Variable stars (examples)

The reasons for changes in the brightness of a star can be divided into two categories: (1) orbiting companions or (2) stellar astrophysics.

(1) In principle, the variability from orbiting companions (this includes eclipsing binaries or transiting planets) should be as regular as clockwork.  In practice, the variability can deviate from clockwork regularity if stellar binaries get too close together, if there are multiple transiting planets, if there is additional background electronic noise or astrophysical noise.

(2) Brightness variations caused by physical processes internal to the star (stellar astrophysics) can arise from pulsations of the star, starspots or flares. Flares are random spikes in the light curve brightness.  Pulsations from stars (like RR Lyraes) are quasi-periodic: they can appear to be regular for a while and the cycles are relatively short (generally hours to a day or so). The Figure below shows two variable stars with short periods that might be best classified as “variable” and “pulsating.” These could be short period binary systems – this could quickly be verified with follow-up observations.

puls1 puls2

Starspots produce complex variations. As the star spins, the spots rotate in and out of view with a   periodicity of a day or two (for the most rapidly spinning stars) to several days for slowly rotating stars (the Sun has a rotation period of 25 days).  Starspots can form at different latitudes on the star.  Since some latitudes rotate faster, spots can show multi-cyclical variations. The light curves below might be best classified as variable and irregular.  However, a case could be made for classifying the light curve in the figure below (and left) as variable and regular. Even though the amplitude of the curves changes, the time from one peak to the next is about the same.

irreg1

irreg2

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8 responses to “Variable stars (examples)”

  1. eriza says :

    Could you give an example of “variable regular” type? thanks

  2. debrafischer says :

    Good question Eriza. The regulars are rare. Give us a few weeks to sieve through the database and classifications and you all will have educated us about these groupings. We are just figuring some of this out, too.

  3. BlackWinny says :

    Please, in such a case, how do we classify the star ?

    http://www.planethunters.org/sources/SPH10122651

    – Regular variable with long periodicity ?
    – Or irregular variable ?
    – Or pulsating variable ? (short pulsations visible… on a progression of a possible other long regular periodicity) ?

    Thank you !

  4. debrafischer says :

    I checked SPH10122651 – I’d classify this as a variable, irregular. cheers, debra

  5. Kentetsu says :

    Thanks for these examples. 🙂
    I have to admit that so far i made quite a few mistakes when classifying stars.I will be more careful from now on.

  6. alien333 says :

    I must admit to chickening out with some classifications. I have seen some that appear quiet for half the quarter and then appear to become variable or even pulse-like. What is the best way to classify these? Also, in cases where there is a recognisable but very small variation (e.g. +/- 0.001 or 0.002) I am tempted to classify as quiet… is this right?

    • Meg says :

      If the variability changes dramatically I’d probably classify it as an irregular variable – on clases where there is small variation I’d probably go with calling the light curve quiet.
      Cheers,
      ~Meg

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