O Telescópio Espacial James Webb da NASA é uma verdadeira maravilha tecnológica. O maior e mais complexo telescópio espacial já construído, o Webb é capaz de coletar luz que viaja há 13,5 bilhões de anos, quase desde o início do universo. Com efeito, Webb é uma máquina do tempo, permitindo-nos observar as primeiras galáxias que se formaram após o Big Bang. Por coletar luz infravermelha, vê através das gigantescas nuvens de poeira que bloqueiam a visão da maioria dos outros telescópios. Webb é 100 vezes mais poderoso que o Telescópio Espacial Hubble. Crédito: NASA/JPL-Caltech
Com a ótica e os instrumentos do telescópio alinhados, a equipe do Webb está agora comissionando os quatro poderosos instrumentos científicos do observatório. Existem 17 “modos” de instrumentos diferentes para conferir em nosso caminho para nos prepararmos para o início da ciência neste verão. Depois de aprovarmos todos os 17 modos,[{” attribute=””>NASA’s James Webb Space Telescope will be ready to begin scientific operations!
In this article we’ll describe the 17 modes, and readers are encouraged to follow along as the Webb team checks them off one by one on the Where is Webb tracker. Each mode has a set of observations and analysis that need to be verified, and it is important to note that the team does not plan to complete them in the order listed below. Some of the modes won’t be verified until the very end of commissioning.
For each mode we have also selected a representative example science target that will be observed in the first year of Webb science. These are just examples; each mode will be used for many targets, and most of Webb’s science targets will be observed with more than one instrument and/or mode. The detailed list of peer-reviewed observations planned for the first year of science with Webb ranges from our solar system to the most distant galaxies.
1. Câmera de infravermelho próximo (NIRCam). Imagens de infravermelho próximo tirarão fotos em parte da luz visível ao infravermelho próximo, comprimento de onda de 0,6 a 5,0 micrômetros. Este modo será usado para quase todos os aspectos da ciência Webb, de campos profundos a galáxias, regiões de formação de estrelas a planetas em nosso próprio sistema solar. Um exemplo de destino em um programa Webb ciclo 1 usando este modo: o campo ultra-profundo do Hubble.
2. Espectroscopia sem fenda de campo amplo NIRCam. A espectroscopia separa a luz detectada em cores individuais. A espectroscopia sem fenda espalha a luz em todo o campo de visão do instrumento para que possamos ver as cores de cada objeto visível no campo. A espectroscopia sem fenda no NIRCam era originalmente um modo de engenharia para uso no alinhamento do telescópio, mas os cientistas perceberam que também poderia ser usado para a ciência. Exemplo de destino: quasares distantes.
3. Coronografia NIRCam. Quando uma estrela tem exoplanetas ou discos de poeira em órbita ao seu redor, o brilho de uma estrela geralmente supera a luz que é refletida ou emitida pelos objetos muito mais fracos ao seu redor. A coronagrafia usa um disco preto no instrumento para bloquear a luz das estrelas e detectar a luz de seus planetas. Exemplo de destino: o exoplaneta gigante gasoso HIP 65426 b.
4. Observações de séries temporais do NIRCam – imagens. A maioria dos objetos astronômicos muda em escalas de tempo grandes em comparação com a vida humana, mas algumas coisas mudam rápido o suficiente para que possamos vê-las. As observações de séries temporais lêem os detectores dos instrumentos rapidamente para observar essas mudanças. Exemplo de destino: uma estrela anã branca pulsante chamada magnetar.
5. Observações de séries temporais do NIRCam – grism. Quando um[{” attribute=””>exoplanet crosses the disk of its host star, light from the star can pass through the atmosphere of the planet, allowing scientists to determine the constituents of the atmosphere with this spectroscopic technique. Scientists can also study light that is reflected or emitted from an exoplanet, when an exoplanet passes behind its host star. Example target: lava rain on the super-Earth-size exoplanet 55 Cancri e.
A sensor array for the NIRCam instrument, designed and tested by Marcia Rieke’s research group at Steward Observatory. For the sensors to detect infrared light without too much noise in the data, Webb and its instruments must be kept as cool as possible. Credit: Marcia Rieke
6. Near-Infrared Spectrograph (NIRSpec) multi-object spectroscopy. Although slitless spectroscopy gets spectra of all the objects in the field of view, it also allows the spectra of multiple objects to overlap each other, and the background light reduces the sensitivity. NIRSpec has a microshutter device with a quarter of a million tiny controllable shutters. Opening a shutter where there is an interesting object and closing the shutters where there is not allows scientists to get clean spectra of up to 100 sources at once. Example target: the Extended Groth Strip deep field.
7. NIRSpec fixed slit spectroscopy. In addition to the microshutter array, NIRSpec also has a few fixed slits that provide the ultimate sensitivity for spectroscopy on individual targets. Example target: detecting light from a gravitational-wave source known as a kilonova.
8. NIRSpec integral field unit spectroscopy. Integral field unit spectroscopy produces a spectrum over every pixel in a small area, instead of a single point, for a total of 900 spatial/spectral elements. This mode gives the most complete data on an individual target. Example target: a distant galaxy boosted by gravitational lensing.
9. NIRSpec bright object time series. NIRSpec can obtain a time series spectroscopic observation of transiting exoplanets and other objects that change rapidly with time. Example target: following a hot super-Earth-size exoplanet for a full orbit to map the planet’s temperature.
10. Near-Infrared Imager and Slitless Spectrograph (NIRISS) single object slitless spectroscopy. To observe planets around some of the brightest nearby stars, NIRISS takes the star out of focus and spreads the light over lots of pixels to avoid saturating the detectors. Example target: small, potentially rocky exoplanets TRAPPIST-1b and 1c.
The beam of light coming from the telescope is then shown in deep blue entering the instrument through the pick-off mirror located at the top of the instrument and acting like a periscope.
Then, a series of mirrors redirect the light toward the bottom of the instruments where a set of 4 spectroscopic modules are located. Once there, the beam of light is divided by optical elements called dichroics in 4 beams corresponding to different parts of the mid-infrared region. Each beam enters its own integral field unit; these components split and reformat the light from the whole field of view, ready to be dispersed into spectra. This requires the light to be folded, bounced and split many times, making this probably one of Webb’s most complex light paths.
To finish this amazing voyage, the light of each beam is dispersed by gratings, creating spectra that then projects on 2 MIRI detectors (2 beams per detector). An amazing feat of engineering! Credit: ESA/ATG medialab
11. NIRISS wide field slitless spectroscopy. NIRISS includes a slitless spectroscopy mode optimized for finding and studying distant galaxies. This mode will be especially valuable for discovery, finding things that we didn’t already know were there. Example target: pure parallel search for active star-forming galaxies.
12. NIRISS aperture masking interferometry. NIRISS has a mask to block out the light from 11 of the 18 primary mirror segments in a process called aperture masking interferometry. This provides high-contrast imaging, where faint sources next to bright sources can be seen and resolved for images. Example target: a binary star with colliding stellar winds.
13. NIRISS imaging. Because of the importance of near-infrared imaging, NIRISS has an imaging capability that functions as a backup to NIRCam imaging. Scientifically, this is used mainly while other instruments are simultaneously conducting another investigation, so that the observations image a larger total area. Example target: a Hubble Frontier Field gravitational lensing galaxy cluster.
14. Mid-Infrared Instrument (MIRI) imaging. Just as near-infrared imaging with NIRCam will be used on almost all types of Webb targets, MIRI imaging will extend Webb’s pictures from 5 to 27 microns, the mid-infrared wavelengths. Mid-infrared imaging will show us, for example, the distributions of dust and cold gas in star-forming regions in our own Milky Way galaxy and in other galaxies. Example target: the nearby galaxy Messier 33.
15. MIRI low-resolution spectroscopy. At wavelengths between 5 and 12 microns, MIRI’s low-resolution spectroscopy can study fainter sources than its medium-resolution spectroscopy. Low resolution is often used for studying the surface of objects, for example, to determine the composition. Example target: Pluto’s moon Charon.
16. MIRI medium-resolution spectroscopy. MIRI can do integral field spectroscopy over its full mid-infrared wavelength range, 5 to 28.5 microns. This is where emission from molecules and dust display very strong spectral signatures. Example targets: molecules in planet-forming disks.
17. MIRI coronagraphic imaging. MIRI has two types of coronagraphy: a spot that blocks light and three four-quadrant phase mask coronagraphs. These will be used to directly detect exoplanets and study dust disks around their host stars. Example target: searching for planets around our nearest neighbor star Alpha Centauri A.
Written by Jonathan Gardner, Webb deputy senior project scientist, NASA’s Goddard Space Flight Center
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