wimvb

A fellow amateur astronomer on a Swedish FB group pointed me to this scientific publication, showing all known structures of the M 31 group, including dwarf galaxies and tidal streams. https://arxiv.org/abs/1810.08234 Figure 12 in this publication is particularly interesting Interestingly enough, the image does show a tidal stream near ngc 147, which so far has eluded amateur astrophotographers. Unfortunately, this stream looks too wide for the fov of my telescope.

I checked and double checked. There are a few articles on spectormetric studies of Andromeda dwarf satellite galaxies. Apparently this one was discoverd ca 2012. It seems to have been identified as a dwarf spheroidal galaxy through the study of 8 (!) of its stars, none of which are visible in this image. Here's a deeper image with 2.25 hrs of integration time. This is luminance only with just a basic stretch applied. Clouds moved in after I collected this data and 30 minutes with a red filter. There's definitely some ifn coming through on the right hand side.

... or at least is about to get away. The centre of the image is supposed to show Andromeda XXX, a satellite galaxy to the Andromeda galaxy (M 31). Both SIMBAD and Wikipedia agree as to its position. The only other information I can find on it is here: https://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/en/community/nearby/ (Btw, don't Google Andromeda XXX without parental guidance 😉 ) The BIG question is: Should I continue to collect data on this object, or not? What do you think? (this is 40 minutes L so far)

Excellent. So, can we expect another image of this group with ifn, any time soon? 😉

Excellent image, Rodd. You're definitely "there". Me too.

@symmetal, just a quick follow up. The last two nights I've pointed my scope at ngc 147, but unfortunately managed to collect only 8 (!) usable subs due to clouds. I've integrated the subs, and even in an extrene stretch, there is no background structure at all visible in this galaxy's neighbourhood. But the galaxy does extend further than what is normally shown. I will collect more data, just to make sure, but for now it seems that this spheroidal galaxy is "exceptionally ordinary".

With an 8" scope on an heq5, you're pushing the limit, even with guiding. The large scope is like a sail in the wind, so I think that the choice of camera is a minor concern. If I were you, I'd look into guiding first, preferrably an off axis guider. That being said, 1s exposures are doable, but you need to take lots of them, think thousands. http://www.astrokraai.nl/viewimages.php?t=y&category=7

You’re trying to image an emission nebula with a camera system that is not intended for this. In short, you’re fighting an uphill battle.

Ifn is ok if it’s a natural part of an image, but in galaxy images ”it should be seen but not heard”. Ie, the image shouldn’t scream: IFN! at the cost of the main target. In this image I’m more pleased with the candidate tidal stream and the dwarf galaxies. The tidal stream is supposedly mag 27, which is by far the faintest I have caught ever. In a superstretched inverted L image it stands out very clearly.

Thank you for the information, Phyllis. I'd never heard of that. Now I just have to change the title of my post. 😀

This is (probably) my final version of this popular galaxy group. This image now has 8 hours of luminance data, and double the amount of colour data, compared to my previous version. 425 minutes (7 hrs) of RGB 240 minutes (4 hrs) of Ha 495 minutes (8 hrs) of Luminance Total time on target: 19 hours I think it paid off. The image now clearly shows the main galaxy's extended halo, IFN, three of four dwarf galaxies (ngc 7331A, ngc 7331B, ngc 7331C, with ngc 7331D being outside the fov), and a very faint (Mag 27) suspected tidal stream. Captured with my SkyWatcher 190MN, and ASI294MM camera, at gain 0, -10 C Processed with boxing gloves in PixInsight ( 😉 @ollypenrice ) I used the data in creative ways. The RGB and Ha data was processed as is. I used continuum subtraction to clean the Ha-signal. For the stars, I selected those subs that had the lowest FWHM and eccentricity values (39 subs), while for the galaxy and ifn, I used all 165 subs. Combined the lot in several stages in PI. The annotated version

Very interesting. I sense that a deep field image of ngc147 is due…

Thanks for those references. I’ll have a look tomorrow. I’ve imaged a few dwarf galaxies before, among others the Ursa Major dwarf UMa1. Atm, I’m working on an image showing three dwarf galaxies belonging to ngc 7331. https://www.astrobin.com/0gvm5z/

It’s just the central gray smudge, the rest is interstellar dust or maybe ifn.

Thanks, both I was a bit careless when collecting data. It seems that Ekos was still set to a gain of 200, from an earlier session. This caused an error in calibration (my darks are at gain 0), and may very well have contributed to the mottled background. Oops. If I decide to collect more data on this object, I will have to be more carefull.

Unexpected clear skies and not in the mood for a new long time project, so what do you do? You go for the faint objects. That makes perfect sense, doesn't it. Yesterday night we had a few hours of clear-ish skies, so I pointed my scope at this faint dwarf galaxy. It is a satellite of the Andromeda galaxy, hence its name: Andromeda VII. This spheroidal galaxy is situated in the constellation Cassiopeia, hence its other name: Cassiopeia dwarf. Scientists refer to it as PGC 2807155. I could find only three images in a Google search, one from the HST, one from the Keck telescope, and a rather blurry one from an amateur. This galaxy was discovered in 1998 by Russian and Ukrainian astronomers, and originally named the Cassiopeia Dwarf Spheroidal Galaxy. It is located 1 600 kLy distant, and being behind the Milky Way plane, it is obscured by dust and stars. Technical data: Imaged with a SkyWatcher 190MN, and ZWO ASI294MM camera with Optolong LRGB filters Total exposure time 200 minutes. Quick process in PixInsight There is dust from our own galaxy in the image, hence the uneven, mottled background (which actually is the foreground, of course).

There are many assumptions in your argument. But regardless of the math, the problem becomes visible in the linear image after background neutralisation and colour calibration. It diminishes when a normal levels stretch (histogram transformation) is applied, but is enhanced by masked stretch and arcsinh stretch, both of which stretch star cores less than the surrounding galaxy/nebula.

That is from background neutralisation. It is particularly strong if you have light pollution and overexposed stars. (Any stars that fall within the non-linear region of the camera.) The background neutralisation process subtracts the colour cast of the background from the entire image, even from blown out (white) stars. Stars end up deficient in that colour which dominated the background. There is a script in PI that can correct this artefact, the HSV repair script.

Just found this on YouTube. The videos that are released so far, only cover the user interface. But they contain a lot of nifty functions that can make life (processing) easier. https://youtube.com/user/PixInsight

Are the cameras supplied with an appropriate diffraction mask?

@robin_astro interesting references. Thanks

Still, a lot cheaper than that other IR camera hanging in the sky. But 15k is more than I’m willing to spend. These cameras will need to have good cooling to work. The longer the wavelength, the more interference from heat and the higher internal losses.

Maybe something to follow up with your "galaxstudsare"?

Not entirely boring. You have a tiny supernova in the image. It's in the fuzzy patch approximately mid between HD 38287 and HD 38449. The fuzzy patch is galaxy 2MFGC 4706. The SN has id SN 2003hz. The galaxy is roughly 270-300 Mly distant Right next to star HD 39044 there is also a very interesting pair of interacting galaxies MCG+08-11-010 UZC J055212.3+465020

Yes, to a certain degree http://wimvberlo.blogspot.com/2016/07/noise-reduction-for-dslr-astroimages.html (Btw, this blog post is dated, but it shows the workflow)