Variability of M giant stars based on Kepler photometry

Interesting paper on Arxiv this week: Variability of M giant stars based on Kepler photometry: general characteristics.

The researchers used Kepler data and looked at red variables, giving them a fairly unprecedented look, with photometry every 29.4 minutes for over 1000 days.

Quite interesting to me, of course, was how well the AAVSO visual data, reduced to 10-day means, matched the Kepler data.  Or vice versa, however you want to look at it!  Both the light curves and the wavelet analysis match very well on AF Cyg, the star used to illustrate their point, and describe how they treated the data.

Also, the first thing I thought of when I saw their methodology was "Flares!".  Back in the day, there was a big debate amongst AAVSO observers and others, with some visual observers believing they had observed short-lived flares of a half or a full magnitude, perhaps more, from LPVs.  This seemed to be borne out by Hipparcos data, see Detection of short-term variations in Mira-type variables from HIPPARCOS photometry.  However, this study does not see such activity using the Kepler data, the authors noting, "We note here that we found no star with flare-like events that would resemble those reported from the Hipparcos data..." (p. 7).  I have not heard any reports of the phenomenon from the visual observers in years.  

The authors also found evidence of a "so far unidentified systematic effect in the Kepler data".  I learned a few things I didn't know about how Kepler was actually operated, and I'll bet we'll hear a little more about this down the road.  

Jim