  Context. The object HD 43587Aa is a G0V star observed during the 145-day
LRa03 run of the COnvection, ROtation and planetary Transits space mission
(CoRoT), for which complementary High Accuracy Radial velocity Planet Searcher
(HARPS) spectra with S/N>300 were also obtained. Its visual magnitude is 5.71,
and its effective temperature is close to 5950 K. It has a known companion in a
highly eccentric orbit and is also coupled with two more distant companions.
Aims. We undertake a preliminary investigation of the internal structure of HD
43587Aa. Methods. We carried out a seismic analysis of the star, using maximum
likelihood estimators and Markov Chain Monte Carlo methods. Results. We
established the first table of the eigenmode frequencies, widths, and heights
for HD 43587Aa. The star appears to have a mass and a radius slightly larger
than the Sun, and is slightly older (5.6 Gyr). Two scenarios are suggested for
the geometry of the star: either its inclination angle is very low, or the
rotation velocity of the star is very low. Conclusions. A more detailed study
of the rotation and of the magnetic and chromospheric activity for this star is
needed, and will be the subject of a further study. New high resolution
spectrometric observations should be performed for at least several months in
duration.
