用SPIRou观测M矮星小尺度磁场的旋转调制和长期演化

IF 5.8 2区 物理与天体物理 Q1 ASTRONOMY & ASTROPHYSICS
P. I. Cristofari, J.-F. Donati, S. Bellotti, É. Artigau, A. Carmona, C. Moutou, X. Delfosse, P. Petit, B. Finociety, J. Dias do Nascimento
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引用次数: 0

摘要

上下文。众所周知,M矮星拥有磁场,影响着系外行星的研究,并在恒星和行星的形成和演化中发挥着关键作用。观测约束对于指导被认为是这些场起源的发电机过程的理论至关重要,特别是对于内部结构不同于部分对流恒星的完全对流恒星。观测结果揭示了用塞曼-多普勒成像重建的大尺度磁场的长期演变及其拓扑结构的多样性。然而,这些大规模的磁场只占恒星表面无符号磁通量的一小部分,可以通过直接模拟非极化光谱中谱线的塞曼展宽来探测。我们的目标是研究完全对流和部分对流M矮星的平均小尺度磁场随时间的长期行为,并评估我们检测旋转调制和从非极化光谱获得的场测量时间序列中检索旋转周期的能力。在SLS和SPICE大型项目的背景下,我们将2019年至2024年期间用ZeeTurbo计算的合成光谱与SPIRou记录的近红外高分辨率光谱进行了拟合。对两颗部分对流M矮星(AD狮子座和DS狮子座)和三颗完全对流M矮星(PM J18482+0741、CN狮子座和巴纳德恒星)以及质量接近完全对流极限的EV Lac进行了光谱分析。我们的分析提供了平均小尺度磁场的测量结果,并将其与从相同数据中获得的纵向磁场和温度变化测量(dTemp)进行了比较。我们在样本中6颗恒星中的4颗的小尺度磁场序列中检测到了自转周期。我们发现平均磁场全年变化可达0.3 kG(例如,CN狮子座),或在旋转阶段变化可达1 kG(例如,EV Lac)。从纵向磁场和小尺度磁场反演的自转周期在误差条内一致。dTemp的测量结果被发现与三颗恒星(EV Lac, DS Leo和Barnard 's star)的小尺度磁场测量结果反相关。结果表明,只要观测目标的倾角足够大,我们有能力通过小尺度磁场测量,从高分辨率数据测量旋转周期。我们观察到平均磁场的长期波动,这可能表明母发电机过程中的磁周期。这些长期变化似乎主要与通过纵向磁场测量探测到的大尺度磁场变化无关。旋转调制信号振幅的巨大变化,尤其暗示了塞曼展宽测量所能达到的表面不均匀性分布的变化。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Rotational modulation and long-term evolution of the small-scale magnetic fields of M dwarfs observed with SPIRou
Context. M dwarfs are known to host magnetic fields, impacting exoplanet studies and playing a key role in stellar and planetary formation and evolution. Observational constraints are essential to guide theories of dynamo processes believed to be at the origin of those fields, in particular for fully convective stars whose internal structure differs from that of partially convective stars. Observations reveal long-term evolution of the large-scale magnetic field reconstructed with Zeeman-Doppler imaging, and a diversity of their topologies. These large-scale magnetic fields, however, only account for a small amount of the unsigned magnetic flux at the stellar surface that can be probed by directly modeling the Zeeman broadening of spectral lines in unpolarized spectra.Aims. We aim to investigate the long-term behavior of the average small-scale magnetic field of fully convective and partially convective M dwarfs with time, and assess our ability to detect rotational modulation and retrieve rotation periods from time series of field measurements derived from unpolarized spectra.Methods. We performed fits of synthetic spectra computed with ZeeTurbo to near-infrared high-resolution spectra recorded with SPIRou between 2019 and 2024 in the context of the SLS and SPICE large programs. The analysis was performed on the spectra of two partially convective (AD Leo and DS Leo) and three fully convective (PM J18482+0741, CN Leo, and Barnard’s star) M dwarfs, along with EV Lac, whose mass is close to the fully convective limit. Our analysis provides measurements of the average small-scale magnetic field, which are compared to longitudinal magnetic field and temperature variation measurements (dTemp) obtained from the same data.Results. We detected the rotation period in the small-scale magnetic field series for four of the 6 stars in our sample. We find that the average magnetic field can vary by up to 0.3 kG throughout the year (e.g., CN Leo), or of up to 1 kG across rotation phases (e.g., EV Lac). The rotation periods retrieved from longitudinal and small-scale magnetic fields are found to agree within error bars. The dTemp measurements are found to anti-correlate with small-scale magnetic field measurements for three stars (EV Lac, DS Leo, and Barnard’s star).Conclusions. The results demonstrate our ability to measure rotation periods from high-resolution data through small-scale magnetic field measurements, provided that the inclination of the observed targets is sufficiently large. We observe long-term fluctuations of the average magnetic field that could indicate magnetic cycles in the parent dynamo processes. These long-term variations appear mainly uncorrelated with large-scale magnetic field variations probed through longitudinal field measurements. Large variations in the amplitude of the rotationally modulated signals, in particular, hint towards a change in the distribution of the surface inhomogeneities accessible to Zeeman broadening measurements.
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来源期刊
Astronomy & Astrophysics
Astronomy & Astrophysics 地学天文-天文与天体物理
CiteScore
10.20
自引率
27.70%
发文量
2105
审稿时长
1-2 weeks
期刊介绍: Astronomy & Astrophysics is an international Journal that publishes papers on all aspects of astronomy and astrophysics (theoretical, observational, and instrumental) independently of the techniques used to obtain the results.
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