Extension and validation of the ZPEKTR code for determining the inclination angles of Be stars

Classical Be stars are non-supergiant B-type stars that rotate at a significant fraction of their critical velocity and are surrounded by an equatorial circumstellar gas disc. Their rapid rotation induces significant geometrical oblateness and gravity darkening. As a consequence, the emergent spectrum depends not only on the fundamental stellar parameters but also on the inclination angle. We aim to assess the reliability of the code for determining inclination angles as a function of the stellar rotation rate, identify the minimum rotation rate required to obtain reliable results, and extend our previous analysis aimed at deriving consistent stellar parameters to a sample of 21 classical Be stars. ZPEKTR We evaluated the reliability of the method using noise-injection tests on synthetic spectra spanning a broad range of rotational rates and inclination angles, with multiple statistically independent noise realisations at S/N code, covering the atmospheric and rotational parameter space of classical Be stars. The stellar and rotational parameters were derived through the ,łambdałambda, 4388, 4471, 6678 Å line profiles, after excluding lines affected by circumstellar disc contamination. The method was applied to 21 classical Be stars using archival BeSOS/PUCHEROS spectra and new observations from the LCO/NRES network. Next, we constructed a grid of gravity-darkened synthetic spectra using the ZPEKTR minimisation of the He I The rotation rate was reliably recovered across the tested inclinations, whereas the recovery of the inclination angle improved in line with an increasing rotation rate. Reliable inclination angle estimates were obtained for V/V_ ̊m c ≥ 0.46. When applied to our sample of Be stars, the derived inclination angles reveal an excellent agreement with independent interferometric measurements, with R^ 2 =0.985. The code provides a promising spectroscopic method for constraining the inclination angles and rotational properties of rapidly rotating massive stars, offering a practical alternative to interferometric observations for larger samples. ZPEKTR