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JWST Data retrieval and processing


TerryMcK

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The James Web Space Telescope is now in position, fully calibrated and sending its data back. All of the data has been uploaded to the Barbara A. Mikulski Archive for Space Telescopes AKA MAST

For those people who don't know this archive comprises archived data from many space telescopes and it is fully searchable. Much of the data is publicly available and can be downloaded anonymously. However some data from active missions is protected during an Exclusive Access Period or EAP. This is so the principal investigator and team have the opportunity to analyze the data and prepare it for publication. When the EAP has expired the data will be freely downloadable.

The information I place here is from my own investigation and shows how to navigate the archive.

 

First off the data archive is located at https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html

 

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Click the Advanced Search button and the next screen shows

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On the columns click into the box next to Release Date (this will add an extra filter to the main screen a little further down) and then start typing JWST into the mission box and press Return. As can be seen from the top of the screen there are many records found

image.png.ea07a0efc1e80bf65e6f0a7af34a2ccc.png

 

But just the Mission filter of JWST is shown.

 

Next to narrow down the data I had a look at what had already been released and was in the public domain. I noticed that there was a release on 13th July 2022 around 15:00 hours of some good data. So I entered this into the Release Date box

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The date is yyyy-mm-dd format and I think the time is in UTC.

 

This narrowed down the data to 2,325 records which is much better than having 100s of thousands of records. You can of course play around with the filters to your hearts content but this seemed to be the easiest.

 

Next click the Search button image.png.c43feb081d9480d1129b4964cf80f22e.png

 

 

This opens a further screen that has the results.

I knew that NIRCAM instrument was the best one to go for so clicked the check box next to it in the instrument field

image.png.e727f2aaf4ade421e8636c93fcb2631a.png

 

This updated the results to just 24. Next I wanted to select just the target of NGC3132 as this had been publicly been published and I fancied a go at it.

 

So selecting the target name field just clicked on NGC 3132

 

The resulting view came up.

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So it then became easier to navigate. There were a number of filters but which ones?

 

I then had to refer to the handbook. Yes the JWST has a handbook and if you go to https://jwst-docs.stsci.edu/jwst-near-infrared-camera/nircam-instrumentation/nircam-filters it outlines what each filter does. As everything is in the infra red it is necessary to visualize where in the spectrum the filters actually are and then work them back to the visual spectrum.

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So any filter towards the short wavelength channel, which is the blue end of the spectrum or the left hand side becomes blue, in the middle becomes green and to the right, long wavelength, becomes red. Of course there are no hard and fast rules to this and anything goes as to how you wish to map to RGB.

 

Referring back to the table and cross referencing it with the NIRCam filters I decided F187N would be a good candidate for mapping to blue. The F356W would be good for green and the F444W for red. However as can be seen there are two F444W's and I downloaded both. One of them which had interesting data within was labelled f444w_f470n - You can see which one that actually is by clicking the 3 dots next to the orange EDB icon and clicking Show Details. A box comes up with the actual data and shows its name.

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So to download click the Floppy Disk icon next to each of the files and it will download a zipped up archive of the data. Once downloaded you can see the zip files all starting the same name. This represents the date of download and nothing else.

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So unzip each of these and you can see a very unhelpful directory structure such as these.

image.thumb.png.d0fdd7bd5b92b894ae3604205361734b.png

 

 

image.thumb.png.5dd1f3d9acb04e9b44236d3d14c3c509.png

 

 

image.thumb.png.6351686a8de3d3d5f81e4b7c19cca413.png

 

The data we are interested in are the fits files which end with _i2d.fits (at least with this particular set of data)

 

The good news is these fits files have been calibrated already and you don't needs flats, darks biases etc so are unstretched calibrated images. All you have to do is register them together using PixInsight, AstroPixelProcessor etc.

 

I opened one of the files in PixInsight and found it comprised several image files

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The ones we are interested in for astro processing are the ones containing SCI in the title. You can delete all the others as they contain data which is for use by the scientists themselves.

 

This ended up with 3 files that could be mapped to the respective colours I outlined earlier.

 

image.thumb.png.5d8e1e098432ea15c6d1a2eea2e1402e.png

 

Here are the 3 files with a rough STF stretch. I then registered them choosing the 444 file as a reference. Then using some basic PixInsight processing I ended up with my first attempt at processing JWST data.

So here is my initial version of NGC3132 - not perfect by any stretch of the imagination but I'm sure if I take it into Photoshop and do a smart heal of the vertical lines it will clean up nicely. 

 

image.thumb.jpeg.2712be4e5de8678bc15d2f60884c39ad.jpeg

NGC 3132 using data from NASA, ESA, JWST, MAST and processed (very roughly) by Terry McKnight 2022

 

Look at the vast number of galaxies in the background of this image. The odd diffraction spikes take a little getting used to but as it is a signature of the JWST c'est la vie.

 

So to sum up it is really easy to download the data from the archive and it is up to you how you process it. I agree it wasn't data you shot from your backyard but you might discover something lurking in the background that professional astronomer may have missed.

 

 

 

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