Rotational velocities of A-type stars - IV. Evolution of rotational velocities
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Context. In previous works of this series, we have shown that late B- and early A-type stars have genuine bimodal distributions of rotational velocities and that late A-type stars lack slow rotators. The distributions of the surface angular velocity ratio Ω/Ω crit (Ω crit is the critical angular velocity) have peculiar shapes according to spectral type groups, which can be caused by evolutionary properties. Aims. We aim to review the properties of these rotational velocity distributions in some detail as a function of stellar mass and age. Methods. We have gathered v sin i for a sample of 2014 B6- to F2-type stars. We have determined the masses and ages for these objects with stellar evolution models. The ( T eff ,log L / L ⊙ )-parameters were determined from the uvby – β photometry and the HIPPARCOS parallaxes. Results. The velocity distributions show two regimes that depend on the stellar mass. Stars less massive than 2.5 M ⊙ have a unimodal equatorial velocity distribution and show a monotonical acceleration with age on the main sequence (MS). Stars more massive have a bimodal equatorial velocity distribution. Contrarily to theoretical predictions, the equatorial velocities of stars from about 1.7 M ⊙ to 3.2 M ⊙ undergo a strong acceleration in the first third of the MS evolutionary phase, while in the last third of the MS they evolve roughly as if there were no angular momentum redistribution in the external stellar layers. The studied stars might start in the ZAMS not necessarily as rigid rotators, but with a total angular momentum lower than the critical one of rigid rotators. The stars seem to evolve as differential rotators all the way of their MS life span and the variation of the observed rotational velocities proceeds with characteristic time scales δt ≈ 0.2 t MS , where t MS is the time spent by a star in the MS.
Subfields: Astronomy and Astrophysics, Instrumentation
View Paper: https://www.semanticscholar.org/paper/46e00d06a87fed7e391c6d1134b88d5996a00e52
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Citations in the corpus
- Discovery of a warm, dusty giant planet around HIP 65426 (2017, methodology): “HIP 65426 is one of the fastest rotators known with similar spectral type (Zorec & Royer 2012) and is therefore likely viewed along mid- to high-inclinations with respect to the rotation axis.”
- The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics from 10 to 100 au (2019, methodology): “A mass-dependent Maxwellian distribution for the rotation rate v (Zorec & Royer 2012) 5.”