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Orbital period study of AK Her
Orbital period changes of the contact binary AK Her are discussed. The(O-C) diagram constructed using all available photoelectric, CCD,photographic and visual minima times including new photoelectric minimatimes determined from our U,B,V observations taken in 1982 and 2003, canbe explained by a long-term orbital period increase modulated by alight-time effect. The period increase is caused either by a masstransfer from the less to more massive component of the binary or by alight-time effect on a very long period orbit. The low-mass third bodypresent in the system is responsible for the 57.2-year light-timeeffect. A Fourier period analysis of the residuals from the fit revealedthe 17.7-year period probably caused by a spot activity cycle.
| Study of the contact binary AK Herculis: Light-curve analysis and orbital period investigation
AK Her is a very interesting contact binary exhibiting variable lightcurves and an obvious O'Connell effect, with max I greater than max II.In the present work an extensive study of this system is made coveringnot only its light curve analysis, but also its orbital period changesin an attempt to give a definite answer regarding the apsidal motion ofAK Her. Photoelectric observations of AK Her, obtained between 1985-1987at the National Observatory of Athens Greece, are presented, analysedand discussed. The light curve analysis was made with the W-D code andthe geometric and photometric elements of the system were derived. TheO'Connell effect was faced with a two dark spot model. Moreover, theorbital period of the system was examined and two periodicities weredetected. Since the first one corresponds to the time interval for whichobservational data exist and the second was found to be half of thefirst, it turns out that none of them is true. Two other significantresults that came from the present analysis are that the orbital periodof AK Her does not follow a sinusoidal variation and that, from thetimes of minimum light at primary and secondary eclipses, it seems thatthere is no apsidal motion.
| On the Orbital Period Changes of AK Herculis
We present 10 unpublished photoelectric minima of the eclipsing binaryAK Her and examine its orbital period changes.
| The new light curves and period study of AK Herculis
B and V observations of the W Ursae Majoris-type eclipsing variablesystem AK Her were made on five nights at the Ege UniversityObservatory. Several times of minima were obtained during theobservations and the new light elements were calculated. The light-timeperiod was found to be about 75.72 years. The light curve of the systemappears to change in each cycle for both colors. The secondary minimumof the system seems to be a total eclipse with a duration of about 42.5min.
| AK Herculis - an atypical W UMa-type system
Seven nights of B and V photoelectric photometry of the W UMa-typeeclipsing binary AK Her are analyzed along with previous observations ofthe same system. Normal-point light curves are tabulated, phases arecomputed, and previously determined times of minima are examined. Theorigin of a quasi-sinusoidal variation in the ephemeris of primaryminimum is considered, plausible masses and separations are given for ahypothetical fourth component, and unusual features in the lightvariation of AK Her are discussed. Light-curve analyses are performedwhich indicate that AK Her is a rather abnormal W UMa-type binary with alarge temperature difference of about 1000 K between components, verylarge albedos in excess of 2, and small limb-darkening coefficients.
| Photoelectric Light Curves of AK Herculis
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972PASP...84..566B&db_key=AST
| Photoelectric observations of six eclipsing binaries
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&AS....6..131V&db_key=AST
| Untersuchungen an W Ursae Majoris-Sternen. IV. Lichtelektrische Beobachtungen von AK Herculis. Mit 11 Textabbildungen
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