Be Stars in the Magellanic Clouds

Keller, Stefan; Bessell, M. S.; Dacosta, G. S.

doi:10.1017/s0252921100055639

Cited by 3 publications

(3 citation statements)

References 3 publications

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“…The location of the red supergiant population on the CMD is a fundamental input into any such study. We have obtained HST/WFPC2 photometry in the visible and far-UV for these four clusters (Keller et al 1999c). With this data we will closely examine the compatibility between our observations and the predictions of standard evolutionary models in a future paper.…”

Section: Introductionmentioning

confidence: 88%

“…In previous studies it has not been possible to use the V −K colour of the red supergiants because of the uncertain effects of crowding. In the present study we utilise the HST/WFPC2 photometry of Keller et al (1999b) of those stars within the aforementioned field. Crowding is not a major concern in the WFPC2 fields.…”

Section: Optical Photometrymentioning

confidence: 99%

“…The adopted reddening corrections are taken from Keller et al (1999b), namely E(B−V )=0.08 for NGC 330, 1818, and 2004 and 0.24 for NGC 2100. Reddening ratios are taken from Bessell et al (1998).…”

Section: Reddening Correctionsmentioning

confidence: 99%

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Infrared Photometry of Red Supergiants in Young Clusters in the Magellanic Clouds

Keller

1999

The Astronomical Journal

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We present broad-band infrared photometry for 52 late-type supergiants in the young Magellanic Clouds clusters NGC 330, NGC 1818, NGC 2004 and NGC 2100 Standard models are seen to differ in the temperature they predict for the red supergiant population on the order of 300K. It appears that these differences most probably due to the calibration of the mixing-length parameter, α P , in the outermost layers of the stellar envelope. Due to the apparent model dependent nature of α P we do not quantitatively compare α P between models. Qualitatively, we find that α P decreases with increased stellar mass within standard models. We do not find evidence for a metallicity dependence of α P .

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Section: Introductionmentioning

confidence: 88%

Section: Optical Photometrymentioning

confidence: 99%

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Infrared Photometry of Red Supergiants in Young Clusters in the Magellanic Clouds

Keller

1999

The Astronomical Journal

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The Be Phenomenon

Balona

2000

International Astronomical Union Colloquium

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An overview of the Be phenomenon is given with particular emphasis on the problem of the mass loss mechanism. We assume that the principal mechanism of mass loss in these stars is magneto-centrifugal acceleration (MCA). Within this framework, we discuss how particular features of Be stars which distinguish them from normal B stars can be understood. The frequency distribution of Be stars relative to normal B stars in the Galaxy and Magellanic Clouds is discussed. The distribution of equatorial velocities, activity in the visual and X-ray regions and photospheric activity all point towards a magnetic model and seem to be qualitatively consistent with the MCA hypothesis. Periodic variations in light and line profiles offer particularly important clues. In this respect, the recent discovery of co-rotating photospheric clouds in several Be stars strongly suggests gas trapped in closed field lines. We investigate the dynamics of an outburst and suggest that the localized nature of these events imply magnetic flaring and acceleration of mass due to connection and disconnection of field lines. Finally, suggestions for further progress are presented.

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Classical Be Stars

Porter

Rivinius²

2003

PUBL ASTRON SOC PAC

595

580

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Recent results for classical Be stars are reviewed and links to general astrophysics are presented. Classical Be stars are B-type stars close to the main sequence that exhibit line emission over the photospheric spectrum. The excess is attributed to a circumstellar gaseous component that is commonly accepted to be in the form of an equatorial disk. Since 1988, when the last such review was published, major progress has been made. The geometry and kinematics of the circumstellar environment can be best explained by a rotationally supported relatively thin disk with very little outflow, consistent with interferometric observations. The presence of shortterm periodic variability is restricted to the earlier type Be stars. This variation for at least some of these objects has been shown to be due to nonradial pulsation. For at least one star, evidence for a magnetic field has been observed. The mechanisms responsible for the production and dynamics of the circumstellar gas are still not constrained. Observations of nonradial pulsation beating phenomena connected to outbursts point toward a relevance of pulsation, but this mechanism cannot be generalized. Either the evidence that Be stars do not form a homogeneous group with respect to disk formation is growing or the short-term periodic variability is less important than previously thought. The statistics of Be stars investigated in open clusters of the Milky Way and the Magellanic Clouds has reopened the question of the evolutionary status of Be stars. The central B star is a fast rotator, although theoretical developments have revived the question of how high rotational rates are, so the commonly quoted mean value of about 70%-80% of the critical velocity may just be a lower limit. Be stars are in a unique position to make contributions to several important branches of stellar physics, e.g., asymmetric mass-loss processes, stellar angular momentum distribution evolution, astroseismology, and magnetic field evolution.

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Be Stars in the Magellanic Clouds

Cited by 3 publications

References 3 publications

Infrared Photometry of Red Supergiants in Young Clusters in the Magellanic Clouds

Infrared Photometry of Red Supergiants in Young Clusters in the Magellanic Clouds

The Be Phenomenon

Classical Be Stars

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