Non-local Thermal Equilibrium Research Articles

How numerical simulations helped to achieve breakeven on the NIF

The inertial confinement fusion program relies upon detailed simulations with inertial confinement fusion (ICF) codes to design targets and to interpret the experimental results. These simulations treat as much physics from essential principles as is practical, including laser deposition, cross beam energy transfer, x-ray production and transport, nonlocal thermal equilibrium kinetics, thermal transport, hydrodynamic instabilities, thermonuclear burn, and transport of reaction products. Improvements in radiation hydrodynamic code capabilities and vast increases in computing power have enabled more realistic, accurate 3D simulations that treat all known asymmetry sources. We describe how numerical simulations helped to guide the program, assess the impediments to breakeven, and optimize every aspect of target design. A preshot simulation of the first National Ignition Facility experiment that surpassed breakeven predicted an increased yield that matches the experimental result, within the preshot predicted uncertainty, with a target gain of 1.5. We will cover the key developments in Lawrence Livermore National Laboratory ICF codes that enabled these simulations and give specific examples of how they helped to guide the program.

Theoretical study of the electron-induced vibrational excitation of H2O

This study presents calculations for cross sections of the vibrational excitation of H2O(X1A1) via electron impact. The theoretical approach employed here is based on first principles only, combining electron-scattering calculations performed using the UK R-matrix codes for several geometries of the target molecule, three-dimensional (3D) vibrational states of H2O, and 3D vibrational frame transformation. The aim is to represent the scattering matrix for the electron incident of the molecule. The vibrational wave functions were obtained numerically, without the normal-mode approximation, so that the interactions and transitions between vibrational states assigned to different normal modes could be accounted for. The thermally averaged rate coefficients were derived from the calculated cross sections for temperatures in the 10–10 000 K interval and analytical fits for rate coefficients were also provided. We assessed the uncertainty estimations of the obtained data for subsequent applications of the rate coefficients in modelling the non-local thermal equilibrium (non-LTE) spectra of water in various astrophysical environments.

Multiline observations of hydrogen, helium, and carbon radio-recombination lines toward Orion A: A detailed dynamical study and direct determination of physical conditions

We present a study of hydrogen, helium, and carbon millimeter-wave radio-recombination lines (RRLs) toward ten representative positions throughout the Orion Nebula complex, using the Yebes 40m telescope in the Q band (31.3 GHz to 50.6 GHz) at an angular resolution of about $45 (sim 0.09\,pc). The observed positions include the Orion Nebula (M42) with the Orion Molecular Core 1, M43, and the Orion Molecular Core 3 bordering on NGC 1973, 1975, and 1977. While hydrogen and helium RRLs arise in the ionized gas surrounding the massive stars in the Orion Nebula complex, carbon RRLs stem from the neutral gas of the adjacent photo-dissociation regions (PDRs). The high velocity resolution ($0.3\ $) enables us to discern the detailed dynamics of the RRL emitting neutral and ionized gas. We compare the carbon RRLs with SOFIA/upGREAT observations of the ii m $ line and IRAM 30m observations of the 13CO (J=2-1) line (the complete map is presented here for the first time). We observe small differences in peak velocities between the different tracers, which cannot always be attributed to geometry but potentially to shear motions. Using the far-infrared ii and ii intensities with the carbon RRL intensities, we can infer physical conditions (electron temperature $T_ e $ and electron density $n_ e $, converted to hydrogen nuclei density $n_ H $ by dividing by the carbon gas-phase abundance $ A C $) in the PDR gas using nonlocal thermal equilibrium excitation models. For positions in OMC1, we infer $n_ e cm^ $ and $T_ e K $. On the border between OMC1 and M43, we observe two gas components with $n_ e cm^ $ and $n_ e cm^ $, and $T_ e K $ and $T_ e K $. In M43, we infer $n_ e cm^ $ and $T_ e K $. The Extended Orion Nebula southeast of OMC1 is characterized by $n_ e cm^ $ and $T_ e K $, while OMC3 has $n_ e cm^ $ and $T_ e K $. Our observations are sensitive enough to detect faint lines toward two positions in OMC1, in the BN/KL PDR and the PDR close to the Trapezium stars, that may be attributed to RRLs of C$^+$ or O$^+$. In general, the RRL line widths of both the ionized and neutral gas, as well as the ii and 13CO line widths, are broader than thermal, indicating significant turbulence in the interstellar medium, which transitions from super-Alfv\'enic and subsonic in the ionized gas to sub-Alfv\'enic and supersonic in the molecular gas. At the scales probed by our observations, the turbulent pressure dominates the pressure balance in the neutral and molecular gas, while in the ionized gas the turbulent pressure is much smaller than the thermal pressure.

The First Spatially Resolved Detection of 13CN in a Protoplanetary Disk and Evidence for Complex Carbon Isotope Fractionation

Recent measurements of carbon isotope ratios in both protoplanetary disks and exoplanet atmospheres have suggested a possible transfer of significant carbon isotope fractionation from disks to planets. For a clearer understanding of the isotopic link between disks and planets, it is important to measure the carbon isotope ratios in various species. In this paper, we present a detection of the 13CN N = 2 − 1 hyperfine lines in the TW Hya disk with the Atacama Large Millimeter/submillimeter Array. This is the first spatially resolved detection of 13CN in disks, which enables us to measure the spatially resolved 12CN/13CN ratio for the first time. We conducted nonlocal thermal equilibrium modeling of the 13CN lines in conjunction with previously observed 12CN lines to derive the kinetic temperature, H2 volume density, and column densities of 12CN and 13CN. The H2 volume density is found to range between (4 − 10) × 107 cm−3, suggesting that CN molecules mainly reside in the disk's upper layer. The 12CN/13CN ratio is measured to be 70−6+9 at 30 < r < 80 au from the central star, which is similar to the 12C/13C ratio in the interstellar medium. However, this value differs from the previously reported values found for other carbon-bearing molecules (CO and HCN) in the TW Hya disk. This could be self-consistently explained by different emission layer heights for different molecules combined with preferential sequestration of 12C into the solid phase toward the disk midplane. This study reveals the complexity of the carbon isotope fractionation operating in disks.

3D NLTE modelling of Y and Eu

Context. Abundances of s- and r-process elements in Sun-like stars constrain nucleosynthesis in extreme astrophysical events, such as compact binary mergers and explosions of highly magnetised rapidly rotating massive stars. Aims. We measure solar abundances of yttrium (Y) and europium (Eu) using 3D non-local thermal equilibrium (NLTE) models. We use the model to determine the abundance of Y, and also explore the model’s ability to reproduce the solar centre-to-limb variation of its lines. In addition, we determine the Eu abundance using solar disc-centre and integrated flux spectra. Methods. We developed an NLTE model of Eu and updated our model of Y with collisional data from detailed quantum-mechanical calculations. We used the IAG spatially resolved high-resolution solar spectra to derive the solar abundances of Y across the solar disc and of Eu for integrated flux and at disc centre using a set of carefully selected lines and a 3D radiation-hydrodynamics model of the solar atmosphere. Results. We find 3D NLTE solar abundances of A(Y)3D NLTE = 2.30 ± 0.03stat ± 0.07syst dex based on observations at all angles and A(Eu) = 0.57 ± 0.01stat ± 0.06syst dex based on the integrated flux and disc-centre intensity. 3D NLTE modelling offers the most consistent abundances across the solar disc, and resolves the problem of severe systematic bias in Y and Eu abundances inherent to 1D LTE, 1D NLTE, and 3D LTE modelling.

Optimization of convection cooling by pressed brick structure and coke conversion rate in coke dry quenching furnace

Segregation of coke temperature and gas flow in Coke Dry Quenching furnace is a crucial issue in coke production, and the pressed brick structure of Coke Dry Quenching furnace plays a significant role in the problem of segregation. In this work, computational fluid dynamics simulation software Ansys Fluent and self-programmed equations were utilized to investigate the fluid flow and heat transfer processes, as well as coke particle combustion behavior, based on the No. 2 Coke Dry Quenching furnace at the Bayuquan coking plant of Ansteel. The focus was on analyzing the impact of gas flow rate and pressed brick structure on the furnace’s flow and temperature fields, as well as assessing the extent of coke particle combustion under different gas flow rates. The simulation involved the use of porous media models, pseudo-fluid models, and non-local thermal equilibrium to simulate the heat transfer processes within the CDQ furnace. The simulation results show that when the coke discharge rate was set at 160 t/h, selecting a circulating gas flow rate of 180,000 m3/h could ensure that the outlet temperature of coke meet the production requirement and reducing energy consumption. Optimizing the pressed brick structure appropriately can clearly improve the segregation in gas flow and temperature within the furnace. This led to a reduction of approximately 0.3 m in the height of coke isotherm line segregation at 500 K, while also lowered the average temperature at the coke outlet. Furthermore, we established the improved random pore model with two new equations to describe the evolution of coke porosity and the molar composition of the ambient gas, and real-time tracking of changes in coke porosity and considered the impact of variable gas concentration on coke conversion rate were provided. These findings offer valuable insights and reference for optimizing operational conditions and coke quality prediction in actual production scenarios.

Improved Quantum-Classical Treatment of N2-N2 Inelastic Collisions: Effect of the Potentials and Complete Rate Coefficient Data Sets.

In this study, complete (i.e., including all vibrational quantum numbers in an N2 vibrational ladder) data sets of vibration-to-vibration and vibration-to-translation rate coefficients for N2-N2 collisions are explicitly computed along with transport properties (shear and bulk viscosity, thermal conductivity, and self-diffusion) in the temperature range 100-9000 K. To reach this goal, we improved a mixed quantum-classical (MQC) dynamics approach by lifting the constraint of a Morse treatment of the vibrational wave function and intramolecular potential and permitting the use of more realistic and flexible representations. The new formulation has also allowed us to separately analyze the role of intra- and intermolecular potentials on the calculated rates and properties. Ab initio intramolecular potentials are indispensable for highly excited vibrational states, though the Morse potential still gives reasonable values up to v = 20. An accurate description of the long-range interaction and the van der Waals well is a requisite for the correct reproduction of qualitative and quantitative rate coefficients, particularly at low temperatures, making physically meaningful analytical representations still the best choice compared to currently available ab initio potential energy surfaces. These settings were used to directly compute the MQC rates corresponding to a large number of initial vibrational quantum numbers, and the missing intermediate values were predicted using a machine learning technique (i.e., the Gaussian process regression approach). The obtained values are reliable in the wide temperature range employed and are therefore valuable data for many communities dealing with nonlocal thermal equilibrium conditions in different environments.

A new Einstein coefficient method for mesopause-lower thermosphere atmosphere temperature retrieval under a non-local thermal equilibrium situation.

The mesopause-lower thermosphere (MLT) region is an important spatial region in the Earth's atmosphere, making it a valuable area to investigate the temperature variations. Kirchhoff's law fails with the altitude increase due to the non-local thermal equilibrium effect, resulting in an increase in the error of the method to retrieve the atmospheric temperature in the MLT region using the A-band spectral line intensity. In the non-LTE state, the temperature retrieval method based on the Einstein coefficients is proposed to retrieve atmospheric temperature in the 92-140 km height range using the airglow radiation intensity images obtained from the Michelson Interferometer for global high-resolution thermospheric imaging (MIGHTI) measurements. Results show that the temperature deviation of the two-channel combinations does not exceed 15 K in the altitude range of 92-120 km. This deviation increases up to 45 K when the altitude is in the range of 120-140 km due to the influence of the N2 airglow spectrum. The two-channel combinations self-consistency is increased by 85 K compared with the temperature obtained using the spectral line intensity retrieval. Additionally, the comparison of the retrieval results with the spectral line intensity method and the comparison with the atmospheric chemistry experiment Fourier transform spectrometer (ACE-FTS) temperature measurement data shows that the Einstein coefficient method is significantly more rational and accurate than the spectral line intensity method.

The molecular chemistry of Type Ibc supernovae and diagnostic potential with the James Webb Space Telescope

Context. A currently unsolved question in supernova (SN) research is the origin of stripped-envelope supernovae (SESNe). Such SNe lack spectral signatures of hydrogen (Type Ib), or hydrogen and helium (Type Ic), indicating that the outer stellar layers have been stripped during their evolution. The mechanism for this is not well understood, and to disentangle the different scenarios’ determination of nucleosynthesis yields from observed spectra can be attempted. However, the interpretation of observations depends on the adopted spectral models. A previously missing ingredient in these is the inclusion of molecular effects, which can be significant. Aims. We aim to investigate how the molecular chemistry in SESNe affect physical conditions and optical spectra, and produce ro-vibrational emission in the mid-infrared (MIR). We also aim to assess the diagnostic potential of observations of such MIR emission with JWST. Methods. We coupled a chemical kinetic network including carbon, oxygen, silicon, and sulfur-bearing molecules into the nonlocal thermal equilibrium (NLTE) spectral synthesis code SUMO. We let four species – CO, SiO, SiS, and SO – participate in NLTE cooling of the gas to achieve self-consistency between the molecule formation and the temperature. We applied the new framework to model the spectrum of a Type Ic SN in the 100–600 days time range. Results. Molecules are predicted to form in SESN ejecta in significant quantities (typical mass 10−3 M⊙) throughout the 100–600 days interval. The impact on the temperature and optical emission depends on the density of the oxygen zones and varies with epoch. For example, the [O I] 6300, 6364 feature can be quenched by molecules from 200 to 450 days depending on density. The MIR predictions show strong emission in the fundamental bands of CO, SiO, and SiS, and in the CO and SiO overtones. Conclusions. Type Ibc SN ejecta have a rich chemistry and considering the effect of molecules is important for modeling the temperature and atomic emission in the nebular phase. Observations of SESNe with JWST hold promise to provide the first detections of SiS and SO, and to give information on zone masses and densities of the ejecta. Combined optical, near-infrared, and MIR observations can break degeneracies and achieve a more complete picture of the nucleosynthesis, chemistry, and origin of Type Ibc SNe.

Pore-scale and volume-averaged simulations of phase change material melting: A comparison between local and nonlocal thermal equilibrium

An investigation of one-temperature or two-temperature models in numerical simulations of the melting process of a phase change material is presented in this work. In this study, Kelvin cell was used to simulate a case in the pore scale and the results were compared with experimental values. For the first time that a real experiment in large dimensions is simulated at the pore scale. The problem was simulated based on the one-temperature porous model. It was shown that the one-temperature porous model compares well with the results of the pore-scale simulation. Furthermore, the two-temperature model is not required for these types of studies. Results for different models were compared carefully and the reasons for the discrepancy between results were explained.

Constraints on the non-thermal desorption of methanol in the cold core LDN 429-C

Context. Cold cores are one of the first steps of star formation, characterized by densities of a few 104–105 cm−3, low temperatures (15 K and below), and very low external UV radiation. In these dense environments, a rich chemistry takes place on the surfaces of dust grains. Understanding the physico-chemical processes at play in these environments is essential to tracing the origin of molecules that are predominantly formed via reactions on dust grain surfaces. Aims. We observed the cold core LDN 429-C (hereafter L429-C) with the NOEMA interferometer and the IRAM 30 m single dish telescope in order to obtain the gas-phase abundances of key species, including CO and CH3OH. Comparing the data for methanol to the methanol ice abundance previously observed with Spitzer allows us to put quantitative constraints on the efficiency of the non-thermal desorption of this species. Methods. With physical parameters determined from available Herschel data, we computed abundance maps of 11 detected molecules with a non-local thermal equilibrium (LTE) radiative transfer model. These observations allowed us to probe the molecular abundances as a function of density (ranging from a few 103 to a few 106 cm−3) and visual extinction (ranging from 7 to over 75), with the variation in temperature being restrained between 12 and 18 K. We then compared the observed abundances to the predictions of the Nautilus astrochemical model. Results. We find that all molecules have lower abundances at high densities and visual extinctions with respect to lower density regions, except for methanol, whose abundance remains around 4.5 × 10−10 with respect to H2. The CO abundance spreads over a factor of 10 (from an abundance of 10−4 with respect to H2 at low density to 1.8 × 10−5 at high density) while the CS, SO, and H2S abundances vary by several orders of magnitude. No conclusion can be drawn for CCS, HC3N, and CN because of the lack of detections at low densities. Comparing these observations with a grid of chemical models based on the local physical conditions, we were able to reproduce these observations, allowing only the parameter time to vary. Higher density regions require shorter times than lower density regions. This result can provide insights on the timescale of the dynamical evolution of this region. The increase in density up to a few 104 cm−3 may have taken approximately 105 yr, while the increase to 106 cm−3 occurs over a much shorter time span (104 yr). Comparing the observed gas-phase abundance of methanol with previous measurements of the methanol ice, we estimate a non-thermal desorption efficiency between 0.002 and 0.09%, increasing with density. The apparent increase in the desorption efficiency cannot be reproduced by our model unless the yield of cosmic-ray sputtering is altered due to the ice composition varying as a function of density.

Tracing the contraction of the pre-stellar core L1544 with HC17O+ J = 1–0 emission

Context. Spectral line profiles of several molecules observed towards the pre-stellar core L1544 appear double-peaked. For abundant molecular species this line morphology has been linked to self-absorption. However, the physical process behind the double-peaked morphology for less abundant species is still under debate. Aims. In order to understand the cause behind the double-peaked spectra of optically thin transitions and their link to the physical structure of pre-stellar cores, we present high-sensitivity and high spectral resolution HC17O+ J =1−0 observations towards the dust peak in L1544. Methods. We observed the HC17O+(1−0) spectrum with the Institut de Radioastronomie Millimétrique (IRAM) 30 m telescope. By using state-of-the-art collisional rate coefficients, a physical model for the core and the fractional abundance profile of HC17O+, the hyperfine structure of this molecular ion is modelled for the first time with the radiative transfer code loc applied to the predicted chemical structure of a contracting pre-stellar core. We applied the same analysis to the chemically related C17O molecule. Results. The observed HC17O+(1−0) and C17O(1−0) lines were successfully reproduced with a non-local thermal equilibrium (LTE) radiative transfer model applied to chemical model predictions for a contracting pre-stellar core. An upscaled velocity profile (by 30%) is needed to reproduce the HC17O+(1−0) observations. Conclusions. The double peaks observed in the HC17O+(1−0) hyperfine components are due to the contraction motions at densities close to the critical density of the transition (~105 cm−3) and to the decreasing HCO+ fractional abundance towards the centre.

Stellar wind properties of the nearly complete sample of O stars in the low metallicity young star cluster NGC 346 in the SMC galaxy

Context. Massive stars are among the main cosmic engines driving the evolution of star-forming galaxies. Their powerful ionising radiation and stellar winds inject a large amount of energy in the interstellar medium. Furthermore, mass-loss (Ṁ) through radiatively driven winds plays a key role in the evolution of massive stars. Even so, the wind mass-loss prescriptions used in stellar evolution models, population synthesis, and stellar feedback models often disagree with mass-loss rates empirically measured from the UV spectra of low metallicity massive stars. Aims. The most massive young star cluster in the low metallicity Small Magellanic Cloud galaxy is NGC 346. This cluster contains more than half of all O stars discovered in this galaxy so far. A similar age, metallicity (Z), and extinction, the O stars in the NGC 346 cluster are uniquely suited for a comparative study of stellar winds in O stars of different subtypes. We aim to use a sample of O stars within NGC 346 to study stellar winds at low metallicity. Methods. We mapped the central 1′ of NGC 346 with the long-slit UV observations performed by the Space Telescope Imaging Spectrograph (STIS) on board of the Hubble Space Telescope and complemented these new datasets with archival observations. Multi-epoch observations allowed for the detection of wind variability. The UV dataset was supplemented by optical spectroscopy and photometry. The resulting spectra were analysed using a non-local thermal equilibrium model atmosphere code (PoWR) to determine wind parameters and ionising fluxes. Results. The effective mapping technique allowed us to obtain a mosaic of almost the full extent of the cluster and resolve stars in its core. Among hundreds of extracted stellar spectra, 21 belong to O stars. Nine of them are classified as O stars for the first time. We analyse, in detail, the UV spectra of 19 O stars (with a further two needing to be analysed in a later paper due to the complexity of the wind lines as a result of multiplicity). This more than triples the number of O stars in the core of NGC 346 with constrained wind properties. We show that the most commonly used theoretical mass-loss recipes for O stars over-predict mass-loss rates. We find that the empirical scaling between mass-loss rates (Ṁ) and luminosity (L), Ṁ ∝ L2.4, is steeper than theoretically expected by the most commonly used recipes. In agreement with the most recent theoretical predictions, we find within Ṁ ∝ Zα that α is dependent upon L. Only the most luminous stars dominate the ionisation feedback, while the weak stellar winds of O stars in NGC 346 and the lack of previous supernova explosions in this cluster restrict the kinetic energy input.

A novel bionic packed bed latent heat storage system filled with encapsulated PCM for thermal energy collection

• A bionic structure brings a more homogeneous temperature difference and a smaller pressure drop compared with conventional systems. • The parameters related to heat transfer and phase transition acquired from numerical study were validated by experiments. • A non-local thermal equilibrium model was employed to characterize the temperature distribution of PCM and HTF in porous media. • The enhancement of flow resistance and heat exchange performance was evaluated. The main content of this work is to propose a novel bionic solution to overcome the nonuniformity of flow and temperature distribution, which is an inherent problem and restriction for conventional latent heat storage devices. By learning from animal circulatory systems, the inner space and flow channel network are distributed hierarchically as arteries, veins, capillaries and ventricles. A conceptual configuration of the bionic system is presented, and its numerical model is established to demonstrate the flow and heat transfer phenomena. The encapsulated PCM that is used in this study is fabricated and parameters related have been measured by experiments. A numerical model of a 3D continuous PCM bed is established to help research the flow of HTF through the surfaces of PCM particles and the heat transfer between them. Then, a model of a simplified bionic device is developed where the PCM region is set as a porous domain. The results show the flow and temperature fields are distributed uniformly, along with a much smaller global pressure drop. By allocating the thermal load on cascaded layers with stepwise PCMs, a more homogeneous global temperature difference can be achieved.

Hyperfine resolved rate coefficients of HC17O+ with H2 (j = 0)

ABSTRACT The formyl cation (HCO+) is one of the most abundant ions in molecular clouds and plays a major role in the interstellar chemistry. For this reason, accurate collisional rate coefficients for the rotational excitation of HCO+ and its isotopes due to the most abundant perturbing species in interstellar environments are crucial for non-local thermal equilibrium models and deserve special attention. In this work, we determined the first hyperfine resolved rate coefficients of HC17O+ in collision with H2 (j = 0). Indeed, despite no scattering calculations on its collisional parameters have been performed so far, the HC17O+ isotope assumes a prominent role for astrophysical modelling applications. Computations are based on a new four dimensional (4D) potential energy surface obtained at the CCSD(T)-F12a/aug-cc-pVQZ level of theory. A test on the corresponding cross-section values pointed out that, to a good approximation, the influence of the coupling between rotational levels of H2 can be ignored. For this reason, the H2 collider has been treated as a spherical body and an average of the potential based on five orientations of H2 has been employed for scattering calculations. State-to-state rate coefficients resolved for the HC17O+ hyperfine structure for temperature ranging from 5 to 100K have been computed using recoupling techniques. This study provides the first determination of HC17O+–H2 inelastic rate coefficients directly computed from full quantum close-coupling equations, thus supporting the reliability of future radiative transfer modellings of HC17O+ in interstellar environments.

High resolved Optical Emission Spectroscopy as accurate physics methodology for plasma freestream temperature characterization

In this work the hypersonic plasma flow generated by SCIROCCO hypersonic facility has been experimentally characterized as test case, using a high resolved Optical Emission Spectroscopy (OES) during a high enthalpy test campaign. The CIRA methodology to measure roto-translational and NO vibrational temperatures of a free jet via analyses performed in the Ultra Violet spectral range has been improved and a comparison between experimental data and Computational Fluid Dynamics (CFD) simulations has been carried out. The revised methodology estimates the roto-translational and vibrational temperatures using high definition spectroscopy carried out at conditions of high values of pressure and enthalpy.In particular, attention is mainly focused on the NO emission band at Non-Local Thermal Equilibrium (NLTE) conditions in the hypersonic flight regime which means equilibrium between the molecular rotational and translational degrees of freedom but not between the roto-translational and vibrational degrees of freedom. Three tests at high enthalpy hypersonic conditions (23.8, 24.0 and 26.0 MJ/kg at a total pressure of about 2.5 bars) have been investigated and experimental data have been compared with numerical simulations in order to verify sensitivity of the method in estimating the small variation in NO roto-translational and vibrational temperatures by changing slightly the total enthalpy fluid-dynamic conditions. The current work presents a high definition spectral method which can be used to determine the temperature of NLTE hypersonic free jets, and may serve as a benchmark in determining the accuracy of various numerical models dedicated to these flow regimes.

The bands method for tabulating NLTE material properties

The use of Non-Local Thermal Equilibrium (NLTE) material properties within radiation-hydrodynamic simulations remains a major challenge. The plasma radiative and EOS properties in NLTE can depend on the detailed local radiation field and electron energy distribution. Fully characterizing each of these quantities may require 10’s to 100’s of parameters, making tabulation effectively impossible and requiring expensive calculations for each set of conditions within the simulation. In this work we present a new method that characterizes the local radiation field with a limited number of parameters. This permits pre-calculation and tabulation of the material properties, allowing codes to perform NLTE radiation-hydrodynamic simulations which would otherwise be computationally prohibitive.

The Extremely Buried Nucleus of IRAS 17208–0014 Observed at Submillimeter and Near-infrared Wavelengths

Abstract The ultraluminous infrared galaxy IRAS 17208−0014 is a late-stage merger that hosts a buried active galactic nucleus (AGN). To investigate its nuclear structure, we performed high-spatial-resolution ( ∼ 0.″04 ∼ 32 pc) Atacama Large Millimeter/submillimeter Array (ALMA) observations in Band 9 (∼450 μm or ∼660 GHz), along with near-infrared AKARI spectroscopy in 2.5–5.0 μm. The Band 9 dust continuum peaks at the AGN location, and toward this position CO(J = 6 − 5) and CS(J = 14 − 13) are detected in absorption. Comparison with nonlocal thermal equilibrium calculations indicates that, within the central beam (r ∼ 20 pc), there exists a concentrated component that is dense (107 cm−3) and warm (&gt;200 K) and has a large column density ( N H 2 &gt; 10 23 cm − 2 ). The AKARI spectrum shows deep and broad CO rovibrational absorption at 4.67 μm. Its band profile is well reproduced with a similarly dense and large column but hotter (∼1000 K) gas. The region observed through absorption in the near-infrared is highly likely in the nuclear direction, as in the submillimeter, but with a narrower beam including a region closer to the nucleus. The central component is considered to possess a hot structure where vibrationally excited HCN emission originates. The most plausible heating source for the gas is X-rays from the AGN. The AKARI spectrum does not show other AGN signs in 2.5–4 μm, but this absence may be usual for AGNs buried in a hot mid-infrared core. Further, based on our ALMA observations, we relate the various nuclear structures of IRAS 17208−0014 that have been proposed in the literature.

The Early-type Stars from the LAMOST Survey: Atmospheric Parameters

Abstract Massive stars play key roles in many astrophysical processes. Deriving the atmospheric parameters of massive stars is important to understanding their physical properties, and thus the atmospheric parameters are key inputs to trace the evolution of massive stars. Here we report our work on adopting the data-driven technique called stellar label machine (SLAM) with the nonlocal thermal equilibrium TLUSTY synthetic spectra as the training data set to estimate the stellar parameters of Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) optical spectra for early-type stars. We apply two consistency tests to verify this machine-learning method and compare stellar labels given by SLAM with the labels in the literature for several objects having high-resolution spectra. We provide the stellar labels of effective temperature (T eff), surface gravity ( log g ), metallicity ([M/H]), and projected rotational velocity ( v sin i ) for 3931 and 578 early-type stars from the LAMOST low-resolution survey (LRS) and medium-resolution survey (MRS), respectively. To estimate the average statistical uncertainties of our results, we calculated the standard deviation between the predicted stellar label and the prelabeled published values from the high-resolution spectra. The uncertainties of the four parameters are σ(T eff) = 2185 K, σ ( log g ) = 0.29 dex, and σ ( v sin i ) = 11 km s − 1 for MRS, and σ(T eff) = 1642 K, σ ( log g ) = 0.25 dex, and σ ( v sin i ) = 42 km s − 1 for LRS spectra, respectively. We note that the parameters of T eff, log g , and [M/H] can be better constrained using LRS spectra than using MRS spectra, most likely due to their broad wavelength coverage, while v sin i is constrained better by MRS spectra than by LRS spectra, probably due to the relatively accurate line profiles of MRS spectra.

Line formation of He I D3 and He I 10 830 Å in a small-scale reconnection event

Context. Ellerman bombs (EBs) and UV bursts are small-scale reconnection events that occur in the region of the upper photosphere to the chromosphere. It has recently been discovered that these events can have emission signatures in the He I D3 and He I 10 830 Å lines, suggesting that their temperatures are higher than previously expected. Aims. We aim to explain the line formation of He I D3 and He I 10 830 Å in small-scale reconnection events. Methods. We used a simulated EB in a Bifrost-generated radiative magnetohydrodynamics snapshot. The resulting He I D3 and He I 10 830 Å line intensities were synthesized in 3D using the non-local thermal equilibrium (non-LTE) Multi3D code. The presence of coronal extreme UV (EUV) radiation was included self-consistently. We compared the synthetic helium spectra with observed raster scans of EBs in He I 10 830 Å and He I D3 obtained at the Swedish Solar Telescope with the TRI-Port Polarimetric Echelle-Littrow Spectrograph. Results. Emission in He I D3 and He I 10 830 Å is formed in a thin shell around the EB at a height of ∼0.8 Mm, while the He I D3 absorption is formed above the EB at ∼4 Mm. The height at which the emission is formed corresponds to the lower boundary of the EB, where the temperature increases rapidly from 6 × 103 K to 106 K. The synthetic line profiles at a heliocentric angle of μ = 0.27 are qualitatively similar to the observed profiles at the same μ-angle in dynamics, broadening, and line shape: emission in the wing and absorption in the line core. The opacity in He I D3 and He I 10 830 Å is generated through photoionization-recombination driven by EUV radiation that is locally generated in the EB at temperatures in the range of 2 × 104 − 2 × 106 K and electron densities between 1011 and 1013 cm−3. The synthetic emission signals are a result of coupling to local conditions in a thin shell around the EB, with temperatures between 7 × 103 and 104 K and electron densities ranging from ∼1012 to 1013 cm−3. This shows that both strong non-LTE and thermal processes play a role in the formation of He I D3 and He I 10 830 Å in the synthetic EB/UV burst that we studied. Conclusions. In conclusion, the synthetic He I D3 and He I 10 830 Å emission signatures are an indicator of temperatures of at least 2 × 104 K; in this case, as high as ∼106 K.