RESUMO
The scientific motivation, design criteria, and specifications for a new ground-based instrument to observe the Sun in the He i 1083-nm spectral line is described. The instrument employs a liquid-crystal tunable Lyot-type spectral filter and an array detector that allows the full solar disk to be observed with a time cadence of minutes. We describe the telescope's optical and mechanical features and discuss computer interface and data-reduction procedures employed. Instrument performance during the initial year of operation of the telescope at its high-altitude site is summarized.
RESUMO
A Lyot-Ohman filter for imaging near the solar He i 1083-nm line is described. Fast and continuous spectral tunability is provided by nematic liquid crystals. This solid-state filter has a free spectral range of 2.35 nm and a spectral resolution of 0.135 nm at the operating wavelength of 1083 nm. A wide-fielded design was used for both static and electro-optic retarder elements, facilitating use in fast imaging systems. A first-light He i image of the Sun is presented.
RESUMO
Analyses of historical data suggest that the solar diameter may vary with time with an amplitude of a few tenths of a second of arc. The High Altitude Observatory has constructed a special purpose telescope, the Solar Diameter Monitor, designed to detect any such changes. The telescope is an f/50 transit instrument with an aperture of 10 cm and is almost completely automated to avoid observer bias. Each day at solar noon, it measures the sun's horizontal diameter by timing the solar disk transit time and the vertical diameter by comparing the image size to that of a stable length standard. Preliminary estimates suggest that these observations will allow a test of the solar diameter's constancy at the 1-sec of arc/century level in an observing time of 3-5 years.
