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(IAAC) Obj: Arp 2 (C 1925-304) NOT SEEN - Inst: 36" f/5 dob



IAAC Deep-Sky Observing Log Entry

Name of observer: Lew Gramer, Barbara Wilson
Your observing skills then: Advanced (many years)
Date/time of observation:  19/20 May 2004, 2:30 Local

Site type: Rural
Location: Texas Star Party, Ft Davis TX USA (Lat 30N, Elev 1700m)
Sky darkness: 7.4 (Limiting magnitude)
Seeing: 4 (1-10 Seeing Scale (10 best))
Moon presence: None - moon not in sky

Instrument: 36" f/5 dob
Powers: 131x, 352x
Filters: None

Deep Sky Object: Arp 2 (C 1925-304) - NOT SEEN!
Object category: Globular cluster.
Object class: (very diffuse)

Constellation: Sgr
Position: 19:28:44 -30:21:14

Object data: mag 13.0 15.5m* (RGB), size 2.5'

Description:
Journal article 1995AJ....109..650B lists the Vt (integrated visual
magnitude) of this obscure cluster as 12.3. However, other sources
seem to say Vm=13.0. In any case, it must be far harder to see than
this bright magnitude would suggest! (Once again demonstrating that
published magnitudes - even when they are V instead of B, R or IR -
can be a mighty poor indicator of object visibility for amateurs.)
--
Arp 2 seems like an easy star hop from bright, beautiful M55, low
down in the bowels of the Archer: From the core of the Messier, I
headed NW just over half an 80mm finder field (1.5 degree), past
an unmistakeable NE/SW chain of stars mags 7-9, then one degree
(1/3 f.o.v.) further to a wide "finder trapezoid" of stars mag 5
to 7. Inside this trapezoid, along the long E base, was a small
nondescript lozenge of stars mags 9-10, that almost fit within our
35mm field on the 36". The small star-lozenge would be my starting
point, while the big trapezoid bounded my search area for Arp2...
--
Tonight was my first attempt at Arp 2: after an initial failure,
I decided to go on to an easier, even more fascinating (to me)
target in the neighborhood of M55, for a little while. (See my
upcoming log of Hickson 86 - a compact galaxy group in Southeast
Sagittarius of all places, just 12 deg from galactic center!)
--
However, as the area neared meridian, I had another go - this time
with none other than Barbara Wilson waiting at the bottom of the
ladder for me to find it. Talk about pressure! :) Repeated sweeps
first with a 35mm Pan (131x) and then an old 13mm Nagler (352x)
showed no hint of haze. Using the handy MegaStar chart provided by
Larry Mitchell in his TSP 2004 "Observing Challenges" sheaf, I was
even able to verify the star area - no hint of a brightening, or of
an additional concentration of stars.
--
At this point, I decided it was time to engage the heavy guns! I
asked Barbara to take a sweep for it through the region - she also
turned up nothing, sweeping back and forth with the 35mm at 131x.
--
Although this made me feel a little better, I still determined to
try again on one of the remaining nights of TSP - but in fact, an
opportunity just never arose again. So until I can try this again
at a dark southern site - perhaps next year at TSP? - I will just
have to leave this object as a "NOPE" for now.
--
If Barbara had had more time to search from the charts, I am sure
we'd have both gotten to take a log of this object on this night.
She also mentioned to me later that tonight's poor seeing was a
likely contributing factor to our not "sweeping up" this object.
This frustrates me (in a fun way), as I know others were seeing
Arp 2 that very week in much smaller apertures than I was using...
--
Any Web URL related to log:
http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?bibcode=1995AJ....109..
650B