Helioseismology
description
Transcript of Helioseismology
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Helioseismology
Jørgen Christensen-Dalsgaard
Institut for Fysik og Astronomi, Aarhus Universitet
Dansk AsteroSeismologisk Center
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The Sun
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Five-min oscillations: A local phenomenon in the solar atmosphere?
Musman & Rust
(1970; Solar Phys. 13, 261)
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Oscillation modes of the Sun
Deubner (1975; Astron. Astrophys. 44, 371)
Models:
•Ulrich (1970):
•Wolff (1972):
•Ando & Osaki (1975):
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The start of global helioseismology
Grec et al. (1980; Nature 288, 541)
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Crucial advantages• Access to modes of degree up to 1000+
• Observations over very extended period (more than 10 years nearly continuously)
• Well-determined global parameters
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Frequencies of solar model
= / 2
Observed solar modes
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Rays
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Inversion with rays
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Observing a Doppler image
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VIRGO on SOHO (whole-disk):
Data on solar oscillationsObservations:
MDI on SOHO
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Observed frequencies
m-averaged frequencies from MDI instrument on SOHO
1000 error bars
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Frequency differences, Sun - model
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No settling
The solar internal sound speed
No settling
Including settling
Sun - model
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The solar internal sound speedSun - model
Basu et al. (1997; MNRAS 292, 243)
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Changes in composition
The evolution of stars is controlled by the changes in their interior composition:
• Nuclear reactions
• Convective mixing
• Molecular diffusion and settling
• Circulation and other mixing processes outside convection zones
Nuclear burning
Settling
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No relativistic effectsIncluding relativistic effects
Relativistic electrons in the Sun
Elliot & Kosovichev (1998; ApJ 500, L199)
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Neon discovery solves mystery of sun's interiorNASA's Chandra X-ray Observatory survey of nearby sun-like stars suggests there is nearly three times more neon in the sun and local universe than previously believed. If true, this would solve a critical problem with understanding how the sun works. FULL STORY
(Spaceflight Now – 14 Aug 2005)
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Improvements:
•Non-LTE analysis
•3D atmosphere models
Consistent abundance determinations for a variety of indicators
Revision of solar surface abundances
Asplund et al. (2004; A&A 417, 751. 2005; astro-ph/0410214 v2):Pijpers, Houdek et al.
Model S
Z = 0.015
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How do we correct the models?
Basu & Antia (2004; ApJ 606 L85): an opacity increase to compensate for lower Z is required
Seaton & Badnell (2004; MNRAS 354, 457): recent Opacity Project results do indicate some increase over the OPAL values, but hardly enough
Antia & Basu (2005; ApJ 620, L129): could the neon abundance be wrong?
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The neon story
Ne x 2.5
Bahcall et al. (2005; ApJ, in the press [astro-ph/0502563])Drake & Testa (2005; Nature 436, 525): X-ray observations of nearby stars indicate such a neon increase
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Spherical harmonics
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Rotational splitting
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Simple rotational splitting
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Kernels for rotational splitting
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Inferred solar internal rotation
Base of convection
zone
TachoclineNear solid-
body rotation of
interior
Schou et al. (1998; ApJ 505, 390)
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Rotation of the solar interior
BiSON and LOWL data; Chaplin et al. (1999; MNRAS 308, 405)
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Tachocline oscillations
See Howe et al. (2000; Science 287, 2456)
● GONG-RLS
▲MDI-RLS
∆ MDI-OLA
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Zonal flowsRotation rate - average value at solar minimum
Vorontsov et al. (2002; Science 296, 101)
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Radial development of zonal flows
Howe et al., (ApJ, in the press)
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Observed and modelled dynamics
6 1/2 year MDI inversion, enforcing 11-yr periodicity
Vorontsov et al. (2002; Science 296, 101)
Non-linear mean-field solar dynamo models
Covas, Tavakol and Moss (2001; Astron. Astrophys 371, 718)