scholarly journals Heavy metals in intermediate He-rich hot subdwarfs: the chemical composition of HZ 44 and HD 127493

2019 ◽  
Vol 630 ◽  
pp. A130 ◽  
Author(s):  
M. Dorsch ◽  
M. Latour ◽  
U. Heber
Keyword(s):  
Chemical Composition ◽  
Diffusion Processes ◽  
Heavy Elements ◽  
Atomic Data ◽  
Uv Spectrum ◽  
Thermodynamical Equilibrium ◽  
Cno Cycle ◽  
Upper Limits ◽  
Metal Abundance ◽  
Quantitative Spectral Analysis

Context. Hot subluminous stars can be spectroscopically classified as subdwarf B (sdB) and O (sdO) stars. While the latter are predominantly hydrogen deficient, the former are mostly helium deficient. The atmospheres of most sdOs are almost devoid of hydrogen, whereas a small group of hot subdwarf stars of mixed H/He composition exists, showing extreme metal abundance anomalies. Whether such intermediate helium-rich (iHe) subdwarf stars provide an evolutionary link between the dominant classes is an open question. Aims. The presence of strong Ge, Sn, and Pb lines in the UV spectrum of HZ 44 suggests a strong enrichment of heavy elements in this iHe-sdO star and calls for a detailed quantitative spectral analysis focusing on trans-iron elements. Methods. Non-local thermodynamical equilibrium model atmospheres and synthetic spectra calculated with TLUSTY/SYNSPEC were combined with high-quality optical, ultraviolet (UV), and far-UV (FUV) spectra of HZ 44 and its hotter sibling HD 127493 to determine their atmospheric parameters and metal abundance patterns. Results. By collecting atomic data from the literature we succeeded in determining the abundances of 29 metals in HZ 44, including the trans-iron elements Ga, Ge, As, Se, Zr, Sn, and Pb and providing upper limits for ten other metals. This makes it the best-described hot subdwarf in terms of chemical composition. For HD 127493 the abundance of 15 metals, including Ga, Ge, and Pb and upper limits for another 16 metals were derived. Heavy elements turn out to be overabundant by one to four orders of magnitude with respect to the Sun. Zr and Pb are among the most enriched elements. Conclusions. The C, N, and O abundance for both stars can be explained by the nucleosynthesis of hydrogen burning in the CNO cycle along with the stars’ helium enrichment. On the other hand, the heavy-element anomalies are unlikely to be caused by nucleosynthesis. Instead diffusion processes are evoked, with radiative levitation overcoming gravitational settlement of the heavy elements.

scholarly journals Heavy metal enrichment in the intermediate He-sdOB pulsator Feige 46

2019 ◽  
Vol 629 ◽  
pp. A148 ◽  
Author(s):  
M. Latour ◽  
M. Dorsch ◽  
U. Heber
Keyword(s):  
Heavy Metal ◽  
Chemical Composition ◽  
Optical Spectrum ◽  
Atmospheric Parameters ◽  
Metal Enrichment ◽  
Uv Spectrum ◽  
Abundance Pattern ◽  
Upper Limits ◽  
Kinematic Properties ◽  
Heavy Metal Enrichment

The intermediate He-enriched hot subdwarf star Feige 46 was recently reported as the second member of the V366 Aqr (or He-sdOBV) pulsating class. Feige 46 is very similar to the prototype of the class, LS IV − 14°116, not only in terms of pulsational properties, but also in terms of atmospheric parameters and kinematic properties. LS IV − 14°116 is additionally characterized by a very peculiar chemical composition, with extreme overabundances of the trans-iron elements Ge, Sr, Y, and Zr. We investigate the possibility that the similarity between the two pulsators extends to their chemical composition. We retrieved archived optical and UV spectroscopic observations of Feige 46 and performed an abundance analysis using model atmospheres and synthetic spectra computed with TLUSTY and SYNSPEC. In total, we derived abundances for 16 elements and provide upper limits for four additional elements. Using absorption lines in the optical spectrum of the star we measure an enrichment of more than 10 000× solar for yttrium and zirconium. The UV spectrum revealed that strontium is equally enriched. Our results confirm that Feige 46 is not only a member of the now growing group of heavy metal subdwarfs, but also has an abundance pattern that is remarkably similar to that of LS IV − 14°116.

scholarly journals Heavy-metal enrichment of intermediate He-sdOB stars: the pulsators Feige 46 and LS IV–14°116 revisited

2020 ◽  
Vol 643 ◽  
pp. A22 ◽  
Author(s):  
M. Dorsch ◽  
M. Latour ◽  
U. Heber ◽  
A. Irrgang ◽  
S. Charpinet ◽  
...  
Keyword(s):  
Diffusion Processes ◽  
Chemical Compositions ◽  
Thermodynamical Equilibrium ◽  
Low Mass Stars ◽  
Atmospheric Diffusion ◽  
Near Ultraviolet ◽  
Abundance Patterns ◽  
Metal Abundance ◽  
Hot Subdwarfs ◽  
Chemically Peculiar Stars

Hot subdwarf stars of spectral types O and B represent a poorly understood phase in the evolution of low-mass stars, in particular of close compact binaries. A variety of phenomena are observed, which make them important tools for several astronomical disciplines. For instance, the richness of oscillations of many subdwarfs are important for asteroseismology. Furthermore, hot subdwarfs are among the most chemically peculiar stars known. Two intermediate He-rich hot subdwarf stars, LS IV–14°116 and Feige 46, are particularly interesting, because they show extreme enrichments of heavy elements such as Ge, Sr, Y, and Zr, which are strikingly similar in both stars. In addition, both stars show light oscillations at periods incompatible with standard pulsation theory and form the class of V366 Aqr variables. We investigated whether the similar chemical compositions extend to more complete abundance patterns in both stars and validate the pulsations in Feige 46 using its recent TESS light curve. High-resolution optical and near-ultraviolet spectroscopy are combined with non-local thermodynamical-equilibrium model atmospheres and synthetic spectra calculated with TLUSTY and SYNSPEC to consistently determine detailed metal abundance patterns in both stars. Many previously unidentified lines were identified for the first time with transitions originating from Ga III, Ge III-IV, Se III, Kr III, Sr II-III, Y III, Zr III-IV, and Sn IV, most of which have not yet been observed in any star. The abundance patterns of 19 metals in both stars are almost identical, light metals being only slightly more abundant in Feige 46, while Zr, Sn, and Pb are slightly less enhanced compared to LS IV–14°116. Both abundance patterns are distinctively different from those of normal He-poor hot subdwarfs of a similar temperature. The extreme enrichment in heavy metals of more than 4 dex compared to the Sun is likely the result of strong atmospheric diffusion processes that operate similarly in both stars while their similar patterns of C, N, O, and Ne abundances might provide clues to their as yet unclear evolutionary history. Finally, we find that the periods of the pulsation modes in Feige 46 are stable to better than Ṗ ≲ 10−8 s s−1. This is not compatible with Ṗ predicted for pulsations driven by the ɛ-mechanism and excited by helium-shell flashes in a star that is evolving, for example, onto the extended horizontal branch.

Diffusion Niobizing of Titanium Grade 2 by Gas-Contact Method

2015 ◽  
Vol 669 ◽  
pp. 158-166
Author(s):  
Dariusz Bartkowski ◽  
Andrzej Mlynarczak ◽  
Adam Piasecki ◽  
Waldemar Matysiak ◽  
Michal Hatala ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Diffusion Layer ◽  
Powder Mixture ◽  
Diffusion Processes ◽  
Contact Method ◽  
Niobium Content ◽  
Structure Quality ◽  
Pure Niobium ◽  
Titanium Grade ◽  
Geometric Surface

The work presents results of diffusion niobizing of titanium Grade 2 by gas-contact method. Microhardness, thickness, chemical composition and microstructure were investigation. Diffusion processes was carried out in a two powder mixture. First consisted of ferro-niobium, kaolin and ammonium chloride, second mixture contained pure niobium instead ferro-niobium. The processes were carried out at 950°C, 1000°C and 1050°C for 2, 4 and 6 hours. Due to the geometric surface structure quality and other properties like thickness or microhardness, the best diffusion layer was obtained using first powder mixture and following parameters: temperature 950°C and time of diffusion equal 2 hours. The diffusion layer established in these conditions, had structure of niobium solution in titanium, and niobium content of about 10%. Its hardness was 550 HV0.05 while thickness was 120 μm.

scholarly journals Formation of Intermediate Phases and Supersaturated Solid Solution in Al-Cu System during Diffusion

2018 ◽  
Vol 383 ◽  
pp. 31-35 ◽  
Author(s):  
Alexey Rodin ◽  
Nataliya Goreslavets
Keyword(s):  
Phase Diagram ◽  
Solid Solution ◽  
High Temperature ◽  
Chemical Composition ◽  
Low Temperature ◽  
Supersaturated Solid Solution ◽  
Diffusion Processes ◽  
Equilibrium Phase ◽  
Equilibrium Phase Diagram ◽  
Intermediate Phases

The study of diffusion processes in the aluminum - copper system was carried out at the temperature 350 and 520 °C. Special attention was paid on the chemical composition of the system near Al/Cu interface. It was determined that the intermediate phases in the system, corresponding to the equilibrium phase diagram, were not formed at low temperature. At high temperature the intermediate phases forms starting with Cu - rich phases. In both cases supersaturated solid solution of copper in aluminum could be observed near the interface.

Molecular Diffusion Processes in Crystalline Microporous Materials

1998 ◽  
Vol 527 ◽  
Author(s):  
G. Sastre ◽  
A. Corma ◽  
C. R. A. Catlow
Keyword(s):  
Molecular Dynamics ◽  
Chemical Composition ◽  
Diffusion Coefficients ◽  
Molecular Diffusion ◽  
Diffusion Processes ◽  
Diffusion Path ◽  
Microporous Structure ◽  
Microporous Material ◽  
Para Xylene ◽  
Channel Systems

ABSTRACTAtomistic Molecular Dynamics are used to simulate diffusion of hydrocarbons inside the microporous structure of siliceous zeolite CIT-I, with chemical composition SiO2. CIT-1 is a crystalline microporous material containing channels formed by rings containing 12 and 10 Si atoms (Figure 1). The dimensions of these two channel systems are sufficient to cause substantial differences in the diffusion of para-xylene and ortho-xylene. Diffusion coefficients as a function of loading of each isomer, and activation energies have been calculated from the simulations. The effect of the isomer size in the diffusion path is also analysed.

scholarly journals The Chemical Composition of Cool Stars: II - The Hydrogen Deficient Stars

1985 ◽  
Vol 87 ◽  
pp. 126-150
Author(s):  
David L. Lambert
Keyword(s):  
Chemical Composition ◽  
Spectral Type ◽  
Heavy Elements ◽  
Carbon Stars ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Cool Stars ◽  
Similarities And Differences ◽  
Lyrae Stars

AbstractThe chemical composition of the R Coronae Borealis and cool hydrogen deficient carbon stars is reviewed. Similarities and differences between these stars and the hot He stars are noted. Proposed origins for the hydrogen deficient stars are sketched. Recent claims that normal (spectral type N) cool carbon stars are hydrogen deficient are shown to be unfounded. Attention is drawn to the curious case of pop. II variables (RV Tauri, W Virginis, and RR Lyrae stars) whose atmospheres show striking deficiencies of heavy elements and may be hydrogen deficient.

scholarly journals A detailed study of lithium in 107 CHEPS dwarf stars

2018 ◽  
Vol 611 ◽  
pp. A27 ◽  
Author(s):  
Ya. V. Pavlenko ◽  
J. S. Jenkins ◽  
O. M. Ivanyuk ◽  
H. R. A. Jones ◽  
B. M. Kaminsky ◽  
...  
Keyword(s):  
Isotopic Ratio ◽  
Small Sample Size ◽  
Small Sample ◽  
Thermodynamical Equilibrium ◽  
Lithium Abundance ◽  
Dwarf Stars ◽  
Upper Limits ◽  
Resonance Doublet ◽  
Non Local ◽  
Local Thermodynamical Equilibrium

Context. We report results from lithium abundance determinations using high resolution spectral analysis of the 107 metal-rich stars from the Calan-Hertfordshire Extrasolar Planet Search programme. Aims. We aim to set out to understand the lithium distribution of the population of stars taken from this survey. Methods. The lithium abundance taking account of non-local thermodynamical equilibrium effects was determined from the fits to the Li I 6708 Å resonance doublet profiles in the observed spectra. Results. We find that a) fast rotators tend to have higher lithium abundances; b) log N(Li) is higher in more massive and hot stars; c) log N(Li) is higher in stars of lower log g; d) stars with the metallicities >0.25 dex do not show the lithium lines in their spectra; e) most of our planet hosts rotate slower; and f) a lower limit of lithium isotopic ratio is 7Li/6Li > 10 in the atmospheres of two stars with planets (SWP) and two non-SWP stars. Conclusions. Measurable lithium abundances were found in the atmospheres of 45 stars located at distances of 20−170 pc from the Sun, for the other 62 stars the upper limits of log N(Li) were computed. We found well defined dependences of lithium abundances on Teff, V sin i, and less pronounced for the log g. In case of V sin i we see two sequences of stars: with measurable lithium and with the upper limit of log N(Li). About 10% of our targets are known to host planets. Only two SWP have notable lithium abundances, so we found a lower proportion of stars with detectable Li among known planet hosts than among stars without planets. However, given the small sample size of our planet-host sample, our analysis does not show any statistically significant differences in the lithium abundance between SWP and stars without known planets.

scholarly journals Spectroscopy of hot subdwarf binaries

2018 ◽  
Vol 27 (1) ◽  
pp. 95-97
Author(s):  
Simon Kreuzer ◽  
Andreas Irrgang ◽  
Ulrich Heber
Keyword(s):  
Spectral Analysis ◽  
Chemical Composition ◽  
Main Sequence ◽  
Spectroscopic Analysis ◽  
Status Report ◽  
Significant Excess ◽  
Composite Spectrum ◽  
Infra Red ◽  
Metal Abundance ◽  
Individual Star

Abstract We present a status report of our spectroscopic analysis of subdwarf binaries consisting of a subdwarf and a F/G/K-type main-sequence companion. These systems selected from SDSS photometry show significant excess in the (infra-)red which can not be explained by interstellar reddening. Inspection of SDSS spectra revealed that most of them are composite spectrum sdB binaries. Once their spectra are disentangled, a detailed spectral analysis can be carried out. It reveals Teff, log g and the metal abundance of each individual star. The cool companion is of particular interest, because its spectrum reveals the original chemical composition of the binary.

Non-local thermodynamical equilibrium abundance analysis of singly ionized praseodymium for the Sun

2020 ◽  
Vol 496 (4) ◽  
pp. 5361-5371
Author(s):  
Abdelrazek M K Shaltout ◽  
Ali G A Abdelkawy ◽  
M M Beheary
Keyword(s):  
Spectral Lines ◽  
Oscillator Strengths ◽  
Atomic Data ◽  
Dimensional Model ◽  
Thermodynamical Equilibrium ◽  
Solar Abundance ◽  
One Dimensional ◽  
Microturbulent Velocity ◽  
Non Local ◽  
Local Thermodynamical Equilibrium

ABSTRACT Determinations of the solar abundance of praseodymium (Pr) depend critically on the local thermodynamical equilibrium (LTE) and non-local thermodynamical equilibrium (NLTE) techniques beyond the capabilities of a classical one-dimensional model atmosphere. Here, in this analysis, we adopt an atomic model atom of Pr consisting of 105 energy levels and 14 bound–bound transitions of singly ionized praseodymium (Pr ii) and the ground state of the Pr iii continuum limit. We briefly analyse the solar abundance of Pr taking the solar model atmospheres of Holweger & Müller (1974, Solar Physics, 39, 19) with the measured equivalent linewidths and invoking a microturbulent velocity treatment. We succeed in accurately selecting nearby clear sections of the spectrum for 14 spectral lines of Pr ii with the improved atomic data of high-quality oscillator strengths available from the laboratory measurements of several possible sources as well as accurate damping constants successfully determined from the literature. We find a Pr abundance revised to be downwards log ϵPr(NLTE) = 0.75 ± 0.09, which is in good agreement with the meteoritic value (log ϵPr = 0.76 ± 0.03). A comparison of the NLTE abundance corrections with the standard LTE analysis, log ϵPr(LTE) = 0.74 ± 0.08, reveals a positive correction of  +0.01 dex, estimated from the selected solar Pr ii lines. The Pr abundance value is clearly superior following the classical one-dimensional model atmospheres of Holweger & Müller, the absolute scales of gf-values, the microturbulent velocity and the adopted equivalent linewidths.

scholarly journals Detection of Heavy Elements in the EUVE Spectrum of a Hot White Dwarf

1996 ◽  
Vol 152 ◽  
pp. 235-240
Author(s):  
S. Jordan ◽  
D. Koester ◽  
D. Finley
Keyword(s):  
White Dwarf ◽  
Theoretical Calculations ◽  
Strong Absorption ◽  
Heavy Elements ◽  
Level Of Confidence ◽  
Upper Limits ◽  
Absorption Features

Observations with the ROSAT satellite have already indicated that metal absorbers must be present in the atmosphere of the hot DA white dwarf PG 1234+482. This is now confirmed by strong absorption features found in the short and medium wavelength EUVE spectrum of the star. With fully blanked model atmospheres, taking into account several million lines of heavy elements, we could attribute the strongest features to absorption by FeVI and FeVII. Since the spectrum has not been dithered during the observation other elements could not be identified with the same level of confidence, but upper limits could be determined. These are in general lower than predicted by models, which attempt to explain the presence of the metals by theoretical calculations of radiative forces in hot DA white dwarf atmospheres.

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