Bumps & Humps

One of the reasons that I chose to observe variable stars is that they represent the truly dynamic nature of our universe. So much of what we observe outside of our solar system tends to be very static. With the exception of a nova, the galaxies we see through our little eye pieces appear the same today as they did a thousand years ago and will be the same as they will appear a thousand, perhaps a million, years from now. It is really difficult to get an understanding of the true dynamic nature of our universe. Enter variable stars. Depending on the nature of variability, these stars can change in apparent brightness in days, or even hours. The subject of this week's blog is on light curves of a somewhat predictable class of variables called Mira's.

When I first started to observe Mira's, my assumption was that they would be fairly predictable and make nice sinusoidal curves when plotted. Well, I now know that I could not be more wrong. To illustrate this, I would like to present light curves of three Mira type variables in Cassiopeia,  W, T and S. The light curves plot the apparent brightness of the star over time. The curves below are on a timescale of 1600 days. The date is the Julian calendar date. Today is the extreme right on the graphs. My personal observations are marked by the blue crosses.

Above is the light curve of W Cas. At first glance you can see quite clearly the sinusoidal oscillation, however, take a look at the minimums. Quite clearly there was one minimum that was noticeably deeper than the others.  

Now here is another Mira, T Cas. The odd thing here is that there appears to be a double maximum. Each time the star reaches its maximum and starts to fall off, there seems to be a rebound and the star brightens again before finally falling off to its minimum. Currently the star is about to enter its 2nd maximum stage. It will be interesting to see what my next estimate will be.

Lastly, here is S Cas. Initially it looks pretty "normal," but again there is something out of place. Look at the last rise to maximum. There appears to be a stall in the progress when the star reached 12th magnitude. This is called a "hump." The previous two cycles show evidence of this hump, but they are less pronounced and occur at a lower brightness than the last one. There is even evidence for a hump on the dimming side of the second cycle.  What will the next cycle look like?

So, there you have it. Three "predictable"  Mira's showing very unpredictable or unexpected behaviors on a time scale that we can witness.

Clear skies;
rw