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Wednesday 12 Jun 2019[Seminar] A new scenario for the magneto-rotational evolution of low-mass stars (< 1.3 solar mass) from pre-main-sequence to mid main-sequence

Prof Alessandro Lanzafame - University of Catania

4th Floor, Physics Building 14:00-15:00

Gaia data is providing unique opportunities to investigate the magneto-rotational evolution of low-mass stars (<1.3 solar mass) from pre-main-sequence to mid-main-sequence. The second Gaia data release revealed an unexpected clustering in the amplitude of the photometric modulation due to spots vs rotation period diagram, which unveils different regimes of surface magnetic field and rapid transitions amongst them in the course of stellar evolution. Surface magnetic fields are linked to the intensity and topology of the coronal magnetic field and therefore to the angular momentum loss through the magnetised wind. Different regimes of surface magnetic field imply, therefore, different rates of variation of the stellar angular velocity. The clustering in the amplitude-period diagram is related to the saturated/unsaturated regimes in the X-ray luminosity vs rotation relationship, revealing previously unknown sub-structures in the saturated regime. In the unsaturated regime the rotational evolution is closely reproduced by a semi-empirical wind braking law and a simple description of the radiative core — convective envelope coupling, this latter playing a significant role in the first ~ 2 Gyr of stellar evolution. The Gaia amplitude—period diagram provides also a simple criterion for identify stars that can be dated via a gyro-chronology relationship derived from such rotational evolution models. Evidence that the magnetic transitions seen in the Gaia data may be related to radius inflation in low-mass stars and the role of magnetic fields in the lithium depletion pattern of young stars are also discussed.

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