Physical Properties and Evolutionary Stage of Be Stars

Harmanec, P.

doi:10.1017/s0252921100055536

Cited by 50 publications

(69 citation statements)

References 33 publications

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“…HR 1910ζ Tau. This is a long known single-line spectroscopic binary CBe (Harmanec 1984;Ruždjak et al 2009). The nature of the companion has not been confirmed and the possibilities include a rather cool sdOB or a late-type main sequence companion (Schaefer et al 2010).…”

Section: A Known Binaries In the Samplementioning

confidence: 99%

Prevalence of SED Turndown among Classical Be Stars: Are All Be Stars Close Binaries?

Klement

Carciofi

Rivinius

et al. 2019

ApJ

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Rapid rotation is a fundamental characteristic of classical Be stars and a crucial property allowing for the formation of their circumstellar disks. Past evolution in a mass and angular momentum transferring binary system offers a plausible solution to how Be stars attained their fast rotation. Although the subdwarf remnants of mass donors in such systems should exist in abundance, only a few have been confirmed due to tight observational constraints. An indirect method of detecting otherwise hidden companions is offered by their effect on the outer parts of Be star disks, which are expected to be disrupted or truncated. In the context of the IR and radio continuum excess radiation originating in the disk, the disk truncation can be revealed by a turndown in the spectral energy distribution due to reduced radio flux levels. In this work we search for signs of spectral turndown in a sample of 57 classical Be stars with radio data, 2 Klement et al.which include new data for 23 stars and the longest wavelength detections so far (λ ≈ 10 cm) for 2 stars. We confidently detect the turndown for all 26 stars with sufficient data coverage (20 of which are not known to have close binary companions). For the remaining 31 stars, data are inconclusive as to whether the turndown is present or not. The analysis suggests that many if not all Be stars have close companions influencing their outer disks. If confirmed to be subdwarf companions, the mass transfer spin-up scenario might explain the existence of the vast majority of classical Be stars.

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Section: A Known Binaries In the Samplementioning

confidence: 99%

Prevalence of SED Turndown among Classical Be Stars: Are All Be Stars Close Binaries?

Klement

Carciofi

Rivinius

et al. 2019

ApJ

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“…(a) Slettebak (1982); (b) Rivinius et al (2006); (c) Harmanec (1988); (d) van Leeuwen (2007) modeled as a combination of a fast-rotating central star surrounded by a VDD. The code uses the Monte Carlo method to solve the radiative transfer, radiative equilibrium, and statistical equilibrium in 3D geometry for the given density and velocity distributions for pure hydrogen gas.…”

Section: Modeling Proceduresmentioning

confidence: 99%

Revealing the structure of the outer disks of Be stars

Klement

Carciofi

Rivinius

et al. 2017

A&A

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Context. The structure of the inner parts of Be star disks ( 20 stellar radii) is well explained by the viscous decretion disk (VDD) model, which is able to reproduce the observable properties of most of the objects studied so far. The outer parts, on the other hand, are not observationally well-explored, as they are observable only at radio wavelengths. A steepening of the spectral slope somewhere between infrared and radio wavelengths was reported for several Be stars that were previously detected in the radio, but a convincing physical explanation for this trend has not yet been provided. Aims. We test the VDD model predictions for the extended parts of a sample of six Be disks that have been observed in the radio to address the question of whether the observed turndown in the spectral energy distribution (SED) can be explained in the framework of the VDD model, including recent theoretical development for truncated Be disks in binary systems. Methods. We combine new multi-wavelength radio observations from the Karl. G. Jansky Very Large Array (JVLA) and Atacama Pathfinder Experiment (APEX) with previously published radio data and archival SED measurements at ultraviolet, visual, and infrared wavelengths. The density structure of the disks, including their outer parts, is constrained by radiative transfer modeling of the observed spectrum using VDD model predictions. In the VDD model we include the presumed effects of possible tidal influence from faint binary companions.Results. For 5 out of 6 studied stars, the observed SED shows strong signs of SED turndown between far-IR and radio wavelengths. A VDD model that extends to large distances closely reproduces the observed SEDs up to far IR wavelengths, but fails to reproduce the radio SED. Using a truncated VDD model improves the fit, leading to a successful explanation of the SED turndown observed for the stars in our sample. The slope of the observed SEDs in the radio is however not well reproduced by disks that are simply cut off at a certain distance. Rather, some matter seems to extend beyond the truncation radius, where it still contributes to the observed SEDs, making the spectral slope in the radio shallower. This finding is in agreement with our current understanding of binary truncation from hydrodynamical simulations, in which the disk does extend past the truncation radius. Therefore, the most probable cause for the SED turndown is the presence of binary companions that remain undetected for most of our sources.

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“…Mass and radius determination for κ CMa from the Harmanec (1988) compilation for the effective temperatures given by Popper (1980), Prinja (1989) and Fremat (2005 (4.98 -6.36) effective temperatures used by Popper (1980), Prinja (1989) and Fremat (2005), we obtain the Table 1. Thus, for a main sequence star the stellar radius should be smaller than the 6 R we have adopted, however, our radius estimate based on the parallax and the chosen V magnitude from the correlation between the brightness and emission strength, as proposed by Harmanec (2000), gives the range of radii comparable to the 6 R used in our modeling.…”

Section: Introductionmentioning

confidence: 96%

An asymmetry detected in the disk of κ Canis Majoris with AMBER/VLTI

Meilland

Millour

Stee

et al. 2006

A&A

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Aims. We study the geometry and kinematics of the circumstellar environment of the Be star κ CMa in the Brγ emission line and its nearby continuum. Methods. We use the AMBER/VLTI instrument operating in the K band, which provides a spatial resolution of about 6 mas with a spectral resolution of 1500, to study the kinematics within the disk and to infer its rotation law. To obtain more kinematical constraints we also use a high spectral resolution Paβ line profile obtain in December 2005 at the Observatorio do Pico do Dios, Brazil and we compile V/R line profile variations and spectral energy distribution data points from the literature. Results. Using differential visibilities and differential phases across the Brγ line we detect an asymmetry in the disk. Moreover, we found that κ CMa seems difficult to fit within the classical scenario for Be stars, illustrated recently by α Arae observations, i.e. a fast rotating B star close to its breakup velocity surrounded by a Keplerian circumstellar disk with an enhanced polar wind. We discuss the possibility that κ CMa is a critical rotator with a Keplerian rotating disk and examine whether if the detected asymmetry can be interpreted within the "one-armed" viscous disk framework.

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Physical Properties and Evolutionary Stage of Be Stars

Cited by 50 publications

References 33 publications

Prevalence of SED Turndown among Classical Be Stars: Are All Be Stars Close Binaries?

Prevalence of SED Turndown among Classical Be Stars: Are All Be Stars Close Binaries?

Revealing the structure of the outer disks of Be stars

An asymmetry detected in the disk of κ Canis Majoris with AMBER/VLTI

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