R Aquarii and Cederblad CE211

[Shiraz (Ray)]

Really interesting and unique object with everything but the kitchen sink. The image is not particularly high resolution (2.8 arc sec seeing and bright sky), but it is good enough to show the main features of the system. The following summary is my interpretation of what is going on, gleaned from a few references, so take it with a grain of salt.

The central star is a symbiotic binary star comprising a pulsating red giant (Mira class variable) and a hot white dwarf in elliptical orbit. The Mira has a period of just over a year and normally varies in brightness by nearly 5 mags. It has just passed minimum which aids in seeing the surrounding nebulae.

The white dwarf is refuelled by accretion and when close to the Mira, brightens to the extent that it damps the Mira pulsations every 44 years or so (other damping mechanisms are possible). Occasionally the dwarf gains enough material to experience nova-like eruptions and the inner jets (up/down and with slightly "s" shaped extension) and outer ring nebula (CE211) are probably the results of two such past activities. The dwarf produces copious UV which activates the hydrogen in the outer nebula, but the closer jets have a greenish tinge which suggests oxygen3. the whole group is surrounded by material which imparts an overall reddish tinge, but there is also a hint of blue reflection nebula that might be real or might just be a product of the low transparency sky during the imaging period.

The Mira is in a fleeting stage (in astro timescales) in star evolution - it will soon blow off its outer shell in a planetary nebula, leaving behind another white dwarf. When the PN eventually disperses, the whole system will become just another point of light of no particular interest.

thanks for looking. Might be worth someone with better sky trying to image it. Regards ray

(L+R)RGB 4.1hrs, 2.9hrs, 1.1hrs, 1.1hrs
GSO 200f4 with RCC1
SX H694 at -15C
NEQ6
heavy crop and scaled x1.2

[Rob_K]

Nice work Ray and very interesting information, thanks. One tiny quibble though, instead of "go nova" I'd put in "experience nova-like eruptions" because of all the things this system might be, a recurrent nova is not one. Papers I've read indicate that R Aqr's nova-like eruptions don't behave as predicted by either accretion or thermonuclear-powered models and it has been suggested that the hot component brightens when the Mira companion loses mass during a helium shell flash. I'm also happy to admit that my information might be out-of-date!

Cheers -

[Shiraz (Ray)]

Thanks Rob. Good advice - there is certainly still some question as to the nature of the eruptions and their cause(s). As far as I can tell there is also some significant uncertainty regarding the causes of the periodic quenching of the Mira pulsation, with at least 3 mechanisms appearing to be viable.

Have done some more reading and find that it is accepted in some sources, but by no means all, that the system has been in nova states in the past - even to the extent of getting dates from Korean astronomical records and identifying a possible corresponding nitrate ion signature in ice cores (unsure of the provenance of that paper though).
http://sait.oat.ts.astro.it/MSAIt830.....83..840T.pdf
http://www.spacetelescope.org/images/opo9015a/
http://www.nature.com/nature/journal.../247532a0.html

Recently also read that there is a shell of water associated with the system - I had to read that carefully to make sure that it was referring to plain old H2O - fascinating.
http://arxiv.org/pdf/0801.3488.pdf

anyway, thanks very much for the feedback and incentive to continue reading. Do you have a particular interest in variable stars?
regards Ray

[Rob_K]

Thanks Ray. I have an interest in recurrent novae and monitor a number of known and candidate RNe on a regular basis in combination with a pretty basic nova search (DSLR widefields, 'blinking'). Sorting out candidate RNes takes you to some interesting literature but I think I've managed to dodge the abyss of obsession thus far.

Cheers -

[RickS (Rick)]

That's an odd and interesting one, Ray!

[Shiraz (Ray)]

Originally Posted by RickS

That's an odd and interesting one, Ray!

Hi Rick. sure is an intriguing mixture - wanted to get an image of this while the big star was low brightness and then another when it is in full bloom. Darned hard imaging through recent sky though - used this as a fallback target when the sky was not good enough for galaxy imaging, so quality is not too good. Regards ray

[Andrew Pearce]

Hi All

I visuall observed R Aqr last night (Oct 14.6 UT) and it was mag 11.2 and is currently at it's minimum brightness, so now would be a good time to get some images.

Regards
Andrew Pearce
Perth, WA

[Shiraz (Ray)]

thanks Andrew. I imagine that the faint nebulosity will be even more difficult to image when the star brightens. I presume that the outer shell cannot be seen visually even at minimum star brightness.