An Evolutionary Considerations for V228 from 47 Tuc

TL;DR

This study models the evolutionary history of the binary system V228 from 47 Tuc, showing how initial parameters lead to its current state and highlighting the importance of orbital momentum loss.

Contribution

It presents a detailed evolutionary model for V228, identifying initial conditions and the role of orbital momentum loss in its formation.

Findings

V228 can originate from a low-mass binary with specific initial parameters.

The system loses about 50% of its initial orbital momentum during evolution.

The less massive star develops a small helium core and exchanges mass over nuclear timescales.

Abstract

We perform evolutionary calculations of binary stars to find progenitors of system with parameters similar to the eclipsing binary system V228. We show that a V228 binary system may be formed starting with an initial binary system which has a low main sequence star as an accretor. The initial parameters for the evolutionary model are as follow: $M_{1,i} = 0.88 M_\odot $, $M_{2,i} = 0.85 M_\odot $, $P_i=1.35 $days, $f_1$=0.05, $f_2$=4.65 and Z=0.006 ([Fe/H]=--0.67). We also show that the best fitting model implies loss of about 50 per cent of initial total orbital momentum but only 5 per cent of initial total mass. The less massive component have a small helium core of mass 0.12--0.17$ M_\odot $ and exchange mass in the nuclear time scale.