Summer Dale Beckstrand and Professor Michael D. Joner, Physics and Astronomy

The evolution of stars is critical to understanding the universe. Many stars go through a stage of instability in their lifetimes. When they are in this stage they are referred to as “intrinsic variable stars,” or pulsators. These stars pulsate, that is they expand and contract periodically, which causes luminosity variations. The study of intrinsic variable stars helps us to better understand the evolution of these stars.

V402 Cephei (V402 Cep) has previously been considered an unclassified variable star. It has not been classified in part because it had never been studied extensively before I began my observations, but also because the complex multi-periodic nature of its light curves (luminosity graphs, see Figure 1) makes it difficult to classify.

I was able to obtain data from BYU’s 16-inch David Derek Telescope in the Orson Pratt Observatory located in the Eyring Science Center, as well as from both the 12-inch and 16-inch telescopes at BYU’s West Mountain Observatory. With all the data, I have been able to refine the period to 0.1228868 days, with an accuracy of ± 5 x 10-7 days. I was also able to verify that V402 Cep’s primary period does indeed have the shape of a pulsating variable star (see Figure 2). I presented my preliminary results at the College of Physical and Mathematical Sciences’ Spring Research Conference last March, and will present the final ones at the next Spring Research Conference.

An interesting feature of V402 Cep’s light curves is the occurrence of an occasional local maximum. I originally thought that these were isolated events, albeit with an apparently periodic nature. The new data, however, seem to suggest that they might be the result of constructive interference of two or more of the star’s pulsations frequencies. In older data, these small maxima occurred rarely, and at times that showed they were clearly not directly related to the primary period. In more recent data, however, they are ubiquitous. On the night of Oct 8, 2005, they dominate the curve, overpowering the primary period (see Figure 3). This increase of frequency could be explained by two constructively interfering periods, which are more in phase with each other now than they used to be. Unfortunately, technical problems with the frequency-finding program I use, “Star,” caused delays in testing this hypothesis. However, these problems have been resolved, and I have been able to move forward once more.

Using a Fourier-type periodogram analysis, I was able to determine six reasonable frequencies for V402 Cep (see Table 1). The sixth one has a rather low amplitude, but this one, combined with the fourth, may be responsible for the unusual maxima. The ratio between the two is close to the frequency necessary to produce this effect.

One unforeseen problem I encountered this past month was that one new night of data will not phase with the rest of the data (see Figure 4). The cause for this will need to be investigated further. It could be a simple case of a miscalculation of the Julian date for that night, or a more intrinsic phenomenon, such as other frequencies constructively interfering during a typical anomalous maximum, thereby overpowering the primary frequency for a short time.

These unexpected turns have caused a delay in preparing the formal paper for publication. The future will bring a more thorough testing of the six frequencies, and a determination for the misalignment of the data from December 5. Then, at last, I will be able to complete my final paper and submit it to a peer-reviewed Astronomical journal for publication.