OpenBU http://open.bu.edu Astronomy BU Open Access Articles 2018-08-20 Stochastic modeling of multiwavelength variability of the classical BL Lac Object OJ287...

HS 0705+6700 is a short-period (P=2.3 hours), close binary containing a hot sdB-type primary and a fully convective secondary. We have monitored this eclipsing binary for more than 2 years and as a result, 32 times of light minimum were obtained. Based on our new eclipse times together with these compiled from the literature, it is discovered that the O-C curve of HS 0705+6700 shows a cyclic variation with a period of 7.15 years and a semiamplitude of 92.4 s. The periodic change was analyzed for the light-travel time effect that may be due to the presence of a tertiary companion. The mass of the third body is determined to be M 3 sin i ′ = 0.0377(±0.0043) M ⊙ when a total mass of 0.617 M ⊙ for HS 0705+6700 is adopted. For orbital inclinations i ′ ≥ 32.8 • , the mass of the tertiary component would be below the stable hydrogen-burning limit of M 3 ∼ 0.072 M ⊙ , and thus it would be a brown dwarf. The third body is orbiting the sdB-type binary at a distance shorter than 3.6 astronomical units (AU). HS 0705+6700 was formed through the evolution of a common envelope after the primary becomes a red giant. The detection of a sub-stellar companion in HS 0705+6700 system at this distance from the binary could give some constraints on stellar evolution in such systems and the interactions between red giants and their companions.

Context. The extension of the KDA analytical model of FR II−type source evolution originally assuming a continuum injection process in the jet−IGM (intergalactic medium) interaction towards a case of the jet's termination is presented and briefly discussed. Aims. The dynamical evolution of FR II−type sources predicted with this extended model, hereafter referred to as KDA EXT, and its application to the chosen radio sources. Methods. Following the classical approach based on the source's continuous injection and self-similarity, I propose the effective formulae describing the length and luminosity evolution of the lobes during an absence of the jet flow, and present the resulting diagrams for the characteristics mentioned. Results. Using an algorithm based on the numerical integration of a modified formula for jet power, the KDA EXT model is fitted to three radio galaxies. Their predicted spectra are then compared to the observed spectra, proving that these fits are better than the best spectral fit provided by the original KDA model of the FR II−type sources dynamical evolution.

To understand the properties of orbital period changes of four short period sdB-type eclipsing binaries, HW Vir, HS 0705 + 6700, HS 2231 + 2441, and NSVS 14256825, we have monitored them photometrically since 2006. Apart from HW Vir, it is found that the O-C diagrams of HS 0705 + 6700 and HS 2231 + 2441 can also be described by a cyclic variation superimposed on a downward parabolic curve, indicating a long-term period decrease in the two systems. Therefore, of the four binary systems, longterm period variations have been detected for three ones that can be explained by magnetic braking of the fully convective component stars. This may drive these systems to evolution into normal cataclysmic variables. As for the cyclic period variations observed in the four systems, the light-travel time effect via the presence of a tertiary component is the most possible mechanism to interpret the periodic change, which reveals the presence of extremely low-mass objects

We constrain the distribution of calcium across the surface of the white dwarf star G29-38 by combining time series spectroscopy from Gemini-North with global time series photometry from the Whole Earth Telescope. G29-38 is actively accreting metals from a known debris disk. Since the metals sink significantly faster than they mix across the surface, any inhomogeneity in the accretion process will appear as an inhomogeneity of the metals on the surface of the star. We measure the flux amplitudes and the calcium equivalent width amplitudes for two large pulsations excited on G29-38 in 2008. The ratio of these amplitudes best fits a model for polar accretion of calcium and rules out equatorial accretion.