Solar Fe abundance and magnetic fields

Fabbian, D.; Moreno‐Insertis, F.; Khomenko, E.; Nordlund, Åke

doi:10.1051/0004-6361/201219335

Cited by 42 publications

(84 citation statements)

References 49 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In deep photospheric layers faculae are cooler than the quiet Sun according to the 1D atmospheric structures employed here, which results in the inversion of the contrast. A similar inversion in the continuum contrast was recently obtained by Criscuoli & Uitenbroek (2014) who based their calculations on 3D MHD simulations calculated by Fabbian et al (2012) using STAGGER code (Galsgaard & Nordlund 1996).…”

Section: Fraunhofer Linessupporting

confidence: 80%

The role of the Fraunhofer lines in solar brightness variability

Шапиро

Solanki

Krivova

et al. 2015

A&A

View full text Add to dashboard Cite

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.

show abstract

Section: Fraunhofer Linessupporting

confidence: 80%

The role of the Fraunhofer lines in solar brightness variability

Шапиро

Solanki

Krivova

et al. 2015

A&A

View full text Add to dashboard Cite

show abstract

“…Khomenko et al 2005;Shelyag et al 2007;Carroll & Kopf 2008) and in particular also for the derivation of abundances Caffau et al 2008;Pereira et al 2009a;Fabbian et al 2010Fabbian et al , 2012. They are capable of predicting phenomena such as small-scale vortices (e.g.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…Tests done for Fabbian et al (2012) indicated that this approach does not introduce any kind of bias in the resulting set of synthetic spectra, while still providing a sufficiently large statistical base of about 4000 independent spectra. The final spatial sampling then corresponded to 0.…”

Section: Convection Simulations and Spectral Synthesismentioning

confidence: 99%

Thermodynamic fluctuations in solar photospheric three-dimensional convection simulations and observations

Beck

Fabbian

Moreno‐Insertis

et al. 2013

A&A

Self Cite

View full text Add to dashboard Cite

Context. Numerical three-dimensional (3D) radiative (magneto-)hydrodynamical [(M)HD] simulations of solar convection are nowadays used to understand the physical properties of the solar photosphere and convective envelope, and, in particular, to determine the Sun's photospheric chemical abundances. To validate this approach, it is important to check that no excessive thermodynamic fluctuations arise as a consequence of the partially incomplete treatment of radiative transfer causing radiative damping that is too modest. Aims. We investigate the realism of the thermodynamics in recent state-of-the-art 3D convection simulations of the solar atmosphere carried out with the Stagger code.Methods. We compared the characteristic properties of several Fe i lines (557.6 nm, 630 nm, 1565 nm) and one Si i line at 1082.7 nm in solar disc-centre observations of different spatial resolution with spectra synthesized from 3D convection simulations. The observations were taken with ground-based (Echelle spectrograph, Göttingen Fabry-Pérot Interferometer (GFPI), POlarimetric LIttrow Spectrograph, Tenerife Infrared Polarimeter, all at the Vacuum Tower Telescope on Tenerife) and space-based instruments (Hinode/Spectropolarimeter). We degraded the synthetic spectra to the spatial resolution of the observations, based on the distribution of the continuum intensity I c . We estimated the spectral degradation to be applied to the simulation results by comparing atlas spectra with averaged observed spectra. In addition to deriving a set of line parameters directly from the intensity profiles, we used the SIR (Stokes Inversion based on Response functions) code to invert the spectra. Results. The spatial degradation kernels yield a similar generic spatial stray-light contamination of about 30% for all instruments. The spectral stray light inside the different spectrometers is found to be between 2% and 20%. Most of the line parameters from the observational data are matched by the degraded HD simulation spectra. The inversions predict a macroturbulent velocity v mac below 10 m s −1 for the HD simulation spectra at full spatial resolution, whereas they yield v mac 1000 m s −1 at a spatial resolution of 0. 3. The temperature fluctuations in the inversion of the degraded HD simulation spectra do not exceed those from the observational data (of the order of 100−200 K rms for −2 log τ 500 nm −0.5). The comparison of line parameters in spatially averaged profiles with the averaged values of line parameters in spatially resolved profiles indicates a significant change in (average) line properties on a spatial scale between 0. 13 and 0. 3. Conclusions. Up to a spatial resolution of 0. 3 (GFPI spectra), we find no indications of excessive thermodynamic fluctuations in the 3D HD simulation. To definitely confirm that simulations without spatial degradation contain fully realistic thermodynamic fluctuations requires observations at even higher spatial resolution (i.e. <0. 13).

show abstract

“…The impact of magnetic fields on the temperature structure of stellar atmospheres is another potential problem. Magnetohydrodynamic simulations of the solar atmosphere (Fabbian et al 2010(Fabbian et al , 2012 show effects on the strength of Fe i lines induced primarily by "magnetic heating" of the upper layers. For an average vertical magnetic field strength of 100 G (Trujillo Bueno et al 2004), the effect on the derived Fe abundance ranges from 0.01 dex for weak lines formed in deep layers to 0.08 dex for stronger lines formed in the upper part of the photosphere.…”

Section: Non-lte and 3d Effectsmentioning

confidence: 99%

High-precision abundances of elements in solar twin stars

Nissen

2015

A&A

239

300

View full text Add to dashboard Cite

Context. High-precision determinations of abundances of elements in the atmospheres of the Sun and solar twin stars indicate that the Sun has an unusually low ratio between refractory and volatile elements. This has led to the suggestion that the relation between abundance ratios, [X/Fe], and elemental condensation temperature, T C , can be used as a signature of the existence of terrestrial planets around a star. Aims. HARPS spectra with S /N 600 for 21 solar twin stars in the solar neighborhood and the Sun (observed via reflected light from asteroids) are used to determine very precise (σ ∼ 0.01 dex) differential abundances of elements in order to see how well [X/Fe] is correlated with T C and other parameters such as stellar age. Methods. Abundances of C, O, Na, Mg, Al, Si, S, Ca, Ti, Cr, Fe, Ni, Zn, and Y are derived from equivalent widths of weak and medium-strong spectral lines using MARCS model atmospheres with parameters determined from the excitation and ionization balance of Fe lines. Non-LTE effects are considered and taken into account for some of the elements. In addition, precise (σ 0.8 Gyr) stellar ages are obtained by interpolating between Yonsei-Yale isochrones in the log g -T eff diagram. Results. It is confirmed that the ratio between refractory and volatile elements is lower in the Sun than in most of the solar twins (only one star has the same [X/Fe]-T C distribution as the Sun), but for many stars, the relation between [X/Fe] and T C is not well defined.

show abstract

Solar Fe abundance and magnetic fields

Cited by 42 publications

References 49 publications

The role of the Fraunhofer lines in solar brightness variability

The role of the Fraunhofer lines in solar brightness variability

Thermodynamic fluctuations in solar photospheric three-dimensional convection simulations and observations

High-precision abundances of elements in solar twin stars

Contact Info

Product

Resources

About