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Non-LTE modelling of prominence fine structures using hydrogen Lyman-line profiles
摘要： Aims. We perform a detailed statistical analysis of the spectral Lyman-line observations of the quiescent prominence observed on May 18, 2005. Methods. We used a pro?le-to-pro?le comparison of the synthetic Lyman spectra obtained by 2D single-thread prominence ?ne-structure model as a starting point for a full statistical analysis of the observed Lyman spectra. We employed 2D multi-thread ?ne-structure models with random positions and line-of-sight velocities of each thread to obtain a statistically signi?cant set of synthetic Lyman-line pro?les. We used for the ?rst time multi-thread models composed of non-identical threads and viewed at line-of-sight angles di?erent from perpendicular to the magnetic ?eld. Results. We investigated the plasma properties of the prominence observed with the SoHO/SUMER spectrograph on May 18, 2005 by comparing the histograms of three statistical parameters characterizing the properties of the synthetic and observed line pro?les. In this way, the integrated intensity, Lyman decrement ratio, and the ratio of intensity at the central reversal to the average intensity of peaks provided insight into the column mass and the central temperature of the prominence ?ne structures.
关键词： radiative transfer,line: pro?les,methods: statistical,Sun: ?laments,prominences
更新于2025-09-23 15:21:21
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Infrared Detection of Abundant CS in the Hot Core AFGL 2591 at High Spectral Resolution with SOFIA/EXES
摘要： We have performed a 5–8 μm spectral line survey of the hot molecular core associated with the massive protostar AFGL 2591, using the Echelon-Cross-Echelle Spectrograph (EXES) on board the Stratospheric Observatory for Infrared Astronomy (SOFIA). We have supplemented these data with a ground-based study in the atmospheric M band around 4.5 μm using the iSHELL instrument on the Infrared Telescope Facility (IRTF), and the full N-band window from 8 to 13 μm using the Texas Echelon Cross Echelle Spectrograph (TEXES) on the IRTF. Here we present the ?rst detection of rovibrational transitions of CS in this source. The absorption lines are centered on average around ?10 km s?1 and the line widths of CS compare well with the hot component of 13CO (around 10 km s?1). Temperatures for CS, hot 13CO, and 12CO v = 1–2 agree well and are around 700 K. We derive a CS abundance of 8 × 10?3 and 2 × 10?6 with respect to CO and H2, respectively. This enhanced CS abundance with respect to the surrounding cloud (1 × 10?8) may re?ect sublimation of H2S ice followed by gas-phase reactions to form CS. Transitions are in local thermodynamic equilibrium and we derive a density of >107 cm?3, which corresponds to an absorbing region of <0.04″. EXES observations of CS are likely to probe deeply into the hot core, to the base of the out?ow. Submillimeter and infrared observations trace different components of the hot core as revealed by the difference in systemic velocities, line widths, and temperatures, as well as the CS abundance.
关键词： ISM: abundances,line: pro?les,infrared: ISM,ISM: individual objects (AFGL 2591),astrochemistry,line: identi?cation
更新于2025-09-10 09:29:36
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Probing photospheric magnetic fields with new spectral line pairs
摘要： Context. The magnetic line ratio (MLR) method has been extensively used in the measurement of photospheric magnetic ?eld strength. It was devised for the neutral iron line pair at 5247.1 ? and 5250.2 ? (5250 ? pair). Other line pairs as well-suited as this pair have not been reported in the literature. Aims. The aim of the present work is to identify new line pairs useful for the MLR technique and to test their reliability. Methods. We used a three-dimensional magnetohydrodynamic 3D MHD simulation representing the quiet Sun atmosphere to synthesize the Stokes pro?les. Then, we applied the MLR technique to the Stokes V pro?les to recover the ?elds in the MHD cube both at original resolution and after degrading with a point spread function. In both these cases, we aim to empirically represent the ?eld strengths returned by the MLR method in terms of the ?eld strengths in the MHD cube. Results. We have identi?ed two new line pairs that are very well adapted to be used for MLR measurements. The ?rst pair is in the visible, Fe i 6820–6842 ?, whose intensity pro?les have previously been used to measure stellar magnetic ?elds, and the other pair is in the infrared (IR), Fe i 15 534–15 542 ?. The lines in these pairs reproduce the magnetic ?elds in the MHD cube rather well and, in fact, somewhat better than the original 5250 ? pair. Conclusions. The newly identi?ed line pairs complement the old pairs. The lines in the new IR pair, because of their higher Zeeman sensitivity, are ideal for the measurement of weak ?elds. The new visible pair works best above 300 G. The new IR pair, due to its large Stokes V signal samples more ?elds in the MHD cube than the old IR pair at 1.56 μm, even in the presence of noise, and hence likely also on the real Sun. Owing to their low formation heights (100–200 km above τ5000 = 1), both the new line pairs are well suited for probing magnetic ?elds in the lower photosphere.
关键词： Sun: photosphere,line: pro?les,Sun: magnetic ?elds,polarization,line: formation
更新于2025-09-10 09:29:36
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H <i>α</i> spectroscopy and multiwavelength imaging of a solar flare caused by filament eruption
摘要： Context. We study a sequence of eruptive events including ?lament eruption, a GOES C4.3 ?are, and a coronal mass ejection. Aims. We aim to identify the possible trigger(s) and precursor(s) of the ?lament destabilisation, investigate ?are kernel characteristics, ?are ribbons/kernels formation and evolution, study the interrelation of the ?lament-eruption/?are/coronal-mass-ejection phenomena as part of the integral active-region magnetic ?eld con?guration, and determine Hα line pro?le evolution during the eruptive phenomena. Methods. Multi-instrument observations are analysed including Hα line pro?les, speckle images at Hα – 0.8 ? and Hα + 0.8 ? from IBIS at DST/NSO, EUV images and magnetograms from the SDO, coronagraph images from STEREO, and the X-ray ?ux observations from Fermi and GOES. Results. We establish that the ?lament destabilisation and eruption are the main triggers for the ?aring activity. A surge-like event with a circular ribbon in one of the ?lament footpoints is determined as the possible trigger of the ?lament destabilisation. Plasma draining in this footpoint is identi?ed as the precursor for the ?lament eruption. A magnetic ?ux emergence prior to the ?lament destabilisation followed by a high rate of ?ux cancellation of 1.34 × 1016 Mx s?1 is found during the ?are activity. The ?are X-ray lightcurves reveal three phases that are found to be associated with three di?erent ribbons occurring consecutively. A kernel from each ribbon is selected and analysed. The kernel lightcurves and Hα line pro?les reveal that the emission increase in the line centre is stronger than that in the line wings. A delay of around 5–6 min is found between the increase in the line centre and the occurrence of red asymmetry. Only red asymmetry is observed in the ribbons during the impulsive phases. Blue asymmetry is only associated with the dynamic ?lament.
关键词： Sun: activity,Sun: ?ares,line: pro?les,Sun: ?laments,prominences
更新于2025-09-10 09:29:36
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Direct observation of the energy release site in a solar flare by SDO/AIA, Hinode/EIS, and RHESSI
摘要： the detection of Aims. We present direct evidence of the main energy release site in a non-eruptive solar ?are, SOL2013-11-09T06:38 UT. This GOES class C2.6 event was characterised by two ?aring ribbons and a compact, bright coronal source located between them, which is the focus of our study. Methods. We use imaging from SDO/AIA, and imaging spectroscopy from RHESSI to characterise the thermal and non-thermal emission from the coronal source, and EUV spectroscopy from the Hinode/Extreme ultraviolet Imaging Spectrometer, which scanned the coronal source during the impulsive peak, to analyse Doppler shifts in Fe xii (log T = 6.2) and Fe xxiv (log T = 7.2) emission lines, and determine the source density. Results. The coronal source exhibited an impulsive emission lightcurve in all SDO/AIA ?lters during the impulsive phase. RHESSI hard X-ray images indicate both thermal and non-thermal emission at the coronal source, and its plasma temperature derived from RHESSI imaging spectroscopy shows an impulsive rise, reaching a maximum at 12–13 MK about 10 s prior to the hard X-ray peak. High red-shifts associated with this bright source indicate down?ows of 40–250 km s?1 at a broad range of temperatures, interpreted as loop shrinkage and/or out?ows along the magnetic ?eld. Out?ows from the coronal source towards each ribbon are also observed by SDO/AIA images at 171, 193, 211, 304, and 1600 ?. The electron density of the source obtained from a Fe xiv line pair is 1011.50 cm?3 which is collisionally thick to electrons with energy up to 45–65 keV, responsible for the source’s non-thermal X-ray emission. Conclusions. Given the rich observational evidence, we conclude that the bright coronal source is the location of the main release of magnetic energy in this ?are, with a geometry consistent with component reconnection between crossing, current-carrying loops. We argue that the energy that can be released via reconnection, based on observational estimates, can plausibly account for the non-thermal energetics of the ?are.
关键词： Sun: UV radiation,Sun: ?ares,line: pro?les,magnetic reconnection,Sun: corona,Sun: X-rays, gamma rays
更新于2025-09-10 09:29:36
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Spatially resolved spectroscopy across stellar surfaces
摘要： Context. High-precision stellar analyses require hydrodynamic modeling to interpret chemical abundances or oscillation modes. Exoplanet atmosphere studies require stellar background spectra to be known along the transit path while detection of Earth analogs require stellar microvariability to be understood. Hydrodynamic 3D models can be computed for widely di?erent stars but have been tested in detail only for the Sun with its resolved surface features. Model predictions include spectral line shapes, asymmetries, and wavelength shifts, and their center-to-limb changes across stellar disks. Aims. We observe high-resolution spectral line pro?les across spatially highly resolved stellar surfaces, which are free from the e?ects of spatial smearing and rotational broadening present in full-disk spectra, enabling comparisons to synthetic pro?les from 3D models. Methods. During exoplanet transits, successive stellar surface portions become hidden and di?erential spectroscopy between various transit phases provides spectra of small surface segments temporarily hidden behind the planet. Planets cover no more than ～1% of any main-sequence star, enabling high spatial resolution but demanding very precise observations. Realistically measurable quantities are identi?ed through simulated observations of synthetic spectral lines. Results. In normal stars, line pro?le ratios between various transit phases may vary by ～0.5%, requiring S /N (cid:38) 5000 for meaningful spectral reconstruction. While not yet realistic for individual spectral lines, this is achievable for cool stars by averaging over numerous lines with similar parameters. Conclusions. For bright host stars of large transiting planets, spatially resolved spectroscopy is currently practical. More observable targets are likely to be found in the near future by ongoing photometric searches.
关键词： line: pro?les,hydrodynamics,stars: atmospheres,planets and satellites: gaseous planets,techniques: spectroscopic,stars: solar-type
更新于2025-09-10 09:29:36
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Thermal Doppler Broadening of Spectral Emissions in Space and Astrophysical Plasmas
摘要： The paper develops analytical modeling of thermal Doppler broadening of spectral pro?les for particle populations described by kappa distributions, in the absence or presence of potential ?elds. The kappa distribution provides a straightforward replacement for the Maxwell distribution, that is, a generalization for describing systems characterized by local correlations among their particles, commonly found in space and astrophysical plasmas. The corresponding Voigt pro?les are derived by convoluting the thermal and natural/collisional Lorentzian pro?les. The kappa velocity distributions are employed to derive the thermal Doppler and Voigt pro?les, while the kappa phase-space distributions in the presence of potential ?elds that depend on the position vector, are used to derive their respective differential pro?les. We focus on attractive power-law potentials (oscillation-type, gravitational-type, and angular potentials), and study the variations of the produced Voigt differential pro?les in detail. The developed formulations and guidelines provide a useful and statistically well-grounded “toolbox” for future reference in data analyses, simulations, analytical modeling, and theories of spectroscopy and related subjects of space and astrophysical plasmas.
关键词： techniques: spectroscopic,Sun: heliosphere,atomic data,plasmas,methods: analytical,line: pro?les
更新于2025-09-09 09:28:46
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Effects of resonant scattering of the Si?IV doublet near 140 nm in a solar active region
摘要： Aims. In a previous study we analysed the C iv 1548.189 ? and 1550.775 ? lines observed with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER), showing cases where the 1548.189 ? spectral pro?le was noticeably di?erent from the 1550.775 ? one, pro?les that we dubbed di?erentially shaped pro?les. We explained this di?erential behaviour by an important radiative contribution, a?ecting multiple plasma motions happening at the instrument sub-resolution scale. In the present study we examine more general cases where radiative e?ects may contribute to the emission from the transition region of an active region. Here we analyse the lines Si iv 1393.757 ? and 1402.772 ? observed with the Interface Region Imaging Spectrograph (IRIS). Methods. We study active region NOAA 12529, observed with IRIS on 18 April 2016. Using sorting techniques we selected individual pro?les for which the intensity line ratio 1393.757 ?/1402.772 ? is signi?cantly higher or lower than 2 and we also tracked di?erentially shaped pro?les. We analyse the physical conditions that create these pro?les and in some cases we estimate electron densities. Results. We found more than 4000 individual pro?les with line ratios higher than 2, about 500 pro?les for which the line ratio is in the range 1.3–1.6, and 15 di?erentially shaped pro?les. Line ratios higher than 2, are found along loops, and mostly at the y = 250 to 300(cid:48)(cid:48) part of the plage. There, we estimated the incident radiation and derived electron densities that can vary from 109 to a few times 1011 cm?3, depending on the plasma temperature. For the low line ratios, the sources are concentrated at the periphery of the active region plage, mostly along ?brils and present optical depths, τ, between 1.5 and 3. in most cases. The electron densities calculated from these Si iv pro?les are comparable with electron densities derived using the O iv 1399.766 ?-1401.163 ? ratios. Conclusions. We found that about 2.4% of the individual pro?les for which we can perform a Gaussian ?t present a line ratio higher than 2. In pro?les with a high line ratio, the resonant scattering appears to be due to the combination of an average incident radiation ?eld with a relatively low local electron density and not due to the vicinity of an ephemeral strong light source. As far as low intensity ratios are concerned, non-negligible optical depths are found at the edge of the plage, near the footpoints of ?brils that are oriented towards quiet Sun areas, where the electron density can be as high as (7 ? 9) × 1011 cm?3 if we assume a plasma in ionization equilibrium.
关键词： line: pro?les,line: formation,Sun: transition region
更新于2025-09-04 15:30:14
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Radiative transfer in cylindrical threads with incident radiation
摘要： Aims. Our aim is to improve on previous radiative transfer calculations in illuminated cylindrical threads to better understand the physical conditions in cool solar chromospheric and coronal structures commonly observed in hydrogen and helium lines. Methods. We solved the radiative transfer and statistical equilibrium equations in a two-dimensional cross-section of a cylindrical structure oriented horizontally and lying above the solar surface. The cylinder is ?lled with a mixture of hydrogen and helium and is illuminated at a given altitude from the solar disc. We constructed simple models made from a single thread or from an ensemble of several threads along the line of sight. This ?rst use of two-dimensional, multi-thread ?ne structure modelling combining hydrogen and helium radiative transfer allowed us to compute synthetic emergent spectra from cylindrical structures and to study the e?ect of line-of-sight integration of an ensemble of threads under a range of physical conditions. We analysed the e?ects of variations in temperature distribution and in gas pressure. We considered the e?ect of multi-thread structures within a given ?eld of view and the e?ect of peculiar velocities between the structures in a multi-thread model. We compared these new models to the single thread model and tested them with varying parameters. Results. The presence of a temperature gradient, with temperature increasing towards the edge of the cylindrical thread, reduces the relative importance of the incident radiation coming from the solar disc on the emergent intensities of most hydrogen and helium lines. We also ?nd that when assuming randomly displaced threads in a given ?eld of view, the integrated intensities of optically thick and thin transitions behave considerably di?erently. In optically thin lines, the emergent intensity increases proportionally with the number of threads, and the spatial variation of the intensity becomes increasingly homogeneous. Optically thick lines, however, saturate after only a few threads. As a consequence, the spatial variation of the intensity retains much similarity with that of the ?rst few threads. The multi-thread model produces complex line pro?les with signi?cant asymmetries if randomly generated line-of-sight velocities are added for each thread. Conclusions. These new computations show, for the ?rst time, the e?ect of integrating the radiation emitted in H and He lines by several cylindrical threads that are static or moving along the line of sight. They can be used to interpret high-spatial and spectral resolutions of cylindrical structures found in the solar atmosphere, such as cool coronal loops or prominence threads.
关键词： line: pro?les,Sun: chromosphere,Sun: corona,radiative transfer,line: formation
更新于2025-09-04 15:30:14
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Spectroscopy of the K0 Binary Giant <i>α</i> UMa
摘要： High-resolution spectroscopic observations of the K0 II–III star α UMa were taken at the Elgin?eld Observatory over 11 years. Radial velocities were measured for nine of these years. They do not cover enough of the 44.5 year orbital period to give de?nitive elements on their own, but combined with published visual orbits, the spectroscopic-orbit parameters are well constrained. The spectra show no evidence of the secondary star, which remains an unsolved puzzle. Line-depth ratios show that α UMa has temperature variations ～3 K, possibly periodic, over the 2001–2010 interval. Fourier analysis of the line broadening gives the projected rotation velocity of 2.66 ± 0.15 km s?1 and a radial-tangential macroturbulence dispersion of 4.97 ± 0.08 km s?1. The third-granulation signature shows the granulation velocities of α UMa to be essentially solar, with a scale factor of 0.98 ± 0.10. The absolute radial velocity of the star, with granulation blueshifts removed is ?10,035 ± 100 m s?1 at the mean time of the observations, 2005.2544. The line bisector of Fe I λ6253 is normal and shows the classic “C” shape with the blue-most point commensurate with its absolute magnitude. Mapping this bisector on to the third signature gives a ?ux de?cit similar to those of other giants, with a fractional area of 0.131, suggesting a temperature difference between granules and lanes of 127 K. The velocity position of the de?cit is slightly higher than that for previously analyzed giants, extending the correlation with absolute magnitude.
关键词： line: pro?les,stars: late-type,techniques: spectroscopic,Sun: granulation,stars: rotation,binaries: spectroscopic
更新于2025-09-04 15:30:14