SPIRou monitoring of the protostar V347 Aur: Binarity, magnetic fields, pulsed dynamo and accretion

IF 4.7 3区 物理与天体物理 Q1 ASTRONOMY & ASTROPHYSICS Monthly Notices of the Royal Astronomical Society Pub Date : 2024-09-05 DOI:10.1093/mnras/stae2076
J-F Donati, P I Cristofari, A Carmona, K Grankin
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Abstract

We present in this paper an analysis of near-infrared observations of the 0.3 M⊙ protostar V347 Aur collected with the SPIRou high-resolution spectropolarimeter and velocimeter at the 3.6-m Canada-France-Hawaii Telescope from October 2019 to April 2023. From a set of 79 unpolarized and circularly polarized spectra of V347 Aur to which we applied Least-Squares Deconvolution (LSD), we derived radial velocities and longitudinal fields, along with their temporal variations over our monitoring campaign of 1258 d. Our data show that V347 Aur is an eccentric binary system with an orbital period 154.6 ± 0.7 d, experiencing strong to extreme accretion events near periastron. The companion is a 29.0 ± 1.6${\rm M}_{2\!_{4}}$ brown dwarf, a rare member of the brown dwarf desert of close companions around M dwarfs. We detect weak longitudinal fields (<100 G) at the surface of V347 Aur, significantly weaker than those of more evolved prototypical T Tauri stars. These fields show small-amplitude rotational modulation, indicating a mainly axisymmetric parent large-scale magnetic topology, and larger fluctuations at half the orbital period, suggesting that what we dub a ‘pulsed dynamo’ triggered by orbital motion and pulsed accretion operates in V347 Aur. Applying Zeeman-Doppler imaging to our circularly polarised LSD profiles, we find that the large-scale field of V347 Aur is mainly toroidal for most of our observations, with the toroidal component switching sign near periastron and apoastron. The weak large-scale dipole (≃ 30 G) is not able to disrupt the disc beyond 1.3 R⋆ even at the lowest accretion rates, implying longitudinally distributed (rather than localized) accretion at the surface of the protostar.
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对 V347 Aur 号原恒星的 SPIRou 监测:二体性、磁场、脉冲动力和吸积
本文分析了2019年10月至2023年4月期间利用3.6米加拿大-法国-夏威夷望远镜的SPIRou高分辨率分光测极计和测速计对0.3 M⊙原恒星V347 Aur进行的近红外观测。我们的数据显示,V347 Aur 是一个偏心双星系统,轨道周期为 154.6 ± 0.7 d,在近主星附近经历了强烈到极端的吸积事件。它的伴星是一颗 29.0 ± 1.6${rm M}_{2\!_{4}}$褐矮星,是 M 矮星周围褐矮星沙漠中罕见的近伴星。我们在V347 Aur的表面探测到了微弱的纵向场(<100 G),明显弱于那些进化程度更高的原型金牛座恒星。这些磁场显示出小振幅的旋转调制,表明主要是轴对称的母体大尺度磁拓扑结构,而在轨道周期的一半处则有较大的波动,这表明我们称之为 "脉冲动力 "的、由轨道运动和脉冲吸积引发的磁场在 V347 Aur 星中运行。将泽曼-多普勒成像技术应用到我们的圆偏振 LSD 曲线上,我们发现 V347 Aur 的大尺度场在我们的大部分观测中主要是环状的,环状成分在近主星和远主星附近会发生符号转换。即使在最低的吸积率下,微弱的大尺度偶极子(≃ 30 G)也无法扰乱超过 1.3 R⋆的圆盘,这意味着原恒星表面的吸积是纵向分布的(而不是局部的)。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
CiteScore
9.10
自引率
37.50%
发文量
3198
审稿时长
3 months
期刊介绍: Monthly Notices of the Royal Astronomical Society is one of the world''s leading primary research journals in astronomy and astrophysics, as well as one of the longest established. It publishes the results of original research in positional and dynamical astronomy, astrophysics, radio astronomy, cosmology, space research and the design of astronomical instruments.
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