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Constraining the Angular Momentum of the Sun with Planetary Orbital Motions and General Relativity
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Lorenzo Iorio Submitted: 2012-07-18 16:30
The angular momentum of a star is an important astrophysical quantity
related to its internal structure, formation and evolution. On
average, helioseismology yields S☉ = 1.92 x
1041 kg m2 s-1 for the angular
momentum of the Sun. We show how it should be possible to measure or,
at least, constrain it in a near future by using the gravitomagnetic
Lense-Thirring effect predicted by general relativity for the orbit of
a test particle moving around a central rotating body. We also discuss
the present-day situation in view of the latest determinations of the
supplementary perihelion precession of Mercury. A fit by Fienga et al.
(Celestial Mech. Dynamical Astron. 111, 363, 2011) of the dynamical
models of several standard forces acting on the planets of the solar
system to a long data record yielded 0.4 ± 0.6 milliarcseconds per
century. The modeled forces did not include the Lense-Thirring effect
itself, which is expected to be as large as -2.0 milliarcseconds per
century.from helioseismology-based values of S. By assuming the
validity of General Relativity, from its theoretical prediction for
the gravitomagnetic perihelion precession of Mercury one can
straightforwardly infer S☉ <= 0.95 x
1041 kg m2 s-1. It disagrees with the
currently available values from helioseismology. Possible sources for
the present discrepancy are examined. Given the current level of
accuracy in the Mercury ephemerides, the gravitomagnetic force of the
Sun should be included in their force models. MESSENGER, in orbit
around Mercury since March 2011, will collect science data until 2013,
while BepiColombo, to be launched in 2015, should reach Mercury in
2022 for a year-long science phase: the analysis of their data will be
important in eectively constraining S in about a decade or, perhaps,
even less.
Authors: Lorenzo Iorio
Projects: Other
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Publication Status: To appear in Solar Physics
Last Modified: 2012-07-19 11:53
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