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تسجيل مستخدم جديدSpectroscopy of 13 high mass stars in the Cyg OB2 association
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Aiming to explore weak spectral features of stellar and interstellar origin we used the NES echelle spectrograph of the 6-m telescope to obtain high-resolution spectra for 13 hot O3 - B4 stars in the Cyg OB2 association, including a high luminous star No. 12. Velocity fields in the atmospheres and interstellar medium, characteristics of optical spectra and line profiles are investigated. The cascade star formation scheme for the association is confirmed. Evidence is presented suggesting that the hypergiant Cyg OB2 No.12 is an LBV object and that its anomalous reddening has a circumstellar nature.
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We present spectroscopic observations of the massive multiple system HD,167971, located in the open cluster NGC,6604. The brighter component of the triple system is the overcontact eclipsing binary MY,Ser with an orbital period of 3.32,days. The radi
al velocities and the previously published UBV data obtained by citet{may10} and the UBVRI light curves by citet{dav88} are analysed for the physical properties of the components. We determine the following absolute parameters: for the primary star M$_p$=32.23$pm$0.54 M$_{odot}$, R$_p$=14.23$pm$0.75 R$_{odot}$; and for the secondary star M$_s$=30.59$pm$0.53 M$_{odot}$, R$_s$=13.89$pm$0.75 R$_{odot}$. Photoelectric times of minimum light are analyzed under the consideration of the light-time orbit. The center-of-mass of the eclipsing binary is orbiting around the common center-of-gravity of the triple system with a period of 21.2$pm$0.7,yr and with a projected semi-major axis of 5.5$pm$0.7,AU. The mass function for the third star was calculated as 0.370$pm$0.036 M$_{odot}$. The light contributions of the third star to the triple system in the UBV pass-bands were derived and the intrinsic magnitudes and colors were calculated individually for the three stars. The components of the eclipsing pair were classified as O7.5 {sc iii} and O9.5 {sc iii}. The intrinsic color indices for the third star yield a spectral type of (O9.5-B0) {sc iii-i}. {bf This classification leads to constrain the inclination of the third-body orbit, which should be about 30$^{o}$, and therefore its mass should be about 29 M$_{odot}$. MY,Ser is one of the rare massive O-type triple system at a distance of 1.65$pm$0.13,kpc, the same as for the NGC,6604 embedded in the Ser,OB2 association.}
Aims: We wish to study the origin of the X-ray emission of three massive stars in the Cyg OB2 association: Cyg OB2 #5, #8A, #12. Methods: To this aim, dedicated X-ray observations from XMM and Swift are used, as well as archival ROSAT and Suzaku data
. Results: Our results on Cyg OB2 #8A improve the phase coverage of the orbit and confirm previous studies: the signature of a wind-wind collision is conspicuous. In addition, signatures of a wind-wind collision are also detected in Cyg OB2 #5, but the X-ray emission appears to be associated with the collision between the inner binary and the tertiary component orbiting it with a 6.7yr period, without a putative collision inside the binary. The X-ray properties strongly constrain the orbital parameters, notably allowing us to discard some proposed orbital solutions. To improve the knowledge of the orbit, we revisit the light curves and radial velocity of the inner binary, looking for reflex motion induced by the third star. Finally, the X-ray emission of Cyg OB2 #12 is also analyzed. It shows a marked decrease in recent years, compatible with either a wind-wind collision in a wide binary or the aftermath of a recent eruption.
We report on the analysis of the Chandra-ACIS data of O, B and WR stars in the young association Cyg OB2. X-ray spectra of 49 O-stars, 54 B-stars and 3 WR-stars are analyzed and for the brighter sources, the epoch dependence of the X-ray fluxes is in
vestigated. The O-stars in Cyg,OB2 follow a well-defined scaling relation between their X-ray and bolometric luminosities: log(Lx/Lbol) = -7.2 +/- 0.2. This relation is in excellent agreement with the one previously derived for the Carina OB1 association. Except for the brightest O-star binaries, there is no general X-ray overluminosity due to colliding winds in O-star binaries. Roughly half of the known B-stars in the surveyed field are detected, but they fail to display a clear relationship between Lx and Lbol. Out of the three WR stars in Cyg OB2, probably only WR144 is itself responsible for the observed level of X-ray emission, at a very low log(Lx/Lbol) = -8.8 +/- 0.2. The X-ray emission of the other two WR-stars (WR145 and 146) is most probably due to their O-type companion along with a moderate contribution from a wind-wind interaction zone.
Stellar photometry derived from the INT/WFC Photometric H$alpha$ Survey of the Northern Galactic Plane (IPHAS) can be used to identify large, reliable samples of A0-A5 dwarfs. For every A star, so identified, it is also possible to derive individual
reddening and distance estimates, under the assumption that most selected objects are on or near the main sequence, at a mean absolute r magnitude of 1.5 -- 1.6. This study presents the method for obtaining such samples and shows that the known reddenings and distances to the open clusters NGC 7510 and NGC 7790 are successfully recovered. A sample of over 1000 A stars is then obtained from IPHAS data in the magnitude range 13.5 < r < 20 from the region of sky including the massive northern OB association Cyg OB2. Analysis of these data reveals a concentration of ~200 A stars over an area about a degree across, offset mainly to the south of the known 1--3 Myr old OB stars in Cyg OB2: their dereddened r magnitudes fall in the range 11.8 to 12.5. These are consistent with a ~7 Myr old stellar population at DM = 10.8, or with an age of ~5 Myr at DM = 11.2. The number of A stars found in this clustering alone is consistent with a lower limit to the cluster mass of ~10000 M-sun.
Our goal is to determine the stellar and wind properties of seven O stars in the cluster NGC2244 and three O stars in the OB association MonOB2. These properties give us insight into the mass loss rates of O stars, allow us to check the validity of r
otational mixing in massive stars, and to better understand the effects of the ionizing flux and wind mechanical energy release on the surrounding interstellar medium and its influence on triggered star formation. We collect optical and UV spectra of the target stars which are analyzed by means of atmosphere models computed with the code CMFGEN. The spectra of binary stars are disentangled and the components are studied separately. All stars have an evolutionary age less than 5 million years, with the most massive stars being among the youngest. Nitrogen surface abundances show no clear relation with projected rotational velocities. Binaries and single stars show the same range of enrichment. This is attributed to the youth and/or wide separation of the binary systems in which the components have not (yet) experienced strong interaction. A clear trend of larger enrichment in higher luminosity objects is observed, consistent with what evolutionary models with rotation predict for a population of O stars at a given age. We confirm the weakness of winds in late O dwarfs. In general, mass loss rates derived from UV lines are lower than mass loss rates obtained from Ha. The UV mass loss rates are even lower than the single line driving limit in the latest type dwarfs. These issues are discussed in the context of the structure of massive stars winds. The evolutionary and spectroscopic masses are in agreement above 25 Msun but the uncertainties are large. Below this threshold, the few late-type O stars studied here indicate that the mass discrepancy still seems to hold.
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