Deneb's Variability as Viewed by BRITE Constellation and the Solar Mass Ejection Imager

Deneb, the prototype alpha Cygni variable, is a bright A2 Ia supergiant that shows irregular variability, presumed to be pulsations, with a 12-day quasi-period. Analyses of radial velocity and photometry data from 1930 to the present (Abt et al. PASP 2023; Guzik et al. 112th Annual AAVSO meeting 2023) suggested that larger amplitude 12-day variations appear to resume abruptly and at an arbitrary phase, and damp out after several cycles, with an interval of around 70 days between these resumptions. The photometric data included observations from the ground-based campaign of Richardson et al. (2011) taken between 1997 and 2001, data from the American Association of Variable Star Observers database (Kloppenborg, AAVSO, 2023) taken between 2021 and 2023, and three 27-day sector observations by the TESS spacecraft. These analyses raised several unanswered questions, among them: How exact and regular is the apparent time interval of ~70 days between resumption of higher amplitude pulsations with period ~12 days? Do these higher amplitude pulsation resumptions occur abruptly at an arbitrary phase in the pulsation cycle? For the above-mentioned data sets, the time between data points was too long, or the time series was too short to answer these questions definitively. However, we have begun analysis of an 8.6-year photometric data set from the Solar Mass Ejection Imager taken between 2003 and 2011, with cadence 1.7 hours. We will also examine BRITE data for Deneb, taken June-November 2014 and June-November 2015. We hope that these studies will answer the questions raised, and lead to a better understanding of the origin of the variability and the evolutionary state of Deneb and the alpha Cyg variables.