VI Lines Research Articles

Quantum Stark widths of Se III–VI lines

Stark broadening for 19 spectral lines of several selenium ions (four Se III lines, eight Se IV lines, three Se V lines and four Se VI lines) have been calculated using our quantum mechanical method. Many lines among them have been recently discovered for the first time in the ultraviolet spectrum of the hot white dwarf (WD) RE 0503−289 and in the atmospheres of the cool DO white dwarfs HD 149499 B and HZ 21. This recent discovery prompts us to calculate the Stark widths of the new lines. Stark widths of only three Se III lines have been compared to the available modified semi-empirical results. We could not find Stark broadening data for the other considered lines. Two calculation stages are carried out before the Stark broadening evaluation: we calculate the atomic structure as a first step, and then we calculate the collision electron–ion as a second step. We present our results for the considered lines at different temperature values and at an electron density Ne=1017 cm−3. The obtained results are useful for the modelling of stellar atmospheres. They will also enter the database of Stark broadening parameters: STARK-B.

DeGaPe 35: Amateur discovery of a new southern symbiotic star

In this work, we present the discovery and characterization of a new southern S-type symbiotic star, DeGaPe 35. We have obtained the low-resolution spectroscopic observations and supplemented them with the photometry from Gaia DR3 and other surveys. The optical spectra of this target show prominent emission lines, including highly ionized [Fe VII] and O VI lines. The cool component of this symbiotic binary is an M4-5 giant with Teff∼3380 – 3470K and luminosity ∼3×103L⊙ (for the adopted distance of 3kpc), the hot component is a shell-burning white dwarf. The photometric observations of the Gaia satellite, published recently in the Gaia DR3 suggested the variability with the period of about 700–800 days, that we tentatively attributed to the orbital motion of the binary.

Transmission spectroscopy of MASCARA-1b with ESPRESSO: Challenges of overlapping orbital and Doppler tracks

Atmospheric studies at high spectral resolution have shown the presence of molecules, neutral and ionised metals, and hydrogen in the transmission spectrum of ultra-hot Jupiters, and have started to probe the dynamics of their atmospheres. We analyse the transmission spectrum of MASCARA-1b, one of the densest ultra-hot Jupiters orbiting a bright (V = 8.3) star. We focus on the CaII H&K, NaI doublet, LiI, Hα, and KI D1 spectral lines and on the cross-correlated FeI, Fe II, CaI, YI, VI, VII, CaH, and TiO lines. For those species that are not present in the stellar spectrum, no detections are reported, but we are able to measure upper limits with an excellent precision (~10 ppm for particular species) thanks to the signal-to-noise ratio (S/N) achieved with Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) observations. For those species that are present in the stellar spectrum and whose planet-occulted spectral lines induce spurious features in the planetary transmission spectrum, an accurate modelling of the Rossiter-McLaughlin effect (RM) and centre-to-limb variations (CLV) is necessary to recover possible atmospheric signals. In the case of MASCARA-1b, this is difficult due to the overlap between the radial velocities of the stellar surface regions occulted by MASCARA-1b and the orbital track along which the planet atmospheric signal is expected to be found. To try to disentangle a possible planetary signal, we compare our results with models of the RM and CLV effects, and estimate the uncertainties of our models depending on the different system parameters. Unfortunately, more precise measurements of the spin-orbit angle are necessary to better constrain the planet-occulted track and correct for the transit effects in the transmission spectrum with enough precision to be able to detect or discard possible planetary absorptions. Finally, we discuss the possibility that non-detections are related to the low absorption expected for a high surface gravity planet such as MASCARA-1b. Other techniques such as emission spectroscopy may be more useful for exploring their atmospheric composition.

Non-parametric inference of impurity transport coefficients in the ASDEX Upgrade tokamak

We present a non-parametric inference of impurity transport coefficients by using charge exchange recombination spectroscopy measurements of Ne X, Ne VIII, O VIII, and C VI lines. Due to their close atomic numbers, neon, oxygen and carbon impurity ions are assumed to have the same diffusion coefficient D and convection velocity v. Unlike conventional techniques that modulate or perturb the impurity contents, we employ a quasi-stationary plasma with static impurity profiles. Since the ratio of v to D only describes the equilibrated profile of the sum of all impurity charge states, steady-state measurements can still decouple D and v if different charge states are simultaneously observed. We have formulated a non-parametric analysis framework based on the Bayesian probability theory and conducted transport coefficient measurements for a Type III ELMy H-mode plasma at ASDEX Upgrade. The charge exchange reactions with the background neutrals, which are known to affect the impurity charge state balance, are taken into account by introducing additional free parameters. While D at the pedestal is close to the neoclassical level (1 m s−2), a large diffusion coefficient and a strong outward convection are inferred right inside the pedestal top.

First observations from the SPICE EUV spectrometer on Solar Orbiter

Aims. We present first science observations taken during the commissioning activities of the Spectral Imaging of the Coronal Environment (SPICE) instrument on the ESA/NASA Solar Orbiter mission. SPICE is a high-resolution imaging spectrometer operating at extreme ultraviolet (EUV) wavelengths. In this paper we illustrate the possible types of observations to give prospective users a better understanding of the science capabilities of SPICE. Methods. We have reviewed the data obtained by SPICE between April and June 2020 and selected representative results obtained with different slits and a range of exposure times between 5 s and 180 s. Standard instrumental corrections have been applied to the raw data. Results. The paper discusses the first observations of the Sun on different targets and presents an example of the full spectra from the quiet Sun, identifying over 40 spectral lines from neutral hydrogen and ions of carbon, oxygen, nitrogen, neon, sulphur, magnesium, and iron. These lines cover the temperature range between 20 000 K and 1 million K (10 MK in flares), providing slices of the Sun’s atmosphere in narrow temperature intervals. We provide a list of count rates for the 23 brightest spectral lines. We show examples of raster images of the quiet Sun in several strong transition region lines, where we have found unusually bright, compact structures in the quiet Sun network, with extreme intensities up to 25 times greater than the average intensity across the image. The lifetimes of these structures can exceed 2.5 hours. We identify them as a transition region signature of coronal bright points and compare their areas and intensity enhancements. We also show the first above-limb measurements with SPICE above the polar limb in C III, O VI, and Ne VIII lines, and far off limb measurements in the equatorial plane in Mg IX, Ne VIII, and O VI lines. We discuss the potential to use abundance diagnostics methods to study the variability of the elemental composition that can be compared with in situ measurements to help confirm the magnetic connection between the spacecraft location and the Sun’s surface, and locate the sources of the solar wind. Conclusions. The SPICE instrument successfully performs measurements of EUV spectra and raster images that will make vital contributions to the scientific success of the Solar Orbiter mission.

Discovery of a multiphase O VI and O VII absorber in the circumgalactic/intergalactic transition region

Aims. The observational constraints on the baryon content of the warm-hot intergalactic medium (WHIM) rely almost entirely on far ultraviolet (FUV) measurements. However, cosmological, hydrodynamical simulations predict strong correlations between the spatial distributions of FUV and X-ray absorbing WHIM. We investigate this prediction by analyzing XMM-Newton X-ray counterparts of FUV-detected intergalactic O VI absorbers known from FUSE and HST/STIS data, thereby aiming to gain understanding on the properties of the hot component of FUV absorbers and to compare this information to the predictions of simulations. Methods. We study the X-ray absorption at the redshift of the only significantly detected O VI absorber in the Ton S 180 sightline’s FUV spectrum, found at zOVI = 0.04579 ± 0.00001. We characterize the spectral properties of the O VI-O VIII absorbers and explore the ionization processes behind the measured absorption. The observational results are compared to the predicted warm-hot gas properties in the EAGLE simulation to infer the physical conditions of the absorber. Results. We detect both O VI and O VII absorption at a 5σ confidence level, whereas O VIII absorption is not significantly detected. Collisional ionization equilibrium (CIE) modeling constrains the X-ray absorbing gas temperature to log TCIE (K) = 6.22 ± 0.05 with a total hydrogen column density NH = 5.8−2.2+3.0 × Z⊙/Zabs × 1019 cm−2. This model predicts an O VI column density consistent with that measured in the FUV, but our limits on the O VI line width indicate > 90% likelihood that the FUV-detected O VI arises from a different, cooler phase. We find that the observed absorber lies about a factor of two further away from the detected galaxies than is the case for similar systems in EAGLE Conclusions. The analysis suggests that the detected O VI and O VII trace two different – warm and hot – gas phases of the absorbing structure at z ≈ 0.046, of which the hot component is likely in collisional ionization equilibrium. As the baryon content information of the studied absorber is primarily imprinted in the X-ray band, understanding the abundance of similar systems helps to define the landscape for WHIM searches with future X-ray telescopes. Our results highlight the crucial role of line widths for the interpretation and detectability of WHIM absorbers.

Laboratory Observation of C and O Emission Lines of the White Dwarf H1504+65-like Atmosphere Model

Abstract White dwarfs play important roles in stellar evolution and help us gauge the age of our galaxy. The white dwarf H1504+65, the hottest known post-asymptotic giant branch star, is peculiar due to its C- and O-rich but He- and H- deficient atmosphere whose composition cannot be well predicted by current stellar evolution models. The analysis of the elemental abundance and the benchmark of stellar atmospheric models depends heavily on spectral data under cosmic conditions, which are currently extremely scarce. We created a well-defined, uniform, relatively large-scale ∼millimeter plasma sample in the laboratory with a temperature and a C/O ratio similar to those of H1504+65’s atmosphere. The emission spectra with high precision in the range of 10–80 nm were obtained and identified according to databases such as NIST and Kelly. A detailed comparison between our emission lines and the Chandra-observed white dwarf H1504+65 atmosphere’s absorption lines was performed. The stongly isolated O VI lines in the range of 10–13 nm are observed in both cases. We observed a wealth of O V lines in the range of 13–14 nm that cannot be well identified or predicted by models due to the weak flux and also probably due to the blending effect of Fe group elements in the Chandra spectrum. Long-wavelength lines ranging from 14 to 80 nm, which are not observed in the Chandra spectrum because of the high interstellar neutral hydrogen column density, show abundant O IV-V, C IV lines, and strong O VI lines. Moreover, the intensities of the lines at 62.973 and 17.216 nm are analyzed to characterize the plasma temperature.

Stark broadening for Br VI and Kr V-VII lines in hot star atmospheres

Context. This paper provides missing Stark broadening of the Br VI and Kr V-VII lines recently discovered in the ultraviolet spectrum of the hot white dwarf RE 0503–289 and investigates the importance of the Stark broadening mechanism versus the Doppler mechanism in that star. As far as we know, this is the first time that Stark widths of Br VI and Kr V-VII lines have been calculated. Aims. The recent discovery of new lines of Br VI and Kr V-VII encourages us to provide their Stark broadening to enrich the STARK-B database and for use in interpretations of the observed spectra. Methods. We used our quantum mechanical method for calculating electron impact broadening to provide Stark widths. The method starts with an evaluation of the structure and collision parameters using the University College London codes SUPERSTRUCTURE/DISTORTED WAVE/JAJOM, which are adapted to the line broadening calculations. We then used the collision parameters to calculate the line widths using our programs. Results. We provide the missing widths of 35 lines of Br VI and Kr V-VII at different electron temperatures and at density Ne = 1017 cm−3. We find that the Stark broadening mechanism is preponderant compared to the Doppler one for almost all the plasma conditions of the considered DO white dwarf atmospheres.

Development of an ultrafast charge exchange spectroscopy system on the KSTAR tokamak.

An ultrafast charge exchange spectroscopy (UFCES) system has been designed for measuring fluctuations in ion temperature and toroidal rotation velocity. The UFCES on the KSTAR tokamak is a powerful tool for investigating plasma instabilities and long-wavelength turbulence related to ion temperature gradient and flow. The UFCES system is designed to measure the C VI line (n = 8 → 7, λ0 = 529.05nm) from the charge exchange reaction between a deuterium-heating neutral beam and the intrinsic carbon impurity in KSTAR. The ion temperature and toroidal rotation velocity at two radial positions will be observed simultaneously with UFCES. The key difference between the UFCES system and conventional charge exchange spectrometers is the application of high-throughput collection optics, a high-efficiency transmission grating combined with prisms, and a high-speed detector. We use a comprehensive spectrum simulation code with input parameters of KSTAR's plasmas and a neutral beam injection system to estimate the performance of the designed UFCES system. The results simulated with the code show that the diagnostic achieves a turbulence-relevant time resolution of 10 µs with a high enough signal-to-noise ratio. Furthermore, a preliminary test is performed using a complementary metal-oxide semiconductor camera and Ne spectral lamp to confirm the linear dispersion and curvature radius.

Energy structure and radiative parameter calculations in the Re-like Pt IV, Au V and Hg VI spectra and preliminary line identifications in Hg VI

We performed extended ab-initio atomic structure calculations for Ir III-like Pt IV, Au V and Hg VI by using the pseudo-relativistic Hartree-Fock approach (HFR). These computations yielded theoretical energy levels and transition data for the electric dipole (E1) transitions. The results obtained in this study compare well with the available experimental data. More precisely, the good agreement of our theoretical calculations with experimental values for Pt IV and Au V allowed us to execute precise calculations for Hg VI by scaling the Slater parameters similar to Au V which is next to Hg VI in Re isoelectronic sequence. Most of our computed energy levels and radiative transition rates for Re-like Hg VI were not reported before. We provide accurate and comprehensive atomic data related to this ion that could be used by astrophysicists for interpretation of stellar spectra. On the basis of these calculations, preliminary identifications of 32 strong Hg VI lines were made in our experimental spectrograms.

Long-term disease control during TAS-102 therapy in the VI line treatment in a 73-year-old mCRC patient. A case report

A case of 73-year-old patient with metastatic colorectal cancer who underwent trifluridine/tipiracil therapy within the VI line was presented. Treatment with trifluridine/tipiracil allowed to achieve stabilization of the existing cancer for nearly 7 months.

EUV spectroscopy of optically thin Ge VI-XI plasmas in the 9-18 nm region

Identification of previously unclassified emission features in the extreme ultraviolet (EUV) spectra of Ge VI to XI has been carried out by recording emission from laser-produced plasmas created using a high-powered Transversely Excited Atmospheric (TEA) CO2 laser. The analysis was carried out using the Cowan suite of atomic structure codes with the aid of the unresolved transition array (UTA) statistical approach to determine the extent of the transition arrays, lines in Ge VI to Ge XI have been identified.

Initial mass function variations cannot explain the ionizing spectrum of low metallicity starbursts

Aims. Observations of both galaxies in the distant Universe and local starbursts are showing increasing evidence for very hard ionizing spectra that stellar population synthesis models struggle to reproduce. Here we explore the effects of the assumed stellar initial mass function (IMF) on the ionizing photon output of young populations at wavelengths below key ionization energy thresholds. Methods. We use a custom set of binary population and spectral synthesis (BPASS) models to explore the effects of IMF assumptions as a function of metallicity, IMF slope, upper mass limit, IMF power law break mass and sampling. Results. We find that while the flux capable of ionizing hydrogen is only weakly dependent on IMF parameters, the photon flux responsible for the He II and O VI lines is far more sensitive to assumptions. In our current models this flux arises primarily from helium and Wolf-Rayet stars which have partially or fully lost their hydrogen envelopes. The timescales for formation and evolution of both Wolf Rayet stars and helium dwarfs, and hence inferred population age, are affected by choice of model IMF. Even the most extreme IMFs cannot reproduce the He II ionizing flux observed in some high redshift galaxies, suggesting a source other than stellar photospheres. Conclusions. We caution that detailed interpretation of features in an individual galaxy spectrum is inevitably going to be subject to uncertainties in the IMF of its contributing starbursts. We remind the community that the IMF is fundamentally a statistical construct, and that stellar population synthesis models are most effective when considering entire galaxy populations rather than individual objects.

First detection of bromine and antimony in hot stars

Bromine (Z = 35) and antimony (Z = 51) are extremely difficult to detect in stars. In very few instances, weak and mostly uncertain identifications of Br I, Br II, and Sb II in relatively cool, chemically peculiar stars were successful. Adopted solar abundance values rely on meteoritic determinations. Here, we announce the first identification of these species in far-ultraviolet spectra of hot stars (with effective temperatures of 49 500–70 000 K), namely in helium-rich (spectral type DO) white dwarfs. We identify the Br VI resonance line at 945.96 Å. A previous claim of Br detection based on this line is incorrect because its wavelength position is inaccurate by about 7 Å in atomic databases. Taking advantage of precise laboratory measurements, we identify this line as well as two other, subordinate Br VI lines. Antimony is detected by the Sb V resonance doublet at 1104.23/1225.98 Å as well as two subordinate Sb VI lines. A model-atmosphere analysis reveals strongly oversolar Br and Sb abundances that are caused by radiative-levitation dominated atomic diffusion.

A D’-type symbiotic binary in the planetary nebula SMP LMC 88

SMP LMC 88 is one of the planetary nebulae (PN) in the Large Magellanic Cloud. We identify in its spectrum Raman scattered O VI lines at 6825 and 7083A. This unambiguously classifies the central object of the nebula as a symbiotic star (SySt). We identified the cold component to be a K-type giant, making this the first D'-type (yellow) SySt discovered outside the Galaxy. The photometric variability in SMP LMC 88 resembles the the orbital variability of Galactic D'-type SySt with its low amplitude and sinusoidal lightcurve shape. The SySt classification is also supported by the He I diagnostic diagram.

Spectrum of Sn5+ in the Region 500–1300 Å

The spectrum of tin, excited in a vacuum spark, was recorded in the region 500–1131 Å on a 6.65-m normal incidence spectrograph. The transitions between 4d85s, 4d86s, 4d85p and 4d85d excited configurations in Sn VI were studied. More than 500 lines of the 4d85p–4d85d and 4d85p–4d86s were identified with the aid of the Cowan code calculations. 67 energy levels (out of 70 possible levels of the 4d85d configuration) and all but two 4d86s levels were found. The wavelength of the 4d85s–4d85p transitions in the region 839–1131 Å were re-measured and supplemented by Sn VI lines in the region 1131–1300 Å measured previously by Srivastava et al. (1977) for optimisation of the energy level values. The SnVI line list in the region 500–1300 Å contains now 741 lines with calculated transition probabilities.

On the Stark broadening of Cr VI spectral lines in astrophysical plasma

Stark broadening parameters for Cr VI lines have been calculated using semiclassical perturbation method for conditions of interest for stellar plasma. Here are presented, as an example of obtained results, Stark broadening parameters for electron- and proton-impact broadening for Cr VI 4s 2S-4p 2P° λ = 1430 Å and Cr VI 4p 2P°-5s 2S λ = 611.8 Å multiplets. The obtained results are used to demonstrate the importance of Stark broadening of Cr VI in DO white dwarf atmospheres. Also the obtained results will enter in STARK-B database which is included in Virtual Atomic and Molecula Data Center - VAMDC.

Erratum to: ‘This World, in the Beginning, was Phenomenally Non-existent’: Āruṇi’s Discourse on Cosmogony in Chāndogya Upaniṣad VI.1–VI.7

This paper critically reads and analyzes the first discourse of Āruṇi and Śvetaketu in the first half of the sixth chapter of the Chāndogya Upaniṣad (VI.1–VI.7). It argues that, except for a few interpolated lines in VI.2 and VI.3, the entire discourse constitutes one integrated whole with a specific indicatory knowledge (ādeśa) at its core that indicates deeper truth underlying all realities, and its characterization and twofold elaboration with reference to macro- and microcosmos. In light of two cosmogonic accounts from the JaiminīyaBrāhmaṇa (JB) and some other Vedic passages, this paper argues that Āruṇi’s cosmogony originally posited asat as the primordial entity, which has not yet acquired any phenomenal form. Incidentally it also demonstrates that in this discourse the term ādeśa cannot denote a ‘method of substitution’ as proposed by Thieme (“ādeśa” in Melanges d’indianisme: a la memoire de Louis Renou, 1968) and taken over since then by several scholars.

Radiation-driven winds of hot luminous stars

Context. The uncertainty in the degree to which radiation-driven winds of hot stars might be affected by small inhomogeneities in the density leads to a corresponding uncertainty in the determination of the atmospheric mass loss rates from the strength of optical recombination lines and - since the mass loss rate is not a free parameter but a function of the stellar parameters mass, radius, luminosity, and abundances - in principle also in the determination of these stellar parameters. Furthermore, the optical recombination lines also react sensitively to even small changes in the density structure resulting from the (often assumed instead of computed) velocity law of the outflow. This raises the question of how reliable the parameter determinations from such lines are. Aims. The currently existing severe discrepancy between central stars of planetary nebulae (CSPN) stellar and wind parameters derived from model fits to the optical spectra and those derived using hydrodynamically consistent model fits to the UV spectra is to be reassessed via a simultaneous optical/UV analysis using a state-of-the-art model atmosphere code. Methods. We have modified our hydrodynamically consistent model atmosphere code with an implementation of the usual ad hoc treatment of clumping (small inhomogeneities in the density) in the wind. This allows us to re-evaluate, with respect to their influence on the appearance of the UV spectra and their compatibility with the observations, the parameters determined in an earlier study that had employed clumping in its models to achieve a fit to the observed optical spectra. Results. The discrepancy between the optical and the UV analyses is confirmed to be the result of a missing consistency between stellar and wind parameters in the optical analysis. While clumping in the wind does significantly increase the emission in the optical hydrogen and helium recombination lines, the influence of the density (velocity field) is of the same order as that of moderate clumping factors. Moderate clumping factors leave the UV spectra mostly unaffected, indicating that the influence on the ionization balance, and thus on the radiative acceleration, is small. Instead of the erratic behavior of the clumping factors claimed from the optical analyses, our analysis based on the velocity field computed from radiative driving yields similar clumping factors for all CSPNs, with a typical value of integral(cl) = 4. With and without clumping, wind strengths and terminal velocities consistent with the stellar parameters from the optical analysis give spectra incompatible with both optical and UV observations, whereas a model that consistently implements the physics of radiation-driven winds achieves a good fit to both the optical and UV observations with a proper choice of stellar parameters. The shock temperatures and the ratios of X-ray to bolometric luminosity required to reproduce the highly ionized O VI line in the FUSE spectral range agree with those known from massive O stars (L-X/L-bol similar to 10(-7) ... 10(-6)), again confirming the similarity of O-type CSPN and massive O star atmospheres and further strengthening the claim that both have identical wind driving mechanisms. Conclusions. The similarity of the winds of O-type CSPNs and those of massive O stars justifies using the same methods based on the dynamics of radiation-driven winds in their analysis, thus supporting the earlier result that several of the CSPNs in the sample have near-Chandrasekhar-limit masses and may thus be possible single-star progenitors of type Ia supernovae.

Absolute wavelength calibration of a Doppler spectrometer with a custom Fabry-Perot optical system.

An Ion Doppler Spectrometer (IDS) is used for fast measurements of C VI line emission (343.4 nm) in the Madison Symmetric Torus. Absolutely calibrated flow measurements are difficult because the IDS records data within 0.25 nm of the line. Commercial calibration lamps do not produce lines in this narrow range. A light source using an ultraviolet LED and etalon was designed to provide a fiducial marker 0.08 nm wide. The light is coupled into the IDS at f/4, and a holographic diffuser increases homogeneity of the final image. Random and systematic errors in data analysis were assessed. The calibration is accurate to 0.003 nm, allowing for flow measurements accurate to 3 km/s. This calibration is superior to the previous method which used a time-averaged measurement along a chord believed to have zero net Doppler shift.