Overlaid DSS image of NGC 3644, 30' x 30' with north at top and west to the right
IC 684, MCG+01-29-037, UGC 6373, PGC 34814, SDSS J112132.87+024837.5
|Size ||1.5' x 0.7' @ 63°|
|Right Ascension ||11h 21' 32.9" (2000)|
|Declination ||2° 48' 38" N|
|Description ||vF, vS|
IC 684 = NGC 3644. Even though Marth's positions, adopted in NGC, for NGC 3643, NGC 3644, and NGC 3647 are good, Bigourdan misidentified the latter two objects. He placed NGC 3644 some 35 arcsec south-following his position for IC 683 (which has a 1 arcmin error in Bigourdan's big table in the distance from the comparison star, and he measured a star as NGC 3647) -- there is nothing in his measured place. He lists two "new" objects in the area, IC 683 and IC 684. His positions for both are good, and that for IC 684 is almost identical to Marth's position for NGC 3644. Also see the discussion under NGC 3645.
NGC 3643, NGC 3644 = IC 684, and NGC 3647. Even though Marth's positions for NGC 3643, NGC 3644, and NGC 3647 are pretty good, this has not prevented later observers from misidentifying these at one time or another. In particular, Bigourdan's "NGC 3647" is a star, and he labeled NGC 3644 as "new" (his positions for both are accurate). Thus, this latter galaxy received an IC number (684) as well as its NGC number. Kobold got the right galaxies for N3643 and NGC 3644, but both he and Wirtz list NGC 3644 as "NGC 3645(?)" (though Kobold does have an erratum saying that though the identity is uncertain it is probably NGC 3644). RNGC has misidentified NGC 3643 and NGC 3645 (which see), and CGCG makes yet another object in the group NGC 3645.
Finally, just about everyone, including me, has misidentified NGC 3647. There are four CGCG galaxies here. Most of us have chosen CGCG 039-141 -- the easternmost -- but the brightest (by half a magnitude) of the three is CGCG 039-135, the westernmost. Steve Gottlieb has gently reminded us that brighter objects are usually easier to see than fainter ones. Even with a 48-inch reflector, Marth called this one an "eF neb *." And he saw only one object here, not four, so the obvious choice is the brightest.
10 objects found within 60'
Drawings, descriptions, and CCD photos are copyright Andrew Cooper unless otherwise noted, no usage without permission.
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