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Session 114 - GONG.
Oral session, Thursday, January 18
La Condesa, Hilton
Helioseismology studies the internal structure and dynamics of the Sun, utilizing very precise measurements of the frequencies of sound waves that propagate throughout the solar interior and are observed at the surface. These waves interfere constructively and form resonant modes with periods near five minutes and lifetimes ranging from weeks to many months. Their frequencies depend directly on the temperature, composition, and motions of the regions of the Sun through which the sound waves propagate, and we will be able to measure these quantities in four dimensions, with remarkable resolution in each. These measurements should provide important new knowledge of the Sun's central temperature, the depth of its convection zone, the abundance of helium and heavy elements, the manner in which the interior rotates, the nature of the internal magnetic field, and how all of these vary in time.
Efforts to accurately and precisely measure the mode frequencies from a single observing site have met with fundamental limitations imposed by the inevitable interruptions arising from the day-night cycle. In order to overcome these limitations, and open a new chapter in our understanding of the Sun and stellar interiors, the NSF-sponsored Global Oscillation Network Group (GONG) project has developed 1) a network of six sites around the world providing velocity images with a duty cycle better than 90%, 2) six identical instruments with a system noise lower than the solar background of incoherent surface motions, 3) a data processing system that can keep up with the massive data flow, and 4) a vigorous community that has shared in all aspects of the development of the project.
Data from the first two stations started in February 1995 and the full six-station network became operational in early October 1995. Preliminary results indicate that the duty cycle, daily artifact reduction, and instrument performance goals will be met. Merging of the images from the six-sites is being carried out, and the overall data processing pipeline appears to be capable of maintaining cadence with the data flood.
