NIRCam

NIRCam is an instrument aboard the to-be-launched James Webb Space Telescope. It has two major tasks, as an imager from 0.6 to 5 micron wavelength, and as a wavefront sensor to keep the 18-section mirrors functioning as one.[1][2] In other words, it is a camera and is also used to provide information to align the 18 segments of the primary mirror.[3] It is an infrared camera with ten mercury-cadmium-telluride (HgCdTe) detector arrays, and each array has an array of 2048x2048 pixels.[1][2] The camera has a field of view of 2.2x2.2 arc minutes with an angular resolution of 0.07 arcsec at 2 microns.[1] NIRCam is also equipped with coronagraphs, which helps to collect data on exoplanets near stars. It helps with imaging anything next to a much brighter object, because the coronagraph blocks that light.[2] NIRCam is housed in the Integrated Science Instrument Module, to which it is attached physically by struts.[3][4][5][6] It is designed to operate at 37 Kelvin (roughly minus 400 degrees Fahrenheit), so it can detect infrared radiation at this wavelength.[3][7] It is connected to the ISIM by struts and thermal straps connect to heat radiators, which helps maintain its temperature.[3] The Focal Plane Electronics operated at 290 kelvin.[3]

NIRCam wrapped up in 2013
NIRCam being installed in 2014

NIRCam should be able to observe as faint as magnitude +29 with a 10000-second exposure (about 2.8 hours).[8] It makes these observations in light from 0.6 (600 nm) to 5 microns (5000 nm) wavelength.[4] It can observe in two fields of view, and either side can do imaging, or from the capabilities of the wave-front sensing equipment, spectroscopy.[9] The wavefront sensing is much finer than the thickness of an average human hair.[10] It must perform at an accuracy of at least 93 nanometers and in testing it has even achieved between 32 and 52 nm.[10] A human hair is thousands of nanometers across.[10]

Main

Components
NIRCam Engineering Test Unit, showing some of the internal optics of NIRCam such as the collimating lenses and the mirrors

Wavefront sensor components include:[9]

  • Dispersed Hartmann sensors
  • Grisms
  • Weak lenses

Parts of NIRCam:[11]

  • Pick-off mirror
  • Coronograph
  • First-fold mirror
  • Collimator lenses
  • Dichroic beam splitter
  • Longwave filter wheel
  • Longwave camera lens group
  • Longwave focal plane
  • Shortwave filter wheel assembly
  • Shortwave camera lens group
  • Shortwave fold mirror
  • Pupil imaging lens
  • Shortwave focal plane

Overview
Infographic of JWST instruments and their observation ranges of light by wavelength

NIRCam has two complete optical systems for redundancy.[3] The two sides can operate at the same time, and view two separate patches of sky; the two sides are called side A and side B.[3] The lenses used in the internal optics are triplet refractors.[3] The lens materials are lithium fluoride (LiF), a barium fluoride (BaF2) and zinc selenide (ZnSe).[3] The triplet lenses are collimating optics.[12] The biggest lens has 90 mm of clear aperture.[12]

The observed wavelength range is broken up into a short wavelength and a long wavelength band.[13] The short wavelength band goes from 0.6 to 2.3 microns and the long wavelength band goes from 2.4 to 5 microns; both have the same field of view and access to a coronagraph.[13] Each side of the NIRCam views a 2.2 arcminute by 2.2 arcminute patch of sky in both the short and long wavelengths; however, the short wavelength arm has twice the resolution.[12] The long wavelength arm has one array per side (two overall), and the short wavelength arm has four arrays per side, or 8 overall.[12] Side A and Side B have a unique field of view, but they are adjacent to each other.[12] In other words, the camera looks at two 2.2 arcminute wide fields of view that are next to each other, and each of these views is observed at short and long wavelengths simultaneously with the short wavelength arm having twice the resolution of the longer wavelength arm.[12]

The builders of NIRCam are the University of Arizona and company Lockheed Martin, in cooperation with the U.S. Space agency, NASA.[2] NIRCam was completed in July 2013 and it was shipped to Goddard Spaceflight Center, which is the NASA center managing the JWST project.[7]

NIRCam's four major science goals include:

1. Exploring the formation and evolution of the first luminous objects and revealing the reionization history of the Universe.

2.Determining how objects seen in the present day (galaxies, active galaxies, and clusters of galaxies) assembled and evolved out of gas, stars, metals present in the early Universe.
3.Improve our understanding of the birth of stars and planetary systems.

4.Study the physical and chemical conditions of objects in our solar system with a goal of understanding the origin of the building blocks of life on Earth.

— Science Opportunities with the Near-IR Camera (NIRCam) on the James Webb Space Telescope (JWST) Biechman, et al.[14]

Electronics
NIRCam Focal Plane Assembly (FPA) undergoing inspection, 2013

Data from the image sensors (Focal Plane Arrays) is collected by the Focal Plane Electronics and sent to the ISIM computer.[3] The data between the FPE and the ISIM computer is transferred by SpaceWire connection.[3] There are also Instrument Control Electronics (ICE).[3] The Focal Plane Arrays contain 40 million pixels.[7]

The FPE provides or monitors the following for the FPA:[7]

Filters

NIRcam includes filter wheels that allow the light coming in from the optics to be sent through a filter before it is recorded by the sensors.[14] The filters have a certain range in which they allow light to pass, blocking the other frequencies; this allows operators of NIRCam some control over what frequencies are observed when making an observation with the telescope.[14]

By using multiple filters the redshift of distant galaxies can be estimated by photometry.[14]

NIRcam filters:[15] Short wavelength filters (below dichroic deadband)

  • F070W
  • F090W
  • F115W
  • F140M
  • F150W
  • F150W2
  • F162M -- in pupil wheel, used in series w/F150W2
  • F164N -- in pupil wheel, used in series w/F150W2
  • F182M
  • F187N
  • F200W
  • F210M
  • F212N

Long wavelength filters (above dichroic deadband)

  • F250M
  • F277W
  • F300M
  • F322W2
  • F323N -- in pupil wheel, used in series w/F322W2
  • F335M
  • F356W
  • F360M
  • F405N -- in pupil wheel, used in series w/F444W
  • F410M
  • F430M
  • F444W
  • F460M
  • F466N -- in pupil wheel, used in series w/F444W
  • F470N -- in pupil wheel, used in series w/F444W
  • F480M

Labeled diagram
Labeled diagram of components of NIRcam

See also

References
  1. "NIRCAM". Retrieved 5 December 2016.
  2. "The James Webb Space Telescope". Retrieved 5 December 2016.
  3. NIRCam Instrument Overview
  4. "NIRCAM". Retrieved 6 December 2016.
  5. "The James Webb Space Telescope". Retrieved 6 December 2016.
  7. "NirCam". www.lockheedmartin.com. Retrieved 2017-01-21.
  10. "Lockheed Martin Readies One of the Most Sensitive IR Instruments Ever Made for NASA Telescope". www.lockheedmartin.com. Retrieved 2017-01-21.
  11. "NIRCam for JWST". Retrieved 5 December 2016.
  15. "NIRCam".
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