Spectroscopically resolving the Algol triple system

Algol (β Persei) is the prototypical semidetached eclipsing binary and a hierarchical triple system. From 2006 to 2010 we obtained 121 high-resolution and high signal-to-noise ratio echelle spectra of this object. Spectral disentangling yields the individual spectra of all three stars, and greatly improved elements both the inner and outer orbits. We find masses of MA = 3.39 ± 0.06 M, MB = 0.770 ± 0.009 M and MC = 1.58 ± 0.09 M. The disentangled spectra also give the light ratios between the components in the B and V bands. Atmospheric parameters for the three stars are determined, including detailed elemental abundances for Algol A and Algol C. We find the following effective temperatures: TA = 12 550 ± 120 K, TB = 4900 ± 300 K and TC = 7550 ± 250 K. The projected rotational velocities are vAsin iA = 50.8 ± 0.8 km s−1, vBsin iB = 62 ± 2 km s−1 and vCsin iC = 12.4 ± 0.6 km s−1. This is the first measurement of the rotational velocity for Algol B, and confirms that it is synchronous with the orbital motion. The abundance patterns of components A and C are identical to within the measurement errors, and are basically solar. They can be summarized as mean metal abundances: [M/H]A = −0.03 ± 0.08 and [M/H]C = 0.04 ± 0.09. A carbon deficiency is confirmed for Algol A, with tentative indications for a slight overabundance of nitrogen. The ratio of their abundances is (C/N)A = 2.0 ± 0.4, half of the solar value of (C/N) = 4.0 ± 0.7. The new results derived in this study, including detailed abundances and metallicities, will enable tight constraints on theoretical evolutionary models for this complex system