2022-08-09 アメリカ・ローレンスリバモア国立研究所(LLNL)
太陽系外惑星ワスプ96Bの赤外線スペクトルが水蒸気の証拠を示していた。
スペクトルは、私たちが直接アクセスできない物体の物質組成を直接的に特定することができます。天体の組成について私たちが知っていることの多くは、分光学によって得られたものです。ヘリウムという元素は、地球上でその存在が発見される前に、太陽のスペクトルで初めて観測された。
＜関連情報＞
- https://www.llnl.gov/news/labs-technology-board-james-webb-space-telescope
- https://jwst-docs.stsci.edu/jwst-near-infrared-imager-and-slitless-spectrograph/niriss-instrumentation/niriss-gr700xd-grism
NIRISS GR700XD グリズム
NIRISS GR700XD Grism
The JWST NIRISS GR700XD grism produces spectra for wavelengths between 0.6 and 2.8 μm with a resolving power at blaze maximum in first order for R ≈ 700. The GR700XD enables single object slitless spectroscopy.
The GR700XD grism produces multiple orders of cross-dispersed spectra for a single object between wavelengths 0.6 and 2.8 μm. It provides resolving power of R ≈ 700 at the blaze wavelength in first order. The GR700XD grism enables the single object slitless spectroscopy mode of NIRISS, which is optimized for time-series observation applications that demand a high degree of spectro-photometric stability.
The GR700XD grism has 2 components that are butted together. In the order that they are encountered by an incoming beam of light, these are:
- A prism made of zinc sulfide (ZnS). The wedge of the prism provides cross-dispersion of the spectral orders diffracted by the grism. In addition, the input surface of the prism has a weak cylindrical lens ground into it, which provides modest defocus for the spectral orders produced by the grism. By design, this defocus spreads the dispersed light over more pixels in the spatial dimension, which mitigates the effect of flat field errors and allows brighter sources to be observed without saturating. An anti-reflection coating was applied to both sides of the prism to minimize losses at the interfaces.
- A grism made of zinc selenide (ZnSe), with the properties listed in Table 1. An anti-reflection coating was deposited on the side of this element that faces the prism.
Figure 1 shows a cutaway view of these 2 components, while Figure 2 shows the flight hardware for both the prism (input) side and the grism (output) side.
