The binary system of the spinning-top Be star Achernar

Kervella, P.; Souza, A. Domiciano de; Mérand, A.; Gallenne, A.; Rivinius, Th.; Lacour, S.; Carciofi, A. C.; Faes, D. M.; Bouquin, J.-B. Le; Taormina, M.; Pilecki, B.; Berger, J.‐P.; Bendjoya, Philippe; Klement, Róbert; Millour, F.; Janot-Pacheco, E.; Spang, A.; Vakili, F.

doi:10.1051/0004-6361/202244009

Cited by 3 publications

(1 citation statement)

References 116 publications

(114 reference statements)

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“…Among the wider systems with main-sequence secondaries, such misalignments may be less rare as suggested by δ Sco (Baade et al, in prep. ) and Achernar (Kervella et al 2008), for which Kervella et al (2022) found that the angle between the equatorial plane of the rotationally distorted Be star (Carciofi et al 2008) and the orbital plane is 30 +7 −4 deg. In both γ Cas and 59 Cyg the misalignment angle is not observationally constrained but, if they are the products of mass transfer in a binary, it is expected to be small.…”

Section: Challengesmentioning

confidence: 99%

The historical active episodes of the disks around γ Cassiopeiae (B0.5 IVe) and 59 Cygni (B1 IVe) revisited

Baade,

Labadie-Bartz,

Rivinius

et al. 2023

A&A

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The observations of all known major activity phases of the disks around the classical Be stars γ Cas and 59 Cyg with low-mass companions are comprehensively reviewed and purely qualitatively evaluated again, though taking advantage of new insights gained over the past 25 yr into the physics of Be disks. Both stars have exhibited activity cycles in the violet-to-red (V/R) flux ratio of emission lines with two peaks. This activity is indistinguishable from those of the vast majority of Be stars and so probably were caused by one-armed (m = 1) disk oscillations. The anomalous high-activity phases from 1932 to 1942 in γ Cas and between 1972 and 1976 in 59 Cyg were distinguished from m = 1 density waves by large variations in the separations of pairs of emission peaks. In two consecutive cycles, shell phases during which the emission peaks were maximally separated alternated with single (blended) emission peaks. The amplitude in peak separation of more than a factor of two implies a high-amplitude variation in the disk aspect angle. When the peaks were blended and the disk was viewed closest to face-on, local maxima in visual brightness probably occurred in γ Cas, and the visibility of the stellar absorption lines was reduced, as is expected from increased free-bound emission into the line of sight (there is no time-resolved photometry for 59 Cyg from the event in the 1970s). In y Cas, the pre-event V/R variability (pre-event observations of 59 Cyg do not exist) was practically identical to m = 1 variability. In spite of the subsequent rapid rise in amplitude (up to ~4), the V/R variations connected smoothly in phase but may require an explanation involving the 3D structure of the disk. The phasing of single-peak and shell stages relative to the V/R activity was the same in both cycles of γ Cas, whereas this is not clear for 59 Cyg. During both high-activity cycles of γ Cas, but at different phases, transient additional pairs of emission lines appeared in γ Cas that were much sharper than the main ones and they also had different peak separations and V/R ratios. In the second instance, their velocities were up to ~+500 km s−1. The extremely rapid excitation of the activity phases and their short duration of only two cycles in both stars may indicate a resonant behavior of an unidentified nature. In both stars, the line emission was strongly developed at the onset of the high-activity phases but it basically disappeared at the end of them, and the disks may have been dynamically destroyed. The atypical disk variations were presumably triggered by enhanced interactions between a disk and companion star. In both systems, there seems to be less evidence for a mass-loss outburst than for a reduced mass-injection rate into the disk. The resulting lower viscous coupling between a disk and star would have facilitated the tilting of the disk.

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Section: Challengesmentioning

confidence: 99%

The historical active episodes of the disks around γ Cassiopeiae (B0.5 IVe) and 59 Cygni (B1 IVe) revisited

Baade,

Labadie-Bartz,

Rivinius

et al. 2023

A&A

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Bayesian sampling with BeAtlas, a grid of synthetic Be star spectra I. Recovering the fundamental parameters of α Eri and β CMi

Rubio,

Carciofi,

Ticiani

et al. 2023

Monthly Notices of the Royal Astronomical Society

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Classical B emission (Be) stars are fast rotating, near-main-sequence B-type stars. The rotation and the presence of circumstellar discs profoundly modify the observables of active Be stars. Our goal is to infer stellar and disc parameters, as well as distance and interstellar extinction, using the currently most favoured physical models for these objects. We present BeAtlas, a grid of $61\, 600$ non-local thermodynamic equilibrium radiative transfer models for Be stars, calculated with the hdust code. The grid was coupled with a Monte Carlo Markov chain (MCMC) code to sample the posterior distribution. We test our method on two well-studied Be stars, α Eri and β CMi, using photometric, polarimetric, and spectroscopic data as input to the code. We recover literature determinations for most of the parameters of the targets, in particular the mass and age of α Eri, the disc parameters of β CMi, and their distances and inclinations. The main discrepancy is that we estimate lower rotational rates than previous works. We confirm previously detected signs of disc truncation in β CMi and note that its inner disc seems to have a flatter density slope than its outer disc. The correlations between the parameters are complex, further indicating that exploring the entire parameter space simultaneously is a more robust approach, statistically. The combination of BeAtlas and Bayesian-MCMC techniques proves successful, and a powerful new tool for the field: The fundamental parameters of any Be star can now be estimated in a matter of hours or days.

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The Components of Cepheid Systems: The FN Vel System*

Evans,

Kervella,

Kuraszkiewicz

et al. 2024

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Cepheid masses continue to be important tests of evolutionary tracks for intermediate-mass stars as well as important predictors of their future fate. For systems where the secondary is a B star, Hubble Space Telescope ultraviolet spectra have been obtained. From these spectra a temperature can be derived, and from this a mass of the companion M 2. Once Gaia DR4 is available, proper motions can be used to determine the inclination of the orbit. Combining mass of the companion, M 2, the mass function from the ground-based orbit of the Cepheid and the inclination produces the mass of the Cepheid, M 1. The Cepheid system FN Vel is used here to demonstrate this approach and what limits can be put on the Cepheid mass for inclination between 50° and 130°.

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The binary system of the spinning-top Be star Achernar

Cited by 3 publications

References 116 publications

The historical active episodes of the disks around γ Cassiopeiae (B0.5 IVe) and 59 Cygni (B1 IVe) revisited

The historical active episodes of the disks around γ Cassiopeiae (B0.5 IVe) and 59 Cygni (B1 IVe) revisited

Bayesian sampling with BeAtlas, a grid of synthetic Be star spectra I. Recovering the fundamental parameters of α Eri and β CMi

The Components of Cepheid Systems: The FN Vel System*

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