“Imaging HII regions, protostellar outflows, and transients”
by Dr. John Bally, University of Colorado, CASA
The HII region Sh2-129 in Cepheus in a H-alpha and [OIII] wide-field image, 4 degrees across. This object is next door to the often-imaged IC1396. Deep images of other HII regions, especially in [OIII], might reveal other, similar ejections (Image Credit: Rolf Geissinger / APOD 27 October 2016).
What do narrow-band images in H-alpha, neutral and ionized oxygen, and sulfur show? How can these images be used to derive physical properties of ionized nebulae?
I will discuss how small telescopes, CCD (or CMOS) cameras, and narrow-band filters enable amateurs to make discoveries. The key is the accumulation of hours to tens of hours of total exposure time in narrow-band filters. A giant, 15 parsec-long, bipolar flow, called Ou4 in Sh2- 129 in Cepheus, which may have been powered by a stellar merger about 100,000 years ago, was found by an amateur, Nicolas Outters.
Shorter exposure, broad-band images with small telescopes or telephoto lenses have also identified luminous, accretion powered, stellar outbursts called FU Orionis and EXOr events on forming stars which result in the emergence of new, but transient nebulae such as McNeil’s Nebula