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James Webb Telescope

Does anyone know exactly what star is in that test image?

I'm finding conflicting information on my internet search.

One thing says that it's a brown dwarf 20 parsecs (about 60 ly) away:

https://en.wikipedia.org/wiki/2MASS_J17554042+6551277

Some other article said it was about 2,000 ly away, but didn't say what kind of star it is.

https://www.cbc.ca/news/science/james-webb-image-1.6387224

I was just wondering if it's bigger, smaller, or about the same size as our sun, as well as how far away it is.

If it really is a brown dwarf, then it's obviously much smaller. Those range from about 13 Jupiter masses on the low end to 80 on the high end. The Sun is about 1000 masses of Jupiter.
 
I think the brown dwarf info must be wrong. Most of the articles agree that it's 2,000 light years away, and this article says that it's intrinsically 16 times brighter than the sun, so likely more massive too.

https://www.sciencealert.com/webb-h...tar-to-demonstrate-its-operational-perfection

To demonstrate its capabilities, Webb focused on a single star, named 2MASS J17554042+6551277, more commonly known as TYC 4212-1079-1.

This bright object, around 2,000 light-years away, is just over 16 times intrinsically brighter than the Sun – a nice, clear target for Webb. A red filter was used to optimize visual contrast; and, although the telescope was just looking at the star, its instruments are so sensitive that background stars and galaxies can also be seen.
Click to expand...
 
Puppycow said:
I think the brown dwarf info must be wrong. Most of the articles agree that it's 2,000 light years away, and this article says that it's intrinsically 16 times brighter than the sun, so likely more massive too.

https://www.sciencealert.com/webb-h...tar-to-demonstrate-its-operational-perfection
Click to expand...

Comparing the relative brightnesses of this star with the sun is a little like comparing apples with oranges. The sun has an absolute magnitude of 4.8, at visual wavelengths that is to say, if it was 10 parsecs (32.6 light-years) away, that's how bright it would appear to the eye. That is not very bright, hardly noticeable, there are literally hundreds of brighter stars in our sky.

However, if the JWST target star,
Edited by jimbob: 
2MASS J10430758+2225236 2MASS J17554042+6551277
, is a brown dwarf, then its worh noting that these stars have relatively low surface temperatures, they are not very bright at visible wavelengths, emitting the majority of their light in the infrared, so while on the face of it, it does not seem as it if will be visible to the eye, it will be very bright in the infrared, and after all, JWST is an infrared telescope, so it make perfect sense to use a brown dwarf for this purpose.


NOTE: I have been unable to find
Edited by jimbob: 
2MASS J10430758+2225236 2MASS J17554042+6551277
listed in any of the major catalogues of brown dwarf stars so it may be a recent discovery

edited at smartcooky's request
Posted By: jimbob
 
Last edited by a moderator:
Puppycow said:
I think that is it. It just doesn't appear to contain any information that I can understand. Probably because I'm not an astronomer.

Like what spectral class, the mass, and the distance from earth. I was just curious about that. It doesn't matter though. I don't think it's a particularly remarkable star.
Click to expand...

B 11.95 [0.14]
V 10.95 [0.07]
G 10.721766 [0.002763]
J 9.197 [0.022]
H 8.666 [0.034]
K 8.549 [0.019]

These are magnitudes using various standard filters.

B = Blue (445nm)
V = Visual (551nm)
G = Green (464nm)
J = Near Infrared (1220nm)
H = Near Infrared (1630nm)
K = Near Infrared (2190nm)

SO this start to our eyes is magnitude 10.95
 
Step 6: Telescope alignment has begun (not to be confused with segment alignment).

Once the Fine Phasing step was completed, the telescope was aligned at just one locations on the NIRCam field of view (NIRCam was used to align the segments). Now the instruments need to be aligned by making measurements at multiple locations, or field points, across each of the science instruments.
 
Puppycow said:
https://www.youtube.com/watch?v=QS2dMTzV5W0

Just zooming in on that test image to appreciate some of the detail. Best viewed full screen.
Click to expand...

Please remember this is only a test. They need to do more adjusting to the telescope before it is fully operational. The images would then be much better than this test image.

Cannot wait for that to happen. Images that would change our understanding like what Hubble's images did.
 
https://blogs.nasa.gov/webb/2022/03/17/webb-begins-multi-instrument-alignment/

The most recent post on the mission blog (March 17th) says this about MIRI and the cryocooler:

Webb’s mid-infrared instrument, MIRI, will be the last instrument that is aligned, as it is still waiting for the cryogenic cooler to chill it to its final operating temperature, just under 7 degrees above absolute zero. Interspersed within the initial MIMF observations, the two stages of the cooler will be turned on to bring MIRI to its operating temperature. The final stages of MIMF will align the telescope for MIRI.
Click to expand...

The cooler "will be turned on" at some point during the current phase. In other words, it hadn't been turned on yet as of March 17th. MIMF stands for multi-instrument multi-field alignment, which is what they are doing now. It's a six-week process according to the blog, which counting from March 17th would put the end of that process at April 28th. Then there's instrument calibration after that.
 
Launch Pad Astronomy has uploaded this video, which IMO, is the absolute best description the alignment steps for the JWST, starting with Step 1: Segment ID, and going right through to Step 6: Telescope alignment.

(And no sorry, I'm not going to even attempt to summarise this, because without the graphics in the video, any written description I could give would be incomprehensible.)


 
There's a new post in the mission blog. These have been coming about once a week recently.

Seems that they are about ready to start cooling MIRI. The reason why it has been warmer than the other instruments that are passively cooled is that there are actually heaters that have been turned on. This is to prevent ice from forming. These heaters will be turned off "soon", whatever that means. Once that happens it should cool down to 7K in a few weeks (supposedly 19 days I thought).

Also, the alignment of the other instruments besides MIRI appears to be already pretty good.

“The first step was to simply look at star fields as seen by NIRCam, NIRISS, FGS, and NIRSpec to see whether they were in focus. The stars looked nearly in-focus, which was a sign that the primary to secondary mirror alignment was already very good. A more accurate optical error measurement has been carried out at five to 10 field positions within each operational science instrument, using data taken with the secondary mirror positioned out of focus. This dataset provided a conclusive determination of the telescope alignment state.

“The Webb optics team analyzed the multi-instrument dataset and determined that only minor focus adjustments are needed on the secondary mirror and science instruments. Since the telescope is still cooling along with the MIRI instrument, we will not apply the corrections at this time and will defer them until the next round.
Click to expand...

So basically, that's it, until they get MIRI cooled down to 7K. I haven't yet seen any big daily change in the temperature according to the tracker yet.
 
Temperature updates

Red = Mar 25
Black = Mar 16
Green = Instrument target temperature reached

Frame and mirror
Primary Mirror -230° (43K) -230° (43K)
Instrument Radiator -236° (37K) -234° (39K)
Fine Steering Motor -239° (35K) -238° (35K)

Instruments
MIRI -187° (86K) -176° (97K)
NIRcam -235° (39K) -232° (42K)
NIRSpec -236° (37K) -234° (39K)
FGS/NIRISS -229° (44K) -227° (46K)

MIRI's cooler has been turned on so now its temperature is dropping much faster - 8° in the last 24 hours
 
Temperature updates

Red = Mar 29
Black = Mar 25
Green = Instrument target temperature reached

Frame and mirror
Primary Mirror -230° (43K) -230° (43K)
Instrument Radiator -236° (37K) -234° (39K)
Fine Steering Motor -239° (34K) -238° (35K)

Instruments
MIRI -201° (72K) -187° (86K)
NIRcam -235° (39K) -235° (39K)
NIRSpec -236° (37K) -236° (37K)
FGS/NIRISS -231° (42K) -229° (44K)


MIRI's temperature is falling at about 3½° per day now that the cooler is running.
FGS/NIRISS could reach its target temperature by the weekend
 
There is a new feature on "Where is Webb", one that shows the progress of the falling instrument temperatures.

JWST-Temps.jpg


There appears to be some evidence that NIRSS and NIRCam temperatures have benefited from MIRI's cryo-cooler. Both plots, having been stable for some time, show marked drops after it was turned on.

ETA: The red dashes on the left and right are not on the "Where is Webb" plot. Those are something I added to show the 40K target temperature.
 
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