Multi-periodic Variables, or Playing Sudoku with Stars

Posted By Pamela on Jun 15, 2008 | 8 comments

As a researcher, I have to admit that I have been a bit unfocused, or perhaps dually focused is a better way to put it. My first research gig was doing a Quasar survey at 17 using a 6-meter optical telescope. My next job had me working in radio on T Tauri variable stars at Haystack observatory using VLA data. These two projects set me up for a lifetime of intellectually ping-ponging between radio emitting galaxies (which lured me into galaxy clusters) and variable stars. Even today I find the research part of my hard drive split between 2 variable stars I need to write up for publication and a galaxy evolution project using SDSS. Diversity keeps me happy. But diversity doesn’t always make me popular.

Over the years I’ve taken a lot of [insert negative word likely related to excrement] for my love of pulsating variable stars. I’ve been told they are scientifically boring (they’re just harmonic oscillators), and that any discoveries I make won’t significantly effect anything other than our knowledge of RR Lyraes (I’m okay with that). Senior folks who mean well have in a various kindly ways recommended that my limited time for research get carefully focused on galaxies and places where I can make Significant Contributions. I smile. I agree. But then I go back to my bad habits and pick up an RR Lyrae data set and plug away at it in tiny scraps of time culled away from my teaching and writing and astronomy new media research.

For me, solving variables is like solving Sudoku. When I see gaps in the data, I find pleasure plugging away to find the one right way to fill things in to get a perfect solution.

The particular stars I like, RR Lyraes that demonstrate multiple periods or period modulations, have light curves that are built out of a combination of beating pulsations of light. These are visible as changes in the brightness of the star with time (see graphic above). Just like a single cavity (for instance, a soda bottle or trumpet) can resonate with multiple sounds, a star can also resonate with multiple pulsation periods. Determining the pitches of a sound is as simple as using a microphone and oscilloscope to record enough data to do a mathematical analysis (called a Fourier analysis for those who wanted to know). Taking data just requires the pitch to be held for a couple of cycles, which is usually no big deal even for a 4th grader with their first flute. Stars are a bit more complicated however.

In studying pulsating variable from Earth, we have to combat to major evils, both with the same source. These evils are commonly referred to as Daylight and Solar Conjunction, and they are caused by the Sun. When a star is in season – when it is up at night – the Earth’s rotation has this nasty habit of carrying observers and their telescopes out of view of stars. Every time the star sets and the Sun rises, there is a gap in the data. This can somewhat be overcome by handing stars off from one observer to another scattered around the globe; from Turkey, to Italy, to the East Coast, to the West Coast, as the world turns new telescope take aim at the target of choice. But this technique only works when the star is up at night.

As the Earth travels around the Sun, stars also ake turns hiding behind the Sun and getting washed away by the day. Today Orion is getting ready to rise with Sol, and in 6 months the Summer Triangle will play peak-a-boo with the day (if you know where to look you can find Vega in the winter daytime sky with binoculars).

When a variable disappears behind the Sun, going in and out of conjunction, we get gaps in our data. When there isn’t an observer somewhere on the Earth to hand the star off to when it is up at night, we again get gaps in our data. This means that the pretty pulsation cycle of a star may go mostly unobserved, and to understand what is going on I have to correctly extrapolate between points, and fold my data to find the overlaps between cycles. For any given star in any given season, there is only one right answer, and finding it is, to my mind, just like solving a puzzle.

A really hard, requiring software and mathematics, puzzle.

I can’t be the only one in the world who enjoys variable star astronomy. The American Association of Variable Star Observers is dedicated to studying variable stars in all their forms. The literature survey I’m working on as I write a new paper has a handful of papers being published each year just on the Blazhko effect, and dozens coming out on different RR Lyraes. There aren’t a lot of folks working on these little stars. But they are out there, plugging away.

Not all research has the potential to lead to a Nobel Prize. Sometimes it’s enough to solve puzzles, and to simply answer the question – What is this star doing this season?


  1. I don’t see a picture above, so I imagined one of what you’re doing.

    What you’re doing is playing with a purpose. Why play a pointless (but fun) puzzle of Sudoku when you can do a puzzle with a purpose in figuring out the variable stars? You’re playing. You’r having fun. Life doesn’t have to be all directed at publications and moving science forward.

    It’s delightful that you enjoy astronomy enough that you even play in it.

  2. Yup, I agree, you do what you want to. If RRs are puzzling & fun, then work on them just for fun. There are plenty of folks working on the galaxies, and if you’re one of only a few variable star observers, then that’s actually an advantage. Keep plugging away with the FFTs and ignore the sticks-in-the-mud that want you to work on something else.

    It sounds like a photometry telescope in space would be worthwhile. Are there any science packages out there like Deep Impact/DIXIE that can be repurposed, I wonder…

  3. Sounds like you’re on the right track. If all science is only focused on Significant Contributions, or worse yet, what can we do to make money with it, then the core of science is lost. The best science is done by those who are doing what they love. Besides, some of the largest discoveries have come from someone saying ‘Huh, that’s odd.’ As they fiddle with some ‘non-significant’ contribution. Keep doing what you love!

  4. Pamela,

    This is a great post. I recent was asked by some young students “How do astronomers decide what to study?” I think this post speaks directly to that, and to why we study at all.

  5. Pamela,

    As an amateur I find variable stars anything but boring. RR Lyrae are neat. I myself have just begun my own program of watching a few Cataclysmic’s. Hopefully my observations can contribute to the whole someday. Keep up the great work and BTW love the podcast. I wear my “Slacker Astronomy” shirt proudly at the local star parties :>


  6. Sudoku is a good example. It’s fun for you, but completing Sudoku puzzles and doing research into some types of variable stars is not likely to grab lots of funding and headlines (F&H). So, good for you, just so long as you don’t need lots of F&H. Also, in my experience, F&H are somewhat fad driven in physics and astronomy anyway. One result of this is that avenues of research that will turn out to be vital for many interconnected areas of astrophysics later, and so should be higher on the F&H scale now, are sadly low on the F&H spectrum now. Quite possibly, due to their relatively high abundance in faint surveys and the accuracy of their distance determining characteristics, RR Lyrae stars will fall into that category.

  7. Let them give you cow cookies. I think there might be some resentment of your enthusiasm. Beside how else are you going to keep carbon neutral if you dont use their supplied energy source.

  8. I really love your posts, having just recently discovered this site and I admire you enthusiasm. this is how science progresses I guess, not in leaps and bounds but in small minute increments, with dedicated scientists like you diligently working away, adding their bits , chiselling away patiently, one hammer strike at a time on the marble chips of ignorance until you have liberated a remarkable sculpture , an edifice that amazes and awes us all.

    don’t make much sense?… you once said , I am working ‘under the influence of too little coffee’. hehe.

    just wanted to say – keep up the good work.

    2.30 am
    Calcutta, India.

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