Period Variation in BW Vulpeculae (Abstract)

Volume 46 number 1 (2018)

David E. Cowall

20361 Nanticoke Drive, Nanticoke, MD 21840; cowall@comcast.net

Andrew P. Odell

Department of Physics and Astronomy, Northern Arizona University, Flagstaff, AZ 86001

Abstract

(Abstract only) BW Vulpeculae (BW Vul) has the largest amplitude of the β Cephei stars. An observing campaign on this star using the AAVSOnet’s Bright Star Monitor (BSM) telescopes was begun in December of 2015 and has yielded 66 nights of observations to date. A period analysis will be presented using the BSM data set in combination with unpublished data from the Lowell Observatory. Over almost 80 years of observations, BW Vul has closely followed a parabolic ephemeris (period increasing by 2.4 seconds/century) plus 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. The first paradigm predicted a necessary change in slope around 2004, which did not occur. Instead, the period decreased abruptly in 2009. That maximum occurred 250 minutes early compared to the first paradigm, and about 25 minutes early compared to the straight-line paradigm from 1982–2009.