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Post Info TOPIC: γ˛ Velorum


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Posts: 131433
Date:
Suhail
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Title: The Outer Wind of gamma Velorum
Authors: P.F. Roche, M.D. Colling, M.J. Barlow

Fine-structure mid-infrared emission lines with critical densities in the regime 10^4 to 10^6 cm^-3 can be employed to probe the outflow from Wolf-Rayet stars at radii of \sim 10^15 cm. Narrow-band mid-infrared imaging and spectroscopy of the nearest WR star to the sun, gamma Velorum is analysed for spatially resolved forbidden line emission in the Wolf-Rayet outer wind. The [S IV] 10.52 and [Ne II] 12.81 micron emission regions are found to be spatially extended, compared to unresolved continuum and He and C recombination line emission. The [S IV] and [{Ne II] emission line distributions have a high degree of azimuthal symmetry, indicating a spherically symmetric outflow. A model wind with a modest degree of clumping (clumping factor f \sim 10) provides a better match to the observations than an unclumped model. The overall line intensity distributions are consistent with a freely expanding, spherically symmetric 1/r^2 outflow with constant ionisation fraction and modestly clumped density structure.

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Posts: 131433
Date:
Gamma Velorum
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Gamma Velorum is a star system in the constellation Vela. At magnitude +1.7, it is one of the brightest stars in the night sky. It has the traditional names Suhail and Suhail al Muhlif, which confusingly also apply to Lambda Velorum. It also has a more modern popular name Regor, which was invented as a practical joke by the Apollo 1 astronaut Gus Grissom for his fellow astronaut Roger Chaffee.
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Posts: 131433
Date:
Gamma˛ Velorum
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Title: A new age determination Gamma˛ Velorum from binary stellar evolution models
Authors: John J. Eldridge

We derive a new age for the Gamma˛ Velorum binary by comparing recent observations to our set of binary models. We find that it is very unlikely the stars have not interacted, which implies that previous estimates of the age from single-star models of 3.5±0.4 Myrs are incorrect. We prefer an older age of 5.5±1 Myrs that agrees with the age of other lower mass stars in the Vela OB association. We also find that our favoured binary model shows the components of the binary have interacted in a Case B, post main-sequence, mass-transfer event. During the mass-transfer event, the envelopes of both components where radiative and therefore the damping of tidal forces are relatively weak. This explains why the binary is still eccentric after mass-transfer.

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Posts: 131433
Date:
γ˛ Velorum
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Title: Direct constraint on the distance of γ˛ Velorum from AMBER/VLTI observations
Authors: F. Millour, et al

In this work, we present the first AMBER observations, of the Wolf-Rayet and O (WR+O) star binary system γ˛ Velorum. The AMBER instrument was used with the telescopes UT2, UT3, and UT4 on baselines ranging from 46m to 85m. It delivered spectrally dispersed visibilities, as well as differential and closure phases, with a resolution R = 1500 in the spectral band 1.95-2.17 micron. We interpret these data in the context of a binary system with unresolved components, neglecting in a first approximation the wind-wind collision zone flux contribution. We show that the AMBER observables result primarily from the contribution of the individual components of the WR+O binary system. We discuss several interpretations of the residuals, and speculate on the detection of an additional continuum component, originating from the free-free emission associated with the wind-wind collision zone (WWCZ), and contributing at most to the observed K-band flux at the 5% level. The expected absolute separation and position angle at the time of observations were 5.1±0.9mas and 66±15° respectively. However, we infer a separation of 3.62+0.11-0.30 mas and a position angle of 73+9-11°. Our analysis thus implies that the binary system lies at a distance of 368+38-13 pc, in agreement with recent spectrophotometric estimates, but significantly larger than the Hipparcos value of 258+41-31 pc.

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