  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, the past of the Sun and the solar system. This is also important for
the atmospheric evolution of the inner planets, Earth in particular. 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. Our results show a
significant decrease in the magnetic field strength and energy as the stellar
age increases from 100Myr to 250Myr while there is no significant age
dependence of the mean magnetic field strength for stars with ages 250-650Myr.
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 has the weakest strength compared to the radial and azimuthal
field components in 15 out 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 do show a twice as strong octupole component compared to
the quadrupole component. This is only seen in one out of 13 maps of the
younger stars. One star, chi1 Ori displays two field polarity switches during
almost 5 years of observations suggesting a magnetic cycle length of either 2,
6 or 8 years.
