Jessica Krick, Patrick Lowrance, Sean Carey, Jason Surace, Carl Grillmair, Seppo Laine, Schuyler Van Dyk, James Ingalls, Matthew L. Ashby, Steven Willner
We investigate differences in Spitzer/IRAC 3.6 and 4.5 μm photometry that depend on observing strategy. Using archival calibration data, we perform an in-depth examination of the measured flux densities (fluxes) of 10 calibration stars, observed with all the possible observing strategies. We then quantify differences in the measured fluxes as a function of (1) array mode (full or subarray), (2) exposure time, and (3) dithering versus staring observations. We find that the median fluxes measured for sources observed using the full array are 1.6% and 1% lower than those observed with the subarray at [3.6] and [4.5], respectively. In addition, we found a dependence on the exposure time such that for [3.6] observations, the long frame times are measured to be lower than the short frame times by a median value of 3.4% in full array and 2.9% in subarray. For [4.5] observations, the longer frame times are 0.6% and 1.5% in full and subarray, respectively. These very small variations will likely only affect science users who require high-precision photometry from multiple different observing modes. We find no statistically significant difference for fluxes obtained with dithered and staring modes. When considering all stars in the sample, the fractional well depth of the pixel is correlated with the different observed fluxes. We speculate the cause to be a small nonlinearity in the pixels at the lowest well depths where deviations from linearity were previously assumed to be negligible.
SPHEREx, the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and ices Explorer, is a NASA MIDEX mission planned for launch in 2024. SPHEREx will carry out the first all-sky spectral survey at wavelengths between 0.75µm and 5µm with spectral resolving power ~40 between 0.75 and 3.8µm and ~120 between 3.8 and 5µm At the end of its two-year mission, SPHEREx will provide 0.75-to-5µm spectra of each 6.”2x6.”2 pixel on the sky - 14 billion spectra in all. This paper updates an earlier description of SPHEREx presenting changes made during the mission's Preliminary Design Phase, including a discussion of instrument integration and test ow and a summary of the data processing, analysis, and distribution plans.
SPHEREx, a mission in NASA’s Medium Explorer (MIDEX) program recently selected for Phase-A implementation, is an all-sky survey satellite that will produce a near-infrared spectrum for every 6 arcsecond pixel on the sky. SPHEREx has a simple, high-heritage design with large optical throughput to maximize spectral mapping speed. While the legacy data products will provide a rich archive of spectra for the entire astronomical community to mine, the instrument is optimized for three specific scientific goals: to probe inflation through the imprint primordial non-Gaussianity left on today’s large-scale cosmological structure; to survey the Galactic plane for water and other biogenic ices through absorption line studies; and to constrain the history of galaxy formation through power spectra of background fluctuations as measured in deep regions near the ecliptic poles. The aluminum telescope consists of a heavily baffled, wide-field off-axis reflective triplet design. The focal plane is imaged simultaneously by two mosaics of H2RG detector arrays separated by a dichroic beamsplitter. SPHEREx assembles spectra through the use of mass and volume efficient linear variable filters (LVFs) included in the focal plane assemblies, eliminating the need for any dispersive or moving elements. Instead, spectra are constructed through a series of small steps in the spacecraft attitude across the sky, modulating the location of an object within the FOV and varying the observation wavelength in each exposure. The spectra will cover the wavelength range between 0.75 and 5.0 µm at spectral resolutions ranging between R=35 and R=130. The entire telescope is cooled passively by a series of three V-groove radiators below 80K. An additional stage of radiative cooling is included to reduce the long wavelength focal plane temperature below 60K, controlling the dark current. As a whole, SPHEREx requires no new technologies and carries large technical and resource margins on every aspect of the design.
The Infrared Array Camera (IRAC) is now the only science instrument in operation on the Spitzer Space Telescope. The
3.6 and 4.5 µm channels are temperature-stabilized at ~28.7K, and the sensitivity of IRAC is nearly identical to what it
was in the cryogenic mission. The instrument point response function (PRF) is a set of values from which one can
determine the point spread function (PSF) for a source at any position in the field, and is dependent on the optical
characteristics of the telescope and instrument as well as the detector sampling and pixel response. These data are
necessary when performing PSF-fitting photometry of sources, for deconvolving an IRAC image, subtracting out a
bright source in a field, or for estimating the flux of a source that saturates the detector. Since the telescope and
instrument are operating at a higher temperature in the post-cryogenic mission, we re-derive the PRFs for IRAC from
measurements obtained after the warm mission temperature set point and detector biases were finalized and compare
them to the 3.6 and 4.5 µm PRFs determined during the cryogenic mission to assess any changes.
We present an overview of the calibration and properties of data from the IRAC instrument aboard the Spitzer Space
Telescope taken after the depletion of cryogen. The cryogen depleted on 15 May 2009, and shortly afterward a two-month-
long calibration and characterization campaign was conducted. The array temperature and bias setpoints were
revised on 19 September 2009 to take advantage of lower than expected power dissipation by the instrument and to
improve sensitivity. The final operating temperature of the arrays is 28.7 K, the applied bias across each detector is 500
mV and the equilibrium temperature of the instrument chamber is 27.55 K. The final sensitivities are essentially the
same as the cryogenic mission with the 3.6 μm array being slightly less sensitive (10%) and the 4.5 μm array within 5%
of the cryogenic sensitivity. The current absolute photometric uncertainties are 4% at 3.6 and 4.5 μm, and better than
milli-mag photometry is achievable for long-stare photometric observations. With continued analysis, we expect the
absolute calibration to improve to the cryogenic value of 3%. Warm IRAC operations fully support all science that was
conducted in the cryogenic mission and all currently planned warm science projects (including Exploration Science
programs). We expect that IRAC will continue to make ground-breaking discoveries in star formation, the nature of the
early universe, and in our understanding of the properties of exoplanets.
The Infrared Array Camera (IRAC) is one of three focal plane instruments on board the Spitzer Space Telescope. IRAC is a four-channel camera that obtains simultaneous broad-band images at 3.6, 4.5, 5.8, and 8.0 μm in two nearly adjacent fields of view. We summarize here the in-flight scientific, technical, and operational performance of IRAC.
KEYWORDS: Calibration, Infrared telescopes, High dynamic range imaging, Space telescopes, Stray light, Infrared cameras, Stars, Infrared radiation, Space operations, Telescopes
We describe the astronomical observation template (AOT) for the Infrared Array Camera (IRAC) on the Spitzer Space Telescope (formerly SIRTF, hereafter Spitzer). Commissioning of the AOTs was carried out in the first three months of the Spitzer mission. Strategies for observing fixed and moving targets are described, along with the performance of the AOT in flight. We also outline the operation of the IRAC data reduction pipeline at the Spitzer Science Center (SSC) and describe residual effects in the data due to electronic and optical anomalies in the instrument.
The Infrared Array Camera (IRAC) on Spitzer Space Telescope includes four Raytheon Vision Systems focal plane arrays, two with InSb detectors, and two with Si:As detectors. A brief comparison of pre- flight laboratory results vs. in-flight performance is given, including quantum efficiency and noise, as well as a discussion of irregular effects, such as residual image performance, "first frame effect", "banding", "column pull-down" and multiplexer bleed. Anomalies not encountered in pre-flight testing, as well as post-flight laboratory tests on these anomalies at the University of Rochester and at NASA Ames using sister parts to the flight arrays, are emphasized.
KEYWORDS: Calibration, Data processing, Image processing, Databases, Space operations, Space telescopes, Infrared cameras, Data centers, Infrared telescopes, Data acquisition
IRAC, the Infrared Array Camera on the Spitzer Space Telescope, generated well over 150,000 images during the in-orbit checkout and science verification phase of the mission. All of these were processed with SIP, the SAO IRAC Pipeline. SIP was created by and for the members of the IRAC instrument team at the Smithsonian Astrophysical Observatory, to allow short-timescale data processing and rapid-turnaround software testing and algorithm modification. SIP makes use of perl scripting and data mirroring to transfer and manage data, a mySQL database to select calibration data, and Python/numarray to process the image data; it is designed to run with no user interaction. SIP is fast, flexible, and robust. We present some 'lessons learned' from the construction and maintenance of SIP, and discuss prospects for future improvement.
The Infrared Array Camera (IRAC) is one of three focal plane instruments in the Space Infrared Telescope Facility (SIRTF). IRAC is a four-channel camera that obtains simultaneous images at 3.6, 4.5, 5.8, and 8 microns. Two adjacent 5.12x5.12 arcmin fields of view in the SIRTF focal plane are viewed by the four channels in pairs (3.6 and 5.8 microns; 4.5 and 8 microns). All four detector arrays in the camera are 256x256 pixels in size, with the two shorter wavelength channels using InSb and the two longer wavelength channels using Si:As IBC detectors. We describe here the results of the instrument functional and calibration tests completed at Ball Aerospace during the integration with the cryogenic telescope assembly, and provide updated estimates of the in-flight sensitivity and performance of IRAC in SIRTF.
The Infrared Array Camera (IRAC) is one of three major scientific instruments to be launched aboard the Space Infrared Telescope Facility (SIRTF). This document briefly describes the features, usage, and limitations of the IRAC Science Data Simulator (ISDS) that can be used to generate simulated data to anticipate data quality and reduction issues for mission operations. The software is a combination of C++ and IRAF SPP routines that implement the features already characterized during the integration and test phase of IRAC's
development. While no guarantee of accuracy is made, the intention is to replicate as faithfully as possible known characteristics and artifacts of the IRAC instrument. The many beneficial applications of the ISDS include facilitating planning of the IRAC pipeline by the SIRTF Science Center (SSC), and validating observing strategies for SIRTF Guaranteed Time Observers and Legacy teams. The simulator has already been used by mission planners to demonstrate the relative effectiveness of different approaches to data reduction. It will also be of great value in demonstrating IRAC's capabilities for mapping and source detection, and in testing post-pipeline software currently being developed for these purposes.
The Infrared Array Camera (IRAC) is one of three focal plane instruments in the Space Infrared Telescope Facility (SIRTF). IRAC is a four-channel camera that obtains simultaneous images at 3.6, 4.5, 5.8, and 8 microns. Two adjacent 5.12 X 5.12 arcmin fields of view in the SIRTF focal plane are viewed by the four channels in pairs (3.6 and 5.8 microns; 4.5 and 8 microns). All four detectors arrays in the camera are 256 X 256 pixels in size, with the two shorter wavelength channels using InSb and the two longer wavelength channels using Si:As IBC detectors. We describe here the results of the instrument functionality and calibration tests completed at Goddard Space Flight Center, and provide estimates of the in-flight sensitivity and performance of IRAC in SIRTF.
The Space IR Telescope Facility (SIRTF) contains three focal plane instruments, one of which is the IR Array Camera (IRAC). IRAC is a four-channel camera that provides simultaneous 5.12 X 5.12 arcmin images at 3.6, 4.5, 5.8 and 8 microns. The pixel size is 1.2 arcsec in all bands. Two adjacent fields of view in the SIRTF focal plane are viewed by the four channels in pairs. All four detector arrays in the camera are 256 by 256 pixels in size, with the two short wavelength channels using InSb and the two longer wavelength channels using Si:As IBS detectors. The IRAC sensitivities at 3.6, 4.5, 5.8, and 8.0 microns are 6, 7, 36, and 54 microJanskys, respectively. Two of the most important scientific objectives of IRAC will be to carry out surveys to study galaxy formation and evolution during the early stage of the Universe, and to search for brown dwarfs and superplanets.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.