Galactic Algols Project

Using high-resolution, multi-epoch spectroscopy to pin down mass-transfer efficiency in massive Algol binaries.

FEROS @ ESO/MPG 2.2 m
Mass transfer in an Algol binary: stream from donor to disc around accretor.
Artist’s impression of an Algol-type binary: gas overflows from the donor star (left) and feeds a disc around the accretor (right).
Image: Jaime Villaseñor (generated with GPT-5 and Google AI Studio, 2025). Licensed under CC BY 4.0.

Overview

Most massive stars (M ≳ 8 M☉) live in binaries and many exchange mass—a process that reshapes their spins, orbits, and final fates. The efficiency of that mass transfer remains one of the biggest unknowns in binary-evolution models. This project searches for mass-transferring Algol systems (semi-detached binaries) at high spectral resolution and over multiple epochs to measure precise orbits, component spectra, and atmospheric parameters, to confronts detailed evolution models.

At a glance
• Telescope/instrument: ESO/MPG 2.2 m + FEROS (R≈48 000, 360–920 nm)
• Time awarded: 76 h in P113 and 92 h in P114
• Sample: 98 southern Algol/semidetached candidates, V ≲ 11, periods ≲ 12 d, earlier than B3
• Observing strategy: 8 epochs per target; individual S/N = 90 at 4000 Å to reach combined S/N ≈ 250 for spectral disentangling.
• Status: Student-led (F. Wallauer) first analysis (RV variability and initial orbital solutions) underway

Science goals

1) Constrain mass-transfer efficiency. Compare measured mass ratios (q), periods (P), and component properties against grids of detailed binary-evolution models to discriminate between conservative and non-conservative mass transfer pathways.

2) Recover component spectra. Use spectral disentangling to isolate both stars, then fit for Teff, log g, v sin i, and key abundances (He, N) to identify interaction products (stripped/bloated donors).

3) Build a benchmark sample. Massive Algols with well-measured parameters are surprisingly rare; this programme aims to deliver a homogeneous set suitable for constraining binary interactions and evolution.

Methods

  • RVs & orbits. Line-profile fitting to obtain RVs for SB1 and SB2 systems; full orbital solutions.
  • Spectral disentangling. Separate composite spectra into primary/secondary contributions; recover K1, K2 and flux ratios directly from the data.
  • Atmosphere analysis. Joint fitting of both components with non-LTE models to obtain Teff, log g, v sin i, He/N abundances and masses.

Team & roles

  • PI / lead: Jaime Villaseñor (programme design, RV/orbital pipeline; disentangling; atmosphere analysis).
  • Student: Farah Wallauer (MPIA Summer Intern) leading the first pass on RVs and orbital solutions (2025).
  • Collaborators: Koushik Sen (University of Arizona), Norbert Langer (Universität Bonn)

Key results (so far)

  • Survey set-up: target sample and observing strategy defined (98 candidates; multi-epoch FEROS spectroscopy).
  • First-pass results: RV variability screening and initial orbital solutions underway (student-led).

Publications

No publications found.

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