Period variation in BW Vulpeculae redux

TL;DR

Over 25 years of monitoring BW Vulpeculae revealed that its period remains constant for decades, contradicting previous models of secular and binary-induced period variations, with abrupt changes followed by long epochs of stability.

Contribution

This study provides the longest continuous photometric dataset showing that BW Vul's period changes are abrupt and episodic, challenging earlier interpretations of gradual period variations.

Findings

Period has remained constant for the last 32 years.

Expected period increase around 2001 did not occur.

Period changes are abrupt, with long stable epochs.

Abstract

For the past 25 years, BW Vulpeculae has been the topic of period analyses centered on a secular period change with a periodic variation superposed, presumed to be due to light time effects in a binary system. According to this paradigm, one would expect what seems like a period increase of about 0.5 s during or soon after the year 2001. I have continued photometric monitoring through the year 2012, adding 35 new timings of maximum and minimum light. This expected change in period did not occur, which rules out that interpretation of the period variation. As of 2012, the observed timings are about two hours early compared to those predicted by the quadratic ephemeris, but are very close to those predicted by the linear ephemeris. In fact, the period has remained constant for the last 32 years, indicating that the previous epochs of constant period are almost certainly the correct interpretation, though the cause of the period changes is still not clear. Continued photometric monitoring of BW Vul leads to the conclusion that the period changes are abrupt, followed by epochs of constant period lasting between 12 and at least 32 years.