http://arxiv.org/abs/1805.11332
The second Gaia data release contains the identification of 147 535 rotation modulation variables candidates of the BY Dra class, together with their rotation period and modulation amplitude. The richness, the period and amplitude range, and the photometric precision of this sample make it possible to unveil, for the first time, structures in the amplitude-period density diagram that are signatures of different magnetic regimes. The modulation amplitude distribution shows a clear bimodality, with an evident gap at periods $P < 2$ d. The low amplitude branch, in turn, shows a period bimodality with a major group of relatively slow rotating stars with periods $P \approx$ 5 – 10 d and a group of ultra-fast rotators at $P < 0.5$ d. The amplitude-period multimodality is correlated with the position in the period-absolute magnitude (or period-color) diagram, with the low- and high-amplitude stars occupying different preferential locations. Here we argue that such a multimodality represents a further evidence of the existence of different surface magnetic field configurations in young and middle-age low-mass stars and we lay out possible scenarios for their magnetic evolution which manifestly include rapid transitions from one configuration to another. The multimodality can be exploited to identify stars in the field belonging to the slow-rotator low-amplitude sequence, for which the age can be estimated from the rotation period via gyrochronology relationships.
A. Lanzafame, E. Distefano, S. Barnes, et. al.
Wed, 30 May 18
60/65
Comments: 7 pages, 4 figures, submitted to ApJL
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