Possible nearest planetary nebula

An unstructured OIII region on the border between the constellations Pegasus and Cygnus was detected in DR0.2 of the Northern Sky Narrowband Survey. Together with a faint [SII] and Hα glow in the outer region, the apparent diameter of this nebula is about 6°. Close to the center of the OIII region and at a distance of about 112 pc (Gaia DR3) lies the hot subdwarf BD+28 4211. Thus, this object might be a planetary nebula (PN) slightly closer than Sh2 216 (about 127 pc according to Gaia DR3), which is usually considered the nearest PN. The morphology and a true diameter of about 12 pc or 38 light-years (assuming the distance mentioned above) suggest a very ancient PN. Interestingly, SIMBAD currently lists 825 papers that mention the subdwarf, but none appear to mention a PN surrounding this star (though not all papers were individually reviewed).

Possible nearest planetary nebula surrounding the hot subdwarf BD+28 4211 in SHO — (Click on the images for a full scale versions.)
Two different color composites of the possible nearest planetary nebula surrounding the hot subdwarf BD+28 4211. In the first panel (denoted with OHS), [OIII] (505.7 nm) is mapped to red, Hα is mapped to green, and [SII] (671.7 nm and 673.0 nm) is mapped to blue. The second panel (denoted with SHO) shows the same emission lines, but the color mapping for red and blue is swapped. In both panels, the brightest stars are added to visualize the regions contaminated by strong continuum light. (Aside from that, the image does not contain continuum light.)
The small circle depicts the position of the possible progenitor BD+28 4211 of the nebula, which lies almost exactly in the center of the OIII region (red in the OHS panel; bluish in the SHO panel). The Hα and [SII] filaments (cyan in the OHS panel; yellow in the SHO panel) belong to supernova remnants originating in Cygnus. Their brightest parts have their own designation — Sh2 111. A faint, unstructured [SII] and Hα glow (orange in the SHO panel; bluish in the SHO) can be seen north of the OIII region and seems to belong to the PN candidate.

Object data

The center of the 5°-large OIII region is located at a right ascension of 21:50:34 h and a declination of 29:05°, just 0.25° away from the possible progenitor. Including the [SII] and Hα outflow in the outer northern region, the size of the PN candidate is 6° and the center position is shifted to a right ascension of 21:49:34 and a declination of 29:34°.

Possible nearest planetary nebula surrounding the hot subdwarf BD+28 4211 in [OIII] — The monochrome images show the PN candidate separately in the light of the three observed emission lines (O: [OIII]; H: Hα S: [SII]). As above, the brightest stars are added and the hot subdwarf is marked by a white circle. The color image marks the regions for which intensity measurements were performed (see below). 9

Possible nearest planetary nebula surrounding the hot subdwarf BD+28 4211 in H-alpha — The monochrome images show the PN candidate separately in the light of the three observed emission lines (O: [OIII]; H: Hα S: [SII]). As above, the brightest stars are added and the hot subdwarf is marked by a white circle. The color image marks the regions for which intensity measurements were performed (see below). 9

The following table contains the results of surface brightness estimations for the regions marked in the upper image. The average intensity is given in Rayleighs and is measured directly from the results of the Northern Sky Narrowband Survey, DR0.2.

Region	[OIII]	Hα	[SII]	Comment
BG	0	0	0	Background reference
A	1.24	N/A	N/A	Including region B. Contains [SII] and Hα filaments that do not belong to the PN candidate.
B	3.25	1.77	-0.04
C	0.41	3.20	2.26	Region in the northern [SII] and Hα outflow that appears to belong to the PN candidate.

Image data

This image was calculated using data from the Northern Sky Narrowband Survey, DR0.2. Click the link for detailed information or visit the instruments page for information about the equipment. Here is some additional image-specific information:

Center position:	RA: 21:50:13 h, DEC: 21:38:13°
FOV:	12°×12°
Orientation:	North is up
Scale:	10 arcsec/pixel (in center at full resolution)
Projection type:	Stereographic

Citing / persistent resources

If referencing a volatile webpage is not appropriate, a persistent snapshot of this page is available via the DOI 10.5281/zenodo.17216263.

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