  Recent studies of solar-type superflare stars have suggested that even old
slowly rotating stars similar to the Sun can have large starspots and
superflares. We conducted high dispersion spectroscopy of 49 nearby
solar-analog stars (G-type main sequence stars with
$T_{\rm{eff}}\approx5,600\sim6,000$ K) identified as ROSAT soft X-ray sources,
which are not binary stars from the previous studies. We expected that these
stars can be used as a proxy of bright solar-analog superflare stars, since
superflare stars are expected to show strong X-ray luminosity. More than half
(37) of the 49 target stars show no evidence of binarity, and their atmospheric
parameters ($T_{\rm{eff}}$, $\log g$, and [Fe/H]) are within the range of
ordinary solar-analog stars. We measured Ca II 8542 and H$\alpha$ lines, which
are good indicators of the chromospheric activity. The intensity of these lines
indicates that all the target stars have large starspots. We also measured
$v\sin i$ (projected rotational velocity) and Lithium abundance for the target
stars. Li abundance is a key to understanding the evolution of the stellar
convection zone, which reflects the stellar age, mass and rotational history.
We confirmed that many of the target stars rapidly rotate and have high Li
abundance, compared with the Sun, as suggested by many previous studies. There
are, however, also some target stars that rotate slowly ($v\sin i$=2$\sim$3 km
s$^{-1}$) and have low Li abundance like the Sun. These results support that
old and slowly rotating stars similar to the Sun could have high activity level
and large starspots. This is consistent with the results of our previous
studies of solar-type superflare stars. In the future, it is important to
conduct long-term monitoring observations of these active solar-analog stars in
order to investigate detailed properties of large starspots from the viewpoint
of stellar dynamo theory.
