Physical properties of the quadruple system with early-type eclipsing binary

An early-type eclipsing binary turns out to be a hierarchical quadruple system. Analysis of its complex configuration, although not easy, yields masses, radii, and temperatures of the inner binary, and mass estimations of the two outermost components.

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Toward Early-type Eclipsing Binaries as Extragalactic Milestones. III. Physical Properties of the O-type Eclipsing Binary OGLE LMC-ECL-21568 in a Quadruple System

M. Taormina, R.P. Kudritzki, B. Pilecki, G. Pietrzyński, I.B. Thompson, J. Puls,M. Górski, B. Zgirski, D. Graczyk, W. Gieren, G. Hajdu

2024, ApJ 967, 64

These results come from a comprehensive study of an eclipsing O-type binary (Aa+Ab), OGLE LMC-ECL-21568, with the inner orbital period P_{orb, A} = 3.2254367 days that forms a higher-order hierarchical system in a configuration of (A+B)+C.

We derived masses, radii, and temperatures of the Aa+Ab binary, and by analysing their radial velocities, we found a spectroscopic orbit of A in the outer A+B system with P_{orb, A+B} = 195.8 days. In the O–C analysis, we found another component orbiting the A+B system with P_AB+C = 2550 days. From the total mass of the inner binary and its outer orbit, we estimated the mass of the third object, M_B = 10.7 M_⊙. From the light travel time effect fit to the O−C data, we obtained the limit for the mass of the fourth component, M_C = 7.3 M_⊙.

These extra components contribute about 20%–30% (increasing with wavelength) to the total system light. From the comparison of model spectra with the multiband photometry, we derived the distance modulus to the system of 18.59 ± 0.06 mag, and the reddening of 0.16 ± 0.02 mag.

This work is part of our ongoing project, which aims to calibrate the surface brightness-color relation for early type stars. Previous papers:

• Towards early-type eclipsing binaries as extragalactic milestones: II. NLTE spectral analysis and stellar parameters of the detached O-type system OGLE-LMC-ECL-06782 in the LMC
  M. Taormina, R.-P. Kudritzki, J. Puls, B. Pilecki, E. Sextl, G. Pietrzyński, M.A. Urbaneja, W. Gieren
  2020, ApJ, 890, 137
• Towards early-type eclipsing binaries as extragalactic milestones: I. Physical parameters of OGLE-LMC-ECL-22270 and OGLE-LMC-ECL-06782
  M. Taormina, G. Pietrzyński, B. Pilecki, R.-P. Kudritzki, I. B. Thompson, D. Graczyk, W. Gieren, N. Nardetto, M. Górski, K. Suchomska, B. Zgirski, P. Wielgórski, P. Karczmarek, W. Narloch
  2019, ApJ, 886, 111