Properties and Problems of Helium Stars

Hunger, K.

doi:10.1007/978-3-642-80919-4_3

Cited by 32 publications

(5 citation statements)

References 45 publications

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“…The object HD 37776 (HIP 26742, V901 Ori) is a B2 IV star residing in the reflection/emission nebula IC 432 (van den Bergh 1966;Finkbeiner 2003) and classified as an intermediate heliumrich or a helium-strong, chemically peculiar (CP) star by Hunger (1975).…”

Section: Introductionmentioning

confidence: 99%

The extremely rapid rotational braking of the magnetic helium-strong star HD 37776

Mikulášek

Krtička²,

Henry

et al. 2008

A&A

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Context. Light and spectrum variations of the magnetic chemically peculiar (mCP) stars are explained by the oblique rigid rotator model with a rotation period usually assumed to be stable on a long time scale. A few exceptions, such as CU Vir or 56 Ari, have been reported as displaying an increase in their rotation period. A possible increase in the period of light and spectrum variations has also been suggested from observations of the helium-strong mCP star HD 37776 (V901 Ori). Aims. In this paper we attempt to confirm the possible period change of HD 37776 and discuss a possible origin of this change as a consequence of i) duplicity; ii) precession; iii) evolutionary changes; and iv) continuous/discrete/transient angular momentum loss. Results. We confirm the previously suspected gradual increase in the 1. d 5387 period of HD 37776 and find that it has lengthened by a remarkable 17.7 ± 0.7 s over the past 31 years. We also note that a decrease in the rate of the period change is not excluded by the data. The shapes of light curves in all colours were found to be invariable. Conclusions. After ruling out light-time effects in a binary star, precession of the rotational axis, and evolutionary changes as possible causes for the period change, we interpret this ongoing period increase as a braking of the star's rotation, at least in its surface layers, due to the momentum loss through events or processes in the extended stellar magnetosphere.

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Section: Introductionmentioning

confidence: 99%

The extremely rapid rotational braking of the magnetic helium-strong star HD 37776

Mikulášek

Krtička²,

Henry

et al. 2008

A&A

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“…Two possible progenitor candidates for the C 2 stars are the extreme helium stars and the R Coronae Borealis stars. According to Hunger (1975) the production rate for the extreme helium stars is N -1.8 X 10" 15 pc" 3 yr" 1 . If the R Coronae Borealis stars are the cool extension of the extreme helium stars (Kaufmann 1974) their production rate is also 1.8 X 10" 15 pc" 3 yr -1 , based upon a typical lifetime of ~ 10 5 years for the red supergiant phase of helium stars (Paczynski 1971;Uus 1973).…”

Section: Resultsmentioning

confidence: 99%

On the evolutionary status of the carbon-band white dwarfs

Sion

Fragola

Odonnell

1979

PASP

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The kinematics and statistics of the updated sample of C 2 (X4670) stars are examined. A blanketing correction for weak-to moderate-band strength C 2 stars is estimated based upon C 2 parallax stars. Space motions are calculated for the entire C 2 sample. A production rate for C 2 stars as a group is derived and compared with estimated production rates for carbon-rich, hydrogen-poor stars at higher luminosity. We conclude that C 2 white dwarfs cannot be linked exclusively with carbon-rich hydrogen-deficient giants as progenitors.The C 2 stars represent 7% of all white dwarfs in their observed absolute magnitude interval. Thus, the present number ratio of non-DA white dwarfs to DA white dwarfs implies that one out of six DB stars should be hotter versions of the À4670 stars.

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“…Only four stars have so far been analyzed using model atmospheres: HD 124448 (Schonberner and Wolf, 1974), BD-9M395 Schonberner, 1977), HD 168476 (Walker and and BD+10°2179 (Hunger andKlinglesmith, 1969, Heber, 1983). These analyses U. HEBER 600 800 1000 1200 ,,,1400 XIA1 1600 1800 2000…”

Section: Fine Analyses Of Visual and Ultraviolet Spectramentioning

confidence: 99%

“…-0.3 © 6.2 Helium-and carbon rich sdO stars Some extremely helium rich objects are known among the subluminous 0 stars (see Hunger, 1975;Berger and Fringant, 1980, Heber et al, these proceedings). It seems to be tempting to search for an evolutionary link between these hot subdwarfs and the B-type extreme helium stars.…”

Section: Bd+13°3224mentioning

confidence: 99%

“…The first modern quantitative spectral analysis using LTE model atmospheres was carried out for BD+10°2179 (Hunger and Klinglesmith, 1969). These early analyses have been discussed in previous reviews (Hunger ,1975, Scholz, 1972, Dinger, 1970, Hack, 1967, Underhill, 1966 to which the reader is referred. Here I will review only the more recent developments.…”

Section: Introductionmentioning

confidence: 99%

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Spectroscopic Analyses of Hot Extreme Helium Stars

Heber

1985

International Astronomical Union Colloquium

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ABSTRACT. Spectroscopic fine analyses of hot extreme helium stars are reviewed. The chemical composition is discussed in detail and conclusions as to the nuclear history of the atmospheric material are drawn. Evidence of inhomogeneities among the hot extreme helium stars is presented and it is concluded that the extreme helium stars can be found in the halo population (BD+10°2179) as well as in the disc population. Their mass loss rates are of the same order of magnitude (10 M /yr) as those of normal stars. Four helium rich sdO stars are identified'as possible descendants of the B-type extreme helium stars.

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Properties and Problems of Helium Stars

Cited by 32 publications

References 45 publications

The extremely rapid rotational braking of the magnetic helium-strong star HD 37776

The extremely rapid rotational braking of the magnetic helium-strong star HD 37776

On the evolutionary status of the carbon-band white dwarfs

Spectroscopic Analyses of Hot Extreme Helium Stars

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