help to identify sky/light pollution lines

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Hamish Barker
Posts: 226
Joined: Thu Jun 20, 2019 12:11 am

help to identify sky/light pollution lines

Post by Hamish Barker »

Hi All,

In the process of attempting to take a spectrum of asassn-21mk ( Be star maybe?) at dec -71 degrees, and the worst possible hour angle (directly below the pole), I got more signal from sky glow or light pollution than the star. I have been able to identify a few lines, but there is one prominent one which I cannot work out, at around 5517 angstrom.

I think I identify oxygen at 5577 and 6300, and
there are a few street lights in town which are still high pressure sodium (most are LED), so I identify various sodium and mercury lines.
mercury 5461 5769 5791
sodium maybe 4983, 5153 5684 5688 and a hint of the high pressure sodium light wings.

but i cannot identify the most prominent line which seems to be 5517 angstrom.

perhaps my whole wavelength calibration is wrong, but everything else seems to fit. I wonder if the line might be some sort of rare earth from phosphors on the LED lamps?

If anyone has any suggestions, I am all ears!

note: the title on the plot is asassn-21mk because this is the same data but without "don't remove sky background" switch on.

I can't attach the fit file for a forum post but am happy to email it.

Cheers,
Hamish

sky-lines.png
sky-lines.png (16.53 KiB) Viewed 4975 times
Hamish Barker
Posts: 226
Joined: Thu Jun 20, 2019 12:11 am

Re: help to identify sky/light pollution lines

Post by Hamish Barker »

False alarm, it was a new hot pixel.
Bernard Heathcote
Posts: 84
Joined: Mon Sep 26, 2011 10:09 am

Re: help to identify sky/light pollution lines

Post by Bernard Heathcote »

Hi Hamish,

Those lines look like a strong 5577 (OI) flanked by Hg 5461 and NaI 5684, but difficult to test without the FIT file. If they fit then there is clearly a wavelength ID/calibration issue.

Cheers,
Bernard
Bernard Heathcote
Posts: 84
Joined: Mon Sep 26, 2011 10:09 am

Re: help to identify sky/light pollution lines

Post by Bernard Heathcote »

Oops ... I missed your 'hot pixel' post.

Bernard
Bernard Heathcote
Posts: 84
Joined: Mon Sep 26, 2011 10:09 am

Re: help to identify sky/light pollution lines

Post by Bernard Heathcote »

But, that strong line looks too broad to just be a hot pixel.

Bernard
Hamish Barker
Posts: 226
Joined: Thu Jun 20, 2019 12:11 am

Re: help to identify sky/light pollution lines

Post by Hamish Barker »

The strong line is a cluster of several adjacent hot pixels When I increased the width of the binning zone to get better s/n of the sky lines, I didn't notice that that line popped up. I went back and manually examined the pixels until I found the pair with values of circa 40000adu compared to rest of the sky which were 400-500.

I addded those pixel locations to the cosmetic damage file and the line disappeared.

Perhaps they were damaged by a cosmic ray? I should go back to previous images and see if they are really new or I just never selected that region before. My dark frames should have removed them if they were preexisting. Or did I miss something?
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