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Searching for links between magnetic fields and stellar evolution: II. The evolution of magnetic fields as revealed by observations of Ap stars in open clusters and associations
Context: The evolution of magnetic fields in Ap stars during the mainsequence phase is presently mostly unconstrained by observation becauseof the difficulty of assigning accurate ages to known field Ap stars. Aims: We are carrying out a large survey of magnetic fields in clusterAp stars with the goal of obtaining a sample of these stars withwell-determined ages. In this paper we analyse the information availablefrom the survey as it currently stands. Methods: We select from theavailable observational sample the stars that are probably (1) clusteror association members and (2) magnetic Ap stars. For the stars in thissubsample we determine the fundamental parameters T{eff},L/L_ȯ, and M/M_ȯ. With these data and the cluster ages weassign both absolute age and fractional age (the fraction of the mainsequence lifetime completed). For this purpose we have derived newbolometric corrections for Ap stars. Results: Magnetic fields arepresent at the surfaces of Ap stars from the ZAMS to the TAMS.Statistically for the stars with M > 3 M_ȯ the fields declinewith advancing age approximately as expected from flux conservationtogether with increased stellar radius, or perhaps even faster than thisrate, on a time scale of about 3×107 yr. In contrast,lower mass stars show no compelling evidence for field decrease even ona timescale of several times 108 yr. Conclusions: Study ofmagnetic cluster stars is now a powerful tool for obtaining constraintson evolution of Ap stars through the main sequence. Enlarging the sampleof known cluster magnetic stars, and obtaining more precise rms fields,will help to clarify the results obtained so far. Further fieldobservations are in progress.Tables 2 and 3 are only available in electronic form athttp://www.aanda.org
| Searching for links between magnetic fields and stellar evolution. I. A survey of magnetic fields in open cluster A- and B-type stars with FORS1
Context: .About 5% of upper main sequence stars are permeated by astrong magnetic field, the origin of which is still matter of debate. Aims: . With this work we provide observational material to studyhow magnetic fields change with the evolution of stars on the mainsequence, and to constrain theory explaining the presence of magneticfields in A and B-type stars. Methods: . Using FORS1 inspectropolarimetric mode at the ESO VLT, we have carried out a survey ofmagnetic fields in early-type stars belonging to open clusters andassociations of various ages. Results: . We have measured themagnetic field of 235 early-type stars with a typical uncertainty of 100 G. In our sample, 97 stars are Ap or Bp stars. For thesetargets, the median error bar of our field measurements was 80 G.A field has been detected in about 41 of these stars, 37 of which werenot previously known as magnetic stars. For the 138 normal A and B-typestars, the median error bar was 136 G, and no field was detected in anyof them.
| A method of open cluster membership determination
A new method for the determination of open cluster membership based on acumulative effect is proposed. In the field of a plate the relative xand y coordinate positions of each star with respect to all the otherstars are added. The procedure is carried out for two epochst1 and t2 separately, then one sum is subtractedfrom another. For a field star the differences in its relativecoordinate positions of two epochs will be accumulated. For a clusterstar, on the contrary, the changes in relative positions of clustermembers at t1 and t2 will be very small. On thehistogram of sums the cluster stars will gather to the left of thediagram, while the field stars will form a tail to the right. Theprocedure allows us to efficiently discriminate one group from another.The greater the distance between t1 and t2 and themore cluster stars present, the greater is the effect. The accumulationmethod does not require reference stars, determination of centroids andmodelling the distribution of field stars, necessary in traditionalmethods. By the proposed method 240 open clusters have been processed,including stars up to m<13. The membership probabilities have beencalculated and compared to those obtained by the most commonly usedVasilevskis-Sanders method. The similarity of the results acquired thetwo different approaches is satisfactory for the majority of clusters.
| 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.
| 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
| 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.
| 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.
| RGU photometry of a field in the Carina region near the cluster IC 2581
A field of 0.21 sq deg containing 2099 stars in the Carina region nearthe cluster IC 2581, has been measured on 14 plates in the RGU system.The reddening is caused by a thin absorbing cloud at 770 pc with E(G-R)= 0.23 mag, as well as an interstellar absorption free zone followed bya moderate gradient which increases with distance. The density gradientscorresponding to late-type giants and main sequence stars of the sameabsolute magnitude do not display the same behavior. Assuming that theouter edge of the arm of Carina is being observed, the present resultsseem to corroborate the existence of external spiral features between 12and 13 kpc. The distribution of F0-F5 stars seems to confirm predictionsof the theory of density waves.
| The frequency of peculiar A and metallic-line stars in open clusters.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976ApJ...205..807H&db_key=AST
| The space distribution of M giants in the Warner and Swasey luminosity function field LF 15.
Abstract image available at:http://adsabs.harvard.edu/abs/1974A&AS...15..141T
| The galactic cluster NGC 3228
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1963MNRAS.125..307H&db_key=AST
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| Takýmyýldýz: | Yelken |
| Sað Açýklýk: | 10h20m55.32s |
| Yükselim: | -51°51'41.7" |
| Görünürdeki Parlaklýk: | 9.067 |
| özdevim Sað Açýklýk: | -11.9 |
| özdevim Yükselim: | 4.3 |
| B-T magnitude: | 8.961 |
| V-T magnitude: | 9.059 |
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