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Recent activity of three semi-regulars

Here are light curves for three of the more interesting semi-regular variable stars, based on observations submitted to the variable star section:

RW Bootis

The catalogued period of RW Bootis is 209 days, although in recent years it seems to have been going up and down with a period closer to 300 days.

In recent years it has also been quite active and varying over a brightness range of more than a magnitude.

So far, 2017 seems to have been a quieter year for RW Boo, with the observed range dropping to little more than half a magnitude.  The ups and downs also seem to be happening at intervals that are closer to the catalogued 209-day period.

AF Cygni

AF Cygni has a catalogued period of approx 92 days.  At times, however, it has seemed that the ups and downs of AF Cyg have been occurring at intervals close to double this period, although this may simply be an illusion due to some intervening "maxima" being quite faint.

2017 has so far produced two maxima, with suggestions that the first one may have been double-peaked.  It is too early to say whether the same will also be the case for the latest peak.

Z Ursae Majoris

Z UMa is generally listed as having a magnitude range of 6.6-9.3 and a period of about 6 months.  However, some recent maxima seem to have exceeded the upper limit and several recent minima have dipped well below the lower limit.  The spring 2017 minimum was however somewhat shallower than those of 2015 and 2016.

Added by:  Tracie Heywood