December 2019 - Picture of the Month
Abell 6 and HFG1 in the Constellation of Cassiopeia
This month we're back to planetary nebula and I've found a pair in the same image. I was particularly taken by this conjunction because, as David pointed out on his blog, it's going to be short-lived (cosmologically speaking).
First we have Abell 6 (PK 136+04.1) in the bottom right which is the smaller round bubble-like structure with a brighter wall: what many of us think of as a typical planetary nebula morphology.
To its north-east we have Heckathorn-Fesen-Gull 1 (HFG1 or PK 136+05). HFG1 is larger, fainter, and more complicated structure generated by a close binary system (V664 Cas) with a period of about 14 hours.
You can clearly see the bow shock on the south-eastern edge of HFG1 and the reddening of the material opposite it to the north-west. This planetary nebula is moving quickly past Abell 6. There's wonderful image of the gas trailing behind HFG1 taken with the Mayall 4-meter telescope at Kitt Peak National Observatory.
Neither planetary nebula shows up terribly well on the POSS plates, perhaps a bit sharper in the blue because of the OIII emission, so I'd guess they'd be a challenge for most visual observers and require a large scope, especially HFG1. Recent images like David's show much more structure and really make these objects special due to the sensitivity of modern cameras and narrowband filters.
James Whinfrey - Website Administrator.