Starship Asterisk*

DaveDerl wrote: ↑Sun Sep 20, 2020 9:58 am What are these bright almost completely white spectra below the center? I thought foreground stars but you probably won't bother doing the data analysis for them if it is about galaxy motion?

heehaw wrote: ↑Sun Sep 20, 2020 10:51 am

DaveDerl wrote: ↑Sun Sep 20, 2020 9:58 am
What are these bright almost completely white spectra below the center? I thought foreground stars but you probably won't bother doing the data analysis for them if it is about galaxy motion?

Maybe just stars too bright and so overexposed?

https://www.eso.org/public/images/eso0209b/ wrote:
<<MOS-spectra obtained with two quadrants totaling 221 slits + 6 reference objects (stars placed in square holes to ensure a correct alignment). Exposure time 900 seconds; LR(red) grism. This is the raw (unprocessed) image of the spectra.>>

Holger Nielsen wrote: ↑Sun Sep 20, 2020 11:53 am I also wondered about the allmost white spectra: If they are foreground stars, why include them?
Further questions:
The parallel horizontal arrangement of the spectra suggests that the positions of the spectra in the image are not correlated with the position of the galaxy in the sky, but then why are there variable horizontal shifts of the spectra?
Are there four spectra in each row?
Why does the height of the spectra vary?
What is the wavelength range, can any prominent lines be identified?
What is the origin of the many white lines appearing mostly on the right hand side?
Are colors used just to prevent a black-end-white image?

Chris Peterson wrote: ↑Sun Sep 20, 2020 1:52 pm Keep in mind that this is a pseudocolor image. That is, it is a grayscale raw image which is presented here with the different intensities mapped to different colors. The colors here have no relationship to actual color of the objects.

Cousin Ricky wrote: ↑Sun Sep 20, 2020 4:48 pm

Chris Peterson wrote: ↑Sun Sep 20, 2020 1:52 pm
Keep in mind that this is a pseudocolor image. That is, it is a grayscale raw image which is presented here with the different intensities mapped to different colors. The colors here have no relationship to actual color of the objects.

I was going to ask about that! Thanks for anticipating my question.

• A stopped clock is right twice a day

Chris Peterson wrote: ↑Sun Sep 20, 2020 1:52 pm
Keep in mind that this is a pseudocolor image. That is, it is a grayscale raw image which is presented here with the different intensities mapped to different colors. The colors here have no relationship to actual color of the objects.

Chris Peterson wrote: ↑Sun Sep 20, 2020 1:52 pm The white lines are the slits, each of which is aligned with a galaxy of interest. They appear white because they show the overexposed direct light of the target galaxy. They correspond to the physical location of the galaxy on the image plane. On the vertical axis they are positioned so they don't overlap, in order to keep the spectra separate. There are four spectra in each row because that's what will fit on the sensor given the nature of the grism. There are rows with fewer than four, presumably because there were not four galaxies available. The height varies because the length of the slits is variable, depending on the size of the galaxy and on the constraint of avoiding overlaps. The actual spectral range depends on the grism they've utilized; nominally they can resolve from 360-1000 nm.

Keep in mind that this is a pseudocolor image. That is, it is a grayscale raw image which is presented here with the different intensities mapped to different colors. The colors here have no relationship to actual color of the objects.

orin stepanek wrote: ↑Sun Sep 20, 2020 5:55 pm
Looks like the gears in an old clock; and it's about time!

TheZuke! wrote: ↑Mon Sep 21, 2020 2:03 pm

orin stepanek wrote: ↑Sun Sep 20, 2020 5:55 pm
Looks like the gears in an old clock; and it's about time!

Or stacks of gold coins viewed edge on?