NIRCam


NIRCam is an instrument aboard the James Webb Space Telescope. It has two major tasks, as an imager from 0.6 to 5 μm wavelength, and as a wavefront sensor to keep the 18-section mirrors functioning as one. In other words, it is a camera and is also used to provide information to align the 18 segments of the primary mirror. It is an infrared camera with ten mercury-cadmium-telluride detector arrays, and each array has an array of 2048×2048 pixels. The camera has a field of view of 2.2×2.2 arcminutes with an angular resolution of 0.07 arcseconds at 2 μm. 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.
NIRCam is housed in the Integrated Science Instrument Module. It is connected to the ISIM mechanically with a system of kinematic mounts in the structural form of struts. There are thermal straps connecting the NIRCam optical bench assembly to the
ISIM structure and to thermal radiators. It is designed to operate between and. The Focal Plane Electronics operate at 290 K.
NIRCam should be able to observe objects as faint as magnitude +29 with a 10,000-second exposure. It makes these observations in light from 0.6 to 5 μm wavelength. 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. The wavefront sensing is much finer than the thickness of an average human hair. It must perform at an accuracy of at least 93 nanometers and in testing it has even achieved between 32 and 52 nm. A human hair is thousands of nanometers across.

Main

Components

components include:
  • Dispersed Hartmann sensors
  • Grisms for slittless spectroscopy in the 2.5–5.0 μm range
  • Weak lenses
Parts of NIRCam:
  • 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

NIRCam has two complete optical systems for redundancy. 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. The lenses used in the internal optics are triplet refractors. The lens materials are lithium fluoride, a barium fluoride and zinc selenide. The triplet lenses are collimating optics. The biggest lens has 90 mm of clear aperture.
The observed wavelength range is broken up into a short wavelength and a long wavelength band. The short wavelength band goes from 0.6 to 2.3 μm and the long wavelength band goes from 2.4 to 5 μm; both have the same field of view and access to a coronagraph. 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. The long wavelength arm has one array per side, and the short wavelength arm has four arrays per side, or 8 overall. Side A and Side B have a unique field of view, but they are adjacent to each other. 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.

Design and manufacturing

The builders of NIRCam are the University of Arizona, company Lockheed Martin, and Teledyne Technologies, in cooperation with the U.S. Space agency, NASA. Lockheed Martin tested and assembled the device. Teledyne Technologies designed and manufactured the ten mercury-cadmium-telluride detector arrays. NIRCam was completed in July 2013 and it was shipped to Goddard Spaceflight Center, which is the NASA center managing the JWST project.
NIRCam's four major science goals include:

Electronics

Data from the image sensors is collected by the Focal Plane Electronics and sent to the ISIM computer. The data between the FPE and the ISIM computer is transferred by SpaceWire connection. There are also Instrument Control Electronics. The Focal Plane Arrays contain 40 million pixels.
The FPE provides or monitors the following for the FPA:
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. 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.
By using multiple filters the redshift of distant galaxies can be estimated by photometry.
NIRcam filters:
;Short wavelength channel :
  • F070W – General purpose
  • F090W – General purpose
  • F115W – General purpose
  • F140M – Cool stars,,
  • F150W – General purpose
  • F150W2 – Blocking filter for F162M, F164N, and DHS
  • F162M – Cool Stars, off-band for
  • F164N –
  • F182M – Cool stars,,
  • F187N – Pa-alpha
  • F200W – General purpose
  • F210M –,
  • F212N –
;Long wavelength channel :
  • F250M –, continuum
  • F277W – General purpose
  • F300M – Water ice
  • F322W2 – Background min. Primarily used w/ grisms. Blocking filter for F323N.
  • F323N –
  • F335M – PAH,
  • F356W – General purpose
  • F360M – Brown dwarfs, planets, continuum
  • F405N – Br-alpha
  • F410M – Brown dwarfs, planets,,
  • F430M –,
  • F444W – General purpose. Blocking filter for F405N, F466N, F470N.
  • F460M – CO
  • F466N – CO
  • F470N –
  • F480M – Brown dwarfs, planets, continuum

    Labeled diagram