[Show abstract][Hide abstract] ABSTRACT: The majority of extra-solar planets discovered to date have been found using Doppler-shift measurements ob-tained with the Hamilton Spectrometer 1 at Lick Observatory and the High Resolution Echelle Spectrometer (HIRES 2) at Keck Observatory. Each of these spectrometers employs an integral exposure meter which enables observers to optimize exposure times so as to achieve the required signal-to-noise and to determine the photon-weighted midpoint of each science exposure (which is needed to correct the Doppler shift to the Solar System barycenter *). In both of these systems, a propeller mirror located behind the spectrometer slit picks off a few percent of the light and directs it to a photo-multiplier tube (PMT) used to measure the exposure level versus time. In late 2006, the new Automated Planet Finder (APF) Telescope and APF Spectrometer are scheduled to begin operations at Lick Observatory; both will be dedicated exclusively to the search for extra-solar planets. Like the Hamilton and HIRES Spectrometers, the APF Spectrometer will employ an integral exposure meter, but one with a significantly different design. The APF exposure meter will employ a stationary pellicle located ahead of the slit to pick off 4% of the light and direct it to the guide camera. That camera will produce images typically at a 1 Hz rate, and those images will be used both for autoguiding and for computing the exposure level delivered to the spectrometer. In each guide camera image obtained during a science exposure, the time-tagged signal from the pixels that correspond to the spectrometer slit will be integrated in software to determine the current exposure level and the photon-weighted midpoint of that science exposure. We compare these two different design approaches, and describe the significant hardware and software features of each of these systems.
Proceedings of SPIE - The International Society for Optical Engineering 01/2006; 6274. DOI:10.1117/12.672048 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The DEIMOS spectrograph is a multi-object spectrograph being built for
Keck II. DEIMOS was delivered in February 2002, became operational in
May, and is now about three-quarters of the way through its
commissioning period. This paper describes the major problems
encountered in completing the spectrograph, with particular emphasis on
optical quality and image motion. The strategies developed to deal with
these problems are described. Overall, commissioning is going well, and
it appears that DEIMOS will meet all of its major performance goals.
Proceedings of SPIE - The International Society for Optical Engineering 03/2003; 4841:1657-1669. DOI:10.1117/12.460346 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Two recent Keck optical imaging spectrographs have been designed with active flexure compensation systems (FCS). These two instruments utilize different methods for implementing flexure compensation. The Echellette Spectrograph and Imager (ESI), commissioned at the Cassegrain focus of the Keck II Tele-scope in late 1999, employs an open-loop control strategy. It utilizes a mathematical model of gravitationally-induced flexure to periodically compute flexure corrections as a function of telescope position. Those corrections are then automatically applied to a tip/tilt collimator to stabilize the image on the detector. The DEep Imaging Multi-Object Spectrograph (DEIMOS), commissioned at the Nasmyth focus of Keck II in June 2002, implements a closed-loop control strategy. It utilizes a set of fiber-fed FCS light sources at the ends of the slitmask to produce a corresponding set of spots on a pair of FCS CCD detectors located on either side of the science CCD mosaic. During science exposures, the FCS detectors are read out several times per minute to measure any translational motion of the FCS spot images. Correction signals derived from these FCS images are used to drive active optical mechanisms which steer the spots back to their nominal positions, thus stabilizing the FCS spot images as well as those on the science mosaic. We compare the design, calibration, and operation of these two systems on the telescope. Long-term performance results will be provided for the ESI FCS, and preliminary results will be provided for the DEIMOS FCS.
Proceedings of SPIE - The International Society for Optical Engineering 03/2003; DOI:10.1117/12.461602 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The DEIMOS spectrograph is a multi-object spectrograph being built for Keck II. DEIMOS was delivered in February 2002, became operational in May, and is now about three-quarters of the way through its commissioning period. This paper describes the major problems encountered in completing the spectrograph, with particular emphasis on optical quality and image motion. The strategies developed to deal with these problems are described. Overall, commissioning is going well, and it appears that DEIMOS will meet all of its major performance goals.
[Show abstract][Hide abstract] ABSTRACT: We describe the control and user interface software for the image rotator on the High Resolution Echelle Spectrometer (HIRES), located at the Nasmyth focus of the Keck-l 10-meter Telescope. This image rotator counteracts the field rotation induced by the alt-az telescope mount and aligns the image delivered to the spectrometer slit and the slit-viewing TV camera. The rotator can align the image so that either a specified position angle on the sky or the atmospheric dispersion vector is held fixed relative to the slit. The rotator is physically an integral part of the spectrometer; but, since it affects telescope pointing and auto-guiding, it can also be considered part of the telescope. Accordingly, it interacts with the control systems for both the telescope and spectrometer. The apportionment of rotator control functions between these two systems poses interesting operational challenges. Since the telescope operator and the observer each need to operate the rotator at various times, their respective user interfaces must provide consistent rotator control and status functions.
[Show abstract][Hide abstract] ABSTRACT: We describe the high resolution echelle spectrometer (HIRES) now in operation on the Keck Telescope. HIRES, which is permanently located at a Nasmyth focus, is a standard in-plane echelle spectrometer with grating post dispersion. The collimated beam diameter is 12', and the echelle is a 1 x 3 mosaic, 12' by 48' in total size, of 52.6 gr mmMIN1, R-2.8 echelles. The cross disperser is a 2 x 1 mosaic, 24' by 16 ' in size. The camera is of a unique new design: a large (30' aperture) f/1.0, all spherical, all fused silica, catadioptric system with superachromatic performance. It spans the entire chromatic range from 0.3 (mu) to beyond 1.1 (mu) , delivering 12.6-micron (rms) images, averaged over all colors and field angles, without refocus. The detector is a thinned, backside-illuminated, Tektronix 2048 x 2048 CCD with 24-micron pixels, which spans the spectral region from 0.3 (mu) to 1.1 (mu) with very high overall quantum efficiency. The limiting spectral resolution of HIRES is 67,000 with the present CCD pixel size. The overall 'throughput' (resolution x slit width) product achieved by HIRES is 39,000 arcseconds. Peak overall efficiency for the spectrograph (not including telescope and slit losses) is 13% at 6000 angstrom. Some first-light science activities, including quasar absorption line spectra, beryllium abundances in metal-poor stars, lithium abundances in brown-dwarf candidates, and asteroseismology are discussed.