The Infrared Spectrograph (IRS) is one of three science instruments on the Spitzer Space Telescope. The IRS comprises four separate spectrograph modules covering the wavelength range from 5.3 to 38 μm with spectral resolutions, R~90 and 650, and it was optimized to take full advantage of the very low background in the space environment. The IRS is performing at or better than the pre-launch predictions. An autonomous target acquisition capability enables the IRS to locate the mid-infrared centroid of a source, providing the information so that the spacecraft can accurately offset that centroid to a selected slit. This feature is particularly useful when taking spectra of sources with poorly known coordinates. An automated data reduction pipeline has been developed at the Spitzer Science Center.
The Spitzer Space Telescope (formally known as SIRTF) was successfully launched on August 25, 2003, and has completed its initial in-orbit checkout and science validation and calibration period. The measured performance of the observatory has met or exceeded all of its high-level requirements, it entered normal operations in January 2004, and is returning high-quality science data. A superfluid-helium cooled 85 cm diameter telescope provides extremely low infrared backgrounds and feeds three science instruments covering wavelengths ranging from 3.6 to 160 microns. The telescope optical quality is excellent, providing diffraction-limited performance down to wavelengths below 6.5 microns. Based on the first helium mass and boil-off rate measurements, a cryogenic lifetime in excess of 5 years is expected. This presentation will provide a summary of the overall performance of the observatory, with an emphasis on those performance parameters that have the greatest impact on its ultimate science return.
The availability of both large aperture telescopes and large
format near-infrared (NIR) detectors are making wide-field NIR
imaging a reality. We describe the Wide-field Infrared Camera
(WIRC), a newly commissioned instrument that provides the Palomar
200-inch telescope with such an imaging capability. WIRC features
a field-of-view (FOV) of 4.33 arcminutes on a side with its
currently installed 1024-square Rockwell Hawaii-I NIR detector. A
2048-square Rockwell Hawaii-II NIR detector will be installed and
commissioned later this year, in collaboration with Caltech, to
give WIRC an 8.7 arcminute FOV on a side. WIRC mounts at the
telescope's f/3.3 prime focus. The instrument's seeing-limited
optical design, optimized for the JHK atmospheric bands,
includes a 4-element refractive collimator, two 7-position filter
wheels that straddle a Lyot stop, and a 5-element refractive f/3
camera. Typical seeing-limited point spread functions are slightly
oversampled with a 0.25 arcsec per pixel plate scale at the detector. The entire optical train is contained within a cryogenic dewar with a 2.5 day hold-time. Entrance hatches at the top of the dewar allow access to the detector without disruption of the optics and optical alignment. The optical, mechanical, cryogenic, and electronic design of the instrument are described, a commissioning science image and performance analyses are presented.
The Infrared Spectrograph, IRS, for SIRTF is a set of four compact low and medium resolution infrared spectrographs designed to work in the wavelength range from 5.3 - 40 micrometers at resolutions, (lambda) /(Delta) (lambda) from 65 to 600. The design involves all reflecting optics with no moving parts. The basic design philosophy, the fabrication process, the test program, and the real-time pointing capabilities are discussed.
This paper describes the design of the space IR telescope Facility (SIRTF) as the project enters the detailed design phase. SIRTF is the fourth of NASA's Great Observatories, and is scheduled for launch in December 2001. SIRTF provides background limited imaging and spectroscopy covering the spectral range from 3 to 180 micrometers , complementing the capabilities of the other great observatories - the Hubble Space Telescope (HST), the Advanced X-ray Astrophysics Facility, and the Compton Gamma Ray Observatory. SIRTF will be the first mission to combine the high sensitivity achievable forma cryogenic space telescope with the imaging and spectroscopic power of the new generation of IR detector arrays. The scientific capabilities of this combination are so great that SIRTF was designated the highest priority major mission for all of US astronomy in the 1990s.
High performance 128 X 128 Si:As and Si:Sb blocked- impurity-band hybrid arrays have been developed for ground- based and airborne astronomy. These devices cover the 5-25 (Si:As) and 15-40 micrometers (Si:Sb) portions of the spectrum. The peak detective quantum efficiencies quantum efficiencies exceed 50 percent for Si:As and 30 percent for Si:Sb. An anti-reflection coat is used to increase responsivity and to reduce internal reflections for the Si:As detectors. The multiplexer yields a linear output response vs. integrated charge. A special design feature of the multiplexer is a changeable nodal capacitance that allows dynamic switching of the well depth between 1.8 X 106 and 1.8 X 107 electrons. The single-sample read noises for the two states are approximately 75 and approximately 760 electrons respectively. These devices have been used successfully to perform astronomical observations in a number of instruments.
SCORE is a cross-dispersed echelle spectrograph, built as a prototype for the Short-High module of SIRTF's IRS instrument. It operates over the 7.5-15 micrometers N-band atmospheric window, and has ben used on Palomar's Hale telescope several times since November, 1996. Since the initial run, a number of improvements have ben undertaken or are in the process being undertaken which enhance SCORE's performance and simplify its operation. One such addition, now completed, is a second detector array which serves as a slit-viewer with 12 inch diameter field of view around the slit. This viewer allows easy acquisition and guidance for sources with dim or absent optical counterparts, and accurately registers the position of the slit on the source with the recorded spectrum. Software written in the IDL environment optimizes the extraction of spectra form SCORE's mid-IR crossed-echelle data. The echelle, while providing the advantage of increased pixel utilization, introduces several difficulties, including curved orders, order cross- talk, and differentially slanted lines. These and other instrumental artifacts must be removed to achieve the highest spectral signal-to-noise. The pixel efficiency will be further increased by the use of a grism predisperser. The grism will provide approximately even spacing between orders of the echelle, in contrast with the decreasing spacing towards shorter wavelength orders generated by the current grating. SCORE is already one of the most powerful short- slit spectrographs operating in this wavelength band, and, with the implementation of these improvements, will deliver even greater capability.
The IR Spectrograph (IRS) will provide the Space IR Telescope Facility (SIRTF) with low and moderate-spectral resolution spectroscopic capabilities from 4 to 40 microns. The IRS is composed of four separate modules, with two of the modules providing R approximately 50 spectral resolution over 4 to 40 microns and two modules providing R approximately 600 spectral resolution over 10 to 37 microns. Each module has its own entrance slit in the focal plane and the IRS instrument has no moving parts. The low-resolution modules employ long slit designs that allow both spectral and 1D spatial information to be acquired simultaneously on the same detector array. Two small imaging sub-arrays in one of the low-resolution modules will also allow IR objects with poorly known positions to be accurately placed into any of the IRS modules' entrance slits. The high-resolution modules use a cross-dispersed echelle design that gives both spectral and limited spatial measurements on the same detector array. The one-sigma continuum sensitivity requirements for the IRS low-resolution modules' one-sigma line sensitivity requirements are 6.0 by 10-23 W- cm-2 in the same integration time. Internal calibration sources allow the IRS to perform self monitoring of detector sensitivity changes. Careful thermal design allows all four modules to be powered up simultaneously and still input less than 4 mW total power into the SIRTF liquid helium bath. The optical, mechanical, thermal, and electrical design of the IRS is discussed, as is the IRS on- orbit operational concept.
We report narrow band adaptive optics near infrared imaging of the planetary nebula IC418. Our 25."6 x 25."6 images were recorded with the SHARP 11+ camera at the ESO 3.6m telescope, using the adaptive optics system ADONIS. The high spatial resolution was combined with the high spectral resolution provided by two Fabry-Perot etalons and a circular variable filter. Here we present images in the Br? and He I emission lines at 2.1655µm and 2.0581µm, respectively and discuss their astrophysical implications. Our results show that combining adaptive optics techniques with high spectral resolution opens a wide field of astrophysical studies.
We describe Corneirs NIR camera system for the Hale 200” telescope adaptive optics system at Palomar Observatory. The instrument is under construction at this time, and we expect first light at the telescope in December 1997. Here we summarize the camera’s design as well as its expected performance.
The optical design of a dual path imaging spectrometer and peak up camera for the IRS instrument on the SIRTF mission is discussed. The dual path configuration allows for a single area array to be simultaneously used for both low resolution spectroscopy and high resolution imagery without overlapping. This is accomplished by the use of off-axis reflective Schmidt cameras in each optical path. These cameras provide a high resolution image and a low resolution spectral image that reside side-by-side on the focal plane without residing side-by-side in the object field.
The optical design of a breadboard high resolution infrared spectrometer for the IRS instrument on the SIRTF mission is discussed. The spectrometer uses a crossed echelle grating configuration to cover the spectral region from 10 to 20 micrometer with a resolving power of approximately equals 600. The all reflective spectrometer forms a nearly diffraction limited image of the two dimensional spectrum on a 128 multiplied by 128 arsenic doped silicon area array with 75 micrometer pixels. The design aspects discussed include, grating numerology, image quality, packaging and alignment philosophy.
Cryogenic telescopes in space offer dramatic reduction in thermal IR background flux. Outstanding performance in the areas of detector dark current, read noise, and radiation hardness are required to take full advantage of the sensitivity improvements possible with such facilities, especially in very low flux (2 to 100 photons/pixel/sec) applications such as the Infrared Spectrograph on SIRTF. We present our testing methods and our results on Si:As and Si:Sb block impurity band (BIB) detectors produced by Rockwell International for our SIRTF and WIRE applications. Remarkable recent results are the reduction of the multiple-sampling read noise to 30 electrons, reduction of dark current to 10 e-/s for Si:As and 40 e-/s for Si:Sb, the use of an antireflective coating to improve the detective quantum efficiency for Si:As, extension of the useful wavelength range of Si:Sb to 40 microns, and confirmation that lab data on a 50 s time scale can be extrapolated to integration times at least 10 times longer.
The infrared spectrograph (IRS) to be flown in the Space Infrared Telescope Facility (SIRTF) makes use of many recent technological advances and will enable numerous new scientific investigations. The IRS is a broad-band (5 to 40 micrometers ) low and medium resolution (R equals (lambda) /(Delta) (lambda) equals 80 and 600) spectrograph, designed to take advantage of the low background conditions provided by SIRTF; it has no moving parts, and it will be background limited over much of its wavelength range. The IRS is a joint project of Cornell University, the California Institute of Technology, the University of Rochester, Ball Aerospace Group, the NASA Ames Research Center, and the Jet Propulsion Laboratory.
SpectroCam-10 is a 10 micrometers spectrograph and camera built at Cornell University as a facility instrument for the 200 inch Hale telescope. The instrument is optimized for operation from (lambda) equals 8 to 13 micrometers in three modes: a medium-resolution spectrography (R equals (lambda) /(Delta) (lambda) approximately equals 2000), a low-resolution spectrography (R approximately equals 100), and a camera with diffraction limited (0.5 arcsec) spatial resolution. An optical flat and two reflection gratings mounted on a cryogenic rotating mechanism allow rapid switching between modes. The detector is a Rockwell 128 X 128 Si:As Back Illuminated Blocked Impurity Band array. We discuss the design and operation of the instrument, and present some scientific results from our early observing runs at Palomar.
This paper describes the current design concepts for the three scientific instruments which are under definition study for NASA's Space Infrared Telescope Facility (SIRTF). These instruments, the Infrared Array Camera (IRAC), the Infrared Spectrograph (IRS), and the Multiband Imaging Photometer for SIRTF (MIPS), will provide imaging and spectroscopy from 2.5 to 200 micrometers . Over much of this range their performance will be limited only be natural astrophysical backgrounds in the solar system, and by diffraction. Changes in the instrument complement from the former Titan launched, Earth orbiting SIRTF concept to the present Atlas launched, solar orbiting concept are discussed.