Systematic Identification of g-Mode Pulsations in Subdwarf B Stars for Kepler Data
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2025
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| author | Guyot, Nathan |
| author_facet | Guyot, Nathan |
| contents | <div> <div> <div> <p>The Kepler and TESS space missions have revealed the g-mode pulsation spectra of many sdB stars, showing complex behaviors, with some stars exhibiting trapped modes interposed in the asymptotic period sequences of regular period spacing, while others do not. We used the STELUM (STELlar modeling at the Université de Montréal) to compute static and evolutionary models of sdB stars with different prescriptions for their chemical and thermal structures, and our PULSE code to compute their associated theoretical spectra from degrees l=1 to l=4 and for periods between 1000s and 15000s, thus covering the range of observed g-modes in such stars. Our results show that the structure of g- modes spectra, and notably the appearance of trapped modes, are dependent on the chemical and thermal structures of the models, and in particular on the region above the He-burning core. We mainly observe three flavors of spectra for mid to high radial orders g-modes: ”flat” spectra of nearly constant period spacing, spectra with regular mode trapping, and spectra of ”wavy” patterns in period spacing. In the two later types of spectra, we identified the region where modes are trapped in the star. The next natural step is comparing observed g-mode spectra to our theoretical models to constrain by asteroseismology the internal structure of sdB stars, and in particular the region above the He-burning core. This starts by extracting and analyzing the g-modes frequencies from available observations, which reach hundreds of frequencies in Kepler datasets, including rotational multiplets and frequency modulation effects. Given this large number of frequencies, and rotational multiplets generally being present for only a minority of them, identifying the degree of each frequency, and thus the pulsation spectra associated to a star, is complex and often includes an arbitrary component, especially in the case of stars presenting mode trapping. We thus aim at making mode identification a systematic process for slow rotating sdB pulsators, through a genetic algorithm currently in development. The latter takes advantages of continuous sequences of l=1 and l=2 modes found in Kepler data for sdB stars, overlapping properties between degrees, and offsets in periods induced by mode trapping, to infer the most likely degree for a given frequency.</p> </div> </div> </div> |
| format | Recurso digital |
| id | zenodo_https___doi_org_10_5281_zenodo_15814300 |
| institution | Zenodo |
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| publishDate | 2025 |
| publisher | Zenodo |
| record_format | zenodo |
| spellingShingle | Systematic Identification of g-Mode Pulsations in Subdwarf B Stars for Kepler Data Guyot, Nathan Session 4: Pulsations & Asteroseismology <div> <div> <div> <p>The Kepler and TESS space missions have revealed the g-mode pulsation spectra of many sdB stars, showing complex behaviors, with some stars exhibiting trapped modes interposed in the asymptotic period sequences of regular period spacing, while others do not. We used the STELUM (STELlar modeling at the Université de Montréal) to compute static and evolutionary models of sdB stars with different prescriptions for their chemical and thermal structures, and our PULSE code to compute their associated theoretical spectra from degrees l=1 to l=4 and for periods between 1000s and 15000s, thus covering the range of observed g-modes in such stars. Our results show that the structure of g- modes spectra, and notably the appearance of trapped modes, are dependent on the chemical and thermal structures of the models, and in particular on the region above the He-burning core. We mainly observe three flavors of spectra for mid to high radial orders g-modes: ”flat” spectra of nearly constant period spacing, spectra with regular mode trapping, and spectra of ”wavy” patterns in period spacing. In the two later types of spectra, we identified the region where modes are trapped in the star. The next natural step is comparing observed g-mode spectra to our theoretical models to constrain by asteroseismology the internal structure of sdB stars, and in particular the region above the He-burning core. This starts by extracting and analyzing the g-modes frequencies from available observations, which reach hundreds of frequencies in Kepler datasets, including rotational multiplets and frequency modulation effects. Given this large number of frequencies, and rotational multiplets generally being present for only a minority of them, identifying the degree of each frequency, and thus the pulsation spectra associated to a star, is complex and often includes an arbitrary component, especially in the case of stars presenting mode trapping. We thus aim at making mode identification a systematic process for slow rotating sdB pulsators, through a genetic algorithm currently in development. The latter takes advantages of continuous sequences of l=1 and l=2 modes found in Kepler data for sdB stars, overlapping properties between degrees, and offsets in periods induced by mode trapping, to infer the most likely degree for a given frequency.</p> </div> </div> </div> |
| title | Systematic Identification of g-Mode Pulsations in Subdwarf B Stars for Kepler Data |
| topic | Session 4: Pulsations & Asteroseismology |
| url | https://doi.org/10.5281/zenodo.15814300 |