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Hubble Space Telescope
IAU XXVIII General Assembly: Special Session #13

Gas Flows in Galaxies

Scientific Rationale

The search for, discovery of, and characterization of planets around other stars has led to a complete revitalization of stellar astrophysics. The essential reason for this is that the signatures of exoplanets are subtle, and you cannot understand the planet's signal if you don't understand the signal from the host star to high accuracy. Just as important, those searches for weak signals from the planet-hosting star have produced a rich dataset of observations of the stars themselves. The search for exoplanets is forcing us to know the stars in our Galaxy much better.

The COROT and Kepler space missions were designed and built to use high-precision photometry to find planets - particularly small ones - around other stars by detecting transits. These missions follow on the path led by surveys and missions such as MOST, MACHO, and OGLE, and are complemented by other photometric surveys for planets (XO, WASP, HATnet, etc.). To do this they stare at large fields for extended periods of time. Also, extremely high photometric precision (about 1:100,000 in the case of Kepler) is needed to find Earth-sized planets.

Such precision is well beyond what has been done before, and having continuous data for a large number of stars is even better. It is no great revelation to note that any study of that kind will unearth types of variations not seen or appreciated before in addition to the trove of planets discovered. Those variations are being studied and are leading to all-new insights into the physics of stars across the H-R diagram.

The time-series observations from these missions and projects can be examined in many ways to gain insight into stars. Singular and unusual events - such as flares or eruptions - are one obvious way. But the most powerful use of these data is when they are used for seismological studies because then we get limits on key physical parameters to a degree that other observations do not provide.

Given this rich trove of new information, how good, in fact, are our stellar models? Are the interior parameters inferred from seismology consistent with solar models? Can we gain insight into the abundance scale controversy for the Sun? Do we understand stellar pulsations as well as we thought? Each of these kinds of stars brings into the picture particular physical processes that get probed by the observations. It is all of that taken together that needs to now be explored in a symposium.