Scientific Rationale
Helio- and asteroseismology have received a tremendous amount of new
information from space missions and ground-based networks. In particular,
SOHO and GONG have observed the Sun for longer than one solar cycle;
Hinode has started sending us high-resolution data; MOST and COROT have
provided unique asteroseismology observations; and SDO/HMI is expected
to be launched and provide initial results by the time of the IAU
General Assembly. Thus, this Joint Discussion will become a timely
meeting for solar physicists and astrophysicists to share new discoveries
and advances in our understanding the interior structure, dynamics
and activity of the Sun and other stars.
The Sun has an activity cycle of 11 years, and GONG and SOHO have
observed the Sun for more than one solar cycle. The temporal variations
of solar interior structures, rotational rates, and meridional flows,
particularly at the tachocline area, are of great importance for better
understanding what causes the solar magnetism and how the solar
dynamo operates. It is also essential to know how the whole solar
cycle observations will help to improve the dynamo simulations for a
better prediction of next solar cycle activity level. Using more than
10 years' observation from SOHO/GOLF, helioseismologists have made new
attempts to find signals of the long-sought solar g-modes, probably
opening a new window for studying the solar core structure and dynamics.
Local helioseismology has made significant advances in inferring solar
interior structures and flow fields on the scales of supergranulation,
active regions and sunspots. The new high-resolution observations
available from Hinode and anticipated from the Solar Dynamics
Observatory will help us to greatly improve our knowledge of the
Sun's local structures and dynamics. On the other hand, the recent
advances in numerical simulations in solar upper convection zone
have given us unprecedented opportunities to evaluate and improve
the diagnostic methods. The interaction between solar magnetic field
and acoustic waves is particularly important for detecting structures
beneath sunspots, and the magnetoseismology investigations have made
significant progress in the past a few years.
The advances in helioseismology are complemented by the tremendous
progress in asteroseismology, in particular by the new results from the
space missions MOST, COROT, WIRE and SMEI. Seismology of distant stars,
particularly, of solar-type stars, is extremely challenging and opens
new opportunities to measure gross properties of many stars in their
various evolutionary stages with unprecedented accuracy. It requires
huge coordinated efforts among space-borne and ground-based projects.
The space missions provide high-precision photometric data, and it is
important to combine these with high S/N, high time-resolution, and
high wavelength-resolution spectroscopic data. The new asteroseismic
observations have discovered a rich world of stellar oscillations in
various type of stars and provide new opportunities to bring our
understanding of the theory of stellar structure and evolution to a new
level of sophistication.
The Joint Discussion of the recent results and new approaches in helio-
and asteroseismology will help to advance our understanding of the
mechanism of solar and stellar oscillations and the physical processes
inside the Sun and other stars.