IC 4688 NGC 6615
Oph
☀13.1mag
Ø 5.0'

Rudolph Spitaler discovered IC 1257 on 7 July 1890 while searching for Barnard's Comet C/1888 RI using the 27" refractor at Wien University Observatory in Austria. His micrometric position is accurate. Barnard independently discovered it the next night while searching for his comet with the 12-inch refractor at Lick Observatory. In fact, Barnard initially mistook it for the comet!

Harlow Shapley listed IC 1257 as an open cluster (1930) and Sven Cederblad as a nebula (1946). Brian Skiff reports in 9/96: Barry Madore to take a handful of short exposures of it at the Palomar 200", and has run through a first-cut data reduction. The color-magnitude diagram shows that it is unquestionably a globular cluster, which is moderately heavily reddened: it has the telltale marks of a metal-poor halo cluster, which are (a) a blue horizontal-branch population and (b) a steep red-giant branch. See Harris et al. http://adsabs.harvard.edu/abs/1997AJ....113..688H for the discovery announcement.

300/350mm - 13.1" not found.

400/500mm - 17.5" (6/30/00): at 280x this small low surface brightness globular appeared very faint, round, ~30" diameter but visible with direct vision. Appears to have an extremely faint knot at the south edge and a slight central brightening.

17.5" (7/27/95): very faint, round patch, ~1' diameter. Appears similar to a 15th magnitude galaxy with no hints of resolution or central concentration. Can hold steadily with averted vision. Located 5.8' W of a mag 11.5 star. Discovered to be a globular in 1996.

600/800mm - 24" (7/11/18): at 200x and 226x; fairly faint, small, round, low surface brightness, very small slightly brighter core, 0.6' diameter. Better at 282x; easily visible steadily though no additional structure. Less contrast at 375x.

Notes by Steve Gottlieb