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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

Short-term variability and mass loss in Be stars III. BRITE and SMEI satellite photometry of 28 Cygni

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Author(s):
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Baade, D. [1] ; Pigulski, A. [2] ; Rivinius, Th. [3] ; Carciofi, A. C. [4] ; Panoglou, D. [5] ; Ghoreyshi, M. R. [4] ; Handler, G. [6] ; Kuschnig, R. [6, 7] ; Moffat, A. F. J. [8, 9] ; Pablo, H. [8, 9] ; Popowicz, A. [10] ; Wade, G. A. [11] ; Weiss, W. W. [7] ; Zwintz, K. [12]
Total Authors: 14
Affiliation:
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[1] European Org Astron Res Southern Hemisphere ESO, Karl Schwarzschild Str 2, D-85748 Garching - Germany
[2] Univ Wroclaw, Astron Inst, Kopernika 11, PL-51622 Wroclaw - Poland
[3] European Org Astron Res Southern Hemisphere ESO, Casilla 19001, Santiago 19 - Chile
[4] Univ Sao Paulo, Inst Astron Geofis & Ciencias Atmosfer, Rua Matao 1226, BR-05508900 Sao Paulo, SP - Brazil
[5] Observ Nacl, Rua Gen Jose Cristino 77, BR-20921400 Rio De Janeiro - Brazil
[6] Graz Univ Technol, Inst Kommunnikat Netze & Satellitenkommunikat, Inffeldgasse 12, A-8010 Graz - Austria
[7] Univ Vienna, Inst Astrophys, Univ Ring 1, A-1010 Vienna - Austria
[8] Univ Montreal, Dept Phys, CP 6128, Succ Ctr Ville, Montreal, PQ H3C 3J7 - Canada
[9] Univ Montreal, CRAQ, CP 6128, Succ Ctr Ville, Montreal, PQ H3C 3J7 - Canada
[10] Silesian Tech Univ, Inst Automat Control, Akad 16, Gliwice - Poland
[11] Royal Mil Coll Canada, Dept Phys, Stn Forces, POB 17000, Kingston, ON K7K 7B4 - Canada
[12] Univ Innsbruck, Inst Astro & Teilchenphys, Technikerstr 25, A-6020 Innsbruck - Austria
Total Affiliations: 12
Document type: Journal article
Source: Astronomy & Astrophysics; v. 610, MAR 5 2018.
Web of Science Citations: 7
Abstract

Context. Be stars are important reference laboratories for the investigation of viscous Keplerian discs. In some cases, the disc feeder mechanism involves a combination of non-radial pulsation (NRP) modes. Aims. We seek to understand whether high-cadence photometry can shed further light on the role of NRP modes in facilitating rotation-supported mass loss. Methods. The BRITE-Constellation of nanosatellites obtained mmag photometry of 28 Cygni for 11 months in 2014-2016. We added observations with the Solar Mass Ejection Imager (SMEI) in 2003-2010 and 118 H alpha line profiles, half of which were from 2016. Results. For decades, 28 Cyg has exhibited four large-amplitude frequencies: two closely spaced frequencies of spectroscopically confirmed g modes near 1.5 c/d, one slightly lower exophotospheric (Stefl) frequency, and at 0.05 c/d the difference (Delta) frequency between the two g modes. This top-level framework is indistinguishable from eta Cen (Paper I), which is also very similar in spectral type, rotation rate, and viewing angle. The circumstellar (Stefl) frequency alone does not seem to be affected by the Delta frequency. The amplitude of the Delta frequency undergoes large variations; around maximum the amount of near-circumstellar matter is increased and the amplitude of the Stefl frequency grows by a factor of a few. During such brightenings dozens of transient spikes appear in the frequency spectrum; these spikes are concentrated into three groups. Only 11 frequencies were common to all years of BRITE observations. Conclusions. Be stars seem to be controlled by several coupled clocks, most of which are not very regular on timescales of weeks to months but function for decades. The combination of g modes to the slow Delta variability and/or the atmospheric response to it appears significantly non-linear. As in eta Cen, the Delta variability seems to be mainly responsible for the modulation of the star-to-disc mass transfer in 28 Cyg. A hierarchical set of Delta frequencies may reach the longest known timescales of the Be phenomenon. (AU)

FAPESP's process: 15/17967-7 - Viscous decretion disks: theory and observations
Grantee:Alex Cavaliéri Carciofi
Support type: Regular Research Grants