The First Comprehensive Photometric Study of the Algol-type System CL Aurigae

TL;DR

This comprehensive photometric study of the Algol-type binary CL Aurigae reveals its orbital period variations, mass transfer dynamics, and possible third-body influence, providing detailed system parameters and evolutionary insights.

Contribution

First extensive BVRI CCD photometry of CL Aur, including new minima timings and analysis of period variations, mass transfer, and third-body effects.

Findings

Orbital period varies with a 21.6-year oscillation.

Mass transfer contributes to period increase.

System parameters and evolutionary status are derived.

Abstract

We present the first extensive photometric results of CL Aur from our BVRI CCD photometry made on 22 nights from 2003 November through 2005 February. Fifteen new timings of minimum light were obtained. During the past 104 years, the orbital period has varied due to a periodic oscillation superposed on a continuous period increase. The period and semi-amplitude of the oscillation are about 21.6 yrs and 0.0133 d, respectively. This detail is interpreted as a light-travel-time effect due to a low-luminosity K-type star gravitationally bound to the CL Aur close system. Our photometric study indicates that CL Aur is a relatively short-period Algol-type binary with values of q=0.602 and i=88$^\circ$.2. Mass transfer from the secondary to the primary eclipsing component is at least partly responsible for the observed secular period change with a rate of dP/dt = +1.4$\times10^{-7}$ d yr$^{-1}$. A cool spot model has been calculated but we think that an alternative hot-spot model resulting from a gas stream impact on the hot star is more reasonable despite two difficulties with the explanation. Absolute dimensions of the eclipsing system are deduced and its present state is compared with tracks for single star and conservative close binary evolution. Finally, we examine the possible reconciliation of two different calculations of the luminosity of the hot spot and a re-interpretation of the secular term of the period variability.