Dunlop 100

I am continuing to go through my notes from the expedition to Australia this March. On that trip, after finishing the Caldwell list I turned to Dunlop 100. This list was compiled by Glen Cozens, an Australian amateur – if you can call somebody an amateur when he defended a PhD in history of science specifically on Dunlop. The "100" list was originally published along with an essay on Dunlop in Sky and Telescope, 2001, 6:112. SEDS has some uniquely useful pages about Dunlop, his original catalog, and the “100” list.

http://messier.seds.org/xtra/similar/dunlop.html

As regards the original full catalog, James Dunlop conducted the first systematic search of the southern skies for nonstellar objects after Lacaille with his 9” homemade “Dob” from Australia in 1826-27. Although a professional astronomer, he was not employed at that time and conducted the observations from his backyard in a Sydney suburb. His catalog extended to the latitudes that had already been partially explored from Europe. Therefore, the northernmost objects in the original Dunlop catalog included the southernmost Messiers and objects discovered by William Herschel. Overall there were more than 600 objects listed. About half of these have been recognized (in part due to Glen Cozens’s work); the others are considered “missing” or are identified with double stars and asterisms.

The Dunlop 100 list is Glen Cozens’s personal selection from the full Dunlop catalog, which I thought was especially suitable for visitors to the southern hemisphere who may not have time to go after all of the Dunlop objects. There is a large overlap between the southern Caldwell and Dunlop 100. Because of this overlap and some of the comparatively “northern” objects such as the several Messiers, I have now seen 85 of the 100 even though it was only a little more than 40 that I had to observe on this trip specifically from the Dunlop 100 list. I will be able to pick out a few more when they show over the horizon where I live this autumn. Should I develop a desire to actually finish the list, I would have to travel again to see those that did not rise or did not rise high enough to really warrant observing in Australia this March.

The following is the beginning of the transcript from my first Dunlop 100 night. As described in earlier posts about this trip, the observations were made with my travel scope, the Orion (US) Maksutov-Cassegrain (nominally 150 mm f/12) on a Voyager mount, equipped with the Orion 50-mm RACI finder and the 6.5-19.5 mm Pentax zoom. The location was an unlit outback campground 100 km from Alice Springs as the crow flies.

Wednesday. Best transparency in the evening so far. Dunlop 100. NGC 1291, galaxy, Eridanus. Near Epsilon Eridani (next in chain to Acamar, Theta Eri). Considered a northern object by Night Sky Observer’s Guide. [I.e. not in volume 3 which I had with me. It is also #12 on O'Meara's Hidden Treasures list.] Slightly off-round, largish.
Revisited NGC 1261 (Caldwell 87), globular cluster in Horologium. Best view yet.
NGC 1433, galaxy in Horologium, Dunlop 100. Prominent core with fainter elongations EW that correspond to the bar in DSS. Sharp nucleus. From Epsilon Eri with Uranometria.
NGC 1512. Near Alpha and Beta Hor. Galaxy. Elongated matching the bar in photos. Bright central core.
NGC 1313 near Beta Reticuli. [Galaxy.] Irregular appearance, shimmering patches. Generally elongated NS.
NGC 1543 near Epsilon Ret. [Galaxy.] Smallish, roundish. Lens extensions in photos not visible. A glimpse of stellar nucleus.
NGC 1763. Bright nebula in the Large Magellanic Cloud. In group with non-Dunlop 100 NGC 1769 (bright nebula), 1773 (bright nebula), and 1761 (open cluster). Group nicely framed.
NGC 1515. [Galaxy.] Near Gamma Doradus (nose of the fish). Elongated NS.
NGC 1566. [Galaxy.] Near the same star. Slightly elongated NE-SW. Comparison with photo in NSOG shows that relative to stars, only the core and the most proximal arms segments (unresolved as such) are seen.

  

For the following objects my journal has only sketches, no notes. Since these were made with the Cassegrain and diagonal, N is left (and W is as indicated down). The first scan (above) shows the field of the Dunlop 100 galaxy NGC 1553 with its true companion, non-Dunlop 100 NGC 1549. The former is an inclined lenticular at 15.6 Mpc and the latter an E0-1 at 16.3 Mpc. According to Wikipedia, the Dunlop 100 NGC 1553 is the second brightest member of the Dorado Group.

The second sketch depicts “NGC 1617 near Alpha Dor (eye of fish)”. According to NED, this SB(s)a (more detailed classification (R')SAB(rs)a) is also a group member, “radial-velocity confirmed”, and lies at 13.5 Mpc and 47 Mly. In this galaxy, like in the previous two, I did not see anything besides the overall shape.

The last sketch shows the Dunlop 100 galaxy NGC 1672, in which two arms were visible with the mere 140 mm of working aperture. Outside the circle is the high-magnification view with two stars superimposed on the NE arm. Wikipedia cites a reference refuting this galaxy’s membership in the Dorado Group. However, according to NED, its mean redshift-independent distance is 14.5 Mpc and by redshift it is 60 Mly away. So perhaps kinematically it is not a member, but cosmographically it still is. Steve Gottlieb has a nice description of its appearance through an 18” in Australia here:
http://www.astronomy-mall.com/Adventures.In.Deep.Space/sogal.htm

Note that the core in my sketch is elongated NNW-SSE. This feature is obscured in film and survey photos by the very prominent and large EW bar. The HST photo vindicates the correctness of my sketch by showing that the orientation of the elongated central core is indeed very different from that of the bar:

http://imgsrc.hubblesite.org/hu/db/images/hs-2007-15-a-compass_large_web.jpg