Apsidal motion and TESS light curves of three southern close eccentric eclipsing binaries: GM Nor, V397 Pup, and PT Vel

The study of apsidal motion in eccentric eclipsing binaries provides an important observational test of theoretical models of stellar structure and evolution. New ground-based and space-based photometric data have been obtained and archival spectroscopic measurements were used in this study of three detached early-type and southern-hemisphere eccentric eclipsing binaries GM Nor (P = 1(d).88, e = 0.05), V397 Pup (3(d).00, 0.30), and PT Vel (1(d).80, 0.12). Their TESS observations in several sectors have also been included and the corresponding light curves were solved using the PHOEBE code. As a result, new accurate photoelectric times of minimum light have been obtained. The newly completed O - C diagrams were analyzed using all reliable timings found in the literature and calculated using the TESS light curves. New or improved values for the elements of apsidal motion were obtained. Using ESO archive spectroscopy, for V397 Pup, the precise absolute parameters were newly derived: M-1 = 3.076(35) M-circle dot, M-2 = 2.306(35) M-circle dot, and R-1 = 2.711(55) R-circle dot, R-2 = 1.680(55) R-circle dot. For PT Vel the absolute dimensions were improved: M-1 = 2.204(25) M-circle dot, M-2 = 1.638(25) M-circle dot, and R-1 = 2.108(30) R-circle dot, R-2 = 1.605(30) R-circle dot. For GM Nor, the less accurate absolute parameters based on the light curve analysis were evaluated: M-1 = 1.94(15) M-circle dot, M-2 = 1.84(14) M-circle dot, and R-1 = 2.27(20) R-circle dot, R-2 = 2.25(20) R-circle dot. We found more precise and relatively short periods of apsidal motion of about 80, 335, and 160 years, along with the corresponding internal structure constants, log k(2), -2.524, -2.361, and -2.563, for GM Nor, V397 Pup, and PT Vel, respectively. Relativistic effects are small but not negligible, making up to 10% of the total apsidal motion rate in all systems. No marks of the presence of the third body were revealed in the light curves, on the O - C diagrams, or in the reduced spectra of the eccentric systems studied here.