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(IAAC) Obj: NGC 6309 (Box, Exclamation Mark nebula) - Inst: 25" f/3.5 dob



IAAC Deep-Sky Observing Log Entry

Name of observer: Lew Gramer
Your observing skills then:  Advanced (many years) 
Date/time of observation:  02/03 June 2003, 0500 UT

Site type:  Exurban
Location: Westford MA USA (Latitude 42 Elevation 86m)
Sky darkness: 5.3 (Limiting magnitude) 
Seeing: 8 (1-10 Seeing Scale (10 best)) 
Moon presence: None - moon not in sky

Instrument: 25" f/3.5 dob
Powers: 110x, 245x, 460x
Filters: None, UHC, OIII

Deep Sky Object: NGC 6309 (PK 9+14.1, Box, Exclamation Mark nebula)
Object category:  Planetary nebula.
Object class: III+II

Constellation: Oph
Position: RA 17:14, DEC -12:54

Object data: mag 11.8, SurfBt 8.9, size 19"x11"

Description:
Tonight the conditions were less than perfect at
ATMs of Boston's Britton Clubhouse and Milon Obser-
ving Field... A fairly even covering of very light
cirrus or haze, forced us to focus on just "high
or bright" objects with Steve Mock's resident 25".
--
The common name for this object is the "Box Nebula".
This is an example of how deceiving a name can be!
In many longer-exposure astrophotographs, and even
visually from a very dark sky if a nebula filter is
in use, n6309 might indeed look like a little box.
(See Yann Pothier's logs on www.visualdeepsky.org!)
--
--
However, under most conditions, a visual observer
will perceive this strange object, together with
the mag 9(?) star < 1' N, as bearing a striking
resemblance to a certain punctuation mark(!) And
so that is just how we refer to it up here. :)
--
This stunning little object lies just inside the SE
"fist" of the Serpentholder, forming an obtuse tri-
angle with mag 2 Eta Oph and mag 4 Nu Ser, roughly
3o N of Eta Oph. It is quite near Oph's border with
Serpens Cauda, in fact. With a finder or very wide
field epc, n6309 is found by moving from Eta Oph 1o
N past mag 7 star HD155413, and then about the same
distance further NNW, to a pretty group of 6 stars,
mags 8-10. These stars form two opposing isosceles
triangles. The NW of the two triangles contains the
brightest star in the grouping at its N-most vertex,
mag 8 yellowish HD 155612, which is itself a neat,
low-power pair (45") with a little mag 11 star.
--
The PN was a barely noticeable blue-green "blip" in
the 80mm finder (probably not visible in a smaller
finder), about 15' due E of the "center of gravity"
of this brighter, NW triangle of stars. I FAILED to
notice the mag 9 star right next to it, although I
did not think to look for it at that point. (As it
was visible in the finder tonight, I'm leads to be-
lieve that even under mediocre conditions, this PN
may be a good target for much smaller scopes, too.)
--
At lowest power, the Exclamation lived up to its
(local) name admirably, appearing at first glance
very much like a highly elongated rectangle aimed
NW toward the mag 9 star that is the "dot". How-
ever, increasing power to 245x (9mm Nagler), the
bizarre shape of this planetary started to become
conspicuous in tonight's steady seeing! At this
power with the UHC, the NW half of the nebula was
clearly somewhat brighter and larger than it was
to the SE. This impression was stronger with UHC.
--
Finally, I got first light with a 4.8 mm Nagler I
had recently bought from Gardner, a fellow amateur
who is in the New Hampshire Astronomical Society.
At this high power (460x), in this unusually good
seeing (for this area), the Exclamation Mark sudden-
ly presented a whole new wealth of detail! What had
looked like a very thin rectangle, now resolved in
to successive lobes or "pulses" of nebulosity, THREE
of them in fact! This impression of three successive
"bubbles" emanating from the nearby mag 9 star was
best seen unfiltered, but was also apparent though
less prominent, with the UHC and OIII.
--
Even more intriguing, fainter wisps of nebulosity
could be seen stretching out from the NW lobe of
the PN, arcing S-ward to a point maybe 5" due W of
the midpoint of the main nebula. These were (again)
strongest with the UHC, though also apparent with
an OIII, and even hinted at with no filter at all.
--
A faint spark (mag 13 or 14) was seen with direct
vision, glimmering off center in the middle lobe.
This (I assume) central star was equally prominent
both unfiltered, and with the UHC. As expected, it
was harder to see with the OIII in place. In add-
ition, though, we got the impression with averted
vision of one or more OTHER stars involved in the
length of the nebula, and just outside its W edge.
--
All in all, the Exclamation is eminently worth your
time to find, while Ophiuchus is still riding high!
--
Any Web URL related to log:
 http://archive.stsci.edu/cgi-bin/mastpreview?mission=hst&dataid=U2SA2702T ,
 http://www.fortunecity.com/greenfield/twyford/637/ngc6309.htm


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