G.A. Wade 1,2,
Y. Debernardi 3,
G. Mathys 4,
D.A. Bohlender 5,
G.M. Hill 6 and
J.D. Landstreet 7
Received 25 April 2000 / Accepted 24 July 2000
We present a detailed investigation of the orbit, component characteristics and magnetic field of the single spectrum (SB1), visual Ap binary HD 81009.
By simultaneously modeling new and archival radial velocity measurements and new and archival speckle interferometric measurements (obtained with the CHARA array) we obtain a unique model of the orbital geometry and constraints on the component masses of HD 81009. Additional constraints provided by the Hipparcos parallax and component magnitude difference and the optical spectral energy distribution allow us to determine a self-consistent solution for the basic physical properties of the components. HD 81009 is a highly eccentric (), long-period ( y) binary composed of two main sequence A-type stars. While its presence is required in order to explain the astrometric and photometric observations, the cooler secondary component is never detected spectroscopically, and is therefore inferred to rotate somewhat more rapidly than the hotter component.
The hotter primary component is identified as the slowly-rotating () magnetic Ap star. We have modeled the magnetic field geometry of this star using new and archival longitudinal magnetic field and mean magnetic field modulus observations. The rotational variations of the magnetic quantities are consistent with a decentered dipole surface magnetic field geometry with small magnetic obliquity (). This is consistent with the observation of Landstreet & Mathys (2000), who report that nearly all magnetic Ap stars with periods longer than around 25 days exhibit , implying that their magnetic fields are approximately aligned with their rotational axes.
Key words: polarization stars: binaries: general stars: chemically peculiar stars: individual: HD 81009 stars: magnetic fields
* Based on observations obtained at the European Southern Observatory (La Silla, Chile), the Haute Provence and Pic du Midi Observtories (France), and the Las Campanas Observatory (Chile)
Send offprint requests to: G.A. Wade (email@example.com)
© European Southern Observatory (ESO) 2000
Online publication: October 10, 2000