Harold Corwin

IC 2115 and IC 2116 are both described in the IC as "Planetary, stellar." Like IC 2111, IC 2114 and IC 2117, both were found on Harvard objective prism plates by Williamina Fleming. Also like those three, the positions are not very good, falling on blank areas of the LMC north and east of NGC 1763. ESO's contention that the IC objects are both identical to NGC 1763 can't be true: The descriptions rule out the identities since NGC 1763 (which see) is a large complex of HII regions and star clusters in the LMC. Annie Cannon in Harvard Obs. Bulletin 891 (my thanks to Dave Riddle for pointing me to this) makes IC 2116 equal to NGC 1769, but the same reasoning also rules out this identity.

Cannon also suggests that IC 2115 is CPD -66 346 = HD 268726. Going over the field again independently before Dave sent the reference to Cannon's paper, I came to the same conclusion. However, Brian Skiff points out that the star is a normal blue giant with no emission lines. This definitively rules it out as Fleming's object -- she discovered that because of its emission lines. So, we clearly need to inspect the original Harvard plate on which Fleming found IC 2115.

This would leave the bright nebulous star (HD 32340) at 04 57 09.8, -66 27 52 (1950; for J2000, 04 57 16.1, -66 23 21; compare with Brian's note below) as IC 2116. This at least is an emission object, so is likely to be one of those that Fleming discovered. I've adopted this identification, though again with some doubt that might be resolved by inspection of the original plate.

There are two fainter stars in the neighborhood besides those I've listed in the main table (both B1950.0):

    04 57 15.92  -66 28 57.2 (or for J2000:  04 57 22.03  -66 24 26.2)
    04 57 19.98  -66 27 55.8 (or for J2000:  04 57 26.25  -66 23 25.1)

Neither of these seems likely to me to be any of Fleming's objects.

In November of 2007, Brian Skiff spent some time going over the field. Here is what he had to say about it:

I have had another look at the ID problems in the region of NGC 1763 that includes HD 32256, HD 32279, and HD 32340. As mentioned previously, the early Harvard coordinates are relatively poor, so a definitive answer may not be had without reference to the original logbooks, plate-marks, etc. All coordinates mentioned below are for J2000.

It is helpful to look at the DSS short-V plate-scan with some sort of coordinates reference (Aladin, SkyView, etc) to see the bright stars/nebulae that would have been all that was detected by the Harvard observers. The various deep sky-survey exposures have the nebulae too overexposed. Also useful is the large-scale chart drawn by Mati Morel and contained in his "LMC selected areas" charts (chart 6 in this publication).

The HD catalogue coordinates and description for HD 32256 seem to apply to the western lobe of the nebula NGC 1763. The HD links this specifically with the nebulous object CPD-66 344 (CPD coords 04 56 45.5 -66 24 36). The HD description mentions that a strong continuum is present along with emission lines, including the remark that "the spectrum may belong to the P Cygni class." So evidently the constituent star(s) were observed. Thus, it seems reasonable to give it the position (rounded to some convenient degree) of PGMW 3120, which is a bright clump of O-type stars at: 04 56 45.80, -66 24 46.8, with the intention that this represent the western lobe of the nebula. This is just 4" from the CPD position, which is clearly what was measured for the CPD itself.

Not entirely incidentally, the second clump about 30" SW is unambiguously HD 268715 at 04 56 43.24, -66 25 02.6, some 29" from the CPD position.

For HD 32279, the HD coordinates and spectral type (Pc = emission nebula) seem to apply to the eastern lobe of NGC 1763. The nominal coordinates are on the north side of this lobe (04 57 00, -66 22.9). The HD remarks say this is IC 2115, which may be correct! Again for the sake of having some reproducible position assigned to the HD (and IC?) object, I adopt the position of PGMW 3223, one of the O-type stars/clumps near the center of the nebula (04 57 00.86, -66 24 25.1). Round-off as desired.

Again the nearby star/clump to the southwest is unambiguously HD 268721 (04 56 58.97, -66 24 38.2), which is very similar in brightness.

Now, the HD position for HD 32340 precesses to 04 57 30, -66 24.0. This is about 90" southeast of the compact nebula IC 2116 = LHA 120-N 11A at 04 57 16.25, -66 23 20.8. Since the discovery is from objective-prism plates (the HD and IC objects are the same object from the same report), we have to assume the object was compact enough to produce a recognizable spectrum on the plates. This argues for this object rather than NGC 1769, which is what is specified in the HD remarks, and which lies about 4' off to the southeast, and which has HD 268743 as its illuminating star (a cluster actually).

Nearby to the west of IC 2116 is the non-emission star HD 268726 (04 57 08.82, -66 23 25.2), which has no identification problem. Lacking emission in the HDE type and in modern spectra, it cannot be IC 2115 or IC 2116.

In summary:

    HD 32256 = NGC 1763-west:              04 56 46    -66 24.8    (J2000)
    HD 32279 = NGC 1763-east = ? IC 2115:  04 57 01    -66 24.1    (J2000)
    HD 32340 = IC 2116 = LHA 120-N 11A:    04 57 16.25 -66 23 20.8 (2MASS, J2000)

I think this all hangs reasonably well. The Harvard source positions are soft enough that it is possible to conclude that IC 2115 is actually LHA 120-N 11A, which then forces the identity NGC 1769 = IC 2116. The large Dec offset compared to how well the other IDs agree makes this less likely in my opinion (and it is only that). I hope this clears up the questions from Francois Ochsenbein, though some rejiggering of SIMBAD aliases is implied!

I think he's done as well as anyone can without reference to the original plates, so I've adopted his identification for IC 2116, and have put his for IC 2115 into the position table, too. I've also kept the smaller knot in NGC 1763 that I picked up on earlier; it is HD 268721 which Brian mentions above, a part of his larger object.

― IC Notes by Harold Corwin

Harold Corwin

IC 2116 is probably not NGC 1769 as some have claimed, but may be a knot in it. See IC 2115.

― IC Notes by Harold Corwin

Drawings, descriptions, and CCD photos are copyright Andrew Cooper unless otherwise noted, no usage without permission.

A complete list of credits and sources can be found on the about page