8 research outputs found
Asteroseismology of ZZ Ceti stars with fully evolutionary white dwarf models: I. The impact of the uncertainties from prior evolution on the period spectrum
ZZ Ceti stars are pulsating white dwarfs with a carbon-oxygen core build up
during the core helium burning and thermally pulsing Asymptotic Giant Branch
phases. Through the interpretation of their pulsation periods by means of
asteroseismology, details about their origin and evolution can be inferred. The
whole pulsation spectrum exhibited by ZZ Ceti stars strongly depends on the
inner chemical structure. At present, there are several processes affecting the
chemical profiles that are still not accurately determined. We present a study
of the impact of the current uncertainties of the white dwarf formation and
evolution on the expected pulsation properties of ZZ Ceti stars. Our analysis
is based on a set of carbon-oxygen core white dwarf models with masses
and 0.837 M_{\sun} derived from full evolutionary computations from the ZAMS
to the ZZ Ceti domain. We have considered models in which we varied the number
of thermal pulses, the amount of overshooting, and the
CO reaction rate within their uncertainties. We
explore the impact of these major uncertainties in prior evolution on the
chemical structure and the expected pulsation spectrum. We find that these
uncertainties yield significant changes in the -mode pulsation periods. We
conclude that the uncertainties in the white dwarf progenitor evolution should
be be taken into account in detailed asterseismological analysis of these
pulsating stars.Comment: 7 pages, 8 figures. To be published in Astronomy and Astrophysic
Probing the Structure of Kepler ZZ Ceti Stars with Full Evolutionary Models-based Asteroseismology
We present an asteroseismological analysis of four ZZ Ceti stars observed with the Kepler spacecraft: GD 1212, SDSS J113655.17+040952.6, KIC 11911480, and KIC 4552982, based on a grid of full evolutionary models of DA white dwarf (WD) stars. We employ a grid of carbon-oxygen core models, characterized by a detailed and consistent chemical inner profile for the core and the envelope. In addition to the observed periods, we take into account other information from the observational data, such as amplitudes, rotational splittings, and period spacing, as well as photometry and spectroscopy. For each star, we present an asteroseismological model that closely reproduces their observed properties. The asteroseismological stellar mass and effective temperature of the target stars are (0.632 ± 0.027 M⊙, 10737 ± 73 K) for GD 1212, (0.745 ± 0.007 M⊙, 11110 ± 69 K) for KIC 4552982, (05480 ± 0.01 M⊙, 12,721 ± 228 K) for KIC11911480, and (0.570 ± 0.01 M⊙, 12,060 ± 300 K) for SDSS J113655.17+040952.6. In general, the asteroseismological values are in good agreement with the spectroscopy. For KIC 11911480 and SDSS J113655.17+040952.6 we derive a similar seismological mass, but the hydrogen envelope is an order of magnitude thinner for SDSS J113655.17+040952.6, which is part of a binary system and went through a common envelope phase.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat
Asteroseismological analysis of the polluted ZZ Ceti star G29-38 with TESS
G\,2938 (TIC~422526868) is one of the brightest () and closest (\,pc) pulsating white dwarfs with a hydrogen-rich atmosphere (DAV/ZZ
Ceti class). It was observed by the {\sl TESS} spacecraft in sectors 42 and 56.
The atmosphere of G~2938 is polluted by heavy elements that are expected to
sink out of visible layers on short timescales. The photometric {\sl TESS} data
set spans days in total, and from this, we identified 56 significant
pulsation frequencies, that include rotational frequency multiplets. In
addition, we identified 30 combination frequencies in each sector. The
oscillation frequencies that we found are associated with -mode pulsations,
with periods spanning from 260 s to 1400 s. We identified %three
distinct rotational frequency triplets with a mean separation of 4.67 Hz and a quintuplet with a mean separation of 6.67 Hz, from which we estimated a rotation period of
about days. We determined a constant period spacing of 41.20~s
for modes and 22.58\,s for modes. We performed
period-to-period fit analyses and found an asteroseismological model with
, K, and
(with a hydrogen envelope mass of ), in good agreement with the values derived from
spectroscopy. We obtained an asteroseismic distance of 17.54 pc, which is in
excellent agreement with that provided by {\sl Gaia} (17.51 pc).Comment: 17 pages, Accepted for publication in MNRA
Probing the Structure of Kepler ZZ Ceti Stars with Full Evolutionary Models-based Asteroseismology
We present an asteroseismological analysis of four ZZ Ceti stars observed with the Kepler spacecraft: GD 1212, SDSS J113655.17+040952.6, KIC 11911480, and KIC 4552982, based on a grid of full evolutionary models of DA white dwarf (WD) stars. We employ a grid of carbon-oxygen core models, characterized by a detailed and consistent chemical inner profile for the core and the envelope. In addition to the observed periods, we take into account other information from the observational data, such as amplitudes, rotational splittings, and period spacing, as well as photometry and spectroscopy. For each star, we present an asteroseismological model that closely reproduces their observed properties. The asteroseismological stellar mass and effective temperature of the target stars are (0.632 ± 0.027 M⊙, 10737 ± 73 K) for GD 1212, (0.745 ± 0.007 M⊙, 11110 ± 69 K) for KIC 4552982, (05480 ± 0.01 M⊙, 12,721 ± 228 K) for KIC11911480, and (0.570 ± 0.01 M⊙, 12,060 ± 300 K) for SDSS J113655.17+040952.6. In general, the asteroseismological values are in good agreement with the spectroscopy. For KIC 11911480 and SDSS J113655.17+040952.6 we derive a similar seismological mass, but the hydrogen envelope is an order of magnitude thinner for SDSS J113655.17+040952.6, which is part of a binary system and went through a common envelope phase.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat
The composition of massive white dwarfs and their dependence on C-burning modeling
Context. Recent computations of the interior composition of ultra-massive white dwarfs (WDs) have suggested that some WDs could be composed of neon (Ne)-dominated cores. This result is at variance with our previous understanding of the chemical structure of massive WDs, where oxygen is the predominant element. In addition, it is not clear whether some hybrid carbon (C) oxygen (O)-Ne WDs might form when convective boundary mixing is accounted for during the propagation of the C-flame in the C-burning stage. Both the Ne-dominated and hybrid CO-Ne core would have measurable consequences for asteroseismological studies based on evolutionary models.
Aims. In this work, we explore in detail to which extent differences in the adopted micro- and macro-physics can explain the different final WD compositions that have been found by different authors. Additionally, we explore the impact of such differences on the cooling times, crystallization, and pulsational properties of pulsating WDs.
Methods. We performed numerical simulations of the evolution of intermediate massive stars from the zero age main sequence to the WD stage varying the adopted physics in the modeling. In particular, we explored the impact of the intensity of convective boundary mixing during the C-flash, extreme mass-loss rates, and the size of the adopted nuclear networks on the final composition, age, as well crystallization and pulsational properties of WDs.
Results. In agreement with previous authors, we find that the inclusion of convective boundary mixing quenches the carbon flame leading to the formation of hybrid CO-Ne cores. Based on the insight coming from 3D hydro-dynamical simulations, we expect that the very slow propagation of the carbon flame will be altered by turbulent entrainment affecting the inward propagation of the flame. Also, we find that Ne-dominated chemical profiles of massive WDs recently reported appear in their modeling due to a key nuclear reaction being overlooked. We find that the inaccuracies in the chemical composition of the ultra-massive WDs recently reported lead to differences of 10% in the cooling times and degree of crystallization and about 8% in the period spacing of the models once they reach the ZZ Ceti instability strip
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Revista Temas Agrarios Volumen 26; Suplemento 1 de 2021
1st International and 2nd National Symposium of Agronomic Sciences: The rebirth of the scientific discussion space for the Colombian Agro.1 Simposio Intenacional y 2 Nacional de Ciencias Agronómicas: El renacer del espacio de discusión científica para el Agro colombiano