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Abell Galaxy Cluster 1913 and Haumea

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#1 Redbetter

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Posted 13 April 2021 - 02:45 AM

I attempt to go deep in an Abell galaxy cluster once or twice each new Moon cycle.  On 4/7/21 I targeted Haumea, picking up various galaxies nearby.  Close to this field was AGC 1913, so I made a finder chart for the session to see how many members/galaxies in the field I could pick up with the 20" in dark sky. 

 

First up was dwarf planet Haumea, using my printed chart from SDSS images, with Haumea's position marked from MPC ephemerides.  Despite being in the range of 17.3 magnitude, I saw it immediately in averted vision at 278x, precisely where I had plotted it relative to  the key sets of two 13 mag, a pair of 15 & 16 and a 17 mag mag field star.  Well west of the 17 mag star at 357x I could just make out PGC 1500912 (17.5 g mag), xxF, xxs, just hints mostly but enough to know it was there.   To the NE of the group of stars near Haumea was CGCG 104-16 at a more recognizable 15.6 g mag, xs, vvF, elongated 2:1 NNW/SSE, with good surface brightness, 16 mag star just W of center.  The only other galaxy I could see nearby was PGC 84153 (KUG1421+164) which was nearer the 6.9 mag star for my star hop.  This one wasn't too hard at 16.1 mag, xs, xF, good SB, some brightening to middle but core not seen.

 

Then it was show time for AGC 1913 at about 750+ MLY distance.  I located the cluster by first observing galaxies IC 4429 and IC 4426 that point to the center of it at 278x.  From there I began working through the brighter members to the NW, CGCG 104-21/22/23/26 (all about 15.2 to 15.6 g mag), then PGC 51544 and 84181 somewhat south.  Then I skipped to CGCG 104-27 near center, then to the far NW for PGC 84169 up against the glare of a 10th mag star. 

 

After that I went after dimmer members in the center of the field PGC's 84176, 84179, 84178, 84174 in the 16.1 to 16.7 g mag range, as well as PGC's 51558, 51576, and 51580 in the 15.4 to 16.2 g mag range.  I then chased down a string to the SE of PGC's 51609, 84187, 84188, and 84189.  These ran from 15.7 g to 16.9 g mag.  The final galaxy I observed was CGCG 104-19, which is perhaps a bit more distant and is somewhat detached from the group.  

 

At this point I was having more difficulty seeing galaxies, and looked up to find thin cirrus was beginning to wash out the sky.  It wasn't my eyes, the already marginal transparency had failed me.  There were a few more outliers that would have been in reach, plus IC 4417, but the weather had other ideas.  


Edited by Redbetter, 13 April 2021 - 04:47 AM.

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#2 sgottlieb

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Posted 21 April 2021 - 08:47 PM

Very nice observations!  Another cluster you might enjoy in Bootes is AGC 2022.

 

It's a similar distance (actually a slightly higher redshift) as AGC 1913 with the cD member CGCG 165-006 at the center (forms a contact pair with 2MASX J15041797+2829430).  A slew of slightly fainter galaxies are swarming nearby to chase after.


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#3 Redbetter

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Posted 22 April 2021 - 12:31 AM

Very nice observations!  Another cluster you might enjoy in Bootes is AGC 2022.

 

It's a similar distance (actually a slightly higher redshift) as AGC 1913 with the cD member CGCG 165-006 at the center (forms a contact pair with 2MASX J15041797+2829430).  A slew of slightly fainter galaxies are swarming nearby to chase after.

Thanks!  Funny you mention that one, I observed Abell Galaxy Cluster 2022 last July (7/22/20) before the fires took over in August.   The same night I observed two Rose Compact Groups in Bootes, #21 and 24.

 

For Abell 2022, I identified 9 galaxies in two groups, but didn't get the opportunity to explore further. Inexplicably, one galaxy had not been identified as a galaxy when I checked in Aladin Lite from what I can tell/recorded afterward, I have it tagged as 2MASX J15051673+2820118--just north of CGCG 165-14.  I was only using about 227x for this cluster, and I didn't get to spend enough time on it to write descriptions because it was drifting into a tree that sticks up above 45 degrees on the western eastern, brighter portion of the sky at the site.  There were other scattered galaxies I hoped to go for, but the tree and time of year thwarted that.  The ones I logged were CGCG's 165-5/6/7/9&14 along with PGC 1837832, 2MASX J15051232+2821181​, 2MASX J15041797+2829430 and the one mentioned above.

 

The Rose groups were observed first.  Rose 21 was found without difficulty.  IC 4461 was largest & brightest of group, vvF, vvs, average surface brightness, some brightening to middle, only hints of core at 278x.  IC 4462 was seen following, xs, vvF, decent surface brightness, with prominent stellar core.  MCG+5-34-76 to south of IC 4461, xs, vvF, average surface brightness, often seems to have stellar core, but this is probably a star just south of the galaxy.  The 4th component was unseen.  I was able to pick up another galaxy just south east of the group, SDSS J143508.41+263124.8, but was not sure of another one just south of it.  I listed the SDSS observation as "xxs, xxF, averted vision hints at 357x."

 

Rose 24 was very difficult to actually resolve in the 20".  I found the group in averted vision and could see the general shape, seeing individual members fleetingly, but I couldn't see all 4 simultaneously so I found it difficult to identify each and describe them other than noting B was the brightest from what I saw.  I was working mostly at 357x.    Members were PGC's 1846759, 1846870, 1846782, 1846817.  I found a galaxy to the south of the group more readily, PGC 1845592, xS, xf, average surface brightness at 357x with 16+ mag star following some distance.  


Edited by Redbetter, 22 April 2021 - 07:57 PM.

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#4 sgottlieb

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Posted 22 April 2021 - 07:05 PM

I picked up a similar list of galaxies in Abell 2022 using my 24" back in 2012, along with PGC 1837813 (just NE of CGCG 165-6), CGCG 165-8 and PGC 1839290.

 

Interestingly, two of the galaxies -- CGCG 165-6 and 165-14 -- just missed out on obtaining NGC designations.  They were both discovered visually by Édouard Stephan (in 1869 and 1878, respectively), but he never got around to measuring precise offsets from known nearby stars, so didn't publishing these discoveries (same with scores of other galaxies he found).   So they essentially remained "lost" in his notebook entries.

 

I observed the Rose 21 trio in my old 18" back in 2008 and didn't have much to say about the faintest southern galaxy -- just "extremely faint and small".  I was just glad it was visible.  By the way, besides the IC designations, the group also goes by Arp 95 and VV 303, though Arp may have only had the northern two galaxies in mind.


Edited by sgottlieb, 22 April 2021 - 11:11 PM.

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