Abstract
HD 66051 is an eclipsing system with an orbital period of about 4.75 d that exhibits out-of-eclipse variability with the same period. New multicolour photometric observations confirm the longevity of the secondary variations, which we interpret as a signature of surface inhomogeneities on one of the components. Using archival and newly acquired high-resolution spectra, we have performed a detailed abundance analysis. The primary component is a slowly rotating late B-type star (Teff = 12500 ± 200 K; log g = 4.0, v sin i = 27 ± 2 km s−1) with a highly peculiar composition reminiscent of the singular HgMn-related star HD 65949, which seems to be its closest analogue. Some light elements as He, C, Mg, Al are depleted, while Si and P are enhanced. Except for Ni, all the iron-group elements, as well as most of the heavy elements, and in particular the REE elements, are overabundant. The secondary component was estimated to be a slowly rotating A-type star (Teff ~ 8000 K; log g = 4.0, v sin i ~ 18 km s−1). The unique configuration of HD 66051 opens up intriguing possibilities for future research, which might eventually and significantly contribute to the understanding of such diverse phenomena as atmospheric structure, mass transfer, magnetic fields, photometric variability and the origin of chemical anomalies observed in HgMn stars and related objects.
Highlights
Peculiar (CP) stars comprise about 10% of upper main-sequence stars
We have identified numerous lines in the composite HARPS spectrum which are not observed in the HIDES spectrum of the primary star, namely various lines of Fe I, the strongest lines of C I, Mg I, Al I, Ca I, Mn I, Cr I, as well as lines of Sc II, Ti II, Cr II, Fe II, Sr II and Y II
While the observed abundance pattern follows the general characteristics of the HgMn stars, which are known to exhibit highly individualistic spectra and huge discrepancies in the abundances for a given element from one star to the some marked peculiarities are present, most notably the strong silicon overabundance and the lack of the odd-Z anomalies in the Cr-Mn-Fe and Sr-Y-Zr triplets
Summary
Peculiar (CP) stars comprise about 10% of upper main-sequence stars (spectral types early B to early F). For most groups of CP stars, the observed chemical peculiarities are attributed to atomic diffusion, i.e. the interplay of radiative levitation and gravitational settling operating in the calm radiative atmospheres of slowly rotating stars[2, 3]. The spot configurations on Ap stars remain stable for decades and more, which is probably a consequence of the magnetic field Another important group is made up of the so-called Mercury-Manganese (HgMn) stars[1]. As their name implies, these stars are characterized by their unusually strong lines of Hg and Mn. Numerous other peculiarities – like He, Ni or Al deficiency and overabundances of elements such as P, Ga and Xe – are regularly observed[14]. Binarity has been proposed to play a vital role in the development and understanding of the observed abundance patterns in HgMn stars
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