Helioseismology, Asteroseismology, and MHD Connections

Laurent Gizon·Paul Cally·John Leibacher Originally published in the journal Solar Physics, Volume 251, Nos 1¿2, 1¿2. DOI: 10. 1007/s11207-008-9248-y © The Author(s) 2008 The seismology of the Sun and stars has come a long way in a short time. The ¿original¿ Global Helioseismology has reached a level of maturity that allows many internal prop- ties of the Sun to be probed with exquisite precision, although it currently faces a severe challenge to reconcile interior models with helioseismic inversions near the base of the c- vection zone in the age of the new solar chemical abundances. Asteroseismology suffers in comparisonbybeingrestrictedtoverylowsphericalharmonicdegree( ),butitmakesupfor this by providing many more subjects for study (including solar-like stars) and many cases of well-identi ed g modes. Where once we were restricted to stellar spectra in studying in- vidual stars, asteroseismology now provides a crucial tool with which we may explore their deep structure. Its natural synergy with planet-search programs also invigorates it. Local Helioseismology has seen the development of an exciting array of techniques and insights over the two decades since observations of surface oscillations in and around active regions gave the rst clues that something different was happening there, and it has been parti- larly important in mapping ows of various types in shallow subsurface layers.