BSN: The First Light Curve Analysis of the Total Eclipse Binary System EL Tuc

Abstract

We conducted the first light curve study of the binary star EL Tuc within the Binary Systems of South and North (BSN) Project framework. The photometric observations were made using standard multiband BV RcIc filters at an observatory in Argentina. We presented a new ephemeris for EL Tuc and a linear fit to the O-C diagram, utilizing our extracted times of minima and additional literature. We employed the PHysics Of Eclipsing BinariEs (PHOEBE) Python code and the Markov chain Monte Carlo (MCMC) approach for the system’s light curve analysis. The target system’s light curve solution required a cold starspot on the hotter component. We conclude that EL Tuc is a total contact binary system with a low mass ratio of q = 0.172 ± 0.002, an orbital inclination of i = 83.74 ± 0.40 degree, and a fillout factor of f = 53.7 ± 1.6%. We used the P − a relationship and the Gaia Data Release 3 (DR3) parallax method to determine the absolute parameters of EL Tuc to compare the precision of our results. This system was classified as W-type based on the mass and effective temperature of the companion stars. The positions of the systems were depicted on the M − L, M − R, T − M, and q − Lratio diagrams. The relationship between the spectroscopic and photometric mass ratios of binaries was discussed.