Résumé
With an orbital period of about 3.078 days, the double-lined spectroscopic binary HD 48099 is, until now, the only short-period O+O system known in the Mon OB2 association. Even though an orbital solution has already been derived for this system, few information are available about the individual stars. We present, in this paper, the results of a long-term spectroscopic campaign. We derive a new orbital solution and apply a disentangling method to recover the mean spectrum of each star. To improve our knowledge concerning both components, we determine their spectral classifications and their projected rotational velocities. We also constrain the main stellar parameters of both stars by using the CMFGEN atmosphere code and provide the wind properties for the primary star through the study of International Ultraviolet Explorer spectra. This investigation reveals that HD 48099 is an O5.5 V ((f)) + O9 V binary with M-1 sin(3) i = 0.70 M-circle dot and M-2 sin(3) i = 0.39 M-circle dot, implying a rather low orbital inclination. This result, combined with both a large effective temperature and log g, suggests that the primary star (v sin i similar or equal to 91 km s(-1)) is actually a fast rotator with a strongly clumped wind and a nitrogen abundance of about 8 times the solar value.