KIC 3868420: A high-amplitude $δ$ Scuti-$γ$ Dor hybrid star crossing the Hertzsprung gap
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arXiv
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| Natura: | Preprint |
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2026
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| author | Yang, Tao-Zhi Zuo, Zhao-Yu |
| author_facet | Yang, Tao-Zhi Zuo, Zhao-Yu |
| contents | We report a photometric and asteroseismic analysis of KIC 3868420, a newly identified high-amplitude $δ$ Scuti-$γ$ Doradus hybrid star located in the Hertzsprung gap - a short-lived and rarely observed post-main-sequence phase. Using four years of Kepler long-cadence photometry, we detect 36 significant frequencies, including 11 independent modes spanning both low- and high-frequency regimes. Grid-based modeling with MESA and GYRE, including rotation, shows that five independent frequencies match a combination of radial p-modes and non-radial g-modes, supporting its hybrid nature. The best-fit models yield an evolved post-main-sequence star ($M \sim 2.26 - 2.30 M_\odot$, $R \sim 4.41 - 4.43 R_\odot$, $τ\sim 5.4 \times 10^{8}$ yr), although degeneracies from rotation and unknown inclination preclude a unique solution. KIC 3868420 thus represents a rare example of a high-amplitude hybrid pulsator in the Hertzsprung gap, demonstrating that high-amplitude pulsation can coexist with mixed p/g-mode behavior in a rapidly evolving star. This finding highlights the value of space-based photometry for identifying such rare objects. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_12399 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | KIC 3868420: A high-amplitude $δ$ Scuti-$γ$ Dor hybrid star crossing the Hertzsprung gap Yang, Tao-Zhi Zuo, Zhao-Yu Solar and Stellar Astrophysics We report a photometric and asteroseismic analysis of KIC 3868420, a newly identified high-amplitude $δ$ Scuti-$γ$ Doradus hybrid star located in the Hertzsprung gap - a short-lived and rarely observed post-main-sequence phase. Using four years of Kepler long-cadence photometry, we detect 36 significant frequencies, including 11 independent modes spanning both low- and high-frequency regimes. Grid-based modeling with MESA and GYRE, including rotation, shows that five independent frequencies match a combination of radial p-modes and non-radial g-modes, supporting its hybrid nature. The best-fit models yield an evolved post-main-sequence star ($M \sim 2.26 - 2.30 M_\odot$, $R \sim 4.41 - 4.43 R_\odot$, $τ\sim 5.4 \times 10^{8}$ yr), although degeneracies from rotation and unknown inclination preclude a unique solution. KIC 3868420 thus represents a rare example of a high-amplitude hybrid pulsator in the Hertzsprung gap, demonstrating that high-amplitude pulsation can coexist with mixed p/g-mode behavior in a rapidly evolving star. This finding highlights the value of space-based photometry for identifying such rare objects. |
| title | KIC 3868420: A high-amplitude $δ$ Scuti-$γ$ Dor hybrid star crossing the Hertzsprung gap |
| topic | Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2604.12399 |