No description available.

Helically shaped magnetic field structuresknown as coronal mass ejections (CMEs) are closely related to so-called eruptive flares. On the one hand, these events are broadly believed to be due tothe buoyant rise of magnetic flux tubes from the bottom of the convection zone to the photosphere where they form structures such as sunspots. On the other hand, models of eruptive flares and CMEs have no connection to the convection zone and the magnetic field generated bydynamo action. It is well known that a dynamo can produce helical structures and twisted magnetic fields as observed in the Sun. In this work we ask, how a dynamo-generated magnetic field appears above the surface without buoyancy force and how this field evolves inthe outer atmosphere of the Sun. We apply a new approach of a two layer model, where the lower one represents the convection zone and the upper one the solar corona. The two layers are included in one single simulation domain. In the lower layer, we use a helical forcing function added to the momentum equation to create a turbulent dynamo. Due to dynamo action, a large-scale field is formed. As a first step we use a Cartesian cube. We solve the equations of the so-called force-free model in the upper layer to create nearly force-free coronal magnetic fields. In a second step we use a spherical wedge, which extends radially from 0.7 to 2 solar radii. We include density stratification due to gravity in anisothermal domain. The wedge includes both hemispheres of the Sun and we apply a helicalforcing with different signs in each hemisphere. As a result, a large-scale field is generated by a turbulent dynamo acting underneath the surface. Due to the latitudinal variation of the helicity produced by the helical forcing, the dynamo is oscillating in the spherical wedge. Twisted magnetic fields emerge above the surface and form arch-like structures with strong current sheets. Plasmoids and CME-like structures are ejected recurrently into the outerlayers. In the spherical simulations we find that the magnetic helicity changes sign in the exterior, which is in agreement with recent analysis of the solar wind data.

No description available.

The advancing resolution of modern spectrometers uncovers increasingly detailed spectral features in astrophysical observations which can be attributed to properties of the energy structure of the corresponding atomic systems such as fine, hyperfine and Zeeman splitting. At the same time, increasing computational power enables us to include these quantum mechanical interactions on different levels of sophistication in our theoretical atomic structure calculations. This project aims at investigating the hyperfine and Zeeman splitting in five spectral lines of singly-ionized Europium which are relevant for astrophysical studies. To that end, we perform ab initio atomic structure calculations with the latest versions of the code packages Grasp2018 and Rhyze in which we treat the two interactions with a) first-order perturbation theory and b) a generalised full-matrix (`all-order') approach. For both sets of atomic data, we synthesize stellar Stokes I and V spectra for a model atmosphere and stellar magnetic field regime typical for magnetic, chemically peculiar Ap stars. We confirm the overall importance of accounting for hyperfine and Zeeman interactions in the atomic data and find significant differences between the two approaches in the synthesized spectra for the Zeeman interaction. The established computational machinery represents a systematic and largely generalised approach to synthesize spectra of magnetic stars from purely ab initio atomic calculations, including hyperfine and Zeeman interaction simultaneously for any atomic species in the periodic table.

The goal of this work is to detect Zeeman split lines and measure magnetic field strength in a sample of Ap stars. This work aims to analyse spectra of 454 stars and find stars that show spectral lines resolved into their magnetically split components. The work included writing and applying a computer code to visualize astronomical spectra and estimate the mean surface magnetic field strength by fitting resolved Zeeman split lines. The data represent spectroscopic measurements obtained from November 2018 to March 2020 with the HERMES spectrograph. This study investigated high-resolution spectra of 454 Ap stars and identified 31 stars showing resolved Zeeman split lines. The majority of these stars were already known to have resolved magnetically split lines, but this paper reports the discovery of 12 new stars having this property. This paper presents 67 measurements of the mean magnetic field modulus of 31 Ap stars with resolved magnetically split lines.

The majority of stars in the Milky Way are M dwarfs whichmake up 75 % of stars in the vicinity of the sun. As the magneticfield of stars can significantly affect the interiors and theatmospheres of the exoplanets they host within the stellar system,characterising this magnetic field is of major importance.In this work, we selected a sample of 23 exoplanet hostM dwarfs and analysed the observations made by the highresolutionspectropolarimeters ESPaDOnS and NARVAL availablein PolarBase for these stars. In particular, we used theLSD Stokes I and V spectra to measure the projection alongthe line of sight of the average magnetic field over the stellarsurface. 60% of stars had a likely magnetic signatures with adetection greater than 2. By taking the maximum value foreach star over the different observations, the median magneticfield strength measured was 55 G and only a few stars exceeded100 G in strength.

Supernova remnants (SNRs) are the end products of supernova (SN) explosions. These explosions happen when certain massive stars face the ends of their evolutionary cycle and create shock waves propagating in the surrounding medium by ejecting part of the star’s material. An SNR is the region defined by these powerful shocks. Due to the nature of SNRs spreading stellar material to their surroundings, they play a major part in the chemical evolution of the universe.  Some SNRs are observed to contain a pulsar (PSR), a spinning neutron star emitting electromagnetic radiation through its magnetic poles, and a pulsar-wind nebula (PWN), where relativistic particles and magnetic fields escaping the pulsar interact with the surroundings. This is the case for SNR 0540-69.3 (SNR0540), the so called twin of one of the most studied astronomical objects in the sky, the Crab Nebula. The attached paper (Paper I) is based on VLT observations of the central regions of SNR 0540 with the instruments MUSE and X-Shooter. The MUSE observations provide a possibility to study the optical spatial variations of SNR 0540 for the first time utilising spectroscopy, and are in general one of the few such studies of PWNe in the optical. On the other hand, earlier works focusing on the shape of the SNR 0540 continuum spectrum in the optical wavelengths have mostly utilised narrow band photometry, which has yielded conflicting results. The X-shooter observations of SNR 0540 providing the first near-infrared (NIR) spectrum with a good coverage in the optical can be used to tackle these problems.  In Paper I, the continuum emission is modelled by power-law models to constrain the underlying conditions in the PSR and PWN in SNR 0540. An important parameter in these models is called the spectral index (α), which determines the slope of the spectrum. We find significant spatial variations in the spectral index that reveal a torus-jet structure around the PSR, confirming earlier results. Surprisingly, we also find that the spectral index decreases (from α ~ 1.7 to α ~ 0.5) toward the outer parts of the PWN and is the largest for the PSR (α1 ~ 1 in the low and α2 ~ 2 in the high frequencies), in contrast to theoretical expectations for the basic scenario of synchrotron cooling. Additionally, two spectral indices seem to be required to characterise both the PSR’s and PWN’s optical(-NIR) spectra.  Future observations in the optical but also in the infrared and X-rays would help understanding the complex conditions in the central regions of SNRs. Most importantly, optical observations of other SNRs would shed light on whether SNR 0540 is a special case. The unexpected spectral index variations in SNR 0540 highlight the need for further theoretical work to better understand the origin of the optical synchrotron emission in PSRs and PWNe. / Supernovarester (SNR) är slutprodukterna av supernovaexplosioner (SN). Dessa explosioner inträffar när vissa massiva stjärnor möter ändarna av sin evolutionära cykel och skapar chockvågor som fortplantar sig i det omgivande mediet genom att stöta ut en del av stjärnans material. En SNR är regionen som definieras av dessa kraftfulla stötar. På grund av naturen hos SNR som sprider stjärnmaterial till sin omgivning spelar de en stor roll i universums kemiska utveckling.  Vissa SNR:er har observerats innehålla en pulsar (PSR), en snurrande neutronstjärna som sänder ut elektromagnetisk strålning genom sina magnetiska poler, och en pulsar-vindnebulosa (PWN), där relativistiska partiklar och magnetfält som flyr pulsarn interagerar med omgivningen. Detta är fallet för SNR 0540-69.3 (SNR 0540), den så kallade tvillingen till ett av de mest studerade astronomiska objekten på himlen, Krabbanebulosan. Bifogade papper (Paper I) är baserad på VLT-observationer av de centrala regionerna i SNR 0540 med instrumenten MUSE och X-Shooter. MUSE-observationerna ger en möjlighet att studera de optiska rumsliga variationerna av SNR 0540 för första gången med hjälp av spektroskopi, och är i allmänhet en av få sådana studier av PWNe i optiken. A andra sidan har tidigare arbeten med fokus på formen av SNR 0540-kontinuumspektrumet i de optiska våglängderna mestadels använt smalbandsfotometri, vilket har gett motstridiga resultat. X-shooter-observationerna av SNR 0540 som ger det första nära-infraröda (NIR) spektrumet med en bra täckning i optiken kan användas för att ta itu med dessa problem.  I Paper I modelleras synkrotronemissionen av potenslagsmodeller för att begränsa de underliggande förhållandena i PSR och PWN i SNR 0540. En viktig parameter i dessa modeller kallas spektralindex (α), som bestämmer spektrumets lutning. Vi hittar betydande rumsliga variationer i det spektrala indexet som avslöjar en torus-jet-struktur runt PSR, vilket bekraftar tidigare resultat. Överraskande nog finner vi också att spektralindexet minskar (från α ~ 1.7 till α ~ 0.5) mot de yttre delarna av PWN och är störst för PSR (α1 ~ 1 i de låga och α2 ~ 2 i de höga frekvenserna), i motsats till teoretiska förväntningar på grundscenariot med synkrotronkylning. Dessutom verkar två spektrala index krävas för att karakterisera både PSR:s och PWN:s optiska(-NIR) spektra.  Framtida observationer inom det optiska, men också i det infraröda och röntgenstrålar skulle hjälpa till att förstå de komplexa förhållandena i de centrala regionerna av SNR. Det viktigaste är att optiska observationer av andra SNR:er skulle belysa om SNR 0540 är ett specialfall. De oväntade spektrala indexvariationerna i SNR 0540 belyser behovet av ytterligare teoretiskt arbete för att bättre förstå ursprunget till den optiska synkrotronemissionen i PSR och PWNe. / <p>QC 2023-05-23</p>

In this report calibration of the four probes attached onto the JUICE spacecraft has been made.The JUICE spacecraft (JUpiter Icy Moon Explorer) is a spacecraft which will investigate theenvironment on and around Jupiter and its four biggest moons. On the spacecraft are 10different instruments onboard, where one of the instruments is the Radio and Plasma WaveInvestigator (RPWI). The mission of RPWI is to measure the electromagnetic field and plasmaparticles, among other things around the Jovian system. To analyse the measured data fromthe probe, the data has to be calibrated. In this report test data and raw flight data of the probeshas been calibrated by digital-analog converting the signal. The data SID 1 and SID 3, whichboth measure the electric field, the calibration was successful both for the ground test data andthe raw flight data. However, the calibration of SID 2, which measure the plasma density, didnot give the calibrated analog signal within expected range. Possible sources of error for thatdeviation includes error in the Fourier Transform of the transfer function. The raw flight data forSID 1 and 2 was further disturbed by solar wind, resulting in high measured signals for theelectric field and the plasma density. For future improvements this calibration method could berepeated on another set of data without disturbance to verify the calibration method and identifypotential source of error.

In this report, we constrain properties of foreground objects in the Milky Way that have the potential of being confused with accretion disks of Population III stellar- mass black holes at high redshift. Following Windhorst et al. (2018), a model for multicolour accretion disks of Population III stellar-mass black holes is presented. The resulting spectra are used to derive observable magnitudes with the James Webb Space Telescope (JWST). Magnification of a factor 103 to 106, depending on the black hole mass, through gravitational lensing is necessary to surpass the JWST detection limit. Spectra of faint Milky Way objects of low-mass main sequence or pre-main sequence stars (Baraffe et al. 2015) and cool brown dwarfs and giant exoplanets (Phillips et al. 2020) were fitted to a distance such that their observable JWST magnitudes are similar to those of the accretion disk. We find that the spectral energy distributions that have the highest chances of being confused with high redshift Population III black hole accretion disks belong to pre-main sequence and low-mass main sequence stars of temperature 1500 K to 4200 K. At redshift 𝑧 = 7, accretion disks most closely resemble the spectral energy distributions of 2830 K Milky Way objects. Cool brown dwarfs or giant exoplanets with chemical equilibrium atmospheres at temperature ∼ 2700 K or chemical non-equilibrium atmospheres at ∼ 1790 K most closely resemble the spectral energy distribution of redshift 𝑧 = 7–8. Although the SEDs produce good fits, a confusion probability can sometimes be reduced because the models are very young (0.5 to 10 Myr) or have distances corresponding to the stellar halo (≳ 200 kpc).

In this project, we investigate the plasma heating associated with coherent structures, such as current sheets and vortices, in different solar wind conditions: slow solar wind, stream interaction regions, and heliospheric current sheets, observed by the Solar Or- biter mission. To unravel this mystery, we first use the Partial Variance of Increment method [1] to locate these coherent structures. We then employ correlation functions to determine the coexistence of these structures and investigate the global elevation of plasma temperature [2]. Additionally, we employ a quantitative analysis of conditioned PVI [3] to examine the local increase in plasma temperature [4]. The results clearly indicate that plasma heating takes place at and near these struc- tures. Specifically, current sheets locally heat the plasma, while plasma vortices have a global impact on heating. A characteristic timescale of approximately 200 seconds emerges, separating the local heating of coherent structures from other heating sources. In slow solar wind and stream interaction regions, we observe clusters of coherent structures with sizes ranging from 4 to 6 hours, underlain by a scale of 1 to 2 hours. The heliospheric current sheet does not exhibit such modulation. These coherent struc- ture clusters are embedded within larger macroscopic structures spanning 12 to 24 hours.