Joseph R. Tufts

Las Cumbres Observatory Global Telescope Network, Goleta, California, United States

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Publications (37)29.04 Total impact

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    ABSTRACT: Las Cumbres Observatory Global Telescope (LCOGT) is a young organization dedicated to time-domain observations at optical and (potentially) near-IR wavelengths. To this end, LCOGT is constructing a world-wide network of telescopes, including the two 2m Faulkes telescopes, as many as 17 x 1m telescopes, and as many as 23 x 40cm telescopes. These telescopes initially will be outfitted for imaging and (excepting the 40cm telescopes) spectroscopy at wavelengths between the atmospheric UV cutoff and the roughly 1-micron limit of silicon detectors. Since the first of LCOGT's 1m telescopes are now being deployed, we lay out here LCOGT's scientific goals and the requirements that these goals place on network architecture and performance, we summarize the network's present and projected level of development, and we describe our expected schedule for completing it. In the bulk of the paper, we describe in detail the technical approaches that we have adopted to attain the desired performance. In particular, we discuss our choices for the number and location of network sites, for the number and sizes of telescopes, for the specifications of the first generation of instruments, for the software that will schedule and control the network's telescopes and reduce and archive its data, and for the structure of the scientific and educational programs for which the network will provide observations.
    Publications of the Astronomical Society of the Pacific 09/2013; DOI:10.1086/673168 · 3.23 Impact Factor
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    ABSTRACT: Las Cumbres Observatory Global Telescope (LCOGT) is developing a world-wide network of robotic optical telescopes dedicated to time-domain astronomy. The last year has seen 3 major expansions in our observing capabilities. (1) We have deployed and commissioned 4 new 1m telescopes at McDonald Observatory and at CTIO, and we are in the process of deploying 5 more at the South African Astronomical Observatory and at Siding Spring Observatory in Australia. (2) We have commissioned low-resolution spectrographs on the Faulkes 2m telescopes; these will become available to users in the 2013A semester, beginning 1 April 2013. (3) We have commissioned the NRES Prototype cross-dispersed echelle spectrograph on our 0.8m telescope in California, giving LCOGT its first capability to perform radial-velocity and spectral classification observations. We describe here early science results from each of these 3 new systems.
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    ABSTRACT: Las Cumbres Observatory Global Telescope (LCOGT) is developing a world-wide network of optical telescopes dedicated to time-domain astronomy. In a few years, the network will consist of more than twenty 0.4m telescopes, about fifteen 1m telescopes, and two 2m telescopes. We are now developing spectrographs to use with this network; here we describe the performance goals and status of these instruments. Furthest along is FLOYDS, a low-resolution spectrograph that will cover 330nm - 1040 nm in one shot, using two diffraction orders. FLOYDS is intended mostly for SN classification and time-evolution studies. We will install copies of this spectrograph on each of LCOGT's 2m Faulkes telescopes, beginning with FTN early in 2012. Still in the prototype stage is MRES, a medium-resolution (R=45,000) fiber-fed cross-dispersed echelle covering 380nm-850nm. It will accept fibers from up to 3 co-located 1m telescopes, so that we can observe multiple targets at once, or gain S/N by devoting multiple telescopes to a single target. The spectrograph is designed for easy control of its light path and environment, to facilitate accurate and repeatable measurements. MRES will be used mostly for validation and study of extrasolar planets, and for time-domain studies of pulsating and magnetically active stars.
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    ABSTRACT: Las Cumbres Observatory Global Telescope (LCOGT) is developing a world-wide network of optical telescopes dedicated to time-domain astronomy. In a few years, the network will consist of more than twenty 0.4m telescopes, about fifteen 1m telescopes, and two 2m telescopes, all of which will initially be equipped for both high-speed and traditional CCD imaging. Instruments for high-speed applications are described in Bianco et al. (this session). Here we describe LCOGT's instruments for relatively wide-field imaging at moderate time cadence. The most notable of these is the "Sinistro" camera system being built for the 1m network. It consists of corrector optics, filter changer, photometric shutter, 16 Mpix CCD camera, and custom CCD controller. Each Sinistro component is optimized for precision photometric measurements, and the system provides a large critically sampled field to the full CCD, rapid access to as many as 21 different filters, minimized shutter overhead, flexible high-speed readout, support for multiple independent regions of interest, the ability to autoguide independently of camera focus, precision CCD temperature control and telemetry, and a dry nitrogen filter environment.
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    ABSTRACT: Las Cumbres Observatory Global Telescope Network (LCOGT) is building a world wide telescope network with an emphasis on time domain astronomy. The final LCOGT network will have at least 40 telescopes in at least 7 sites around the world to continuously cover the dark sky in both hemispheres: two 2.0m telescopes, already available on Haleakala - HI, USA (FTN), and Siding Spring - Australia (FTS), roughly fifteen 1m, and twenty-five 0.4m telescopes now in various stages of construction and commissioning. We are integrating our telescopes with high speed EMCCD cameras to provide high speed photometry as well as lucky imaging capabilities. Here we present our first generation high speed solutions, already installed at FTN and FTS and currently being integrated into our robotic system. Similar facilities are being fabricated for the 0.4m network, and designed for the 1m network.
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    ABSTRACT: We present a catalog of emission-line galaxies selected solely by their emission-line fluxes using a wide-field integral field spectrograph. This work is partially motivated as a pilot survey for the upcoming Hobby-Eberly Telescope Dark Energy Experiment. We describe the observations, reductions, detections, redshift classifications, line fluxes, and counterpart information for 397 emission-line galaxies detected over 169 ' with a 3500-5800 Å bandpass under 5 Å full-width-half-maximum (FWHM) spectral resolution. The survey's best sensitivity for unresolved objects under photometric conditions is between 4 and 20× 10–17 erg s–1 cm–2 depending on the wavelength, and Lyα luminosities between 3 × 1042 and 6 × 1042 erg s–1 are detectable. This survey method complements narrowband and color-selection techniques in the search of high-redshift galaxies with its different selection properties and large volume probed. The four survey fields within the COSMOS, GOODS-N, MUNICS, and XMM-LSS areas are rich with existing, complementary data. We find 105 galaxies via their high-redshift Lyα emission at 1.9 < z < 3.8, and the majority of the remainder objects are low-redshift [O II]3727 emitters at z < 0.56. The classification between low- and high-redshift objects depends on rest-frame equivalent width (EW), as well as other indicators, where available. Based on matches to X-ray catalogs, the active galactic nuclei fraction among the Lyα emitters is 6%. We also analyze the survey's completeness and contamination properties through simulations. We find five high-z, highly significant, resolved objects with FWHM sizes >44 ' which appear to be extended Lyα nebulae. We also find three high-z objects with rest-frame Lyα EW above the level believed to be achievable with normal star formation, EW0>240 Å. Future papers will investigate the physical properties of this sample.
    The Astrophysical Journal Supplement Series 12/2010; 192(1):5. DOI:10.1088/0067-0049/192/1/5 · 14.14 Impact Factor
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    ABSTRACT: We study the escape of Ly-alpha photons from Ly-alpha emitting galaxies (LAEs) and the overall galaxy population using a sample of 99 LAEs at 1.9<z<3.8 detected through integral-field spectroscopy of blank fields by the HETDEX Pilot Survey. For 89 LAEs showing counterparts in deep broad-band images we measure the rest-frame UV luminosity and the UV slope, which we use to estimate E(B-V) under the assumption of a constant intrinsic UV slope for LAEs. These two quantities are used to measure the dust-corrected star formation rate (SFR). A comparison between the observed Ly-alpha luminosity and that predicted by the dust-corrected SFR yields the Ly-alpha escape fraction. We also measure the Ly-alpha luminosity function. Integration of the luminosity function provides a measurement of the Ly-alpha luminosity density across our redshift range. We combine our data with that from other surveys at 0.3<z<7.7 to trace the evolution of the Ly-alpha luminosity density. We then compare it to that expected from the star-formation history of the universe in order to characterize the evolution of the Ly-alpha escape fraction of the overall galaxy population [abriged]
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    ABSTRACT: We present a catalog of emission-line galaxies selected solely by their emission-line fluxes using a wide-field integral field spectrograph. This work is partially motivated as a pilot survey for the upcoming Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). We describe the observations, reductions, detections, redshift classifications, line fluxes, and counterpart information for 397 emission-line galaxies detected over 169 sq.arcmin with a 3500-5800 Ang. bandpass under 5 Ang. full-width-half-maximum (FWHM) spectral resolution. The survey's best sensitivity for unresolved objects under photometric conditions is between 4-20 E-17 erg/s/sq.cm depending on the wavelength, and Ly-alpha luminosities between 3-6 E42 erg/s are detectable. This survey method complements narrowband and color-selection techniques in the search for high redshift galaxies with its different selection properties and large volume probed. The four survey fields within the COSMOS, GOODS-N, MUNICS, and XMM-LSS areas are rich with existing, complementary data. We find 104 galaxies via their high redshift Ly-alpha emission at 1.9<z<3.8, and the majority of the remainder objects are low redshift [OII]3727 emitters at z<0.56. The classification between low and high redshift objects depends on rest frame equivalent width, as well as other indicators, where available. Based on matches to X-ray catalogs, the active galactic nuclei (AGN) fraction amongst the Ly-alpha emitters (LAEs) is 6%. We also analyze the survey's completeness and contamination properties through simulations. We find five high-z, highly-significant, resolved objects with full-width-half-maximum sizes >44 sq.arcsec which appear to be extended Ly-alpha nebulae. We also find three high-z objects with rest frame Ly-alpha equivalent widths above the level believed to be achievable with normal star formation, EW(rest)>240 Ang. Comment: 45 pages, 36 figures, 5 tables, submitted to ApJS
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    ABSTRACT: Scientific performance specifications, a necessity for ease of commissioning and minimal maintenance, and a desire for automated sensing and remote collimation have led to novel designs and features in LCOGT's one-meter Optical Tube Assembly (OTA). We discuss the design and performance of the quasi-RC optical system with 18 point whiffletree and radial hub mount. Position probes and IR temperature sensors on the primary and secondary mirrors give feedback for active collimation and thermal control. A carbon fiber/epoxy composite truss, with unique spherical node connections, mounts to parallel and offset Invar vanes. A flexure based, closed loop, 3-DOF secondary mirror mechanism is used for tip/tilt collimation. The optics and deflections of the OTA components were iteratively designed for passive collimation with a changing gravity vector. We present the FEA predictions, measured deflections, and measured hysteresis for many of the components. Vibration modes, amplitudes, and damping of the system are presented with an FFT frequency analysis. Thermal CTE effects on loading and focal position are quantified. All of these system effects are then related to the overall scientific performance of the 1.0 m telescope.
    Proceedings of SPIE - The International Society for Optical Engineering 07/2010; DOI:10.1117/12.857809 · 0.20 Impact Factor
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    ABSTRACT: Las Cumbres Observatory Global Telescope (LCOGT) is a privately-funded observatory dedicated to time-domain astronomy. Our main observing tool will be a homogeneous world-wide network of 12 x 1m optical telescopes, each equipped for both imaging and spectroscopy. Here we describe the LCOGT 1m telescope design, its development status, and our plans for deploying a dozen or so such telescopes in a worldwide network capable of continuous observing. We also describe the 80 cm Sedgwick telescope, which is now in regular operation as a research instrument, and which has served as a prototype for many of the 1m mechanical and control systems.
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    ABSTRACT: Flat fielding is necessary to have for calibrating data and traditional methods can sometimes be troublesome. With limited twilight time available for sky flats and difficulties with uniform illumination, clearance space, or with mounting (as with clamshell style domes) for dome flats, consistency between sites will be difficult to obtain. The Las Cumbres Observatory Global Telescope Network (LCOGT) is going to have approximately thirty telescopes ranging from 0.4m to 2.0m, and so a reliable and consistent way of taking flat fields needs to be implemented. Lambert is a device that has been designed and currently being tested on the two 2.0m Faulkes Telescope North and South as a way to simplify the flat fielding process. Lambert has been designed as a 1-D bar of LED lights equal in length to the primary mirror that scans horizontally across the pupil of the telescope. This system has the advantages over traditional dome flats of having a theoretically uniform illumination in the scan direction, minimal sources, ease of deployment, and minimal space requirements. The two 2.0m Lamberts have been deployed and are currently being tested with the 0.4m Lambert and the 1.0m Lambert still in the design phase. By comparing the Lambert flats to sky flats, LCOGT will hope to show that the two methods of flat fielding are comparable and therefore be able to save calibration time during the twilight hours by performing Lambert flats during the day. Initial tests show that the Lambert flats and sky flats agree to better than 1% on the 2.0m Lambert and to about 1% on the 0.4m Lambert in spectral ranges where the LEDs have meaningful output.
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    ABSTRACT: The Las Cumbres Observatory Global Telescope Network (LCOGT) is an ambitious project to build and operate, within 5 years, a worldwide robotic network of 50 0.4, 1, and 2 m telescopes sharing identical instrumentation and optimized for precision photometry of time-varying sources. The telescopes, instrumentation, and software are all developed in house with two 2 m telescopes already installed. The LCOGT Imaging Lab is responsible for assembly and characterization of the network's cameras and instrumentation. In addition to a fully equipped CNC machine shop, two electronics labs, and a future optics lab, the Imaging Lab is designed from the ground up to be a superb environment for bare detectors, precision filters, and assembled instruments. At the heart of the lab is an ISO class 5 cleanroom with full ionization. Surrounding this, the class 7 main lab houses equipment for detector characterization including QE and CTE, and equipment for measuring transmission and reflection of optics. Although the first science cameras installed, two TEC cooled e2v 42-40 deep depletion based units and two CryoTiger cooled Fairchild Imaging CCD486-BI based units, are from outside manufacturers, their 18 position filter wheels and the remainder of the network's science cameras, controllers, and instrumentation will be built in house. Currently being designed, the first generation LCOGT cameras for the network's 1 m telescopes use existing CCD486-BI devices and an in-house controller. Additionally, the controller uses digital signal processing to optimize readout noise vs. speed, and all instrumentation uses embedded microprocessors for communication over ethernet.
    Proceedings of SPIE - The International Society for Optical Engineering 08/2008; DOI:10.1117/12.790144 · 0.20 Impact Factor
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    ABSTRACT: We present the design and performance of the prototype Visible Integral-field Replicable Unit Spectrograph (VIRUS-P) camera. Commissioned in 2007, VIRUS-P is the prototype for 150+ identical fiber-fed integral field spectrographs for the Hobby-Eberly Telescope Dark Energy Experiment. With minimal complexity, the gimbal mounted, double-Schmidt design achieves high on-sky throughput, image quality, contrast, and stability with novel optics, coatings, baffling, and minimization of obscuration. The system corrector working for both the collimator and f / 1.33 vacuum Schmidt camera serves as the cryostat window while a 49 mm square aspheric field flattener sets the central obscuration. The mount, electronics, and cooling of the 2k × 2k, Fairchild Imaging CCD3041-BI fit in the field-flattener footprint. Ultra-black knife edge baffles at the corrector, spider, and adjustable mirror, and a detector mask, match the optical footprints at each location and help maximize the 94% contrast between 245 spectra. An optimally stiff and light symmetric four vane stainless steel spider supports the CCD which is thermally isolated with an equally stiff Ultem-1000 structure. The detector/field flattener spacing is maintained to 1 mum for all camera orientations and repeatably reassembled to 12 mum. Invar rods in tension hold the camera focus to +/-4 mum over a -5-25 °C temperature range. Delivering a read noise of 4.2 e- RMS, sCTE of 1-10-5 , and pCTE of 1-10-6 at 100 kpix/s, the McDonald V2 controller also helps to achieve a 38 hr hold time with 3 L of LN2 while maintaining the detector temperature setpoint to 150 muK (5sigma RMS).
    Proceedings of SPIE - The International Society for Optical Engineering 08/2008; DOI:10.1117/12.790099 · 0.20 Impact Factor
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    ABSTRACT: Traditional dome flat fielding methods typically have difficulties providing spatially uniform illumination and adequate flux over a telescopic instrument's entire spectral range. Traditional flat fielding screens, with an illumination source at least the size of the primary, can be difficult or impractical to mount and uniformly illuminate. The Las Cumbres Observatory Global Telescope Network (LCOGTN) will consist of approximately 50 robotic telescopes of 0.4 m, 1.0 m, and 2.0 m apertures with instrument bandwidth ranging from 350 - 1800 nm. The network requires a robust flat-field solution to fit in compact enclosures. A scanning illuminated flat fielding bar, Lambert, was developed to meet these requirements. Illumination is from a linear arrangement of sources that are spatially dispersed by a narrow holographic or glass diffuser equal in length to the primary's diameter. We have investigated a linearly scanning, enclosure mounted, deployable unit, and a rotary scanning, telescope mounted unit. For complete visible-light bandwidth, a set of different color LEDs is used. The source density, scan speed, and variable intensity tunes the flux to the instrument wavelength and bandwidth. The Lambert flat fields in comparison to sky flats match pixel to pixel variations better than 0.5%; large scale illumination differences, which are stable and repeatable, are ~1%.
    Proceedings of SPIE - The International Society for Optical Engineering 08/2008; DOI:10.1117/12.790007 · 0.20 Impact Factor
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    ABSTRACT: Las Cumbres Observatory Global Telescope Network, Inc. (LCOGT) operates a privately funded global network of 0.4 - 2.0 m telescopes with the primary mission of precision photometry. Presently LCOGT operates the two 2 m Faulkes telescopes (Hawaii, US and Siding Spring, AU) with designs in progress for a network of 20 1 m telescopes and 30 0.4 m telescopes. When complete, the network will allow continuous simultaneous multiband photometry from both the northern and southern hemispheres. The LCOGT imaging lab is responsible for the design, construction, assembly, and characterization of all network cameras. Since it started in April of 2007, the lab has already characterized and commissioned two 2k2 deep depletion cameras with 18 live filters in each. We are also nearing deployment of two 4k2 cameras also with 18 filters each. Ultimately the 1 m network, deployed in groups of 3 - 4 telescopes at each site, will have at least a 4k2 camera with full filter complement on each telescope. The lab's planned facilities include a Class 100 clean room, test and measurement setups for fully characterizing filter transmission from 300- 1100 nm, and detector quantum efficiency, charge transfer efficiency, residual image, gain, and read noise.
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    ABSTRACT: We describe the design, construction, and performance of VIRUS-P (Visible Integral-field Replicable Unit Spectrograph – Prototype), the prototype for 150+ identical fiber-fed integral field spectrographs for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). VIRUS-P was commissioned in 2007, is in regular service on the McDonald Observatory 2.7 m Smith telescope, and offers the largest field of any integral field spectrograph. The 246-fiber IFU uses a densepak-type fiber bundle with a 1/3 fill factor. It is fed at f/3.65 through a telecentric, two-group dioptric focal reducer. The spectrograph's double-Schmidt optical design uses a volume phase holographic grating at the pupil between the articulating f/3.32 folded collimator and the f/1.33 cryogenic prime focus camera. High on-sky throughput is achieved with this catadioptric system by the use of high reflectivity dielectric coatings, which set the 340-670 nm bandwidth. VIRUS-P is gimbal-mounted on the telescope to allow short fibers for high UV throughput, while maintaining high mechanical stability. The instrument software and the 18 square arcmin field, fixed-offset guider provide rapid acquisition, guiding, and precision dithering to fill in the IFU field. Custom software yields Poisson noise limited, sky subtracted spectra. The design characteristics are described that achieved uniformly high image quality with low scattered light and fiber-to-fiber cross talk. System throughput exceeds requirements and peaks at 40%. The observing procedures are described, and example observations are given.
    Proceedings of SPIE - The International Society for Optical Engineering 01/2008; 7014. DOI:10.1117/12.790235 · 0.20 Impact Factor
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    ABSTRACT: Low-dispersion optical spectra have been obtained with the Hobby-Eberly Telescope of 22 very red objects found in early imaging data from the Sloan Digital Sky Survey (SDSS). The objects are assigned spectral types on the Two Micron All Sky Survey (2MASS) system and are found to range from late M to late L. The red and near-infrared colors from SDSS and 2MASS correlate closely with each other, and most of the colors are closely related to spectral type in this range; the exception is the i*-z* color, which appears to be independent of spectral type between about M7 and L4. The spectra suggest that this independence is due to the disappearance of the TiO and VO absorption in the i band for later spectral types, the presence of strong Na I and K I absorption in the i band, and the gradual disappearance of the 8400 Å absorption of TiO and FeH in the z band.
    The Astronomical Journal 12/2007; 123(1):458. DOI:10.1086/338095 · 4.05 Impact Factor
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    ABSTRACT: The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) will outfit the 10 m HET with a new wide field and an array of 145 integral-field spectrographs to survey a 400 sq. degree area in the north galactic cap. Each fiber-coupled unit spectrograph will cover 350-590 nm, simultaneously at 5 A resolution, providing 40,000 spectra per exposure. This instrument, called VIRUS, will open up surveys of the emission-line universe for the first time, and in particular will be used to detect 1 million Lyman-alpha emitting (LAE) galaxies with 1.9 < z < 3.8. The prototype of the VIRUS unit spectrograph (VIRUS-P) is a powerful instrument in its own right. Used on the McDonald 2.7 m Smith reflector, it covers the largest area of any integral field spectrograph, and has coverage down to 340 nm. It is currently in use for a pilot survey to better measure the properties of LAE galaxies in support of HETDEX, among other investigations where it is uniquely powerful. We report details of the VIRUS-P design and its performance. VIRUS-P has been made possible by a generous donation from the Cynthia and George Mitchell Foundation. This work is supported by Texas Advanced Research Program Grant No. 003658-0005-2006
  • Joseph R. Tufts, Phillip J. MacQueen
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    ABSTRACT: The McDonald Observatory detector group recently added IR capability to their Version 2 (V2) CCD controller. With minimal hardware and software modifications, we are operating HAWAII-nRG devices. Principally modified to support a HA WAH-1RG detector for LRS-J, a J-band extension to the HET's low-resolution spectrograph, our existing system can be used to operate 2RG devices in 4-amplifier mode as well. LRS-J based on a cryogenic prime focus camera optical design, uses an unusual approach to mounting a 1RG device, and it requires custom cryostat circuitry to minimize heat load, obscuration, and changes to the CCD-based electronics. It takes advantage of the nRGs programmability and makes dual use of the serial interface programming lines. AC coupling the preamplifier to the detector requires line-by-line DC restoration, but yields stable reference pixel values between frames. The performance of the reference amplifier and reference pixels are under investigation for use in long integration time, low background spectrometry.
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    ABSTRACT: We present the design of, and the science drivers for, the Visible Integral-field Replicable Unit Spectrograph (VIRUS). This instrument is made up of 145 individually small and simple spectrographs, each fed by a fiber integral field unit. The total VIRUS-145 instrument covers ~30 sq. arcminutes per observation, providing integral field spectroscopy from 340 to 570 nm, simultaneously, of 35,670 spatial elements, each 1 sq. arcsecond on the sky. This corresponds to 15 million resolution elements per exposure. VIRUS-145 will be mounted on the Hobby-Eberly Telescope and fed by a new wide-field corrector with 22 arcminutes diameter field of view. VIRUS represents a new approach to spectrograph design, offering the science multiplex advantage of huge sky coverage for an integral field spectrograph, coupled with the engineering multiplex advantage of >100 spectrographs making up a whole. VIRUS is designed for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) which will use baryonic acoustic oscillations imprinted on the large-scale distribution of Lyman-α emitting galaxies to provide unique constraints on the expansion history of the universe that can constrain the properties of dark energy.
    Proceedings of SPIE - The International Society for Optical Engineering 01/2006; 6269. DOI:10.1117/12.672630 · 0.20 Impact Factor