Harland W. Epps

The Keck low - resolution imaging spectrometer

The Low Resolution Imaging Spectrometer (LRIS) for the Cassegrain focus of the Keck 10-meter telescope on Mauna Kea is described. It has an imaging mode so it can also be used for taking direct images. The field of view in both spectrographic and imaging modes is 6 by 7.8 arcmin. It can be used with both conventional slits and custom-punched slit masks. The optical quality of the spectrograph is good enough to take full advantage of the excellent imaging properties of the telescope itself. The detector is a cooled back-illuminated Tektronics Inc. 2048 CCD which gives a sampling rate of 4.685 pixels per arcsec. In the spectrographic mode the spectrograph has a maximum efficiency at the peak of the grating blaze of 32-34% for the two lowest resolution gratings and 28% for the 1200 g/mm grating. This efficiency includes the detector but not the telescope or the atmosphere.

The multi-object, fiber-fed spectrographs for the Sloan Digital Sky Survey and the Baryon Oscillation Spectroscopic Survey

We present the design and performance of the multi-object fiber spectrographs for the Sloan Digital Sky Survey (SDSS) and their upgrade for the Baryon Oscillation Spectroscopic Survey (BOSS). Originally commissioned in Fall 1999 on the 2.5 m aperture Sloan Telescope at Apache Point Observatory, the spectrographs produced more than 1.5 million spectra for the SDSS and SDSS-II surveys, enabling a wide variety of Galactic and extra-galactic science including the first observation of baryon acoustic oscillations in 2005. The spectrographs were upgraded in 2009 and are currently in use for BOSS, the flagship survey of the third-generation SDSS-III project. BOSS will measure redshifts of 1.35 million massive galaxies to redshift 0.7 and Lyα absorption of 160,000 high redshift quasars over 10,000 deg2 of sky, making percent level measurements of the absolute cosmic distance scale of the universe and placing tight constraints on the equation of state of dark energy. The twin multi-object fiber spectrographs utilize a simple optical layout with reflective collimators, gratings, all-refractive cameras, and state-of-the-art CCD detectors to produce hundreds of spectra simultaneously in two channels over a bandpass covering the near-ultraviolet to the near-infrared, with a resolving power R = λ/FWHM ~ 2000. Building on proven heritage, the spectrographs were upgraded for BOSS with volume-phase holographic gratings and modern CCD detectors, improving the peak throughput by nearly a factor of two, extending the bandpass to cover 360 nm < λ < 1000 nm, and increasing the number of fibers from 640 to 1000 per exposure. In this paper we describe the original SDSS spectrograph design and the upgrades implemented for BOSS, and document the predicted and measured performances.

Hectospec, the mmt's 300 optical fiber-fed spectrograph

ABSTRACT The Hectospec is a 300 optical fiber fed spectrograph commissioned at the MMT in the spring of 2004. In the configuration pioneered by the Autofib instrument at the Anglo‐Australian Telescope, Hectospec’s fiber probes are arranged in a radial “fisherman on the pond” geometry and held in position with small magnets. A pair of high‐speed, six‐axis robots move the 300 fiber buttons between observing configurations within ∼300 s, and to an accuracy of ∼25 μm. The optical fibers run for 26 m between the MMT’s focal surface and the bench spectrograph, operating at \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textc...

ESI, a New Keck Observatory Echellette Spectrograph and Imager

The Echellette Spectrograph and Imager (ESI) is a multipurpose instrument that has been delivered by the Instrument Development Laboratory of Lick Observatory for use at the Cassegrain focus of the Keck II telescope. ESI saw first light on 1999 August 29. ESI is a multimode instrument that enables the observer to seamlessly switch between three modes during an observation. The three modes of ESI are an R p 13,000 echellette mode, a low-dispersion prismatic mode, and a direct-imaging mode. ESI contains a unique flexure compensation system that reduces the small instrument flexure to negligible proportions. Long-exposure images on the sky show FWHM spot diameters of 34 m m( 0 .34) averaged over the entire field of view. These are the best non-adaptive optics images taken in the visible at Keck Observatory to date. Maximum efficiencies are measured to be 28% for the echellette mode and greater than 41% for low-dispersion prismatic mode including atmospheric, telescope, and detector losses. In this paper, we describe the instrument and its development. We also discuss the performance testing and some observational results.

The ROTSE‐III Robotic Telescope System

The observation of a prompt optical flash from GRB 990123 convincingly demonstrated the value of autonomous robotic telescope systems. Pursuing a program of rapid follow-up observations of gamma- ray bursts, the Robotic Optical Transient Search Experiment (ROTSE) has developed a next-generation instrument, ROTSE-III, that will continue the search for fast optical transients. The entire system was designed as an economical robotic facility to be installed at remote sites throughout the world. There are seven major system components: optics, optical tube assembly, CCD camera, telescope mount, enclosure, environmental sensing and protection, and data acquisition. Each is described in turn in the hope that the techniques developed here will be useful in similar contexts elsewhere.

Design for a 1--5-um cryogenic echelle spectrograph for the NASA IRTF

The design of an infrared cryogenic echelle spectrograph for use on the NASA Infrared Telescope Facility is described. The resolving power achieved over the range 1-5.4 microns is 1-40,000 with slit widths of 2.0-0.5 arcsec. The spectrograph is used in a single order with a 30-arcsec-long slit. No cross dispersion is provided because of the small number of orders that can be observed at once and the need to keep the instrument as small as possible. A closed-cycle cooler is used in lieu of cryogens in order to achieve greater reliability and ease of use at the telescope. The optical layout, the design philosophy, the modes of operation, and the construction details are provided.

COSMIC: A Multiobject Spectrograph and Direct Imaging Camera for the 5 Meter Hale Telescope Prime Focus

We describe the design, construction, and operation of the Carnegie Observatories Spectroscopic Multislit and Imaging Camera (COSMIC) for the prime focus of the Hale 5 m telescope at Palomar Observatory. COSMIC is a reimaging grism spectrograph with a 13.65 arcmin square field of view, which can also be used as a direct imaging camera with a 9.75 arcmin square field of view. The wavelength coverage extends from 350 nm to almost 1 mm; the detector is a thinned, back-illuminated SITe CCD with high quantum 2048 # 2048 efficiency and excellent cosmetics. Multislit aperture masks are produced photographically, with spectra of up to ∼50 objects fitted on a single row of a slit mask. The instrument exhibits very little flexure and uses an active thermal control to maintain focus over a wide range of ambient temperature. In direct mode COSMIC is typically used with Kron-Cousins, Gunn, and narrow bandpass filters. The instrument achieves throughputs of greater than 50% for direct imaging and, in spectroscopic mode, a peak efficiency at 5500 A u of slightly better than 24% of light falling on the 5 m mirror. COSMIC is optimized for faint-object imaging, down to Gunn mag, and r 26 multiobject spectroscopy, down to mag, with typically 30 objects per spectroscopic exposure. r 23

A New Observational Upper Limit to the Low-Redshift Ionizing Background Radiation

We report a new Fabry-Perot search for Hα emission from the intergalactic cloud H I 1225+01 in an attempt to measure the low-redshift ionizing background radiation. We set a new 2 σ upper limit on Hα emission of 8 mR (5 × 10-20 ergs cm-2 s-1 arcsec-2). Conversion of this limit to limits on the strength of the ionizing background requires knowledge of the ratio of the projected to total surface area of this cloud, which is uncertain. We discuss the plausible range of this ratio and within this range find that the strength of the ionizing background is in the lower range of, but consistent with, previous observational and theoretical estimates.

IMACS: the multiobject spectrograph and imager for the Magellan I telescope

The Inamori Magellan Areal Camera and Spectrograph (IMACS) will be one of three first-generation instruments for the Magellan 6.5 m telescopes. It will be installed at the f/11 (Gregorian) Nasmyth focus. This instrument drove the specification and design of the f/11 configuration, which it uses to feed an all-spherical, wide-field collimator. The combination of the Gregorian secondary and refracting collimator lead to 0.2 arc-sec images over a 17 arc-min field with an f/2.66 camera, and 0.4 arc-sec images over a 27 arc- min field with an f/1.49 camera. This paper describes the preliminary specifications for the multiple spectrographic and imaging modes, the optical layout of the instrument and Epps cameras, and strategies for the design and fabrication of the instrument.

Very Isolated Early-Type Galaxies

We use the Karachentseva Catalogue of Very Isolated Galaxies to investigate a candidate list of more than 100 very isolated early-type galaxies. Broadband imaging and low-resolution spectroscopy are available for a large fraction of these candidates and result in a sample of 102 very isolated early-type galaxies, including 65 elliptical (E) and 37 S0 galaxies. Many of these systems are quite luminous, and the resulting optical luminosity functions of the E and early-type (E+S0) galaxies show no statistical differences when compared to luminosity functions dominated by group and cluster galaxies. However, whereas S0 galaxies outnumber E galaxies 4 : 1 in the CfA survey, isolated E outnumber S0 galaxies by nearly 2 : 1. We conclude that very isolated elliptical galaxies show no evidence of a different formation and/or evolution process compared to those formed in groups or clusters, but that most S0 galaxies are formed by a mechanism (e.g., gas stripping) that occurs only in groups and rich clusters. Our luminosity function results for elliptical galaxies are consistent with very isolated elliptical galaxies being formed by merger events, in which no companions remain. Chandra observations were proposed specifically to test the merger hypothesis for isolated elliptical galaxies. However, this program has resulted in the observation of only one isolated early-type galaxy, the S0 KIG 284, which was not detected at a limit well below that expected for a remnant group of galaxies. Therefore, the hypothesis remains untested that very isolated elliptical galaxies are the remains of a compact group of galaxies that have completely merged.