摘要：Aims. The goal of this work is to study the magnetic fields of six young
solar-analogue stars both individually, and collectively, to search for possible magnetic
field trends with age. If such trends are found, they can be used to understand magnetism
in the context of stellar evolution of solar-like stars and to understand the past of the
Sun and the solar system. This is also important for the atmospheric evolution of the
inner planets, Earth in particular.
Methods. We used Stokes IV data from two different spectropolarimeters,
NARVAL and HARPSpol. The least-squares deconvolution multi-line technique was used to
increase the signal-to-noise ratio of the data. We then applied a modern Zeeman-Doppler
imaging code in order to reconstruct the magnetic topology of all stars and the brightness
distribution of one of our studied stars.
Results. Our results show a significant decrease in the magnetic field
strength and energy as the stellar age increases from 100 Myr to 250 Myr, while there is
no significant age dependence of the mean magnetic field strength for stars with ages
250−650 Myr. The spread in
the mean field strength between different stars is comparable to the scatter between
different observations of individual stars. The meridional field component is weaker than
the radial and azimuthal field components in 15 of the 16 magnetic maps. It turns out that
89−97% of the magnetic field
energy is contained in l = 1 −
3. There is also no clear trend with age and distribution of field
energy into poloidal/toroidal and axisymmetric/non-axisymmetric components within the
sample. The two oldest stars in this study show an octupole component that is twice as
strong as the quadrupole component. This is only seen in 1 of the 13 maps of the younger
stars. One star, χ1 Ori, displays two field polarity
switches during almost 5 yr of observations suggesting a magnetic cycle length of 2, 6, or
8 yr.
关键词：polarization;magnetic fields;stars: late-type;stars: general
