Microturbulent Velocity Research Articles

Fourier analysis of spectra of solar-type stars

Fourier transform techniques were used to determine the macroturbulent velocity under the condition that mictoturbulent and stellar rotation velocities are not known. In order to distinguish the effects of rotation from macroturbulence effects in slowly rotating stars, primarily the main lobe of residual Fourier transforms of the observed lines, which were taken from the solar spectrum and the spectra of two other stars, was used. This case of Fourier analysis of spectral lines is the most complicated one. The end results were in a satisfactory agreement with the data obtained using different methods. The average values of microturbulent, macroturbulent, and rotation velocities were 0.85, 2.22, and 1.75 km/s for the Sun as the star; 0.58, 1.73, and 0.78 km/s for HD 10700; and 1.16, 3.56, and 6.24 km/s for HD 1835. It was found that the macroturbulent velocity decreases with height in the atmosphere of the Sun and HD 1835. In the case of HD 10700, the macroturbulent velocity did not change with height, and the determined rotation velocity was two times lower than the one obtained using other methods. It was concluded that Fourier transform techniques are suitable for determining the velocities in atmospheres of solar-type stars with very slow rotation.

Chemical Composition of RM_1-390 - Large Magellanic Cloud Red Supergiant

A high resolution spectroscopic observation of the red supergiant star RM_1-390 in the Large Magellanic Cloud was made from a 3.6 m telescope at the European Southern Observatory. Spectral resolving power was R=20,000, with a signal-to-noise ratio S/N > 100. We found the atmospheric parameters of RM_1-390 to be as follows: the effective temperature Teff = 4,250 ± 50 K, the surface gravity log g = 0.16 ± 0.1, the microturbulent velocity vmicro = 2.5 km/s, the macroturbulence velocity vmacro = 9 km/s and the iron abundance [Fe/H] = -0.73 ± 0.11. The abundances of 18 chemical elements from silicon to thorium in the atmosphere of RM_1-390 were found using the spectrum synthesis method. The relative deficiencies of all elements are close to that of iron. The fit of abundance pattern by the solar system distribution of r- and s-element isotopes shows the importance of the s-process. The plot of relative abundances as a function of second ionization potentials of corresponding chemical elements allows us to find a possibility of convective energy transport in the photosphere of RM_1-390.

Analysis of the Non-LTE Lithium Abundance for a Large Sample of F-, G-, and K-Giants and Supergiants

A five-dimensional interpolation method and corresponding computer program are developed for using published calculations to determine the non-LTE correction {\Delta\}NLTE to the lithium abundance log{\epsilon}(Li) derived from the Li I 6707.8 {\AA} line. The {\Delta\}NLTE values is determined from the following five parameters: {\Delta\}NLTE the effective temperature Teff, the acceleration of gravity logg, the metallicity index [Fe/H], the microturbulent velocity Vt, and the LTE Li abundance log {\epsilon}(Li). The program is used to calculate values of {\Delta\}NLTE and the non-LTE Li abundance for 91 single bright giants from the list of Lebre, et al. By combining these results with data for 55 stars, we obtain the non-LTE values of log {\epsilon}(Li) for 146 FGK-giants and supergiants. We confirm that, in the spectra of most of these stars, it is only possible to estimate for them an upper limit for the Li abundance. A large spread is confirmed in log {\epsilon}(Li) for stars with masses M<6Msun. A comparison of these results with model calculations of stars confirms the unique sensitivity of the lithium abundance to the initial rotation velocity V0. We discuss the giants and supergiants with lithium abundances log {\epsilon}(Li) = 1.4 +- 0.3, which could have a rotation velocity V0=0 km/s and have already undergone deep convective mixing. Li-rich giants with lithium abundances log {\epsilon}(Li)>2 and nearly up to the initial value of log {\epsilon}(Li) = 3.2 +- 0.1 are examined. It is shown that the fraction of Li-rich giants with V0 = 0 - 50 km/s is consistent with current evolutionary models. The other stars of this type, as well as all of the "super Li-rich" giants, for which the standard theory is untenable, can be explained by invoking the hypothesis of recent lithium synthesis in the star or an alternative hypothesis according to which a giant planet is engulfed by the star.

GALEX J184559.8−413827: a new extreme helium star identified using SALT★

A high-resolution spectrum of the helium-rich `hot subdwarf' GALEX J184559.8-413827 (J1845-4138) obtained with SALT HRS demonstrates it to be the first extreme helium (EHe) star to be discovered in nearly 40 years. A quantitative analysis demonstrates it to have an atmosphere described by Teff = 26 170 +/- 750 K, log g /(cm s^-2) = 4.22 +/- 0.10, and a surface chemistry characterised by CNO-processed helium, a 1% contamination of hydrogen (by number), and a metallicity 0.4 dex subsolar. Its distance and position are consistent with membership of the Galactic bulge. Its sharp absorption lines place strong constraints on both the rotation and microturbulent velocities. Spectroscopically, J1845-4138 closely resembles the pulsating EHe star V652 Her, generally considered to be the product of a double helium white dwarf merger evolving to become a helium-rich sdO star.

The Origin of B-type Runaway Stars: Non-LTE Abundances as a Diagnostic

Abstract There are two accepted mechanisms to explain the origin of runaway OB-type stars: the binary supernova (SN) scenario and the cluster ejection scenario. In the former, an SN explosion within a close binary ejects the secondary star, while in the latter close multibody interactions in a dense cluster cause one or more of the stars to be ejected from the region at high velocity. Both mechanisms have the potential to affect the surface composition of the runaway star. tlusty non-LTE model atmosphere calculations have been used to determine the atmospheric parameters and the C, N, Mg, and Si abundances for a sample of B-type runaways. These same analytical tools were used by Hunter et al. for their analysis of 50 B-type open-cluster Galactic stars (i.e., nonrunaways). Effective temperatures were deduced using the Si-ionization balance technique, surface gravities from Balmer line profiles, and microturbulent velocities derived using the Si spectrum. The runaways show no obvious abundance anomalies when compared with stars in the open clusters. The runaways do show a spread in composition that almost certainly reflects the Galactic abundance gradient and a range in the birthplaces of the runaways in the Galactic disk. Since the observed Galactic abundance gradients of C, N, Mg, and Si are of a similar magnitude, the abundance ratios (e.g., N/Mg) are as obtained essentially uniform across the sample.

Spectroscopic survey of Kepler stars – II. FIES/NOT observations of A- and F-type stars

We have analysed high-resolution spectra of 28 A and 22 F stars in the Kepler field, observed with the FIES spectrograph at the Nordic Optical Telescope. We provide spectral types, atmospheric parameters and chemical abundances for 50 stars. Balmer, Fe I, and Fe II lines were used to derive effective temperatures, surface gravities, and microturbulent velocities. We determined chemical abundances and projected rotational velocities using a spectrum synthesis technique. Effective temperatures calculated by spectral energy distribution fitting are in good agreement with those determined from the spectral line analysis. The stars analysed include chemically peculiar stars of the Am and Lambda Boo types, as well as stars with approximately solar chemical abundances. The wide distribution of projected rotational velocity, Vsini, is typical for A and F stars. The microturbulence velocities obtained are typical for stars in the observed temperature and surface gravity ranges. Moreover, we affirm the results of Niemczura et al., that Am stars do not have systematically higher microturbulent velocities than normal stars of the same temperature.

An abundance analysis from the STIS-HST UV spectrum of the non-magnetic Bp star HR 6000

The sharp-line spectrum of the Bp star HR 6000 has peculiarities that distinguish it from those of the HgMn stars with which it is sometimes associated. The position of the star close to the center of the Lupus 3 molecular cloud, whose estimated age is on the order of 9.1 +/- 2.1 Myr, has lead to the hypothesis that the anomalous peculiarities of HR 6000 can be explained by the young age of the star. Observational material from HST provides the opportunity to extend the abundance analysis previously performed for the optical region and clarify the properties of this remarkable peculiar star. Our aim was to obtain the atmospheric abundances for all the elements observed in a broad region from 1250 to 10000 A. An LTE synthetic spectrum was compared with a high-resolution spectrum observed with STIS equipment in the 1250-3040 A interval. The adopted model is an ATLAS12 model already used for the abundance analysis of a high-resolution optical spectrum observed at ESO with UVES. The stellar parameters are Teff=13450K, logg=4.3, and zero microturbulent velocity. Abundances for 28 elements and 7 upper limits were derived from the ultraviolet spectrum. Adding results from previous work, we have now quantitative results for 37 elements, some of which show striking contrasts with those of a broad sample of HgMn stars. The analysis has pointed out ionization anomalies and line-to-line variation in the derived abundances, in particular for silicon. The inferred discrepancies could be explained by non-LTE effects and with the occurrence of diffusion and vertical abundance stratification. In the framework of the last hypothesis, we obtained, by means of trial and error, empirical step functions of abundance versus optical depth log(tau_5000) for carbon, silicon, manganese, and gold, while we failed to find such a function for phosphorous.

Limb and gravity-darkening coefficients for the TESS satellite at several metallicities, surface gravities, and microturbulent velocities

We present new gravity and limb-darkening coefficients for a wide range of effective temperatures, gravities, metallicities, and microturbulent velocities. These coefficients can be used in many different fields of stellar physics as synthetic light curves of eclipsing binaries and planetary transits, stellar diameters, line profiles in rotating stars, and others. The limb-darkening coefficients were computed specifically for the photometric system of the space mission TESS and were performed by adopting the least-square method. In addition, the linear and bi-parametric coefficients, by adopting the flux conservation method, are also available. On the other hand, to take into account the effects of tidal and rotational distortions, we computed the passband gravity-darkening coefficients $y(\lambda)$ using a general differential equation in which we consider the effects of convection and of the partial derivative $\left(\partial{\ln I(\lambda)}/{\partial{\ln g}}\right)_{T_{\rm eff}}$. To generate the limb-darkening coefficients we adopt two stellar atmosphere models: ATLAS (plane-parallel) and PHOENIX (spherical, quasi-spherical, and $r$-method). The specific intensity distribution was fitted using five approaches: linear, quadratic, square root, logarithmic, and a more general one with four terms. These grids cover together 19 metallicities ranging from 10$^{-5}$ up to 10$^{+1}$ solar abundances, 0 $\leq$ log g $\leq$ 6.0 and 1500 K $\leq$ T$_{\rm eff}$ $\leq$ 50000 K. The calculations of the gravity-darkening coefficients were performed for all plane-parallel ATLAS models.

The metal-rich abundance pattern – spectroscopic properties and abundances for 107 main-sequence stars

We report results from the high resolution spectral analysis of the 107 metal rich (mostly [Fe/H]$\ge$7.67 dex) target stars from the Calan-Hertfordshire Extrasolar Planet Search program observed with HARPS. Using our procedure of finding the best fit to the absorption line profiles in the observed spectra, we measure the abundances of Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Fe, Ni, Cu, and Zn, and we then compare them with known results from different authors. Most of our abundances agree with these works at the level of $\pm$0.05 dex or better for the stars we have in common. However, we do find systematic differences that make direct inferences difficult. Our analysis suggests that the selection of line lists and atomic line data along with the adopted continuum level influence these differences the most. At the same time, we confirm the positive trends of abundances versus metallicity for Na, Mn, Ni, and to a lesser degree, Al. A slight negative trend is observed for Ca, whereas Si and Cr tend to follow iron. Our analysis allows us to determine the positively skewed normal distribution of projected rotational velocities with a maximum peaking at 3 km s$^{-1}$. Finally, we obtained a Gaussian distribution of microturbulent velocities that has a maximum at 1.2 km s$^{-1}$ and a full width at half maximum $\Delta v_{1/2}=$0.35 km s$^{-1}$, indicating that metal rich dwarfs and subgiants in our sample have a very restricted range in microturbulent velocity.

Determination of abundances in the atmospheres of F-, G-, and K-dwarfs

The algorithm of the determination of abundances in atmospheres of stars of spectral classes F, G, and K using fits to the observed spectral lines or selected parts of the blended lines is discussed. The technique allows to determine the parameters of the atmosphere, i.e., gravity, microturbulent velocity, rotational velocity of the star, and abundance of elements, for a given effective temperature of the star. At each stage of the iterative process the model atmosphere is recalculated for a new set of input data. The results of applying the procedure for the analysis of the spectra of the Sun (G2 V) and HD 101348 (G3 V) are discussed.

Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars

Although oxygen is an important tracer of the early Galactic evolution, its abundance trends with metallicity are still relatively poorly known at [Fe/H] < -2.5. This is in part due to a lack of reliable oxygen abundance indicators in the metal-poor stars, in part due to shortcomings in 1D LTE abundance analyses. In this study we determined the oxygen abundance in the metal-poor halo giant HD 122563 using a 3D hydrodynamical CO5BOLD model atmosphere. Our main goal was to understand whether a 3D LTE analysis may help to improve the reliability of oxygen abundances determined from OH UV lines in comparison to those obtained using standard 1D LTE methodology. The oxygen abundance in HD 122563 was determined using 71 OH UV lines located in the wavelength range between 308-330 nm. The analysis was done using a high-resolution VLT UVES spectrum with a 1D LTE spectral line synthesis performed using the SYNTHE package and classical ATLAS9 model atmosphere. Subsequently, a 3D hydrodynamical CO5BOLD, and 1D hydrostatic LHD model atmospheres were used in order to compute 3D-1D abundance corrections. For this, the microturbulence velocity used with the 1D LHD model atmosphere was derived from the hydrodynamical CO5BOLD model atmosphere. As in previous studies, we found trends of the 1D LTE oxygen abundances determined from OH UV lines with line parameters, such as the line excitation potential and the line strength. These trends become significantly less pronounced in 3D LTE. Using OH UV lines we determined a 3D LTE oxygen abundance in HD 122563 of A(O) = 6.23 +/- 0.13. This is in fair agreement with the oxygen abundance obtained from OH IR lines, A(O) = 6.39 +/- 0.11, but it is noticeably lower than that determined using the forbidden [OI] line, A(O) = 6.53 +/- 0.15. While the exact cause for this discrepancy remains unclear, it is very likely that non-LTE effects may play a decisive role here.

Chemical abundance analysis of 13 southern symbiotic giants from high-resolution spectra at ∼1.56 μm

Symbiotic stars (SySt) are binaries composed of a star in the later stages of evolution and a stellar remnant. The enhanced mass-loss from the giant drives interacting mass exchange and makes these systems laboratories for understanding binary evolution. Studies of the chemical compositions are particularly useful since this parameter has strong impact on the evolutionary path. The previous paper in this series presented photospheric abundances for 24 giants in S-type SySt enabling a first statistical analysis. Here we present results for an additional sample of 13 giants. The aims are to improve statistics of chemical composition involved in the evolution of SySt, to study evolutionary status, mass transfer and to interpret this in terms of Galactic populations. High-resolution, near-IR spectra are used, employing the spectrum synthesis method in a classical approach, to obtain abundances of CNO and elements around the iron peak (Fe, Ti, Ni). Low-resolution spectra in the region around the Ca II triplet were used for spectral classification. The metallicities obtained cover a wide range with a maximum around ~-0.2 dex. The enrichment in the 14N isotope indicates that these giants have experienced the first dredge-up. Relative O and Fe abundances indicate that most SySt belong to the Galactic disc; however, in a few cases, the extended thick-disc/halo is suggested. Difficult to explain, relatively high Ti abundances can indicate that adopted microturbulent velocities were too small by ~0.2-0.3 km/s. The revised spectral types for V2905 Sgr, and WRAY 17-89 are M3 and M6.5, respectively.

Plasma Motions and Turbulent Magnetic Diffusivity of Active Region AR 12158 Using a Minimum Energy Functional and Non-Force-Free Reconstructions of Vector Magnetograms

We present a generalization of the resistive minimum-energy fit (MEF-R: Tremblay and Vincent, Solar Phys. 290, 437, 2015) for non-force-free (NFF) magnetic fields. In MEF-R, an extremum principle is used to infer two-dimensional maps of plasma motions [ $\boldsymbol{v}(x,y)$ ] and magnetic eddy diffusivity [ $\eta _{\mathrm{eddy}}(x,y)$ ] at the photosphere. These reconstructions could be used as boundary conditions in data-driven simulations or in data assimilation. The algorithm is validated using the analytical model of a resistive expanding spheromak by Rakowski, Laming, and Lyutikov (Astrophys. J. 730, 30, 2011). We study the flaring Active Region AR 12158 using a series of magnetograms and Dopplergrams provided by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). The results are discussed for a non-force-free magnetic-field reconstruction [ $\boldsymbol{B}_{\mathrm{NFF}}$ ] (Hu and Dasgupta in Solar Phys. 247, 87, 2008). We found that the vertical plasma velocities [ $v_{z}(x,y)$ ] inferred using MEF-R are very similar to the observed Doppler velocities [ $v_{r}(x,y)$ ]. Finally, we study the potential spatial correlation between microturbulent velocities and significant values of $\eta_{\mathrm{eddy}}(x,y)$ .

Stellar and wind parameters of massive stars from spectral analysis

AbstractThe only way to deduce information from stars is to decode the radiation it emits in an appropriate way. Spectroscopy can solve this and derive many properties of stars. In this work we seek to derive simultaneously the stellar and wind characteristics of a wide range of massive stars. Our stellar properties encompass the effective temperature, the surface gravity, the stellar radius, the micro-turbulence velocity, the rotational velocity and the Si abundance. For wind properties we consider the mass-loss rate, the terminal velocity and the line–force parameters α, k and δ (from the line–driven wind theory). To model the data we use the radiative transport code Fastwind considering the newest hydrodynamical solutions derived with Hydwind code, which needs stellar and line–force parameters to obtain a wind solution. A grid of spectral models of massive stars is created and together with the observed spectra their physical properties are determined through spectral line fittings. These fittings provide an estimation about the line–force parameters, whose theoretical calculations are extremely complex. Furthermore, we expect to confirm that the hydrodynamical solutions obtained with a value of δ slightly larger than ~ 0.25, called δ-slow solutions, describe quite reliable the radiation line-driven winds of A and late B supergiant stars and at the same time explain disagreements between observational data and theoretical models for the Wind–Momentum Luminosity Relationship (WLR).

Abundances in a sample of turnoff and subgiant stars in NGC 6121 (M 4)

{The aim of this work is to investigate the relations between the abundances of different elements in the globular cluster M4, selected for its uniform deficiency of iron, to explore the best models explaining the pattern of these observed abundances. Moreover, in turnoff stars, the abundances of the elements are not suspected to be affected by internal mixing. In M4, using low and moderate resolution spectra obtained for 91 turnoff (and subgiant) stars with the ESO FLAMES-Giraffe spectrograph, we have extended previous measurements of abundances (of Li, C and Na) to other elements (C, Si, Ca, Sr and Ba), using model atmosphere analysis. We have also studied the influence of the choice of the microturbulent velocity. Firstly, the peculiar turnoff star found to be very Li-rich in a previous paper does not show any other abundance anomalies relative to the other turnoff stars in M4. ~Secondly, an anti-correlation between C and Na has been detected, the slope being significative at more than $3\sigma$. This relation between C and Na is in perfect agreement with the relation found in giant stars selected below the RGB bump. ~Thirdly, the strong enrichment of Si and of the neutron-capture elements Sr and Ba, already observed in the giants in M4, is confirmed. ~Finally, the relations between Li, C, Na, Sr and Ba constrain the enrichment processes of the observed stars. The abundances of the elements in the turnoff stars appear to be compatible with production processes by massive AGBs, but are also compatible with the production of second generation elements (like Na) and low Li produced by, for example, fast rotating massive stars.

DATA-DRIVEN RADIATIVE HYDRODYNAMIC MODELING OF THE 2014 MARCH 29 X1.0 SOLAR FLARE

ABSTRACT Spectroscopic observations of solar flares provide critical diagnostics of the physical conditions in the flaring atmosphere. Some key features in observed spectra have not yet been accounted for in existing flare models. Here we report a data-driven simulation of the well-observed X1.0 flare on 2014 March 29 that can reconcile some well-known spectral discrepancies. We analyzed spectra of the flaring region from the Interface Region Imaging Spectrograph (IRIS) in Mg ii h&amp;k, the Interferometric BIdimensional Spectropolarimeter at the Dunn Solar Telescope (DST/IBIS) in Hα 6563 Å and Ca ii 8542 Å, and the Reuven Ramaty High Energy Solar Spectroscope Imager (RHESSI) in hard X-rays. We constructed a multithreaded flare loop model and used the electron flux inferred from RHESSI data as the input to the radiative hydrodynamic code RADYN to simulate the atmospheric response. We then synthesized various chromospheric emission lines and compared them with the IRIS and IBIS observations. In general, the synthetic intensities agree with the observed ones, especially near the northern footpoint of the flare. The simulated Mg ii line profile has narrower wings than the observed one. This discrepancy can be reduced by using a higher microturbulent velocity (27 km s−1) in a narrow chromospheric layer. In addition, we found that an increase of electron density in the upper chromosphere within a narrow height range of ≈800 km below the transition region can turn the simulated Mg ii line core into emission and thus reproduce the single peaked profile, which is a common feature in all IRIS flares.

HD 179821 (V1427 Aql, IRAS 19114+0002) – a massive post-red supergiant star?

We have derived elemental abundances of a remarkable star, HD 179821, with unusual composition (e.g. [Na/Fe]=1.0$\pm$0.2 dex) and extra-ordinary spectral characteristics. Its metallicity at [Fe/H]=0.4 dex places it among the most metal-rich stars yet analyzed. The abundance analysis of this luminous star is based on high resolution and high quality (S/N$\approx$120--420) optical echelle spectra from McDonald Observatory and Special Astronomy Observatory. The data includes five years of observations over twenty-one epochs. Standard 1D {\sc LTE} analysis provides a fresh determination of the atmospheric parameters over all epochs: \Teff = 7350$\pm$200 \kelvin, \logg = +0.6$\pm$0.3, and a microturbulent velocity $\xi =$ 6.6$\pm$1.6 km s$^{\rm -1}$ and [Fe/H] = 0.4$\pm$0.2, and a carbon abundance [C/Fe]= $-$0.19$\pm$0.30. We find oxygen abundance [O/Fe]= $-$0.25$\pm$0.28 and an enhancement of 0.9 dex in N. A supersonic macroturbulent velocity of 22.0 $\pm$ 2.0 km s$^{\rm -1}$ is determined from both strong and weak Fe\,{\sc i} and Fe\,{\sc ii} lines. Elemental abundances are obtained for 22 elements. HD 179821 is not enriched in s-process products. Eu is overabundant relative to the anticipated [X/Fe] $\approx$ 0.0. Some peculiarities of its optical spectrum (e.g. variability in the spectral line shapes) is noticed. This includes the line profile variations for H$\alpha$ line. Based on its estimated luminosity, effective temperature and surface gravity, HD 179821 is a massive star evolving to become a red supergiant and finally a Type II supernova.

ULTRAVIOLET EMISSION LINES OF Si ii IN QUASARS—INVESTIGATING THE “Si ii DISASTER”

ABSTRACT The observed line intensity ratios of the Si ii λ1263 and λ1307 multiplets to that of Si ii λ1814 in the broad-line region (BLR) of quasars are both an order of magnitude larger than the theoretical values. This was first pointed out by Baldwin et al., who termed it the “Si ii disaster,” and it has remained unresolved. We investigate the problem in the light of newly published atomic data for Si ii. Specifically, we perform BLR calculations using several different atomic data sets within the CLOUDY modeling code under optically thick quasar cloud conditions. In addition, we test for selective pumping by the source photons or intrinsic galactic reddening as possible causes for the discrepancy, and we also consider blending with other species. However, we find that none of the options investigated resolve the Si ii disaster, with the potential exception of microturbulent velocity broadening and line blending. We find that a larger microturbulent velocity ( ) may solve the Si ii disaster through continuum pumping and other effects. The CLOUDY models indicate strong blending of the Si ii λ1307 multiplet with emission lines of O i, although the predicted degree of blending is incompatible with the observed λ1263/λ1307 intensity ratios. Clearly, more work is required on the quasar modeling of not just the Si ii lines but also nearby transitions (in particular those of O i) to fully investigate whether blending may be responsible for the Si ii disaster.

Hot prominence detected in the core of a coronal mass ejection: Analysis of SOHO/UVCS Lαand SOHO/LASCO visible-light observations

Context. The paper deals with the physics of erupting prominences in the core of coronal mass ejections (CME). Aims. We determine the physical parameters of an erupting prominence embedded in the core of a CME using SOHO/UVCS hydrogen L α and L β lines and SOHO/LASCO visible light observations. In particular we analyze the CME event observed on August 2, 2000. We develop the non-LTE (NLTE; i.e. considering departures from the local thermodynamic equilibrium – LTE) spectral diagnostics based on L α and visible light observations. Methods. Our method is based on 1D NLTE modeling of eruptive prominences and takes into account the effect of large flow velocities, which reach up to 300 km s -1 for the studied event (the so-called Doppler dimming). The NLTE radiative-transfer method can be used for both optically thin and thick prominence structures. We combine spectroscopic UVCS observations of an erupting prominence in the core of a CME with visible light images from LASCO-C2 in order to derive the geometrical parameters like projected thickness and velocity, together with the effective temperature and column density of electrons. These are then used to constrain our NLTE radiative transfer modeling which provides the kinetic temperature, microturbulent velocity, gas pressure, ionization degree, the line opacities, and the prominence effective thickness (geometrical filling factor). Results. Analysis was made for 69 observational points (spatial pixels) inside the whole erupting prominence. Roughly one-half of them show a non-negligible L α optical thickness for flow velocity 300 km s -1 and about one-third for flow velocity 150 km s -1 . All pixels with L α τ 0 ≤ 0.3 have been considered for further analysis, which is presented in the form of statistical distributions (histograms) of various physical quantities such as the kinetic temperature, gas pressure, and electron density for two representative flow velocities (150 and 300 km s -1 ) and non-zero microturbulence. For two pixels co-temporal LASCO visible-light data are also available, which further constrains the diagnostics of the electron density and effective thickness. Detailed NLTE modeling is presented for various sets of input parameters. Conclusions. The studied CME event shows that the erupting prominence expands to large volumes, meaning that it is a low-pressure structure with low electron densities and high temperatures. This analysis provides a basis for future diagnostics using the METIS coronagraph on board the Solar Orbiter mission.

The magnetic field of the double-lined spectroscopic binary system HD 5550

(Abridged) In the framework of the BinaMicS project, we have begun a study of the magnetic properties of a sample of intermediate-mass and massive short-period binary systems, as a function of binarity properties. We report in this paper the characterisation of the magnetic field of HD 5550, a double-lined spectroscopic binary system of intermediate-mass, using high-resolution spectropolarimetric Narval observations of HD 5550. We first fit the intensity spectra using Zeeman/ATLAS9 LTE synthetic spectra to estimate the effective temperatures, microturbulent velocities, and the abundances of some elements of both components, as well as the light-ratio of the system. We then fit the least-square deconvolved $I$ profiles to determine the radial and projected rotational velocities of both stars. We then analysed the shape and evolution of the LSD $V$ profiles using the oblique rotator model to characterise the magnetic fields of both stars. We confirm the Ap nature of the primary, previously reported in the literature, and find that the secondary displays spectral characteristics typical of an Am star. While a magnetic field is clearly detected in the lines of the primary, no magnetic field is detected in the secondary, in any of our observation. If a dipolar field were present at the surface of the Am star, its polar strength must be below 40 G. The faint variability observed in the Stokes $V$ profiles of the Ap star allowed us to propose a rotation period of $6.84_{-0.39}^{+0.61}$ d, close to the orbital period ($\sim$6.82 d), suggesting that the star is synchronised with its orbit. By fitting the variability of the $V$ profiles, we propose that the Ap component hosts a dipolar field inclined with the rotation axis at an angle $\beta=156\pm17$ $^{\circ}$ and a polar strength $B_{\rm d}=65 \pm 20$ G. The field strength is the weakest known for an Ap star.