We present the flight performance and preliminary science results from the first flight of the Sub-orbital Local
Interstellar Cloud Experiment (SLICE). SLICE is a rocket-borne far-ultraviolet instrument designed to study the diffuse
interstellar medium. The SLICE payload comprises a Cassegrain telescope with LiF-coated aluminum optics feeding a
Rowland Circle spectrograph operating at medium resolution (R ~ 5000) over the 102 – 107 nm bandpass. We present a
novel method for cleaning LiF-overcoated Al optics and the instrumental wavelength calibration, while the details of the
instrument design and assembly are presented in a companion proceeding (Kane et al. 2013). We focus primarily on
first results from the spring 2013 launch of SLICE in this work. SLICE was launched aboard a Terrier-Black Brant IX
sounding rocket from White Sands Missile Range to observe four hot stars sampling different interstellar sightlines. The
instrument acquired approximately 240 seconds of on-target time for the science spectra. We observe atomic and
molecular transitions (HI, OI, CII, OVI, H2) tracing a range of temperatures, ionization states, and molecular fractions in
diffuse interstellar clouds. Initial spectral synthesis results and future plans are discussed.
We present the fabrication and testing of the Sub-orbital Local Interstellar Cloud Experiment (SLICE), a rocket-borne
payload for ultraviolet astrophysics in the 1020 to 1070 Å bandpass. The SLICE optical system is composed of an
ultraviolet-optimized telescope feeding a Rowland Circle spectrograph. The telescope is an 8-inch Classical Cassegrain
operating at F/7, with Al optics overcoated with LiF for enhanced far-ultraviolet reflectivity. The holographically-ruled
grating focuses light at an open-faced microchannel plate detector employing an opaque RbBr photocathode. In this
proceeding, we describe the design trades and calibration issues confronted during the build-up of this payload. We
place particular emphasis on the technical details of the design, modifications, construction, and alignment procedures
for SLICE in order to provide a roadmap for the optimization of future ruggedized experiments for ultraviolet imaging
and spectroscopy.
We present a conceptual design for a high-resolution optical spectrograph appropriate for mounting at Cassegrain on a large aperture telescope. The design is based on our work for the Gemini High Resolution Optical Spectrograph (CUGHOS) project. Our design places the spectrograph at Cassegrain focus to maximize throughput and blue wavelength coverage, delivering R=40,000 resolving power over a continuous 320–1050 nm waveband with throughputs twice those of current instruments. The optical design uses a two-arm, cross-dispersed echelle format with each arm optimized to maximize efficiency. A fixed image slicer is used to minimize optics sizes. The principal challenge for the instrument design is to minimize flexure and degradation of the optical image. To ensure image stability, our opto-mechanical design combines a cost-effective, passively stable bench employing a honeycomb aluminum structure with active flexure control. The active flexure compensation consists of hexapod mounts for each focal plane with full 6-axis range of motion capability to correct for focus and beam displacement. We verified instrument performance using an integrated model that couples the optical and mechanical design to image performance. The full end-to-end modeling of the system under gravitational, thermal, and vibrational perturbations shows that deflections of the optical beam at the focal plane are <29 μm per exposure under the worst case scenario (<10 μm for most orientations), with final correction to 5 μm or better using open-loop active control to meet the stability requirement. The design elements and high fidelity modeling process are generally applicable to instruments requiring high stability under a varying gravity vector.
A key astrophysical theme that will drive future UV/optical space missions is the life cycle of cosmic matter, from the
flow of intergalactic gas into galaxies to the formation and evolution of exoplanetary systems. Spectroscopic systems
capable of delivering high resolution with low backgrounds will be essential to addressing these topics. Towards this
end, we are developing a rocket-borne instrument that will serve as a pathfinder for future high-sensitivity, highresolution
UV spectrographs. The Colorado High-resolution Echelle Stellar Spectrograph (CHESS) will provide 2 km
s-1 velocity resolution (R = 150,000) over the 100 - 160 nm bandpass that includes key atomic and molecular spectral
diagnostics for the intergalactic medium (H I Lyman-series, O VI, N V, and C IV), exoplanetary atmospheres (H I
Lyman-alpha, O I, and C II), and protoplanetary disks (H2 and CO electronic band systems). CHESS uses a novel
mechanical collimator comprised of an array of 10 mm x 10 mm stainless steel tubes to feed a low-scatter, 69 grooves
mm-1 echelle grating. The cross-disperser is a holographically ruled toroid, with 351 grooves mm-1. The spectral orders
can be recorded with either a 40 mm cross-strip microchannel plate detector or a 3.5k x 3.5k δ-doped CCD. The
microchannel plate will deliver 30 μm spatial resolution and employs new 64 amp/axis electronics to accommodate high
count rate observations of local OB stars. CHESS is scheduled to be launched aboard a NASA Terrier/Black Brant IX
sounding rocket from White Sands Missile Range in the summer of 2013.
We present the Colorado High-resolution Echelle Stellar Spectrograph (CHESS) sounding rocket payload. The
design uses a mechanical collimator made from a grid of square tubing, an objective echelle grating, a holographically-ruled
cross-disperser, a new 40 mm MCP with a cross strip anode or a delta-doped 3.5k x 3.5k CCD detector. The optics
are suspended using carbon fiber rods epoxied to titanium inserts to create a space frame structure. A preliminary design
is presented.
The Cosmic Origins Spectrograph (COS) was installed into the Hubble Space Telescope (HST) during Servicing
Mission 4 (SM4) in May 2009. COS is designed to obtain spectra of faint objects at moderate spectral resolution (R >
16,000) in two channels: FUV, covering wavelengths from 1150 to 1450 Å; and NUV, covering 1700 - 3200 Å. Two
low resolution gratings (R > 1500) cover the < 900 - 2050 Å (FUV) and 1650 - 3200 Å (NUV) wavelength regions. An
imaging capability is also available on the NUV channel.
As part of the Hubble Servicing Mission Observatory Verification (SMOV) program, an extensive period of checkout,
fine-tuning and preliminary characterization began after the installation of COS. The COS SMOV program was a
cooperative effort between the Space Telescope Science Institute and the Instrument Definition Team based at the
University of Colorado. Nearly 2800 COS exposures in 34 separate observing programs were obtained during the course
of SMOV. Early activities included an initial instrument functional checkout, turn-on and initial characterization of the
detectors, NUV and FUV channel focus and alignment, and target acquisition verification and assessment. Once this
initial period was completed, science-related calibrations and verifications were performed in order to prepare the
instrument for normal science operations. These activities included wavelength calibration, flux calibration, detector flat
field characterization, spectroscopic performance verification, high S/N operation, and thermal and structural stability
measurements. We discuss the design, execution and results of the SMOV program, including the interrelationships
between the various tasks, and how the pre-launch plan was adjusted in real-time due to changing conditions.
We have assembled and launched the Diffuse Interstellar Cloud Experiment (DICE), an instrument capable of
recording high resolution (λ/δλ = 30,000) spectra in the Far Ultraviolet (FUV). Absorption measurements toward nearby
bright stars can provide new insight into the processes governing warm-hot gas in the Local Interstellar Medium. It flew
on May 21st, 2010. An anomaly in the Black Brant motor subjected the payload to abnormally high vibration. As a
result, the optics were misaligned and no spectral data fell on the detector. Here we present the details of mechanical and
electrical integration with NASA launch systems, as well as optical alignment of the telescope and spectrograph. In
addition, we summarize the flight results.
We discuss the design of a new high-efficiency, high-resolution far ultraviolet echelle spectrograph. Our project
concentrates on utilizing new technologies for gratings and detectors to reduce the impact of scattered light and
maximize quantum efficiency over a large bandpass. This program will enable advances in a vast number of
astrophysical subjects. Topics ranging from protoplanetary disks to the intergalactic medium can be addressed by
incorporating such a spectrograph into a future, long-duration mission.
The Southern African Large Telescope is nearing the end of its commissioning phase and scientific performance
verification programmes began in 2006 with two of its First Generation UV-visible instruments, the imaging camera,
SALTICAM, and the multi-mode Robert Stobie Spectrograph (RSS). Both instruments are seeing limited and designed to
operate in the UV-visible region (320 - 900 nm). This paper reviews the innovative aspects of the designs of these
instruments and discusses the commissioning experience to date, illustrated by some initial scientific commissioning
results. These include long-slit and multi-object spectroscopy, spectropolarimetry, Fabry-Perot imaging spectroscopy and
high-speed photometry. Early spectroscopic commissioning results uncovered a serious underperformance in the
throughput of RSS, particularly at wavelengths < 400nm. We discuss the lengthy diagnosis and eventual removal of this
problem, which was traced to a material incompatibility issue involving index-matching optical coupling fluid. Finally,
we briefly discuss the present status of the third and final First Generation instrument, a vacuum enclosed fibre-fed high
resolution, dual beam, white pupil echelle spectrograph, SALT HRS, currently under construction.
The Prime Focus Imaging Spectrograph (PFIS) is a first light instrument for the Southern African Large Telescope
(SALT). PFIS is a versatile instrument designed to operate in a number of scientific modes by utilizing volume phase
holographic gratings, Fabry-Perot etalons, and polarimetric optics, which are manipulated in and out of the beam using
various placement mechanisms. The instrument is mounted at the prime focus 15m above the primary mirror and tilted at
37°. This remote placement and the need for 240° of rotation about the optical axis raises important design issues with
mass, flexure and access. The instrument structure provides the interface to the telescope Prime Focus Instrument
Platform (PFIP) as well as support points for all the optics, mechanisms and electrical equipment. The structure is a
welded open truss of hollow, square-section Invar beams. The open truss provides the highest stiffness to weight ratio
and minimizes the effect of wind loading, while the use of Invar negates the effects of thermal expansion. It has been
designed using finite element analysis in conjunction with an optical tolerance analysis of the optics nodes to minimize
effective image motion under the varying gravity load. The fundamentals of the design of the structure to minimize the
flexure and its effect on image motion, the motivation for using the open Invar truss structure, and the design of the
remotely operated mechanisms are discussed. In 2005 PFIS was installed and commissioned on SALT in South Africa.
Included in this text are some of the results and experiences of taking PFIS into operation.
"First light" of the Southern African Large Telescope was declared on 1 Sep 2005 and the first scientific programs have now begun. This paper discusses the completion and commissioning of the first-light instruments: the UV-visible imaging camera, SALTICAM, and the prime focus imaging spectrograph, the Robert Stobie Spectrograph (RSS). The
innovative aspects and tight constraints on the design of these prime focus instruments are described, as well as the first scientific results. These instruments, which are all seeing limited, operate in the UV-visible region (320 - 900 nm), and will provide capabilities for broad and narrow band imaging, long-slit and multi-object spectroscopy (R ~ 6000 for seeing limit), spectropolarimetry and Fabry-Perot imaging spectroscopy (R ~ 320-9,000). Time resolved studies are an important aspect of the overall SALT science drivers and special efforts were made to ensure an ability to run at ~10 Hz, with minimal dead time, by employing frame transfer CCDs. Finally, we present the design and status of the fiber-fed high resolution echelle spectrograph, SALTHRS, the last of the "first generation" SALT instruments.
The Prime Focus Imaging Spectrograph (PFIS) will be the workhorse first-light instrument on the Southern African Large Telescope (SALT). Scheduled for commissioning in late 2004, PFIS is a versatile high-throughput imaging spectrograph with a complement of 5 volume-phase holographic gratings for spectroscopic programs from 3200Å to 9000Å at resolutions of R=1500 to R=6000. A magazine of 6 longslits and 30 custom laser-milled slitmasks enables single- or multi-object spectroscopy over an 8 arcminute diameter field. With the gratings stowed, a dual-etalon Fabry-Perot subsystem enables imaging spectroscopy at R=500, R=3000, and R=12,500. The polarization subsystem, consisting of a polarizing beam-splitter used in conjunction with half- and quarter-wave plates, allow linear or circular polarimetric measurements in ANY of the spectroscopic modes. Three mosaiced rapid-readout frame-transfer CCDs provide the capability for time-resolved sampling at rates in excess of 10 Hz. Combinations of these subsystems permit novel observing modes for specialized scientific programs. Examples include high-time resolution multi-object spectral polarizmetry of accreting compact objects, and Fabry-Perot polarimetry or imaging spectral polarimetry of nebulae and stellar clusters. The demands of queue-scheduled observing on a fixed-altitude telescope require that the instrument be capable of rapid reconfiguration between modes.
The University of Wisconsin - Madison, together with Rutgers University and the South African Astronomical Observatory, is designing and building an imaging spectrograph for the Prime Focus Instrument Package of the Southern African Large Telescope (SALT). The Prime Focus Imaging Spectrograph (PFIS) will be a versatile instrument specializing in very high throughput, low and medium resolution (R=500-12,500) imaging spectroscopy, using volume phase holographic (VPH) gratings and a double etalon Fabry-Perot interferometer, and spectropolarimetry from 320 to 900 nm. The optical design includes all transmissive optics for high efficiency and compactness. To maintain throughput in the ultraviolet, only fused silica, CaF2 and NaCl are used. As NaCl is very hygroscopic, the design uses NaCl as the inner element in sealed triplets only. For the highest possible first-order spectral resolution, the collimated beam size is 150 mm - the maximum for practical Fabry-Perot etalons. The F/2.2 camera can be articulated to tune the efficiency of the VPH gratings; a complement of six gratings (5 VPH and 1 standard transmission grating) has been designed to fill the resolution-wavelength space available to the instrument. Linear, circular, and all-stokes spectropolarimetry will be performed through the use of Pancharatnam superachromatic waveplates and a Wollaston beamsplitter.
Linear spectropolarimetry of spectral lines is a neglected field in astronomy, largely because of the lack of instrumentation. Techniques that have been applied, but rarely, include investigation of the dynamics of scattering envelopes through the polarization of electron- or dust-scattered nebular light. Untried techniques include promising new magnetic diagnostics like the Hanle Effect in the far-ultraviolet and magnetic realignment in the visible. The University of Wisconsin Space Astronomy Lab is developing instrumentation for such investigations. In the visible, the Prime Focus Imaging Spectrograph (PFIS) is a first light instrument for the Southern African Large Telescope (SALT), which at an aperture of 11m will be the largest single telescope in the Southern Hemisphere. Scheduled for commissioning in late 2004, PFIS is a versatile high-throughput imaging spectrograph using volume-phase holographic gratings for spectroscopic programs from 320nm to 900nm at resolutions of R=500 to R=6000. A dual-etalon Fabry-Perot subsystem enables imaging spectroscopy at R=500 and R=3000 or 12,500. The polarization subsystem, consisting of a very large calcite polarizing beam-splitter used in conjunction with half- and quarter-wave Pancharatnam superachromatic plates, allow linear or circular polarimetric measurements in any of the spectroscopic modes. In the FUV, the Far-Ultraviolet SpectroPolarimeter (FUSP) is a sounding rocket payload, scheduled for its first flight in 2003, that will obtain the first high-precision spectropolarimetry from 105 - 150 nm, and the first astronomical polarimetry of any kind below 130 nm. The 50 cm primary mirror of the telescope is F/2.5. At the prime focus are the polarimetric optics, a stressed lithium fluoride rotating waveplate, followed by a synthetic diamond Brewster-angle mirror. The spectrometer uses an aberration-corrected spherical holographic grating and a UV-sensitized CCD detector, for a spectral resolution of R=1800.
We describe a vacuum collimator that we have assembled to characterize the windowless ultraviolet properties of a sounding rocket spectrographic telescope. The collimator comprises a Cassegrain telescope, with SiC coated optics, used in the pre-flight calibration phase of the Far Ultraviolet Spectroscopic Explorer, and vacuum skins provided by NASA/Wallops. The collimator focal plane has a three-axis motorized stage, which we have used for the precision placement of a knife edge focal locator along with pinhole and flat-field sources. We describe the focusing procedure and present the results of a number of experiments whereby the collimator, telescope and spectrograph point spread functions were determined and a spectro-spatial flat-field of the detector was acquired.
We present the design of a pinhole lamp recently flown aboard two NASA/JHU sounding rocket missions as a wavelength standard for a far-UV spectrograph with a 900 - 1400 Angstrom bandpass. Lamp configuration, spectral output, gas supplies, payload accommodation and operation procedures are discussed. This lamp could easily be incorporated into future far-UV spectroscopic orbital missions and would benefit science return. We also discuss the use of Bayard-Alpert tubes (ionization gauges) as far-UV sources, which have the advantage of not requiring an external gas supply. At pressures between 10-5 and 10-7 Torr these tubes produce a strong emission line spectra, caused by electron impact with residual gas atoms in the vacuum. Below 10-7 Torr the residual gas line intensities have weaken enough to reveal the long wavelength tail of a 150 eV bremsstrahlung spectrum produced by electron impact onto tungsten grid. The use of ionization gauges in flat field and end-to-end calibration experiments is described. We show how an ionization gauge and spectrograph can be used as a real- time residual gas analyzer sensitive to atomic and molecular gas species that emit within the bandpass. Such a device could be useful in material processing and contamination control environments.
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