The detection of periodicity in the broadband non-thermal emission of blazars has so far been proven to be elusive. However, there are a number of scenarios that could lead to quasi-periodic variations in blazar light curves. For example, an orbital or thermal/viscous period of accreting matter around central supermassive black holes could, in principle, be imprinted in the multi-wavelength emission of small-scale blazar jets, carrying such crucial information about plasma conditions within the jet launching regions. In this paper, we present the results of our time series analysis of the ∼9.2 yr long, and exceptionally well-sampled, optical light curve of the BL Lac object OJ 287. The study primarily used the data from our own observations performed at the Mt. Suhora and Kraków Observatories in Poland, and at the Athens Observatory in Greece. Additionally, SMARTS observations were used to fill some of the gaps in the data. The Lomb–Scargle periodogram and the weighted wavelet Z-transform methods were employed to search for possible quasi-periodic oscillations in the resulting optical light curve of the source. Both methods consistently yielded a possible quasi-periodic signal around the periods of ∼400 and ∼800 days, the former with a significance (over the underlying colored noise) of . A number of likely explanations for this are discussed, with preference given to a modulation of the jet production efficiency by highly magnetized accretion disks. This supports previous findings and the interpretation reported recently in the literature for OJ 287 and other blazar sources.

Radial-velocity measurements and sine-curve fits to the orbital velocity variations are presented for the fifth set of ten close binary systems: V376 And, EL Aqr, EF Boo, DN Cam, FN Cam, V776 Cas, SX Crv, V351 Peg, EQ Tau, KZ Vir. All systems are double-lined spectroscopic contact binaries (KZ Vir may be a low inclination, close, non-contact binary), with seven (all except EL Aqr, SX Crv and EQ Tau) being the recent photometric discoveries of the Hipparcos satellite project. The most interesting object is SX Crv, a contact system with an unprecedently low mass ratio, q=0.066+/-0.003, whose existence challenges the current theory of tidal stability of contact systems. Several of the studied systems are prime candidates for combined light and radial-velocity synthesis solutions.Comment: aastex5.0, 3 figures in PS; submitted to Astron.

Radial velocity measurements and sine-curve fits to the orbital velocity variations are presented for the sixth set of 10 close binary systems: SV Cam, EE Cet, KR Com, V410 Cyg, GM Dra, V972 Her, ET Leo, FS Leo, V2388 Oph, and II UMa. All systems except FS Leo are double-lined spectroscopic binaries. The type of FS Leo is unknown, while SV Cam is a close, detached binary; all remaining systems are contact binaries. Eight binaries (all except SV Cam and V401 Cyg) are the recent photometric discoveries of the Hipparcos satellite project. Five systems, EE Cet, KR Com, V401 Cyg, V2388 Oph, and II UMa, are members of visual/spectroscopic triple systems. We were able to observe EE Cet separately from its companion, but in the remaining four triple systems we could separate the spectral components only through the use of the broadening-function approach. Several of the studied systems are prime candidates for combined light and radial velocity synthesis solutions.

Radial-velocity measurements and sine-curve fits to the orbital velocity variations are presented for the seventh set of ten close binary systems: V410 Aur, V523 Cas, QW Gem, V921 Her, V2357 Oph, V1130 Tau, HN UMa, HX UMa, HD 93917, NSV 223. All systems, but three (V523 Cas, HD 93917, NSV 223), were discovered photometrically by the Hipparcos mission. All systems are double-lined (SB2) binaries and all, but the detached, very close system V1130 Tau, are contact binaries. The broadening-function permitted improvement of the orbital elements for V523 Cas, which was the only system observed before for radial velocity variations. Spectroscopic/visual companions were detected for V410 Aur and HX UMa.

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