HD 96446: a long-period binary with a strongly magnetic He-rich primary with β Cephei pulsations^⋆

¹ Instituto de Ciencias Astronómicas, de la Tierra y del Espacio (CONICET-Universidad Nacional de San Juan), Casilla de Correo 49, 5400 San Juan, Argentina
e-mail: jfgonzalez@conicet.gov.ar
² Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
³ Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Allée du 6 Août 19C, Bât. B5C, 4000 Liège, Belgium
⁴ Institut für Astro- und Teilchenphysik, Universität Innsbruck, Technikerstr. 25/8, 6020 Innsbruck, Austria
⁵ Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium
⁶ Département d’astronomie de l’Université de Genève, Chemin des Maillettes 51, 1290 Versoix, Switzerland
⁷ Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
⁸ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁹ Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
¹⁰ Universitäts-Sternwarte München, Scheinerstr. 1, 81679 München, Germany

Received: 31 January 2019
Accepted: 17 April 2019

Abstract

Aims. HD 96446 is a magnetic B2p He-strong star that has been reported to be a β Cep pulsator. We present a detailed spectroscopic analysis of this object based on an intensive observational data set obtained in a multisite campaign with the spectrographs CORALIE, FEROS, and HARPS (La Silla); UVES (Paranal); HERCULES (Mt. John Observatory); and GIRAFFE (SAAO).

Methods. Radial velocities were measured by cross-correlations and analysed to detect periodic variations. On the other hand, the mean spectrum was fit with spectral synthesis to derive atmospheric parameters and chemical abundances.

Results. From the analysis of radial velocities, HD 96446 was found to be a spectroscopic binary with a period of 799 days. The stellar companion, which contributes only ∼5% of the total flux, is an A0-type star. A frequency analysis of the radial velocities allowed us to detect two pulsational modes with periods 2.23 h and 2.66 h. The main mode is most probably a low-inclination, dipole mode (l, m) = (1, 0), and the second pulsation mode corresponds to (l, m) = (2, 2) or to a pole-on (l, m) = (3, 2) configuration. In addition to radial velocities, the main pulsation mode is evidenced through small variations in the spectral morphology (temperature variations) and the light flux. The rotation period of 23.4 d, was detected through the variation in line intensities. Chemical abundances are unevenly distributed over the stellar surface, with helium concentrated at the negative magnetic pole and most metals strengthened at lower latitudes. The mean chemical abundance of helium is strongly abnormal, reaching a value of 0.60 (number fraction).