R Canis Majoris is the prototype of a small group of Algol-type stars showing short orbital periods and low mass ratios .
A previous detection of short-term oscillations in its light curve has not yet been confirmed .
We investigate a new time series of high-resolution spectra with the aim to derive improved stellar and system parameters , to search for the possible impact of a third component in the observed spectra , to look for indications of activity in the Algol system , and to search for short-term variations in radial velocities .

We disentangled the composite spectra into the spectra of the binary components .
Then we analysed the resulting high signal-to-noise spectra of both stars .
Using a newly developed program code based on an improved method of least-squares deconvolution , we were able to determine the radial velocities of both components also during primary eclipse .
This allowed us to develop a better model of the system including the Rossiter–McLaughlin effect and to derive improved orbital parameters .
Combining the results with those from spectrum analysis , we obtain accurate stellar and system parameters .
We further deduce at least one oscillation frequency of 21.38 c d ^ { -1 } .
It could be detected during primary eclipses only and confirms a previous photometric finding .
Results point to an amplitude amplification of non-radial pulsation modes due to the eclipse mapping effect .
The presence of a He I line in the spectra indicates mass transfer in the R CMa system .
Calculations of its Roche geometry give evidence that the cool secondary component may fill its Roche lobe .
No evidence of a third body in the system could be found in the observed spectra .