September 2024 - Picture of the Month
R Aquarii and Ced 211 in Aquarius
Something a bit different from the usual nebulosity, although there is still a nebula associated with R Aquarii. This month I'm featuring the variable star, or perhaps that should be stars at the heart of this nebula: R Aquarii is a symbiotic binary system with the larger of the pair also being a Mira-type variable star from which a white dwarf that is accreting material.
The variability of R Aquarii has been known for a long time, first noted by Karl Ludwig Harding in the early 1800s, because of the amplitude of the light-curve. The Mira component has a range of over four magnitudes during its broadly annual cycle. However the system as a whole has been seen to range between 5th and 12th magnitude. This is far from a simple light-curve and there's still conjecture surrounding the causes of its variability.
Typically these binary system undergo periodic outbursts during which material is ejected from the accreting star. This is the theorised source of the nebula surrounding the binary which is designated as Cederblad (Ced) 211. There are a couple of shells visible in Peter's image which are thought to be from two separate events about 640 and 185 years ago. Additionally you can see the bright and roughly 'S' shaped feature which comprises superheated material being accelerated in jets.
There an interesting article about R Aquarii in the American Association of Variable Star Observers Variable Star of the Season archive from Summer 2003. The European Southern Observatory also turned their Very Large Telescope (VLT) on the Ced 211 back in 2012.
Alternatively you might like to make a few magnitude estimates with binoculars or a modest telescope. Apparently Ced 211 is possible to observe visually, but it seems to take a relatively large scope, and I should imagine that it's best attempted with a good sky when the variable is near minimum.
James Whinfrey - Website Administrator.
