[Show abstract][Hide abstract] ABSTRACT: We describe the design, manufacture, and performance of bare-fiber integral
field units (IFUs) for the SDSS-IV survey MaNGA (Mapping Nearby Galaxies at
APO) on the the Sloan 2.5 m telescope at Apache Point Observatory (APO). MaNGA
is a luminosity-selected integral-field spectroscopic survey of 10,000 local
galaxies covering 360-1030 nm at R ~ 2200. The IFUs have hexagonal dense
packing of fibers with packing regularity of 3 um (RMS), and throughput of
96+/-0.5% from 350 nm to 1 um in the lab. Their sizes range from 19 to 127
fibers (3-7 hexagonal layers) using Polymicro FBP 120:132:150 um
core:clad:buffer fibers to reach a fill fraction of 56%. High throughput (and
low focal-ratio degradation) is achieved by maintaining the fiber cladding and
buffer intact, ensuring excellent surface polish, and applying a multi-layer AR
coating of the input and output surfaces. In operations on-sky, the IFUs show
only an additional 2.3% FRD-related variability in throughput despite repeated
mechanical stressing during plate plugging (however other losses are present).
The IFUs achieve on-sky throughput 5% above the single-fiber feeds used in
SDSS-III/BOSS, attributable to equivalent performance compared to single fibers
and additional gains from the AR coating. The manufacturing process is geared
toward mass-production of high-multiplex systems. The low-stress process
involves a precision ferrule with hexagonal inner shape designed to lead
inserted fibers to settle in a dense hexagonal pattern. The ferrule inner
diameter is tapered at progressively shallower angles toward its tip and the
final 2 mm are straight and only a few um larger than necessary to hold the
desired number of fibers. This process scales to accommodate other fiber sizes
and to IFUs with substantially larger fiber count. (Abridged)
Preview · Article · Dec 2014 · The Astronomical Journal
[Show abstract][Hide abstract] ABSTRACT: The near infrared upgrade to the Robert Stobie Spectrograph (RSS/NIR) for the Southern African Large Telescope
(SALT) extends the capabilities of the visible arm RSS into the Near Infrared (NIR). In order to extend into the NIR
range, the upgrade components of the instrument are required to be cooled. Thus the NIR arm is predominantly housed
in the instrument pre-dewar which is cooled to -40°C, at ambient pressure. The multiple modes, prime focus location and
partially cooled instrument introduce interesting engineering considerations. The NIR spectrograph has an ambient
temperature collimator, a cooled (-40°C) dispersers and camera and a cryogenic detector. The cryogenic dewar and
many of the mechanisms are required to operate within the cooled, atmospheric environment. Cooling the pre-dewar to -
40°C at prime focus of the telescope is also an engineering challenge. Mechanical and thermal aspects of the design are
addressed in this paper with a particular emphasis on the unique considerations of building a semi-warm infrared
[Show abstract][Hide abstract] ABSTRACT: We report on the implementation of a star tracker camera to improve the telescope pointing and tracking, at the
WIYN 3.5 m telescope on Kitt Peak, Arizona. We base the overall concept on a star tracker system developed
at the University of Wisconsin and routinely in use now for rocket and high-altitude balloon navigation. This
fairly simple system provides pointing and station-keeping information, accurate to a few arcseconds, typically
within a second.
[Show abstract][Hide abstract] ABSTRACT: The Robert Stobie Spectrograph Near Infrared Instrument (RSS-NIR), a prime focus facility instrument for the 11-meter
Southern African Large Telescope (SALT), is well into its laboratory integration and testing phase. RSS-NIR will
initially provide imaging and single or multi-object medium resolution spectroscopy in an 8 arcmin field of view at
wavelengths of 0.9 - 1.7 μm. Future modes, including tunable Fabry-Perot spectral imaging and polarimetry, have been
designed in and can be easily added later. RSS-NIR will mate to the existing visible wavelength RSS-VIS via a dichroic
beamsplitter, allowing simultaneous operation of the two instruments in all modes. Multi-object spectroscopy covering a
wavelength range of 0.32 - 1.7 μm on 10-meter class telescopes is a rare capability and once all the existing VIS modes
are incorporated into the NIR, the combined RSS will provide observational modes that are completely unique.
The VIS and NIR instruments share a common telescope focal plane, and slit mask for spectroscopic modes, and
collimator optics that operate at ambient observatory temperature. Beyond the dichroic beamsplitter, RSS-NIR is
enclosed in a pre-dewar box operating at -40 °C, and within that is a cryogenic dewar operating at 120 K housing the
detector and final camera optics and filters. This semi-warm configuration with compartments at multiple operating
temperatures poses a number of design and implementation challenges. In this paper we present overviews of the RSSNIR
instrument design and solutions to design challenges, measured performance of optical components, detector
system optimization results, and an update on the overall project status.
[Show abstract][Hide abstract] ABSTRACT: We report on the status of the detector system for the Robert Stobie
Spectrograph Near Infrared Arm (RSS-NIR) for the Southern African Large
Telescope (SALT). The detector is a HAWAII-2RG array with a 1.7 μm
cutoff wavelength. The controller incorporates a Teledyne cryogenic
SIDECAR ASIC board inside the dewar and an FPGA interface card,
developed by the Inter-University Centre for Astronomy and Astrophysics
(IUCAA), outside the dewar. Data acquisition software written by IUCAA
runs under a Linux operating system and communicates to the detector
system through USB to fiber optic converters for electrical isolation on
the telescope. System characterization is performed at the University of
Wisconsin RSS-NIR Lab in a liquid nitrogen cooled test dewar. The test
dewar contains a thermal control system that emulates operation of the
cryocooler used in the instrument dewar and maintains a stable detector
operating temperature of 120 K. Light is provided to the detector with
near infrared LEDs mounted inside the dewar. We present preliminary data
on system noise and plans for further characterization tests.
No preview · Article · Jul 2012 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: The ST5000 is a star tracker developed at the University of Wisconsin and used in NASA's sounding rocket payloads. In order to demonstrate the ST5000's suitability for pointed balloon-borne telescopes, we flew an ST5000 on a stratospheric balloon on May 6, 2011. This flight addressed our four basic questions: will the ST5000 work from 120,000 ft (it does), what was the rms performance (about 0.6"), what angular rates of motion would cause the ST5000 to fail (greater than 0.5 degrees/sec) and could the ST5000 serve as a daytime star tracker (not without modifications). We will briefly present the results from the flight and describe the ST5000's quantitative performance. We will also describe the problems with background light as a function of wavelength, altitude and angle from the Sun. We will discuss approaches to improve the daytime performance using infrared detectors and longer focal lengths/reduced platescales. Solutions that have finer platescales have the potential to improve the star tracker's error signal to the 0.1" level, which is better than the diffraction limit of a one meter telescope at 5000 Å.
No preview · Article · Mar 2012 · IEEE Aerospace Conference Proceedings
[Show abstract][Hide abstract] ABSTRACT: After a year of observations from its new location on Cerro Tololo, the Wisconsin Halpha Mapper (WHAM) has nearly completed survey observations below delta < -30°. This new data combined with the Northern Sky Survey provides the first kinematic, all-sky survey of diffuse Halpha from the Milky Way. Aside from many large-scale, locally-ionized regions, much of this emission arises from the Warm Ionized Medium (WIM), a diffuse but thick component of the ISM that extends several kiloparsecs into the Galactic halo. WHAM was designed primarily to study the WIM, delivering a spatially integrated spectrum from a one-degree beam on the sky covering 200 km s-1 with 12 km s-1 spectral resolution. The short exposures of the survey reach sensitivity levels of about 0.1 R (EM 0.2 pc cm-6) and reveal emission toward nearly every direction in the sky. Here, we present our early efforts at reducing this new southern dataset and offer a first look at the global distribution and kinematics of diffuse ionized gas throughout the Galaxy. WHAM and the research presented here are funded by NSF award AST-0607512. We also thank the excellent and responsive staff at CTIO in Chile for helping to keep our remote installation fully operational.
[Show abstract][Hide abstract] ABSTRACT: After a successful eleven-year campaign at Kitt Peak, we moved the Wisconsin H-Alpha Mapper (WHAM) to Cerro Tololo in early 2009. Here we present some of the early data after a few months under southern skies. These maps begin to complete the first all-sky, kinematic survey of the diffuse H-alpha emission from the Milky Way. Much of this emission arises from the Warm Ionized Medium (WIM), a significant component of the ISM that extends a few kiloparsecs above the Galactic disk. While this first look at the data focuses on the H-alpha survey, WHAM is also capable of observing many other optical emission lines, revealing fascinating trends in the temperature and ionization state of the WIM. Our ongoing studies of the physical conditions of diffuse ionized gas will continue from the southern hemisphere following the H-alpha survey. In addition, future observations will cover the full velocity range of the Magellanic Stream, Bridge, and Clouds to trace the ionized gas associated with these neighboring systems. Comment: 4 pages, 2 figures. To appear in "The Dynamic ISM: A celebration of the Canadian Galactic Plane Survey," ASP Conference Series
[Show abstract][Hide abstract] ABSTRACT: We report on the detector testing status for the Robert Stobie Spectrograph's near-infrared arm. The instrument utilizes a Teledyne HAWAII-2RG HgCdTe detector array with a 1.7 mum cutoff wavelength. We have selected an operating temperature of 120 K. The characterization effort will take place in our detector-testing laboratory at the University of Wisconsin-Madison. The laboratory is equipped with a test dewar, vacuum system, temperature controller, monochromator, and warm detector test enclosure. We will measure detector performance characteristics such as readout noise, gain, dark current, linearity, quantum efficiency, and persistence, and develop calibration strategies. Persistence could have a substantial impact on the spectrograph's science data, and therefore, the development of mitigation techniques for this effect will be emphasized.
Full-text · Article · Jul 2010 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: The results of a project to develop a spatial heterodyne spectrometer (SHS) for a sounding rocket mission to study the Cygnus Loop, a prototypical middle-aged supernova remnant, are discussed. The goal was to obtain a radial velocity-resolved spectrum of the C IV
emission line from bright features of the Cygnus Loop, as a test for mapping the diffuse hot interstellar medium (ISM). A full Fourier-transform analysis of Cygnus Loop emission data is presented, showing lack of velocity-resolved C IV emission detection. Optics contamination is shown to be the most likely problem, and ways to eliminate this contamination for future SHS sounding rocket and satellite missions are discussed.
[Show abstract][Hide abstract] ABSTRACT: The University of Wisconsin's Space Astronomy Laboratory has designed and built a Star Tracker suitable for use on sounding rockets and class D satellites. This device brings together autonomous attitude determination ("Lost in Space" mode), multi-star tracking, and a novel form of Progressive Image Transmission (US patent #5,991,816), which allows the device to be used as an ultra-low bandwidth imager. The Star Tracker 5000 (ST5000) reached operational status in a suborbital sounding rocket flight in August 2007. The ST5000 determined the rocket's inertial (FK5) attitude with arcsecond precision using its autonomous attitude determination capability, and then provided continuous sub-arc-second tracking for the full 360-second on-target portion of the flight. The ST5000 RMS tracking error was 0.54 arc-seconds in yaw and pitch, and 17 arc-seconds in roll. The vehicle RMS jitter was 0.5 arc-seconds in yaw and pitch, and 10 arc-seconds in roll. The ST5000 was funded by NASA grants NAG5-7026 and NAG5-8588.
Preview · Article · Aug 2008 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: The University of Wisconsin's Space Astronomy Laboratory has designed and built a Star Tracker suitable for use on sounding rockets and class D satellites. This device brings together autonomous attitude determination ("Lost in Space" mode), multi-star tracking, and a novel form of Progressive Image Transmission, which allows the device to be used as an ultra-low bandwidth imager. The Star Tracker 5000 reached operational status in a suborbital sounding rocket flight in August 2007. The ST5000 determined the rocket's inertial (FK5) attitude using its autonomous attitude determination capability, and then provided continuous sub-arcsecond tracking for the full 360-second on-target portion of the flight. The ST5000 RMS tracking error was 0.54 arc-seconds in Yaw and Pitch, and 17 arc-seconds in Roll. The vehicle RMS jitter was 0.5 arc-seconds in Yaw and Pitch, and 10 arc-seconds in Roll. The ST5000 was funded by NASA grant NAG5-8588.
[Show abstract][Hide abstract] ABSTRACT: Using a newly developed spatial heterodyne spectrometer, we have obtained the first radial velocity resolved observations of interstellar 3727 A emission and confirmed the superb performance of the technique for observing spatially extended faint sources.
[Show abstract][Hide abstract] ABSTRACT: This paper describes the use of a newly developed Spatial Heterodyne Spectrometer (SHS) designed to observe radial velocity resolved profiles of diffuse [OII] 3726 Å and 3729 Å emission lines from the warm (104 K), low-density (10-1 cm-3), ionized component of our Galaxy's interstellar medium (WIM). The [OII] SHS combines interferometric and field-widening gains to achieve sensitivities much larger than conventional grating instruments of similar size and resolving power, and comparable to the Wisconsin Halpha Mapper (WHAM) Fabry-Perot, but in the near UV where WHAM cannot observe. The high spectral resolution and sensitivity of the SHS allowed us to spectrally isolate for the first time Galactic from terrestrial [OII] emission. We were able to identify the terrestrial [OII] foreground emission and other nearby airglow lines in directions toward very low intensity Galactic [OII] emission regions. The terrestrial [OII] lambda 3729/lambda 3726 line intensity ratio was measured to be 0.47 ± .05:1, compared to an emission ratio of 1.5:1 predicted (and observed) for the interstellar [OII] emission lines in the low density limit. Atmospheric foreground characterization, spectral calibration and absolute intensity calibration are discussed. This research was supported by the NSF through an Astronomy and Astrophysics REU site grant (AST-0453442) at UW-Madison.
[Show abstract][Hide abstract] ABSTRACT: Using a newly developed Spatial Heterodyne Spectrometer (SHS), we have achieved the first detection of diffuse [OII] 372.6 nm and 372.9 nm emission lines from the warm (10,000 K), low density (0.1 cm-3) ionized component of our Galaxy's interstellar medium (WIM). These [OII] lines are a principal coolant for this wide spread, photoionized gas and are a potential tracer of variations in the gas temperature resulting from unidentified interstellar heating processes that appear to be acting within the Galaxy's disk and halo. We have also detected numerous, weak airglow lines, including terrestrial [OII] emission. In our SHS system, Fizeau fringes of wavenumber-dependent spatial frequency are produced by a Michelson interferometer modified by replacing the return mirrors with diffraction gratings. These fringes are recorded on a position sensitive detector and Fourier transformed to recover a spectrum over a limited range centered at the grating Littrow wavenumber. SHS combines interferometric and field-widening gains to achieve sensitivities much larger than conventional grating instruments of similar size and resolving power, and comparable to the Wisconsin Halpha Mapper (WHAM) Fabry-Perot, but in the near UV where WHAM cannot observe. Our early results confirm the superb performance of the SHS technique for measurements of spatially extended faint emissions, including the first detection of [OII] emission lines extending out to 20 degrees from the Galactic equator in the longitude range of 110 to 150 degrees. [OII] intensities range from tens of Rayleighs near the Galactic plane to less than one Rayleigh at high Galactic latitudes. The [OII] line profiles clearly show structure indicating emission along the lines of sight from both local interstellar gas and more distant gas in the Perseus spiral arm. Preliminary line ratio comparisons with WHAM [NII] (658.4 nm) and Halpha (656.3 nm) observations confirm the utility of the [OII] observations as a temperature diagnostic for the WIM. This work is supported by the National Science Foundation through grants AST-0138228 and AST-0138197. The Wisconsin Halpha Mapper is funded by the National Science Foundation through grant AST- 0204973.
[Show abstract][Hide abstract] ABSTRACT: This paper describes the characteristics and performance of a novel spatial heterodyne spectrometer designed to measure the extremely faint [OII] 372.6 nm (lambda3726 Å) and 372.9 nm (lambda3729 Å) emission lines from the warm (10,000 K) ionized component of our Galaxy's interstellar medium. These [OII] lines are a principal coolant for this wide spread, photoionized gas and are a potential tracer of variations in the gas temperature resulting from unidentified interstellar heating processes that appear to be acting within the Galaxy. In the basic SHS system, Fizeau fringes of wavenumber-dependent spatial frequency are produced by a Michelson interferometer modified by replacing the return mirrors with diffraction gratings; these fringes are recorded on a position sensitive detector and Fourier transformed to recover the spectrum over a limited spectral range centered at the Littrow wavenumber of the gratings. The system combines interferometric and field-widening gains in tandem to achieve 10,000-fold sensitivity gains compared to conventional grating instruments of similar size and resolving power. SHS systems also have relaxed flatness tolerances (20-50 times compared to Fabry-Perots) and do not require precision imaging to achieve diffraction-limited spectroscopic performance. Defects can largely be removed in data processing. Early results from our [OII] SHS system confirm the superb performance of the SHS technique for measurements of spatially extended faint emissions, including the first detection of [OII] emission lines extending out to 20 degrees from the Galactic equator ([OII] intensities ranged from tens of rayleighs near the Galactic plane to less than one rayleigh at high latitudes; the [OII] line profiles show structure indicating emission along the lines of sight from both the local interstellar gas and more distant gas in the Perseus spiral arm).
No preview · Article · Sep 2004 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: The Wisconsin H-Alpha Mapper (WHAM) has surveyed the distribution and kinematics of ionized gas in the Galaxy above declination -30 degrees. The WHAM Northern Sky Survey (WHAM-NSS) has an angular resolution of one degree and provides the first absolutely-calibrated, kinematically-resolved map of the H-Alpha emission from the Warm Ionized Medium (WIM) within ~ +/-100 km/s of the Local Standard of Rest. Leveraging WHAM's 12 km/s spectral resolution, we have modeled and removed atmospheric emission and zodiacal absorption features from each of the 37,565 spectra. The resulting H-Alpha profiles reveal ionized gas detected in nearly every direction on the sky with a sensitivity of 0.15 R (3 sigma). Complex distributions of ionized gas are revealed in the nearby spiral arms up to 1-2 kpc away from the Galactic plane. Toward the inner Galaxy, the WHAM-NSS provides information about the WIM out to the tangent point down to a few degrees from the plane. Ionized gas is also detected toward many intermediate velocity clouds at high latitudes. Several new H II regions are revealed around early B-stars and evolved stellar cores (sdB/O). This work presents the details of the instrument, the survey, and the data reduction techniques. The WHAM-NSS is also presented and analyzed for its gross properties. Finally, some general conclusions are presented about the nature of the WIM as revealed by the WHAM-NSS. Comment: 42 pages, 14 figures (Fig 6-9 & 14 are full color); accepted for publication in 2003, ApJ, 149; Original quality figures (as well as data for the survey) are available at http://www.astro.wisc.edu/wham/
Full-text · Article · Sep 2003 · The Astrophysical Journal Supplement Series
[Show abstract][Hide abstract] ABSTRACT: The Wisconsin Halpha Mapper has been designed to produce a survey of Halpha emission from the interstellar medium (ISM) over the entire northern sky. The instrument combines a 0.6 meter telescope and a dual-etalon 15cm Fabry-Perot spectrometer. In the primary spectral mode, an exposure captures a 200km/s spectral region with 8-12km/s velocity resolution from a one-degree beam on the sky. With a large-aperture design and modern CCD technology, WHAM can detect Galactic emission as faint as 0.05 Rayleighs in a 30 second exposure. For gas at 10000K, this observed intensity corresponds to an emission measure of about 0.1cm-6pc, more than 10 million times fainter than the Orion Nebula. (1 data file).
[Show abstract][Hide abstract] ABSTRACT: Spatial Heterodyne Spectroscopy stands poised to play a significant role in astrophysics and atmospheric remote sensing from space and ground-based platforms. This paper will briefly describe the technique and applications in process.
[Show abstract][Hide abstract] ABSTRACT: 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 w ill 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.
Preview · Article · Feb 2003 · Proceedings of SPIE - The International Society for Optical Engineering