Barnes 2002 Review

On the Rotational Evolution of Solar- and Late-type Stars, Its Magnetic Origins, and the Possibility of Stellar Gyrochronology


purpose: explain how magnetic braking can slow the spin of a star in a predictable way over time, such that age determination becomes possible using color and rotation data.



Abstract

• rotating stars lie on either the interface (I) or convective (C) sequence
• the cause of the sequence seems to be magnetic
• interface magnetic fields connect the radiative zone, convective envelope, and stellar exterior
• carries away angular momentum through wind
• star spins down Skumanich-ly
• convective magnetic fields do not connect to the radiative zone or stellar exterior
• inefficient at carrying away angular momentum
• only outer envelope spins down (exponentially)
• transition occurs when the magnetic field couples the radiative and convective zones
• this happens because of a shear between the two zones
• This picture explains many stellar phenomena which depend on rotation

Introduction

• Each spectral type has a different rotational isochrone
• the original picture of spin down said that because angular momentum transport in the radiative zone is slower than in the convective zone, shear between the two regions would spin down the star.
• This picture does not allow for recoupling, which is an observed phenomenon
• more than just vsini information was needed
• photometric periods were measured using starspots on solar- and late-type stars
• DEBRIS DISKS HAVE NO OBSERVABLE EFFECT ON THE SPIN OF THE HOST STAR

Observation and Sources

• used 42" Hall Telescope (Lowell Observatory, AZ) for M34
• used 0.9m telescope (Cerro Tololo Inter-American Observatory) for NGC 3532
• sometimes used Noyes et al. 1984 to calculate periods from activity indices

Morphology of the Observations

What seems different about Barnes' organization of the material is that he used multiple clusters of the same age overplotted together to get tighter sequences for the rotational isochrones. 

Later on in the paper, he includes the (mathematical) physics behind these observations. His equations for P(B-V,t) have since been revised, but the basic physical background is good to know.