The birth of Be star disks III. SPH models of localised mass ejections
Abstract
Classical Be stars exhibit mass ejection events that feed their viscous decretion disks. Recent TESS space photometry and simultaneous spectroscopy revealed that these flickers are localised, short-lived, and associated with near-Keplerian rotating material close to the stellar surface. We aim to constrain the geometrical and dynamical conditions required for a localised surface ejection to generate a Keplerian decretion disk and to predict the corresponding photometric, spectroscopic, and polarimetric observables. Material, and the injection radius. The SPH outputs were post-processed with the radiative transfer code HDUST to obtain synthetic observables. We scaled the density of the models to match the reference flicker for the Be star f\,Car. A mildly super-Keplerian rotation of the injection volume, a high viscosity, and a mass-loss rate of the order 10−6 M⊙ yr−1 str−1 are required for the ejected material to remain in orbit and form a small disk. The synthetic observables reproduce the behaviour of the reference flicker. The simulations confirm that during mass ejection the disk is asymmetric and dynamically evolving, and circularises within a few days after the end of the flicker. Models with too wide mass ejection angle or too high angular velocity fail to reproduce the observed light curve and line profile behaviour. The models are consistent with mass ejection happening very close to the stellar equator. Localised, short-duration, mildly super-Keplerian ejections combined with high viscosity and high mass-loss rates can account for the short-timescale variability of the circumstellar environment of Be stars. Be disks can be formed from such outbursts and realistic 3D injection geometries are essential to connect surface dynamics to disk build-up within the framework of the viscous decretion disk model.
Versions
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BibTeX
@misc{rubio2026birth,
title = {{The birth of Be star disks III. SPH models of localised mass ejections}},
author = {A. C. Rubio and A. C. Carciofi and D. Baade and J. Labadie-Bartz and T. H. de Amorim and I. A. Gabitova and M. W. Suffak},
howpublished = {arXiv},
year = {2026},
month = jul,
doi = {10.48550/arxiv.2607.05270},
eprint = {2607.05270},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.05270},
}
RIS
TY - UNPB
TI - The birth of Be star disks III. SPH models of localised mass ejections
AU - A. C. Rubio
AU - A. C. Carciofi
AU - D. Baade
AU - J. Labadie-Bartz
AU - T. H. de Amorim
AU - I. A. Gabitova
AU - M. W. Suffak
PY - 2026
DA - 2026/07/06
PB - arXiv
DO - 10.48550/arxiv.2607.05270
UR - https://arxiv.org/abs/2607.05270
AB - Classical Be stars exhibit mass ejection events that feed their viscous decretion disks. Recent TESS space photometry and simultaneous spectroscopy revealed that these flickers are localised, short-lived, and associated with near-Keplerian rotating material close to the stellar surface. We aim to constrain the geometrical and dynamical conditions required for a localised surface ejection to generate a Keplerian decretion disk and to predict the corresponding photometric, spectroscopic, and polarimetric observables. Material, and the injection radius. The SPH outputs were post-processed with the radiative transfer code HDUST to obtain synthetic observables. We scaled the density of the models to match the reference flicker for the Be star f\,Car. A mildly super-Keplerian rotation of the injection volume, a high viscosity, and a mass-loss rate of the order 10^−6 M_⊙ yr^−1 str^−1 are required for the ejected material to remain in orbit and form a small disk. The synthetic observables reproduce the behaviour of the reference flicker. The simulations confirm that during mass ejection the disk is asymmetric and dynamically evolving, and circularises within a few days after the end of the flicker. Models with too wide mass ejection angle or too high angular velocity fail to reproduce the observed light curve and line profile behaviour. The models are consistent with mass ejection happening very close to the stellar equator. Localised, short-duration, mildly super-Keplerian ejections combined with high viscosity and high mass-loss rates can account for the short-timescale variability of the circumstellar environment of Be stars. Be disks can be formed from such outbursts and realistic 3D injection geometries are essential to connect surface dynamics to disk build-up within the framework of the viscous decretion disk model.
ER -