On the existence of warm H-rich pulsating white dwarfs
| Autor: | María E. Camisassa, Leandro Gabriel Althaus, Andrzej S. Baran, M. Vučković, Francisco C. De Gerónimo, Roberto Silvotti, Alejandro H. Córsico, Leila M. Calcaferro, Murat Uzundag, Keaton J. Bell, Souza Oliveira Kepler |
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| Rok vydání: | 2019 |
| Předmět: |
010504 meteorology & atmospheric sciences
Star (game theory) FOS: Physical sciences Astrophysics 01 natural sciences Instability purl.org/becyt/ford/1 [https] Ionization Evolucao estelar 0103 physical sciences 010303 astronomy & astrophysics Solar and Stellar Astrophysics (astro-ph.SR) 0105 earth and related environmental sciences Physics White dwarfs White dwarf Order (ring theory) Astronomy and Astrophysics purl.org/becyt/ford/1.3 [https] Effective temperature Evolution [Stars] Stars Astrophysics - Solar and Stellar Astrophysics Anãs brancas Pulsacoes estelares Space and Planetary Science Content (measure theory) Oscillations [Stars] |
| Zdroj: | Repositório Institucional da UFRGS Universidade Federal do Rio Grande do Sul (UFRGS) instacron:UFRGS CONICET Digital (CONICET) Consejo Nacional de Investigaciones Científicas y Técnicas instacron:CONICET |
| DOI: | 10.48550/arxiv.1911.02442 |
| Popis: | The possible existence of warm ($T_{\rm eff}\sim19\,000$ K) pulsating DA white dwarf (WD) stars, hotter than ZZ Ceti stars, was predicted in theoretical studies more than 30 yr ago. However, to date, no pulsating warm DA WD has been discovered. We re-examine the pulsational predictions for such WDs on the basis of new full evolutionary sequences. We analyze all the warm DAs observed by TESS satellite up to Sector 9 in order to search for the possible pulsational signal. We compute WD evolutionary sequences with H content in the range $-14.5 \lesssim \log(M_{\rm H}/M_{\star}) \lesssim -10$, appropriate for the study of warm DA WDs. We use a new full-implicit treatment of time-dependent element diffusion. Non-adiabatic pulsations were computed in the effective temperature range of $30\,000-10\,000$ K, focusing on $\ell= 1$ $g$ modes with periods in the range $50-1500$ s. We find that extended He/H transition zones inhibit the excitation of $g$ modes due to partial ionization of He below the H envelope, and only in the case that the H/He transition is assumed much more abrupt, models do exhibit pulsational instability. In this case, instabilities are found only in WD models with H envelopes in the range of $-14.5 \lesssim \log(M_{\rm H}/M_{\star}) \lesssim -10$ and at effective temperatures higher than those typical of ZZ Ceti stars, in agreement with previous studies. None of the 36 warm DAs observed so far by TESS satellite are found to pulsate. Our study suggests that the non-detection of pulsating warm DAs, if WDs with very thin H envelopes do exist, could be attributed to the presence of a smooth and extended H/He transition zone. This could be considered as an indirect proof that element diffusion indeed operates in the interior of WDs. Comment: 13 pages, 15 figures, 2 tables. Accepted for publication in Astronomy and Astrophysics |
| Databáze: | OpenAIRE |
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