Perpinyà-Vallès, M.Rebassa-Mansergas, A.Gänsicke, B.T.Toonen, S.Hermes, James J.Gentile Fusillo, Nicola PietroTremblay, P.-E.2020-04-102020-04-102019-02-11M. Perpinyà-Vallès, A. Rebassa-Mansergas, B.T. Gänsicke, S. Toonen, J.J. Hermes, N.P. Gentile Fusillo, P.-.E. Tremblay. 2019. "Discovery of the first resolved triple white dwarf." Monthly Notices of the Royal Astronomical Society, Volume 483, Issue 1, pp. 901 - 907. https://doi.org/10.1093/mnras/sty31490035-87111365-2966https://hdl.handle.net/2144/40093We report the discovery of J1953–1019, the first resolved triple white dwarf system. The triplet consists of an inner white dwarf binary and a wider companion. Using Gaia DR2 photometry and astrometry combined with our follow-up spectroscopy, we derive effective temperatures, surface gravities, masses, and cooling ages of the three components. All three white dwarfs have pure-hydrogen (DA) atmospheres, masses of 0.60--0.63M⊙⁠, and cooling ages of 40–290 Myr. We adopt eight initial-to-final mass relations to estimate the main-sequence progenitor masses (which we find to be similar for the three components, 1.6–2.6 M⊙) and lifetimes. The differences between the derived cooling times and main sequence lifetimes agree for most of the adopted initial-to-final mass relations, hence the three white dwarfs in J1953–1019 are consistent with coeval evolution. Furthermore, we calculate the projected orbital separations of the inner white dwarf binary (303.25 ± 0.01 au) and of the centre of mass of the inner binary and the outer companion (⁠6398.97±0.09 au). From these values, and taking into account a wide range of possible configurations for the triplet to be currently dynamically stable, we analyse the future evolution of the system. We find that a collision between the two inner white dwarfs due to Lidov–Kozai oscillations is unlikely, though if it occurs it could result in a sub-Chandrasekhar Type Ia supernova explosion.p. 901 - 907en-US© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical SocietyAstronomical and space sciencesAstronomy & astrophysicsBinaries: closeStars: individual: J1953-1019White dwarfsArticle10.1093/mnras/sty3149503844