Physics – Optics
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994pasp..106.1285b&link_type=abstract
Astronomical Society of the Pacific, Publications (ISSN 0004-6280), vol. 106, no. 706, p. 1285-1297
Physics
Optics
45
Brightness Distribution, Calibrating, Doppler Effect, Echelle Gratings, Fiber Optics, Radial Velocity, Atmospherics, Charge Coupled Devices, Data Reduction, Spectrographs, Stellar Luminosity, Telescopes
Scientific paper
The Advanced Fiber Optic Echelle (AFOE) is a fiber-fed echelle spectrograph designed for the measurement of stellar Doppler shifts. Using a 2kx2k CCD detector, it samples about 55% of the wavelength range between 450 and 700 nm (20 echelle orders) at a single shot, with spectral resolution R = 32,000 to 70,000 at 500 nm, depending on the slit width employed. The AFOE employs a number of devices to assure that the calibrations necessary for accurate Doppler measurements can be properly performed. The most important of these are: (1) coupling to the telescope via a double-scrambling optical fiber system; (2) continuous calibration of the wavelength scale and point-spread function by means of an atomic emission lamp entering the spectrograph via a separate fiber and/or a molecular iodine absorption cell; (3) availability of fiber-coupled sunlight for regular calibration against the solar spectrum; (4) appropriate mechanical design and active thermal control, yielding good mechanical stability. The AFOE is coupled to the Tillinghast 1.5-m telescope at the F.L. Whipple Observatory. It presently achieves S/N = 500 in the continuum near 500 nm in 60 s when observing Arcturus (alpha Bootis, mnu = -0.04). This noise level sets a limit of about 0.7 m/s to the Doppler precision attainable in this length of observing time. Currently, our actual frame-to-frame repeatability is worse than the photon noise limited value by about a factor of 3 for this bright star, and about 1.5 for stars with mnu = 4. Work is continuing to refine data processing methods so that the ultimate noise limit may be approached more closely, and to improve the spectrograph's relatively low efficiency.
Brown Timothy M.
Horner Scott
Korzennik Sylvain G.
Nisenson Peter
Noyes Robert W.
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