23 research outputs found
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) Spectrographs
We describe the design and performance of the near-infrared (1.51--1.70
micron), fiber-fed, multi-object (300 fibers), high resolution (R =
lambda/delta lambda ~ 22,500) spectrograph built for the Apache Point
Observatory Galactic Evolution Experiment (APOGEE). APOGEE is a survey of ~
10^5 red giant stars that systematically sampled all Milky Way populations
(bulge, disk, and halo) to study the Galaxy's chemical and kinematical history.
It was part of the Sloan Digital Sky Survey III (SDSS-III) from 2011 -- 2014
using the 2.5 m Sloan Foundation Telescope at Apache Point Observatory, New
Mexico. The APOGEE-2 survey is now using the spectrograph as part of SDSS-IV,
as well as a second spectrograph, a close copy of the first, operating at the
2.5 m du Pont Telescope at Las Campanas Observatory in Chile. Although several
fiber-fed, multi-object, high resolution spectrographs have been built for
visual wavelength spectroscopy, the APOGEE spectrograph is one of the first
such instruments built for observations in the near-infrared. The instrument's
successful development was enabled by several key innovations, including a
"gang connector" to allow simultaneous connections of 300 fibers; hermetically
sealed feedthroughs to allow fibers to pass through the cryostat wall
continuously; the first cryogenically deployed mosaic volume phase holographic
grating; and a large refractive camera that includes mono-crystalline silicon
and fused silica elements with diameters as large as ~ 400 mm. This paper
contains a comprehensive description of all aspects of the instrument including
the fiber system, optics and opto-mechanics, detector arrays, mechanics and
cryogenics, instrument control, calibration system, optical performance and
stability, lessons learned, and design changes for the second instrument.Comment: 81 pages, 67 figures, PASP, accepte
The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope II. Multi-object spectroscopy (MOS)
We provide an overview of the capabilities and performance of the
Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope (JWST)
when used in its multi-object spectroscopy (MOS) mode employing a novel Micro
Shutter Array (MSA) slit device. The MSA consists of four separate 98 arcsec
91 arcsec quadrants each containing individually
addressable shutters whose open areas on the sky measure 0.20 arcsec
0.46 arcsec on a 0.27 arcsec 0.53 arcsec pitch. This is the first time
that a configurable multi-object spectrograph has been available on a space
mission. The levels of multiplexing achievable with NIRSpec MOS mode are
quantified and we show that NIRSpec will be able to observe typically fifty to
two hundred objects simultaneously with the pattern of close to a quarter of a
million shutters provided by the MSA. This pattern is fixed and regular, and we
identify the specific constraints that it yields for NIRSpec observation
planning. We also present the data processing and calibration steps planned for
the NIRSpec MOS data. The significant variation in size of the mostly
diffraction-limited instrument point spread function over the large wavelength
range of 0.6-5.3 m covered by the instrument, combined with the fact that
most targets observed with the MSA cannot be expected to be perfectly centred
within their respective slits, makes the spectrophotometric and wavelength
calibration of the obtained spectra particularly complex. These challenges
notwithstanding, the sensitivity and multiplexing capabilities anticipated of
NIRSpec in MOS mode are unprecedented, and should enable significant progress
to be made in addressing a wide range of outstanding astrophysical problems
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The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope II. Multi-object spectroscopy (MOS)
We provide an overview of the capabilities and performance of the
Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope (JWST)
when used in its multi-object spectroscopy (MOS) mode employing a novel Micro
Shutter Array (MSA) slit device. The MSA consists of four separate 98 arcsec
91 arcsec quadrants each containing individually
addressable shutters whose open areas on the sky measure 0.20 arcsec
0.46 arcsec on a 0.27 arcsec 0.53 arcsec pitch. This is the first time
that a configurable multi-object spectrograph has been available on a space
mission. The levels of multiplexing achievable with NIRSpec MOS mode are
quantified and we show that NIRSpec will be able to observe typically fifty to
two hundred objects simultaneously with the pattern of close to a quarter of a
million shutters provided by the MSA. This pattern is fixed and regular, and we
identify the specific constraints that it yields for NIRSpec observation
planning. We also present the data processing and calibration steps planned for
the NIRSpec MOS data. The significant variation in size of the mostly
diffraction-limited instrument point spread function over the large wavelength
range of 0.6-5.3 m covered by the instrument, combined with the fact that
most targets observed with the MSA cannot be expected to be perfectly centred
within their respective slits, makes the spectrophotometric and wavelength
calibration of the obtained spectra particularly complex. These challenges
notwithstanding, the sensitivity and multiplexing capabilities anticipated of
NIRSpec in MOS mode are unprecedented, and should enable significant progress
to be made in addressing a wide range of outstanding astrophysical problems
The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope: III. Integral-field spectroscopy
The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope
(JWST) offers the first opportunity to use integral-field spectroscopy from
space at near-infrared wavelengths. More specifically, NIRSpec's integral-field
unit can obtain spectra covering the wavelength range m for a
contiguous 3.1 arcsec 3.2 arcsec sky area at spectral resolutions of
, 1000, and 2700. In this paper we describe the optical and
mechanical design of the NIRSpec integral-field spectroscopy mode, together
with its expected performance. We also discuss a few recommended observing
strategies, some of which are driven by the fact that NIRSpec is a multipurpose
instrument with a number of different observing modes, which are discussed in
companion papers. We briefly discuss the data processing steps required to
produce wavelength- and flux-calibrated data cubes that contain the spatial and
spectral information. Lastly, we mention a few scientific topics that are bound
to benefit from this highly innovative capability offered by JWST/NIRSpec
Venus Observations at 40 and 90 GHz with CLASS
Using the Cosmology Large Angular Scale Surveyor, we measure the
disk-averaged absolute Venus brightness temperature to be 432.3 2.8 K and
355.6 1.3 K in the Q and W frequency bands centered at 38.8 and 93.7 GHz,
respectively. At both frequency bands, these are the most precise measurements
to date. Furthermore, we observe no phase dependence of the measured
temperature in either band. Our measurements are consistent with a
CO-dominant atmospheric model that includes trace amounts of additional
absorbers like SO and HSO.Comment: 7 pages, 3 figures, published in PS
In-orbit Performance of the Near-infrared Spectrograph NIRSpec on the James Webb Space Telescope
The Near-Infrared Spectrograph (NIRSpec) is one of the four focal plane instruments on the James Webb Space Telescope. In this paper, we summarize the in-orbit performance of NIRSpec, as derived from data collected during its commissioning campaign and the first few months of nominal science operations. More specifically, we discuss the performance of some critical hardware components such as the two NIRSpec Hawaii-2RG detectors, wheel mechanisms, and the microshutter array. We also summarize the accuracy of the two target acquisition procedures used to accurately place science targets into the slit apertures, discuss the current status of the spectrophotometric and wavelength calibration of NIRSpec spectra, and provide the "as measured" sensitivity in all NIRSpec science modes. Finally, we point out a few important considerations for the preparation of NIRSpec science programs
The Science Performance of JWST as Characterized in Commissioning
This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies
The James Webb Space Telescope Mission
Twenty-six years ago a small committee report, building on earlier studies,
expounded a compelling and poetic vision for the future of astronomy, calling
for an infrared-optimized space telescope with an aperture of at least .
With the support of their governments in the US, Europe, and Canada, 20,000
people realized that vision as the James Webb Space Telescope. A
generation of astronomers will celebrate their accomplishments for the life of
the mission, potentially as long as 20 years, and beyond. This report and the
scientific discoveries that follow are extended thank-you notes to the 20,000
team members. The telescope is working perfectly, with much better image
quality than expected. In this and accompanying papers, we give a brief
history, describe the observatory, outline its objectives and current observing
program, and discuss the inventions and people who made it possible. We cite
detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space
Telescope Overview, 29 pages, 4 figure