Hα Spectral Line Research Articles

A magnetic reconnection model for the hot explosion with both ultraviolet and Hα wing emissions

Context. Ellerman bombs (EBs) with significant Hα wing emissions and ultraviolet bursts (UV bursts) with strong Si IV emissions are two kinds of small transient brightening events that occur in the low solar atmosphere. The statistical observational results indicate that about 20% of the UV bursts connect with EBs. While some promising models exist for the formation mechanism of colder EBs in conjunction with UV bursts, the topic remains an area of ongoing research and investigation. Aim. We numerically investigated the magnetic reconnection process between the emerging arch magnetic field and the lower atmospheric background magnetic field. We aim to find out if the hot UV emissions and much colder Hα wing emissions can both appear in the same reconnection process and how they are located in the reconnection region. Methods. The open-source code NIRVANA was applied to perform the 2.5D magnetohydrodynamic (MHD) simulation. We developed the related sub-codes to include the more realistic radiative cooling process for the photosphere and chromosphere and the time-dependent ionization degree of hydrogen. The initial background magnetic field is 600 G, and the emerged magnetic field in the solar atmosphere is of the same magnitude, meaning that it results in a low- β magnetic reconnection environment. We also used the radiative transfer code RH1.5D to synthesize the Si IV and Hα spectral line profiles based on the MHD simulation results. Results. Magnetic reconnection between emerged and background magnetic fields creates a thin, curved current sheet, which then leads to the formation of plasmoid instability and the nonuniform density distributions. Initially, the temperature is below 8000 K. As the current sheet becomes more vertical, denser plasmas are drained by gravity, and hotter plasmas above 20 000 K appear in regions with lower plasma density. The mix of hot tenuous and much cooler dense plasmas in the turbulent reconnection region can appear at about the same height, or even in the same plasmoid. Through the reconnection region, the synthesized Si IV emission intensity can reach above 106 erg s−1 sr−1 cm−2 Å−1 and the spectral line profile can be wider than 100 km s−1, the synthesized Hα line profile also show the similar characteristics of a typical EB. The turbulent current sheet is always in a dense plasma environment with an optical depth larger than 6.5 × 10−5 due to the emerged magnetic field pushing high-density plasmas upward. Conclusions. Our simulation results indicate that the cold EB and hot UV burst can both appear in the same reconnection process in the low chromosphere, the EB can either appear several minutes earlier than the UV burst, or they can simultaneously appear at the similar altitude in a turbulent reconnection region below the middle chromosphere.

Observational study of intermittent solar jets:p-mode modulation

Aims.Recurring jets are observed in the solar atmosphere. They can erupt intermittently over a long period of time. By the observation of intermittent jets, we wish to understand what causes the characteristics of the periodic eruptions.Methods.We report intermittent jets observed by the Goode Solar Telescope (GST) with the TiO Broadband Filter Imager (BFI), the Visible Imaging Spectrometer (VIS) in Hα, and the Near-InfraRed Imaging Spectropolarimeter (NIRIS). The analysis was aided and complemented by 1400 Å and 2796 Å data from the Interface Region Imaging Spectrograph (IRIS). These observational instruments allowed us to analyze the temporal characteristics of the jet events. By constructing the Hαdopplergrams, we found that the plasma first moves upward, but during the second phase of the jet, the plasma flows back. Working with time slice diagrams, we investigated the characteristics of the jet dynamics.Results.The jet continued for up to 4 h. The time-distance diagram shows that the peak of the jet has clear periodic-eruption characteristics (5 min) during 18:00 UT–18:50 UT. We also found a periodic brightening phenomenon (5 min) during the jet bursts in the observed bands in the transition region (1400 Å and 2796 Å), which may be a response to intermittent jets in the upper solar atmosphere. The time lag is 3 min. Evolutionary images in the TiO band revealed a horizontal movement of the granulation at the location of the jet. By comparison to the quiet region of the Sun, we found that the footpoint of the jet is enhanced at the center of the Hαspectral line profile, without significant changes in the line wings. This suggests prolonged heating at the footpoint of the jet. In the mixed-polarity magnetic field region of the jet, we observed the emergence of magnetic flux, its cancellation, and shear, indicating possible intermittent magnetic reconnection. This is confirmed by the nonlinear force-free field model, which was reconstructed using the magneto-friction method.Conclusions.The multiwavelength analysis indicates that the events we studied were triggered by magnetic reconnection that was caused by mixed-polarity magnetic fields. We suggest that the horizontal motion of the granulation in the photosphere drives the magnetic reconnection, which is modulated byp-mode oscillations.

Multiwavelength observation of 1A 0535+262=HD 245770 from 2010 to 2021

Context. 1A 0535+262 is a high-mass X-ray binary that went into a giant X-ray outburst in 2020. During this event, the X-ray luminosity reached the highest value measured over the last 30 years. Aims. Our aim is to study the long-term variability of 1A 0535+262 before and after the 2020 major X-ray outburst and to uncover the mechanism that led to the X-ray outburst. Methods. We used the long-term photometric light curve and the equivalent widths of the Hα and He I λ6678 lines to monitor the state of the Be star’s circumstellar disk. The Hα line profiles show evidence for V/R variability, which we revealed by fitting the Hα spectral line profiles with two Gaussian functions. In addition, we divided our data into four periods according to the intensity of the X-ray, optical, and infrared emission. Results. The Hα line profiles show single-peaked profiles in most cases. This is consistent with the previously reported orbital inclination of i = 37° ±2°. Unlike the Hα lines, the He I λ6678 lines show a maximal intensity in October 2020, which is one month before the giant X-ray outburst in 2020. Based on the behavior of the equivalent widths of the Hα and He I λ6678 lines, and the V-band magnitude, we find two mass ejection processes from the Be star to the Be disk on MJD 55820 and MJD 56600. The V/R quasi-period is about two years during 2011–2015, which is different from 1994 to 1995. Furthermore, the periods I → II → III → IV in the (B − V) color index versus V-band magnitude diagram constitute a cycle. From the behavior of the V/R ratio of Hα lines, and the variability of the V band, we believe that the precession of the density perturbation inside the disk is retrograde.

Application of laser-induced breakdown spectroscopy for the analysis of pig bones

An application of the laser-induced breakdown spectroscopy technique (LIBS) for the elemental analysis of pig shoulder bone samples is reported. Measurements were performed using a compact laboratory-made LIBS system based on the TEA CO2 laser and time-integrated signal detection. The recorded spectra consisted of well-defined atomic and single-charged ionic lines of bone matrix elements (Ca and P) and other constituent elements (e.g. Mg, Zn, Na, K, and C) with a good signal-to-noise ratio suitable for chemical analysis. Based on the elemental composition of bone samples measured by inductively coupled plasma emission spectroscopy, limits of detection (LOD) of LIBS analysis were estimated for several elements. LOD ranged from 2.2 ppm (K) to 16 ppm (Zn). Carbon and Hα spectral lines were used for plasma diagnostics by measuring Stark widths. Optical profilometry was used to assess the capability of LIBS for depth profile analysis. For laser fluence between 13.0 and 18.2 J cm−2, the ablation rate per pulse ranged from 6 to 10 μm.

H i 21 cm Extended Structures to the Northeast and Southwest of NGC 5595: VLA Observations of the Disk Galaxy Pair NGC 5595 and NGC 5597

We report VLA B-configuration observations of the H i 21 cm line on the close disk galaxy pair NGC 5595 and NGC 5597. At the angular resolution of the observations, ∼7.″1 × 4.″2, while most of the H i 21 cm in NGC 5595 and NGC 5597 has the same extent as the optical disk, we have detected for the first time extended structures (streamers) to the northeast (NE) and southwest (SW) of NGC 5595 with no counterparts in blue, red optical (continuum), 20 cm radio continuum, or Hα spectral line emission. One structure is extended by ∼45″ to the NE with blueshifted velocities, and the other is extended by ∼20″ to the SW with redshifted velocities with respect to the systemic velocity. No H i 21 cm emission is detected from the innermost central (nuclear) regions of either galaxy. Lower angular resolution H i 21 cm imaging indicates the nonexistence of any intergalactic hydrogen atomic H i 21 cm gas as tails or bridges between the two galaxies. Our new 20 cm radio continuum emission image of NGC 5597 shows a strong unresolved elongated structure in the central region, in the NE–SW direction, very similar to the spatial location of the innermost Hα spectral line emission. There is no 20 cm continuum emission from its northern spiral arm. In NGC 5595, the 20 cm radio continuum image shows no continuum emission from the NE or SW extended structures with H i 21 cm emission.

TIME BEHAVIOR OF THE Hα SPECTRAL LINE AND THE MOLECULAR HYDROGEN SPECTRAL LINE IN HYDROGEN PLASMA IN THE URAGAN-2M STELLARATOR

The studies of the scenario of hydrogen plasma creation with two sequential RF discharges during one pulse were carried out for the Uragan-2M stellarator. The first-stage discharge initiated the hydrogen pre-ionization at the generator anode voltage of 4 kV. The second-stage discharge was performed at the generator anode voltage selected from 6 to 9 kV. As result, plasma with an electron density up to 3.9·1018 m-3 was produced in a confinement volume. An increase of voltage resulted in an earlier appearance of signals of electron density, the intensity of the Hα spectral line, and the intensity of the molecular hydrogen spectral line. The increase of the time-dependent intensities of these signals was also registered.

Do Hα Stokes V Profiles Probe the Chromospheric Magnetic Field? An Observational Perspective* * Not yet released.

We investigated the diagnostic potential of the Stokes V profile of the Hα line to probe the chromospheric line-of-sight (LOS) magnetic field (B LOS) by comparing the B LOS inferred from the weak field approximation (WFA) with that inferred from the multiline inversions of the Caii 8542 Å, Si i 8536 Å, and Fe i 8538 Å lines using the STiC inversion code. Simultaneous spectropolarimetric observations of a pore in the Ca ii 8542 Å and Hα spectral lines obtained from the SPINOR at the Dunn Solar Telescope on 2008 December 4 are used in this study. The WFA was applied on the Stokes I and V profiles of Hα line over three wavelength ranges, viz., around line core (Δλ = ±0.35 Å), line wings (Δλ = [−1.5, −0.6], and [+0.6, +1.5] Å), and full spectral range of the line (Δλ = ± 1.5 Å) to derive the B LOS. We found the maximum B LOS strengths of ∼+800 and ∼+600 G at = −1 and −4.5, respectively, in the pore. The morphological map of the B LOS inferred from the Hα line core is similar to the B LOS map at = −4.5 inferred from multiline inversions. The B LOS map inferred from the Hα line wings and full spectral range have a similar morphological structure to the B LOS map inferred at = −1. The B LOS estimated from Hα using WFA is weaker by a factor of ≈0.53 than that of inferred from the multiline inversions.

Plasma spectroscopy of electric spark discharge between silver granules immersed in water

This work is devoted to optical emission spectroscopy of plasma of underwater electric discharge, which is used for the synthesis of silver nanoparticles. The main aim of this work is to investigate the possibility and validity of using plasma optical emission spectroscopy to determine its main physical characteristics, such as excitation temperature, electron density, the degree of ionization, etc. The specially developed pulse power source was used to initiate a discharge between silver granules immersed into the deionized water. Typical values of voltage vary from 40 to 200 V, the current is up to 150 A, and pulse frequency is in the range of 0.2–2 kHz. Applied to electrodes, the voltage caused a current flow along the chain of closely arranged granules in the stochastic switching mode. Special attention is paid to methods of spectrum treatment of underwater discharge plasma between silver granules. The method of Boltzmann plots and the method of relative intensities on the basis of both atomic and ionic silver spectral lines are used in order to determine the excitation temperature. The spectral lines, which were investigated and treated in detail, were used. Exposed to the Stark mechanism of spectral line broadening, the spectral profile of Hα spectral line is used to determine the electron density. The degree of ionization of the studied plasma was calculated using the obtained values of the electron density and temperature.

SAMI-H i: the connection between global asymmetry in the ionized and neutral atomic hydrogen gas in galaxies

ABSTRACT Observations of the neutral atomic hydrogen (${\rm H\, {\small I}}$) gas in galaxies are predominantly spatially unresolved, in the form of a global ${\rm H\, {\small I}}$ spectral line. There has been substantial work on quantifying asymmetry in global ${\rm H\, {\small I}}$ spectra (‘global ${\rm H\, {\small I}}$ asymmetry’), but due to being spatially unresolved, it remains unknown what physical regions of galaxies the asymmetry traces, and whether the other gas phases are affected. Using optical integral field spectrograph (IFS) observations from the Sydney AAO Multi-object IFS (SAMI) survey for which global ${\rm H\, {\small I}}$ spectra are also available (SAMI-${\rm H\, {\small I}}$), we study the connection between asymmetry in galaxies’ ionized and neutral gas reservoirs to test if and how they can help us better understand the origin of global ${\rm H\, {\small I}}$ asymmetry. We reconstruct the global Hα spectral line from the IFS observations and find that while some global Hα asymmetries can arise from disturbed ionized gas kinematics, the majority of asymmetric cases are driven by the distribution of Hα-emitting gas. When compared to the ${\rm H\, {\small I}}$, we find no evidence for a relationship between the global Hα and ${\rm H\, {\small I}}$ asymmetry. Further, a visual inspection reveals that cases where galaxies have qualitatively similar Hα and ${\rm H\, {\small I}}$ spectral profiles can be spurious, with the similarity originating from an irregular 2D Hα flux distribution. Our results highlight that comparisons between global Hα and ${\rm H\, {\small I}}$ asymmetry are not straightforward, and that many global ${\rm H\, {\small I}}$ asymmetries trace disturbances that do not significantly impact the central regions of galaxies.

Multiwavelength observations of Swift J0243.6+6124 from 2017 to 2022

Context.Swift J0243.6+6124 is a high-mass X-ray binary that went into a giant X-ray outburst in 2017. During this event, the X-ray luminosity reached the highest value ever measured in a galactic Be/X-ray binary. Aims. Our aim is to study the long-term variability of Swift J0243.6+6124 after the 2017 major X-ray outburst. Methods. We have obtained optical spectroscopy and photometry data during four years after the event. The long-term photometric light curve and the equivalent widths of the Hα and He I λ6678 lines were used to monitor the state of the Be star’s circumstellar disk. The Hα line profiles show evidence for V/R variability that was accounted for by fitting the Hα spectral line profile with two Gaussian functions. We divided our data into three phases according to the intensity of the X-ray, optical, and infrared emission. Results. Phase I covers the rise and decay of the giant X-ray outburst that took place in October–November 2017. We interpret phase II as the dissipation of the Be star’s equatorial disk and phase III as its recovery. The timescale of a complete formation and dissipation process is about 1250 days. The epoch when the dissipation process stopped and the reformation period began is estimated to be around MJD 58530. We find a delay of ∼100–200 days between the minimum of the optical or infrared intensity and the strength of the Hα line after the X-ray outburst, which may indicate that the dissipation of the disk begins from the inner parts. The motion of the density perturbation inside the disk is prograde, with a V/R quasi-period of about four years. The source shows a positive correlation in the (B − V) color index versus V-band magnitude diagram, which implies that the system is seen at a small or moderate inclination angle. Conclusions. Despite the super-Eddington X-ray luminosity during the outburst, the subsequent pattern of long-term optical and IR variability of Swift J0243.6+6124 is typical of Be/X-ray binaries.

Chromospheric swirls

Context. Chromospheric swirls are related to convectively driven vortex flows and considered to play a significant role in the dynamics and heating of the upper solar atmosphere. It is important to automatically detect and track them in chromospheric observations and determine their properties. Aims. We aim to detect and track chromospheric swirls both in space and time by applying a newly developed novel automated method on high quality time series of Hα observations and to conduct a statistical analysis to determine their properties. Methods. We applied a recently developed automated chromospheric swirl detection method to time-series observations of a quiet region of the solar chromosphere obtained in the Hα-0.2 Å wavelength of the Hα spectral line by the CRISP instrument at the Swedish 1-m Solar Telescope. The algorithm exploits the morphological characteristics of swirling events in high contrast chromospheric observations and results in the detection of these structures in each frame of the time series and their tracking over time. We conducted a statistical analysis to determine their various properties, including a survival analysis for deriving the mean lifetime. Results. A mean number of 146 ± 9 swirls was detected within the Hα-0.2 Å field of view at any given time. The mean surface density is found equal to ∼0.08 swirls Mm−2 and the occurrence rate is ∼10−2 swirls Mm−2 min−1. These values are much higher than those previously reported from chromospheric observations. The radii of the detected swirls range between 0.5 and 2.5 Mm, with a mean value equal to 1.3 ± 0.3 Mm, which is slightly higher than previous reports. The lifetimes range between 1.5 min and 33.7 min (equal to the duration of the observations) with an arithmetic mean value of ∼8.5 min. A survival analysis of the lifetimes, however, using the Kaplan-Meier estimator in combination with a parametric model results in a mean lifetime of 10.3 ± 0.6 min. Conclusions. Swirls are ubiquitous in the solar chromosphere. An automated method sheds more light on their abundance than visual inspection, while higher cadence, higher resolution observations will most probably result in the detection of a higher number of such features on smaller scales and with shorter lifetimes.

Plasma temperature determination based on the ratio of plasma electron densities obtained from hydrogen Hα and Hβ spectral lines

Method for plasma electron temperature determination based on the ratio of electron densities obtained from hydrogen Hα and Hβ spectral lines based on electron densities ratio obtained from hydrogen Hα and Hβ spectral lines is considered. In order to verify its validity, the method was applied to wall stabilized DC and pulsed arc plasmas together with three other methods. Temperature range was 9600–13,600 K. The values obtained by applying the method presented in this paper differ from the average values obtained from all methods for <6%. Results are also in good agreement with the newer theories of Stark broadening of hydrogen spectral lines.

Solar Hαexcess during Solar Cycle 24 from full-disk filtergrams of the Chromospheric Telescope

Context.The chromospheric Hαspectral line is a strong line in the spectrum of the Sun and other stars. In the stellar regime, this spectral line is already used as a powerful tracer of stellar activity. For the Sun, other tracers, such as Ca IIK, are typically used to monitor solar activity. Nonetheless, the Sun is observed constantly in Hαwith globally distributed ground-based full-disk imagers.Aims.The aim of this study is to introduce the imaging Hαexcess and deficit as tracers of solar activity and compare them to other established indicators. Furthermore, we investigate whether the active region coverage fraction or the changing Hαexcess in the active regions dominates temporal variability in solar Hαobservations.Methods.We used observations of full-disk Hαfiltergrams of the Chromospheric Telescope and morphological image processing techniques to extract the imaging Hαexcess and deficit, which were derived from the intensities above or below 10% of the median intensity in the filtergrams, respectively. These thresholds allowed us to filter for bright features (plage regions) and dark absorption features (filaments and sunspots). In addition, the thresholds were used to calculate the mean intensityImeanE/Dfor Hαexcess and deficit regions. We describe the evolution of the Hαexcess and deficit during Solar Cycle 24 and compare it to the mean intensity and other well established tracers: the relative sunspot number, the F10.7 cm radio flux, and the Mg IIindex. In particular, we tried to determine how constant the Hαexcess and number density of Hαexcess regions are between solar maximum and minimum. The number of pixels above or below the intensity thresholds were used to calculate the area coverage fraction of Hαexcess and deficit regions on the Sun, which was compared to the imaging Hαexcess and deficit and the respective mean intensities averaged for the length of one Carrington rotation. In addition, we present the Hαexcess and mean intensity variation of selected active regions during their disk passage in comparison to the number of pixels of Hαexcess regions.Results.The Hαexcess and deficit follow the behavior of the solar activity over the course of the cycle. They both peak around solar maximum, whereby the peak of the Hαdeficit is shortly after the solar maximum. Nonetheless, the correlation of the monthly averages of the Hαexcess and deficit is high with a Spearman correlation ofρ = 0.91. The Hαexcess is closely correlated to the chromospheric Mg IIindex with a correlation of 0.95. The highest correlation of the Hαdeficit is found with the F10.7 cm radio flux, with a correlation of 0.89, due to their peaks after the solar activity maximum. Furthermore, the Hαdeficit reflects the cyclic behavior of polar crown filaments and their disappearance shortly before the solar maximum. We investigated the mean intensity distribution for Hαexcess regions for solar minimum and maximum. The shape of the distributions for solar minimum and maximum is very similar, but with different amplitudes. Furthermore, we found that the area coverage fraction of Hαexcess regions and the Hαexcess are strongly correlated with an overall Spearman correlation of 0.92. The correlation between the Hαexcess and the mean intensity of Hαexcess regions is 0.75. The correlation of the area coverage fraction and the mean intensity of Hαexcess regions is in general relatively low (ρ = 0.45) and only for few active regions is this correlation above 0.7. The weak correlation between the area coverage fraction and mean intensity leaves us pessimistic that the degeneracy between these two quantities can be broken for the modeling of unresolved stellar surfaces.

Interpretation of Stark broadening measurements on a spatially integrated plasma spectral line

In thermal plasma spectroscopy, Stark broadening measurement of hydrogen spectral lines is considered to be a good and reliable measurement for electron density. Unlike intensity based measurements, Stark broadening measurements can pose a problem of interpretation when the light collected is the result of a spatial integration. Indeed, when assuming no self-absorption of the emission lines, intensities simply add up but broadenings do not. In order to better understand the results of Stark broadening measurements on our thermal plasma which has an unneglectable thickness, a Python code has been developed based on local thermodynamic equilibrium (LTE) assumption and calculated plasma composition and properties. This code generates a simulated pseudo experimental (PE) Hα spectral line resulting from an integration over the plasma thickness in a selected direction for a given temperature profile. The electron density was obtained using the Stark broadening of the PE spectral line for different temperature profiles. It resulted that this measurement is governed by the maximum electron density profile up until the temperature maximum exceeds that of the maximum electron density. The electron density obtained by broadening measurement is 60–75% of the maximum electron density.

Interpretation of Stark broadening measurements on a spatially integrated plasma spectral line

In thermal plasma spectroscopy, Stark broadening measurement of hydrogen spectral lines is considered to be a good and reliable measurement for electron density. Unlike intensity based measurements, Stark broadening measurements can pose a problem of interpretation when the light collected is the result of a spatial integration. Indeed, when assuming no self-absorption of the emission lines, intensities simply add up but broadenings do not. In order to better understand the results of Stark broadening measurements on our thermal plasma which has an unneglectable thickness, a Python code has been developed based on local thermodynamic equilibrium (LTE) assumption and calculated plasma composition and properties. This code generates a simulated pseudo experimental (PE) H α spectral line resulting from an integration over the plasma thickness in a selected direction for a given temperature profile. The electron density was obtained using the Stark broadening of the PE spectral line for different temperature profiles. It resulted that this measurement is governed by the maximum electron density profile up until the temperature maximum exceeds that of the maximum electron density. The electron density obtained by broadening measurement is 70–80% of the maximum electron density.

Spicules and downflows in the solar chromosphere

Context. High-speed downflows have been observed in the solar transition region (TR) and lower corona for many decades. Despite their abundance, it has been hard to find signatures of such downflows in the solar chromosphere. Aims. In this work, we target an enhanced network region which shows ample occurrences of rapid spicular downflows in the Hα spectral line, which could potentially be linked to high-speed TR downflowing counterparts. Methods. We used the k-means algorithm to classify the spectral profiles of on-disk spicules in Hα and Ca II K data observed from the Swedish 1 m Solar Telescope and employed an automated detection method based on advanced morphological image processing operations to detect such downflowing features, in conjunction with rapid blue-shifted and red-shifted excursions (RBEs and RREs). Results. We report the existence of a new category of RREs (termed as downflowing RRE) for the first time that, contrary to earlier interpretation, are associated with chromospheric field aligned downflows moving toward the strong magnetic field regions. Statistical analysis performed on nearly 20 000 RBEs and 15 000 RREs (including the downflowing counterparts), which were detected in our 97 min long dataset, shows that the downflowing RREs are very similar to RBEs and RREs except for their oppositely directed plane-of-sky motion. Furthermore, we also find that RBEs, RREs, and downflowing RREs can be represented by a wide range of spectral profiles with varying Doppler offsets, and Hα line core widths, both along and perpendicular to the spicule axis, that causes them to be associated with multiple substructures which evolve together. Conclusions. We speculate that these rapid plasma downflows could well be the chromospheric counterparts of the commonly observed TR downflows.

Classification of High-resolution Solar Hα Spectra Using t-distributed Stochastic Neighbor Embedding

Abstract The Hα spectral line is a well-studied absorption line revealing properties of the highly structured and dynamic solar chromosphere. Typical features with distinct spectral signatures in Hα include filaments and prominences, bright active-region plages, superpenumbrae around sunspots, surges, flares, Ellerman bombs, filigree, and mottles and rosettes, among others. This study is based on high-spectral resolution Hα spectra obtained with the Echelle spectrograph of the Vacuum Tower Telescope (VTT) located at Observatorio del Teide, Tenerife, Spain. The t-distributed stochastic neighbor embedding (t-SNE) is a machine-learning algorithm, which is used for nonlinear dimensionality reduction. In this application, it projects Hα spectra onto a two-dimensional map, where it becomes possible to classify the spectra according to results of cloud model (CM) inversions. The CM parameters optical depth, Doppler width, line-of-sight velocity, and source function describe properties of the cloud material. Initial results of t-SNE indicate its strong discriminatory power to separate quiet-Sun and plage profiles from those that are suitable for CM inversions. In addition, a detailed study of various t-SNE parameters is conducted, the impact of seeing conditions on the classification is assessed, results for various types of input data are compared, and the identified clusters are linked to chromospheric features. Although t-SNE proves to be efficient in clustering high-dimensional data, human inference is required at each step to interpret the results. This exploratory study provides a framework and ideas on how to tailor a classification scheme toward specific spectral data and science questions.

Calibration-free analysis of a tungsten-based target for diagnostics of relevant fusion materials comparing picosecond and nanosecond LIBS

The elemental analysis of plasma-facing components (PFCs) with deposits is vital for the study of the material erosion, deposition, and fuel retention. For ITER-like divertor, first wall is formed by W-based deposit containing Be, O, D, H and other impurities. The quantification of fuel retention in these materials, including the depth dependence of the fuel retention and the elemental composition, is important. Calibration free laser-induced breakdown spectroscopy (CF-LIBS) is the only technique possible for online remote diagnostics with recognition of the hydrogen isotopes. But the most commonly used ns-LIBS leads to material's overheating; thus, larger non-realistic retention of hydrogen isotopes is generally obtained. In this work, we report the quantitative ps- and ns-CF LIBS analysis of W-based model material (WCu). A WCu alloy has been selected to permit the analysis of tungsten spectral lines in a binary alloy with an element with not too many weak lines. Surface experiments are performed by LIBS using ~30 ps and 5 ns, 1064 nm laser pulses at atmospheric pressure. One of the advantages of ps laser is that it ablates the surface more efficiently, without overheating the ablated material. The laser ablation threshold for the plasma creation in the ps regime is situated at lower energy, thus less material is needed and better depth resolution can be obtained. Suitable Cu and W spectral lines have been selected for the precise evaluation of the electron temperature using the Saha-Boltzmman plots. The electron density values were found from the Saha-Boltzmann plots and the Stark broadening of the Hα spectral line. The results demonstrate the successful detection of W and Cu spectral lines using ps- and ns-LIBS and its quantification.

Comprehensive photometric investigation of an active early K-type contact system—IL Cancri

Abstract Comprehensive photometric investigation of the early K-type contact binary IL Cnc was carried out. A few light curves from both ground-based telescopes and the Kepler space telescope were obtained (or downloaded) and then analyzed in detail. They are mostly found to be asymmetric and there are even continuously changing O’Connell effects in the light curves from Kepler K2 data, suggesting the system to be highly active. Using the Wilson–Devinney code (version 2013), photometric solutions were derived and then compared. It is found that the calculation of the mass ratio is easily affected by the spot settings. Combining the radial velocities determined from LAMOST median resolution spectral data, the mass ratio of the binary components is found to be M2/M1 = 1.76 ± 0.05. The components are in shallow contact ($f\sim 9\%$) and have a temperature difference about T2 − T1 = −280 ± 20 K. The system is demonstrated to be W-subtype, which may be a common feature of K-type contact binaries. The masses of the binary components were estimated to be $M_1\sim 0.51\, M_{\odot }$ and $M_2\sim 0.90\, M_{\odot }$. The values are in good agreement with that deduced from the parallax data of Gaia. The results suggest that the primary component lacks luminosity compared with the zero main sequence. The Hα spectral line of the primary component is found to be peculiar. Combining newly determined minimum light times with those collected from literature, the orbital period of IL Cnc is studied. It is found that the (O − C) values of the primary minima show sinusoidal variation while those of the secondary do not. The oscillation is more likely to be caused by the starspot activities, yet this assumption needs more data to support.

Plasma density determination by using hydrogen Balmer Hα spectral line with improved accuracy

In this paper, we demonstrate the use of hydrogen Balmer Hα spectral line for plasma electron density determination with a similar accuracy as is obtained by using the hydrogen Balmer Hβ spectral line. The reason for this is that Hβ often cannot be used for plasma electron density determination in many experiments. Theories that treat Hα line give different relation between halfwidth and electron density. The corresponding numerical procedure for the correction of electron density obtained from Hα line is established in this paper. For that purpose, experimental line profiles emitted from an electric wall stabilized dc and pulsed arc and laser produced plasma were used, as well as the experimental data available in the literature.