (1985b) 39] method. The metallicity radial gradient alongthe galactic plane is found to be -0.09 dex/kpc; which is in a very goodagreement with Panagia and Tosi [A&A 96 (1981) 306] and Carraro etal. [MNRAS 296 (1998) 1045]. Vertically on the galactic disk, withinabout 800 pc, the metallicity gradient is found to be so trivial. Anaverage age-metallicity relation has been examined, which confirms theprevious suggestion that the metallicity of a cluster depending mainlyon its position on the galactic disk more than its age.
| Distances to Cepheid open clusters via optical and K-band imaging
We investigate the reddening and main-sequence-fitted distances to 11young, Galactic open clusters that contain Cepheids. Each clustercontains or is associated with at least one Cepheid variable star.Reddening to the clusters is estimated using the U-B:B-V colours of theOB stars and the distance modulus to the cluster is estimated via B-V:Vand V-K:V colour-magnitude diagrams. Our main-sequence fitting assumesthat the solar-metallicity zero-age main sequence of Allen appliesuniversally to all the open clusters, although this point iscontroversial at present. In this way we proceed to calibrate theCepheid period-luminosity (PL) relation and find MV=-2.87× logP- 1.243 +/- 0.09, MK=-3.44 × logP- 2.21 +/-0.10 and absolute distance moduli to the Large Magellanic Cloud (LMC) of18.54 +/- 0.10 from the V-band and 18.48 +/- 0.10 from the K-band givingan overall distance modulus to the LMC of μ0= 18.51 +/-0.10. This is in good agreement with the previous Cepheid PL-K result ofLaney & Stobie at μ0= 18.51 +/- 0.09 and with theHipparcos parallax-calibrated Cepheid PL-K estimate of Feast &Catchpole at μ0= 18.66 +/- 0.10 when no account is takenof the LMC metallicity.We also find that the two-colour U-B:B-V diagrams of two importantclusters are not well fitted by the standard main-sequence line. In onecase, NGC 7790, we find that the F stars show a UV excess and in thesecond case, NGC 6664, they are too red in U-B. Previous spectroscopicestimates of the metallicity of the Cepheids in these clusters appear tosuggest that the effects are not due to metallicity variations. Otherpossible explanations for these anomalies are positional variations inthe dust reddening law and contamination by foreground or backgroundstars.
| The nature of the Cepheid T Antliae
The variable star T Antliae, sometimes suspected to be a type IIpulsator, is demonstrated to be a classical Cepheid in the thirdcrossing of the instability strip. It exhibits a positive period changeof +0.514 +/- 0.016 s yr-1, consistent with a star on theblue side of the instability strip and evolving through it for the thirdtime. The Cepheid exhibits no random fluctuations in pulsation period,although superimposed upon its evolutionary O-C trend are very subtlevariations that may be indicative of orbital motion about an unseencompanion. Archival spectroscopic data also indicate that the star sitson the edge of a putative cluster of B-type stars that may be physicallyassociated with the Cepheid. Additional photometric and spectroscopicdata for the Cepheid and cluster are needed to strengthen the case. Thefield reddening of T Ant established from nearby early-type stars isEB-V=0.30 +/- 0.01 (EB-V(B0)=0.316 +/- 0.014).
| Proper Motions of Open Star Clusters and the Rotation Rate of the Galaxy
The mean proper motions of 167 Galactic open clusters withradial-velocity measurements are computed from the data of the Tycho-2catalog using kinematic and photometric cluster membership criteria. Theresulting catalog is compared to the results of other studies. The newproper motions are used to infer the Galactic rotation rate at the solarcircle, which is found to be ω0=+24.6±0.8 km s-1 kpc-1.Analysis of the dependence of the dispersion of ω0 estimates onheliocentric velocity showed that even the proper motions of clusterswith distances r>3 kpc contain enough useful information to be usedin kinematic studies demonstrating that the determination of propermotions is quite justified even for very distant clusters.
| The source content of low galactic latitude XMM-Newton surveys
We present results from a project conducted by the Survey Science Centerof the XMM-Newton satellite and aiming at the identification andcharacterisation of serendipitous EPIC sources at low galacticlatitudes. Deep multi-colour optical imaging and spectroscopicobservations have been obtained in the framework of several observingcampaigns carried out at ING, CFHT and ESO. These observations have leadto a number of optical identifications, mostly with active stars. Wedescribe the identified source content at low galactic latitudes andcompare stellar populations properties at low and high galacticlatitudes with those expected from stellar X-ray count models.
| Morphological analysis of open clusters' propertiesII. Relationships projected onto the galactic plane
A morphological analysis study of open clusters' properties has beenachieved for a sample of 160 UBVCCD open star clusters of approximately128,000 stars near the galactic plane. The data was obtained and reducedfrom using the same reduction procedures, which makes this catalogue thelargest homogeneous source of open clusters' parameters.
| 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].
| Integrated photometric characteristics of galactic open star clusters
Integrated UBVRI photometric parameters of 140 galactic open clustershave been computed. Integrated I(V-R)0 and I(V-I)0colours as well as integrated parameters for 71 star clusters have beenobtained for the first time. These, in combination with published data,altogether 352 objects, are used to study the integrated photometriccharacteristics of the galactic open clusters. The I(MV)values range from -9.0 to -1.0 mag corresponding to a range in totalmass of the star clusters from ~ 25 to 4*E4 Msun.The integrated colours have a relatively narrow range, e.g., I(B-V){_0}varies from -0.4 to 1.2 mag. The scatter in integrated colours at agiven integrated magnitude can be understood in terms of differences infraction of red giants/supergiants in the clusters. The observedintegrated magnitudes and colours agree with the synthetic ones, exceptthe dependences of I(V-R)0 and I(V-I)0 colours forclusters younger than ~ 100 Myrs and also of the integrated magnitudesof oldest clusters. The large sample provides the most accurate agedependence of integrated magnitudes and colours determined so far. Theluminosity function of the I(MV) has a peak around -3.5 magand its slope indicates that only ~ 1% of the open clusters in thegalactic disc are brighter than I(MV)=-11 mag. No variationhas been found of integrated magnitude with galactocentric distance andmetallicity.
| Morphological analysis of open clusters' propertiesI. Properties' estimations
A sample of 160 UBVCCD observations of open star clusters near thegalactic plane has been studied, and a catalogue of their propertiesobtained. The main photometrical properties have been re-estimated selfconsistently and the results have been compared with those of Lynga[Lynga, G., 1987. Catalog of Open Cluster Data, 5th Edition, StellarData Centers, Observatoire de Strasbourg, France].
| The Pulsation Mode of the Cluster Cepheid V1726 Cygni
CCD V-band observations and archival O-C estimates are presented for the4.237 day Cepheid V1726 Cyg, which is a member of the open clusterC2128+488 (Anon. Platais), and the data are analyzed in conjunction withother available photometric data in order to study the star's periodvariations. An O-C analysis of the data yields the following improvedephemeris for the variable,HJDmax=2,444,020.5892+4.2369334E+2.044×10-8E2, which implies that the period of V1726 Cyg isincreasing at a rate of +0.304+/-0.026 s yr-1, consistentwith a star in the third crossing of the instability strip provided thatit is pulsating in the first-overtone, rather than fundamental, mode.Overtone pulsation for V1726 Cyg is also indicated by its low amplitude,sinusoidal light curve, and derived Fourier parameters, despitereservations about the significance of the latter. No evidence is foundfor random cycle-to-cycle variations in period for V1726 Cyg.
| Statistical parallaxes and kinematical parameters of classical Cepheids and young star clusters
The statistical-parallax method is applied for the first time to spacevelocities of 270 classical Cepheids with proper motions adopted fromHIPPARCOS (1997) and TRC (Hog et al. 1998) catalogs and distances basedon the period-luminosity relation by Berdnikov et al. (1996). Thedistance scale of short-period Cepheids (with periods less than 9 days)is shown to require an average correction of 15-20%, whereas statisticalparallaxes of Cepheids with periods > 9 days are found to agree wellwith photometric distances. It is shown that the luminosities ofshort-period Cepheids must have been underestimated partly due to thecontamination of this subsample by a substantial (20 to 40%) fraction offirst-overtone pulsators. The statistical-parallax technique is alsoapplied for the first time to 117 open clusters younger than 100 millionyears and with proper motions reduced to the HIPPARCOS reference system.It is concluded that a 0.12-0.15 mag increase of the distance scales ofopen clusters and Cepheids would be sufficient to reconcile thestatistical-parallax results inferred for these two types of objects.Such approach leads to an LMC distance modulus of less than 18.40 mag,which agrees, within the errors, with the short distance scale for RRLyrae variables and is at variance with the conclusions by Feast andCatchpole (1998) and Feast et al. (1998), who argue that the LMCdistance modulus should be increased to 18.70 mag. The distance scalebased on the Cepheid period-luminosity relation by Berdnikov and Efremov(1985) seems to be a good compromise. Extragalactic distances, whichrely on long-period Cepheids, seem to require no substantial correction.In addition to statistical parallaxes, kinematical parameters have beeninferred for the combined sample consisting of Cepheids andopen-clusters: solar-motion components (U0 ,V0,W0) = (9, 12, 7) km/s (+/- 1 km/s); velocity-ellipsoid axes(σU; σV; σW) = (15.0,10.3, 8.5) km/s (+/- 1 km/s); the angular velocity of rotation of thesubsystem, ω0 = 28.7 +/- 1 km/s/kpc, the Oort constantA = 17.4 +/- 1.5 km/s, and the second derivative of angular velocity,⋰ω0= 1.15 +/- 0.2 km/s/kpc3.
| Absolute proper motions of 181 young open clusters.
Not Available
| The year of the Comet.
Not Available
| The Progenitors of Classical Cepheid Variables
Properties are deduced for the main-sequence O and B-type stars thatwere the immediate progenitors to classical Cepheids belonging to thelocal sample of galactic calibrating clusters. The sample of suchclusters and stellar groups is presently large enough to allow thederivation of statistically-significant properties related to theirCepheid members. In particular, the turnoff point colour for a clusteris demonstrated to be linearly related to the pulsational period (Po) ofits associated Cepheid via the empirical relationship: (B=96V)o(turnoff) =3D =960.057 =96 0.113= log Po; the masses of stars at the redturnoff point for the cluster follow a semi-empirical relationshipdescribed by: log M(RTO)/Ms =3D +0.36 + 0.50 log Po. The adoptedrelationship for the Cepheid progenitors is: log M/Ms =3D +0.41 + 0.50log Po. The properties deduced for Cepheid progenitors as a consequenceof these relationships reveal intriguing information about classicalCepheids themselves.
| BVRIJHK period-luminosity relations for Galactic classical Cepheids.
Not Available
| Estimates of geometric and dynamic parameters of star-gas complexes in the Galaxy
Parameters of geometric models of 11 gas-star complexes (GSCs) wereobtained. We used information about GSC projections onto the celestialsphere and the Galactic plane and about GSC extension along the line ofsight. GSCs were represented as triaxial ellipsoids. To estimate thesemiminor axis of the GSC ellipsoidal model and GSC slope angle to theGalactic plane, we used data on spatial location of open stellarclusters (OSCs) entering GSCs. GSC slopes to the Galactic plane varybetween 2.5 and 20.5 deg. Their semiminor axes are between 11 and 164pc. GSC total masses are estimated from GSC tidal effect on OSCs thatare members of the corresponding GSCs. The effect manifests itself insmaller sizes of young OSCs as compared to their tidal sizes in theforce field of the Galaxy. We used studies of stability of an OSC movingin the joint force field of the Galaxy and spheroidal stationary GSC, aswell as studies of evolution of a virialized cluster located at thecenter of a nonstationary ellipsoidal GSC. Estimated total masses fordifferent GSCs lie between 0.65 x 10 exp 5 solar masses and 11.5 x 10exp 7 solar masses.
| Catalogue of blue stragglers in open clusters.
An extensive survey of blue straggler candidates in galactic openclusters of both hemispheres is presented. The blue stragglers wereselected considering their positions in the cluster colour-magnitudediagrams.They were categorized according to the accuracy of thephotometric measurements and membership probabilities. An amount of 959blue straggler candidates in 390 open clusters of all ages wereidentified and classified. A set of basic data is given for everycluster and blue straggler. The information is arranged in the form of acatalogue. Blue stragglers are found in clusters of all ages. Thepercentage of clusters with blue stragglers generally grows with age andrichness of the clusters. The mean ratio of the number of bluestragglers to the number of cluster main sequence stars is approximatelyconstant up to a cluster age of about 10^8.6^ yr and rises for olderclusters. In general, the blue stragglers show a remarkable degree ofcentral concentration.
| Chemical composition of selected double-mode Cepheids and the P_1_/P_0_ - [Fe/H] relation.
We present the results of the detailed spectroscopic investigation ofthree double-mode Cepheids: EW Sct, VX Pup and BQ Ser. The abundanceanalysis has shown: (1) Carbon is deficient (the abundance normalized tothe iron content with respect to the solar value). (2) This carbondeficiency is accompanied by nitrogen overabundance and normal oxygencontent. (3) α - and iron group elements with little exceptionshow solar ratio [M/Fe]. (4) The heavy elements in EW Sct areunderabundant. (5) Normal iron abundance for EW Sct ([Fe/H]=-0.08) andmetal deficiency for VX Pup ([Fe/H]=-0.39) and BQ Ser ([Fe/H]=-0.36)strongly support the existence of a P_1_/P_0_-metallicity relation, asfirst discussed in work of Andrievsky et al. (1993).
| Integrated photometric properties of open clusters
Galactic open clusters provide an abundant sample of stellar aggregatesof various sizes, ages and metal abundances, apt to constitute atemplate for comparison with star systems in other galaxies. In thispaper we present and discuss a standard methodology to synthesize U,B,Vfluxes and colours, and apply it to a set of 138 open clusters. Resultsare compared with previous ones available in the literature. We wereable to calibrate a mass-luminosity relation by which we evaluated themass of ~400 open clusters, leading to a well defined present-day massfunction. The number-complete sample of galactic open clusters presentedin Battinelli & Capuzzo-Dolcetta (1991) is enlarged of a 15%.
| An Investigation of the Double-Mode Cepheid Tu-Cassiopeiae - Part One - Atmospheric Parameters and Chemical Composition
Abstract image available at:http://adsabs.harvard.edu/abs/1993MNRAS.265..257A
| Comparison of the open cluster and surface-brightness distance scales for galactic classical Cepheids
We have derived a new period-luminosity (PL) relation for galacticCepheids in open clusters and associations from the ZAMS-fitting method,using the most reliable cluster photometric data and Cepheid reddeningdata available, and homogeneous treatment of absorption corrections. Forabout half of the cluster Cepheid sample (17 stars) we also derivedistances and absolute magnitudes from the surface-brightness method.From a comparison we find that the surface-brightness PL relation has azero point about 0.15 mag brighter than the cluster ZAMS-fitting PLrelation, but in view of the sources of systematic error involved inboth methods, this discrepancy is clearly not significant. Rather, weconclude from our results that the two currently most important methodsto derive distances to galactic Cepheids produce consistent results, andthat neither of the two methods contain systematic errors in excess ofabout 0.10 mag. The results of this paper imply a distance to the LMC of18.65 +/- 0.10 mag. We identify four stars in our cluster/ associationCepheid sample for which the discrepancies between ZAMS-fitting andsurface brightness are so large (greater than 0.6 mag) that seriousdoubt is cast on their membership to the proposed host clusters orassociations.
| Galactic clusters with associated Cepheid variables. III - NGC 1647 and SZ Tauri
Observational data and analysis are used to argue that the Cepheid Z Tauis an outlying member of the open cluster NGC 1647. The spatialcoincidence of the Cepheid with the cluster corona, as well ascoincidences in radial velocity, proper motion, and age with clustermembers, present a convincing case for cluster membership, which is alsosupported by independent estimates for the mean radius of SZ Tau. Theevidence presented by the derived luminosity of the Cepheid and itslight curve strongly indicates that SZ Tau is pulsating in the firstovertone, rather than fundamental, mode.
| Tuning the Cepheid distance scale
Ongoing observational programs (both from the ground and space) willprovide a significantly larger sample of galaxies with well-studiedCepheids both within the Local Group and in more distant galaxies.Recent efforts in the calibration of the Cepheid distance scaleutilizing Cepheids in star clusters in the Galaxy and in the MagellanicClouds are described. Some of the significant advantages of utilizingLMC Cepheids in particular are emphasized, and the current status of thefield is summarized.
| The characteristics of open star clusters according to photometrical data - Cepheids in the open clusters
The color excesses, distance moduli, and ages of 16 open clusters with19 Cepheids in their fields are revised. The absolute magnitudes andunreddened colors are derived, assuming the cluster membership of theCepheids. The Cepheids CS Vel, BB Sgr, and RU Sct probably are notmembers of associating open clusters. The standard period-luminosity andperiod-color relations are corrected using the data on 15 Cepheids.
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