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J/A+A/610/A70       28 Cygni BRITE and SMEI satellite photometry  (Baade+, 2018)

Short-term variability and mass loss in Be stars. III. BRITE and SMEI satellite photometry of 28 Cygni. Baade D., Pigulski A., Rivinius T., Carciofi A.C., Panoglou D., Ghoreyshi M., Handler G., Kuschnig R., Moffat A.F.J., Pablo H., Popowicz A., Wade G.A., Weiss W.W., Zwintz K. <Astron. Astrophys. 610, A70 (2018)> =2018A&A...610A..70B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, Be ; Photometry Keywords: circumstellar matter - stars: emission line, Be - stars: mass loss - stars: oscillations - stars: individual: 28 Cyg Abstract: The BRITE Constellation of nanosatellites obtained mmag photometry of 28 Cygni for 11 months in 2014-2016. Observations with the Solar Mass Ejection Imager in 2003-2010 and 118 Hα line profiles were added. For decades, 28 Cyg has exhibited four large-amplitude frequencies: two closely spaced frequencies of spectroscopically confirmed g modes near 1.5c/d, one slightly lower exophotospheric (Stefl) frequency, and at 0.05c/d the difference 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 Stefl frequency is the only one that does not seem to be affected by the difference frequency. The amplitude of the latter undergoes large variations; around maximum the amount of near-circumstellar matter is increased, and the amplitude of the Stefl frequency grows by some factor. During such brightenings dozens of transient spikes appear in the frequency spectrum, concentrated in three groups. Only eleven frequencies were common to all years of BRITE observations. 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 low difference frequency and/or the atmospheric response to it appears significantly nonlinear. Like in eta Cen, the difference-frequency variability seems the main responsible for the modulation of the star-to-disc mass transfer in 28 Cyg. A hierarchical set of difference frequencies may reach the longest timescales known of the Be phenomenon. Description: Photometry with BRITE-Constellation satellite BTr in 2015 and 2016 as well as with the Solar Mass Ejection Imager (SMEI) is provided. Zeropoints of magnitude scales are arbitrary. Objects: ----------------------------------------------- RA (2000) DE Designation(s) ----------------------------------------------- 20 09 25.62 +36 50 22.6 28 Cyg = HR 7708 ----------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file btr15.dat 18 2273 28 Cyg BTr magnitudes (2015 data) btr16.dat 18 1747 28 Cyg BTr magnitudes (2016 data) smei.dat 18 26157 28 Cyg SMEI magnitudes
Byte-by-byte Description of file: btr15.dat btr16.dat smei.dat
Bytes Format Units Label Explanations
1- 9 F9.4 d HJD Heliocentic Julian Date (HJD-2457000) 13- 18 F6.3 mag mag Magnitude in filter (BTr or SMEI) (1)
Note (1): Zeropoints of magnitude scales are arbitrary.
Acknowledgements: Dietrich Baade, dbaade(at) References: Baade et al., Paper I 2016A&A...588A..56B Rivinuis et al., Paper II 2016A&A...593A.106R
(End) Dietrich Baade [ESO, Germany], Patricia Vannier [CDS] 07-Nov-2017
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