Forty eclipsing binaries in the Small Magellanic Cloud: fundamental parameters and Cloud distance

By Tim Harries, R. Hilditch, I. Howarth. 2003

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We have conducted a programme to determine the fundamental parameters of a substantial number of eclipsing binaries of spectral types O and B in the Small Magellanic Cloud (SMC). New spectroscopic data, obtained with the two- degree- field (2dF) multi- object spectrograph on the 3.9- m Anglo- Australian Telescope, have been used in conjunction with photometry from the Optical Gravitational Lens Experiment (OGLE- II) data base of SMC eclipsing binaries. Previously we reported results for 10 systems; in this second and concluding paper we present spectral types, masses, radii, temperatures, surface gravities and luminosities for the components of a further 40 binaries. The uncertainties are typically +/- 10 per cent on masses, +/- 4 per cent on radii and +/- 0.07 on log L. The full sample of 50 OB- type eclipsing systems is the largest single set of fundamental parameters determined for high- mass binaries in any galaxy. We find that 21 of the systems studied are in detached configurations, 28 are in semidetached post- mass- transfer states, and one is a contact binary.The overall properties of the detached systems are consistent with theoretical models for the evolution of single stars with SMC metal abundances (Z similar or equal to 0.004); in particular, observed and evolutionary masses are in excellent agreement. Although there are no directly applicable published models, the overall properties of the semidetached systems are consistent with them being in the slow phase of mass transfer in case A. About 40 per cent of these semidetached systems show photometric evidence of orbital- phase- dependent absorption by a gas stream falling from the inner Lagrangian point on the secondary star towards the primary star. This sample demonstrates that case- A mass transfer is a common occurrence amongst high- mass binaries with initial orbital periods P less than or similar to 5 d, and that this slow phase has a comparable duration to the detached phase preceding it.Each system provides a primary distance indicator. We find a mean distance modulus to the SMC of 18.91 +/- 0.03 +/- 0.1 (internal and external uncertainties; D = 60.6 +/- 1.0 +/- 2.8 kpc). This value represents one of the most precise available determinations of the distance to the SMC.

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Citations in the corpus

Rotational mixing in massive binaries - Detached short-period systems (2009, methodology): “With the Small Magellanic Cloud sample of double-lined eclipsing binaries by Harries et al. (2003) and Hilditch et al. (2005) in mind, which contains 21 detached systems3 with orbital periods ranging from 1–4 days and primary masses ranging from 7–23 M , we chose to model the following binary…”
The VLT-FLAMES survey of massive stars: observations centered on the Magellanic Cloud clusters NGC 330, NGC 346, NGC 2004, and the N11 region (2006, methodology): “…types, and from Balona (1994) for the cooler stars; the ratio of total to selective extinction (R) in the LMC was taken as 3.1 (e.g. Howarth 1983) and as 2.7 in the SMC (Bouchet et al. 1985); distance moduli were taken as 18.5 to the LMC (e.g. Gibson 2000) and 18.9 to the SMC (Harries et al. 2003).”
CLUSTERING OF LOCAL GROUP DISTANCES: PUBLICATION BIAS OR CORRELATED MEASUREMENTS? III. THE SMALL MAGELLANIC CLOUD (2014, methodology): “The latter authors refer to Harries et al. (2003) to support their claim of a 0.10 mag systematic uncertainty.”