发表机构
Uppsala University（乌普萨拉大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究将最小二乘反卷积扩展至弱场极限之外，通过二阶项提取场模量，将弱场近似失效转化为新可观测量，适用于任何具有Stokes V信号的恒星。
AI 中文摘要
最小二乘反卷积（LSD）是从圆偏振光谱测量恒星磁场的标准技术。它基于弱场近似，仅能获得纵向场。我们旨在将LSD扩展到弱场极限之外，并将偏离线性场响应的部分解释为场模量。Stokes V吸收系数按强度轮廓的奇数波长导数展开，系数由塞曼模式矩给出。截断至两项后，每条谱线获得由分裂模式三阶矩构成的第二权重，两个平均Stokes V轮廓由多轮廓LSD得到。该描述通过偏振光谱合成进行测试，并应用于两颗Ap星和两颗活跃M矮星的档案光谱。第二平均轮廓与第一轮廓的二阶导数成正比，其系数衡量由纵向通量加权的均方场模量。该可观测量将场强度与其覆盖区域分离。在现实信噪比下的模拟表明，第二分量可从约500 G起可靠检测，并将场模量约束至数千高斯。将该方法应用于Ap星时，我们发现模量与其已知场强一致，而对于M矮星，模量接近塞曼展宽测量值，且远高于塞曼-多普勒成像得到的大尺度场。二阶LSD将弱场近似的失效从误差来源转变为新的磁性可观测量，首次揭示了发射圆偏振区域中的场强。它适用于任何具有可检测Stokes V特征的恒星，并弥合了偏振测量与塞曼展宽之间的差距，最有前景的是对红外波段活跃冷恒星的应用。
英文摘要
Least-squares deconvolution (LSD) is the standard technique for measuring stellar magnetic fields from circular polarisation spectra. It rests on the weak-field approximation and yields the longitudinal field alone. We aim to extend LSD beyond the weak-field limit and interpret departures from a linear field response in terms of the field modulus. The Stokes V absorption coefficient is expanded in odd wavelength derivatives of the intensity profile, with coefficients given by the Zeeman pattern moments. Truncation after two terms gives every line a second weight, formed from the third moment of its splitting pattern, and two mean Stokes V profiles follow from multiprofile LSD. This description was tested with polarised spectrum synthesis and applied to archival spectra of two Ap stars and two active M dwarfs. The second mean profile is proportional to the second derivative of the first, with a coefficient measuring the mean square field modulus weighted by the longitudinal flux. This observable separates field strength from the area it covers. Simulations at realistic signal-to-noise ratios show that the second component is reliably detected from about 500 G and constrains the field modulus up to several kG. Applying this methodology to the Ap stars, we found the modulus consistent with their known field strengths, whereas for the M dwarfs it was close to the Zeeman-broadening measurements and far above the large-scale fields from Zeeman-Doppler imaging. Second-order LSD turns the breakdown of the weak-field approximation from a source of error into a new magnetic observable, revealing for the first time the field strength in the regions emitting circular polarisation. It applies to any star with a detectable Stokes V signature and bridges the gap between polarimetry and Zeeman broadening, most promisingly for cool active stars in the infrared.
Comments15 pages, 9 figures; accepted for publication in Astronomy & Astrophysics
