The Period Changes of the Cepheid RT Aurigae

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 the Cepheid are necessary to confirm the long-term trend and to provide data for a proper spectroscopic solution to the orbit.