NLTE modeling of Stokes vector center-to-limb variations in the CN violet system

Шапиро, А. И.; Fluri, D. M.; Berdyugina, S. V.; Bianda, M.; Ramelli, R.

doi:10.1051/0004-6361/200811299

Cited by 25 publications

(43 citation statements)

References 31 publications

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“…Fontenla et al 2011). The strongest vibrational bands of the CN violet system and CH G-band are calculated using the molecular constants by Krupp (1974), Knowles et al (1988), Wallace et al (1999) (see also Shapiro et al 2010Shapiro et al , 2011a, and references therein for more details).…”

Section: The Modelmentioning

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: The Modelmentioning

confidence: 99%

The role of the Fraunhofer lines in solar brightness variability

Шапиро

Solanki

Krivova

et al. 2015

A&A

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“…In the case of molecular lines, elastic collisions mainly come from neutral hydrogen atoms, and both electrons and neutral hydrogen contribute to inelastic collisions (Shapiro et al 2011). Unfortunately, accurate collision rates are presently not available for the molecular lines we are considering here.…”

Section: Collision Ratesmentioning

confidence: 99%

“…In order to get order-of-magnitude values for the collisional rates we use the following approach. As in Shapiro et al (2011), we write…”

Section: Inelastic Collisionsmentioning

confidence: 99%

“…This polarization is due to scattering processes and is further modified by magnetic field and depolarizing collisions. It is used as a tool for magnetic field diagnostic via the Hanle effect and differential Hanle effect on lines with different magnetic sensitivity (Faurobert & Arnaud 2003;Berdyugina & Fluri 2004;Bommier et al 2006;Shapiro et al 2011). Planeparallel geometry is sufficient to model outgoing radiation for observations made on the solar disk.…”

Section: Introductionmentioning

confidence: 99%

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Modeling scattering polarization in molecular solar lines in spherical geometry

Milić

Faurobert

2012

A&A

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Context. The atmosphere of the Sun is permeated by a vast amount of magnetic flux that remains invisible in magnetograms based on the Zeeman effect. A model-independent way of measuring weak hidden magnetic fields makes use of the differential Hanle effect on the scattering polarization of molecular lines with different sensitivities to magnetic fields. Aims. The observed line scattering polarization steeply increases at the solar limb. Here we are interested in interpreting observations performed at the solar limb, where plane-parallel semi-infinite geometry is not valid. The main reason is that the sphericity of the atmosphere means that the line-of-sight optical path intersects only a finite part of the solar atmosphere. In this paper we revisit the modeling of scattering polarization in two molecular lines of C 2 and MgH in the spectral range from 515.60 nm to 516.20 nm, where observations performed both inside and above the solar limb are available. Methods. The solar atmosphere is described by a one-dimensional, spherically symmetric medium following either the FALC or the FALX quiet Sun model. Both the line and background continuum scattering polarizations are computed by means of the "along-theray" approach. We assume a two-level atom formalism for the line source function, and we compute the molecule number densities and line opacities assuming LTE. We estimate the elastic and inelastic collision rates by fitting the line intensity and linear polarization in several couples of lines of the Second Solar Spectrum Atlas. Results. The limb variations of scattering polarization, both in the lines and in the continuum, are strongly modified when the sphericity of the solar atmosphere is accounted for. We show that the line polarization goes through a maximum at 0.4 above the limb, for both MgH and C 2 lines. The contribution of the line rapidly goes to zero at a larger limb distance, but continuum polarization keeps increasing. The maximum polarization rates have an amplitude of 2% to 2.5% when the FALC model is used, which agrees with previous observations, whereas the FALX model leads to much higher rates. We then investigate the Hanle effect of microturbulent magnetic fields on the C 2 line linear polarization. We show that polarization observed close to the limb would provide valuable diagnostics of weak magnetic fields in the region of the temperature minimum.

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“…With integration times of several minutes and averaging over most of the length of the spectrograph slit (few dozen of arcsec), one obtains a puzzling result: it seems as if the field strength of the turbulent magnetic field depends on the spectral line that was observed. For example, measurements in the atomic Sr I line consistently give higher magnetic field values on the order of 100 G (Trujillo Bueno et al 2006), than molecular lines, such as CN (∼ 80 G) or C 2 (∼ 10 G) (Shapiro et al 2011;Kleint et al 2011b). An explanation based on modeling was proposed by Trujillo Bueno (2003), suggesting that Sr I may be formed in intergranular lanes, where the magnetic field is stronger and C 2 in granules, where the field is weaker.…”

Section: The Need For Large Aperturesmentioning

confidence: 99%

Prospects of Solar Magnetometry—From Ground and in Space

Kleint¹,

Gandorfer²

2015

Space Sci Rev

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In this review we present an overview of observing facilities for solar research, which are planned or will come to operation in near future. We concentrate on facilities, which harbor specific potential for solar magnetometry. We describe the challenges and science goals of future magnetic measurements, the status of magnetic field measurements at different major solar observatories, and provide an outlook on possible upgrades of future instrumentation.

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NLTE modeling of Stokes vector center-to-limb variations in the CN violet system

Cited by 25 publications

References 31 publications

The role of the Fraunhofer lines in solar brightness variability

The role of the Fraunhofer lines in solar brightness variability

Modeling scattering polarization in molecular solar lines in spherical geometry

Prospects of Solar Magnetometry—From Ground and in Space

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