NIRCam filters in JWST

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In the previous post we were discussed about how to download the fits data image files of JWST mission from MAST portal. In that post, we learnt how to select the required image by entering the mission and required name of the celestial object. That is the simplest way of searching a celestial object using this MAST portal. There is another method to search the required fits image files by using advanced search option. In this post we are not going to learnt about that, but today we are going to learn some details about NIRCAM filter wheel in JWST. There are several cameras and filter wheels in JWST but especially today we focus on NIRCam filter wheels.

There are two types of wavelength channels and they are short wavelength channel and long wavelength channel. Short wavelength channel is 0.6–2.3 μm while long wavelength channel is 2.4–5.0 μm. Each channel has a pupil wheel and a filter wheel. Each wheel contains 12 optical element filters each. All together (2 pupil wheels + 2 filter wheels) contains 48 optical element filters. Filter wheel is always use as a combination with pupil wheel optical elements. 

 

Filter Wheels in NIRCam (Image Credit: NASA, STScl) [Link]

 

In the pupil wheel “Clear” means the empty holes in the pupil wheel. If they want to take only using a filter optical element without using pupil optical element then they use the combination of pupil optical element as “Clear” and the filter element as required.

The following image processed picture was taken using different filters and filter combinations. Then image should be processed to make it a colored image.
 

NIRCam filters used in Southern Ring Nebula image (Image Credit: NASA, ESA, CSA, STScI) [Link]

 

In this image several filters were used to sample short and long wavelengths ranges. Each fits file is a monochromatic image (Gray scale image) associated with each individual filter. These gray scale images were then assigned by colors to get this colored image. For this image, the filters and the assigned colors are as follows.

  • F470N: Red

  • F405N: Red

  • F356W: Yellow

  • F212N: Green

  • F187N: Cyan

  • F090W: Blue

Even though it is mentioned only as F470N and F405N pupil wheel filters in the image above, both these two filters are combined with the F444W filter wheel optical element to generate the fits image file. The following MAST portal search will show you the exact optical combinations of the fits files.

 

Filter combinations mentioned in MAST Portal search result

Other filters mentioned above (F356W, F212N,F187N and F090W) were combined with “Clear” optical element. That means they were individual filter fits files. Also the downloaded fits file folders clearly mentioned the filter combinations as shown in the figure below,
 
 

Downloaded fits file folders of the Southern Ring Nebula from MAST Portal

 

 


 

 

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