We present a new optical spectroscopic study of the O-type binary HD 165052 based on high- and intermediate-resolution CCD observations .
We re-investigated the spectral classification of the binary components , obtaining spectral types of O6.5 V and O7.5 V for the primary and secondary , respectively , finding that both stars display weak C iii \lambda 5696 emission in their spectra .
We also determined a radial-velocity orbit for HD 165052 with a period of 2.95510 \pm 0.00001 d , and semiamplitudes of 94.8 and 104.7 \pm 0.5 km s ^ { -1 } , resulting in a mass ratio Q = 0.9 .
From a comparison with previous radial-velocity determinations , we found evidence of apsidal motion in the system .
Several signatures of wind-wind collision , such as phase-locked variability of the X-ray flux and the Struve-Sahade effect , are also considered .
It was also found that the reddening in the region should be normal , in contrast with previous determinations .