Absolute magnitudes of OB and Be stars based on Hipparcos parallaxes - II

Wegner, W.

doi:10.1111/j.1365-2966.2006.10549.x

Cited by 78 publications

(89 citation statements)

References 14 publications

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“…If the companion is an OB star of known spectral type, we use the synthetic photometry of Martins & Plez (2006), or Hipparcos-based absolute magnitudes (Wegner 2006), to correct for its contribution. Otherwise we determine a WR/companion continuum flux ratio by considering dilution of the WR emission lines in the bands that line measurements are available.…”

Section: Correction For Binary Companionsmentioning

confidence: 99%

Spatial distribution of Galactic Wolf–Rayet stars and implications for the global population

Rosslowe

Crowther

2015

Monthly Notices of the Royal Astronomical Society

128

143

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We construct revised near-infrared absolute magnitude calibrations for 126 Galactic Wolf-Rayet (WR) stars at known distances, based in part upon recent large scale spectroscopic surveys. Application to 246 WR stars located in the field, permits us to map their Galactic distribution. As anticipated, WR stars generally lie in the thin disk (∼40 pc half width at half maximum) between Galactocentric radii 3.5-10 kpc, in accordance with other star formation tracers. We highlight 12 WR stars located at vertical distances of 300 pc from the midplane. Analysis of the radial variation in WR subtypes exposes a ubiquitously higher N W C /N W N ratio than predicted by stellar evolutionary models accounting for stellar rotation. Models for non-rotating stars or accounting for close binary evolution are more consistent with observations. We consolidate information acquired about the known WR content of the Milky Way to build a simple model of the complete population. We derive observable quantities over a range of wavelengths, allowing us to estimate a total number of 1200 +300 −100 Galactic WR stars, implying an average duration of ∼ 0.25 Myr for the WR phase at the current Milky Way star formation rate. Of relevance to future spectroscopic surveys, we use this model WR population to predict follow-up spectroscopy to K S ≃ 13 mag will be necessary to identify 95% of Galactic WR stars. We anticipate that ESA's Gaia mission will make few additional WR star discoveries via low-resolution spectroscopy, though will significantly refine existing distance determinations. Appendix A provides a complete inventory of 322 Galactic WR stars discovered since the VIIth catalogue (313 including Annex), including a revised nomenclature scheme.

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Section: Correction For Binary Companionsmentioning

confidence: 99%

Spatial distribution of Galactic Wolf–Rayet stars and implications for the global population

Rosslowe

Crowther

2015

Monthly Notices of the Royal Astronomical Society

128

143

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“…These include the effects due to surface differential rotation, bivalued relations between line broadening and the Vsin i, expansion velocities in atmospheres of active stars, and effects on spectral lines due to tides in binaries. (Deutschman et al 1976), SK (Aller et al 1982), and W (Wegner 2006). The blocks a), b), and c) are for average MK luminosity classes V, IV, and III, respectively.…”

Section: Comments and Conclusionmentioning

confidence: 99%

“…In this last case, M V is transformed into absolute bolometric magnitude using the T eff (λ 1 , D) and bolometric corrections (Flower 1996;Torres 2010;Nieva 2013) with M bol = +4.742 mag. The calibrations of M V against the spectral classes used are from Wegner (2006), Deutschman et al (1976), and Aller et al (1982). The log L/L against the average MK spectral type determined for the average luminosity classes V, IV, and III with the cited methods are shown in Figs.…”

Section: Comments and Conclusionmentioning

confidence: 99%

Critical study of the distribution of rotational velocities of Be stars

Zorec

Frémat

Souza

et al. 2016

A&A

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Context. Among intermediate-mass and massive stars, Be stars are the fastest rotators in the main sequence (MS) and, as such, these stars are a cornerstone to validate models of structure and evolution of rotating stars. Several phenomena, however, induce under-or overestimations either of their apparent Vsin i, or true velocity V. Aims. In the present contribution we aim at obtaining distributions of true rotational velocities corrected for systematic effects induced by the rapid rotation itself, macroturbulent velocities, and binarity. Methods. We study a set of 233 Be stars by assuming they have inclination angles distributed at random. We critically discuss the methods of Cranmer and Lucy-Richardson, which enable us to transform a distribution of projected velocities into another distribution of true rotational velocities, where the gravitational darkening effect on the Vsin i parameter is considered in different ways. We conclude that iterative algorithm by Lucy-Richardson responds at best to the purposes of the present work, but it requires a thorough determination of the stellar fundamental parameters. Results. We conclude that once the mode of ratios of the true velocities of Be stars attains the value V/V c 0.77 in the main-sequence (MS) evolutionary phase, it remains unchanged up to the end of the MS lifespan. The statistical corrections found on the distribution of ratios V/V c for overestimations of Vsin i, due to macroturbulent motions and binarity, produce a shift of this distribution toward lower values of V/V c when Be stars in all MS evolutionary stages are considered together. The mode of the final distribution obtained is at V/V c 0.65. This distribution has a nearly symmetric distribution and shows that the Be phenomenon is characterized by a wide range of true velocity ratios 0.3 V/V c 0.95. It thus suggests that the probability that Be stars are critical rotators is extremely low. Conclusions. The corrections attempted in the present work represent an initial step to infer indications about the nature of the Be-star surface rotation that will be studied in the second paper of this series.

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“…The differences between M V values for spectral types O and B, given by different authors (e.g. Schmidt-Kaler 1982;Zorec & Briot 1991;Vacca et al 1996;Wegner 2006), in some cases (B0III) exceed 1 mag; differences of 0.5 mag. are common.…”

Section: Introductionmentioning

confidence: 99%

The interstellar Ca II distance scale

Megier

Strobel

Галазутдинов

et al. 2009

A&A

100

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Aims. We attempt to extend the relation between the strengths of the interstellar Ca ii lines and the distances to early-type stars to objects beyond 1 kiloparsec, with the line saturation taken into account.Methods. We measure the Ca ii K and Ca ii H equivalent widths, and compute Ca ii column densities for 262 lines of sight towards early-type stars with available Hipparcos parallaxes (π). The targets are located within a few hundred parsecs of the Galactic plane, and span all the range of Galactic longitudes. We fit the N Ca ii -parallax relation with a function of the form π = 1/(a · N Ca ii + b), using a maximum-likelihood approach to take account of errors in both variables. We use the resultant formula to estimate distances to stars in OB associations and clusters, and compare them to those found in the literature, usually estimated by spectrophotometric methods. 1.3, we obtain the following approximate formula for the distance: D Ca ii = 77 + (2.78 + Results. For lines of sight with EW(K)/EW(H) > EW(K) EW(H) −0.932 )EW(H), where the equivalent widths EW(K) and EW(H) are in mÅ, and the distance D Ca ii in parsecs.The errors in D Ca ii , resulting from the uncertainty in the fit parameters and errors in the equivalent widths, are typically about 15% of the distance. We can also expect the equation not to hold for objects situated farther than a few hundred parsecs from the Galactic plane. We find several cases of significant column density differences between association or cluster members, especially notable in the Trumpler 16 cluster, indicating either a local contribution to the Ca ii column density, or background/foreground stars being confused with members. The ratio D Ca ii /D assoc appears to depend on the Galactic longitude, being highest in the range 70 • < l < 120 • and lowest for 200 • < l < 300 • . This effect may be due to large-scale structure being present in the Ca ii layer, or to the nonmember confusion being enhanced in these directions.

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Absolute magnitudes of OB and Be stars based on Hipparcos parallaxes - II

Cited by 78 publications

References 14 publications

Spatial distribution of Galactic Wolf–Rayet stars and implications for the global population

Spatial distribution of Galactic Wolf–Rayet stars and implications for the global population

Critical study of the distribution of rotational velocities of Be stars

The interstellar Ca II distance scale

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