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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
| Be stars in open clusters. II. Balmer line spectroscopy
We present Hα line profiles (R ~= 3x103, S/N ~=102 at continuum level, ~= 50 for some objects) for 58 starsin 8 northern open clusters and associations, complemented with Hβand Hγ profiles for 36 of them as well as Hdelta and Hepsilon for16 programme stars. Our observations, though lower in resolution, yieldresults which are in good agreement with those obtained in earlier worksbased mainly on field Be stars. Our data suggest a similar spectroscopicbehavior for both field and cluster Be stars. The line parameters (EW,FWHM, Delta vp) have been obtained for each line. Nearly thewhole set of stars have previously published quasi-simultaneousuvby\beta photometry, so a study of reliable correlations betweenphotometric and spectroscopic data can be undertaken. Based onobservations made at the German-Spanish Astronomical Center, Calar Alto,Spain which is operated by the Max Planck Institut fuer Astronomie,Heidelberg, jointly with the spanish National Commission for Astronomy.
| 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.
| UBVRI-CCD photometry of Cepheus OB3 association.
Johnson CCD photometry was performed in the two subgroups of theassociation Cepheus OB3, for selected fields each containing at leastone star with previous UBV photoelectric photometry. Photometry forabout 1000 stars down to visual magnitude 21 is provided, although thecompleteness tests show that the sample is complete down to V=19mag.Individual errors were assigned to the magnitude and colours for eachstar. Colour-colour and colour-magnitude diagrams are shown. Astrometricpositions of the stars are also given. Description of the reductionprocedure is fully detailed.
| 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
| Internal motions in the association Cep OB3.
Abstract image available at:http://adsabs.harvard.edu/abs/1973AJ.....78..185G
| 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
| Photoelectric Photometry of the Association III Cephei.
Abstract image available at:http://adsabs.harvard.edu/abs/1959ApJ...130...69B
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