Tuesday, 10 April 2012

The mighty few - the two missing NGC clusters

In 1863, G. P. Bond (director of the observatory at that time) published a list of 33 new deep sky objects discovered by astronomers who worked in the Harvard college observatory. These observers include George Phillips Bond himself (1825-1865), Phillip Sidney Coolidge (1830-1863), Horace Parnell Tuttle (1837-1923), and Truman Henry Safford (1836-1901). (As a side note, I'd like to note that in the 2010 book "Observing and Cataloguing Nebulae and Star Clusters" by Wolfgang Steinicke, there seems to be a typo regarding the age of Coolidge when he died. It says in the book that Coolidge "was born on 22 August 1830 and died in the civil war on 19 September 1863 being only 29 years old". Unless there are something wrong with the birth/death date, I'd say Sidney Coolidge died at the age of 33)

Bond's paper was published in the Astronomische Nachricten (No. 1453) but the paper had some quirks. First, the discovery of the two of our objects in questions NGC 2189 and NGC 2198 are credited as having been discovered by J. H. Safford. This is at least corrected (by whom?) in the copied version of the publication (J crossed and T added to the right side margin). The second one is, as everyone who's had a look at this particular dilemma, the position of the two missing NGC clusters in Orion. There are no coordinates for any of the clusters, only 1863 coordinates for the near by position stars! What a bummer. We know that the clusters were pretty certainly found with a magnification of 141 and field of view of 11'. Either there is something I'm not seeing here or there is something profoundly wrong with the original coordinates.

Object 7(a) & 7(b) - NGC 2189

"Two clusters, seen 1863 March 19 near two stars of the 10.11th magnitude, by J. H. Safford, with the Great Refractor [15 inch Merz refractor]. In Harvard Zones [IV]. Position of stars:

06h 04m 44.9s +01° 08' 37" (1863) = possibly GSC 131:1117
06h 05m 47.2s +01° 10' 02" (1863) = possibly GSC 131:1065

Not only are these two stars nearly 15' apart, there is no sign of any clusters in the area. It is also important to notice that Safford specifically mentions TWO clusters not a single one like the single NGC designation suggests. Safford's description "near two stars mag 10-11" is also fairly vague. Visual inspection of the region comes up pretty empty as well. 1908 paper by Pickering gives us coordinates of 06 12 22 +01 07 34 which is pretty much at the current non-ex position of NGC 2189. The asterisms discovered previously with the 15 inch refractor (1852-1853 for example) are pretty vague and are often very difficult to to discern from the background sky at all so in that aspect these clusters are a good match.

Object 8 - NGC 2198

"A cluster, see 1869 March 19, by J. H. Safford, between two stars in the following position. With the Great Refractor. In Harvard Zones [IV].

Star of 10.11 mag. 06h 06m 27.8s +01° 01' 10" (1863) = possibly GSC 131:870
Star of 9.10 mag. 06h 07m 12.7s +01° 00' 27" (1863) = possibly GSC 131:1266

What is between these two stars? A load of black space that's what! These two stars are separated by a mere 6'. Pickering's 1908 do not differ much from the current non-ex position of NGC 2198 just like with NGC 2189.

Simply from a visual observer's point of view, there is one possibility hanging in the air. A fairly good looking asterism can be seen more to the north, nearly in the middle of NGC 2189 and NGC 2198. The asterism is flanked by 9th magnitude HD 288493 and 10th magnitude HD 288534.

The position is however quite far away from the given positions of NGC 2189 and NGC 2198 and there is just one object - not three.

Unless someone takes a look at Safford's original observing logs like Dr. Harold G. Corwin suggest... I'm willing to go with the fact that these are nothing more than two very poor, uninteresting groups of few stars as suggested in the NGC/IC project home page. Sadly.