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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)).
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| 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.
| A homogeneous catalog of new UBV and H-beta photometry of B- and A-type stars in and around the Scorpius-Centaurus OB association
B- and A-type stars in and near the Sco-Cen OB association areinvestigated with UBV and H-beta photometry to acquire data relevant tothe luminosity function of Sco-Cen. The measurements generally consistof two 10-s integrations of U, B, V, (W, N) filters, and theobservations are corrected iteratively for atmospheric extinction andinstrumental response. The data presented give the mean V magnitude,mean B-V, mean U-B, and the estimated uncertainties for these values.The catalog provides a homogeneous catalog of data for a large fieldwith stellar objects delineating membership to the association Sco-Cenand that affect the luminosity function of the aggregate.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
| The classification of intrinsic variables.5 The large-amplitude red variables.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975ApJ...195..661E&db_key=AST
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| קבוצת-כוכבים: | עקרב |
| התרוממות ימנית: | 16h55m52.25s |
| סירוב: | -31°28'11.4" |
| גודל גלוי: | 7.665 |
| מרחק: | 1587.302 פארסק |
| תנועה נכונה: | -5.5 |
| תנועה נכונה: | -9.7 |
| B-T magnitude: | 7.623 |
| V-T magnitude: | 7.662 |
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