AN INSTRUMENT TO OBSERVE LOW-DEGREE SOLAR OSCILLATIONS

We have constructed an instrument optimized to observe solar oscillati ons of low degree. The primary goal of this instrument, which we call LOWL, is to measure the frequency splitting of the low-degree modes in order to determine the rotation rate of the solar core.The LOWL is a Doppler imager based on a magneto-optical filter. It employs a two-bea m technique to simultaneously observe solar images in opposite wings o f the absorption line of potassium at 769.9 nm. This instrument is ver y stable against drifts in the wavelength zero-point, is insensitive t o noise sources due to intensity fluctuations and image motion, and ha s a Doppler analyzer with no moving parts. The LOWL has been deployed at HAO's observing station on Mauna Loa, Hawaii and will operate for a period of at least two years.