The solar physics group is currently investigating many different physical phenomena observed on the Sun. Facilities used in this research include several telescopes at Big Bear Solar Observatory (BBSO), a dedicated solar microwave interferometer array at Owens Valley Radio Observatory (OVRO), as well as an image processing computer facility on campus.
BBSO is located in the San Bernardino mountains, about a two-hour drive from Caltech, at a site which was chosen for its excellent solar viewing conditions. Telescopes at BBSO include a 65-cm vacuum reflector used for very high-resolution observations, a 25-cm vacuum refractor used for intermediate-resolution synoptic studies, a 20-cm vacuum refractor for full-disk observations, and a small full-disk heliostat dedicated to helioseismology measurements. Three high-quality 0.24-Angstrom bandpass Zeiss filters are available for use on these telescopes, in addition to a number of other optical filters; detectors include a 1024x1024 CCD camera, plus many video and film camera systems.
Observations are made year round at BBSO by professional staff, but Caltech students frequently participate in the variety of observational programs, particularly during the summer months when conditions are most favorable. With several different telescopes it is possible to observe a particular solar feature in five or six narrow wavelength bands simultaneously, in addition to measuring the magnetic and velocity on the solar surface. Some important questions attacked by these multifarious observations include the origins of solar flares, how sunspots and active regions develop, the physical significance of observed flows around sunspots, and the relation of the polar fields to the Sun's magnetic cycle.
The helioseismology program makes precise measurements of the Sun's acoustic oscillation modes; the frequencies of about a thousand modes have already been measured to a part in 100,000. With these data the Sun's internal differential rotation has been quantified, and measurements of the frequency changes with solar cycle are now being made. Observations of the amplitudes and linewidths of the modes are being used to try to understand the mode excitation and damping problem.
The solar microwave array at OVRO consists of a pair of 27-meter antennas and two recently-installed 2-meter antennas, with a third small dish on the way. Each telescope is equipped with a frequency-agile receiver capable of observing between 1 and 18 GHz with high time resolution. The array routinely observes gyrosynchrotron and bremsstrahlung emission from solar bursts. The observations are used in conjunction with optical observations from BBSO to develop physical models for the solar atmosphere, solar active regions, and the acceleration of high-energy electrons in flares.
The Big Bear Home Page (http://sundog.caltech.edu) contains a selection of images and movies. The Contents contains links to the other Physics departments.
More information may be found at the following WWW addresses:
PMA Home Page:
http://www.pma.caltech.edu
Caltech Home Page:
http://www.caltech.edu