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- ID:
- ivo://CDS.VizieR/J/ApJ/791/14
- Title:
- 18 Sco atomic data and equivalent widths
- Short Name:
- J/ApJ/791/14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study with unprecedented detail the chemical composition and stellar parameters of the solar twin 18 Sco in a strictly differential sense relative to the Sun. Our study is mainly based on high-resolution (R ~ 110,000), high signal-to-noise ratio (800-1000) Very Large Telescope UVES spectra, which allow us to achieve a precision of about 0.005 dex in differential abundances. The effective temperature and surface gravity of 18 Sco are T_eff_= 5823+/-6 K and log g = 4.45+/-0.02 dex, i.e., 18 Sco is 46+/-6 K hotter than the Sun and log g is 0.01+/-0.02 dex higher. Its metallicity is [Fe/H] = 0.054+/-0.005 dex, and its microturbulence velocity is +0.02+/-0.01 km/s higher than solar. Our precise stellar parameters and differential isochrone analysis show that 18 Sco has a mass of 1.04+/-0.02 M_{sun}_ and that it is ~1.6 Gyr younger than the Sun. We use precise High Accuracy Radial velocity Planet Searcher (HARPS) radial velocities to search for planets, but none are detected. The chemical abundance pattern of 18 Sco displays a clear trend with condensation temperature, thus showing higher abundances of refractories in 18 Sco than in the Sun. Intriguingly, there are enhancements in the neutron-capture elements relative to the Sun. Despite the small element-to-element abundance differences among nearby n-capture elements (~0.02 dex), we successfully reproduce the r-process pattern in the Solar System. This is independent evidence for the universality of the r process. Our results have important implications for chemical tagging in our Galaxy and nucleosynthesis in general.
- ID:
- ivo://CDS.VizieR/J/A+A/634/A117
- Title:
- Screening potential and continuum lowering
- Short Name:
- J/A+A/634/A117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An accurate description of the screening potential induced by a hot, dense plasma is a fundamental problem in atomic physics and plasma physics, and it plays a pivotal role in the investigation of microscopic atomic processes and the determination of macroscopic physical properties, such as opacities and equations of state as well as nuclear fusion cross sections. Recent experimental studies show that currently available analytical models of plasma screening have difficulty in accurately describing the ionization-potential depression, which is directly determined by the screening potential. Here, we propose a consistent approach to determine the screening potential in dense plasmas under solar-interior conditions from the free-electron micro-space distribution. It is assumed that the screening potential for an ion embedded in a dense plasma is predominately determined by the free electrons in the plasma. The free-electron density is obtained by solving the ionization-equilibrium equation for an average-atom model to obtain the average degree of ionization of the plasma. The proposed model was validated by comparing the theoretically predicted ionization-potential depression of a solid-density Si plasma with recent experiments. Our approach was applied to investigate the screening potential and ionization-potential depression of Si plasmas under solar-interior conditions over a temperature range of 150-500eV and an electron-density range of 5.88x10^22^-3.25x10^24^cm^-3^. It can be easily incorporated into atomic-structure codes and used to investigate basic atomic processes, such as photoionization, electron-ion collisional excitation and ionization, and Auger decay, in a dense plasma.
- ID:
- ivo://CDS.VizieR/J/ApJS/221/24
- Title:
- SDSS-III APOGEE H-band spectral line lists
- Short Name:
- J/ApJS/221/24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the H-band spectral line lists adopted by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). The APOGEE line lists comprise astrophysical, theoretical, and laboratory sources from the literature, as well as newly evaluated astrophysical oscillator strengths and damping parameters. We discuss the construction of the APOGEE line list, which is one of the critical inputs for the APOGEE Stellar Parameters and Chemical Abundances Pipeline, and present three different versions that have been used at various stages of the project. The methodology for the newly calculated astrophysical line lists is reviewed. The largest of these three line lists contains 134457 molecular and atomic transitions. In addition to the format adopted to store the data, the line lists are available in MOOG, Synspec, and Turbospectrum formats. The limitations of the line lists along with guidance for its use on different spectral types are discussed. We also present a list of H-band spectral features that are either poorly represented or completely missing in our line list. This list is based on the average of a large number of spectral fit residuals for APOGEE observations spanning a wide range of stellar parameters.
- ID:
- ivo://CDS.VizieR/J/A+A/658/A85
- Title:
- Search for thioacetamide CH3CSNH2 in the ISM
- Short Name:
- J/A+A/658/A85
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- One of the biggest unsolved mysteries of modern astrochemistry is understanding chemical formation pathways in the interstellar medium (ISM) and circumstellar environments (CSEs). The detections (or even nondetections) of molecules composed of low-abundance atomic species (such as S, P, Si, and Mg) may help to constrain chemical pathways. Thioacetamide (CH_3_CSNH_2_) is the sulfur analog to acetemide (CH_3_CONH_2_) and it is a viable candidate to search for in astronomical environments - specifically toward regions where other S-bearing molecules have been found and, if possible, that also contain a detection of CH_3_CONH_2_. If detected, it would not only continue to expand the view of molecular complexity in astronomical environments, but also help to better elucidate the possible formation pathways of these types of species in these environments. Our aim is to expand the frequency range of the measured rotational spectrum of CH_3_CSNH_2_ beyond 150GHz and then to use those measurements to extend the search for this species in the ISM. The new laboratory measurements and expanded search cover more parameter space for determining under what conditions CH_3_CSNH_2_ may be detected, leading to possible constraints on the formation of large S-bearing molecules found in the ISM. The rotational spectrum of CH_3_CSNH_2_ was investigated up to 650GHz. Using the newly refined spectrum of CH_3_CSNH_2_, as well as additional spectroscopic data on the chemically related species CH_3_CONH_2_, a variety of astronomical sources were searched including data from the following large surveys: Prebiotic Interstellar Molecule Survey (PRIMOS) conducted with the Green Bank Telescope (GBT); Exploring molecular complexity with ALMA (EMoCA) conducted with the Atacama Large Millimeter/submillimeter Array (ALMA); and Astrochemical Surveys At IRAM (ASAI) conducted with the Institut de Radioastronomie Millim'etrique (IRAM) 30m Telescope. A total of 1428 transitions from the v_t_=0 state with maximum values J=47 and K_a_=20 in the range up to 330GHz, and J=95 and K_a_=20 in the range from 400-660GHz were assigned. We also assigned 321 transitions from the v_t=1 state with the maximum values J=35 and K_a_=9 up to 330GHz. We achieved a final fit with a root-mean-square deviation of 43.4kHz that contains 2035 measured lines from our study and the literature for v_t_=0 and v_t_=1 states of A and E symmetries. The final fit is based on the rho-axis- method (RAM) Hamiltonian model that includes 40 parameters. An astronomical search for CH_3_CSNH_2_ was conducted based on all the new spectroscopic data. No transitions of CH_3_CSNH_2_ were detected toward any of the sources contained in our survey. Using the appropriate telescope and physical parameters for each astronomical source, upper limits to the column densities were found for CH_3_CSNH_2_ toward each source.
- ID:
- ivo://CDS.VizieR/VI/10
- Title:
- Semiempirical gf Values
- Short Name:
- VI/10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This table of gf values for 265,587 atomic lines is selected from the line data used to calculate line-blanketed model atmospheres (Kurucz et al. 1974). The data are especially useful for line identification and spectral synthesis in solar and stellar spectra. Except for 10,100 lines taken from the literature, the gf values have been calculated semiempirically by using scaled Thomas-Fermi-Dirac radial wavefunctions and eigenvectors found through least-squares fits to observed energy levels. Included in the calculation were the first five or six stages of ionization for sequences up through nickel. Published gf values have been included for elements heavier than nickel. The tabulation is restricted to lines with wavelengths less than 10um.
- ID:
- ivo://CDS.VizieR/J/A+A/623/A155
- Title:
- SII, ClII, ArIV energy levels & transition data
- Short Name:
- J/A+A/623/A155
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of this work is to present accurate and extensive results of energy spectra and transition data for the SII, ClIII, and ArIV ions. These data are useful for understanding and probing physical processes and conditions in various types of astrophysical plasmas. The multiconfiguration Dirac-Hartree-Fock (MCDHF) and relativistic configuration interaction (RCI) methods, which are implemented in the general-purpose relativistic atomic structure package GRASP2K, are used in the present work. In the RCI calculations the transverse-photon (Breit) interaction, the vacuum polarization, and the self-energy corrections are included. Energy spectra are presented comprising the 134, 87, and 103 lowest states in SII, ClIII, and ArIV, respectively. Energy levels are in very good agreement with NIST database recommended values and associated with smaller uncertainties than energies from other theoretical computations. Electric dipole (E1), magnetic dipole (M1), and electric quadrupole (E2) transition data are computed between the above states together with the corresponding lifetimes. Based on internal validation, transition rates for the majority of the stronger transitions are estimated to have uncertainties of less than 3%.
- ID:
- ivo://CDS.VizieR/J/ApJ/780/76
- Title:
- SII energy levels and transition line strengths
- Short Name:
- J/ApJ/780/76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Absorption-line spectroscopy is a powerful tool used to estimate element abundances in both the nearby and distant universe. The accuracy of the abundances thus derived is naturally limited by the accuracy of the atomic data assumed for the spectral lines. We have recently started a project to perform new extensive atomic data calculations used for optical/UV spectral lines in the plasma modeling code Cloudy using state of the art quantal calculations. Here, we demonstrate our approach by focussing on S II, an ion used to estimate metallicities for Milky Way interstellar clouds as well as distant damped Lyman-alpha (DLA) and sub-DLA absorber galaxies detected in the spectra of quasars and gamma-ray bursts. We report new extensive calculations of a large number of energy levels of S II, and the line strengths of the resulting radiative transitions. Our calculations are based on the configuration interaction approach within a numerical Hartree-Fock framework, and utilize both non-relativistic and quasirelativistic one-electron radial orbitals. The results of these new atomic calculations are then incorporated into Cloudy and applied to a lab plasma, and a typical DLA, for illustrative purposes. The new results imply relatively modest changes ({approx}0.04dex) to the metallicities estimated from SII in past studies. These results will be readily applicable to other studies of SII in the Milky Way and other galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/780/110
- Title:
- SIII collision strengths
- Short Name:
- J/ApJ/780/110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Maxwellian-averaged effective collision strengths for the electron-impact excitation of SIII over a wide range of electron temperatures of astrophysical importance, log T_e_(K)=3.0-6.0. The calculation incorporates 53 fine-structure levels arising from the six configurations--3s^2^3p^2^, 3s3p^3^, 3s^2^3p3d, 3s^2^3p4s, 3s^2^3p4p, and 3s^2^3p4d--giving rise to 1378 individual lines and is undertaken using the recently developed RMATRX II plus FINE95 suite of codes. A detailed comparison is made with a previous R-matrix calculation and significant differences are found for some transitions. The atomic data are subsequently incorporated into the modeling code CLOUDY to generate line intensities for a range of plasma parameters, with emphasis on allowed ultraviolet extreme-ultraviolet emission lines detected from the Io plasma torus. Electron density-sensitive line ratios are calculated with the present atomic data and compared with those from CHIANTI v7.1, as well as with Io plasma torus spectra obtained by Far-Ultraviolet Spectroscopic Explorer and Extreme-Ultraviolet Explorer. The present line intensities are found to agree well with the observational results and provide a noticeable improvement on the values predicted by CHIANTI.
- ID:
- ivo://CDS.VizieR/J/A+A/631/A29
- Title:
- Si III and Si IV MCDHF and RCI calculations
- Short Name:
- J/A+A/631/A29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present extensive multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction calculations including 106 states in doubly ionized silicon (SiIII) and 45 states in triply ionized silicon (SiIV), which are important for astrophysical determination of plasma properties in different objects. These calculations represents an important extension and improvement of earlier calculations especially for SiIII. The calculations are in good agreement with available experiments for excitation energies, transition properties, and lifetimes. Important deviations from the NIST-database for a selection of perturbed Rydberg series are discussed in detail.
