December 2022 - Picture of the Month
Hubble’s Variable Nebula (NGC 2261) in Monoceros
I've chosen an object that will be much more familiar to most of you than last month's. Many of you will have observed NGC 2261 both visually and with a camera.
R Monocerotis is a massive Herbig Ae/Be star with a T Tauri type companion. It has recently formed from the dust and gas onto which this nebula is projected, and probably possesses a circumstellar disc. It is also the source of the light that's reflect in our direction, resulting in this nebula which is about a light-year across at a distance of 2,500 light-years.
Considering the pair of variable stars at it's core, it's perhaps unsurprising that the form of the nebula is also is highly variable. The best explanation of this behaviour is that the form of the reflection nebula is determined by the passage of dense clouds of dust, and possibly the circumstellar disc, as they interfere with the light as it is cast onto the distant backdrop of dust. If true, the morphological changes in the nebular tell us something about the conditions near R Monocerotis itself: not easy data to come by for young stellar objects like these. This is an object that will certainly reward periodic observation.
This image from Capella Observatory is an great close-up of the beautiful patterns of shadow and light that R Monocerotis throws onto the clouds of dust and gas that surround it. It's a snapshot in time, so don't expect it to look like this when you image it.
James Whinfrey - Website Administrator.