Properties and nature of Be stars

Koubský, P.; Harmanec, P.; Brož, M.; Kotková, L.; Yang, S.; Božić, H.; Sudar, D.; Frémat, Y.; Korčáková, Daniela; Votruba, V.; Škoda, Petr; Šlechta, M.; Ruždjak, Domagoj

doi:10.1051/0004-6361/201834597

Cited by 4 publications

(7 citation statements)

References 42 publications

(53 reference statements)

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“…A powerful bias that needs to be considered is the fact that researchers in the field have rarely published non-detections. For example, studies based on data acquired with the Ondȓejov observatory report on quite a few unique systems, for example on Be binaries with sdO companions, systems with unidentified companions, or systems that do not contain Be stars after all (see e.g., Harmanec et al 2002;Saad et al 2004;Linnell et al 2006;Koubský et al 2010Koubský et al , 2019. However, no studies on non-detections were published.…”

Section: Time Sampling and Multiplicity Studiesmentioning

confidence: 99%

Investigating the lack of main-sequence companions to massive Be stars

Bodensteiner

Shenar

Sana

2020

A&A

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Context. About 20% of all B-type stars are classical Be stars – stars whose spectra imply the presence of a circumstellar decretion disk. The disk phenomenon is strongly correlated with rapid rotation, the origin of which remains unclear. It may be rooted in single- or binary-star evolution. In the framework of the binary channel, the initially more massive star transfers mass and angular momentum to the original secondary, which becomes a Be star. The system then evolves into a Be binary with a post-main-sequence companion, which, depending on the companion mass, may later be disrupted in a supernova event. Hence, if the binary channel dominates the formation of Be stars, one may expect a strong lack of close Be binaries with main sequence (MS) companions. Aims. We want to test the prediction of the binary channel. Through an extensive, star-by-star review of the literature of a magnitude-limited sample of Galactic early-type Be stars, we investigate whether Be binaries with MS companions are known to exist. Methods. Our sample is constructed from the BeSS database and cross-matched with all available literature on the individual stars. Archival and amateur spectra are used to verify the existing literature when conflicting reports are found. Results. Out of an initial list of 505 Be stars, we compile a final sample of 287 Galactic Be stars earlier than B1.5 with V ≤ 12 mag. Out of those, 13 objects were reported as Be binaries with known post-MS companions (i.e., compact objects or helium stars) and 11 as binaries with unknown, uncertain or debated companions. We find no confirmed reports of Be binaries with MS companions. For the remaining 263 targets, no significant reports of multiplicity exist in the literature, implying that they are either Be binaries with faint companions, or truly single. Conclusions. The clear lack of reported MS companions to Be stars, which stands in contrast to the high number of detected B+B MS binaries, strongly supports the hypothesis that early-type Be stars are binary interaction products that spun up after mass and angular momentum transfer from a companion star. Taken at face value, our results may suggest that a large majority of the early-type Be stars have formed through binary mass-transfer.

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Section: Time Sampling and Multiplicity Studiesmentioning

confidence: 99%

Investigating the lack of main-sequence companions to massive Be stars

Bodensteiner

Shenar

Sana

2020

A&A

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“…Still is not clear if magnetic fields are present in DPVs in general, and why some semi-detached binaries containing B-type components do not show long-term photometric modulations (e.g. Koubský et al 2019). We acknowledge support by VRID-Enlace 216.016.002-1.0, the BASAL Centro de Astrofísica y Tecnologías Afines (CATA) PFB-06/2007, FONDECYT 1190621 and FONDECYT 1161247.…”

mentioning

confidence: 99%

“…Actually, magneto-hydrodynamical simulations reveal changes in the stellar structure due to magnetic cycles and suggest how relevant the stellar rotation can be in rapidly rotating orbitally synchronized binary star components (Navarrete et al 2019). Rapid rotation might generate stellar dynamos even in early A-type giants, as suggested by the presence of chromospheric emission 2017), Rosales & Mennicken (2017, 2018, 2019 and the VSX database (https://www.aavso.org/vsx/). MNIC V99, reported by Nikolay Mishevskiy in VSX, has a period ratio of 21.67, similar to β Lyrae (21.25).…”

mentioning

confidence: 99%

mentioning

confidence: 99%

“…The new DPVs found by Rojas (M.Sc. thesis 2019) are shown by dots while the rest are listed in Mennickent (2017),Rosales & Mennicken (2017, 2018, 2019 and the VSX database (https://www.aavso.org/vsx/). MNIC V99, reported by Nikolay Mishevskiy in VSX, has a period ratio of 21.67, similar to β Lyrae (21.25).…”

mentioning

confidence: 99%

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Possible evidence for a magnetic dynamo in hot Algols

et al. 2019

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Orbital variability of the optical linear polarization of the γ-ray binary LS I +61° 303 and new constraints on the orbital parameters

Kravtsov

Berdyugin²,

Piirola³

et al. 2020

A&A

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We studied the variability of the linear polarization and brightness of the γ-ray binary LS I +61° 303. High-precision BVR photopolarimetric observations were carried out with the Dipol-2 polarimeter on the 2.2 m remotely controlled UH88 telescope at Mauna Kea Observatory and the 60 cm Tohoku telescope at Haleakala bservatory (Hawaii) over 140 nights in 2016−2019. We also determined the degree and angle of the interstellar polarization toward LS I +61° 303 using two out of four nearby field stars that have Gaia’s parallaxes. After subtracting the interstellar polarization, we determined the position angle of the intrinsic polarization θ ≃ 11°, which can either be associated with the projection of the Be star’s decretion disk axis on the plane of sky, or can differ from it by 90°. Using the Lomb-Scargle method, we performed timing analyses and period searches of our polarimetric and photometric data. We found statistically significant periodic variability of the normalized Stokes parameters q and u in all passbands. The most significant period of variability, PPol = 13.244 ± 0.012 d, is equal to one half of the orbital period Porb = 26.496 d. The fits of the polarization variability curves with Fourier series show a dominant contribution from the second harmonic which is typical for binary systems with circular orbits and nearly symmetric distribution of light scattering material with respect to the orbital plane. The continuous change of polarization with the orbital phase implies co-planarity of the orbit of the compact object and the Be star’s decretion disk. Using a model of Thomson scattering by a cloud that orbits the Be star, we obtained constraints on the orbital parameters, including a small eccentricity e < 0.2 and periastron phase of ϕp ≈ 0.6, which coincides with the peaks in the radio, X-ray, and TeV emission. These constraints are independent of the assumption about the orientation of the decretion disk plane on the sky. We also extensively discuss the apparent inconsistency with the previous measurements of the orbital parameters from radial velocities. By folding the photometry data acquired during a three-year time span with the orbital period, we found a linear phase shift of the moments of the brightness maximum, confirming the possible existence of superorbital variability.

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Properties and nature of Be stars

Cited by 4 publications

References 42 publications

Investigating the lack of main-sequence companions to massive Be stars

Investigating the lack of main-sequence companions to massive Be stars

Possible evidence for a magnetic dynamo in hot Algols

Orbital variability of the optical linear polarization of the γ-ray binary LS I +61° 303 and new constraints on the orbital parameters

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