Open AccessCyclical period changes in Z Chamaeleontis
Author(s) -
Baptista R.,
Jablonski F.,
Oliveira E.,
Vrielmann S.,
Woudt P. A.,
Catalán M. S.
Publication year - 2002
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2002.05880.x
Subject(s) - physics , ephemeris , astrophysics , orbital period , amplitude , eclipse , period (music) , astronomy , satellite , stars , optics , acoustics
We report the identification of cyclical changes in the orbital period of the eclipsing dwarf nova Z Cha. We used times of mid‐eclipse collected from the literature and our new eclipse timings to construct an observed‐minus‐calculated diagram covering 30 yr of observations (1972–2002). The data present cyclical variations that can be fitted by a linear plus sinusoidal function with period 28 ± 2 yr and amplitude 1.0 ± 0.2 min . The statistical significance of this period by an F ‐test is larger than 99.9 per cent. The derived fractional period change, Δ P / P = 4.4 × 10 −7 , is comparable to that of other short‐period cataclysmic variables (CVs), but is one order of magnitude smaller than those of the long‐period CVs. Separate fits to the first and second halves of the data lead to ephemerides with quite different cycle periods and amplitudes, indicating that the variation is not sinusoidal or, most probably, is not strictly periodic. The observed cyclical period change is possibly caused by a solar‐type magnetic activity cycle in the secondary star. An incremental variation in the Roche lobe of the secondary star of is required in order to explain both the observed period change and the modulation of the quiescent brightness previously reported by Ak, Ozkan & Mattei.