RU Psc: A Period Shifting Variable Star

03/28/2019 - 3:30pm
Blazer Dining 339
Speaker(s) / Presenter(s): 
Ron Wilhelm
Radially pulsating variable stars found in the instability strip on the H-R Diagram have been known for
over a century now. For these stars, the principle mechanism causing pulsation has also been
understood for many decades. There remains, however, two pulsation characteristics that have never
been fully explained. These are the well-studied, Blazhko Effect and the period shifting variable stars.
The former effect causes periodic changes to the maximum brightness of the variable, while the later
causes the pulsation period to increase and decrease in a random fashion. Period shifting has not been
studied in detail to date and is often assumed to be a by-product of the Blazhko Effect. The period
shifting effect has been seen often in large variable star surveys where the period shifting occurs for
anywhere between 10 and 30% of the variables survived.
We have begun a program to explore the period shifting effect in RR Lyrae variables by investigating
the properties of a well known, bright, period shifting variable, RU Psc. Observations over the course
of nine years show random period shifts that amount to variations as large as 30 seconds/cycle. This
data also shows that RU Psc has temporal delays in its maximum light (up to 30 minutes) and a small
flicker in the maximum brightness which amounts to a variation of about 1.5%. High precision
observations conducted at the MacAdam Student Observatory during the Fall 2018, show a strong
correlation between the size of the rising compression hump and the delay in maximum light. This
suggests that the period shifting is likely related to intermittent shock waves that periodically occur
during the maximum compression phase. I will also discuss the differences between the shocks found
in Blazhko stars and that of RU Psc, which indicates that a mechanism, different from that of the
Blazhko Effect, is likely the cause of the period shifting phenomenon.
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