The mass transfer from A to B isn't a quiet, gentle exchange. Conservation of momentum prevents the transferred material from just gravitationally "falling" onto B – the transferred material is being whipped about, generating both an accretion disk (sort of like Saturn's rings) around B and a strong jet of material that is being expelled from the pair. The jet is now interacting with the old material that B shed a long time ago when it reached end-of-life, creating a complex system. This is the closest known example of a symbiotic star system, where there is strong interaction between members of a binary pair. (See also the Wikipedia article on R Aqr.)
![Image](https://cdn.spacetelescope.org/archives/images/screen/opo9015b.jpg)
Artist' Rendering of R Aqr, showing large red giant, tiny white dwarf, blue accretion disk, and narrow ejected jets
Credit: Dana Berry (STScI) via ESA/Hubble
Earth-based observation of the system is unable to separate the two stars. We do see a complex nebulosity surrounding the system. (Any astrophotographers want to try to image it??) Dr. Margarita Karovska (Harvard-Smithsonian Center for Astrophysics) is studying this system with the Hubble and Chandra space telescopes, and has requested ground-based observations through the American Association of Variable Star Observers (AAVSO) to supplement her observing time in space. The light curve of the pair tends to be dominated by the long-period variability of the red giant.
Just about any small telescope will suffice for observing this star visually. At its faintest it gets to about magnitude 12.5. (Which is close to the limiting magnitude of our library scopes.) Right now, it is around magnitude 10 or so. R Aqr is low to the south, so you do need pretty good access to the southern horizon.
To observe this star, you need to fetch a star chart from the AAVSO, and then get (or make) a finder chart. (I used maps 3 and 4 in my trusty old Norton's Star Atlas to start my star-hopping. I've attached one of the fine charts from Taki, which also works.) Find a star-hopping path to get to the right field, and then shift to the AAVSO chart. (I went from Formalhaut north about 7 degrees, then east-northeast to a group of mag 5 stars, then north to R Aqr and stars labeled "53" and "50" on the AAVSO chart.) You estimate the brightness of R Aqr by finding a brighter comparison star and a fainter comparison star and then interpolating. (When I looked a couple days ago, I found R Aqr dimmer than the "103" comparison star – the "103" means mag 10.3 – and brighter than the "95" comparison star. I estimated that R Aqr was half way between the two, so I declared my estimate to be mag 9.9.)
If you give it a try, post your experience (joyous or frustrating) here!
- Mark M