The Hanle Effect in 1D, 2D and 3D

This paper addresses the problem of scattering line polarization and the Hanle effect in one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) media for the case of a two-level model atom without lower-level polarization and assuming complete frequency redistribution. The theoretical framework chosen for its formulation is the QED theory of Landi Degl'Innocenti (1983), which specifies the excitation state of the atoms in terms of the irreducible tensor components of the atomic density matrix. The self-consistent values of these density-matrix elements is to be determined by solving jointly the kinetic and radiative transfer equations for the Stokes parameters. We show how to achieve this by generalizing to Non-LTE polarization transfer the Jacobi-based ALI method of Olson et al. (1986) and the iterative schemes based on Gauss-Seidel iteration of Trujillo Bueno and Fabiani Bendicho (1995). These methods essentially maintain the simplicity of the Lambda-iteration method, but their convergence rate is extremely high. Finally, some 1D and 2D model calculations are presented that illustrate the effect of horizontal atmospheric inhomogeneities on magnetic and non-magnetic resonance line polarization signals.Comment: 14 pages and 5 figure

The contrast of magnetic elements in synthetic CH- and CN-band images of solar magnetoconvection

We present a comparative study of the intensity contrast in synthetic CH-band and violet CN-band filtergrams computed from a high-resolution simulation of solar magnetoconvection. The underlying simulation has an average vertical magnetic field of 250 G with kG fields concentrated in its intergranular lanes, and is representative of a plage region. To simulate filtergrams typically obtained in CH- and CN-band observations we computed spatially resolved spectra in both bands and integrated these spectra over 1 nm FWHM filter functions centred at 430.5 nm and 388.3 nm, respectively. We find that the average contrast of magnetic bright points in the simulated filtergrams is lower in the CN-band by a factor of 0.96. This result strongly contradicts earlier semi-empirical modeling and recent observations, which both etimated that the bright-point contrast in the CN-band is \emph{higher} by a factor of 1.4. We argue that the near equality of the bright-point contrast in the two bands in the present simulation is a natural consequence of the mechanism that causes magnetic flux elements to be particularly bright in the CN and CH filtergrams, namely the partial evacuation of these elements and the concomitant weakening of molecular spectral lines in the filter passbands. We find that the RMS intensity contrast in the whole field-of-view of the filtergrams is 20.5% in the G band and 22.0% in the CN band and conclude that this slight difference in contrast is caused by the shorter wavelength of the latter. Both the bright-point and RMS intensity contrast in the CN band are sensitive to the precise choice of the central wavelength of the filter.Comment: 24 pages, 9 figures, submitted to Ap

Advanced Forward Modeling and Inversion of Stokes Profiles Resulting from the Joint Action of the Hanle and Zeeman Effects

A big challenge in solar and stellar physics in the coming years will be to decipher the magnetism of the solar outer atmosphere (chromosphere and corona) along with its dynamic coupling with the magnetic fields of the underlying photosphere. To this end, it is important to develop rigorous diagnostic tools for the physical interpretation of spectropolarimetric observations in suitably chosen spectral lines. Here we present a computer program for the synthesis and inversion of Stokes profiles caused by the joint action of atomic level polarization and the Hanle and Zeeman effects in some spectral lines of diagnostic interest, such as those of the He I 10830 A and D_3 multiplets. It is based on the quantum theory of spectral line polarization, which takes into account all the relevant physical mechanisms and ingredients (optical pumping, atomic level polarization, Zeeman, Paschen-Back and Hanle effects). The influence of radiative transfer on the emergent spectral line radiation is taken into account through a suitable slab model. The user can either calculate the emergent intensity and polarization for any given magnetic field vector or infer the dynamical and magnetic properties from the observed Stokes profiles via an efficient inversion algorithm based on global optimization methods. The reliability of the forward modeling and inversion code presented here is demonstrated through several applications, which range from the inference of the magnetic field vector in solar active regions to determining whether or not it is canopy-like in quiet chromospheric regions. This user-friendly diagnostic tool called "HAZEL" (from HAnle and ZEeman Light) is offered to the astrophysical community, with the hope that it will facilitate new advances in solar and stellar physics.Comment: 62 pages, 19 figures, 3 tables. Accepted for publication in Ap

Dichroic Masers due to Radiation Anisotropy and the Influence of the Hanle Effect on the Circumstellar SiO Polarization

The theory of the generation and transfer of polarized radiation, mainly developed for interpreting solar spectropolarimetric observations, allows to reconsider, in a more rigorous and elegant way, a physical mechanism that has been suggested some years ago to interpret the high degree of polarization often observed in astronomical masers. This mechanism, for which the name of 'dichroic maser' is proposed, can operate when a low density molecular cloud is illuminated by an anisotropic source of radiation (like for instance a nearby star). Here we investigate completely unsaturated masers and show that selective stimulated emission processes are capable of producing highly polarized maser radiation in a non-magnetic environment. The polarization of the maser radiation is linear and is directed tangentially to a ring equidistant to the central star. We show that the Hanle effect due to the presence of a magnetic field can produce a rotation (from the tangential direction) of the polarization by more that 45 degrees for some selected combinations of the strength, inclination and azimuth of the magnetic field vector. However, these very same conditions produce a drastic inhibition of the maser effect. The rotations of about 90 degrees observed in SiO masers in the evolved stars TX Cam by Kemball & Diamond (1997) and IRC+10011 by Desmurs et al (2000) may then be explainedby a local modification of the anisotropy of the radiation field, being transformed from mainly radial to mainly tangential.Comment: Accepted for publication on Ap

Magnetic Field Measurement with Ground State Alignment

Observational studies of magnetic fields are crucial. We introduce a process "ground state alignment" as a new way to determine the magnetic field direction in diffuse medium. The alignment is due to anisotropic radiation impinging on the atom/ion. The consequence of the process is the polarization of spectral lines resulting from scattering and absorption from aligned atomic/ionic species with fine or hyperfine structure. The magnetic field induces precession and realign the atom/ion and therefore the polarization of the emitted or absorbed radiation reflects the direction of the magnetic field. The atoms get aligned at their low levels and, as the life-time of the atoms/ions we deal with is long, the alignment induced by anisotropic radiation is susceptible to extremely weak magnetic fields ($1{\rm G}\gtrsim B\gtrsim 10^{-15}$G). In fact, the effects of atomic/ionic alignment were studied in the laboratory decades ago, mostly in relation to the maser research. Recently, the atomic effect has been already detected in observations from circumstellar medium and this is a harbinger of future extensive magnetic field studies. A unique feature of the atomic realignment is that they can reveal the 3D orientation of magnetic field. In this article, we shall review the basic physical processes involved in atomic realignment. We shall also discuss its applications to interplanetary, circumstellar and interstellar magnetic fields. In addition, our research reveals that the polarization of the radiation arising from the transitions between fine and hyperfine states of the ground level can provide a unique diagnostics of magnetic fields in the Epoch of Reionization.Comment: 30 pages, 12 figures, chapter in Lecture Notes in Physics "Magnetic Fields in Diffuse Media". arXiv admin note: substantial text overlap with arXiv:1203.557

Assessment of the Life Cycle Environmental Impact of the Olive Oil Extraction Solid Wastes in the European Union

There is an increasing interest in developing sustainable systems in the European Union (EU) to recover and upgrade the solid wastes of the olive oil extraction process, i.e. wet husk. A Life Cycle Environmental Impact Assessment (LCIA) of wet husk has been carried out aiming at facilitating an appropriate Life Cycle Management of this biomass. Three scenarios have been considered, i.e. combustion for domestic heat, generation of electric power, and composting. The Environmental Product Declaration and the ReCiPe method were used for Life Cycle Impact Assessment. Domestic heating and power generation were the most important impact factors in damaging human health, ecosystems, and natural resources depletion. Composting was 2-4 orders of magnitude less impacting than domestic heat and power generation. Considering human health, the impact of climate change, human toxicity and particulate matter formation represented the main impact categories. Considering ecosystems, climate change and natural land transformation were the main impact categories. Within natural resources, fossil fuel depletion was impacted three orders more than metal depletion. Within domestic heating and power generation scenarios, storage of wet husk along with the extraction by organic solvent, and the waste treatment were the most impacting phases for global warming potential, ozone layer depletion, acidification and non renewable fossil resources depletion. The results obtained for the waste disposal have been comparatively assessed with respect to the environmental impact of the olive oil production chain

Constraining the Variation of G by Cosmic Microwave Background Anisotropies

We use the Cosmic Microwave Background Anisotropies (CMBA) power spectra to constrain the cosmological variation of gravitational constant G. It is found that the sensitivity of CMBA to the variation of G is enhanced when G is required to converge to its present value. The variations of G from the CMB decoupling epoch z ~ 1000 to the present time are modelled by a step function and a linear function of scale factor $a$ respectively, and the corresponding 95% confidence intervals for G/G_0 are [0.95, 1.05] and [0.89, 1.13], G_0 being the present value. The CMBA constraint is unique in the sense that it entails the range of redshift from z \approx 1000 to 0.Comment: 7 pages, 8 figures, discussion added, references adde

The Height of Chromospheric Loops in an Emerging Flux Region

Context. The chromospheric layer observable with the He I 10830 {\AA} triplet is strongly warped. The analysis of the magnetic morphology of this layer therefore requires a reliable technique to determine the height at which the He I absorption takes place. Aims. The He I absorption signature connecting two pores of opposite polarity in an emerging flux region is investigated. This signature is suggestive of a loop system connecting the two pores. We aim to show that limits can be set on the height of this chromospheric loop system. Methods. The increasing anisotropy in the illumination of a thin, magnetic structure intensifies the linear polarization signal observed in the He I triplet with height. This signal is altered by the Hanle effect. We apply an inversion technique incorporating the joint action of the Hanle and Zeeman effects, with the absorption layer height being one of the free parameters. Results. The observed linear polarization signal can be explained only if the loop apex is higher than \approx5 Mm. Best agreement with the observations is achieved for a height of 6.3 Mm. Conclusions. The strength of the linear polarization signal in the loop apex is inconsistent with the assumption of a He I absorption layer at a constant height level. The determined height supports the earlier conclusion that dark He 10830 {\AA} filaments in emerging flux regions trace emerging loops.Comment: 7 pages, 4 figure

Recent Advances in Chromospheric and Coronal Polarization Diagnostics

I review some recent advances in methods to diagnose polarized radiation with which we may hope to explore the magnetism of the solar chromosphere and corona. These methods are based on the remarkable signatures that the radiatively induced quantum coherences produce in the emergent spectral line polarization and on the joint action of the Hanle and Zeeman effects. Some applications to spicules, prominences, active region filaments, emerging flux regions and the quiet chromosphere are discussed.Comment: Review paper to appear in "Magnetic Coupling between the Interior and the Atmosphere of the Sun", eds. S. S. Hasan and R. J. Rutten, Astrophysics and Space Science Proceedings, Springer-Verlag, 200

Restrictions on dilatonic brane-world models

We consider dilatonic brane-world models with a non-minimal coupling between a dilaton and usual matter on a brane. We demonstrate that variation of the fundamental constants on the brane due to such interaction leads to strong restrictions on parameters of models. In particular, the experimental bounds on variation of the fine structure constant rule out non-minimal dilatonic models with a Liouville-type coupling potential f(varphi) = exp (b varphi) where b is order of 1.Comment: MiKTeX2-LaTeX2e, 10 pages, minor changes, improved references, to appear in IJMP