2005A&A...429..317A

Differential Stroemgren uvby observations from the Four College Automated Photoelectric Telescope are presented for the magnetic CP (mCP) stars HR 2258, MW Vul, and HR 9017 and the HgMn star 46 ρ Aqr. A period for HR 2258 of 15.0313 days satisfactorily phases photometry over a 30 year time span. Recent observations of MW Vul agree in phasing with those taken 13 years ago, but the amplitudes in u, v, b, and y are greater and the light curves have changed shape especially in the falling branch. This type of behavior has not been seen before in any slowly rotating mCP star. It is a signature of the precession of the rotational axis which brings different parts of the surface into view. A period of 0.92738 days is found for HR 9017 which is similar to that derived by Winzer. Changes in the v-c values between observations taken in the Spring and Fall of 2003 for 46 ρ Aqr may be due to its companion.