Empirical determination of atomic line parameters of the 1.5 μm spectral region

Arjona, J. C. Trelles; Cobo, B. Ruiz; González, M. J. Martínez

doi:10.1051/0004-6361/202038941

Cited by 9 publications

(8 citation statements)

References 48 publications

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“…Future studies that use SIR may be able to improve on these results if nodes can be placed at specifically selected optical depths, but ultimately more spectral lines will be required to probe the atmosphere at a greater range of optical depths. The recent publication of an expanded list of empirically determined atomic line parameters of spectral lines contained in the spectral region observed by GRIS (Trelles Arjona et al 2021) is worthy of further investigation to examine whether the inclusion of any of the spectral lines could improve the inversions. Otherwise, future multi-instrument telescopes (e.g.…”

Section: Discussionmentioning

confidence: 99%

Constraining the magnetic vector in the quiet solar photosphere and the impact of instrumental degradation

Campbell

Shelyag

Noda

et al. 2021

A&A

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Context. With the advent of next generation high resolution telescopes, our understanding of how the magnetic field is organized in the internetwork (IN) photosphere is likely to advance significantly. Aims. We aim to evaluate the extent to which we can retrieve accurate information about the magnetic vector in the IN photosphere using inversion techniques. Methods. We use a snapshot produced from high resolution three-dimensional magnetohydrodynamic (MHD) simulations and employ the Stokes Inversions based on Response functions (SIR) code to produce synthetic observables in the same near infrared spectral window as observed by the GREGOR Infrared Spectrograph (GRIS), which contains the highly magnetically sensitive photospheric Fe I line pair at 15 648.52 Å and 15 652.87 Å. We then use a parallelized wrapper to SIR to perform nearly 14 million inversions of the synthetic spectra to test how well the ‘true’ MHD atmospheric parameters can be constrained statistically. Finally, we degrade the synthetic Stokes vector spectrally and spatially to GREGOR resolutions and examine how this influences real observations, considering the impact of stray light, spatial resolution and signal-to-noise (S/N) in particular. Results. We find that the depth-averaged parameters can be recovered by the inversions of the undegraded profiles, and by adding simple gradients to magnetic field strength, inclination, and line of sight velocity we show that an improvement in the χ2 value is achieved. We also evaluate the extent to which we can constrain these parameters at various optical depths, with the kinematic and thermodynamic parameters sensitive deeper in the atmosphere than the magnetic parameters. We find the S/N and spatial resolution both play a significant role in determining how the degraded atmosphere appears. At the same time, we find that the magnetic and kinematic parameters are invariant upon inclusion of an unpolarized stray light. We compare our results to recent IN observations obtained by GREGOR. We studied a linear polarization feature which resembles those recently observed by GRIS in terms of appearing as ‘loop-like’ structures and exhibiting very similar magnetic flux density. Thus, we demonstrate that realistic MHD simulations are capable of showing close agreement with real observations, and the symbiosis between them and observations continues to prove essential. We finally discuss the considerations that must be made for DKIST-era observations.

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Section: Discussionmentioning

confidence: 99%

Constraining the magnetic vector in the quiet solar photosphere and the impact of instrumental degradation

Campbell

Shelyag

Noda

et al. 2021

A&A

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“…We have relied on the Zeeman effect and performed intensity-only inversions to reveal the spatial distribution of the average strength of the hidden quiet Sun magnetism. Reaching such an important goal has required the inversion of many spectral lines simultaneously and the precise determination of atomic parameters (Trelles Arjona et al 2021). The hidden field has a spatial variation clearly correlated with the convection phenomena of granulation, with granules almost devoided of fields and intergranules populated by much stronger fields.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

“…To prove that the average strength of an unresolved field can be reliably retrieved from the inversion of only the intensity of many spectral lines (see Table 1 in Trelles Arjona et al (2021) for the description of the spectral lines used in this work), we have synthesized and inverted theoretical GRIS spectra using the Stokes Inversion based on Response functions inversion code (SIR, Ruiz Cobo & del Toro Iniesta 1992) in a MANCHARAY magnetohydrodynamical simulation (Khomenko et al 2017). The quiet Sun simulation used in this work was done with the MANCHA3D code (Khomenko & Collados 2006;Felipe et al 2010).…”

Section: Testing Stokes I Multiline Inversions With Numerical Simulat...mentioning

confidence: 99%

“…However, this is never the case, and to obtain the model atmosphere, we need the atomic parameters. We proposed a novel, iterative methodology to compute both the atomic parameters of the lines in our spectral window and the model atmosphere, simultaneously (Trelles Arjona et al 2021). Once the atomic parameters of all lines are fixed, we use SIR to infer the physical properties of the quiet solar atmosphere from the information contained in the data.…”

Section: Testing Stokes I Multiline Inversions With Numerical Simulat...mentioning

confidence: 99%

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Mapping the Hidden Magnetic Field of the Quiet Sun

Arjona

González

Cobo

2021

ApJL

Self Cite

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The Sun is the only star where we can resolve the intricate magnetism that all convective stars harbor. Yet, more than 99% of its visible surface along the solar cycle (the so-called quiet Sun) is filled with a tangled, unresolved magnetism. These "hidden" fields are thought to store enough magnetic energy to play a role in the heating of the Sun's outer atmosphere, but its field strength is still not constrained. Previous investigations based on the Hanle effect in atomic lines claim a strong magnetization of about 100 G, while the same effect in molecules show a factor of 10 weaker fields. The discrepancy disappears if the magnetic field strength of the hidden is not homogeneous in the solar surface. In this letter, we prove using magnetohydrodynamical simulations that it is possible to infer the average field strength of the hidden quiet Sun magnetic fields using multi-line inversions of intensity profiles in the Zeeman regime. Using this technique with 15 spectral lines in the 1.5 µm spectral range, we reveal that the spatial distribution of the hidden field is strongly correlated with convection motions, and that the average magnetization is about 46 G. Reconciling our findings with the Hanle ones is not obvious and will require future work on both sides, since it implies an increase of the field strength with height, something that is physically questionable.

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“…However, in this case, line broadening has to be treated with caution since it can arise from several mechanisms: magnetic field, temperature, collision of the light-emitting particle with other particles, velocity gradients, macro-and micro-turbulence, etc (for example, Stenflo & Lindegren 1977). One way to separate the different contributions, and consequently to get accurate magnetic field information, is to use simultaneously a large enough number of spectral lines with high SNR (for instance, Trelles Arjona et al 2021). Such an optimal spectral range can be found in the visible around the Cr i 5781.75 Å line, which presents a simple Zeeman triplet with large g eff of 2.5 and is not blended according to Harvey (1973).…”

Section: Introductionmentioning

confidence: 99%

Multiple Stokes I inversions to infer magnetic fields in the spectral range around Cr I 5782 Å

Kuckein,

Balthasar,

Noda

et al. 2021

Preprint

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Aims. The spectral window, containing Fraunhofer lines formed in the solar photosphere, around the magnetically sensitive Cr i lines at 5780.9, 5781.1, 5781.7, 5783.0, and 5783.8 Å, with Landé g-factors between 1.6 and 2.5, is explored. The goal is to analyze simultaneously 15 spectral lines, which comprise Cr i, Cu i, Fe i, Mn i, and Si i lines, without polarimetry to infer the thermodynamic and magnetic properties in strongly magnetized plasmas using an inversion code. Methods. The study is based on a new setup at the Vacuum Tower Telescope (VTT, Tenerife) which includes fast spectroscopic scans in the wavelength range around the Cr i 5781.75 Å line. The oscillator strengths log(g f ) of all spectral lines, as well as their response functions to temperature, magnetic field, and Doppler velocity, are determined using the SIR code. The snapshot 385 of the Enhanced Network simulation from the Bifrost code serves to synthesize all the lines, which are in turn inverted simultaneously with SIR to establish the best inversion strategy. This strategy is then applied to VTT observations of a sunspot belonging to NOAA 12723 on 2018 September 30 and the results are compared to full-disk vector field data obtained with the Helioseismic and Magnetic Imager (HMI). Results. The 15 simultaneously inverted intensity profiles (Stokes I) delivered accurate temperatures and Doppler velocities when compared against the simulations. The derived magnetic fields and inclinations are most accurate when the fields are oriented along the line-of-sight (LOS) and less accurate when the fields are transverse to the LOS. In general, the results appear similar to the HMI vector-field data, although some discrepancies exist. Conclusions. The analyzed spectral range has the potential to deliver thermal, dynamic, and magnetic information in strongly magnetized features on the Sun, such as pores and sunspots, even without polarimetry. The highest sensitivity of the lines is found in the lower photosphere, on average around log τ = −1. The multiple-line inversions provide smooth results across the whole field-of-view. The presented spectral range and inversion strategy will be used for future VTT observing campaigns.

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Empirical determination of atomic line parameters of the 1.5 μm spectral region

Cited by 9 publications

References 48 publications

Constraining the magnetic vector in the quiet solar photosphere and the impact of instrumental degradation

Constraining the magnetic vector in the quiet solar photosphere and the impact of instrumental degradation

Mapping the Hidden Magnetic Field of the Quiet Sun

Multiple Stokes I inversions to infer magnetic fields in the spectral range around Cr I 5782 Å

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