Date: May 10, 2012
Title: Twinkle Twinkle little star …… How I wonder FS Aur?
Podcaster: Peter Lake
Organization: AARTScope Blog
Links: http://aartscope.blogspot.com
http://vitaly.neustroev.net/research/observing-campaigns/
http://www.twitter.com/fs_Aur
http://www.aavso.org
Description: FS Aur is one of the most strangest and erratic variable Stars. Peter Lake reports on the data collected as part of the broader work with Dr Vitaly Neustroev of the Oulu University Finland and discusses the past two seasons of observations. Peter Lake is an Amateur Astronomer from Melbourne Australia and regularly discusses how people can be involved in citizen science and observation programs.
Bio: Peter Lake is an amateur Astronomer from Melbourne, Australia, a member of Variable Stars South and the AAVSO and he owns and operates a 0.5m Planewave CDK Telescope at New Mexico skies, which is affiliated to iTelescope.net. Peter has been a participant in citizen science and recovered asteroid 2000 EV70 during the Spacewatch FMO program. More recently Peter has been actively involved in the study of cataclysmic variable star FS Aur, and followup exoplanet observations on Kepler targets of interest.
Sponsor: “This episode of 365 days of astronomy is sponsored with thanks to all non-US contributors for showing us that the night sky is something we can all share.”
“Additional sponsorship for this episode of 365 days of astronomy was provided by iTelescope.net – Expanding your horizons in astronomy today. The premier on-demand telescope network, at dark sky sites in Spain, New Mexico and Siding Spring, Australia.”
Transcript:
Like duck hunting, Variable Stars have their “Seasons” also. A season being where the variable star in question is in the optimal position for “shooting with CCDs” ie observable for most of the night, during this time ideally it can be visible for as many as 6-7 hours per night. FS Aur is a Cataclysmic Variable is now low in the west at sunset at the close of an intensive second season. So I though it would be good to review these past two seasons, before once again, it comes around for observations in the next northern winter.
FS Aur is one of the strangest and complex objects in the extensive variable star family. It is thought to be a magnetic white dwarf and red giant binary Star with a third object acting on it in a circumbinary orbit. (Tovmassian et al., 2010)
Back in 2010 there was a sporadic and incomplete light curve and astronomers wanted answers. When they want answers they often leverage the collective effort of the American Association of Variable Star Observers (AAVSO), to muscle up some more observations and data.
FS Aur has a number of photometric and spectroscopic cycles going on. On top of this it goes into outburst about every 12-15 days. The outburst duration is so short (2-3 days) it has been regularly missed in the past – so in the 2010/11 season Dr Neustroev rallied a special effort. For the first time, members of the AAVSO mapped the entire outburst cycle, a good number of times.
Dr Vitaly Neustroev is the University Researcher (Yliopistotutkija) at the University of Oulu, Finland and he is a key researcher on FS Aur, working hard to better understand its erratic behaviour. Visit the observing campaign page here, and also follow on (Twitter).
I like following Cataclysmic Variables, after catching Simostronomy fever, and I have been a regular on FS Aur since Dr Neustroev’s call to action.
During the campaign FS Aur has been dancing away with a little periodic wobble at about 15.9 with the odd subtle change in brightness, then it goes really dull to 16.2 then literally within 24-36 hours it pops up to magnitude about Mag 14.
As an amateur astronomer I am always careful to point out that I’m not qualified to say how or why, but I can tell you when, where and how bright! 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.
When variables are in season you can get nice long lightcurves and do time-series analysis and this is very valuable data. During the season I submitted some thousands of observations in V filter and color times-series in BVRI as this is also useful data.
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.
At AARTScope my mission is to “keep creating the sense of anticipation and discovery that keeps scientists asking questions” so if you are an AAVSO member and would like to join the campaign, please do.
Unlike ducks, no variable stars are harmed during “peak season”.
So now we turn our attention to the 2011/12 season where FS Aur just gets weirder and weirder.
Just when you think you’ve seen it all, there is always something new in Astronomy. The world of variable stars and in particular – Cataclysmic Variables, is no exception. As the 2011/12 season open in the northern winter Vitaly Neustroev released his awaited paper on the data from the 2010/11 season.
The highlight for me, is of course my name included as a co-author for my first paper…..its been a long journey from hearing an Astronomy Cast podcast about science papers and how amateurs can be involved, to having my name at the top of a paper along with some of the greats of Variable Star research. (Thanks for the inspiration Pamela and Fraser & to Mike Simonsen for his mentorship as an AAVSO member).
The winter campaign of 2010-2011 gathered over 14,000 individual observations in the “V” band, and many more in B,R,I from over 41 observers around the world in an exemplary collaboration effort between professional astronomers, amateurs, and AAVSO members. The 2011/12 campaign has focus less on the color variations in the various BVRI filters, but more closer focus on what going on whilst the system is in quiescence.
Previously Tovmassian et al had established that FS Aur has a long photomentric period of 205.5 mins that exceeds the Spectroscopic orbital period of 85.7 mins by 2.4 times. A second long spectroscopic period of 147 minutes was also discovered and Tovmassian et al (2007) suggested that this was evidence of a third body in circumbinary orbit. The purpose of the 2010-2011 was to gather more data and photometrically confirm the specroscopic data.
Vitaly’s paper now add to Tovmassian’s work. In summary, the observations found a modulation in the B-I Color index, and for the first time the precession period for the White Dwarf was identified from photmetric data, and confirmed the previous spectroscopic data.
I asked Vitaly about the significance of the findings:
“Should the free precession be accepted as the correct explanation of the phenomena, it will give an important tool to study white dwarf equations of state. The theory of compact objects predicts certain relations between the spin and precession periods, and our finding provides a good test for the theory and establishes a qualitative model to be explored both theoretically and observationally. Detection of precession can become a powerful tool in searching for the internal properties of compact stars, which would be otherwise inaccessible for us. Combined with other methods to estimate masses and density of the WDs in CVs, the precession period will help to refine these values, which in turn, allows for testing and proving the theory for the precession of compact stars and may allow for further advances in our knowledge of the structure of WDs and the influence of accretion on them.”
Some interesting things were also observed in the quiescent state prompting additional scrutiny during this year’s season of the longer term behaviour of the system when at quiescence.
It has been great to be a part of the wonderful science research that is still ongoing. Its all part of the great science you can do as a part of any number of citizen science initiatives. The AAVSO and Variable Stars South have many and varied research projects just like this one where you can play a significant part in gathering the data and working with professional astronomers.
It was great working with such professional people ably lead by Vitaly and George Sjoberg. Participation in campaigns like this is a great way to get to know other astronomers, and build your credibility as a capable amateur astronomer.
End of podcast:
365 Days of Astronomy
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