We present our analysis aimed at inferring average magnetic fields in slowly-rotating solar-like stars. Using the spectral line inversion code SPINOR, we perform high-accuracy line profile fitting and investigate whether Zeeman broadening can be reliably detected in optical data of unprecedented quality. We argue that our usage of both high- and low-g_{eff} lines does provide a certain sensitivity to magnetic fields that may, indeed, be detected. However, the measurement is subject to a model dependence and prone to ambiguities, e.g. due to spectral blends. Hence, while a field may be successfully recovered, the quantification of this field is subject to large uncertainties, even for the highest-quality optical data.
Low-mass stars are known to have magnetic fields that are believed to be of dynamo origin. Two complementary techniques are principally used to characterise them. Zeeman-Doppler imaging (ZDI) can determine the geometry of the large-scale magnetic field while Zeeman broadening can assess the total unsigned flux including that associated with small-scale structures such as spots. In this work, we study a sample of stars that have been previously mapped with ZDI. We show that the average unsigned magnetic flux follows an activity-rotation relation separating into saturated and unsaturated regimes…
Almost three decades ago, Mathys (1990) demonstrated the importance of studying Ap stars showing resolved Zeeman split Fe II 6147.7 and 6149.2 lines. Such Zeeman split lines can be seen in stars whose projected rotational velocity is sufficiently small and whose magnetic field is strong enough to exceed the rotational Doppler broadening. Observations of resolved Zeeman split lines permit the diagnosis of the average of the modulus of the magnetic field over the visible stellar hemisphere. Although Zeeman splitting is not expected in faster rotating hot massive stars, we have recently been disc…
With the recent advent of circular polarization capabilities at the Atacama Large Millimeter/submillimeter Array (ALMA), Zeeman effect measurements of spectral lines are now possible as a means to directly probe line-of-sight magnetic fields in protoplanetary disks (PPDs). We present a modeling study that aims to guide physical interpretation of these anticipated observations. Using a fiducial density structure based on a typical ringed disk, we simulate line emission for the hyperfine components of the CN $J = 1-0$ transition with the POLARIS radiative transfer code. Since the expected magnet…
Measuring the surface magnetic fields of magnetic stars with unresolved Zeeman splitting
高色散，档案光谱的磁性Ap星与解决塞曼组件斯托克斯我被用来推导一个简单的关系，可以用来估计平均表面场强度的恒星与v sin i > 10公里/秒。对于每一个明星，平均表面场，从观测到的分裂在Fe II在6149 A，进行比较，以产生一个关系，以估计磁场强度的磁星与未解决的塞曼模式的谱线与大，小朗德因素的差分加宽。该方法被证明是可靠的旋转速度高达约50公里/秒的磁场强度下降到约5公斤。这些结果应允许更好的约束放置在平均表面磁场的Ap星塞曼模式是未解决的。
Milne-Eddington inversions of the He I 10830 Å Stokes profiles: Influence of the Paschen-Back effect
Paschen-Back效应影响He I多重态在10830 μ m处的塞曼子能级，导致这些谱线塞曼分量的强度和位置发生变化。我们说明了这种效果的相关性，使用合成斯托克斯配置文件的He I 10830的多重线，并调查其对极化数据反演的影响。我们反演的特内里费岛红外偏振仪（TIP）在德国真空塔望远镜（VTT）获得的数据。我们比较的反演结果的基础上计算的合成配置文件和没有Paschen-Back效应被包括在内。我们发现，当考虑到不完整的Paschen-Back效应，平均16%的高场强值。我们还表明，这种效果是不是主要原因的面积不对称性所表现出的许多He I 10830斯托克斯V-配置文件。这表明在这些线的形成高度范围内速度和磁场梯度的重要性。
Strong Zeeman effects in the Fe I 5434.5 Å line observed in a sunspot on August 17, 2024
Institute of Physics of the National Academy of Sciences of Ukraine（乌克兰国家科学院物理研究所）；Astronomical Observatory of the Taras Shevchenko National University of Kyiv（基辅塔拉斯舍甫琴科国立大学天文台）
本研究通过Fe I等三条不同磁灵敏度谱线的高保真斯托克斯光谱，分析2024年8月17日太阳黑子的磁场分布，发现Fe I 5434.5 Å线对应空间分量存在高达22 kG的极强磁场。
We aim to characterise the surface magnetic fields of a sample of 8 T Tauri stars from high-resolution near-IR spectroscopy. Some stars in our sample are known to be magnetic from previous spectroscopic or spectropolarimetric studies. Our goals are 1) to apply Zeeman broadening modelling to T Tauri stars with high-resolution data, 2) to expand the sample of stars with measured surface magnetic field strengths, 3) to investigate possible rotational or long-term magnetic variability by comparing spectral time series of given targets, and 4) to compare the magnetic field modulus <B> tracing small…
Approximately 7% of massive stars host stable surface magnetic fields that are strong enough to alter stellar evolution through their effect on the stellar wind. It is therefore crucial to characterize the strength and structure of these large-scale fields in order to quantify their influence on massive star evolution. This is traditionally done by measuring the circular polarization caused by Zeeman splitting in optical photospheric lines, but we investigate here the possibility of detecting Stokes $V$ signatures in the wind-sensitive resonance lines formed in magnetically confined winds in t…
Global magnetic fields of active solar-like stars are nowadays routinely detected with spectropolarimetric measurements and are mapped with Zeeman-Doppler imaging (ZDI). However, due to the cancellation of opposite field polarities, polarimetry captures only a tiny fraction of the magnetic flux and cannot assess the overall stellar surface magnetic field if it is dominated by a small-scale component. Analysis of Zeeman broadening in high-resolution intensity spectra can reveal these hidden complex magnetic fields. Historically, there were very few attempts to obtain such measurements for G dwa…
Observations of the Joint Action of the Hanle and Zeeman Effects in the D2 Line of BaII
我们选择的高灵敏度光谱偏振观测在过去几年中获得的Ba II D2线与苏黎世成像偏振仪（ZIMPOL）连接到格雷戈里库德望远镜的IRSOL。测量数据是在靠近太阳边缘的几个磁场活动程度不同的区域收集的。我们观察到的斯托克斯轮廓显示了汉勒和塞曼效应联合作用的清晰特征，与理论预期非常好的定性一致。这条线的偏振测量表明，非常适合低太阳色球层的磁场诊断，从磁场强度低至1高斯的区域到具有KG磁场强度的强磁化区域。
Classical Cepheids are essential objects in the study of stellar evolution and cosmology; however, we know little about their magnetic properties. We report the detection of Stokes $V$ features interpreted as Zeeman signatures in four classical Cepheids using high-resolution spectropolarimetric observations obtained with ESPaDOnS at CFHT. Eight observations of $η$ Aql were acquired in 2017 covering its 7.2 d pulsation period, and single observations of Polaris, $ζ$ Gem, $δ$ Cep and RT Aur were obtained in 2020 as part of our ongoing systematic survey. We use mean circular polarization Stokes $…
Synthetic polarimetric spectra from stellar prominences
在快速旋转的恒星中探测到的恒星磁场可以作为冷恒星日冕中磁性的探测器。我们已经合成的斯托克斯配置文件中产生的He I 10830和5876 A三胞胎在日珥围绕恒星旋转的时间演化。合成进行了HAZEL代码使用云模型，其中的突出的特点是位于一个固定的纬度和高度的板。它解释了散射极化和塞曼和汉勒效应。分析了几种不同日珥磁场强度和方向的情况。结果表明，当日珥在恒星盘外时，辐射特征在剖面上漂移。当日珥遮蔽恒星时，强度轮廓显示出吸收。由日珥引起的散射产生斯托克斯Q和U分布中的线偏振信号，当存在磁场时，该线偏振信号被汉勒效应修改。由于塞曼效应，当沿视线的磁场不为零时，Stokes V剖面显示具有非常低幅度的信号。估计的线偏振信号可能会被未来的分光偏振计MIRADAS检测到，将被附加到GTC望远镜。
We present a Zeeman-Doppler imaging study of two weak-line T Tauri stars TAP 4 and TAP 40, based on the high-resolution spectropolarimetric observations with ESPaDOnS at the Canada-France-Hawaii Telescope in November 2013, in the framework of the MaTYSSE large programme. We apply two Zeeman-Doppler imaging codes to the Stokes I and V profiles to reconstruct their brightness and large-scale magnetic field images. The results given by the two imaging codes are in good agreement with each other. TAP 4 shows a large polar cool spot and several intermediate-latitude warm spots on its surface, where…
Evolution of solar magnetic tubes and its manifestation in Stokes parameters
小尺度磁性元素的形成和衰变的基本方案和机制及其表现在合成斯托克斯配置文件的Fe I 15648.5 A红外线被认为是在太阳上的非稳态磁粒的二维建模的背景下。对流坍缩阶段的特点是伴随着完整的塞曼分裂的I配置文件的V配置文件中的大红移。这是由于强烈的向下流动的材料，这有利于集中的纵向场的振幅约为几个kG的管。强磁结构的耗散的特征在于斯托克斯轮廓中的蓝移，这是由于向上的磁通量降低了管中的磁场。致密磁性元素演化关键阶段的典型特征应可通过具有足够高的空间和时间分辨率的观测来探测。
We present a blind comparison of two methods to measure the mean surface magnetic field strength of the classical T Tauri star CI Tau based on Zeeman broadening of sensitive spectral lines. Our approach takes advantage of the greater Zeeman broadening at near-infrared compared to optical wavelengths. We analyze a high signal-to-noise, high spectral resolution spectrum from 1.5-2.5um observed with IGRINS (Immersion GRating INfrared Spectrometer) on the Discovery Channel Telescope. Both stellar parameterization with MoogStokes (which assumes an uniform magnetic field) and modeling with SYNTHMAG …
Observational astrophysics started when spectroscopy could be applied to astronomy. Similarly, observational work on stellar magnetic fields became possible with the application of spectro-polarimetry. In recent decades there have been dramatic advances in the observational tools for spectro-polarimetry. The four Stokes parameters that provide a complete representation of partially polarized light can now be simultaneously imaged with megapixel array detectors with high polarimetric precision (0.001% in the degree of polarization). This has led to new insights about the nature and properties o…
We present a new approach for correcting instrumental polarization by modeling the non-depolarizing effects of a complex series of optical elements to determine physically realizable Mueller matrices. Provided that the Mueller matrix of the optical system can be decomposed into a general elliptical diattenuator and general elliptical retarder, it is possible to model the cross-talk between both the polarized and unpolarized states of the Stokes vector and then use the acquired science observations to determine the best-fit free parameters. Here, we implement a minimization for solar spectropol…
Future ground-based telescopes will expand our capabilities for simultaneous multi-line polarimetric observations in a wide range of wavelengths, from the near-ultraviolet to the near-infrared. This creates a strong demand to compare candidate spectral lines to establish a guideline of the lines that are most appropriate for each observation target. We focused in this first work on Zeeman-sensitive photospheric lines in the visible and infrared. We first examined their polarisation signals and response functions using a 1D semi-empirical atmosphere. Then we studied the spatial distribution of …
