Misc,
The magnetic field of the double-lined spectroscopic binary system HD 5550
(Jan 28, 2016)
Abstract
(Abridged) In the framework of the BinaMicS project, we have begun a study of
the magnetic properties of a sample of intermediate-mass and massive
short-period binary systems, as a function of binarity properties. We report in
this paper the characterisation of the magnetic field of HD 5550, a
double-lined spectroscopic binary system of intermediate-mass, using
high-resolution spectropolarimetric Narval observations of HD 5550. We first
fit the intensity spectra using Zeeman/ATLAS9 LTE synthetic spectra to estimate
the effective temperatures, microturbulent velocities, and the abundances of
some elements of both components, as well as the light-ratio of the system. We
then fit the least-square deconvolved \$I\$ profiles to determine the radial and
projected rotational velocities of both stars. We then analysed the shape and
evolution of the LSD \$V\$ profiles using the oblique rotator model to
characterise the magnetic fields of both stars.
We confirm the Ap nature of the primary, previously reported in the
literature, and find that the secondary displays spectral characteristics
typical of an Am star. While a magnetic field is clearly detected in the lines
of the primary, no magnetic field is detected in the secondary, in any of our
observation. If a dipolar field were present at the surface of the Am star, its
polar strength must be below 40 G. The faint variability observed in the Stokes
\$V\$ profiles of the Ap star allowed us to propose a rotation period of
\$6.84\_-0.39^+0.61\$ d, close to the orbital period (\$\sim\$6.82 d),
suggesting that the star is synchronised with its orbit. By fitting the
variability of the \$V\$ profiles, we propose that the Ap component hosts a
dipolar field inclined with the rotation axis at an angle \$\beta=156\pm17\$
\$^\circ\$ and a polar strength \$B\_d=65 20\$ G. The field strength is
the weakest known for an Ap star.
