Mauna Kea is a superb site because of the very stable airflow over the long reach of the Pacific ocean which leads to very good images. The median ``seeing'' on Keck I has been measured to be 0.55" (FWHM) and the best 0.25". The telescope optics have reached the design goal of putting 80 percent of the light into a circle 0.4" in diameter (corresponding to a FWHM of 0.2"). The site also has extremely good transmission in the infrared, due to the high altitude.
The primary mirror design of the Keck telescopes is a radical departure from that of existing telescopes; it consists of 36 actively controlled hexagonal segments, each 1.8 meters in diameter. The control system has been found to work extremely well in practice and, apart from the unusually complex diffraction pattern seen on images of bright stars, the average user is largely unaware of the segmented primary.
Three scientific instruments are currently being routinely used on the Keck I telescope. A low resolution imaging spectrograph (LRIS) built by Oke and J. Cohen at Caltech is mounted at the f/15 cassegrain focus below the primary mirror. LRIS will ultimately be a double spectrograph in which a dichroic filter below the entrance slit diverts the light into separate red and blue detector trains. At present only the red side of LRIS has been implemented; construction of the blue side is proceding under McCarthy and J. Cohen at Caltech. LRIS uses a 2048 by 2048 pixel CCD and gives spectral resolutions between 1 A and 5 A; the field for imaging is 6' by 8'. LRIS is also equiped with a spectropolarimeter built by M. Cohen at Caltech. A very large high resolution echelle spectrograph (HIRES), built by S. Vogt at the Lick Observatory, is permanently installed at one of the f/15 nasmyth platforms. This device also uses a 2048 by 2048 pixel CCD and covers 2400 A over any part of the spectrum from 3000 A to 10,000 A at resolutions between 10 km/s and 4.3 km/s. Finally, a near infrared camera (NIRC), built by Soifer and Matthews at Caltech, is operated at the f/25 forward cassegrain focus above the primary mirror. NIRC is built around a 256 by 256 pixel InSb array; each pixel subtends 0.15" on the sky. A long wavelength spectrograph (LWS), optimimized for the thermal infrared (5-20 microns), was being built by Jones and Puetter and UC San Diego. LWS is currently undergoing commissioning tests.
The design and construction of additional instruments for Keck II is proceeding after the completion of Phase A studies in 1994. These are DEIMOS, a deep imaging spectrograph designed expressly for redshift surveys of very faint galaxies, NIRC II, a version of NIRC with a larger array and smaller pixels and NIRSPEC, a high resolution 2 micron spectrograph. These last two instruments are being designed to take advantage of the smaller images afforded by a program of adaptive optics for Keck II which will ultimately use artificial reference stars generated in the upper atmosphere by a sodium laser mounted on the telescope.
Astronomers observing on all of the radio and optical telescopes on Mauna Kea eat their main meals and sleep at Hale Pohaku, a large complex maintained by the University of Hawaii at the 9000 foot level on the south side of the mountain. The road from Hale Pohaku to the summit is 8 miles long and only the upper half is paved. The air pressure at the summit is 60 percent of that at sea level and water boils at 86 deg C. Observers are required to spend at least 24 hours at Hale Pohaku in order to become at least partially acclimated to the high altitude before going to observe at the summit. Despite this, about 75 percent of observers experience mild headaches on the summit and a few experience more severe symptoms.
The Hawaii operations of CARA, the organization formed jointly by UC and Caltech to build and operate the observatory, are conducted from a large complex of buildings in Waimea, a small community about 20 miles north of the summit of Mauna Kea. Waimea has an altitude of 2500 feet and is situated in a saddle which joins the ``wet'' and ``dry'' sides of the Big Island. The complex includes living quarters for visiting scientists and a large remote operations room. An increasing number of people are choosing to observe remotely from CARA headquarters in Waimea. Development of the capability for remote observing from Caltech is also underway. The nearest airport with connections to Honolulu and the US mainland is at Kailua-Kona, about 35 miles from Waimea. The Keck Observatory now has 66 employees in Hawaii.
The 3 instruments currently being operated on Keck I have all yielded spectacular results over a wide variety of problems. Several Caltech graduate students have already been out to share the excitement and exhilaration of observing on the Keck I telescope during the first year of scientific operations. Even for seasoned observers it is an unforgettable experience.
--Wallace W. Sargent