IC 1644 = SMC-N81 is classified as a HEB -- high excitation blob. This object, along with N88A, are rare objects in the SMC exhibiting very high surface brightness, absolute magnitude and compactness. It harbors one or more hot, massive, young stars that ionizes the nebula.

Williamina Fleming discovered IC 1644 = HN 83 in 1901 on photographic spectrum plates taken at the Arequipa station. It was included in a 1901 table "Objects having peculiar spectra" in ApJ, 14, 144-146.

600/800mm - 30" (11/6/10 - Coonabarabran, 264x): very bright, small, compact high surface brightness HII region, 20" diameter, good response to a NPB filter. Located 14' NE of IC 1626 and 20' WNW of NGC 456. Mag 10.6 HD 6932 lies 7.7' W and a mag 10.3 star is 9' ENE with IC 1644 on the line connecting these stars. Within Hodge Association 60.

Notes by Steve Gottlieb