(IAAC) Obj: Pegasus I (Galaxy Cluster) - Inst: 20" f/5 dob newt
Observer: Lew Gramer
Your skills: Intermediate
Date and UT of Observation: 1997-11-04/05, 03:30 UT
Location: Miles Standish State Forest, MA, USA (41N, elev 30m)
Site classification: rural
Limiting magnitude: 6.9 (zenith)
Seeing: 6 of 10 - above average
Moon up: no
Instrument: 20" f/5 Tectron truss-tube dob Newtonian reflector
Magnification: 70x, 160x, 210x, 420x
Filters used: None
Object: Pegasus I
Category: Cluster of galaxies
Constellation: Peg (border with Psc)
Data: mag 11.1 (brightest gx) size 90'x60' (main field)
RA/DE: 23h21m +08o11m
Tonight's observing session became the Night of the Galaxy Fields,
as we swung from one Abell cluster, non-Abell cluster, or galaxy
group to another. The first target Field of the evening was this
intriguing and (relatively) bright grouping of galaxies nestled
in the hollow shoulder of the Winged Horse. Although I have been
able to find out very little about Pegasus I, I do understand it
to be a gravitationally related group of galaxies. I've not even
been able to find out if it's on the Abell list, but it does not
appear so. Nor is it a member of the "Hickson Catalog" of galaxy
groups. But despite this, Peg I is a GORGEOUS group for larger-
aperture dobs, and the brightest members offer a good prospect
of visibility even in relatively small (6"-8") deep-sky scopes.
*THANKS* to Steve Clarity of the ATMoB for pointing out Peg I to
me, and for the timely use of a 16mm Nagler while observing it.
Peg I is fairly easy to find in DARK skies, as it lies just 2o
from a distinctive but faint asterism on the border of Pegasus
and Pisces. Begin either with the W-most star in the Circlet of
Pisces (gamma Psc) or with Markab (alpha Peg). Roughly mid-way
between these two bright stars is a tiny quadrilateral asterism
of 5th magnitude stars, namely 55, 57, 58, and 59 Peg. (By the
way, these form a pretty grouping in a finder, as the two Wmost
stars are red-orange, while the Emost pair are pale blue-white.)
The NW and SE corner stars (55 and 59) of this little trapezoid
point SE exactly 2o to a mag 7 orangeish star (HD 219949). In
the same wide-angle field, and just 15' NW of this star lies a
pretty pair of fuzzies - the two brightest members of Peg I...
ngc 7619 mag 11.1 size 2.6'x2.3' type E2
Brightest of the entire field, n7619 is quite prominent in a low
power view, nicely paired with its "twin" 10' W - n7626 (see below).
It seemed fairly round, but with rapid, stepped brightening toward
the middle. At least three different "steps" of brightness could
be seen visually, in contrast to the burned-in photographic images
of this massive galaxy. At 210x, it showed some elongation NW-SE,
and mere glimpses of a nucleus were seen - better seeing may help.
ngc 7626 mag 11.1 size 2.5'x2.3' type E1:P
Forming the left "eye" of a nice pair with n7619 (above), this
galaxy was remarkably similar to its companion at first glance in
70x. But with the use of a friend's 16mm Nagler (160x), suddenly
the two "twins" began to diverge from one another. First n7626 was
slightly fainter than its neighbor. Second, it showed no brightness
"steps" like -19, brightening gradually to a diffuse core without a
nucleus. Finally even at 420x, 7626 appeared quite round, with the
notable exception of a "notch" or flattened area to the W, perhaps
due somehow to interaction with -19. I'd love to be able to apply
yet MORE power to this curious object - again, with better seeing!
ngc 7617 mag 13.7 size 0.9'x0.7' type SA0:
Easily mistaken for a star, just a few minutes SE of 7619. This
little spiral showed no detail at all in its barely visible halo,
and only a hint of elongation in its bright inner core.
ugc 12510 mag 16.0p size 1.3'x0.9' type dE?
SHOULD HAVE BEEN VISIBLE as the right vertex of a right triangle,
where a pretty mag 9 triple called HD 219866 is the E vertex, and
a little mag 10 pair NE of this triple is the N vertex. Not seen!
ngc 7623 mag 12.9 size 1.2'x0.9' type SAO+
An easy object to averted vision, with a hint of an irregular halo
to N and S of a brighter, roundish core. Don't confuse this object
with the mag 10 star midway between it and n7619, nor with the MUCH
more challenging, nearly stellar spindle n7621, nearby to the SW...
ngc 7621 mag 15.6 size 0.8'x0.2' type S0sp
An averted vision star, showing no detail but just visible near a
line between brighter n7623 to the NE and much brighter n7619 SW.
Careful of a mag 13 star just 2' NW and interfering with the view!
ngc 7631 mag 13.1 size 1.8'x0.7' type SA(r)b?
In a line with and due E of n7619 and n7626, this brightish little
spiral was an intriguing object - again begging better seeing and
higher magnification! At 210x and 420x the bright, mottled core was
obviously elongated due N-S, while the averted-vision halo appeared
very irregular, with wisps to SW, N, and ENE occasionally visible.
Perhaps hints of ring structure were visible, despite the distance!
ngc 7611 mag 12.5 size 1.5'x0.6' type SB0a?
Actually the first object seen, just 5' NW of the mag 7 anchor star,
this galaxy's bright core was at first mistaken to be a mag 10 star!
After consulting the chart in Luginbuhl & Skiff however, I rechecked
this "field star", and immediately noticed that it comprised both a
distinct stellar nucleus and a seemingly overpowered elongated core,
stretching NW-SE perhaps a full minute of arc. No hint of a halo or
detail could be seen, although the object may bear a better look.
ugc 12518 mag 15.5p size 1.3'x0.2' type Sbsp
Last stop on my sweep through Peg I, this little "extended star" was a
suprisingly easy catch to averted vision, just 5-10' SE of that mag 7
anchor, and nearly in a line from it to nearby n7611 (above). However,
once found, it showed only a hint of its N-S elongation and no detail.
That was it! Even more time could have been taken with this pretty
field - several more galaxies SHOULD'VE been in the range of the 20"
under these skies (including bright n7612 and n7608, and a number of
Upsalla, MCG, and Zwicky members). But other galaxy groupings, some
even bigger and/or more challenging, beckoned to us on this beautiful
dark night. Oh well, once my dob's TRUSSES are fixed dob, some future
Fall or early Winter night will offer this pretty grouping for study...