Massive binaries in the Cepheus OB2/3 region. Constraining the formation mechanism of massive stars
Context. Two different formation scenarios for stars of masses largerthan 10 M&sun; exist. Although simulations within bothscenarios are capable of producing stars up to the highest observedmasses, the relevance of the two formation scenarios for massivestar-formation is not yet clear. Aims: We aim to detectcompanions to massive stars to constrain the binary parameters of themultiple systems. These findings will help to constrain the formation ofmassive stars. Methods: We performed z'-band observations ofmassive and intermediate-mass stars in the Cep OB2/3 associations withthe Lucky imaging camera AstraLux on the 2.2 m telescope of the CalarAlto observatory. The analysis aimed at detecting binary systems withseparations out to 2".2 (~1700 AU), the inner limit depending on thecontrast. The maximum contrast of 7 mag in z' (corresponding to a masscontrast of 17:1 versus an O9V primary) requires a minimum separation of0".7 (~550 AU). Results: We found 28 new companions for oursample of 148 intermediate-mass and massive stars in Cep OB2/3. Thecompanion star fraction of the massive stars is 0.7; about 50% of thesystems are triples. The mass function of the companions to the massivestars is strongly top-heavy. We found that the sample parameters closelyagreed with those found in the Orion Trapezium cluster. Conclusions: The multiplicity of massive stars seems to be significantlyhigher than that of intermediate-mass stars, independently of theenvironment. The comparison of our findings with the theories of massivestar-formation favor the formation of massive stars by the fragmentationof proto-stellar cores combined with competitive accretion.Appendix A in available in electronic form at http://www.aanda.org
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Are pre-main-sequence stars older than we thought?
We fit the colour-magnitude diagrams of stars between the zero-agemain-sequence and terminal-age main sequence in young clusters andassociations. The ages we derive are a factor of 1.5-2 longer than thecommonly used ages for these regions, which are derived from thepositions of pre-main-sequence stars in colour-magnitude diagrams. Froman examination of the uncertainties in the main-sequence andpre-main-sequence models, we conclude that the longer age scale isprobably the correct one, which implies that we must revise upwards thecommonly used ages for young clusters and associations. Such a revisionwould explain the discrepancy between the observational lifetimes ofprotoplanetary discs and theoretical calculations of the time to formplanets. It would also explain the absence of clusters with ages between5 and 30Myr.We use the ?2 statistic to fit the main-sequence data,but find that we must make significant modifications if we are to fitsequences which have vertical segments in the colour-magnitude diagram.We present this modification along with improvements to the methods ofcalculating the goodness-of-fit statistic and parameter uncertainties.Software implementing the methods described in this paper is availablefrom http://www.astro.ex.ac.uk/people/timn/tau-squared/.
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Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
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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.
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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.
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UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
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Be stars in open clusters I. uvbyβ photometry.
We present uvbyβ photometry for Be stars in eight open clusters andtwo OB associations. It is shown that Be stars occupy anomalouspositions in the photometric diagrams, which can be explained in termsof the circumstellar continuum radiation contribution to the photometricindices. In the (b-y)_0_-M_V_ plane Be stars appear redder than the nonemission B stars, due to the additional reddening caused by the hydrogenfree-bound and free-free recombination in the circumstellar envelope. Inthe c_0_-M_V_ plane the earlier Be stars present lower c_0_ values thanabsorption-line B stars, which is caused by emission in the Balmerdiscontinuity, while the later Be stars deviate towards higher c_0_values, indicating absorption in the Balmer discontinuity ofcircumstellar origin.
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Derivation of the Galactic rotation curve using space velocities
We present rotation curves of the Galaxy based on the space-velocitiesof 197 OB stars and 144 classical cepheids, respectively, which rangeover a galactocentric distance interval of about 6 to 12kpc. Nosignificant differences between these rotation curves and rotationcurves based solely on radial velocities assuming circular rotation arefound. We derive an angular velocity of the LSR of{OMEGA}_0_=5.5+/-0.4mas/a (OB stars) and {OMEGA}_0_=5.4+/-0.5mas/a(cepheids), which is in agreement with the IAU 1985 value of{OMEGA}_0_=5.5mas/a. If we correct for probable rotations of the FK5system, the corresponding angular velocities are {OMEGA}_0_=6.0mas/a (OBstars) and {OMEGA}_0_=6.2mas/a (cepheids). These values agree betterwith the value of {OMEGA}_0_=6.4mas/a derived from the VLA measurementof the proper motion of SgrA^*^.
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Intrinsic colour indices of O- and B- type stars in the Vilnius photometric system.
Not Available
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Hα Interferometric Optical and Near Infrared Photometric Studies of Star Forming Regions - Part One - the Cepheus-B / SH:2-155 / CEPHEUS-OB3 Association Complex
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...273..619M&db_key=AST
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Galactic OB associations in the northern Milky Way Galaxy. I - Longitudes 55 deg to 150 deg
The literature on all OB associations was reviewed, and their IRAS pointsource content was studied, between galactic longitude 55 and 150 deg.Only one third of the 24 associations listed by Ruprecht et al. (1981)have been the subject of individual studies designed to identify thebrightest stars. Distances to all of these were recomputed using themethod of cluster fitting of the B main sequence stars, which makes itpoossible to reexamine the absolute magnitude calibration of the Ostars, as well as for the red supergiant candidate stars. Also examinedwas the composite HR diagram for these associations. Associations withthe best defined main sequences, which also tend to contain very youngclusters, referred to here as OB clusters, have extremely few evolved Band A or red supergiants. Associations with poorly defined mainsequences and few OB clusters have many more evolved stars. They alsoshow an effect in the upper HR diagram referred to as a ledge byFitzpatrick and Garmany (1990) in similar data for the Large MagellanicCloud. It is suggested that the differences in the associations are notjust observational selection effects but represent real differences inage and formation history.
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Photoelectric photometry of OB stars in the Vilnius system
Not Available
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The thermal radio emission from the S 155 nebula and the Cepheus OB 3 association.
Abstract image available at:http://adsabs.harvard.edu/abs/1978A&A....69..199F
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The influence of interstellar absorption on measured strengths of the Balmer discontinuity
The definition of the Balmer-discontinuity strength from observationalspectrophotometric data is discussed in relation to detailed results onthe wavenumber dependence of the interstellar absorption. The break inthe interstellar absorption curve at a wavenumber of about 2.33permicrons is found to introduce systematic errors in many currentlydefined strengths of the Balmer discontinuity. The errors should beproportional to the amount of the color excess caused by interstellarabsorption. Using the interstellar absorption curves established byDivan (1954) and by Nandy (1964) theoretical relations are derivedbetween the amount of interstellar absorption and the correspondinginfluence on the Balmer-discontinuity strength. These linear relationsare confirmed through tests on larger sets of observational data. At thesame time the derived relations are useful as correction formulas.
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Internal motions in the association Cep OB3.
Abstract image available at:http://adsabs.harvard.edu/abs/1973AJ.....78..185G
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Spectral classification in the association III Cephei and the ratio of total-to-selective absorption.
Abstract image available at:http://adsabs.harvard.edu/abs/1970AJ.....75.1001G
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Photoelectric photometry of early-type stars in a Milky Way field in Cepheus
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970A&AS....2..251S&db_key=AST
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Photoelectric Photometry of the Association III Cephei.
Abstract image available at:http://adsabs.harvard.edu/abs/1959ApJ...130...69B
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