FS Aur in Outburst again!

FS Aur has leapt back into life again! ….or should I say continued on its merry, and highly erratic way.

[See my previous post]

Dr Vitaly Neustroev is the University Researcher (Yliopistotutkija) at the University of Oulu, Finland and he is doing some particular reseach on FS Aur, in order to better understand its erratic behaviour. Visit the observing campaign page here also follow on  (Twitter).

I like following Cataclysmic Variables, after catching Simostronomy fever, and I have been a regular on FS Aur. During the past week FS Aur has been dancing away with a little periodic wobble at about 15.9 with the odd subtle change in brightness, then over the weekend it went really dull to 16.2 then within literally hours it popped to Magnitude 14.3 when I did my first image of the day today. It has steadily grown to 14.035 throughout the day.

Below is today’s image.  FS Aur can be seen in the Green annulus.

Now take a look at this image only 36 hours or so ago. FS Aur can hardly been seen. It is at magnitude 16.2 at its lowest point in its quiescent cycle.

So what is going on with FS Aur - Dr Neustroev describes it this way:

“FS Aur is an extremely unusual cataclysmic variable renown for the presence of a variety of uncommon and largely incomprehensible periodic variabilities of brightness and radial velocity. The outlandish peculiarity of FS Aur is the existence of a very coherent photometric period of 205.5 min that exceeds the spectroscopic orbital period of 85.7 minutes by 2.4 times. Such a discrepancy in the photometric and spectroscopic periods is highly unusual for cataclysmic variables.

Based on the short orbital period, FS Aur has been classified as a SU UMa star. Nevertheless, long‐term monitoring of the system by several groups failed to detect any superoutburst in its light curve. The publicly available AAVSO light curve show instead a steady‐cyclic outburst pattern that is more similar to a SS Cyg–type dwarf nova light curve. However, this monitoring reveals an additional, discordant, and very long photometric period of ~900 days. We explain the latter by the result of eccentricity modulation of a close binary orbit induced by the presence of a third body on a circumbinary orbit (Tovmassian et al., 2010).”

So it is indeed a complex beast. as can be evidenced by the light curves collected today and previously.

This was a time series I ran when it was at quiescence.

I’m not sure yet if it has reached the peak of its current out burst but history says its probably fairly close.

Finally this is the light curve of FS Aur climbing to its peak today.

 Finally, one final shot of the day’s light curve which now spans an almost continuous/contiguous 6 hours. It is very interesting as it shows quite clearly the erratic nature an massive forces involved in the outburst. Vitaly has also requested I run some BVRI color analysis - I’ll have to process that another day.

So this is indeed a fascinating object and could indeed be a new class of object. Only time will tell. AAVSO members are playing an important role in gathering the data to refine the lightcurve. Once the observing campaign is complete we await with interest to see what the astronmers and astrophysicists can tell about what they have learned.