Detecting circumbinary planets using eclipse timing of binary stars - numerical simulations

The presence of a body in an orbit around a close eclipsing binary star manifests itself through the light time effect influencing the observed times of eclipses as the close binary and the circumbinary companion both move around the common centre of mass. This fact combined with the periodicity with which the eclipses occur can be used to detect the companion. Given a sufficient precision of the times of eclipses, the eclipse timing can be employed to detect substellar or even planetary mass companions. The main goal of the paper is to investigate the potential of the photometry based eclipse timing of binary stars as a method of detecting circumbinary planets. In the models we assume that the companion orbits a binary star in a circular Keplerian orbit. We analyze both the space and ground based photometry cases. In particular, we study the usefulness of the on-going COROT and Kepler missions in detecting circumbinary planets. We also explore the relations binding the planet discovery space with the physical parameters of the binaries and the geometrical parameters of their light curves. We carry out detailed numerical simulations of the eclipse timing by employing a relatively realistic model of the light curves of eclipsing binary stars. We study the influence of the white and red photometric noises on the timing precision. We determine the sensitivity of the eclipse timing technique to circumbinary planets for the ground and space based photometric observations. We provide suggestions for the best targets, observing strategies and instruments for the eclipse timing method. Finally, we compare the eclipse timing as a planet detection method with the radial velocities and astrometry.Comment: 9 pages, 15 figures, accepted for publication in MNRA

Effective Mg Incorporation in CdMgO Alloy on Quartz Substrate Grown by Plasma-assisted MBE

The development of CdMgO ternary alloy with a single cubic phase is challenging but meaningful work for technological advancement. In this work, we have grown a series of Cd1-xMgxO ternary random alloys with various Mg concentrations (x = 0, 30, 32, 45, and 55%) on quartz substrate by plasma-assisted molecular beam epitaxy (PA-MBE) technique. The structural investigations of alloys were performed using the X-ray diffraction (XRD) technique. The decreases in average crystallite size and lattice parameters were observed with an increase in Mg content in the alloys. XRD analysis confirms a single cubic phase is obtained for alloy compositions. The elemental and morphological studies were carried out using energy dispersive x-ray (EDX) spectroscopy and atomic force microscope (AFM) technique, respectively. The optical investigation was carried out using UV-Vis spectroscopy. The optical bandgaps were estimated using the Tauc relation and it was varied from 2.34 eV to 3.47 eV by varying the Mg content from zero to 55% in the alloys. The Urbach energy increases from 112 meV to 350 meV which suggests a more disordered localized state with an increase in Mg incorporation in the alloys.Comment: 22 pages, 8 figures, 2 table

MBE grown preferentially oriented CdMgO alloy on m- and c-plane sapphire substrates

Unlike other II-VI semiconductors, CdO-based transparent oxide has great potential application for the fabrication of many optoelectronic devices. In this work, we study the growth of CdxMg1-xO alloys on m- and on c-plane sapphire substrates in Cd-rich to Mg-rich conditions using the plasma-assisted molecular beam epitaxy method. A structural and morphological study of CdMgO random alloys was carried out using X-ray diffraction and Atomic Force Microscope (AFM) techniques whereas composition analysis was done by Energy-dispersive X-ray (EDX) spectroscopy method. The optical properties of thin films were investigated by UV-Vis spectroscopy at room temperature. X-ray analysis confirmed the presence of cubic rock salt structure with CdMgO crystallographic orientation on c-plane sapphire and CdMgO preferential orientation on m-plane sapphire. The surface roughness was measured by the AFM. From the absorption curve, the optical bandgaps were determined using Tauc relation and it was found that the bandgap of films is influenced by the incorporation of Mg2+ ions into the CdO lattice. Bowing parameter was calculated both for samples on m- and c- sapphires.Comment: 19 pages, 11 figure