Evidence for quasiperiodicity in orbital period modulation of WW Cygni

• Published in: Astrophysics and space science Vol. 362; no. 4; pp. 1 - 15
• Main Authors: Pop, Alexandru, Crăciun, Maria, Mocanu, Gabriela Raluca, Vamoş, Călin
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.04.2017; Springer Nature B.V
• Subjects: Astrobiology; Astronomy; Astrophysics; Astrophysics and Astroparticles; Computer simulation; Cosmology; Data analysis; Double stars; Modulation; Monte Carlo methods; Monte Carlo simulation; Observations and Techniques; Orbits; Original Article; Physics; Physics and Astronomy; Polynomials; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Statistical methods; Texts; Thermal cycling; Time; Stars: individual: WW Cyg; Binaries: eclipsing; Methods: data analysis, statistical
• ISSN: 0004-640X; 1572-946X
• DOI: 10.1007/s10509-017-3057-4

The Algol type binary system WW Cygni is known to display an intricate orbital period variability phenomenon which consists in the presence of an alternating component superposed on a secular trend. The alternating component clearly deviates from a strictly periodic pattern. In the present paper we studied WW Cyg using a data set consisting of 309 times of primary minimum, free of outliers, covering a time base of 113.8 yr. We investigated these timing data using periodicity detection methods relying on both amplitude spectrum and enhanced self-correlation (ESC) methods through Monte Carlo simulations. The problem of estimation of the statistical significance in the ESC method was further developed. The multiperiodicity of the O − C residuals was investigated via iterative prewhitening using three types of models consisting of polynomial (P) + multiperiodic (MP) terms, P + light travel time effect (LTTE) terms, and P + MP terms + LTTE terms. The interpretation of the results led us to the following two hypotheses: (i) a quasiperiodic modulation at a time scale of about 46 yr induced by the cyclic magnetic activity occurring in the cool secondary component of WW Cyg, or (ii) the coexistence of a periodic modulation with a period of 50.41 yr related to the presence of an unseen compact stellar object of at least 2.22 M ⊙ in the system and a quasiperiodic modulation at a time scale of about 19.7 yr, caused by the mechanism (i).