Kepler, S.O.Winget, D.E.Vanderbosch, Zachary P.Castanheira, Barbara GarciaHermes, J.J.Bell, Keaton J.Mullally, FergalRomero, Alejandra D.Montgomery, M.H.DeGennaro, StevenWinget, Karen I.Chandler, DeanJeffery, Elizabeth J.Fritzen, Jamile K.Williams, Kurtis A.Chote, PaulZola, Staszek2021-03-112021-03-11S.O. Kepler, D.E. Winget, Zachary P Vanderbosch, Barbara Garcia Castanheira, J.J. Hermes, Keaton J Bell, Fergal Mullally, Alejandra D Romero, M.H. Montgomery, Steven DeGennaro, Karen I Winget, Dean Chandler, Elizabeth J Jeffery, Jamile K Fritzen, Kurtis A Williams, Paul Chote, Staszek Zola. "The Pulsating White Dwarf G117-B15A: Still the Most Stable Optical Clock Known." The Astrophysical Journal, Volume 906, Issue 1, pp. 7 - 7. https://doi.org/10.3847/1538-4357/abc6261538-4357https://hdl.handle.net/2144/42242The pulsating hydrogen atmosphere white dwarf star G 117-B15A has been observed since 1974. Its main pulsation period at 215.19738823(63) s, observed in optical light curves, varies by only (5.12 ± 0.82) × 10−15 s s−1 and shows no glitches, as pulsars do. The observed rate of period change corresponds to a change of the pulsation period by 1 s in 6.2 million yr. We demonstrate that this exceptional optical clock can continue to put stringent limits on fundamental physics, such as constraints on interaction from hypothetical dark matter particles, as well as to search for the presence of external substellar companions.p. 7en-US© 2020. The American Astronomical Society. All rights reserved.White dwarf starsLate stellar evolutionAstronomical and space sciencesAtomic, molecular, nuclear, particle and plasma physicsPhysical chemistry (incl. structural)Astronomy & astrophysicsArticle10.3847/1538-4357/abc626589198