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New magnetic field measurements of ? Cephei stars and slowly pulsating B stars
We present the results of the continuation of our magnetic survey withFORS 1 at the VLT of a sample of B-type stars consisting of confirmed orcandidate ? Cephei stars and Slowly Pulsating B (hereafter SPB)stars, along with a small number of normal B-type stars. A weak meanlongitudinal magnetic field of the order of a few hundred Gauss wasdetected in three ? Cephei stars and two stars suspected to be ?Cephei stars, in five SPB stars and eight stars suspected to be SPBstars. Additionally, a longitudinal magnetic field at a level largerthan 3? has been diagnosed in two normal B-type stars, thenitrogen-rich early B-type star HD 52089 and in the B5 IV star HD153716. Roughly one third of ? Cephei stars have detected magneticfields: Out of 13 ? Cephei stars studied to date with FORS 1, fourstars possess weak magnetic fields, and out of the sample of sixsuspected ? Cephei stars two show a weak magnetic field. Thefraction of magnetic SPBs and candidate SPBs is found to be higher:Roughly half of the 34 SPB stars have been found to be magnetic andamong the 16 candidate SPBs eight stars possess magnetic fields. In anattempt to understand why only a fraction of pulsating stars exhibitmagnetic fields, we studied the position of magnetic and non-magneticpulsating stars in the H-R diagram. We find that their domains in theH-R diagram largely overlap, and no clear picture emerges as to thepossible evolution of the magnetic field across the main sequence. It ispossible that stronger fields tend to be found in stars with lowerpulsating frequencies and smaller pulsating amplitudes. A somewhatsimilar trend is found if we consider a correlation between the fieldstrength and the v sin i-values, i.e. stronger magnetic fields tend tobe found in more slowly rotating stars.Based on observations obtained at the European Southern Observatory,Paranal, Chile (ESO programmes 078.D-0140(A), 078.D-0330(A),079.D-0241(A), and 080.D-0383(A)).
| Speckle Interferometry of Southern Double Stars. III. Measures from the Cesco Observatory, 1994-1996
Position angle and separation measures of 482 primarily southern binarystars are presented. These were obtained from speckle observations takenat the Carlos U. Cesco Observatory, El Leoncito, Argentina, using amultianode microchannel array detector during the period 1994 July to1996 July. When comparing our measures to the ephemeris predictions inthe case of objects with well-determined orbits, we find that ourmeasures have a precision of approximately 13 mas per observation inseparation and 0.75d/ρ in position angle, where ρ is theseparation in arcseconds. We briefly discuss the photometric propertiesof the data and highlight four southern binaries of particular interestthat emerge from the list presented.
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| A Search for Star Clusters from the HIPPARCOS Data
We present results of a search for nearby star clusters and associationsusing Hipparcos Catalogue data, restricting the sample to stars withparallaxes above 2 mas (d <~ 500 pc). Two new OB associations havebeen identified in the Carina-Vela and Cepheus-Cygnus-Lyra-Vulpecularegions. A very probable new open cluster has been discovered in Carina.The cluster, a Car, named after its brightest member, is young (60 Myr)and nearby (d = 132 pc). However, only seven bona fide members can bedrawn from the Hipparcos data. We report a detection of nine opencluster candidates in the distance range of 150 to 400 pc, and sixpossible associations almost all located within the Gould belt, althoughslightly older than the known nearby associations. In all cases, wepresent Yale theoretical isochrone fits to the color-magnitude diagrams,which indicate a moderate spread of ages between 60 to 200 Myr.Evidently, these young open cluster and association candidates arerelated to the overall distribution of young OB and A-type stars in thesolar neighborhood.
| Study of an unbiased sample of B stars observed with Hipparcos: the discovery of a large amount of new slowly pulsating B stars
We present a classification of 267 new variable B-type stars discoveredby Hipparcos. We have used two different classification schemes and theyboth result in only a few new beta Cephei stars, a huge number of newslowly pulsating B stars, quite some supergiants with alpha Cyg-typevariations and variable CP stars, and further some new periodic Be starsand eclipsing binaries. Our results clearly point out the biased naturetowards short-period variables of earlier, ground-based surveys ofvariable stars. The position of the new beta Cephei stars and slowlypulsating B stars in the HR diagram is determined by means of Genevaphotometry and is confronted with the most recent calculations of theinstability strips for both groups of variables. We find that the newbeta Cephei stars are situated in the blue part of the instability stripand that the new slowly pulsating B stars almost fully cover thetheoretical instability domain determined for such stars. Thesupergiants with alpha Cyg-type variations are situated between theinstability strips of the beta Cephei and the slowly pulsating B starson the one hand and previously known supergiants that exhibitmicrovariations on the other hand. This suggests some connection betweenthe variability caused by the kappa mechanism acting in a zone ofpartially ionised metals and the unknown cause of the variations insupergiants.
| ICCD speckle observations of binary stars. VIII - Measurements during 1989-1991 from the Cerro Tololo 4 M telescope
One-thousand eighty-eight observations of 947 binary star systems,observed by means of speckle interferometry with the 4 m telescope onCerro Tololo, are presented. These measurements, made during the period1989-1991, comprise the second installment of results stemming from theexpansion of our speckle program to the southern hemisphere.
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Besorolás csoportokba:
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Pozíciós és asztrometriai adatok
| Csillagkép: | Oltár |
| Rektaszcenzió: | 16h57m29.92s |
| Deklináció: | -60°36'00.4" |
| Vizuális fényesség: | 6.532 |
| Távolság: | 235.294 parszek |
| RA sajátmozgás: | -3.5 |
| Dec sajátmozgás: | -14.8 |
| B-T magnitude: | 6.451 |
| V-T magnitude: | 6.526 |
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