Gravitational lenses: the Cosmic Horseshoe

[Xilman]

This one is for REAL men, REAL women and REAL small furry creatures from Alpha Centauri.

Almost all known gravitationally lensed objects are beyond the abilities of almost all amateurs to image with a reasonable amount of data collection from reasonably sized telescope. The Cosmic Horseshoe is a notable exception. It is the BAA Deep Sky section's object of interest for March 2023.

Here is my attempt.

and here are the technical details: https://britastro.org/observations/observation.php?id=20230225_235430_a0cc7592c8804113

David Strange has picked up the lensing galaxy but did not wait long enough for the lensed galaxy to show up.  I am certain he could manage it.

OK, so what are you waiting for?  Let's see some more images of what are truly deep sky objects. Neither an exceptionally large telescope nor particularly dark skies are necessary. They lie in Leo and so are easily visible from essentially the whole world. All that is needed is a desire to expand your comfort zone.

 

Edited March 30 by Xilman
Fix tyop: s/ling/long/

[DaveS]

OK, challenge accepted. I had been planning on imaging as many of the HCGs that are accessible from my location and with my setup, but will put them on hold.

I've got the coordinates from the wiki link in the BAA article.

RA 11h 48m 33.1s, Dec +19d 30m 0.3s J2000 coordinates.

[Elp]

1 hour ago, Xilman said:

Almost all known gravitationally lensed objects are beyond the abilities of almost all amateurs to image with a reasonable amount of data collection from reasonably sized telescope

Any imaging is beyond the abilities of all amateurs due to cloud.

Seriously, I would do such things with better weather.

[Xilman]

35 minutes ago, Elp said:

Any imaging is beyond the abilities of all amateurs due to cloud.

Seriously, I would do such things with better weather.

You only need one night of decent weather, something which will almost certainly happen within the next two months, even in these ${DEITY}-forsaken parts.

Added in edit: not even that.  The CH doesn't move so you can stack subs taken over several small periods of half-way decent visibility.

 

Edited March 30 by Xilman

[Paul M]

Since the other thread where this was mentioned, it's been at the top of my ToDo list. Not had a clear sky since

I've just seen your note about the ring being only 10" dia, so no easy task!

 

 

[Elp]

What sort of focal length does this need?

[Xilman]

38 minutes ago, Elp said:

What sort of focal length does this need?

It depends on the resolution of your camera. The smaller the pixels on your camera, the smaller the size of each pixel on the sky for any given focal length. My scope has a focal length of 2600mm (400mm at f/6.5) and a Starlight Xpress 814 camera which has 3.7 micron pixels, giving a native 0.29 arcsec per pixel. I run at 2x binning except under unusual circumstances so each pixel is 0.58 arcsec on the sky. Note that is markedly smaller than the seeing (typically 2-3 arcsec), and that oversampling permits subsequent super-resolution in software. My diffraction limit is 0.31 arcsec, so 1x binning is used for experiments with Lucky imaging, not that I have done much of that so far.

A pixel size in the range 0.3 through 1.0 arcsec is likely appropriate for this object. The ring is 5 arcsec from the center of the galaxy, which will be 2.5 arcsec in radius when the seeing is reasonable. This diagram may help in which each "pixel" is 0.3 arcsec and R are ring pixels, _ are sky pixels, and G are lensing galaxy pixels, assuming 2 arcsec seeing.

RRRRRR_______GGGGGGGG_______RRRRRR

Do not take this too literally. Reality will depend on seeing, your camera, guidinjg/stacking, and the like.

Remember: no-one said it would be easy.  A whole bunch of people have said, and proved, that it is possible if you are prepared to give it a try. Who wants an easy life anyway? It can be excessively boring.

 

[DaveS]

I currently have my old Trius 694 on my ODK 12 for capturing the HCGs that I was going after. This gives a sampling of 0.46"/px, similar to the Rayleigh limit for my 'scope.

An ASI 533 would give a finer theoretical resolution, but since I'm not spending any more money on this futile hobby I'll go with what I have.

Edited March 31 by DaveS

[Xilman]

I very strongly recommend that you go with what you have. You already have sub-seeing resolution and easily enough aperture and camera sensitivity to reach below 22nd magnitude within a single clear night. You could quite likely reach mag 24 by collecting subs over a week or two,

(Incidentally, I have over 1200 hours subs of a single field yet to be analysed. I will be very surprised if the faintest objects detectable are brighter than 24th magnitude and they could well be below 26th mag. One day I will analyse that field and report back here at SGL)

What you have described is very much  sufficient to image the Cosmic Horseshoe,  so go for it this spring if the weather will let you.

More generally: those of us with 12-20 inch apertures these days can take images which would have required 100-200 inch apertures only 60 years ago. CCD cameras and modern image processing software have made an amazing difference.  Amazing to me, anyway.

 

Edited March 31 by Xilman
s/reuired/required/

[Paul M]

I got a few subs collected on this elusive target last night.

Not a serious atempt, more of a fesibillity study. 7 x 300 sec. RC10, ASI071 camera and a nearly full moon washing over the area.

I have just about got some pixels of the lensing galaxy, but only just. This image is down to mag 18, and as always nowhere near enough integration time. But I wanted to get a feel for the area before wasting a full. dark night on it. I think it's within my grasp. But as longer days and shorter nights catch up with Leo, as it slides off into southwest, time is suddenly a factor!

Enough blather:

[Xilman]

  

Looks promising to me.  A higher than normal concentration of bright pixels, and, this is important in my view, of a reddish colour.

Remember that you don't have to take all your subs on a single night - this thing doesn't move around the sky.

[Paul M]

45 minutes ago, Xilman said:

Remember that you don't have to take all your subs on a single night

Indeed. I think I'll start from scratch on the next usable night. These Moonwashed "test" subs maybe won't add much more than noise. 

So now I've got two challenges this spring. Capture both the Cosmic Horseshoe and 3C273's jet.

Perhaps the one ingrediant I need most is a dark southern sky. Unfortunately the one I have is pants!

[DaveS]

Having looked at my capture folders I see that in March I managed exactly 0 sessions. Yup, that's right, a big fat zero.

I seriously wonder if I will manage anything at all during this "Galaxy Season".

[Paul M]

I've had an unbelievable 4 nights this month already. Mostly leaving the toys out doing their thing while I sleep.

Of course it's only been clear because of the full Moon.🤨

[Paul M]

Right, my last go for this year. A total 51 x 300 sec subs, binned 2x2, collected over 3 nights. RC10 no filters. 

Perhaps a hint of fainter outer halo to the lensing galaxy, or maybe wishful thinking? The image exceeds mag 20.

It's the fuzzy just about center of the image.

[DaveS]

A preliminary result from the ODK 12 and SX 694. 36 x 600 sec Luminance subs over the 18th / 19th. Stacked in AstroArt, DDP and Richardson-Lucy deconvolution, with a denoise to finish.

It's the ridiculously tiny bullseye in the centre. It does show a broken ring when examined at 100%. In the unlikely event of my getting more clear nights (Yeah, right) I will add to the data and process in PI with BX (If i manage o purchase a licence)

This may, however, have used up my clear sky quota for april and Galaxy Season.

Centre crop given another R-L deconvolution

Edited April 21 by DaveS

[Paul M]

14 minutes ago, DaveS said:

A preliminary result from the ODK 12

You got it!

A rather excellent result. 

I think light pollution is my main enemy with this one.

There are three or so quasars in the field too. My image only picks out one of them, which is clear in your image. Immediately to the left of the target and fractionally below. It's the brightest of the three stars in the little triangle. 

 

[DaveS]

I've decided to put this to bed and move on. I've got the ring so will consider it a success. 6 hours might be considered a rather short integration time, but I want to see what else I might be able to image before the end of astro dark.

[Xilman]

On 21/04/2023 at 16:09, DaveS said:

A preliminary result from the ODK 12 and SX 694. 36 x 600 sec Luminance subs over the 18th / 19th. Stacked in AstroArt, DDP and Richardson-Lucy deconvolution, with a denoise to finish.

It's the ridiculously tiny bullseye in the centre. It does show a broken ring when examined at 100%.

Centre crop given another R-L deconvolution

Excellent result, coingratulations!

 It appears so tiny because the ring is only 10 arcsec in diameter.