AAVSO: American Association of Variable Star Observers

Continued Period Changes in BW Vulpeculae

Volume 48 number 1 (2020)

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David E. Cowall
Member, American Association of Variable Star Observers 20361 Nanticoke Drive, Nanticoke, MD 21840; cowall@comcast.net
Brian A. Skiff
Research Assistant, Lowell Observatory 1400 West Mars Hill Road, Flagstaff, AZ 86001; bas@lowell.edu
Andrew P. Odell
Emeritus Associate Professor of Physics and Astronomy Northern Arizona University (deceased May 2019)


BW Vulpeculae (BW Vul) has the largest amplitude of the β Cephei stars. Over almost 80 years of observations, BW Vul has closely followed a parabolic ephemeris and possibly a light-travel-time effect. This parabola, with excursions on either side, also could be viewed as a sequence of straight lines (constant period) with abrupt period increases. This paradigm predicted a period increase around 2004, which did not occur. A recent observing campaign on this star using the AAVSOnet’s Bright Star Monitor telescopes as well as the 0.7-m Lowell Observatory telescope has been undertaken. A period analysis of our data suggests that the period may have paradoxically decreased beginning around 2009. Further observations are necessary to confirm this analysis.