Near IR 742nm on Andromeda Galaxy core

[Menno555]

I did fit my scope with the Zwo ASI482MC camera (rather good in IR range) and Astronomik ProPlanet 742 IR-pass filter. This for the moon and Mars. But clouds and aftermath from the flu did prevent me from doing that.
But in preparation, I thought to capture the core of M31 just as experiment. Could be interesting with this very small FOV but this brought nothing.
But 2 days later, it dawned to me that there was a lot of nothing in the capture? Compared it with a shot a made a while ago with a normal IR/UV Cut filter, and behold: the dust lanes were all but visible?

I do know that in full IR, the IR light is captured that is "going through" the dust. But is this also the case with Near IR at 742nm?

Full version: https://i.ibb.co/rcbXWGg/M31-Compare.jpg



Also (and this might be wishful thinking), I think I captured the elongated core/nucleus of M31? In the Near IR capture all the stars are round but the core seems to be somewhat elongated caused by the 2 nuclei?
Here a blown up version.

Full version: https://i.ibb.co/XFQCMV3/M31-elongated.jpg


Menno

Bortle 6/7
Meade LX200 8" f/10 ACF OTA
Ioptron CEM25EC mount
Astronomik ProPlanet 742 IR-pass filter
Zwo ASI482MC camera

Captured with SharpCap Pro @ -10 Celsius / White balance R50 B50
240 x 15sec / Gain 150 / Offset 10
80 x darks, 50 x flats and 50 x darkflats

Stacked with DeepskyStacker

Siril and Photoshop
Siril: Histogram
Photoshop: Camera Raw Filter (darks, lightness, clarity, sharpening), noise reduction NoiseXterminator plug-in.

[timh]

Interesting observation..

It is quite a big difference in contrast! I think that it makes sense though --i.e. if the dust particles are average size about a micron (normal distribution) and the peak wavelength of emission of the galaxy x peak camera QE is down in the visible at 5-600 nm somewhere then maybe only 5% of the visible light does not get scattered and the dust contrast is therefore high. On the other hand the 742 nm filter cuts off everything below that and the response of the camera goes right up above 900 nm with the green peak (half the pixels) in that upper range peaking at well above 800 nm --- so a relatively high proportion of light at those wavelengths that are best detected won't be scattered (e.g. maybe 25% of the light goes straight through?) and the dust contrast much less (e.g. 5X less taking my particular guestimates) ... i.e so you can sort of still see the dust in near IR but at lower contrast?

Maybe one could view the experiment with different filters as an indirect way of measuring the average size of dust particles in teh Andromeda galaxy ---which is actually quite cool when you think about it

Tim

[Menno555]

I understand what you mean Tim.
I forgot about the camera and it's sensitivity. If you look at the 482MC scheme below, at the 742nm range the Red is at around 57%, Green around 27% and Blue around 4%.So it's logical that if the dust is showing most in the Blue and Green it's almost not visible here or only at higher contrast.
My other camera (385MC) should give then also another result with R 80%, G 38% and B 8% at 742nm. But it has a smaller pixelsize.

Menno

[timh]

One thing that I didn't understand before and that your post caused me to learn is that the dependence of scattering on wavelength is huge ...its to the 4 th power of the wavelength. So --if I understand correctly ...then - for example - light at 500nm gets scattered some 16 fold more than does light at 1000 nm. --so just a two fold difference in wavelength has a very big effect. By the time you get up to some of the JWST wavelengths of 2-4 microns the dust must be ~ fully transparent?

[oopfan]

Hi Tim,

This is my understanding also. A couple years ago I got hold of B-V photometric magnitudes of Cepheid variable stars in the arms of the Milky Way. I applied Leavitt's Law to calculate distance given the period and then plotted it. I could see the structure of the arms in the approximate neighborhood of the Sun but the farther away from the Sun it became unrecognizable. The problem, as you might have guessed, is the extreme scattering at short wavelengths that makes those stars appear much farther away than they actually are. I read that when the HST was launched one of its first tasks was to measure the IR magnitude of stars in the galactic plane, and then derive adjustments to Leavitt's Law. Cool stuff!

Brian

[oopfan]

Menno,

I wonder if M31's elongated core is the result of the gravitational force of one or more of its satellites (M32 or NGC 205). I haven't researched it but seems plausible considering how distorted NGC 205 is:

viewtopic.php?t=3146

Brian

[Menno555]

Brian

Here some more about the M31 core: https://skyandtelescope.org/astronomy-n ... uble-core/
As I understand it, the bright core are stars rotating around the black hole in the center. They now think that it got lobsided because a group of stars entered but started spinning in the opposite direction. This deformed the ring, making it a kind of oval shape.

Menno

[RMSQueenMary]

I used the 742 nm filter. I can see distant galaxy clusters and quasars.

[Menno555]

I used the 742 nm filter. I can see distant galaxy clusters and quasars.

Ah, cool! What equipment did you use?
Cool thing for me to try too. Around 2 years ago I did some mapping of globular clusters in M31 (see https://i.imgur.com/SRi9jEm.jpg ).
It was with a different camera but could try it again with my current ASI071MC Pro and the 742nm IR Pass and see if more is showing.

Menno

[RMSQueenMary]

I used the 742 nm filter. I can see distant galaxy clusters and quasars.

Ah, cool! What equipment did you use?
Cool thing for me to try too. Around 2 years ago I did some mapping of globular clusters in M31 (see https://i.imgur.com/SRi9jEm.jpg ).
It was with a different camera but could try it again with my current ASI071MC Pro and the 742nm IR Pass and see if more is showing.

Menno

I use the ASI294mc Pro. It is the one shot color. I just put the saturation level at 0 when I use IR long pass filter. I have the #29 red filter, Lumicon Nighy Sky H-Alpha, Astronomik 742 nm, and ZWO 850 nm filter. There is the IMX462 monochrome version out with the ASI462mm and Mars-M II USB3.0 Mono Camera. It should go deeper as IMX462 is sensitive in the near infrared. Perhaps, it could see some high red shift objects of 7 or greater.........