What is the James Webb Space Telescope currently doing? (6) – Sciencetimes

What is the James Webb Space Telescope doing now, which will become mankind’s new eyes? Let’s summarize the progress from the launch of the James Webb Space Telescope to the present, and summarize the plans for the future.

Commissioning of the James Webb Space Telescope is underway

On May 5, 2022, Eastern Standard Time (EST), NASA communications officer Thaddeus Cesari reported that the James Webb Space Telescope (JWST) team was It was found that the thermal stability test was successfully performed. Meanwhile, the commissioning of four scientific instruments is also being carried out successfully. There are a total of 17 test runs, and if all 17 test runs are successfully performed, JWST will start the official first observation after a long wait. For reference, according to the National Aeronautics and Space Administration, the test drive is expected to take place in one to two months.

Commissioning of JWST is underway as of May 2022 © JWST/NASA/ESA

A total of 17 test runs are divided into four scientific equipment categories. For example, a total of five trials are planned for the near-infrared camera (NIRCam), and the remaining instruments are the near-infrared spectrometer (NIRSpec), the near-infrared imager and the slitless spectrometer (NIRISS)./FGS) and mid-infrared (MIRI) devices, each of four types of test runs are planned.

As of May 2022, commissioning of the JWST is in progress. Commissioning does not necessarily proceed in the order shown in the diagram above. For reference, as of May 20, it is known that no test run has been completed yet. © JWST/NASA/ESA

In some test runs, it is possible to confirm whether it is operating properly through observation and analysis, but there are cases in which confirmation is possible only after all test runs are completed, as in the case of some test runs. Also, not all commissioning is necessarily performed in the order shown in the diagram.

Commissioning of a near-infrared camera (NIRCam)

NIRCam devices © JWST/NASA/ESA

1st commissioning – imaging tests of NIRCam: Imaging of a near-infrared camera is taken using a part of the wavelength from visible light to near-infrared, that is, 0.6 ~ 5.0 μm. Similar to the Hubble Ultra-Deep Field image of the Hubble Telescope, the above camera will be used for almost all images of JWST, from galaxies, star forming regions to planets in our solar system.

2nd commissioning – NIRCam wide field slitless spectroscopy test: Slitless spectroscopy (spectroscopy using spectroscopy performed without a slit, which allows diffraction of only a small area of ​​light) can scatter light over the entire field of view of the device. NIRCam’s slitless spectrometer was originally included in the engineering mode used to align the telescope, but scientists at JWST put it into commissioning after realizing that the device could also be used for scientific observations, such as observations of distant quasars.

3rd commissioning – NIRCam coronagraphy test: If there are exoplanets or debris disks around the stars, much more effective observations can be made if they block the star’s light much brighter than the planet or disk dust. NIRCam’s coronagraphy uses a circular black disk to block starlight.

4th commissioning – NIRCam time series observation test: Most of the celestial bodies evolve over a much longer period of time compared to the human lifetime or observation time, but there are celestial bodies that show a short evolutionary time, such as neutron stars. In order to study this time series change, we conduct a test on how quickly the detector of the device responds.

5th commissioning – NIRCam time series Grim test: A grism (an optical tool that combines a prism and a diffraction grating) was inserted into the NIRCam for wavefront sensing. When an exoplanet passes its parent star, if starlight passes through the planet’s atmosphere, the grism can be used to determine the atmospheric components.

Commissioning of Near Infrared Spectroscopy (NIRSpec)

NIRSpec Instruments © JWST/NASA/ESA/Astrium

1st commissioning – NIRSpec multi-object spectroscopy test: There are 250,000 controllable micro-shutter devices in NIRSpec. If you open the shutter when you find an interesting object, you can get up to 100 spectra at a time. For reference, a spectrometer without a slit can obtain the spectrum of all objects in the field of view, but there is a disadvantage that the spectrum of several objects may overlap each other.

2nd commissioning – NIRSpec fixed slit spectroscopy test: There are several fixed slit spectrometers in NIRSpec that provide maximum sensitivity for individual target spectrometers. They will be primarily used for light sensing from a gravitational wave source known as a kilonova.

3rd commissioning – NIRSpec integral field unit spectroscopy test: Using the above spectrometer, it is possible to obtain spectra for a total of 900 spatial or spectral elements over all pixels in a small area instead of a single target. The above mode is mainly used for observing distant galaxies through the gravitational lensing effect, and is expected to provide the most complete data for a single target.

4th commissioning – NIRSpec bright object time series test: NIRSpec, like the NIRCam device, is capable of spectral observation of exoplanets passing through the parent star or celestial bodies that evolve rapidly with time.

Near Infrared Imager and Slitless Spectroscopy (NIRISS)/FGS) commissioning

NIRISS FGS device, for reference NIRISS is equipped with FGS and is a scientific instrument. © JWST/NASA/ESA

1st commissioning – testing single-object slitless spectrometers from NIRISS: The above mode will be used to observe planets around bright stars such as TRAPPIST-1b and 1c, which are considered rocky planets.

2nd commissioning – NIRISS widefield slitless spectrometer test: NIRISS also includes a slit-free spectrometer. It is expected that active star forming galaxies will be observed through the crisis phase and mode.

3rd commissioning – NIRISS aperture masking interferometry test: NIRISS uses an aperture masking interferometer to block light in 11 out of 18 primary mirror segments. The above mode is suitable for imaging dim sources next to bright sources, and is useful for high-contrast imaging observations, such as stellar wind impacting binary stars.

4th commissioning – NIRISS imaging test: NRISS can basically serve as a backup function for NIRCam imaging. The above mode is used while different instruments are performing different observations at the same time, so testing is essential.

Commissioning of Mid-Infrared Instruments (MIRI)

MIRI Instruments © JWST/NASA/ESA

1st commissioning – MIRI imaging test: NIRCam and MIRI have similar functions, but the observation wavelength is different. NIRCam uses visible and near-infrared rays, while MIRI’s imaging mode uses mid-infrared wavelengths of 5 to 27 μm. Using mid-infrared wavelengths, we expect to see the distribution of dust and cold gases in the star forming regions of our Milky Way and other galaxies.

Wavelength comparison by JWST device © JWST/NASA/ESA

2nd commissioning – MIRI low-resolution spectroscopy test: MIRI has a low-resolution spectrometer mode, which can study light sources that are fainter than the medium-resolution spectrometer mode. It uses a wavelength of 5 to 12 μm and is expected to be used to study the surface of celestial bodies such as Pluto’s moon Charon.

3rd commissioning – MIRI mid-resolution spectroscopy test: Can perform integrated field spectroscopy function in mid-infrared wavelength range using 5 ~ 28.5μm wavelength. Through the above mode, it is expected to observe a very strong spectral signal from the emission of molecules or dust from the disk where the planet is being formed.

4th commissioning – MIRI coronagraphy test: The MIRI is equipped with two types of coronagraphs. This will be used to directly detect exoplanets or to study the dust disks around stars.

First test images from commissioning released

MIRI, the coolest device at JWST, became a hot topic when it released its first test image in early May. The JWST team performed some observations of the Large Magellanic Cloud using MIRI (7.7 μm wavelength) for comparison with the results of past infrared missions. The previous infrared mission used for comparison was a Spitzer mission (8 μm wavelength). The now retired telescope, the Spitzer, was one of NASA’s missions and was the first telescope to provide high-resolution images of the infrared and mid-infrared space. Numerous astronomers have used data from the Spitzer telescope for their research, and it is now considered one of the most successful telescopes.

Comparison of observations made by two telescopes at the same location, left: LMC observation by Spitzer (8 μm wavelength observation), right: LMC observation by James Webb telescope (7.7 μm wavelength observation) © NASA/JPL-Caltech (left), NASA/ ESA/CSA/STScI (right)

JWST made headlines by showing stars and interstellar gas that performed far better than we could have imagined. Basically, the JWST telescope has a much larger main mirror than the Spitzer mission and is equipped with very sensitive detectors, allowing for a much clearer view of the infrared sky. Astronomers are hopeful that this will provide new insights into the formation of stars and protoplanetary systems.


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