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(IAAC) Obj: Abell 1367 (Leo galaxy cluster) - Inst: Newt 20" f/5



Observer: Lew Gramer
Your skills: Intermediate
Date and UT of Observation: 1997-2-6/7, 06:45-8:30 UT
Location: ATMs of Boston Clubhouse, Westford, MA, USA (43N)
Site classification: semirural
Limiting magnitude: 6.2
Seeing: 2 to 3 - medium good
Moon up: no
Instrument: Newt Reflector 20" f/5 (Tectron dob)
Magnification: 70x, 210x, 360x
Filters used: None, DeepSky
Object: Abell 1367 (Leo galaxy cluster)
Category: Cluster of galaxies
Constellation: Leo
Data: Abell richness=2 (out of possible 5), brightness=1 (7 is faintest)
      Galaxies ranging in magnitude from 11.8 to 15.1. Sizes 3' to 0.5'.
RA/DE: Centered around 11h45m  +19o50m
Description:
On this particular morning, I spent a rewarding couple of hours ferreting out
some of the brightest members of A1367 - one of the BRIGHTEST GALAXY CLUSTERS
accessible to amateur telescopes! The observing session itself could best be
described as "The Night of Endless Fixation": both the visual kind (using
averted vision on a single small area for many seconds), and the mental kind
(poring over Sky Survey charts of a single square-degree area, high up at the
eyepiece, mumbling disjointedly). It was all fun, though. :>
-
The field of A1367 is easily found from the white mag 4 star 93 Leonis. This
star forms a neat naked-eye rectangle with the three "haunches" stars at the
hind-end of Leo: Beta, Delta, and Theta. In the eyepiece, 93 is a wide visual
double with a mag 7 bluish "comes". This pretty pair forms a complex triangle
with two mag 8 stars in the same wide field. The SWmost star is another visual
double, more widely separated, with a mag 10 companion separated 3' at PA
200o. It is THAT little double which I will call the "cornerstone" for this
Abell cluster, as it is shown on both the Webb Society and Luginbuhl&Skiff
charts, and is the base I used to find most of the member galaxies.
-
The initial impression formed by A1367 on this occasion was UNDERwhelming:
with direct vision, at most two galaxies were ever visible in the same wide
field. With averted vision, three or sometimes four could be seen, but
generally all near the surface-brightness limit for my sky... In all, 12
galaxies were seen - out of 18 attempted. The Webb Sociey Handbook Vol. 5
actually states that some *sixty* galaxies are visible in 16"+ scopes! My only
excuses for not seeing more were the mag 6 skies, impatience with the task,
severe dewing that night, AND HASTY COLLIMATION - all but the first being my
own fault!
-
HERE ARE THE GALAXY OBSERVATIONS! Enjoy...
  Name        J2000 posn    Mag        Size          Morphology
  ngc3842     1144+1957     V=11.8     1.5'x1.0'     E3
This brightest member of A1367 is both easy to see at 70x without any filter,
and is easy to find. The "cornerstone double" points almost directly at it, at
a distance of perhaps 20'. This faintish blob showed two or three distinct
"tiers" of brightness, brightening pretty suddenly within 30" of the middle.
To averted vision at 210x, the halo had a slight elongation in PA 90o (E-W).
  ngc3861     1145+1958     V=12.7     2.3'x1.3'     (R')SAB(r)b
This faint haze brightened gradually toward the middle, and the core and halo
were both quite elongated to PA 70o (ENE). Averted vision hinted at much
structure in the halo, including spiral arms which appeared to arc off of both
ends, especially to the N off the E edge of the halo. Intriguing!
  mcg3-30-94  1145+1958     ?          0.6'x0.2'     SB(r)bc?
Apparent as a slight brightening off the edge of ngc3861 near PA 135o (SE). 
  mcg3-30-98  1145+1950     P=15.1     0.4'x0.3'     SA0
This tiny "dot" yielded to long fixated/averted vision, being easily found
between the cornerstone double and it's nearest bright neighbor, a mag 10 star
about 7' to the S. It was slightly elongated 112o (ESE), seeming ~50"x30".
  ngc3837     1144+1954     V=13.3     0.6'x0.6'     E
This little round galaxy is actually pointed to directly by the cornerstones.
Averted vision brought out a nondescript haze, less bright than nearby 3842,
  ngc3860     1145+1948     V=13.4     1.0'x0.5'     SAB(R)ab
Found about 8' W of the mag 10 star mentioned above, and forming a nice right
triangle with it and the cornerstone pair! This object was much fainter than
either 3842 or 3861, being comparable to 3837. It was much larger however,
especially with a DeepSky filter and averted vision, and showed a distinctly
mottled inner area, as well as an *irregular* elongated halo, PA 45o (NE).
  ngc3862     1145+1935     V=12.7     1.5'x1.5'     E0
Found from the "cornerstone double" by following a short chain of mag 10-11
stars about 30' S to a mag 9 star. Midway between this brighter star and the
last mag 11 star of the chain, the bright core of 3862 was obvious! The halo
dimmed very rapidly away from the core, and no stellar nucleus was
seen. However, the dim outer halo appeared to be interacting with ic2955!
  ic2955      1145+1937     V=14.0     0.2'x0.2'     SAB0?
Although this tiny companion(?) to 3862 took averted vision to see, it
actually appeared brighter (i.e., more concentrated) than its neighbor.  Again
the hint of a halo around this "dot" seemed to merge with that from 3862... ?
  ngc3857     1145+1932     V=14.1     1.0'x0.5'     SA0-
Just 5' NW of the mag 9 "end-of-chain" star used to find ngc3862. A hint of a
spindle with fixated vision, this galaxy appeared elongated at PA 45o (NE) in
both of its distinct outer and inner cores. The inner core seemed in moments
of excellent seeing to condense into a stellar nucleus?
  ngc3859     1145+1927     V=14.1     1.2'x0.3'     SA(r)cP
This galaxy of the intriguing morphology was both brighter and easier to find
than ngc3857, being 6' S of it, and forming a nice isoceles triangle with it
and the mag 9 "chain-end" star mentioned above. The galaxy LOOKED interesting
to fixated vision, showing a bare brighter core to the E, concentrating into a
stellar nucleus just 20" inside the core. Meanwhile to the W and SW (PA 225o
to 270o), the halo hinted at an irregularity that reached even into the core.
(A look at POSS later showed this was in fact a very unusual galaxy!)
  ngc3873     1146+1946     V=12.9     1.5'x1.3'     E
  ngc3875     1146+1945     V=14?      1.0'x0.3'     SA0-P
The positions of both 3873 and 3875 were uncertain for me this night, as the
Webb Society Vol 5 shows these two galaxies near a mag 10 star just 12' SE of
the cornerstone - and no such star could be seen! Perhaps this star is an
undiscovered variable? (Anyone reading this far who happens to be interested
in checking variable catalogs, please let me know what you find!) However, at
the position indicated by that star, a complex of haze WAS observed, with a
highly irregular halo and AT LEAST two stellar condensations (I noted a
possible third, and in fact Jeff Bondono's 'dObjects' lists yet another
companion for 3873...)
-
THE ONES THAT GOT AWAY:
  Z97-115     1145+1954     P=15.5     ?             ?
The first galaxy I looked for, being the first one clearly pointed to by my
cornerstone double star. Nothing could be seen of it.
  ngc3841     1144+1959     V=13.6     0.7'x0.7'     SA0-
Very near bright 3842. It SHOULD have been visible, but was not noted.
  ngc3851     1144+1959     V=15.2     0.3'x0.3'     SAB0
Collinear with 3842 and a mag 10 star NE of it - but I couldn't see it!
  Z97-143     1146+1947     V<15.5?    < 0.3' ?      ?
An outlier beyond the uncertain pair 3873/3875: no sign of it that night.
  Z97-123     1145+1929     V<15.5?    < 0.3' ?      ?
Inside the isoceles triangle of 3857, 3859, and the mag 9 "chain-end" star I
used to find both galaxies. This little bugger was nowhere to be seen!
  U6697       1144+1958     V=13.6     1.9'x0.3'     SB(s)m:sp
Another fascinating galaxy, but sadly by this time, the dew had made me loose
patience! So, despite looking for this bright enigma, I missed it. :(
===============================================================================
Karen Simmons & Lew Gramer dedalus@alum.mit.edu http://www.tiac.net/users/lewkaren
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