Efficiency of mass transfer in massive close binaries, Tests from double-lined eclipsing binaries in the SMC

TL;DR

This study investigates the efficiency of mass transfer in massive close binaries in the SMC by comparing detailed binary evolution models with observations, revealing a wide range of efficiencies and highlighting the need for more precise data.

Contribution

The paper provides a comprehensive grid of binary evolution models and systematically compares them with observed binaries to constrain mass transfer efficiency in massive systems.

Findings

Good agreement for detached systems.

Large spread in efficiency for semi-detached systems.

Surface abundances could further constrain models.

Abstract

One of the major uncertainties in close binary evolution is the efficiency of mass transfer beta: the fraction of transferred mass that is accreted by a secondary star. We attempt to constrain the mass-transfer efficiency for short-period massive binaries undergoing case A mass transfer. We present a grid of about 20,000 detailed binary evolution tracks with primary masses 3.5-35 Msun, orbital periods 1-5 days at a metallicity Z=0.004, assuming both conservative and non-conservative mass transfer. We perform a systematic comparison, using least-squares fitting, of the computed models with a sample of 50 double-lined eclipsing binaries in the Small Magellanic Cloud, for which fundamental stellar parameters have been determined. About 60% of the systems are currently undergoing slow mass transfer. In general we find good agreement between our models and the observed detached systems. However, for many of the semi-detached systems the observed temperature ratio is more extreme than our models predict. For the 17 semi-detached systems that we are able to match, we find a large spread in the best fitting mass-transfer efficiency; no single value of beta can explain all systems. We find a hint that initially wider systems tend to fit better to less conservative models. We show the need for more accurate temperature determinations and we find that determinations of surface abundances of nitrogen and carbon can potentially constrain the mass-transfer efficiency further.