Browsing by Author "Corsico, Alejandro H."

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    Impact of Current Uncertainties in the 12C+12C Nuclear Reaction Rate on Intermediate-mass Stars and Massive White Dwarfs
    (2024) De Geronimo, Francisco C.; Bertolami, Marcelo M. Miller; Battich, Tiara; Tang, Xiaodong; Catelan, Marcio; Corsico, Alejandro H.; Li, Yunjun; Fang, Xiao; Althaus, Leandro G.
    Recent determinations of the total rate of the 12C+12C nuclear reaction show non-negligible differences with the reference reaction rate commonly used in previous stellar simulations. In addition, the current uncertainties in determining each exit channel constitute one of the main uncertainties in shaping the inner structure of super asymptotic giant branch stars that could have a measurable impact on the properties of pulsating ultramassive white dwarfs (WDs). We explore how new determinations of the nuclear reaction rate and its branching ratios affect the evolution of WD progenitors. We show that the current uncertainties in the branching ratios constitute the main uncertainty factor in determining the inner composition of ultramassive WDs and their progenitors. We found that the use of extreme branching ratios leads to differences in the central abundances of 20Ne of at most 17%, which are translated into differences of at most 1.3% and 0.8% in the cooling times and size of the crystallized core, respectively. However, the impact on the pulsation properties is small, less than 1 s for the asymptotic period spacing. We found that the carbon burns partially in the interior of ultramassive WD progenitors within a particular range of masses, leaving a hybrid CONe-core composition in their cores. The evolution of these new kinds of predicted objects differs substantially from the evolution of objects with pure CO cores. Differences in the size of the crystallized core and cooling times of up to 15% and 6%, respectively, lead to distinct patterns in the period spacing distribution.
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    WD J004917.14-252556.81: the most massive pulsating white dwarf
    (2023) Kilic, Mukremin; Corsico, Alejandro H.; Moss, Adam G.; Jewett, Gracyn; De Geronimo, Francisco C.; Althaus, Leandro G.
    We present Apache Point Observatory (APO) and Gemini time-series photometry of WD J004917.14-252556.81, an ultramassive DA white dwarf with T-eff = 13 020 K and log g = 9.34. We detect variability at two significant frequencies, making J0049-2525 the most massive pulsating white dwarf currently known with M-circle dot = 1.31 M-circle dot (for a CO core) or 1.26 M-circle dot(for an ONe core). J0049-2525 does not display any of the signatures of binary mergers, there is no evidence of magnetism, large tangential velocity, or rapid rotation. Hence, it likely formed through single star evolution and is likely to have an ONe core. Evolutionary models indicate that its interior is greater than or similar to 99 per cent crystallized. Asteroseismology offers an unprecedented opportunity to probe its interior structure. However, the relatively few pulsation modes detected limit our ability to obtain robust seismic solutions. Instead, we provide several representative solutions that could explain the observed properties of this star. Extensive follow-up time-series photometry of this unique target has the potential to discover a significant number of additional pulsation modes that would help overcome the degeneracies in the asteroseismic fits, and enable us to probe the interior of an approximate to 1.3 M-circle dot crystallized white dwarf.