220 research outputs found
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
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