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New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| ROSAT PSPC/HRI observations of the open cluster NGC 2422
We present the results of a ROSAT study of NGC 2422, a southern opencluster at a distance of about 470 pc, with an age close to thePleiades. Source detection was performed on two observations, a 10-ksPSPC and a 40-ks HRI pointing, with a detection algorithm based onwavelet transforms, particularly suited to detecting faint sources incrowded fields. We have detected 78 sources, 13 of which were detectedonly with the HRI, and 37 detected only with the PSPC. For each source,we have computed the 0.2-2.0 keV X-ray flux. Using optical data from theliterature and our own low-dispersion spectroscopic observations, wefind candidate optical counterparts for 62 X-ray sources, with more than80% of these counterparts being late type stars. We have assigned to theoptical sources an astrometric and/or a photometric membership flag,depending on which data are available to us. The number of sources (38of 62) with high membership probability counterparts is consistent withthat expected for Galactic plane observations at our sensitivity. Wehave computed maximum likelihood X-ray luminosity functions (XLF) for Fand early-G type stars with high membership probability. Heavy datacensoring due to our limited sensitivity permits determination of onlythe high-luminosity tails of the XLFs; the distributions areindistinguishable from those of the nearly coeval Pleiades cluster.
| 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
| Open clusters with Hipparcos. I. Mean astrometric parameters
New memberships, mean parallaxes and proper motions of all 9 openclusters closer than 300 pc (except the Hyades) and 9rich clusters between 300 and 500 pc have been computed using Hipparcosdata. Precisions, ranging from 0.2 to 0.5 mas for parallaxes and 0.1 to0.5 mas/yr for proper motions, are of great interest for calibratingphotometric parallaxes as well as for kinematical studies. Carefulinvestigations of possible biases have been performed and no evidence ofsignificant systematic errors on the mean cluster parallaxes has beenfound. The distances and proper motions of 32 more distant clusters,which may be used statistically, are also indicated. Based onobservations made with the ESA Hipparcos astrometry satellite
| Photoelectric uvby-beta photometry of the open cluster NGC 2422
New and previously observed uvby-beta photometry has been utilized todetermine membership in the cluster. Reddening and age of the clusterhas been determined.
| Catalogue of Eclipsing and Spectroscopic Binary Stars in the Regions of Open Clusters
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| Stellar content of young open clusters. III - The 'sn' stars
Twelve out of 16 stars in the sample of 17 cluster stars belonging tothe recently recognized class of 'sn' stars have V sin i values lowerthan 50 km/sec. It is ascertained that this represents true lowrotation, and does not result from an inclination effect, therebyexcluding both the pole-on hypothesis and the shell-like nature of thesharp lines as probable explanations. Either the 'sn' stars are thenormal state of slowly rotating stars, or they are peculiar. If thelatter, then normal rotating stars cannot exist for more than 50 millionyears before developing any peculiarity.
| Photometric search for Ap-stars in open cluster. IV - NGC 2287, CR 121, NGC 2422 and supplementary measurements in NGC 1662 and NGC 2516
Additional results are presented concerning the search for Ap-stars inopen clusters with the photoelectric peculiarity index Delta-a (Maitzen,1976). NGC 2287-56, NGC 2422-P3, and NGC 1662-4 are found to beCP2-stars as members in their respective clusters. The findings indicatethat HD 51088, which is also peculiar according to its Delta-a value,may be a member of one of the two very young star concentrationspreviously called Cr 121. It is determined that there is only a smallprobability for HD 49333 to be a member of NGC 2287, and that HD 49333is very likely to be a CP4 ( = He weak) star with a Delta-a significantfor peculiarity. It was necessary to reject 10 other stars with reportedindications of peculiarity as CP2 stars since their Delta-a values werenormal. It is concluded that the frequency of peculiar objects is ratherlow in the actual sample considering the number of CP2 detections.
| Spectroscopic study of the open cluster NGC 2422
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975AJ.....80..131D&db_key=AST
| Polarization of Galactic Clusters M25, NGC 869, 884, 1893, 2422, 6823, 6871, and Association VI Cygni.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1965ApJ...141.1340S&db_key=AST
| Three-colour photometry of southern galactic clusters I,
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