Seismic Cartography of White-Dwarf Interiors From the Toulouse-Montréal Optimal-Design Approach

• DOI: 10.3389/fspas.2022.879045
• Publication Date: 2022-06-14T07:59:28Z
• Authors: Noemi Giammichele; Stéphane Charpinet; Pierre Brassard
• Keywords: Asteroseismology; Stellar structure

Probing internal properties of white-dwarf stars has been amongst the earliest objectives asteroseismology, following first discovery in late 1960s non-radial pulsations these evolved compact stars. It was swiftly recognized that pulsators could offer new opportunities to unravel their inner structure and dynamics from observed low-degree, low-order gravity ( g -)modes. From early days on, many approaches have attempted fully exploit this potential, with various levels success. Here, we review most recent efforts our group perform a complete seismic cartography interiors. Our approach involves models incorporating flexible profiles for main chemical constituents (H, He, C, O) are optimized, along other fundamental parameters T eff log ), determine stellar best reproduces period spectrum given star. The method is meant reduce as much possible solution dependency relative evolution uncertainties. outcome full model pulsating star under consideration, including its core envelope stratification. Searching solutions do not depend on calculations key requirement strategy. Late stages ultimately shape white dwarf known rely still uncertain processes. One hopes be able test processes, therefore requiring incorporate strong preconceived expectations evolutionary models. We present discuss results obtained so far application handful DB DA pulsators. In all cases, significant qualitative improvements obtained, providing an quantitative constraints particular, consistently find homogeneous C/O mixed core, inherited helium-burning phase, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m1"><mml:mo>∼</mml:mo><mml:mn>40</mml:mn><mml:mi>%</mml:mi></mml:math> larger (in mass) id="m2"><mml:mo>∼</mml:mo><mml:mn>15</mml:mn><mml:mi>%</mml:mi></mml:math> richer oxygen mass fraction) than expected standard calculations. Such constitute precious guidelines modeling better understanding constitutive physics. As illustration this, show central fraction measured by seismology can indeed reproduced when cores experience so-called breathing pulses. latter usually suppressed calculations, result old debate whether such events real or numerical artefacts. words, determination amount dwarfs provides evidence pulses occurred progenitors should dismissed after all.