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uvby - β Photoelectric Photometry of the Open Cluster α Per
Absolute photoelectric photometry of stars in the direction of the OpenCluster α Per has been secured and is presented along with ananalysis reinforced with all the available data in Strömgrenuvby-β photometry compiled from the literature. Cluster membershipis analyzed and the physical characteristics of the stars have beendeduced. The membership determined in this paper is compared with thatof proper motion studies and Hipparcos.
| Astrometric radial velocities. III. Hipparcos measurements of nearby star clusters and associations
Radial motions of stars in nearby moving clusters are determined fromaccurate proper motions and trigonometric parallaxes, without any use ofspectroscopy. Assuming that cluster members share the same velocityvector (apart from a random dispersion), we apply a maximum-likelihoodmethod on astrometric data from Hipparcos to compute radial and spacevelocities (and their dispersions) in the Ursa Major, Hyades, ComaBerenices, Pleiades, and Praesepe clusters, and for theScorpius-Centaurus, alpha Persei, and ``HIP 98321'' associations. Theradial motion of the Hyades cluster is determined to within 0.4 kms-1 (standard error), and that of its individual stars towithin 0.6 km s-1. For other clusters, Hipparcos data yieldastrometric radial velocities with typical accuracies of a few kms-1. A comparison of these astrometric values withspectroscopic radial velocities in the literature shows a good generalagreement and, in the case of the best-determined Hyades cluster, alsopermits searches for subtle astrophysical differences, such as evidencefor enhanced convective blueshifts of F-dwarf spectra, and decreasedgravitational redshifts in giants. Similar comparisons for the ScorpiusOB2 complex indicate some expansion of its associations, albeit slowerthan expected from their ages. As a by-product from the radial-velocitysolutions, kinematically improved parallaxes for individual stars areobtained, enabling Hertzsprung-Russell diagrams with unprecedentedaccuracy in luminosity. For the Hyades (parallax accuracy 0.3 mas), itsmain sequence resembles a thin line, possibly with wiggles in it.Although this main sequence has underpopulated regions at certaincolours (previously suggested to be ``Böhm-Vitense gaps''), suchare not visible for other clusters, and are probably spurious. Futurespace astrometry missions carry a great potential for absoluteradial-velocity determinations, insensitive to the complexities ofstellar spectra. Based on observations by the ESA Hipparcos satellite.Extended versions of Tables \ref{tab1} and \ref{tab2} are available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.125.8) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/446
| 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
| Metal abundances of A-type stars in galactic clusters. III. alpha Persei: new results
We complete our study (Hui-Bon-Hoa et al. 1997) of the abundances of Mg,Ca, Sc, Cr, Fe, and Ni in alpha Per cluster stars using new spectra oftwo stars of the previous sample and also adding two more objects. Thenew spectra of BD +48°894 and HD 21527 show that the former has analmost solar composition whereas the latter is an Am star with the ironpeak elements being all enhanced and Ca marginally underabundant. As forthe additional stars of this study, HD 19954 has a pattern very close tosolar, and HD 20135 is an SB2 system where both components seem to be Amstars: Ca and Sc are strongly deficient; Cr and Ni are overabundant inone component. A more thorough study is needed for confirmation. Basedon observations collected at the Observatoire de Haute-Provence (France)
| A HIPPARCOS Census of the Nearby OB Associations
A comprehensive census of the stellar content of the OB associationswithin 1 kpc from the Sun is presented, based on Hipparcos positions,proper motions, and parallaxes. It is a key part of a long-term projectto study the formation, structure, and evolution of nearby young stellargroups and related star-forming regions. OB associations are unbound``moving groups,'' which can be detected kinematically because of theirsmall internal velocity dispersion. The nearby associations have a largeextent on the sky, which traditionally has limited astrometricmembership determination to bright stars (V<~6 mag), with spectraltypes earlier than ~B5. The Hipparcos measurements allow a majorimprovement in this situation. Moving groups are identified in theHipparcos Catalog by combining de Bruijne's refurbished convergent pointmethod with the ``Spaghetti method'' of Hoogerwerf & Aguilar.Astrometric members are listed for 12 young stellar groups, out to adistance of ~650 pc. These are the three subgroups Upper Scorpius, UpperCentaurus Lupus, and Lower Centaurus Crux of Sco OB2, as well as VelOB2, Tr 10, Col 121, Per OB2, alpha Persei (Per OB3), Cas-Tau, Lac OB1,Cep OB2, and a new group in Cepheus, designated as Cep OB6. Theselection procedure corrects the list of previously known astrometricand photometric B- and A-type members in these groups and identifiesmany new members, including a significant number of F stars, as well asevolved stars, e.g., the Wolf-Rayet stars gamma^2 Vel (WR 11) in Vel OB2and EZ CMa (WR 6) in Col 121, and the classical Cepheid delta Cep in CepOB6. Membership probabilities are given for all selected stars. MonteCarlo simulations are used to estimate the expected number of interloperfield stars. In the nearest associations, notably in Sco OB2, thelater-type members include T Tauri objects and other stars in the finalpre-main-sequence phase. This provides a firm link between the classicalhigh-mass stellar content and ongoing low-mass star formation. Detailedstudies of these 12 groups, and their relation to the surroundinginterstellar medium, will be presented elsewhere. Astrometric evidencefor moving groups in the fields of R CrA, CMa OB1, Mon OB1, Ori OB1, CamOB1, Cep OB3, Cep OB4, Cyg OB4, Cyg OB7, and Sct OB2, is inconclusive.OB associations do exist in many of these regions, but they are eitherat distances beyond ~500 pc where the Hipparcos parallaxes are oflimited use, or they have unfavorable kinematics, so that the groupproper motion does not distinguish it from the field stars in theGalactic disk. The mean distances of the well-established groups aresystematically smaller than the pre-Hipparcos photometric estimates.While part of this may be caused by the improved membership lists, arecalibration of the upper main sequence in the Hertzsprung-Russelldiagram may be called for. The mean motions display a systematicpattern, which is discussed in relation to the Gould Belt. Six of the 12detected moving groups do not appear in the classical list of nearby OBassociations. This is sometimes caused by the absence of O stars, but inother cases a previously known open cluster turns out to be (part of) anextended OB association. The number of unbound young stellar groups inthe solar neighborhood may be significantly larger than thoughtpreviously.
| The Pleiades and alpha Persei Clusters
The upper-main-sequence members of the Pleiades and alpha Perseiclusters, considered as members of the Local Association, yield meanparallaxes that are only 4% larger than the mean values from Hipparcosobservations. The (log T_eff, M_V) diagram reveals that in thetemperature range from 6000 to 8000 K, the Hyades and alpha Perseimain-sequence members are nearly identical and several tenths of amagnitude brighter than similar stars on the Pleiades main sequence. Thedeparture of the Pleiades main sequence cannot be traced to either ageor heavy-element abundance differences in the range thought to apply tothese clusters. A 50% increase in the helium abundance of Pleiades overHyades stars could account for the luminosity difference. Alternativeexplanations are that the Pleiades cluster is rejected from superclustermembership and/or that the Hipparcos parallax results for the Pleiadesare in error by some 10%.
| Metal abundances of A-type stars in three galactic clusters.
Investigations have been carried out for 11 A stars in young openclusters (α Per, Coma, and Praesepe) and three field stars bymeans of high resolution spectroscopy. Detailed abundance analyses havebeen made for Mg, Ca, Sc, Cr, Fe, and Ni. The results are discussed inthe framework of element stratification processes as invoked bytime-dependent diffusion mechanisms in Am stars. The youngest cluster ofour sample, α Per, seems to show some untypical abundance patternswhich might be identified as early Am phases.
| The X-ray properties of the young open cluster around α Persei.
We present ROSAT PSPC pointed observations of the 50Myr old α Peropen cluster. The X-ray observations, which were carried out as a rasterscan, cover an area of about 10deg^2^. In total, we detect about 160X-ray sources, 88 of which have an optical counterpart (within 30arcsec)associated with α Per cluster candidates. Within the centralregion of our field of view, which is characterized by a limitingsensitivity L_X_~10^28.8-29^erg/sec, we detect basically all late-F, Gand K stars, while the detection rate among the M dwarfs is on the orderof 60%. Given the sensitivity of our X-ray observations, the lowerdetection rate among the very low mass objects is consistent with theROSAT results obtained for the Pleiades cluster. Although stars in eachcolor range show a large spread in X-ray luminosity, the maximal X-rayluminosities appear to decrease from the range of late-F - G type starsto the M-type dwarfs. We interpret this as due to the fact that themaximum X-ray luminosity cannot exceed the saturation levelL_X_/L_bol_~10^-3^, and is hence a function of the bolometricluminosity. The availability of rotational velocities for many of theX-ray detected objects permits us to study correlations between rotationand X-ray activity. For B-V_o_>0.6, at a given mass, the weakestX-ray sources are slow rotators, while the strongest X-ray sources arerapid rotators. The relation between L_X_/L_bol_ and rotation we findfor the α Per low mass stars is the same as previously determinedfor low mass stars in the Pleiades, and a similar relation is found oncorrelating L_X_/L_bol_ with rotation period. Using directly measuredperiods as well as periods estimated from rotational velocities, wederive Rossby numbers (R_0_) for stars with B-V_o_>0.3 finding that awell-defined relationship between L_X_/L_bol_ and R_0_ is present bothfor early (i.e., F) and late-type stars. A comparison of the X-rayluminosity distribution functions (XLDF) for our α Per sample andthe Pleiades indicates that F and G-type stars in α Per are, as awhole, more X-ray luminous than their older counterparts in thePleiades. On the other hand, no significant difference is found betweenthe distributions of the K and M-type dwarfs in the two clusters. Weargue that this finding is a consequence of the longer spin-downtimescales of later-type objects, and hence of the fact that there aremore rapid rotators among G stars in α Per than in the Pleiades,while this is not the case for K and M dwarfs.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Seven-Color Photoelectric Photometry of Stars in the Alpha-Persei Open Cluster
Not Available
| Membership of low-mass stars in the open cluster Alpha Persei
The results of a combined astrometric, photometric, and spectroscopicsearch for low-mass members in the intermediate-age open cluster AlphaPersei are presented. Over 130 low-mass new members have been identifiedto M(v) about 12.5, almost doubling the previous number of knownmembers. The new membership information suggests a slight upwardrevision of Alpha Per's age to about 8 x 10 exp 7 yr. Alpha Per isnoticeably spatially elongated in a direction parallel to the Galacticplane, most likely due to tidal deformation. Analysis of thedistribution of relative H-alpha emission strengths among Alpha Permembers confirms the view that the mean H-alpha strength decreases inincreasingly older systems. Allowing for survey incompleteness, onecannot reject the idea that the luminosity function is consistent withthe field luminosity function to M(v) about 9 or 10.
| Liste des étoiles Ap et Am dans les amas ouverts (édition révisée)
Not Available
| Liste des étoiles Ap et Am dans les amas ouverts (Edition révisée)
Not Available
| Catalog of AP and AM stars in open clusters
The previous results of Raab (1922), Markarian (1951), and Collinder(1931) have been used to catalog Ap and Am stars that are in the fieldof open clusters. Tabular data are presented for the clusterdesignation, the HD or HDE number, the right ascension (1900), thedeclination (1900), and the magnitude. Also listed are the spectraltypes and, for certain stars, the probability of cluster membership.
| Starbursts, binary stars, and blue stragglers in local superclusters and groups. I - The very young disk and young disk populations
The distributions in the HR diagram with theoretical time-constant locifor stars in several young clusters and superclusters are compared todemonstrate that 'blue stragglers' in these aggregates are mostfrequently simply single massive (mode B) stars formed in bursts of starformation that occur at discrete intervals in time following theformation of the bulk of the low-mass (mode A) stars in the aggregate.The characteristics of the close binary systems in these aggregates areexamined to show that, in several cases, mass transfer by Roche lobeoverflow has or will occur and that, in some instances, the system wouldhave appeared as a blue straggler prior to the mass-transfer event, and,in other instances, mass transfer will lead to the identification of thesystem as a blue straggler. Thus, it is concluded that the bluestraggler phenomenon has at least two distinct physical origins: it mayoriginate from delayed formation (starbursts) or from 'delayedevolution' in some close binaries (mass transfer from an evolvedprimary).
| Effects of rotation on the colours and line indices of stars. I - The Alpha Persei Cluster
Analysis of the available observational data for the Alpha-Perseicluster members shows that rotation effects on the intermediate-bandindices c1 and (u-b) are considerable. In c1, rotation produces areddening of 0.040 magnitudes per 100 km/s. In (u-b), the effect for Bstars is found to be 0.06 magnitudes per 100 km/s of V sin i. Thebinaries and peculiar stars are found to behave differently in the colorexcess (due to rotation) versus V sin i diagrams. These empiricaleffects can be utilized to recalibrate these color indices and also toseparate members that are either chemically peculiar or in binarysystems.
| Chemically peculiar stars in open clusters. I - The catalog
The largest existing compilation is presented of Ap and Am open clusterstars. The catalog contains information on 381 chemically peculiar (CP)stars of the upper main sequence in 79 open clusters. The catalog iscomposed of the following tables: (1) the main body, which lists CP (orsuspected CP) stars which are kinematical (or suspected kinematical)members of open clusters; (2) the list of CP (or suspected CP) starssometimes numbered among cluster members but which are actuallykinematical nonmembers; (3) the list of stars sometimes designated as'peculiar' but, in fact, probably not CP; (4) references for numberingsystems of cluster stars; (5) references for membership; and (6)references for spectral and/or peculiarity types.
| Photoelectric search for CP2-stars in open clusters. XII - Alpha Persei, Praesepe and NGC 7243
Observations of 95 stars in the open clusters Alpha Persei, Praesepe,and NGC 7243 have been performed by Delta-a photometry in order tosearch for the presence of the 5200-A feature of CP2 (or CP4) stars.Although peculiarity has been claimed for half a dozen stars in AlphaPersei, the photometry detects only the CP4 star (= He-weak) HL 985among the cluster members. The behavior of 3 Be/shell stars (HL 861,1164, 904) concerning the 5200-A feature is discussed. Praesepe, by farthe oldest cluster in the survey program, presents a very new andspecial case: 3 stars, previously classified as Am have Delta-a valuesaround 0.020 mag, i.e., they exhibit photometric peculiarity likeCP2-stars. Such values are incompatible with preceding results for fieldand cluster Am-stars (= CP3). These objects deserve further attentionboth photometrically and spectroscopically. NGC 7243 exhibits anoutstanding high frequency of CP2-stars; two certain Delta a-peculiarstars have been found: L 370, already known as peculiar, and the newlyidentified L 114. Two stars are near the detection level: L 58 and 121.According to Geneva photometry, L 487 is markedly peculiar.
| Measurements of 258 radial velocities in two fields near Alpha Per
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987A&AS...68..515F&db_key=AST
| Supplement to the Second Catalogue of Am Stars with Known Spectral Types (end 1981)
Not Available
| Empirical Calibrations of the UVBY, Beta Systems - Part Three - the A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979AJ.....84.1858C&db_key=AST
| The occurrence of abnormal stars in open clusters
The age dependence of the frequencies of various types of abnormal starsin open clusters and associations is discussed. Spectra acquired atdispersions of 39 A/mm and 129 A/mm were used to determine the spectraltypes and luminosity classes of 661 stars in 14 open clusters andassociations. The frequencies of Ap(Si), Ap(Hg,Mn) and Ap(Sr,Cr) starsare found to increase with age to a level about that of field stars,while the rotational velocities of Ap(Si) and Ap(Hg,Mn) stars decreasewith time. Be stars in clusters exhibit a relatively constant frequency,roughly equal to that of Be field stars. The frequencies of stars withpronounced shell spectra are observed to remain constant with age, whilestars with unusually broad hydrogen lines (Vb stars) occur only in theyoungest clusters. The frequency of Am stars in clusters is notsignificantly different from that of field stars, and does not seem todepend on age, although rotational velocity is seen to decrease. It isconcluded that Ap or Am stars develop from stars of various rotationalspeeds, with a subsequent decrease in rotational velocity.
| Spectral types in the alf Per cluster.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978PASP...90..692A&db_key=AST
| A photometric survey of the Alpha Persei cluster for Delta Scuti variables
To investigate the incidence of Delta Scuti variables in the AlphaPersei cluster, a program of differential photometry was undertakenwhich included 24 A- and F-type stars (V no more than 9.48) in or nearthe Delta Scuti instability strip. All stars in the sample weredetermined to have a high probability of cluster membership on the basisof multiple criteria, including proper motions, radial velocities, andextensive photometric data. Three variables were detected (BD +48 deg894, BD +48 deg 905, and BD +47 deg 842). These are located in theregion of the instability strip and have periods close to thosepredicted from the period-color-luminosity relation. The relativeincidence of Delta Scuti variables in the cluster is approximately 25%.As in the Pleiades cluster, the main-sequence variables may be slowerrotators than the nonvariables in the instability strip. The exclusionof pulsation among main-sequence Am stars in the cluster is alsoconfirmed.
| Four-color and H beta photometry for open clusters. 10. The alf Per cluster.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974AJ.....79..687C&db_key=AST
| The H-R diagram of the alf Per cluster.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971AJ.....76..242M&db_key=AST
| The radial velocities., luminosities of 77 stars in the field of the alf Per cluster.
Not Available
| Studies of Stellar Rotation.IV. a Comparison of Rotational Velocities in the Alpha Persei Cluster and the Pleiades
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1967ApJ...148..129K&db_key=AST
| Photometry of the α Persei Cluster.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1960ApJ...132...68M&db_key=AST
| Eigenbewegungen in der Umgebung von α Persei
Not Available
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