SIMBAD references

By analysis of data from the SWASP database, the Qatar exoplanet survey and recent observations, 83 maxima of the RRc star DD Boo could be derived. In combination with the available CCD max. in the GEOS database, a Blazhko period of PB = 9.706 d was found. This is in agreement with the PB found by the Qatar group and illustrates the constancy of the period from at least 1995 until now. The 2015 measurements revealed that the secondary period affects the light curve not only in phase, but also in shape and amplitude. The period seems to be slightly variable; the best fit is produced by the quadratic ephemeris HJD (max.) = 2457176.6463 + 0.33944806 x E + 2.4992*10-10x E^2.