New high resolution spectra of the short period ( P \sim 1.76 days ) young detached binary LT CMa are reported for the first time .
By combining the results from the analysis of new radial velocity curves and published light curves , we determine values for the masses , radii and temperatures as follows : M _ { 1 } = 5.59 ( 0.20 ) M _ { \odot } , R _ { 1 } = 3.56 ( 0.07 ) R _ { \odot } and T _ { eff 1 } = 17000 ( 500 ) K for the primary and M _ { 2 } = 3.36 ( 0.14 ) M _ { \odot } , R _ { 2 } = 2.04 ( 0.05 ) R _ { \odot } and T _ { eff 2 } = 13140 ( 800 ) K for the secondary .
Static absorbtion features apart from those coming from the close binary components are detected in the several spectral regions .
If these absorbtion features are from a third star , as the light curve solutions support , its radial velocity is measured to be RV _ { 3 } = 70 ( 8 ) km s ^ { -1 } .

The orbit of the binary system is proved to be eccentric ( e = 0.059 ) and thus the apsidal motion exists .
The estimated linear advance in longitude of periastron corresponds to an apsidal motion of U = 69 \pm 5 yr for the system .
The average internal structure constant \log k _ { 2 ,obs } =–2.53 of LT CMa is found smaller than its theoretical value of \log k _ { 2 ,theo } =–2.22 suggesting the stars would have more central concentration in mass .
The photometric distance of LT CMa ( d = 535 \pm 45 pc ) is found to be much smaller than the distance of CMa OB1 association ( 1150 pc ) which rules out membership .
A comparison with current stellar evolution models for solar metallicity indicates that LT CMa ( 35 Myr ) is much older than the CMa OB1 association ( 3 Myr ) , confirming that LT CMa is not a member of CMa OB1 .
The kinematical and dynamical analysis indicate LT CMa is orbiting the galaxy in a circular orbit and belongs to the young thin-disk population .