Three-dimensional simulations of solar magneto-convection including effects of partial ionization

Over the last decades, realistic 3D radiative-MHD simulations have become the dominant theoretical tool for understanding the complex interactions between the plasma and the magnetic field on the Sun. Most of such simulations are based on approximations of magnetohydrodynamics, without directly considering the consequences of the very low degree of ionization of the solar plasma in the photosphere and bottom chromosphere. The presence of large amount of neutrals leads to a partial decoupling of the plasma and the magnetic field. As a consequence of that, a series of non-ideal effects (ambipolar diffusion, Hall effect and battery effect) arises. The ambipolar effect is the dominant one in the solar chromosphere. Here we report on the first three-dimensional realistic simulations of magneto-convection including ambipolar diffusion and battery effects. The simulations are done using the newly developed Mancha3D code. Our results reveal that ambipolar diffusion causes measurable effects on the amplitudes of waves excited by convection in the simulations, on the absorption of Poynting flux and heating and on the formation of chromospheric structures. We provide a low limit on the chromospheric temperature increase due to the ambipolar effect using the simulations with battery-excited dynamo fields.Comment: To appear in Astronomy & Astrophysic

Numerical simulations of quiet Sun magnetic fields seeded by Biermann battery

The magnetic fields of the quiet Sun cover at any time more than 90\% of its surface and their magnetic energy budget is crucial to explain the thermal structure of the solar atmosphere. One of the possible origins of these fields is due to the action of local dynamo in the upper convection zone of the Sun. Existing simulations of the local solar dynamo require an initial seed field, and sufficiently high spatial resolution, in order to achieve the amplification of the seed field to the observed values in the quiet Sun. Here we report an alternative model of seeding based on the action of the Bierman battery effect. This effect generates a magnetic field due to the local imbalances in electron pressure in the partially ionized solar plasma. We show that the battery effect self-consistently creates from zero an initial seed field of a strength of the order of micro G, and together with dynamo amplification, allows the generation of quiet Sun magnetic fields of a similar strength to those from solar observations.Comment: To appear in Astronomy & Astrophysic

Formation of MnI lines in the solar atmosphere

We present a detailed NLTE analysis of 39 MnI lines in the solar spectrum. The influence of NLTE effects on the line formation and element abundance is investigated. Our goal is the derivation of solar log gfe values for manganese lines, which will later be used in differential abundance analysis of metal-poor stars. The method of spectrum synthesis is employed, which is based on a solar model atmosphere with initially specified element abundances. A manganese abundance of 5.47 dex is used with the theoretical line-blanketed model atmosphere. Statistical equilibrium calculations are carried out for the model atom, which comprises 245 and 213 levels for MnI and MnII, respectively. Photoionization cross-sections are assumed hydrogenic. For line synthesis van der Waals broadening is calculated according to Anstee & O'Mara's formalism. It is shown that hyperfine structure of the Mn lines also has strong broadening effects, and that manganese is prone to NLTE effects in the solar atmosphere. The nature of the NLTE effects and the validity of the LTE approach are discussed in detail. The role of photoionization and collisional interaction is investigated.Comment: 17 pages, 27 figures, accepted for publication in A&

Central pontine myelinolysis in a chronic alcoholic: A clinical and brain magnetic resonance imaging follow-up

Introduction. Central pontine myelinolysis (CPM) is a noninflammatory, demyelinating lesion usually localised in the basis pontis. Chronic alcoholism is frequently associated with this condition which may have a variable clinical outcome. Until now, brain magnetic resonance imaging (MRI) follow-up in alcoholic CPM cases after alcohol withdrawal has been rarely described. Case report. We reported a 30- year-old male with a 12-year history of alcohol abuse, who presented with inability to stand and walk, nausea, vomiting and somnolence. Neurological examination revealed: impared fixation on lateral gaze, dysarthria, mild spastic quadriparesis, truncal and extremity ataxia, sock-like hypesthesia and moderate decrease in vibration sense in legs. Brain MRI showed a trident-shaped non-enhancing pontine lesion highly suggestive of CPM. After an eight-month alcoholfree follow-up period, the patient’s clinical status significantly improved, while the extent of MRI pontine lesion was merely slightly reduced. Conclusion. The presented case demonstrates that CPM in chronic alcoholics may have a benign clinical course after alcohol withdrawal, which is not necessarily associated with the reduction of lesions on brain MRI. [Projekat Ministarstva nauke Republike Srbije, br. 175031

Is the solar spectrum latitude dependent? An investigation with SST/TRIPPEL

Context: In studies of the solar spectrum relative to spectra of solar twin stars, it has been found that the chemical composition of the Sun seems to depart systematically from those of the twins. One possible explanation is that the effect is due to the special aspect angle of the Sun when observed from Earth, as compared with the aspect angles of the twins. Thus, a latitude dependence of the solar spectrum, even with the heliocentric angle constant, could lead to effects of the type observed. Aim: We explore a possible variation in the strength of certain spectral lines, used in the comparisons between the composition of the Sun and the twins, at loci on the solar disk with different latitudes but at constant heliocentric angle. Methods: We use the TRIPPEL spectrograph at the Swedish 1-m Solar Telescope on La Palma to record spectra in five spectral regions in order to compare different locations on the solar disk at a heliocentric angle of 45 deg. Equivalent widths and other parameters are measured for fifteen different lines representing nine atomic species. Results: The relative variations in equivalent widths at the equator and at solar latitude 45 deg are found to be less than 1.5 % for all spectral lines studied. Translated to elemental abundances as they would be measured from a terrestrial and a hypothetical pole-on observer, the difference is estimated to be within 0.005 dex in all cases. Conclusion: It is very unlikely that latitude effects could cause the reported abundance difference between the Sun and the solar twins. The accuracy obtainable in measurements of small differences in spectral line strengths between different solar disk positions is very high.Comment: 9 pages, 10 figures, accepted by Astronomy & Astrophysic

ArchaeoGates Danube River Submerged Heritage Scanning and Data-base

The objective of ArchaeoGates project is to identify the cultural sites submerged under the Danube, to collect and process the data to develop a database (Danube River Submerged Heritage D.A.R.S.H.), with the possibility to extend it to include other river basins and/or lakes. The equipment used in the implementation of the project are side-scan sonar, seismic radar, scuba diver recognitions. For a tangible perception of the discovered cultural patrimony on the bottom of the river, 3D models and projections will be created: these reconstructions of the submerged sites will add an immeasurable value to the area and to the whole Danube Region. The case study is focusing on the Iron Gates area. The recovery of previously unexplored submerged cultural heritage will foster knowledge on cultural heritage and history of Europe, with the goal of preserving and promoting the value of the sites on local, regional, national and international level

Monumental altar from Singidunum with scenes of a sacrificial procession: Pompa et immolatio

Tokom građevinskih radova u samom centru Beograda, antičkog Singidunuma, godine 1932. pronađen je monumentalni rimski spomenik. Na tri strane spomenika prikazane su ikonografske predstave rimske svečane žrtvene procesije, dok je četvrta strana, na kojoj su se nalazili natpisno polje i natpis, na žalost, oštećena do neprepoznatljivosti. Na zadnjoj, široj strani spomenika, nasuprot onoj na kojoj se nalazio natpis, predstavljene su dve muške figure, u stojećem položaju, sa različitim ritualnim predmetima u rukama i s koničnim kapama, tesno priljubljenim uz glavu, koje imaju vrpce za vezivanje ispod brade. U pitanju su sveštenici nižeg reda koji su pomagali glavnom svešteniku prilikom prinošenja žrtve - tzv. tutulati (tutulati), od kojih jedan u desnoj ruci drži krčag za vino, dok mu se u levoj ruci nalazi posuda za libaciju ili nošenje žrtvenih ponuda - patera (patera). Na njegovom levom ramenu nalazi se predmet sa resama, sličan peškiru - tzv. mantele (mantele), odnosno peškir za brisanje ruku što ga je sveštenik nižeg ranga dodavao glavnom svešteniku tokom prinošenja žrtve. Drugi sveštenik nižeg reda drži obema rukama otvorenu kutiju za tamjan - tzv. aceru (acerra), ornamentisanu figuralnom predstavom, verovatno vučice koja doji Romula i Rema. Na levoj bočnoj strani spomenika (u odnosu na zadnju stranu sa predstavom dvojice sveštenika) nalazi se scena čoveka koji vodi bika. U pitanju je sluga odnosno viktimarijus (victimarius), čiji je posao bio da vodi žrtvenu životinju i brine o njenom ponašanju, da je ubije tokom samog rituala žrtvovanja i da potom iseče njeno telo na komade. Viktimarijus vodi bika levom rukom, dok u desnoj ruci drži sekiru kojom će ga ubiti prilikom žrtvovanja. Na desnoj bočnoj strani spomenika prikazan je viktimarijus sa žrtvenim nožem, odnosno kultrarijus (cultrarius), koji nož drži u desnoj ruci, dok levom rukom vodi ovna. Na leđima obe žrtvene životinje prikazana je ritualna traka dorsuale (dorsuale), koja je označavala posvećenje životinje u ritualne svrhe. Analiza i interpretacija monumentalnog spomenika iz Singidunuma pokazale su da je u pitanju arheološki spomenik jedinstvene ikonografije sa prostora rimske provincije Gornje Mezije, s obzirom na to da su predstavljene scene svečane žrtvene procesije. Izuzetan značaj oltara ogleda se u tome što su dvojica sveštenika nižeg reda, pomagača glavnom svešteniku, prikazana na jednoj od širih strana spomenika. To samo dodatno osnažuje hipotezu da je u pitanju bila važna ritualna svečanost koja je, verovatno, priređena u čast vrhovnog rimskog boga Jupitera, genija imperatora ili predaka rimskog cara. Najbližu geografsku analogiju predstavlja scena žrtvene procesije sa žrtvenika iz Aserije, dok se druge analogije mogu pronaći na reljefu dve žrtve iz Luvra i bareljefu iz Sabrate u Libiji. Može se pretpostaviti da je spomenik iz Singidunuma sa predstavama svečane žrtvene procesije bio votivni oltar koji se nalazio u prostoru hrama posvećenog bogu Jupiteru ili, manje verovatno, nekom od drugih značajnih rimskih bogova, blizu pretpostavljenog rimskog foruma u Singidunumu, gde je i pronađen. Monumentalni spomenik iz Singidunuma datuje se u vreme od druge polovine 2. veka do početka 3. veka.A monumental altar was found in the very centre of Belgrade, ancient Singidunum, in 1932, with iconographic scenes of the sacrificial procession for a ritual animal sacrifice - immolatio. The scenes depict the procession of sacrificial animals to the altar known as pompa, by the victimarii, but also represent priests of a lower rank (flamines minores), with ritual utensils like a wine-pitcher, patera and acerra, used for the ritus of purification which precedes the sacrifice and for ritual acts during the sacrifice. The altar from Singidunum represents a unique monument with the described iconography in the territory of Moesia Superior and it has only been published in catalogue form to date, never fully analysed or interpreted. Through the analysis of its iconography, typology, function, geographically closest analogies and possible context of its finding, new conclusions regarding the praxis of public ritual sacrifice are brought to light related to the period from the second half of the 2nd century to the first decades of the 3rd century in Singidunum, one of the main centres of Moesia Superior

NLTE solar irradiance modeling with the COSI code

Context. The solar irradiance is known to change on time scales of minutes to decades, and it is suspected that its substantial fluctua- tions are partially responsible for climate variations. Aims. We are developing a solar atmosphere code that allows the physical modeling of the entire solar spectrum composed of quiet Sun and active regions. This code is a tool for modeling the variability of the solar irradiance and understanding its influence on Earth. Methods. We exploit further development of the radiative transfer code COSI that now incorporates the calculation of molecular lines. We validated COSI under the conditions of local thermodynamic equilibrium (LTE) against the synthetic spectra calculated with the ATLAS code. The synthetic solar spectra were also calculated in non-local thermodynamic equilibrium (NLTE) and compared to the available measured spectra. In doing so we have defined the main problems of the modeling, e.g., the lack of opacity in the UV part of the spectrum and the inconsistency in the calculations of the visible continuum level, and we describe a solution to these problems. Results. The improved version of COSI allows us to reach good agreement between the calculated and observed solar spectra as measured by SOLSTICE and SIM onboard the SORCE satellite and ATLAS 3 mission operated from the Space Shuttle. We find that NLTE effects are very important for the modeling of the solar spectrum even in the visual part of the spectrum and for its variability over the entire solar spectrum. In addition to the strong effect on the UV part of the spectrum, NLTE effects influence the concentration of the negative ion of hydrogen, which results in a significant change of the visible continuum level and the irradiance variability.Comment: 14 pages, 14 figures, accepted for publication in Astronomy&Astrophysic

Explanation of the activity sensitivity of Mn I 5394.7 \AA

There is a long-standing controversy concerning the reason why the Mn I 5394.7 A line in the solar irradiance spectrum brightens more at larger activity than most other photospheric lines. The claim that this activity sensitivity is caused by spectral interlocking to chromospheric emission in Mg II h & k is disputed. Classical one-dimensional modeling is used for demonstration; modern three-dimensional MHD simulation for verification and analysis. The Mn I 5394.7 A line thanks its unusual sensitivity to solar activity to its hyperfine structure. This overrides the thermal and granular Doppler smearing through which the other, narrower, photospheric lines lose such sensitivity. We take the nearby Fe I 5395.2 A line as example of the latter and analyze the formation of both lines in detail to demonstrate and explain granular Doppler brightening. We show that this affects all narrow lines. Neither the chromosphere nor Mg II h & k play a role, nor is it correct to describe the activity sensitivity of Mn I 5394.7 A through plage models with outward increasing temperature contrast. The Mn I 5394.7 A line represents a proxy diagnostic of strong-field magnetic concentrations in the deep solar photosphere comparable to the G band and the blue wing of H-alpha, but not a better one than these. The Mn I lines are more promising as diagnostic of weak fields in high-resolution Stokes polarimetry.Comment: 12 pages, 8 figures, accepted by A&