Watching and Waiting

Ideas more or less related to teaching and learning physics at Luther College.

In my last post I babbled for a while about unorthodox grammatical structures and songs by John Cougar Mellencamp and Paul McCartney. Feeling like I was on a roll, I figured I could start this post with more talk about nearly forgotten songs from the 70s. A few days ago I heard Carly Simon sing “Anticipation is making me wait.” I wondered if it is really anticipation or merely the flow of time that makes one wait. One must wait for the arrival of future events whether one anticipates them or not. If I wrote pop songs I’d probably write something like “The second law of thermodynamics is making me wait,” which, of course, goes a long way toward explaining why I am not a writer of pop songs.

If you have read my recent posts, and I am sure you have, you know that I designed an ongoing research program specifically to be accessible to undergraduate students and to take advantage of the fact that we have access to the observing equipment night after night, year after year. We look for subtle long-term changes or rare events hidden in noise. Whatever we search for requires a long time of amassing data and careful, often tedious, handling of that data. It just doesn’t happen that something exciting pops instantly out of the data. Still, I eagerly anticipate the start of each observing season and now that we are two (very cloudy) months into the 2014 campaign we can start to get a hint of whether something interesting might be going on this year.

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Above is the light curve for a semi-regular pulsating star we have discovered. In 2010 and 2011 this star showed a sudden doubling or tripling of the amplitude of variability. These sudden increases in amplitude are not rare in our data (see another example) and in our research group we refer to these as “Sudden Amplitude Shift” stars. We don’t know what causes the shifts. We do know that these are multi-periodic variables and that when the sudden increases in amplitude occur the light curves look cleaner and more periodic as well. Thus, it might be that one of the oscillation modes has weakened or disappeared, leading to less inter-mode interference and allowing larger global oscillations of the star. We currently lack the data to be certain of the strengths of these modes on timescales as short as a few years. Of course, if mode  weakening is a cause for the observed behavior of the light curve all we have done is push the question back one level since we don’t know what would cause a mode to weaken or disappear and then, perhaps, to reappear. Such reappearance would account for the fact that 2013 into early 2014 the star seems to have reverted to its low-amplitude state. The pre-outburst and post-outburst stages are shown in greater detail below. Note that the 2014 data appear prior to having passed photometric quality tests and some of the nights are likely to be removed. The photometric quality tests are one of those things we have to take our time and wait for in order to do it right. Still, asking questions like whether this star will maintain its increased amplitude or will revert to its low amplitude state or if a high amplitude state will return is sufficient to keep us anticipating each new month of data and that’s enough to keep us plugging away.

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