A comprehensive analysis of the magnetic standard star HD 94660: Host of a massive compact companion?⋆
1 Max-Planck Insitut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
2 ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
3 Armagh Observatory, College Hill, Armagh, BT61 9DG, Northern Ireland, UK
4 Department of Physics and Astronomy, The University of Western Ontario, London, Ontario, N6A 3K7, Canada
Received: 11 November 2014
Accepted: 24 January 2015
Aims. Detailed information about the magnetic geometry, atmospheric abundances and radial velocity variations has been obtained for the magnetic standard star HD 94660 based on high-dispersion spectroscopic and spectropolarimetric observations from the UVES, HARPSpol and ESPaDOnS instruments.
Methods. We perform a detailed chemical abundance analysis using the spectrum synthesis code ZEEMAN for a total of 17 elements. Using both line-of-sight and surface magnetic field measurements, we derive a simple magnetic field model that consists of dipole, quadrupole and octupole components.
Results. The observed magnetic field variations of HD 94660 are complex and suggest an inhomogeneous distribution of chemical elements over the stellar surface. This inhomogeneity is not reflected in the abundance analysis, from which all available spectra are modelled, but only a mean abundance is reported for each element. The derived abundances are mostly non-solar, with striking overabundances of Fe-peak and rare-earth elements. Of note are the clear signatures of vertical chemical stratification throughout the stellar atmosphere, most notably for the Fe-peak elements. We also report on the detection of radial velocity variations with a total range of 35 km s-1 in the spectra of HD 94660. A preliminary analysis shows the most likely period of these variations to be of order 840 d and, based on the derived orbital parameters of this star, suggests the first detection of a massive compact companion for a main sequence magnetic star.
Conclusions. HD 94660 exhibits interestingly complex magnetic field variations and remarkable radial velocity variations. Long term monitoring is necessary to provide further constraints on the nature of these radial velocity variations. Detection of a companion will help establish the role of binarity in the origin of magnetism in stars with radiative envelopes.
Key words: stars: abundances / stars: magnetic field / stars: chemically peculiar / binaries: spectroscopic
Based in part on our own observations made with the European Southern Observatory (ESO) telescopes under the ESO programme 093.D-0367(A) and programmes 076.D-0169(A), 088.D-0066(A), 087.D-0771(A), 084.D-0338(A), 083.D-1000(A) and 60.A-9036(A), obtained from the ESO/ST-ECF Science Archive Facility. It is also based in part on observations carried out at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Science de l’Univers of the Centre National de la Recherche Scientifique of France and the University of Hawaii.
© ESO, 2015