The Past and Future History of Regulus

TL;DR

This paper investigates the evolutionary history of the star Regulus, revealing its past interactions with a white dwarf companion and predicting its future binary evolution stages, including potential phases like sdB and AM CVn.

Contribution

It provides the first detailed evolutionary scenario for Regulus based on recent discovery of its white dwarf companion, including initial mass estimates and future evolution predictions.

Findings

Regulus has a white dwarf companion with a likely initial mass of 1.7 M_sun.

The system's age exceeds 1 Gyr based on evolutionary modeling.

Future evolution may include a common envelope, sdB, and AM CVn phases.

Abstract

We show how the recent discovery of a likely close white dwarf companion to the well known star Regulus, one of the brightest stars in the sky, leads to considerable insight into the prior evolutionary history of this star, including the cause of its current rapid rotation. We infer a relatively narrow range for the initial masses of the progenitor system: M_{10} = 2.3 +/- 0.2 M_sun and M_{20} = 1.7 +/- 0.2 M_sun, where M_{10} and M_{20} are the initial masses of the progenitors of the white dwarf and Regulus, respectively. In this scenario, the age of the Regulus system would exceed 1 Gyr. We also show that Regulus, with a current orbital period of 40 days, has an interesting future ahead of it. This includes (i) a common envelope phase, and, quite possibly, (ii) an sdB phase, followed by (iii) an AM CVn phase with orbital periods < 1 hr. Binary evolution calculations are presented in support of this scenario. We also discuss alternative possibilities, emphasizing the present uncertainties in binary evolution theory. Thus, this one particular star system illustrates many different aspects of binary stellar evolution.