A new investigation on the characteristics of a W UMa type system LO Andromedae

Abstract

In this study, a W Ursae Majoris (W UMa) type system LO Andromedae (LO And) was observed over nine nights at Durham to fully investigate its physical properties and update its stellar parameters. After obtaining the observational data in both V-filter and B-filter, the Gaia CCD images of LO And were extracted from the Astrolab internal archive using Linux commands. By applying the "Nightfall" program and local Python scripts, the calibrated light curves of LO And can be plotted, phase-folded, and fitted to derive the period of this system as $0.3804573 \pm 0.0000482\, \mathrm{d}$. Then, 2D chi-squared heat maps were illustrated to determine LO And's best-fit stellar parameters and estimate their uncertainties, including the mass ratio $q = 0.371 \pm 0.207$, the inclination $i = 78.5 \pm 3.8\, \mathrm{deg}$, the primary temperature $T_1 = 6290 \pm 358\, \mathrm{K}$, the secondary temperature $T_2 = 6449 \pm 445\, \mathrm{K}$, and two fill factors $f_1 = f_2 = 1.02258$. In addition, the "Nightfall" program built the 3D models and evaluated the spot distribution parameters to visualize the configuration of LO And. There were seven new eclipsing timings added in this study to reconstruct the O-C diagram together with LO And's previous observational data. It was clearly found that the period of LO And is currently undergoing an accelerated increase with a change rate $d\mathrm{P}/d\mathrm{t} = 2.27 \times 10^{-7}\, \mathrm{day\, yr^{-1}}$, which was attributed to the mass transfer in this system with a transfer rate $dM_1/d\mathrm{t} = 1.43 \times 10^{-7}\, \mathrm{M_\odot\, yr^{-1}}$ and the light time effect caused by the possible existence of a third star $M_3 = 0.224\, M_\odot$ orbiting around LO And.