Contents
Images
Upload your image
DSS Images Other Images
Related articles
The reliability of Cepheid reddenings based on BVIC photometry
Externally determined values of E(B - V) (Espacered) for 40Galactic Cepheids are compared to reddenings determined using B - V andV - IC colour indices and the method of Dean, Warren &Cousins (EBVIC), updated to allow for metallicitycorrections. With three stars omitted on the grounds of uncertainty intheir space reddenings, we find thatThe two scales agree well in scale and zero-point, and there is nosignificant trend with period. Given the non-zero errors in the Cepheidspace reddenings, the estimated error in BVIC Cepheidreddenings is no more than 0.02.The above results are not significantly changed whether one corrects thereddenings for metallicity using older Bell models, or using more recentmodels by Sandage, Bell & Tripicco. Using the SBT models to correctthe reddenings of Cloud Cepheids for metallicity gives slightly smallerreddenings at a given metal deficiency, yielding `new' median reddeningsof 0.056 (Small Magellanic Cloud) and 0.076 (Large Magellanic Cloud) ifwe assume the same metal deficiencies as Caldwell and Coulson. Withmetal deficiencies of [M/H] = -0.7 and -0.25, the median reddenings are0.040 and 0.058.
| 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.
| The Evolutionary Status of Be Stars: Results from a Photometric Study of Southern Open Clusters
Be stars are a class of rapidly rotating B stars with circumstellardisks that cause Balmer and other line emission. There are threepossible reasons for the rapid rotation of Be stars: they may have beenborn as rapid rotators, spun up by binary mass transfer, or spun upduring the main-sequence (MS) evolution of B stars. To test the variousformation scenarios, we have conducted a photometric survey of 55 openclusters in the southern sky. Of these, five clusters are probably notphysically associated groups and our results for two other clusters arenot reliable, but we identify 52 definite Be stars and an additional 129Be candidates in the remaining clusters. We use our results to examinethe age and evolutionary dependence of the Be phenomenon. We find anoverall increase in the fraction of Be stars with age until 100 Myr, andBe stars are most common among the brightest, most massive B-type starsabove the zero-age main sequence (ZAMS). We show that a spin-up phase atthe terminal-age main sequence (TAMS) cannot produce the observeddistribution of Be stars, but up to 73% of the Be stars detected mayhave been spun-up by binary mass transfer. Most of the remaining Bestars were likely rapid rotators at birth. Previous studies havesuggested that low metallicity and high cluster density may also favorBe star formation. Our results indicate a possible increase in thefraction of Be stars with increasing cluster distance from the Galacticcenter (in environments of decreasing metallicity). However, the trendis not significant and could be ruled out due to the intrinsic scatterin our data. We also find no relationship between the fraction of Bestars and cluster density.
| Time dependent mixing in He-burning cores: The case of NGC 1866
We examine the helium burning phase of the convective core ofintermediate mass stars, and investigate the role of the coupling ofnuclear burning and mixing on the extension and duration of the blueloop phase. We compare the theoretical scenario with the distribution ofstars in the colour-magnitude (CM) diagram of the Large Magellanic Cloud(LMC) cluster NGC 1866, whose densely populated clump of He-burningstars is equally populated on the blue and red side. We compare thedistributions expected by adopting either a diffusive scheme within theinstability regions, in which nuclear burning and mixing areself-consistently coupled, or the traditional instantaneous mixingapproximation. We analyze with particular care the sensitivity of theresults to: a) the e-folding distance with which the velocity ofconvective eddies decays outside the formal border of the convectiveregions fixed by the Schwarzschild criterion; b) the convective modeladopted to evaluate the temperature gradient; c) the rate of reaction12C+α -> 16O. Models not includingconvective overshoot are also commented.
| 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.
| On the Galactic Disk Metallicity Distribution from Open Clusters. I. New Catalogs and Abundance Gradient
We have compiled two new open cluster catalogs. In the first one, thereare 119 objects with ages, distances, and metallicities available, whilein the second one, 144 objects have both absolute proper motion andradial velocity data, of which 45 clusters also have metallicity dataavailable. Taking advantage of the large number of objects included inour sample, we present an iron radial gradient of about -0.063+/-0.008dex kpc-1 from the first sample, which is quite consistentwith the most recent determination of the oxygen gradient from nebulaeand young stars, about -0.07 dex kpc-1. By dividing clustersinto age groups, we show that the iron gradient was steeper in the past,which is consistent with the recent result from Galactic planetarynebulae data, and also consistent with inside-out galactic diskformation scenarios. Based on the cluster sample, we also discuss themetallicity distribution, cluster kinematics, and space distribution. Adisk age-metallicity relation could be implied by those properties,although we cannot give conclusive result from the age- metallicitydiagram based on the current sample. More observations are needed formetal-poor clusters. From the second catalog, we have calculated thevelocity components in cylindrical coordinates with respect to theGalactic standard of rest for 144 open clusters. The velocitydispersions of the older clusters are larger than those of youngclusters, but they are all much smaller than that of the Galactic thickdisk stars.
| CCD uvbyCaHβ Photometry of Clusters. III. The Most Metal-Rich Open Cluster, NGC 6253
CCD photometry on the intermediate-band uvbyCaHβ system ispresented for the old open cluster NGC 6253. Despite a high level offield star contamination because of its location toward the Galacticcenter, combination of the data from the multiple color indices with thecore cluster sample derived from radial star counts leads to theidentification of a set of highly probable, single cluster members.Photometric analysis of a select sample of 71 turnoff stars produces areddening value of E(b-y)=0.190+/-0.002 (s.e.m.) or E(B-V)=0.260+/-0.003(s.e.m.). The metallicity indices, δm1 and δhk,both identify this cluster as the most metal-rich object studied oneither system to date. Simple extrapolation of the available metallicitycalibrations leads to [Fe/H] values ranging from +0.7 to +0.9.Metal-rich isochrones with overshoot imply an age between 2.5 and 3.5Gyr, with an apparent distance modulus between (m-M)=11.6 and 12.2,depending upon the isochrones used. The improvement in the fit usingα-enhanced isochrones may indicate that the cluster [Fe/H] iscloser to +0.4, but the photometric indices are distorted by anelemental distribution other than a scaled solar. The Galactocentricposition of the cluster, in conjunction with data for other clusters andCepheids, is consistent with the inner disk reaching and maintaining ametallicity well above solar since the early history of the disk, unlikethe solar neighborhood.
| 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 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].
| The blue to red supergiant ratio in young clusters at various metallicities
We present new determinations of the blue to red supergiant ratio (B/R)in young open clusters at various metallicities. For this purpose, weexamine the HR diagrams of 45 clusters in the Galaxy and of 4 clustersin the Magellanic Clouds. The identification of supergiants is based onspectroscopic measurements (with photometric counts to check theresults). The new counts confirm the increase of the B/R ratio when themetallicity increases with the following normalized relation:(B/R)/((B/R)sun) =~ 0.05* e3(Z)/(Zsun)}, where Zsun=0.02 and(B/R)sun is the value of B/R at Zsun which dependson the definition of B and R and on the age interval considered (e.g.for spectroscopic counts including clusters with log age between 6.8 and7.5, (B/R)sun =~ 3 when B includes O, B and A supergiants).
| Astrophysics in 2000
It was a year in which some topics selected themselves as importantthrough the sheer numbers of papers published. These include theconnection(s) between galaxies with active central engines and galaxieswith starbursts, the transition from asymptotic giant branch stars towhite dwarfs, gamma-ray bursters, solar data from three major satellitemissions, and the cosmological parameters, including dark matter andvery large scale structure. Several sections are oriented aroundprocesses-accretion, collimation, mergers, and disruptions-shared by anumber of kinds of stars and galaxies. And, of course, there are theusual frivolities of errors, omissions, exceptions, and inventories.
| 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.
| Spectroscopic investigations of classical Cepheids and main-sequence stars in galactic open clusters and associations. I. Association Cas OB2 and the small-amplitude Cepheid SU Cassiopeae
The small-amplitude Cepheid SU Cas and four membersof the association Cas OB2 (HD 16893, HD17327a and b, HD 17443) were investigated,using high-resolution CCD spectra. The following results were obtained:1) All these objects have the same metallicity values, close to that ofthe Sun; 2) Elemental abundance indicates that SU Cas is a post firstdredge-up star with an age from 1 108 to 1.45 108yr, and it is not crossing the Cepheid instability strip for the firsttime. The mean value of log g = 2.35 corresponds to pulsations in thefundamental tone, although errors in gravity estimations provideovertone pulsations. The questions about its pulsational mode andmembership in Cas OB2 remained open; 3) HD17327a is a slowly rotating HgMn-star with the highest heliumcontent among such objects, while HD 16893 also has a manganeseoverabundance and might be classified as an Am-star; 4) HD17327b and HD 17443 are rapidly rotating main-sequence stars,while HD 17443 has a helium content comparable with that of the Sun.
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| EV SCT - a double system with two Cepheid components in NGC 6664?
Spectroscopic manifestations of the s-Cepheid EV Sct binarity arereported. All the lines in the spectrum of this faint Cepheid arestrongly asymmetrical or even splitted indicating that this systemconsists of two components. Both components have close effectivetemperatures, the difference in the visual magnitudes seems to be notgreat. Together with the preliminary results of the frequency analysisbased on the published photometrical data, this means that the secondarycomponent is probably also situated within the instability strip, beinga very short-period Cepheid (P ~ 1.2 day)
| 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.
| Red giants in open clusters. VI. Orbits of ten spectroscopic binaries.
We present new orbits for ten (single-lined) spectroscopic binaries inseven open clusters: NGC 2489, 2567, 3033, 5822, 6134, 6664 and IC 2488based on 243 individual radial velocities obtained with the southernCORAVEL scanner. The orbital periods range from 98.5 to 3566 days. Theshortest-period orbit is circular, as expected. Seven of the binariesare confirmed cluster members, one is a possible member, and two areclearly non-members. Maximum masses from photometric separation andminimum masses from the spectroscopic orbits define the mass of thesecondaries within an interval of M_max_-M_min_=0.5Msun_. NGC6664 #54 seems to have a rather massive secondary(M>3Msun_), but the UBV colours appear normal for aluminous red giant, while significantly bluer (B-V) and (U-B) colourswould be expected. It could be a triple system, the secondary beingitself a short period binary. This paper brings the number of orbitspublished in this programme to 53, 45 of which are confirmed red-giantcluster members and 8 are non-members.
| Parameters of open star clusters from uvby-beta photometry.
Not Available
| Absolute proper motions of 181 young open clusters.
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.
| 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.
| 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.
| Formation and evolutionary properties of the Galactic open cluster system
Results are reported from a statistical analysis of observational dataon 100 open clusters within 2 kpc of the sun, selected from the catalogof Lynga (1987). The selection criteria and the completeness of thesample are discussed; the data are compiled in a table; and the analysisresults are presented in a series of graphs and characterized in detail.A cluster formation rate of 0.45 clusters/kpc Myr is found,significantly lower than the rates determined previously (using clusterswithin 1 kpc of the sun) and corresponding to a cluster star-formationefficiency of 0.0063. The low average cluster lifetime (about 10 Myr)suggests that clusters are formed as unstable systems.
| Colour excesses and absolute magnitudes for non-Cepheid F-G supergiants from uvbybeta photometry
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990A&A...239..205A&db_key=AST
| Some remarks on delta Cephei stars in open clusters.
Not Available
| Some characteristics of complexes of open star clusters
Mean coordinates and velocities, phase sizes, mean elements of galacticorbits, mean ages, and metal abundances are given for 11 complexes ofopen clusters, and correlations between these characteristics arediscussed. The possible existence of a supercomplex encompassing 9 or 10complexes, and probably a number of individual clusters, is discussed.This rotates at an angular velocity of 10 to 13 km/s kpc.
| The zero point of the Cepheid period-luminosity relation in the 1.05 micron wave band
New observations of the Cepheids in the galactic clusters and externalgalaxies LMC, NGC 6822, NGC 300, and Sex A in the 1.05-micron wave band(IV) are presented. The slope of the P-L(IV) relation derived from theCepheids in the LMC agree with that in the SMC and that obtained forGalactic Cepheids. The zero point of the relation has been determinedfrom the distances to the galactic Cepheid clusters obtained throughZAMS fitting and referenced to the Pleiades modulus of 5.57. Thebolometric P-L relations derived individually using the data in V, J, Kwave bands are found to have the same slope and the zero point asobserved in the IV wave band. The comparison of the bolometric P-Lrelation with that obtained theoretically by Becker, Iben, and Tuggleshows agreement in the value of the slope. But the theoreticalmagnitudes are brighter by 0.4 mag. The true distance moduli to the LMC,the SMC, NGC 6822, NGC 300, and Sex A have been derived from P-L(IV)data and are found to be as 18.42, 18.83, 23.18, 25.72, and 25.27,respectively.
| Integrated parameters of open clusters
Integrated magnitudes and colors of population I synthetic clusters havebeen derived using theoretical evolutionary tracks and an age-dependedntinitial mass function. A comparison of the theoretically obtainedintegrated parameters with the observational data of open clusters inthe Milky Way and clusters in the LMC has also been made. It is foundthat the observed dependences show a better agreement with thetheoretical dependences obtained in the present work than thetheoretical dependences obtained by earlier authors. It is alsoconcluded that the clusters in the LMC in general show a mean reddeningof E(B-V) = 0.12 mag.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
NEWS@SKY (Science&Space News)
