HD 12098：一颗斜脉动 roAp 星中高度畸变的偶极模
HD 12098: a highly distorted dipole mode in an obliquely pulsating roAp star
AI总结：
该研究利用 TESS 数据揭示 roAp 星 HD 12098 具有迄今最畸变的偶极模，周期 7.85 分钟，磁极处存在光度斑点，并发现模式选择难题及与理论不符的低频 p 模和可能 g 模。
摘要：
HD 12098 是一颗 roAp 星，其脉动模式是迄今在该类恒星中观测到的最畸变的偶极模。利用 TESS 第 58 扇区的观测数据，我们表明该恒星的两个磁极处均存在光度斑点。它主要以一颗强畸变的偶极模进行斜脉动，周期为 $P_{\ m puls} = 7.85$ 分钟（$\ u_{\ m puls} = 183.34905$ 天$^{-1}$；2.12210 毫赫兹），这在振幅谱中产生了一个不寻常的四重态。我们的磁脉动模型无法解释一个半球内脉动的强畸变，尽管在另一个半球是成功的。存在高频 overtone p 模，其频率间隔大于大间隔，这是模式选择中的一个难题。在 TESS 数据中观测到的模式频率与先前在地面 Johnson $B$ 波段数据中观测到的频率范围相同，但并非相同的模式。因此，该恒星要么改变了模式，要么不同大气深度处的观测探测到了不同的模式。此外，还存在一个低频 overtone p 模，以及可能存在的 g 模，而这些在理论上并不预期，因为该恒星观测到有 $> 1$ 千高斯的磁场。
英文摘要：
HD 12098 is an roAp star pulsating in the most distorted dipole mode yet observed in this class of star. Using TESS Sector 58 observations we show that there are photometric spots at both the magnetic poles of this star. It pulsates obliquely primarily in a strongly distorted dipole mode with a period of $P_{\rm puls} = 7.85$ min ($ν_{\rm puls} = 183.34905$ d$^{-1}$; 2.12210 mHz) that gives rise to an unusual quadruplet in the amplitude spectrum. Our magnetic pulsation model cannot account for the strong distortion of the pulsation in one hemisphere, although it is successful in the other hemisphere. There are high-overtone p~modes with frequencies separated by more than the large separation, a challenging problem in mode selection. The mode frequencies observed in the TESS data are in the same frequency range as those previously observed in ground-based Johnson $B$ data, but are not for the same modes. Hence the star has either changed modes, or observations at different atmospheric depth detect different modes. There is also a low-overtone p mode and possibly g modes that are not expected theoretically with the $> 1$ kG magnetic field observed in this star.
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