Critical study of the distribution of rotational velocities of Be stars. I: Deconvolution methods, effects due to gravity darkening, macro-turbulence and binarity.

ZOREC, J.; ROYER, F.; FREMAT, Y.; SEMAAN, T.; CIDALE, L.; ARIAS, M. L.; MARTAYAN, C.; AIDELMAN, Y.; DOMINICIANO DE SOUZA, A.; HUBERT, A. M.; COCHETTI, Y.; STEE, P.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2016 vol. 595 p. 1 - 26

0004-6361

Context. Among massive and of intermediate-mass stars, Be stars are the fastest rotators in the main sequence (MS), and as such, a cornerstoneto validate models of structure and evolution of rotating stars. However, several phenomena induce under- or over-estimations either of theirapparent Vsin i, or ?true? velocity V.Aims. In the present contribution we aim at obtaining distributions of true rotational velocities corrected for systematic eects induced by therapid rotation itself, macro-turbulent velocities, and binarity.Methods. We study a set of 233 Be stars by assuming they have inclination angles distributed at random. A critical discussion is carried on Cranmer?s and Lucy-Richardson?s methods that enable to transform a distribution of projected into another of true rotational velocities, where the gravitational darkening eect on the Vsin i parameter is considered in dierent ways. We conclude that Lucy-Richardson?s iterative algorithm responds at best to the purposes of the present work, but it requires a thorough determination of the stellar fundamental parameters.Results. We conclude that once the mode of ratios of true velocities of Be stars attains the value V=Vc ´ 0:77 in the MS evolutionary phase,it remains unchanged up to the end of the MS lifespan. When Be stars in all MS evolutionary stages are considered together, the statisticalcorrections carried on the distribution of ratios V=Vc for over-estimations of Vsin i due to macro-turbulent motions and binarity, produce a shiftof this distribution towards lower values of V=Vc. The mode of the final distribution obtained is at V=Vc ´ 0:65. It has a nearly symmetricdistribution and shows that the Be phenomenon is characterized by a wide range of true velocity ratios: 0:3 . V=Vc . 0:95. It Thus suggeststhat the probability for Be stars being critical rotators is extremely low.Conclusions. The corrections attempted in the present work represent a previous step to infer indications on the nature of the Be-star surfacerotation that will be studied in the second paper of this series.