The line of sight toward the planetary nebula Jonckheere 900

J-900
Image credit: ESA/Hubble and NASA

The object in this image is Jonckheere 900 or J 900, a planetary nebula — glowing shells of ionized gas pushed out by a dying star. Discovered in the early 1900s by astronomer Robert Jonckheere, the dusty nebula is small but fairly bright, with a relatively evenly spread central region surrounded by soft wispy edges.

Despite the clarity of this Hubble image, the two objects in the picture above can be confusing for observers. J 900’s nearby companion, a faint star in the constellation of Gemini, often causes problems for observers because it is so close to the nebula — when observation conditions are bad, this star seems to merge into J 900, giving it an elongated appearance. Hubble’s position above the Earth’s atmosphere means that this is not an issue for the space telescope.

The nebula lies close to the galactic plane and is 4.9 kpc distant. It is coincident with a radio source. The bright star in the field is not associated, and lies in the foreground. It is angularly separated from the nebula by about 12 arcseconds. In the 2MASS point source catalogue it has designation 06255700+1747161, with J, H and K magnitudes 11.34, 11.04 and 10.96 respectively. These colours suggest it is a mid-G dwarf (see Fig. 2 of this link) with absolute J magnitude ~ +3.6 (Table 3), yielding a distance of ~ 350 pc. Even if it were a giant, with absolute magnitude ~ 0, it would be only 2 kpc distant. There is no counterpart in the WISE data, because the nebula itself becomes overwhelmingly bright in the longer WISE passbands. The Hubble imaging presented here shows that the star itself has a faint companion, although there is no proof the two are physically related. The companion may itself lie serendipitously in the line of sight, as does the extended reddish object at lower left, which is likely a galaxy.

The central star of the planetary nebula is of the 18th magnitude. The faint companion to the star looks comparable, so I roughly estimate V ~ 18. Therefore, if the faint companion does lie at 350 pc, this gives an absolute V band magnitude of +10.3, which corresponds to a spectral type ~ M2.5 dwarf.

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