|The X-ray Luminosity Distributions of the high-metallicity open cluster Blanco 1|
We present X-ray Luminosity Distributions (XLDs) of late-type members(dF, dG, dK, dM) of the Blanco 1 cluster, based on ROSAT-HRI data andnew astrometric-photometric membership obtained from the GSC-II project.For the first time we present the XLD of dM stars of this cluster. Thehigh metallicity of Blanco 1 allows us to investigate the role ofchemical composition on the coronal emission of late-type stars.Comparison between X-ray Luminosity Distributions of Blanco 1 andPleiades, NGC 2516 and alpha Per suggests a possible metallicity effectin dM stars.
|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 (184.108.40.206) 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
|X-ray observations of the young open cluster Blanco 1|
We present results from two deep ROSAT HRI exposures on the Blanco 1open cluster. Blanco 1 is one of the few open clusters at large distancefrom the Galactic Plane. This circumstance has suggested that it mayhave formed through a mechanism different from that responsible for theother nearby clusters. The age of Blanco 1 is rather uncertain since,depending on the adopted age indicator, it ranges between 30 and 90 Myr.Many cluster members show chromospheric emission typical of young stars.The X-ray observations presented here reveal a high number of X-raysources, consistent with the young age of the cluster. The typical X-rayluminosity of the cluster members is consistent with that of thePleiades and significantly lower than the alpha Per members. Theseresults suggest than the age of Blanco 1 is more similar to the age ofthe Pleiades than to that of alpha Per. The time sampling of the X-rayobservations allows us to study the variability of the sources on timescales from hours to 6 months - 1 year.
|Spectroscopy of the open cluster Blanco 1 II. H alpha emission as an indicator of relative age|
We present the results of H alpha (6562\AA) and Li i (6708\AA)observations of 114 low-mass stars of the young open cluster Blanco 1.We also present observations of 30 stars in Ca ii(K). This work extendsthe first Blanco 1 spectroscopic study of Panagi et al. (1994). From asample of four well-studied clusters, including Blanco 1, we find thatthe fraction of H alpha emission-line stars amongst K dwarfs is a goodindicator of relative age, with a smaller fraction indicative of olderage. Blanco 1 shows a relatively small fraction of emitters,inconsistent with previous age estimates for the cluster. We estimatethe cluster age to to be 90 +/- 25 Myr, slightly older than thePleiades. The method is shown to be more sensitive to age than lithiumand a useful alternative to other age measurement techniques. Thevariation of H alpha with (B-V) is similar to that observed in the oldersolar neighbourhood dwarfs, suggesting that, at least for theabsorption-line stars, the contribution of stellar rotation to theequivalent width is unclear. We combine both spectroscopy and photometryto revise cluster membership and give accurate positions for all thesestars. Tables A1 and A2 are available at the CDS via anonymous ftp220.127.116.11 or http://cdsweb.u-strabg.fr./Abstract.html
|UBV and uvby-beta photometry of stars in the region of the Zeta SCULPTORIS cluster|
Photoelectric observations of 130 stars in the region of Zeta Sculptorishave been obtained in UBV and uvby-beta. A total of 32 stars areidentified as cluster members, and several other F and G type stars areidentified as probable members. Results indicate an interstellarreddening of E(B-V) = 0.02 mag and that the cluster is slightly metaldeficient.
|Photometric study of Zeta SCULPTORIS cluster|
Photographic photometry of about 1500 stars in the region of the ZetaSculptoris cluster has been accomplished, and relations between thisphotometry and broad- and intermediate-band photoelectric photometryestablished. From observation of the H-R diagrams, it is concluded thatabout 150 stars belong to the unevolved main sequence of the cluster. Asmall reddening of E(B - V) = 0.013 m similar to values given by otherauthors, and a mean modulus of about 6.9 mag, have been determined. Twogaps exist in the main sequence, one between (B - V) about 0.06 m andabout 0.30 m and the other around (B - V) about 1.00.
|The South Galactic Pole - Results from uvby-beta photometry of 572 O-F stars|
Photometric observations on the uvby-beta system are presented for 572O-F stars within about 20 deg of the South Galactic Pole. Theinterstellar extinction near the pole is found to be zero out to 400 pcfrom the sun, in agreement with the H I maps of Burstein and Heiles(1982). Several evolved and Population II objects are identified.
|Spectral types in the Zeta SCULPTORIS open cluster|
The spectral types of 20 stars in the Blanco 1 open cluster (ZetaSculptoris) are reported. Spectral classification in the MK system wasperformed on the basis of 125-A/mm dispersion spectra obtained with a0.9-m telescope and a Cassegrain spectrograph. Of the stars classified,one classical Am star, one peculiar star with a weak K-line and one Apstar with marginal Si II lines enhancement were found, while the starZeta Scl itself is observed to be a main sequence object and thusprobably a foreground star. An H-R diagram of the cluster is alsopresented, and other probable members and nonmembers are indicated.
|Multicolor photometry of the ZET Scl open cluster.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978PASP...90...81P&db_key=AST
|A finding list of stars of spectral type A7 and earlier in regions at high galactic latitudes. VI. Near South Galactic Pole.|
|NGC 2516 and the Pleiades Group|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972ApJ...173...63E&db_key=AST
|A Very Young Cluster with a Moderate Metal Deficiency|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970ApJ...161..159E&db_key=AST
|Four-color photoelectric photometry of two high-latitude clusters.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968AJ.....73..556E&db_key=AST