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An Extrasolar Planet Transit Search with Subaru Suprime-Cam
We report the results of a prototype photometric search for transitingextrasolar planets using Subaru Suprime-Cam. Out of about 100000 starsmonitored around the Galactic plane (l=90°, b=0°) we find that7700 show photometric precision better than 1% for 60s exposures, whichis required to detect extrasolar planets by the transit method. Thus,Suprime-Cam has the photometric stability and accuracy necessary for atransiting planet survey. During this observing run, we detected threeobjects (around 18.5mag for i'-band) that exhibit a single fulltransit-like light curve with a fractional depth of < 5%. While aspectroscopic follow-up remains to be done using future telescopes inthe 20-30m class, the estimated parameters for the three systems areconsistent with the planetary size companions around main-sequencestars. We also found two eclipsing binary candidates and eleven variablestars exhibiting W UMa-like light curves.
| Survey for Transiting Extrasolar Planets in Stellar Systems. IV. Variables in the Field of NGC 1245
The Survey for Transiting Extrasolar Planets in Stellar Systems (STEPSS)project is a search for planetary transits in open clusters. In thispaper we analyze the STEPSS observations of the open cluster NGC 1245 todetermine the variable-star content of the cluster. Out of 6787 starsobserved with V<22, of which ~870 are cluster members, we find 14stars with clear intrinsic variability that are potential clustermembers and 29 clear variables that are not cluster members. None ofthese variables have been previously identified. We present lightcurves, finder charts, and stellar/photometric data on these variableobjects. Several of the interacting binaries have estimated distancesconsistent with the cluster distance determined from isochrone fits tothe color-magnitude diagram. Four stars at the main-sequence turnoff ofthe cluster have light curves consistent with γ Doradusvariability. If these γ Doradus candidates are confirmed, theyrepresent the oldest and coolest members of this class of variablediscovered to date.
| Astrophysics in 2005
We bring you, as usual, the Sun and Moon and stars, plus some galaxiesand a new section on astrobiology. Some highlights are short (the newlyidentified class of gamma-ray bursts, and the Deep Impact on Comet9P/Tempel 1), some long (the age of the universe, which will be found tohave the Earth at its center), and a few metonymic, for instance theterm ``down-sizing'' to describe the evolution of star formation rateswith redshift.
| 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.
| Astrophysical parameters of Galactic open clusters
We present a catalogue of astrophysical data for 520 Galactic openclusters. These are the clusters for which at least three most probablemembers (18 on average) could be identified in the ASCC-2.5, a catalogueof stars based on the Tycho-2 observations from the Hipparcos mission.We applied homogeneous methods and algorithms to determine angular sizesof cluster cores and coronae, heliocentric distances, mean propermotions, mean radial velocities, and ages. For the first time we derivedistances for 200 clusters, radial velocities for 94 clusters, and agesof 196 clusters. This homogeneous new parameter set is compared withearlier determinations, where we find, in particular, that the angularsizes were systematically underestimated in the literature.
| BVRI CCD-Photometry of Comparison Stars in the Neighborhoods of Galaxies with Active Nuclei. II
Results are presented from CCD BVRI-observations of 145 comparison starsin the neighborhoods of 14 Seyfert galaxies, 3 quasars, and 5 BL Lacobjects with right ascensions of 12 to 24 hours. The magnitudes of theobserved stars ranged from V=11 to V=17. The typical photometric errorfor stars brighter V=14 is 0m.01. The B, V, Rc, and Ic magnitudes ofmost of these stars were not known previously. 14′ x 14′finding charts are provided. These results can be used for differentialphotometry of the nuclei of active galaxies in the B, V, Rc, and Icbands.
| A dearth of planetary transits in the direction of NGC 6940
We present results of our survey for planetary transits in the field ofNGC 6940. We think nearly all of our observed stars are field stars. Wehave obtained high precision (~3-10 mmag at the bright end) photometricobservations of ~50000 stars spanning 18 nights in an attempt toidentify low-amplitude and short-period transit events. We have used amatched filter analysis to identify 14 stars that show multiple eventsand four stars that show single transits. Of these 18 candidates, wehave identified two that should be further researched. However, none ofthe candidates is a convincing hot Jupiter.
| Photometric Monitoring of Open Clusters. I. The Survey
Open clusters, which have age, abundance, and extinction informationfrom studies of main-sequence turnoff stars, are the ideal location inwhich to determine the mass-luminosity-radius relation for low-massstars. We have undertaken a photometric monitoring survey of openclusters in the Galaxy designed to detect low-mass eclipsing binarysystems through variations in their relative light curves. Our aim is toprovide an improved calibration of the mass-luminosity-radius relationfor low-mass stars and brown dwarfs, to test stellar structure andevolution models, and to help quantify the contribution of low-massstars to the global mass census in the Galaxy. In this paper we presentour survey, describing the data and outlining the analysis techniques.We study six nearby open clusters, with a range of ages from ~0.2 to 4Gyr and metallicities from approximately solar to -0.2 dex. We monitor afield of view of greater than 1 deg2 per target cluster, wellbeyond the characteristic cluster radius, over timescales of hours,days, and months with a sampling rate optimized for the detection ofeclipsing binaries with periods of hours to days. Our survey depth isdesigned to detect eclipse events in a binary with a primary star of<~0.3 Msolar. Our data have a photometric precision of ~3mmag at I~16.
| An Examination of Main Sequence Stars within the Instability Strip for Open Clusters Over a Range of Ages
We are conducting a study of 14 open clusters which have an approximateage range of 7 to 9 Gyr. The observations for this project were takenwith the 1.8-m telescope at the Dominion Astrophysical Observatory usinga y filter and with the 0.4-m David Derrick telescope of the Orson PrattObservatory using a set of VRI filters. The exposure lengths wereoptimized for main sequence stars in the A-F range in order to bracketthe instability strip. We plan to correlate the cluster ages with 1) thenumber of pulsating variables in the instability strip, 2) thepercentage of variable stars in the instability strip, and 3) theamplitude of the pulsations. We will present preliminary results for 4of the 14 clusters: NGC 6811, NGC 6940, NGC 7142, and NGC 7160.We wish to thank the Dominion Astrophysical Observatory for access tothe 1.8-m telescope. We also acknowledge funding from an AAS SmallResearch Grant that helped make the telescope time at DAO possible.
| X-ray astronomy of stellar coronae
X-ray emission from stars in the cool half of the Hertzsprung-Russelldiagram is generally attributed to the presence of a magnetic coronathat contains plasma at temperatures exceeding 1 million K. Coronae areubiquitous among these stars, yet many fundamental mechanisms operatingin their magnetic fields still elude an interpretation through adetailed physical description. Stellar X-ray astronomy is thereforecontributing toward a deeper understanding of the generation of magneticfields in magnetohydrodynamic dynamos, the release of energy in tenuousastrophysical plasmas through various plasma-physical processes, and theinteractions of high-energy radiation with the stellar environment.Stellar X-ray emission also provides important diagnostics to study thestructure and evolution of stellar magnetic fields from the first daysof a protostellar life to the latest stages of stellar evolution amonggiants and supergiants. The discipline of stellar coronal X-rayastronomy has now reached a level of sophistication that makes tests ofadvanced theories in stellar physics possible. This development is basedon the rapidly advancing instrumental possibilities that today allow usto obtain images with sub-arcsecond resolution and spectra withresolving powers exceeding 1000. High-resolution X-ray spectroscopy has,in fact, opened new windows into astrophysical sources, and has played afundamental role in coronal research.
| A Chandra observation of the old open cluster M 67
We present the results of a 47-ks Chandra-ACIS observation of the oldopen cluster M 67. We detected 25 proper-motioncluster members (including ten new sources) and 12 sources (all new)that we suspect to be members from their locations close to the mainsequence (1 < B-V <1.7). Of the detected members, 23 are binaries.Among the new sources that are members and probable members are fourspectroscopic binaries with Porb < 12 d, two contactbinaries and two periodic photometric variables with Pph <8.4 d. Their X-rays are likely the result of coronal activity enhancedby tidally locked rapid rotation. The X-rays of the new sourceS 997, a blue straggler in a wide eccentric orbit,are puzzling. Spectral fits show that the X-rays of the brightestsources S 1063 (a binary with a sub-subgiant),S 1082 (a triple blue straggler with a close binary)and S 1040 (a circular binary of a giant and a coolwhite dwarf), are consistent with coronal emission. We detected a newbright source that must have brightened at least about ten times sincethe time of the ROSAT observations. It is not clear whether its faintblue optical counterpart belongs to M 67. We discuss the possibilitythat this source is a low-mass X-ray binary in quiescence, which wouldbe the first of its kind in an open cluster. In addition to clustermembers, we detected about 100 background sources, many of which weidentify with faint objects in the ESO Imaging Survey.Tables 1 and 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/509
| Intermediate-age Galactic open clusters: fundamental parameters of NGC 2627
Charge-coupled device (CCD) photometry in the Johnson V, Kron-Cousins Iand Washington CMT1 systems is presented in the field of thepoorly known open cluster NGC 2627. Four independent Washingtonabundance indices yield a mean cluster metallicity of [Fe/H]=-0.12 +/-0.08, which is compatible with the existence of a radial gradient in theGalactic disc. The resultant colour-magnitude diagrams indicate that thecluster is an intermediate-age object of 1.4 Gyr. Based on the best fitsof the Geneva group's isochrones to the (V, V-I) and (T1,C-T1) diagrams, we estimate E(V-I) = 0.25 +/- 0.05 andV-MV= 11.80 +/- 0.25 for logt= 9.15, and E(C-T1) =0.23 +/- 0.07 and T1-MT1= 11.85 +/-0.25 for logt= 9.10, respectively, assuming solar metal content. Thederived reddening value E(C-T1) implies E(B-V) = 0.12 +/-0.07 and a distance from the Sun of 2.0 +/- 0.4 kpc. Using the WEBDAdata base and the available literature, we re-examined the overallproperties of all the open clusters with ages between 0.6 and 2.5 Gyr.We identified peaks of cluster formation at 0.7-0.8, 1.0-1.1, 1.6-1.7and 2.0-2.1 Gyr, separated by relative quiescent epochs of ~0.2-0.3 Gyr.We also estimated a radial abundance gradient of -0.08 +/- 0.02, whichis consistent with the most recent determinations for the Galactic disc,but no clear evidence for a gradient perpendicular to the Galactic planeis found.
| Recent developments on studies of open clusters
Studies on open clusters are of great significance for astronomy andastrophysics, for which distinct developments have been made recently inboth observational and theoretical respects. In this paper, currentresearch of open cluster is reviewed, and membership determination,basic parameters determination, evolution of cluster and clustermembers, structure and dynamics of open cluster are also described indetail.
| Searching for planetary transits in the field of open cluster NGC 6819 - I
We present results from our survey for planetary transits in the fieldof the intermediate-age (~2.5 Gyr), metal-rich ([Fe/H]~+0.07) opencluster NGC 6819. We have obtained high-precision time-series photometryfor over 38 000 stars in this field and have developed an effectivematched-filter algorithm to search for photometric transits. Thisalgorithm identified 8 candidate stars showing multiple transit-likeevents, plus 3 stars with single eclipses. On closer inspection, whilemost are shown to be low-mass stellar binaries, some of these eventscould be the result of brown dwarf companions. The data for one of thesingle-transit candidates indicate a minimum radius for the companionsimilar to that of HD 209458b.
| 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.
| Carbon Star Survey in the Local Group. V. The Outer Disk of M31
We employ the CFH12K mosaic to identify carbon stars, using the R, I,CN, and TiO photometric technique, in a 2240 arcmin2 area,ranging from 17 to 30 kpc of the southwest disk of M31, barely reachingthe edge of the observed H I disk. We found 945 C stars with=19.94 and σ=0.47. The surface density of Cstars along the major axis of M31 follows an exponential profile with ascale length of 4.85+/-0.35 kpc, in agreement with adopted values forthe scale length of the disk population. Our survey partially overlapswith the recently discovered G1 density enhancement by Ferguson et al.We confirm that no AGB star excess is detectable in the surveyed part ofthe clump. The C/M ratio, along the major axis, is derived over adistance range of 7 kpc. The strong C/M gradient seen contrasts withresults of previous studies of the C stars in M31.
| 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.
| University of St. Andrews Open Cluster Survey for Hot Jupiters
We are using the Isaac Newton Telescope Wide Field Camera to survey opencluster fields for transiting hot Jupiter planets. Clusters wereselected on the basis of visibility, richness of stars, age andmetallicity. Observations of NGC 6819, 6940 and 7789 began in 1999 andcontinued in 2000. We have developed an effective matched-filtertransit-detection algorithm which has proved its ability to identifyvery low amplitude eclipse events in real data. Here we present ourresults for NGC 6819. We have identified 7 candidates showingtransit-like events. Colour information suggests that most of thecompanion bodies are likely to be very-low-mass stars or brown dwarfs,intrinsically interesting objects in their own right.
| Metallicities of Old Open Clusters
We present radial velocities and metallicities for a sample of 39 openclusters with ages greater than about 700 million years. For 24 clustersnew moderate-resolution spectroscopic data obtained with multiobjectspectrographs on the Kitt Peak National Observatory and the Cerro TololoInter-American Observatory 4 m telescopes are used to determine radialvelocities and mean cluster metallicities. These new results arecombined with data published previously by Friel & Janes to providea sample of 459 giants in 39 old open clusters, which are used toinvestigate radial abundance gradients in the Galactic disk. Based on anupdated abundance calibration of spectroscopic indices measuring Fe andFe-peak element blends, this larger sample yields an abundance gradientof -0.06+/-0.01 dex kpc-1 over a range in Galactocentricradius of 7 to 16 kpc. There is a slight suggestion of a steepening ofthe abundance gradient with increasing cluster age in this sample, butthe significance of the result is limited by the restricted distancerange for the youngest clusters. The clusters show no correlation ofmetallicity with age in the solar neighborhood. Consistent with theevidence for a steepening of the gradient with age, the clusters in theouter disk beyond 10 kpc show a suggestion at the 1.5 σ level of adependence of metallicity on age.
| Variable stars in the field of open cluster NGC 6819
We report on the discovery of 25 variable stars plus 13 suspectedvariables found in the field of the open cluster NGC 6819. The starswere identified from time-series photometric data obtained on the IsaacNewton Telescope, La Palma, during two observing runs covering the 19nights between 1999 June and 1999 July . The variables found include 12eclipsing binaries with an additional three suspected, nine BY Draconissystems, plus four variables of other types, including one star believedto be a Cepheid. Three of the 15 eclipsing binaries are believed to becluster members. Details of a further 10 suspected variable stars arealso included.
| Abundance Gradient from Open Clusters and Implications for the Galactic Disk Evolution
We compile a new sample of 89 open clusters with ages, distances andmetallicities available. We derive a radial iron gradient of about-0.099±0.008 dexkpc (unweighted) for the whole sample, which issomewhat greater than the most recent determination of oxygen gradientfrom nebulae and young stars. By dividing the clusters into age groups,we show that the iron gradient was steeper in the past and has evolvedslowly in time. Current data show a substantial scatter of the clustermetallicities indicating that the Galactic disk has undergone a veryrapid, inhomogeneous enrichment.Also, based on a simple, but quitesuccessful model of chemical evolution of the Milky Way disk, we make adetailed calculation of the iron abundance gradient and its timeevolution. The predicted current iron gradient is about -0.072 dexkpc.The model also predicts a steady flattening of the iron gradient withtime, which agrees with the result from our open cluster sample.
| A study of spatial structure of galactic open star clusters
In order to study the relation between the core and corona in galacticstar clusters, the spatial structure of 38 rich open star clusters hasbeen studied using radial density profiles derived from the photometricdata of the Digital Sky Survey. The shape of the radial density profileindicates that the corona, most probably, is the outer region around thecluster. It can exist from the very beginning of the cluster formationand dynamical evolution is not the reason for its occurrence. The studydoes not find any relation between cluster size and age but indicatesthat the clusters with galacto-centric distances >9.5 kpc have largersizes. Further, we find that the average value of the core radius is1.3+/- 0.7 pc and that of annular width of the corona is 5.6+/- 1.9 pc,while average values of densities of cluster members in the core andcorona are 15.4+/- 9.9 star/pc2 and 1.6+/- 0.99star/pc2 respectively. Average field star contaminations inthe core and corona are ~ 35% and 80% respectively. In spite of smallerdensities in the coronal region, it contains ~ 75% of the clustermembers due to its larger area in comparison to the core region. Thisclearly demonstrates the importance of the coronal region in studiesdealing with the entire stellar contents of open star clusters as wellas their dynamical evolution. In contrast to the cluster cores, thestructure of coronal regions differs significantly from one cluster toother.
| Proper motions of open clusters within 1 kpc based on the TYCHO2 Catalogue
We present mean absolute proper motions of 112 open clusters, determinedusing the data from the Tycho2 Catalogue. For 28 clusters, this is thefirst determination of proper motion. The measurements made use of alarge number of stars (usually several tens) for each cluster. The totalnumber of stars studied in the fields of the 164 open clusters is 5016,of which 4006 were considered members. The mean proper motions of theclusters and membership probability of individual stars were obtainedfrom the proper motion data by applying the statistical method proposedby Sanders (\cite{Sanders71}). Based on observations of the ESAHipparcos satellite. Tables 1, 2 and 5 to 117 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/376/441
| An optical study of X-ray sources in the old open clusters NGC 752 and NGC 6940
We observed the optical counterparts of X-ray sources in the old openclusters NGC 752 and NGC 6940 to search for the origin of the X-rays.The photometric variability reported earlier for the blue straggler H209 is not confirmed by our light curves, nor is an indication forvariability seen in the spectra; thus its X-rays remain unexplained. TheX-rays of VR 111 and VR 114 are likely not a result of magnetic activityas these stars lack strong Ca II H&K emission, while in VR 108 thelevel of activity could be enhanced. The short-period binary H 313 is aphotometric variable; this supports the interpretation that it is amagnetically active binary. From the detection of the Li I 6707.8Å line, we classify the giant in VR 84 as a first-ascent giant;this leaves its circular orbit unexplained. As a side-result we reportthe detection of Li I 6707.8 Å in the spectrum of the giant H 3and the absence of this line in the spectrum of the giant H 11; thisclassifies H 3 as a first-ascent giant and H 11 as a core-helium-burningclump star, and confirms the faint extension of the red-giant clump inNGC 752. Based on observations made with the Jacobus Kapteyn Telescopeand the William Herschel Telescope operated on the island of La Palma bythe Isaac Newton Group in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias.
| Exploring Halo Substructure with Giant Stars. I. Survey Description and Calibration of the Photometric Search Technique
We have begun a survey of the structure of the Milky Way halo, as wellas the halos of other Local Group galaxies, as traced by theirconstituent giant stars. These giant stars are identified vialarge-area, CCD photometric campaigns. Here we present the basis for ourphotometric search method, which relies on the gravity sensitivity ofthe Mg I triplet+MgH features near 5150 Å in F-K stars, and whichis sensed by the flux in the intermediate-band DDO51 filter. Ourtechnique is a simplified variant of the combined Washington/DDO51four-filter technique described by Geisler, which we modify for thespecific purpose of efficiently identifying distant giant stars forfollow-up spectroscopic study: We show here that for most stars theWashington T1-T2 color is correlated monotonicallywith the Washington M-T2 color with relatively low scatter;for the purposes of our survey, this correlation obviates the need toimage in the T1 filter, as originally proposed by Geisler. Tocalibrate our (M-T2, M-DDO51) diagram as a means todiscriminate field giant stars from nearby dwarfs, we utilize newphotometry of the main sequences of the open clusters NGC 3680 and NGC2477 and the red giant branches of the clusters NGC 3680, Melotte 66,and ω Centauri, supplemented with data on field stars, globularclusters and open clusters by Doug Geisler and collaborators. Bycombining the data on stars from different clusters, and by takingadvantage of the wide abundance spread within ω Centauri, weverify the primary dependence of the M-DDO51 color on luminosity anddemonstrate the secondary sensitivity to metallicity among giant stars.Our empirical results are found to be generally consistent with thosefrom analysis of synthetic spectra by Paltoglou & Bell. Finally, weprovide conversion formulae from the (M, M-T2) system to the(V, V-I) system, corresponding reddening laws, as well as empirical redgiant branch curves from ω Centauri stars for use in derivingphotometric parallaxes for giant stars of various metallicities (butequivalent ages) to those of ω Centauri giants.
| 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
| Foreground and background dust in star cluster directions
This paper compares reddening values E(B-V) derived from the stellarcontent of 103 old open clusters and 147 globular clusters of the MilkyWay with those derived from DIRBE/IRAS 100 mu m dust emission in thesame directions. Star clusters at |b|> 20deg showcomparable reddening values between the two methods, in agreement withthe fact that most of them are located beyond the disk dust layer. Forvery low galactic latitude lines of sight, differences occur in thesense that DIRBE/IRAS reddening values can be substantially larger,suggesting effects due to the depth distribution of the dust. Thedifferences appear to arise from dust in the background of the clustersconsistent with a dust layer where important extinction occurs up todistances from the Plane of ~ 300 pc. For 3 % of the sample asignificant background dust contribution might be explained by higherdust clouds. We find evidence that the Milky Way dust lane and higherdust clouds are similar to those of several edge-on spiral galaxiesrecently studied in detail by means of CCD imaging.
| X-rays from old open clusters: M 67 and NGC 188
We have observed the old open clusters M 67 and NGC 188 with the ROSATPSPC. In M 67 we detect a variety of X-ray sources. The X-ray emissionby a cataclysmic variable, a single hot white dwarf, two contactbinaries, and some RS CVn systems is as expected. The X-ray emission bytwo binaries located below the subgiant branch in the HertzsprungRussell diagram of the cluster, by a circular binary with a cool whitedwarf, and by two eccentric binaries with P_b > 700 d is puzzling.Two members of NGC 188 are detected, including the FK Com type starD719. Another possible FK Com type star, probably not a member of NGC188, is also detected.
| The Open Cluster NGC 7789. I. Radial Velocities for Giant Stars
A total of 597 radial velocity observations for 112 stars in the ~1.6Gyr old open cluster NGC 7789 have been obtained since 1979 with theradial velocity spectrometer at the Dominion Astrophysical Observatory.The mean cluster radial velocity is -54.9+/-0.12 km s^-1 and thedispersion is 0.86 km s^-1, from 50 constant velocity stars selected asmembers from this radial velocity study and the 1981 proper motion studyof McNamara & Solomon. Twenty-five stars (32%) among 78 members arepossible radial velocity variable stars, but no orbits are determinedbecause of the sparse sampling. Seventeen stars are radial velocitynonmembers, while the membership estimates of six stars are uncertain.There is a hint that the observed velocity dispersion falls off at largeradius. This may due to the inclusion of long-period binariespreferentially in the central area of the cluster. The known radialvelocity variables also seem to be more concentrated toward the centerthan members with constant velocity. Although this is significant atonly the 85% level, when combined with the similar result of Raboud& Mermilliod for three other clusters, the data strongly support theconclusion that mass segregation is being detected.
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