James Webb update.

https://www.youtube.com/watch?v=w_Sl8JcxGII

These are the first images for each of the twelve infrared spectral bands, illustrating the image quality for observations of star HD 37122. Accuracy is better than 1 arcsecond. While the star is bright at short wavelengths it fades toward longer wavelengths, where the background brightens because of thermal emission from Webb’s primary mirror.

So, wavelength bands of 5.3 to 26 microns. How does that compare to Hubble, Spitzer, and Wise?
Hubble is 0.8 to 2.5 microns.
Spitzer was 3.6 to 160 microns.
Wise is 3.4 to 22 microns. Similar wavelengths.
(As a side note, the Wise space telescope is still operating 12 years after launch, its planned mission was only 10 months).

What type of star is HD 37122? It turns out to be type K2, which makes it a lot cooler than the Sun (type G) but hotter than a red dwarf (type M). Type K stars are sometimes called “yellow dwarfs”.

I thought so. The nearby star Epsilon Eridani also has spectral type K2.
So what we learn from the spectrum of HD 37122 will also hold for Epsilon Eridani.

MIRI camera on Webb

Galaxy spectrum

Webb to re-image the Hubble Ultra-Deep Field.

in the constellation Fornax where Hubble spent more than 11 days taking deep exposures. With NIRCam, they’ll observe for over 125 hours

Hubble Ultra-deep Field = whole image.
Parts seen by three different Webb cameras are shown as rectangles.

Pretty crappy ewetube intro at https://youtu.be/RQo6nDES7Lk

mollwollfumble said:

Webb to re-image the Hubble Ultra-Deep Field.

in the constellation Fornax where Hubble spent more than 11 days taking deep exposures. With NIRCam, they’ll observe for over 125 hours

Hubble Ultra-deep Field = whole image.
Parts seen by three different Webb cameras are shown as rectangles.

Pretty crappy ewetube intro at https://youtu.be/RQo6nDES7Lk

Should be interesting.

https://blogs.nasa.gov/webb/2022/06/23/webbs-nirspec-acquires-multiple-targets/

The Webb team has now approved 10 out of 17 science instrument modes; since last week we added (14) MIRI imaging, (2) NIRCam wide-field slitless spectroscopy, and our final NIRISS mode, (1) single-object slitless spectroscopy. As we ramp down the final commissioning activities, some openings in the schedule have appeared. The team has started to take some of the first science data, getting it ready to release starting July 12, 2022, which will mark the official end of commissioning Webb and the start of routine science operations.

How Webb gets the targets lined up for observation with the NIRSpec instrument

The Near-Infrared Spectrograph (NIRSpec) is the instrument on the Webb telescope that observes spectra of astrophysical and planetary objects at near infrared wavelengths. The NIRSpec Grating Wheel Assembly (GWA) uses diffraction gratings or a prism to separate the wavelengths of incoming light into a spectrum.

In addition to the gratings and a prism, the NIRSpec GWA also has a mirror that is primarily used to ‘acquire’ targets – to image them and place them at the proper locations in the instrument to observe a spectrum. NIRSpec has two methods for target acquisition (TA): the Wide Aperture Target Acquisition (WATA) and the Micro-Shutter Assembly (MSA) -based Target Acquisition (MSATA).

The WATA process takes an image of a single astrophysical target through the wide ‘S1600A1’ fixed slit to determine its position on the sky as seen through the instrument. The software on-board the Webb telescope autonomously calculates an offset to move the telescope and accurately position this target.

NIRSpec includes the multi-object spectroscopy (MOS) mode, where spectra of dozens to hundreds of science targets will be observed at one time. This requires specialized apertures that can be configured by opening and closing specific tiny doorways (microshutters) of the 250,000 total that are arranged in a rectangular grid in the MSA, allowing individual targets to be observed with little contamination from nearby objects or background light.

Wow!

To allow accurate correction of the observed spectra for the centering of each source in its shutter, this process must place the MOS science targets across the full span of the NIRSpec field of view with an accuracy of just 20 milli-arcseconds.

A simulation of target acquisition

https://www.universetoday.com/159790/webb-niriss-instrument-has-gone-offline/

Link