Radiative Diagnostics in the Solar Photosphere and Chromosphere

Rodríguez, J. de la Cruz; Noort, M. van

doi:10.1007/s11214-016-0294-8

Cited by 56 publications

(2 citation statements)

References 114 publications

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“…In this paper we investigate and compare the variability of line properties of the Hα 656.3 nm and Ca II 854.2 nm lines obtained from sun-as-a-star observations. We focus on these two lines because, together with Ca II UV lines, Hα 656.3 nm and of Ca II 854.2 nm are among the few lines forming in the chromosphere accessible from the ground, and as such, are widely used chromospheric diagnostics (e.g., de la Cruz Rodríguez and van Noort, 2017).…”

Section: Introductionmentioning

confidence: 99%

Sun-as-a-star variability of Hα and Ca II 854.2 nm lines

Zills,

Criscuoli,

Bertello

et al. 2024

Front. Astron. Space Sci.

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Studies of stellar magnetic fields mostly rely on proxies derived from chromospheric lines, typically forming in the UV and shorter wavelengths and therefore accessible only from space based observatories. Even Ca II K or H observations, forming in regions accessible from the ground, are not always available. As a result, there is a crucial need to explore alternative activity proxies to overcome the limitations posed by observational constraints. Using sun-as-a-star observations acquired with the ISS at SOLIS we investigated the correlation between the Ca II K emission index and indices derived from the Hα 656.3 nm and Ca II 854.2 nm lines, which are well known chromospheric diagnostics. We found that both the core intensities and widths of the two lines are positively correlated with the Ca II K emission index (ρ ≳ 0.8), indicating their suitability as reliable indicators of magnetic activity, the width of the Hα line showing the highest correlation (ρ = 0.9). We also found that such correlations vary with the activity cycle. Specifically, during the analyzed cycle 24, the correlations with the Ca II K index varied 14% for the Hα width, 33% for the Hα core intensity, and doubled for the two Ca II 854.2 nm line indices. These results suggest that, among the investigated indices, the Hα width best traces magnetic activity. Results are discussed at the light of current knowledge of the formation heights of the two lines, and of spatially resolved solar observations.

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Section: Introductionmentioning

confidence: 99%

Sun-as-a-star variability of Hα and Ca II 854.2 nm lines

Zills,

Criscuoli,

Bertello

et al. 2024

Front. Astron. Space Sci.

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“…Following sections heavily relay on the textbooks by Stenflo (1994); del Toro Iniesta (2003); Degl'Innocenti (2006), as well as in the reviews by del Toro Iniesta and Ruiz Cobo (2016); de la Cruz Rodríguez and van Noort (2017).…”

Section: The Zeeman Effectmentioning

confidence: 99%

Strong magnetic fields and unusual flows in sunspots

Duran¹

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Analysis of photospheric magnetic fields in AR 12546: a case study

Abdel-Kawy

Shaltout

2023

Astrophys Space Sci

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We investigate high-resolution observations with the spectropolarimeter (SP) aboard the Hinode satellite of the Solar Optical Telescope (SOT) of a positive polarity sunspot of an active region (AR) (NOAA 12546). We present a case study for the properties of the thermal, magnetic field, and plasma flows as a function of the optical depth from the inversion of the observed Stokes profiles, covering a wide field of view area. Particular attention is paid to the examination of the net circular polarization (NCP) and area asymmetry of spectral lines in sunspots. We detect a large red-shifted velocity of 10 km sec−1 localized with the presence of a strong magnetic field corresponding to the NCP best fit of the inverted profiles. In addition, the comparison between the observed and calculated NCPs or Stokes V area asymmetries of spectral lines fitted well for most pixels in the field of view region, with a significant indication of a single-component inversion. We study the vertical gradients of temperature, magnetic strength, inclination field, and LOS velocity in the deeper and higher layers of the photosphere. The difference in the penumbral temperature between the two atmospheric layers is −130 K. The penumbral regions reveal a magnetic field gradient of $\Delta B \sim -0.5$ Δ B ∼ − 0.5 to −0.9 G km−1. The inclination gradient in the limb-side penumbra is between $(\Delta \gamma /\Delta z) = -9 \times 10^{-3}$ ( Δ γ / Δ z ) = − 9 × 10 − 3 deg km−1 to $-3.5 \times 10^{-2}$ − 3.5 × 10 − 2 deg km−1. In particular, we find a higher positive inclination gradient in the disk center-side penumbra $(\Delta \gamma /\Delta z)= 0.2 - 1.5 \deg \text{ km}^{-1}$ ( Δ γ / Δ z ) = 0.2 − 1.5 deg km − 1 . The velocity gradient is $(\Delta V_{LOS}/\Delta \log \tau )= -0.13$ ( Δ V L O S / Δ log τ ) = − 0.13 to −0.30 km sec−1 in the limb-side penumbra, and the disk center-side penumbra is given by $(\Delta V_{LOS}/\Delta \log \tau )= 0.11$ ( Δ V L O S / Δ log τ ) = 0.11 to 0.29 km sec−1.

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Radiative Diagnostics in the Solar Photosphere and Chromosphere

Cited by 56 publications

References 114 publications

Sun-as-a-star variability of Hα and Ca II 854.2 nm lines

Sun-as-a-star variability of Hα and Ca II 854.2 nm lines

Strong magnetic fields and unusual flows in sunspots

Analysis of photospheric magnetic fields in AR 12546: a case study

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