Abstract
We present phase-resolved spectroscopy and extensive survey photometry of the detached eclipsing binary system XY Cet, which is composed of two metallic-lined stars. We measure their masses to be 1.773 ± 0.016 and 1.615 ± 0.014 M⊙ and their radii to be 1.873 ± 0.035 and 1.773 ± 0.029 R⊙, resulting in logarithmic surface gravities of 4.142 ± 0.016 and 4.149 ± 0.014 (cgs). We determine effective temperatures of 7870 ± 115 and 7620 ± 125 K. The projected rotational velocities are 34.4 ± 0.4 and 34.1 ± 0.4 km s−1, which are close to synchronous. Theoretical models cannot match all of these properties, but come closest for a solar helium and metal abundance and an age in the region of 850 Myr. We obtain the individual spectra of the two stars by the spectral disentangling method, and compare them to synthetic spectra calculated for the measured effective temperatures and a solar chemical composition. Both stars show enhanced abundances of iron-group elements and clear deficiencies of Ca i and Sc ii, confirming their classification as Am stars. We also find strong overabundances of Zr ii and the rare-earth species La ii, Ce ii and Nd ii, a hallmark of chemically peculiar A stars. XY Cet is a prime candidate for detailed spectroscopic analyses of metallic-lined stars whose masses and radii are known to accuracies of 1–2 per cent.
Highlights
Eclipsing binary star systems are of immense value as our primary source of empirical measurements of the properties of stars (Andersen 1991; Torres et al 2010)
We present phase-resolved spectroscopy and extensive survey photometry of the detached eclipsing binary system XY Cet, which is composed of two metallic-lined stars
We obtain the individual spectra of the two stars by the spectral disentangling method, and compare them to synthetic spectra calculated for the measured effective temperatures and a solar chemical composition
Summary
Eclipsing binary star systems are of immense value as our primary source of empirical measurements of the properties of stars (Andersen 1991; Torres et al 2010). Am stars are A stars which show photospheric abundance anomalies thought to be caused by radiative diffusion and gravitational settling (Michaud 1970; Turcotte et al 2000; Talon et al 2006) These effects are able to operate in the radiative atmospheres possessed by A stars with rotational velocities slower than roughly 100 km s−1 Am stars are preferentially found in short-period binaries where tidal effects have been able to slow their rotation (Abt 1961, 1965; Carquillat & Prieur 2007) This in turn means that Am stars are strongly represented among the well-studied dEBs1, such as β Aur (Southworth et al 2007), V364 Lac (Torres et al 1999), V624 Her (Popper 1984), V459 Cas (Lacy et al 2004), WW Cam (Lacy et al 2002) and RR Lyn (Tomkin & Fekel 2006). 8.115 ± 0.021 number of long-term variability surveys, in particular those which have the photometric precision to search for extrasolar planetary transits
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