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.
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Effects of rotation on the colours and line indices of stars. VI - The reality of the blue straggler phenomenon
The effect of rotation on the observed colors of stars has beenconsidered as a possible cause for the blue straggler phenomenon inclusters listed by Mermilliod (1982). It appears that this phenomenon isdefinitely not real in the case of the late B and early A spectral typeblue stragglers that are intrinsic slow rotators. Among clusterscontaining the early B type blue stragglers it is found that theanomalous position of the stragglers in NGC 6633, NGC 4675, and NGC 2516cannot be accounted for by rotation effects alone.
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Liste des étoiles Ap et Am dans les amas ouverts (édition révisée)
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Blue stragglers - A search for binaries in the infrared
Infrared photometry in the J, H and K bands, performed on a sample of 33blue stragglers (BS) belonging to 8 open clusters is presented. Thisphotometry has been combined with published Johnson UBV photometry tosearch for possible cold companions among the BS, as expected for Case Bclose binary evolution. Probable binaries were identified by comparisonwith standard mean color relations for single stars. The number ofbinary detections is discussed together with the results of a previousspectroscopic search for binaries among BS (Manteiga et al. 1989), andthe consequences for the hypothesis of binarity for the origin of BS areanalyzed.
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Liste des étoiles Ap et Am dans les amas ouverts (Edition révisée)
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Blue stragglers and the binary hypothesis
An observational test of the binary hypothesis for the origin of bluestraggler stars is conducted by searching for radial velocity variablesamong 30 blue stragglers in several galactic clusters. Only one of theslowly rotating blue stragglers is detected as a radial velocityvariable, and it is shown that this finding does not correspond to theclose binary model at the 99 percent confidence level. It is concludedthat binarity is almost certainly not a causal requirement for any bluestraggler. The results are compared to the binary distribution expectedunder the model of Collier and Jenkins (1984).
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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.
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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.
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The early A type stars - Refined MK classification, confrontation with Stroemgren photometry, and the effects of rotation
The MK classification system for the early A-type stars is refined, anda parallel system of standards for the broad-lined stars is introduced.With this improved system, stars may be classified with significantlygreater precision than before. It is shown that spectral types in thissystem are not systematically affected by rotational line broadening. Atotal of 372 early A-type stars are classified, and a confrontation ofthese spectral types with Stroemgren photometry reveals a number ofsystematic photometric effects of rotation. In particular, high v sin istars are systematically redder than low v sin i stars of the samespectral type, and the beta index is weakened by rotation. It isconcluded that precise spectral classification in conjunction withStroemgren and H-beta photometry can potentially provide a valuablecheck and input to the theory of the atmospheres of rotating stars.
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Blue straggler stars in the ultraviolet
The spectra of 27 blue straggler stars from galactic clusters and fromthe field, observed between 1150 and 3200 A, with the IUE are comparedwith data of normal stars of similar temperatures. Results show in allthe A type stars an absorption in the region 1200 to 2000 A similar tothat existing in Ap(Si) stars.
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The spectra and ages of blue stragglers
A mechanism similar to Wheeler's 'quasi-homogeneous evolution' and Finziand Wolf's proposal for blue stragglers is proposed as the origin of theblue stragglers in intermediate-age clusters. Blue stragglers are starswhose positions in color-magnitude diagrams of open and globularclusters are significantly above the turn-off points and in the regionof the (former) main sequence; they seem to represent a conflict withthe general conclusion that all stars in a cluster originated at aboutthe same time. It is concluded that there are at least two kinds of bluestragglers: (1) those stars of types about B3-A2 are primarily Ap starsand slow rotators, occur in the intermediate age clusters and remain inthe main sequence region probably through magnetic mixing; and (2) thestars of type O6-B2 frequently have emission lines, are rapid rotators,occur in the young cluster, and remain in the main sequence regionprobably by rotational mixing.
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Stellar content of young open clusters. I - Blue stragglers. II - Be stars
The properties of the blue stragglers and Be stars found in openclusters younger than the Hyades are examined. Thirty-nine bluestragglers were detected at the left of the upper main sequence in thecolor-magnitude diagrams of 75 open clusters, with the frequency ofdetection noted to increase with cluster age. About half of thestragglers show peculiar abundance characteristics corresponding tospectral classes Am, Ap, Bp, Be and Of. The spectroscopic andphotometric behavior of the blue stragglers is, however, identical withthat of main sequence stars of the same type and peculiarity. It issuggested that the blue stragglers with peculiar spectroscopiccharacteristics may result from the evolution, perhapsquasi-homogeneous, of abnormal stars. Analysis of the absolutemagnitudes and dereddened colors calculated for 94 Be stars in 34 openclusters indicates the distribution to peak at spectral types B1-B2 andB7-B8, and in clusters with turn-up types at B1-B2. Cluster Be starsoccupy the whole main sequence band, and evolutionary states from nearlyunevolved to fully evolved. They may be classified according to theirposition on the color-magnitude diagram, with the distinctions betweenclasses also related to spectroscopic differences.
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Spectral types in the open cluster NGC 6633
Spectral types are given for the 26 brightest stars in the region of NGC6633. Only two of the giants are definitely cluster members. Twoapparent blue stragglers are present, as well as one extreme Ap star,four marginal Am stars, and two stars with weak shell lines.
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A Photoelectric Search for Optical Variability in Blue Stragglers
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Are all blue stragglers close binaries ?
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974ApJ...194..657H&db_key=AST
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Southern open clusters II. UBV and Hbeta photometry of 11 clusters between galactic longitudes 259d and 280d
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973A&AS....9...97V&db_key=AST
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The Galactic Cluster, NGC 6633.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1958ApJ...127..539H&db_key=AST
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Untersuchung der offenen Sternhaufen IC 4665, NGC 6633, IC 4756
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