Whole Earth Telescope observations of the subdwarf B star KPD 1930+2752: a rich, short-period pulsator in a close binary

Abstract

KPD 1930+2752 is a short‐period pulsating subdwarf B (sdB) star. It is also an ellipsoidal variable with a known binary period of 2.3 h. The companion is most likely a white dwarf and the total mass of the system is close to the Chandresekhar limit. In this paper, we report the results of Whole Earth Telescope (WET) photometric observations during 2003 and a smaller multisite campaign of 2002. From 355 h of WET data, we detect 68 pulsation frequencies and suggest an additional 13 frequencies within a crowded and complex temporal spectrum between 3065 and 6343 μHz (periods between 326 and 157 s). We examine pulsation properties including phase and amplitude stability in an attempt to understand the nature of the pulsation mechanism. We examine a stochastic mechanism by comparing amplitude variations with simulated stochastic data. We also use the binary nature of KPD 1930+2752 for identifying pulsation modes via multiplet structure and a tidally induced pulsation geometry. Our results indicate a complicated pulsation structure that includes short‐period (≈16 h) amplitude variability, rotationally split modes, tidally induced modes and some pulsations which are geometrically limited on the sdB star.

Filling the gap between synchronized and non-synchronized sdBs in short-period sdBV+dM binaries with TESS: TIC 137608661, a new system with a well-defined rotational splitting

“…Resonance between tides and g-modes pulsations is predicted by theory (Zahn 1975(Zahn , 1977Preece et al 2018) and may have been seen in a few sdB pulsators (e.g. Reed et al 2011;Silvotti et al 2014).…”

“…• A clear detection of rotational splitting is missing in KPD 1930+2752, an sdB+WD binary with an orbital period of only 2.3 hours that shows ellipsoidal variations (Billéres et al 2000;Reed et al 2011) nized or very close to synchronization.…”

Asteroseismic Observations of Hot Subdwarfs

“…Maxted et al (2000) stimulate further interest in the system; their spectra suggest a total mass for the system of 1.47M ⊙ , if the sdB star has the canonical 0.5M ⊙ , making it a candidate Type Ia Supernova Progenitor as gravitational radiation will eventually result in binary component merger. Reed et al (2011b) report photometric observations of V2214 Cyg they make during 2003 with WET, and a smaller multisite campaign made in 2002. Sixty-eight pulsation frequencies are found in 355 hours of WET data, these showing many of the stochastic characteristics seen in PG 0048 + 091.…”

Multiyear and multisite photometric campaigns on the bright high-amplitude pulsating subdwarf B star EC 01541-1409

“…During three nights in 2008, EC 01541 appeared to have been amplitude and phase stable, but was not during 2009. We examined amplitude and phase stability, which has been used to infer stochastically excited oscillations in the sdBV star PG 0048 (Reed et al 2007a) and possibly KPD 1930 (Reed et al 2011b). While during 2009 the amplitudes varied, they were insufficient to be stochastically driven and the phases were reasonably stable.…”