HD 66051, an eclipsing binary hosting a highly peculiar, HgMn-related star

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 (T eff = 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 (T eff ~ 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.

New and improved rotational periods of magnetic CP stars from ASAS-3, KELT, and MASCARA data

“…We have identified four eclipsing binary systems among our targets, which are potentially of great interest because mCP stars are very rarely found in close binary systems, particularly eclipsing ones (Renson & Manfroid 2009;Niemczura et al 2017;Kochukhov et al 2018). Using archival spectra, we find strong evidence that the system of HD 252519 indeed harbours an mCP star component; all other systems should be investigated with time-resolved spectroscopy for confirmation.…”

“…No secondary variability due to ACV-type rotational variability of one (or both) components could be identified. mCP stars are very rarely found in close binary systems, in particular eclipsing ones (Niemczura et al 2017;Kochukhov et al 2018); if proven that at least one component of this system is indeed a CP2 star, as suggested by the spectral type, HD 244391 would be an object of high interest. We therefore strongly encourage spectroscopic and spectropolarimetric studies to shed more light on the nature of the HD 244391 system.…”

Orbital parameters and evolutionary status of the highly peculiar binary system HD 66051

“…The reductions were performed with the MAXIM DL program 1 and the determination of magnitudes using the LesvePhotometry program 2 . These data have been presented in Niemczura et al (2017), although without further analysis and model fitting.…”

“…-Five spectra from the HIgh-Dispersion Echelle Spectrograph (HIDES) at the 1.88m telescope of the Okayama Astrophysical Observatory (OAO) in Japan, R ∼ 50 000, 4090Å to 7520Å, taken during two runs between February and April 2017. The in-eclipse observation procured with the same instrument and employed by Niemczura et al (2017) was taken during the same time, but we did not use it here. -Six spectra from the REOSC spectrograph at the 2.15m telescope of CASLEO in Argentina, R ∼ 12 000, 4150Å to 5750Å, taken during two nights in May 2017.…”

“…Niemczura et al (2017) published detailed abundances of this binary system, which consists of a highly peculiar CP3 primary and an A-type secondary and boasts an orbital period of about 4.75 d. Outof-eclipse variability with the same period was identified and attributed to rotational modulation caused by chemical spots. The unique configuration of HD 66051 allows studying phenomena such as atmospheric structure, mass transfer, magnetic fields, photometric variability, and the origin of chemical anomalies observed in CP3 stars and related objects (Niemczura et al 2017). Furthermore, the study of the system during eclipses allows precise ZeemanDoppler imaging of the components (Hubrig & Mathys 1995).…”