The Period Changes of the Cepheid RT Aurigae
David G. Turner, Ivan S. Bryukhanov, Igor I. Balyuk, Alexey M. Gain,, Roman A. Grabovsky, Valery D. Grigorenko, Igor V. Klochko, Attila Kosa-Kiss,, Alexey S. Kosinsky, Ivan J. Kushmar, Vyacheslav T. Mamedov, Natalya A., Narkevich, Andrey J. Pogosyants, Andrey S. Semenyuta

TL;DR
This study analyzes the period changes of the Cepheid RT Aurigae, revealing a long-term increase and evidence of a binary companion affecting its observed pulsation period.
Contribution
It provides the first evidence of a long-term period increase and sinusoidal variations due to a binary companion in RT Aur, with new orbital parameters derived from O-C analysis.
Findings
Period increase of +0.082 s/yr since 1980
Sinusoidal O-C variations suggest binary orbit
Derived orbital period of approximately 72 years
Abstract
Observations of the light curve for the 3.7-day Cepheid RT Aur both before and since 1980 indicate that the variable is undergoing an overall period increase, amounting to +0.082 +-0.012 s/yr, rather than a period decrease, as implied by all observations prior to 1980. Superposed on the star's O-C variations is a sinusoidal trend that cannot be attributed to random fluctuations in pulsation period. Rather, it appears to arise from light travel time effects in a binary system. The derived orbital period for the system is P = 26,429 +-89 days (72.36 +-0.24 years). The inferred orbital parameters from the O-C residuals differ from those indicated by existing radial velocity data. The latter imply the most reasonable results, namely a1 sin i = 9.09 (+-1.81) x 10^8 km and a minimum secondary mass of M2 = 1.15 +-0.25 Msun. Continued monitoring of the brightness and radial velocity changes in…
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