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

S. E. de Mink, O. R. Pols+1 more|ArXiv.org|Mar 19, 2007

Stellar, planetary, and galactic studies26 references79 citations

TL;DR

This study constrains mass transfer efficiency (β) in massive close binaries using 50 double-lined eclipsing binaries in the Small Magellanic Cloud. By comparing detailed binary evolution models with observed stellar parameters—especially temperature ratios and flux ratios—it finds no single β value explains all systems, indicating non-conservative mass transfer is essential and β varies with system properties.

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.

Motivation & Objective

• To determine the efficiency of mass transfer (β) in massive close binaries undergoing case A mass transfer.
• To test whether conservative mass transfer (β = 1) can explain observed properties of double-lined eclipsing binaries in the Small Magellanic Cloud.
• To identify systematic discrepancies between models and observations that could constrain mass transfer physics.
• To assess the potential of surface abundance measurements (N/C ratio) in further constraining β.
• To evaluate the impact of initial orbital separation and mass ratio on mass transfer efficiency.

Proposed method

• Generated a grid of ~20,000 detailed binary evolution tracks for primary masses 3.5–35 M☉ and orbital periods 1–5 days at Z = 0.004.
• Simulated both conservative (β = 1) and non-conservative mass transfer (β < 1) with a parametrized angular momentum loss.
• Used least-squares fitting to match model evolution tracks to individual observed systems based on fundamental parameters.
• Employed I-band flux ratios and temperature ratios derived from light-curve solutions as key observables.
• Compared model predictions for radius ratios (R_D/R_A), temperature ratios, and mass ratios to observed values.
• Assessed the potential of high-resolution spectroscopy for improved temperature and surface abundance (N/C) determinations.

Experimental results

Research questions

• RQ1 Can conservative mass transfer (β = 1) reproduce the observed properties of massive semi-detached eclipsing binaries in the SMC?
• RQ2 What range of mass transfer efficiency β is required to match the observed temperature ratios in semi-detached systems?
• RQ3 Do systems with initially wider orbits show better agreement with non-conservative models, suggesting a role for spin-up or tidal effects?
• RQ4 How do discrepancies in radius ratios and temperature ratios inform the physical mechanisms of mass transfer?
• RQ5 Can surface abundance ratios (N/C) from high-resolution spectroscopy provide additional constraints on β?

Key findings

• Conservative mass transfer (β = 1) fails to explain the observed temperature ratios in many semi-detached systems, which are more extreme than predicted.
• No single value of β can explain all 17 semi-detached systems that could be matched, indicating β is not universal across case A binaries.
• Systems with initially wider orbits show better agreement with non-conservative models, suggesting spin-up or tidal interactions may influence β.
• The duration of the slow mass transfer phase increases under non-conservative evolution, potentially allowing statistical tests via detached vs. semi-detached system counts.
• Discrepancies in radius ratios (R_D/R_A) and temperature-mass combinations suggest accretor radii are often under-predicted in models.
• High-resolution spectroscopy for accurate temperature and N/C abundance measurements is essential to further constrain β, as surface abundances reflect deeper mixing during non-conservative mass transfer.