Reduction of the maximum mass-loss rate of OH/IR stars due to unnoticed binary interaction

Decin, L.; Homan, W.; Danilovich, T.; Koter, A. de; Engels, D.; Waters, L. B. F. M.; Müller, S.; Gielen, C.; García-Hernández, D. A.; Stancliffe, Richard J.; Sande, M. Van de; Molenberghs, Geert; Kerschbaum, F.; Zijlstra, A. A.; Mellah, I. El

doi:10.1038/s41550-019-0703-5

Cited by 36 publications

(34 citation statements)

References 56 publications

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“…Second, superwinds at the tip of the AGB phase could be actually gravity-enhanced winds in binary systems approaching RLOF (see e.g. Decin et al 2019). Third, the stellar evolution of the primary could be driven by the presence of a companion star rather than by intrinsic properties (see e.g.…”

Section: Discussionmentioning

confidence: 99%

AGB winds in interacting binary stars

Bermúdez-Bustamante

Garcı́a-Segura

Steffen

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We perform numerical simulations to investigate the stellar wind from interacting binary stars. Our aim is to find analytical formulae describing the outflow structure. In each binary system the more massive star is in the asymptotic giant branch and its wind is driven by a combination of pulsations in the stellar surface layers and radiation pressure on dust, while the less massive star is in the main sequence. Time averages of density and outflow velocity of the stellar wind are calculated and plotted as profiles against distance from the centre of mass and colatitude angle. We find that mass is lost mainly through the outer Lagrangian point L 2 . The resultant outflow develops into a spiral at low distances from the binary. The outflowing spiral is quickly smoothed out by shocks and becomes an excretion disk at larger distances. This leads to the formation of an outflow structure with an equatorial density excess, which is greater in binaries with smaller orbital separation. The pole-to-equator density ratio reaches a maximum value of ∼ 10 5 at Roche-Lobe Overflow state. We also find that the gas stream leaving L 2 does not form a circumbinary ring for stellar mass ratios above 0.78, when radiation pressure on dust is taken into account. Analytical formulae are obtained by curve fitting the 2-dimensional, azimuthally averaged density and outflow velocity profiles. The formulae can be used in future studies to setup the initial outflow structure in hydrodynamic simulations of common-envelope evolution and formation of planetary nebulae.

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Section: Discussionmentioning

confidence: 99%

AGB winds in interacting binary stars

Bermúdez-Bustamante

Garcı́a-Segura

Steffen

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…Theoretical models (Vassiliadis & Wood 1993;Doherty et al 2014) predict that during the TP phase the photometric period becomes longer. Vassiliadis & Wood (1993) proposed that once the AGB reaches P = 500 d the mass-loss rate undergoes a sudden increase, which according to the most recent evidence can reach 3 × 10 −5 M a −1 (Decin et al 2019). This effect is known as superwind and should take place at some point during the TP phase.…”

Section: The Nature Of Vx Sgrmentioning

confidence: 99%

The nature of VX Sagitarii

Tabernero

Dorda

Negueruela

et al. 2021

A&A

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Aims. We present a spectroscopic analysis of the extremely luminous red star VX Sgr based on high-resolution observations combined with AAVSO light curve data. Given the puzzling characteristics of VX Sgr, we explore three scenarios for its nature: a massive red supergiant (RSG) or red hypergiant (RHG), a Thorne Żytkow object, and an extreme asymptotic giant branch (AGB) star. Methods. Sampling more than one whole cycle of photometric variability, we derive stellar atmospheric parameters by using state-of-the-art PHOENIX atmospheric models. We compare them to optical and near-infrared spectral types. We report on some key features due to neutral elemental atomic species such as Li I, Ca I, and Rb I. Results. We provide new insights into its luminosity, its evolutionary stage, and its pulsation period. Based on all the data, there are two strong reasons to believe that VX Sgr is some sort of extreme AGB star. Firstly, it has Mira-like behaviour during active phases. VX Sgr shows light variation with amplitude that is much larger than any known RSG and clearly larger than all RHGs. In addition, it displays Balmer line emission and, as shown here for the first time, line doubling of its metallic spectrum at maximum light, both characteristics typical of Miras. Secondly, unlike any known RSG or RHG, VX Sgr displays strong Rb I lines. In addition to the photospheric lines that are sometimes seen, it always shows circumstellar components whose expansion velocity is compatible with that of the OH masers in the envelope, demonstrating a continuous enrichment of the outer atmosphere with s-process elements, a behaviour that can only be explained by a third dredge-up during the thermal pulse phase.

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“…Our proposed scenario explains the formation of a silicate-rich EDE around carbon-rich stars (so-called silicate carbon stars; (27)). During the early AGB phase, when the mass-loss rate was still modest and the C/O ratio lower than 1, a stable disk-like structure can be formed which favours the formation of crystalline silicate dust (55). Later, as mass-loss rate and C/O ratio increase due to dredge-ups, the star will gradually become carbon-rich implying a velocity vector field which is predominantly radial.…”

Section: S62 Morphological Characteristics On and Beyond The Agb Phasementioning

confidence: 99%

(Sub)stellar companions shape the winds of evolved stars

Decin

Montargès

Richards

et al. 2020

Science

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Binary interactions dominate the evolution of massive stars, but their role is less clear for low- and intermediate-mass stars. The evolution of a spherical wind from an asymptotic giant branch (AGB) star into a nonspherical planetary nebula (PN) could be due to binary interactions. We observed a sample of AGB stars with the Atacama Large Millimeter/submillimeter Array (ALMA) and found that their winds exhibit distinct nonspherical geometries with morphological similarities to planetary nebulae (PNe). We infer that the same physics shapes both AGB winds and PNe; additionally, the morphology and AGB mass-loss rate are correlated. These characteristics can be explained by binary interaction. We propose an evolutionary scenario for AGB morphologies that is consistent with observed phenomena in AGB stars and PNe.

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Reduction of the maximum mass-loss rate of OH/IR stars due to unnoticed binary interaction

Cited by 36 publications

References 56 publications

AGB winds in interacting binary stars

AGB winds in interacting binary stars

The nature of VX Sagitarii

(Sub)stellar companions shape the winds of evolved stars

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