Why One-Dimensional Models Fail in the Diagnosis of Average Spectra From Inhomogeneous Stellar Atmospheres

Uitenbroek, H.; Criscuoli, S.

doi:10.1088/0004-637x/736/1/69

Cited by 71 publications

(70 citation statements)

References 47 publications

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“…At the same time they are deemed (e.g. Koesterke et al 2008;Uitenbroek & Criscuoli 2011) to be inherently unreliable for diagnostics of solar atmospheric properties (see however Vitas et al 2009), unless differential techniques are used (Stenflo et al 1998). The 1D models cannot directly account for the hot walls of flux tubes which to large extent determine the centre-tolimb variation in facular brightness (Steiner 2005).…”

Section: Discussionmentioning

confidence: 99%

The role of the Fraunhofer lines in solar brightness variability

Шапиро

Solanki

Krivova

et al. 2015

A&A

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Context. The solar brightness varies on timescales from minutes to decades. A clear identification of the physical processes behind such variations is needed for developing and improving physics-based models of solar brightness variability and reconstructing solar brightness in the past. This is, in turn, important for better understanding the solar-terrestrial and solar-stellar connections. Aims. We estimate the relative contributions of the continuum, molecular, and atomic lines to the solar brightness variations on different timescales. Methods. Our approach is based on the assumption that variability of the solar brightness on timescales greater than a day is driven by the evolution of the solar surface magnetic field. We calculated the solar brightness variations employing the solar disc area coverage of magnetic features deduced from the MDI/SOHO observations. The brightness contrasts of magnetic features relative to the quiet Sun were calculated with a non-LTE radiative transfer code as functions of disc position and wavelength. By consecutive elimination of molecular and atomic lines from the radiative transfer calculations, we assessed the role of these lines in producing solar brightness variability. Results. We show that the variations in Fraunhofer lines define the amplitude of the solar brightness variability on timescales greater than a day and even the phase of the total solar irradiance variability over the 11-year cycle. We also demonstrate that molecular lines make substantial contribution to solar brightness variability on the 11-year activity cycle and centennial timescales. In particular, our model indicates that roughly a quarter of the total solar irradiance variability over the 11-year cycle originates in molecular lines. The maximum of the absolute spectral brightness variability on timescales greater than a day is associated with the CN violet system between 380 and 390 nm.

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Section: Discussionmentioning

confidence: 99%

The role of the Fraunhofer lines in solar brightness variability

Шапиро

Solanki

Krivova

et al. 2015

A&A

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“…Apart from these problems, we have to keep in mind that the conditions in the layers around the temperature minimum probably deviate from the gray LTE radiative transfer used in the simulations. Furthermore, a direct comparison between horizontal temperature averages (or even averages over surfaces of constant optical depth) from simulations with semi-empirical models would be problematic owing to the strong horizontal inhomogeneities and the nonlinear averaging underlying observed spectral mean line profiles (Uitenbroek & Criscuoli 2011).…”

Section: Summary and Discussionmentioning

confidence: 99%

Vortices, shocks, and heating in the solar photosphere: effect of a magnetic field

Moll

Cameron

Schüßler

2012

A&A

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Aims. We study the differences between non-magnetic and magnetic regions in the flow and thermal structure of the upper solar photosphere. Methods. Radiative MHD simulations representing a quiet region and a plage region, respectively, which extend into the layers around the temperature minimum, are analyzed. Results. The flow structure in the upper photospheric layers of the two simulations is considerably different: the non-magnetic simulation is dominated by a pattern of moving shock fronts while the magnetic simulation shows vertically extended vortices associated with magnetic flux concentrations. Both kinds of structures induce substantial local heating. The resulting average temperature profiles are characterized by a steep rise above the temperature minimum due to shock heating in the non-magnetic case and by a flat photospheric temperature gradient mainly caused by Ohmic dissipation in the magnetic run. Conclusions. Shocks in the quiet Sun and vortices in the strongly magnetized regions represent the dominant flow structures in the layers around the temperature minimum. They are closely connected with dissipation processes providing localized heating.

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“…A creation of an archive from 3D numerical simulations might thus be anyway required for a consistent spectral synthesis (cf. Uitenbroek & Criscuoli 2011;Sheminova 2012;Leenaarts et al 2012). Such an archive then also allows one to improve the inversion procedure beyond the common single-pixel approach in which every pixel is inverted individually neglecting its surroundings.…”

Section: Discussionmentioning

confidence: 99%

The energy of waves in the photosphere and lower chromosphere

Beck

Rezaei

Puschmann

2012

A&A

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Context. The Ca ii H line is one of the strongest lines in the solar spectrum, and it provides continuous information on the solar atmosphere from the photosphere to the lower chromosphere.Aims. We describe an inversion approach that reproduces observed Ca ii H spectra by assuming local thermal equilibrium (LTE). Methods. We developed an inversion strategy based on the SIR code that reproduces Ca ii H spectra in the LTE approximation. The approach uses a two-step procedure with an archive of pre-calculated spectra to fit the line core and a subsequent iterative modification to improve the fit mainly in the line wing. Simultaneous spectra in the 630 nm range can optionally be used to fix the continuum temperature. The method retrieves one-dimensional (1D) temperature stratifications while neglecting lateral radiative transport. Lineof-sight velocities are included post facto with an empirical approach.Results. An archive of about 300 000 pre-calculated spectra is more than sufficient to reproduce the line core of observed Ca ii H spectra both in the quiet Sun and in active regions. The subsequent iterative adjustment of the thermodynamical stratification matches observed and best-fit spectra to a level of about 0.5% of I c in the line wing and about 1% of I c in the line core. Conclusions. The successful application of the LTE inversion strategy suggests that inversion schemes based on pre-calculated spectra allow a reliable and relatively fast retrieval of solar properties from observed chromospheric spectra. The approach can be easily extended to a 1D non-LTE (NLTE) case by a simple exchange of the pre-calculated archive spectra. Using synthetic NLTE spectra from numerical three-dimensional (3D) simulations instead will finally allow one to extend the approach from the static 1D-case to dynamical atmosphere models, including the complete 3D radiative transport.

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Why One-Dimensional Models Fail in the Diagnosis of Average Spectra From Inhomogeneous Stellar Atmospheres

Cited by 71 publications

References 47 publications

The role of the Fraunhofer lines in solar brightness variability

The role of the Fraunhofer lines in solar brightness variability

Vortices, shocks, and heating in the solar photosphere: effect of a magnetic field

The energy of waves in the photosphere and lower chromosphere

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