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The historical active episodes of the disks around γ Cassiopeiae (B0.5 IVe) and 59 Cygni (B1 IVe) revisited
Indexado
WoS WOS:001088472800004
Scopus SCOPUS_ID:85174187281
DOI 10.1051/0004-6361/202244149
Año 2023
Tipo artículo de investigación

Citas Totales

Autores Afiliación Chile

Instituciones Chile

% Participación
Internacional

Autores
Afiliación Extranjera

Instituciones
Extranjeras


Abstract



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.

Revista



Revista ISSN
Astronomy & Astrophysics 0004-6361

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Disciplinas de Investigación



WOS
Astronomy & Astrophysics
Scopus
Sin Disciplinas
SciELO
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Publicaciones WoS (Ediciones: ISSHP, ISTP, AHCI, SSCI, SCI), Scopus, SciELO Chile.

Colaboración Institucional



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Autores - Afiliación



Ord. Autor Género Institución - País
1 Baade, D. Hombre Observatorio Europeo Austral - Alemania
2 Labadie-Bartz, Jonathan Hombre L'Observatoire de Paris - Francia
The University of Oklahoma - Estados Unidos
Universidade de São Paulo - Brasil
Sorbonne Univ - Francia
UNIV OKLAHOMA - Estados Unidos
UNIV SAO PAULO - Brasil
3 Rivinius, Th Hombre European Southern Observatory Santiago - Chile
Observatorio Europeo Austral - Chile
Observatorio Europeo Austral - Alemania
4 Carciofi, A. C. - Universidade de São Paulo - Brasil
UNIV SAO PAULO - Brasil

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Financiamiento



Fuente
Conselho Nacional de Desenvolvimento Científico e Tecnológico
Fundação de Amparo à Pesquisa do Estado de São Paulo
NASA’s Science Mission

Muestra la fuente de financiamiento declarada en la publicación.

Agradecimientos



Agradecimiento
We warmly thank Professor Douglas Gies, whose referee report enabled us to clarify and correct various aspects of the paper. We especially acknowledge the motivation he provided for the discussion in Sect. 7.4. D.B. sincerely thanks Mrs. Sarah Burbidge for providing him with a copy of her mother’s PhD thesis; we appreciate her generous permission to reproduce Appendix A from that thesis. D.B. is grateful to Prof. Ian Howarth for having established the contact with Mrs. Burbidge. We acknowledge with gratitude the permission by the editors of the Journal of the Royal Astronomical of Canada to reproduce the figure in Heard (1938) as our Fig. 4. This work has made use of NASA’s Astrophysics Data System (ADS) bibliographic services, the SIMBAD database, operated at CDS, Strasbourg, France, and the Be Star Spectra (BeSS) database, operated at LESIA, Observatoire de Meudon, France ( http://basebe.obspm.fr ). The authors warmly thank the BeSS observers, most notably Eric Bruyssinck, Christian Buil, Bertrand de Batz, Joan Guarra Flo, Keith Graham, Benjamin Mauclaire, Coralie Neiner, and Carl Sawicki, for obtaining and publicly sharing their spectra, and they acknowledge with thanks the variable star observations from the AAVSO International Database contributed by observers worldwide and used in this research. This work makes use of observations from the Las Cumbres Observatory global telescope network with the NRES instruments at the Cerro Tololo Interamer-ican Observatory, McDonald Observatory, and Wise Observatory. This paper includes data collected by the TESS mission, which are publicly available from the Mikulski Archive for Space Telescopes (MAST). Funding for the TESS mission is provided by NASA’s Science Mission directorate. This research made use of Lightkurve, a Python package for Kepler and TESS data analysis (Lightkurve Collaboration 2018). This research made use of Astropy ( http://www.astropy.org ), a community-developed core Python package for Astronomy (Astropy Collaboration 2013, 2018). J.L.-B. acknowledges support from FAPESP (grant 2017/23731-1). A.C.C. acknowledges support from CNPq (grant 311446/2019-1) and FAPESP (grants 2018/04055-8 and 2019/13354-1).

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