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 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:
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RA (2000) DE Designation(s)
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20 09 25.62 +36 50 22.6 28 Cyg = HR 7708
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File Summary:
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FileName Lrecl Records Explanations
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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
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Byte-by-byte Description of file: btr15.dat btr16.dat smei.dat
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Bytes Format Units Label Explanations
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1- 9 F9.4 d HJD Heliocentic Julian Date (HJD-2457000)
13- 18 F6.3 mag mag Magnitude in filter (BTr or SMEI) (1)
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Note (1): Zeropoints of magnitude scales are arbitrary.
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Acknowledgements:
Dietrich Baade, dbaade(at)eso.org
References:
Baade et al., Paper I 2016A&A...588A..56B 2016A&A...588A..56B
Rivinuis et al., Paper II 2016A&A...593A.106R 2016A&A...593A.106R
(End) Dietrich Baade [ESO, Germany], Patricia Vannier [CDS] 07-Nov-2017