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arXiv 2408.05482astro-ph.SR
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β Hydri 的 TESS 星震学研究:一颗拥有“重生”发电机的亚巨星

TESS asteroseismology of $β$ Hydri: a subgiant with a born-again dynamo

Travis S. Metcalfe, Jennifer L. van Saders, Daniel Huber, Derek Buzasi, Rafael A. Garcia, Keivan G. Stassun, Sarbani Basu, Sylvain N. Breton, Zachary R. Claytor… 展开作者

Travis S. Metcalfe, Jennifer L. van Saders, Daniel Huber, Derek Buzasi, Rafael A. Garcia, Keivan G. Stassun, Sarbani Basu, Sylvain N. Breton, Zachary R. Claytor, Enrico Corsaro, Martin B. Nielsen, J. M. Joel Ong, Nicholas Saunders, Amalie Stokholm, Timothy R. Bedding

AI总结:

本文利用 TESS 星震学直接测量了亚巨星 β Hyi 的自转周期和基本参数,发现其自转与减弱磁制动一致,并支持亚巨星中存在“重生”发电机以维持磁活动周期。

摘要:

太阳型亚巨星 β Hyi 长期以来被作为太阳的老年类比天体进行研究。尽管其自转周期从未被直接测量过,但据估计接近 27 天。作为南半球目标,它未被长期恒星活动巡天监测,但档案中的国际紫外探测器(International Ultraviolet Explorer)数据揭示了一个 12 年的活动周期。先前的地基星震学研究提示该恒星比太阳质量略大、体积明显更大且更年老,因此其自转速率和活动周期长度与太阳值的相似性令人困惑。我们利用来自凌星系外行星巡天卫星(Transiting Exoplanet Survey Satellite,TESS)的两个月高精度时序测光数据,在 β Hyi 中探测到类太阳振荡,并通过星震学建模确定了其基本恒星参数。我们还获得了自转周期的直接测量值,此前该值是由紫外活动-自转关系估算得到的。随后,我们利用自转演化模型预测了标准自转减慢或减弱磁制动(weakened magnetic braking,WMB)两种情形下预期的自转周期。我们得出结论:β Hyi 的自转周期与减弱磁制动情形一致,并且亚巨星支上恒星结构的变化能够重新激发大尺度发电机并短暂维持磁活动周期。我们的结果支持在演化后的亚巨星中存在“重生”发电机——此前为解释 94 Aqr Aa 的活动周期而提出——这一现象可以在减弱磁制动情景中得到最好的理解。

英文摘要:

The solar-type subgiant $β$ Hyi has long been studied as an old analog of the Sun. Although the rotation period has never been measured directly, it was estimated to be near 27 days. As a southern hemisphere target it was not monitored by long-term stellar activity surveys, but archival International Ultraviolet Explorer data revealed a 12 year activity cycle. Previous ground-based asteroseismology suggested that the star is slightly more massive and substantially larger and older than the Sun, so the similarity of both the rotation rate and the activity cycle period to solar values is perplexing. We use two months of precise time-series photometry from the Transiting Exoplanet Survey Satellite (TESS) to detect solar-like oscillations in $β$ Hyi and determine the fundamental stellar properties from asteroseismic modeling. We also obtain a direct measurement of the rotation period, which was previously estimated from an ultraviolet activity-rotation relation. We then use rotational evolution modeling to predict the rotation period expected from either standard spin-down or weakened magnetic braking (WMB). We conclude that the rotation period of $β$ Hyi is consistent with WMB, and that changes in stellar structure on the subgiant branch can reinvigorate the large-scale dynamo and briefly sustain magnetic activity cycles. Our results support the existence of a "born-again" dynamo in evolved subgiants -- previously suggested to explain the cycle in 94 Aqr Aa -- which can best be understood within the WMB scenario.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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