This object is located 4000 light years away in the constellation of Monoceros at a declination of -11 degrees. It spans 1.5 arc-minutes in our apparent view. This corresponds to a diameter of 2 light years. This object lies just west of the head of the Seagull Nebula (IC 2177), the top of which can be seen at the bottom of the image.
The unique red-yellow color of this object is due to narrowband imaging. HII is most prominent on the rim, while in the central region both HII and SII are present in roughly equal amounts. OIII is not seen here at all.
Although this object was identified as part of the Kohoutek planetary nebulae catalog, and is still recognized by the K 1-8 designation, it has since been identified as a HII region, not a PN. SIMBAD and other sources say this, although I have not been able to find the data on which the HII assumption is based. I question whether this object is a HII region or a planetary nebula (PN).
The reasons why it may be a planetary nebula:
- Diameter of 2 light years is the typical PN diameter. HII regions like this are often much larger.
- Gradient of HII signal across the object, with HII strongest along the rim in opposite sides (5 and 11 o’clock) relative to the progenitor star.
- Almost perfectly round object
- Bright (progenitor?) star at the center
- No winding dust lanes, which are often seen silhouetted in a HII region
The reasons why it may be a HII region:
- No OIII signal
- The progenitor star is white/yellow, not the characteristic blue.
A detailed spectral analysis would resolve the issue. Such an analysis may have been done already but I cannot find it.
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