Computer Science – Sound
Scientific paper
Feb 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aipc.1094..206b&link_type=abstract
COOL STARS, STELLAR SYSTEMS AND THE SUN: Proceedings of the 15th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun.
Computer Science
Sound
2
Magnetic And Electric Fields, Polarization Of Starlight, Star Formation, Infrasound And Acoustic-Gravity Waves
Scientific paper
A key ingredient of solar-type dynamo action is the interface between the convective and radiative zones, so there has been considerable interest in the workings of dynamos in fully convective objects (lacking radiative zones). These constitute by far the majority of objects with dynamos. In the solar-type case, rotation period and convective overturn time (whose ratio yields the Rossby number) have been implicated in the production levels of ``activity.'' This is measured through coronal or chromospheric emission, or by direct field determinations. Activity can lead to magnetic braking, so the angular momentum history of the object is also connected to it. With the advent of large telescopes, most of the techniques applied to solar-type stars (or good substitutes) have now been applied to low-mass stars and brown dwarfs. We measure atmospheric heating produced by magnetic dissipation primarily through Hα emission, and directly measure magnetic fields in M stars through a molecular Zeeman diagnostic (L dwarfs provide fields through radio flares). Rotation is measured through Doppler broadening, but further progress will require photometric periods. I summarize this work, which has led to a number of interesting conclusions: 1) magnetic fields are produced down to very low masses, with magnetic fields remaining strong and large-scale at least through M dwarfs (and likely L dwarfs) 2) rotation, convection, and activity are still connected in M dwarfs, but not in L dwarfs (where heating and fields are disconnected due to atmospheric neutrality) 3) saturation of both heating and total magnetic flux occurs at similar a Rossby number whether fully convective or not; 4) magnetic braking (implying coronae) is present in M stars, but drops with effective temperature (mass), and dies out (braking times become very long) in L dwarfs; 5) variable magnetic activity extends well into L dwarfs, though at decreasing levels; and 6) there are some oddities which still require explanation.
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