NGC/IC Project Restoration Effort

===== NGC 2816. Years ago, I wrote this about NGC 2816: [This] is probably JH's second observation of NGC 2742. The first came on 8 March 1832 where the galaxy is recorded at its correct position, close to where his father placed it when he found it in 1790. JH called it "vF, pL, R, vgbM, 60 arcsec; moon very troublesome. A * 8 m np." (This compares to his father's rather more interesting note, "cB, E near par., er, bM; 4' l, 2' b. I suppose, with a higher power and longer attention, the stars would become visible." WH's "er" means "extremely mottled," which leads to his comment about the stars.) Just three weeks later, on 30 March 1832, JH swept over the area again, this time recording a "F, pmE" nebula 13m 30s to the east at the same north polar distance. There is nothing at that position, a fact first noticed by Reinmuth in his 1926 "Die Herschel Nebel." Since the declination is the same, and the description for N2816 appropriate for N2742, I'm going to suggest that the two nebulae are the same. Even though the RA difference is large, there is nothing else around that JH might have seen that makes more sense to me. Still, I'm not convinced, so I've put colons on the identification. (At least I had the sense to mark the identity uncertain.) In fact, NGC 2816 is simply non-existent. The observation that led to it is indeed one by JH on 30 March 1832, but, as Wolfgang pointed out in March 2014, that was actually of NGC 2820. In that same sweep, JH picked up, just 45 seconds earlier, another galaxy that he believed to be H II 869 and became h 576. His second object, h 579, eventually led to the numbers GC 1800 and NGC 2816. But the north polar distance for this second object is clearly mis-reduced. In the log book for the sweep, preserved in the Herschel Archive, we find that the raw observations for the NPDs, referred to a zero point within the sweep, read 01 53 18 for h 576, and 01 54 30 for h 579. Yet the reduced north polar distances for 1830 read 25 02 45 for h 576, and 28 50 33 for h 579, over 3 3/4 degrees apart. (These are the numbers that also appear in JH's 1833 monograph. Only two other objects appear in the sweep, the stars HD 80953 and 81161; their positions are correctly reduced as is that for h 576 = NGC 2814). Using the difference between the raw and reduced NPDs for h 576 = NGC 2814 as a guide, the correct reduction of JH's NPD for h 579 becomes 25 01 33. His position is therefore a good match for NGC 2820, and there is no doubt that NGC 2816 is identical to this large, faint, edgewise spiral galaxy. So, the NGC needs fixing: Add the number h 576 to NGC 2814, note GC 1800 = NGC 2816 as being identical with GC 1798 = NGC 2820, and change the JH number "576" on NGC 2820 to "579". The NGC positions for the two galaxies are about 10 seconds of time too far east, but are otherwise OK, so there is no doubt about the identifications. By the way, the faint companion to NGC 2820, Markarian 108, is not IC 2458 (which see) as I and many others had suggested. The IC object is actually the northeastern part of NGC 2820 itself. I've retained the alternate designation for Markarian 108, however, so you will find it listed as "NGC 2820A" in the big position tables.

===== NGC 2816 See observing notes for NGC 2820.