2005MNRAS.361..559K

Thirty-four new timings of maxima of the radially pulsating extreme helium (EHe) star V652 Her (= BD+13° 3224) obtained during 1996-2004 are reported. The quartic ephemeris (for the pulsation period decrease) is extended and the higher-order terms are defined more accurately. We also report 45 new timings of maxima for the closely similar star BX Cir (= LSS 3184) over the same baseline and present the first evidence that this star also shows a decreasing period. The data obtained thus far can be represented by a quadratic ephemeris - a linearly decreasing period in BX Cir - though the decrease rate (dP/dn∼ 3.7x10^–10 d) is much smaller than in V652 Her.