The magnetic Bp star 36 Lyncis

I. Magnetic and photospheric properties

¹ Department of Physics, Royal Military College of Canada, PO Box 17000, Station `Forces', Kingston, Ontario, K7K 4B4, Canada e-mail: Gregg.Wade@rmc.ca
² Computer Sciences Corporation/Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD, 21218, USA
³ National Research Council of Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC, V9E 2E7, Canada
⁴ Institute für Astronomie, Universitat Wien, Türkenschanzstrasse 17, 1180 Vienna, Austria
⁵ Institute of Astronomy, Russian Academy of Sciences, Pyatnitskaya 48, 109017 Moscow, Russia
⁶ David Dunlap Observatory, University of Toronto, PO Box 360, Richmond Hill, ON, L4C 4Y6, Canada
⁷ Department of Physics & Astronomy, The University of Western Ontario, London, Ontario, N6A 3K7, Canada
⁸ Max-Planck Institut für Aeronomie Max-Planck-Str. 2 37191 Katlenburg-Lindau, Germany
⁹ Department of Astronomy, University of Minnesota, 116 Church Street, S.E., Minneapolis, Minnesota 55455, USA
¹⁰ W. M. Keck Observatory, 65-1120 Mamalahoa Highway, Kamuela, HI, 96743, USA

Received: 22 December 2005
Accepted: 28 July 2006

Abstract

Aims.This paper reports the photospheric, magnetic and circumstellar gas characteristics of the magnetic B8p star 36 Lyncis (HD 79158).

Methods.Using archival data and new polarised and unpolarised high-resolution spectra, we redetermine the basic physical properties, the rotational period and the geometry of the magnetic field, and the photospheric abundances of various elements.

Results.Based on magnetic and spectroscopic measurements, we infer an improved rotational period of  d. We determine a current epoch of the longitudinal magnetic field positive extremum (HJD 2 452 246.033), and provide constraints on the geometry of the dipole magnetic field (,  G, β unconstrained). We redetermine the effective temperature and surface gravity using the optical and UV energy distributions, optical photometry and Balmer line profiles ( K, ), and based on the Hipparcos parallax we redetermine the luminosity, mass, radius and true rotational speed (, , ,  km s^-1). We measure photospheric abundances for 21 elements using optical and UV spectra, and constrain the presence of vertical stratification of these elements. We perform preliminary Doppler Imaging of the surface distribution of Fe, finding that Fe is distributed in a patchy belt near the rotational equator. Most remarkably, we confirm strong variations of the Hα line core which we interpret as due to occultations of the star by magnetically-confined circumstellar gas.