Spectral classification and properties of the O Vz stars in the Galactic O-Star Spectroscopic Survey (GOSSS)

Arias, Julia I.; Walborn, Nolan R.; Simon-Diaz, Sergio; Barba, Rodolfo H.; Maiz Apellaniz, Jesus; Sabin-Sanjulian, Carolina; Gamen, Roberto C.; Morrell, Nidia I.; Sota, Alfredo; Marco, Amparo; Negueruela, Ignacio; Leao, Joao R. S.; Herrero, Artemio; Alfaro, Emilio J.
The Astronomical Journal, Volume 152, Issue 2, article id. 31, pp. (2016).


On the basis of the Galactic O Star Spectroscopic Survey (GOSSS), we present a detailed systematic investigation of the O Vz stars. The currently used spectral classification criteria are rediscussed, and the Vz phenomenon is recalibrated through the addition of a quantitative criterion based on the equivalent widths of the He i λ4471, He ii λ4542, and He ii λ4686 spectral lines. The GOSSS O Vz and O V populations resulting from the newly adopted spectral classification criteria are comparatively analyzed. The locations of the O Vz stars are probed, showing a concentration of the most extreme cases toward the youngest star-forming regions. The occurrence of the Vz spectral peculiarity in a solar-metallicity environment, as predicted by the fastwind code, is also investigated, confirming the importance of taking into account several processes for the correct interpretation of the phenomenon.