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Martin Meredith

A trio of Hicksons

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Martin Meredith    1,520

Having complained about the number of rainy/snowy days here (about 80% of all days so far this year), last night was reasonably clear although gusty, so I (literally) dusted off the scope for a quick session, the first one since January. I've been observing the 100 Hickson Compact Groups intermittently over the last couple of years and 6 months ago decided to make an effort to observe the remaining 20-odd over the coming season. Given the lack of opportunities I was keen to observe whatever was visible in the south last night, although it would have made more sense to wait for later in the season (or stay up later into the night...).

My main aim was to test out the EAA tool I've been developing recently, so the session was a bit fraught as theory and reality didn't quite meet (long story involving the automatic estimation of exposure durations in order to select from a dark library), which is why I didn't remember to save many screenshots. For this reason, these images are actually post-hoc reconstructions of what I saw at the scope and using the same tool (I reloaded/restacked/inverted/zoomed/rotated, and added some annotation). The view is theoretically identical but in practice very similar to what I had live at the scope. (One of the features of the tool is to be able to revisit previous sessions and operate as if in 'live' mode). 

N is up in all cases. I applied a x/(x+c) form of compression which I find enables me to stretch the image without altering the white point. I used mean stacking, bad pixel mapping/removal (but no darks), and gradient removal. Scope: 8" f4 Quattro, alt-az mount, camera: Lodestar X2 mono, no filters. I was hoping to use Nebulosity as a capture engine, scripted from within my tool, but that didn't come off on the night so I ended up using StarlightLive as a mere capture slave (much as it pains me to say it!).

 

First up is HCG 67, also known as VV 135, in Virgo, observed at 24 degrees above the horizon. This appears to be a physically-related group at around 360 million light years distance. Three members of the group are very close together, with a near edge-on b member at some distance.

magnitudes
a = NGC 5306 mag 13.1
b 15.1
c 15.7
d 15.8

This is a stack of 18 x 15 subs

HCG67.thumb.png.a0d2f6e9e5f64fc4a1a6dfb99c2ee9d8.png


Next, HCG 71 in Bootes, at a more healthy altitude of 40 degrees. This whole part of the sky is littered with tens of thousands of faint (but observable) galaxies. The 'a' member is a delicate face-on galaxy with some open spiral structure evident, while 'b' is a barred spiral. 'a'-'c' are at a similar distance, around 450 MLYs, while d seems to be unrelated at nearly 1 billion LYs.

magnitudes:
a = ngc 5009 14.4
b = ic 4382 15.5
c 16.2
d 17.2

Stack of 14 x 15s subs

HCG71.thumb.png.18c23a2dbbf90d1c3ee168265cd780c0.png

 

Finally, here is HCG 76 in Serpens, observed in the murk at 20 degrees (gradient removal really helped for this group.) Atypically for the Hicksons, this is a 7-strong group, consisting of 4 'bright' and 3 much fainter members, but all have a similar estimated distance of around 500 MLYs. Bizarrely, while 3 of the 4 brightest members are in the NGC, the brightest of all (b) is not. 

magnitudes:
a = ngc 5944 15.9
b 14.9
c = ngc 5941 15.3
d = ngc 5942 15.8
e 17.0
f 17.0
g 17.4

The region from the centre to the top of the image  contains the Abell-Corwin-Olowin Galaxy Cluster ACO 2085, estimated to contain at least 52 galaxies, the brightest of which shines at mag 17.6. There are a few I've been able to track down in the image down to mag 19.4. I can't find a redshift but the cluster is of distance class 6, which probably places it at around 1.2-2.5 billion LYs.

HCG76.thumb.png.b97fc2f7488baa94e87b53e2f469a536.png

 

With these three added to the tally I'm down to my last 10 Hicksons, mainly in Hydra and Ursa Major, but with a real toughie in HCG 63 at a declination of nearly -33 in Centaurus.... 

Thanks for reading

Martin

 

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RobertI    1,168

Well done for finally getting some observing time Martin, some nice captures there. Still no sign of a clear night here, the Spring galaxies are fast disappearing for another year. I always find the Spring sky is gone so quickly, blink and you miss it,  whereas the summer constellations seem to hang around for half the year.

Your EAA tool is coming on nicely by the look of things, very much looking forward to having a go. I like the inverted view and, apart from the novel interface, you seem to have included some great features. Does the tool allow annotation or is that done afterwards?

Perhaps a video taster at some point? :) 

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Martin Meredith    1,520

Thanks Rob. You're right, spring observing seems to rush by what with the later sunset and hour change...

At present the tool supports session and observation logging and observing lists, but annotation is on the to-do list. These were done with the usual method for me, Preview on the Mac. Inversion I find is really useful as I can apply some incredibly brutal stretches to pull out details (the ones above are quite mild stretches by comparison).

I'll put together a vid at some point but there is still some work to do before release, not least compiling the whole thing into a single application (I'm sure that is not going to be straightforward). A few more clear nights of testing would be very welcome.

Martin

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HiloDon    802

As always, Martin, excellent results and presentation.  I love capturing the Hickson’s as well.  You were the one who put me onto them a few years back.  Our weather here in Hawaii has been terrible, too.  I think I’ve only had three sessions so far this year.

I look forward to your release of the new EAA tool.  Let me know if I can be of any help.

Don

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umasscrew39    10

Well done Martin.  These are always a challenge but a fun one at that and your new EAA tool seems to be coming along.  Like Don, I think I have had about 3 nights over the past 3 months where I could actually see something.   Continued success on the development of your tool.

Bruce

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Martin Meredith    1,520
Posted (edited)

Thanks Don and Bruce. Sorry to hear about your weather and I hope things improve before summer. Bad weather seems to be have been fairly extensive.

I managed another session the night before last and was able to collect my very first flats (and bias) and integrate them into the tool. I tried pre-twilight T-shirt flats, twilight flats, and just-post-twilight flats. While the latter two types contain several stars, since the mount was static I could remove them automatically with median, or preferably percentile-clipped stacking. All of these types of flats seem to be useable for EAA and easy to collect. I might implement an auto-flat procedure which searches for the optimum exposure. Anyway, the user now has numerous ways to kill artefacts (median, percentile stack combination; bad pixel mapping; darks; flats; gradient removal).

Here's a longish stack of Arp 248, also known as Wild's Triplet, a fascinating trio of interacting galaxies in Virgo, at the border with Leo and Crater. Arp's original image can be seen here.

5ad7411d579e3_ScreenShot2018-04-18at10_26_46.thumb.png.1f4e4bc127ea9bba349fa7e031c4f954.png

 

Very close by I spotted this photogenic group of mainly mag 15-16 galaxies, with close double BRT 1938 at its head. The group appears to have a designation but I haven't been able to track it down precisely yet  (edit: the first and only mention is in this 2000 paper: http://iopscience.iop.org/article/10.1086/308967/meta). 

This is a stack of 29 x 15s. Unmarked, but readily visible and identifiable at the top left of the attached chart, is a Vmag 19.6 quasar with a redshift of 3.22 which equates to a light travel time of 9.6-11.7 billion years.  This is quite bright for such an exceptionally distant object.

5ad7434d826d8_ScreenShot2018-04-16at22_57_19.thumb.png.89cd82ae366655eb2111beb761e1bb5b.png

 

5ad743595ef6b_ScreenShot2018-04-18at15_06_01.thumb.png.a6a81f2212acf37727697e436658db3f.png

 

 

Martin

Edited by Martin Meredith
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stash_old    223

Nice one Martin - looks like you are looking out the portal of a Spacecraft.

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HiloDon    802

Very cool, Martin!

Don

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