scholarly journals Chemical fingerprints of He-sdO stars

2018 ◽  
Vol 27 (1) ◽  
pp. 27-34 ◽  
Author(s):  
Markus Schindewolf ◽  
Peter Németh ◽  
Ulrich Heber ◽  
Tiara Battich ◽  
Marcelo M. Miller Bertolami ◽  
...  
Keyword(s):  
Spectroscopic Analysis ◽  
Atmospheric Parameters ◽  
Intermediate Mass ◽  
Solar Abundance ◽  
Hydrogen Burning ◽  
Cd 31 ◽  
Chemical Fingerprints ◽  
Synthetic Spectra ◽  
Cno Cycle ◽  
Formation History

Abstract The chemical composition of helium-rich hot subluminous O stars plays an important role to understand and model their formation history. We present a spectroscopic analysis of four He-sdO stars,CD-31° 4800, [CW83] 0904- 02, LSS 1274 and LS IV +10° 9. The analysis is based on archival optical and UV high-resolution spectra. We used Tlusty200/Synspec48 to compute line blanketed non-LTE model atmospheres and their corresponding synthetic spectra and derive the atmospheric parameters as well as the abundances of the most prominent elements. All stars have helium-dominated atmospheres with hardly any hydrogen and temperatures between 42000 K and 47000 K while their surface gravity spans between log g = 5.4 and 5.7. CD-31° 4800 shows an enrichment of nitrogen and the characteristic pattern of hydrogen burning via the CNO-cycle, while the rest of the elements have about the solar abundance. This points to the slow merger of two helium white dwarfs as the most likely origin for this system. The other three stars are enriched in carbon, nitrogen and neon while their intermediate mass element’s abundance scatters around the solar value. They were possibly formed in the deep mixing late hot flasher scenario.

LITHIUM IN THE STELLAR OPEN CLUSTER M67

2007 ◽  
Vol 16 (02n03) ◽  
pp. 391-396 ◽  
Author(s):  
B. L. CANTO MARTINS ◽  
J. D. DO NASCIMENTO ◽  
J. R. DE MEDEIROS ◽  
A. LÈBRE ◽  
O. RICHARD ◽  
...  
Keyword(s):  
High Resolution ◽  
Spectroscopic Analysis ◽  
Open Cluster ◽  
Atmospheric Parameters ◽  
Large Sample ◽  
Giant Stars ◽  
Evolved Stars ◽  
Synthetic Spectra

In this work we present atmospheric parameters and Li abundances, obtained from a detailed spectroscopic analysis, for a large sample of stars with different evolutionary stages (turn-off, subgiant and giant stars) in the open cluster M67. The observations were carried out with high resolution (R ~ 47,000) and high S/N using the UVES+FLAMES at VLT/UT2. From available photometry and computed synthetic spectra for the region around the lithium line at 6707.75 Å, we derive atmospheric parameters (T eff , log g, [ Fe/H ], v sin i) and Li abundances for each star, in order to better understand the level of mixing and convective dilution of evolved stars in M67.

scholarly journals The Near Infrared FeH Lines as Indicators of Surface Gravity of M stars

1996 ◽  
Vol 171 ◽  
pp. 441-441
Author(s):  
Ricardo Piorno Schiavon ◽  
Beatriz Barbuy
Keyword(s):  
Near Infrared ◽  
Synthesis Method ◽  
Population Synthesis ◽  
Atmospheric Parameters ◽  
M Dwarfs ◽  
Synthetic Spectra ◽  
Iron Hydride ◽  
M Stars ◽  
M Dwarf ◽  
Ongoing Project

We compute synthetic spectra in the region around 1 μm, including the Wing-Ford band (WFB) of Iron Hydride (FeH) in the calculations. This band is known to be a good indicator of surface gravities of M stars. Employing Kurucz model atmospheres, we study the response of the intensity of the WFB to atmospheric parameters and check our results against observations of M dwarfs. This study is part of an ongoing project which aims to investigate the M dwarf-to-giant ratio in galaxies, through a population synthesis method, exploring a number of spectral indicators in the near infrared, such as the WFB, the NaI, CaII and CO near infrared features.

scholarly journals Dynamical and Chemical Evolution of IZw18

2004 ◽  
Vol 21 (2) ◽  
pp. 157-160
Author(s):  
Simone Recchi
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Dwarf Galaxy ◽  
Star Formation History ◽  
Intermediate Mass ◽  
Intermediate Mass Stars ◽  
Formation History ◽  
Type Ia ◽  
Ia Supernovae ◽  
Detailed Chemical

AbstractWe study the effect of different star formation regimes on the dynamical and chemical evolution of IZw18, the most metal-poor dwarf galaxy locally known. To do that we adopt a two-dimensional hydrocode coupled with detailed chemical yields originating from Type II and Type Ia supernovae and from intermediate-mass stars. Particular emphasis is devoted to the problem of mixing of metals. We conclude that, under particular conditions, cooling of metals occurs with a timescale of the order of 10 Myr, thus confirming the hypothesis of instantaneous mixing adopted in chemical evolution models. We try to draw conclusions about the star formation history and the age of the last burst in IZw18.

scholarly journals Spectroscopic Analysis of HR 1099

1991 ◽  
Vol 130 ◽  
pp. 449-451
Author(s):  
I.S. Savanov ◽  
I. Tuominen
Keyword(s):  
Spectroscopic Analysis ◽  
Theoretical Calculations ◽  
Wavelength Region ◽  
Surface Imaging ◽  
Line Profiles ◽  
Late Type ◽  
Synthetic Spectra ◽  
Solar Abundances

AbstractWe have calculated synthetic spectra for HR 1099 for the wavelength region λ6425-6445 Å, which includes the Cal λ6439 Å and FeI λ6430 Å lines, often used for the surface imaging of rapidly rotating late-type stars. The best agreement between the theoretical and observed spectra can be achieved with solar abundances in the both components of the system, except for Ca in the primary. Theoretical calculations give the possibility of estimating the influence of microturbulence, damping and blending on Ca I and Fe I line profiles.

Hydrogen burning of 17O in the CNO cycle

1975 ◽  
Vol 250 (2) ◽  
pp. 295-308 ◽  
Author(s):  
C. Rolfs ◽  
W.S. Rodney
Keyword(s):  
Hydrogen Burning ◽  
Cno Cycle

scholarly journals Model atmospheres and spectral analyses of Wolf-Rayet stars

1995 ◽  
Vol 163 ◽  
pp. 105-115
Author(s):  
W.-R. Hamann
Keyword(s):  
Chemical Compositions ◽  
Vertical Strip ◽  
Hydrogen Burning ◽  
Spectral Analyses ◽  
Fundamental Parameters ◽  
Processed Material ◽  
Cno Cycle ◽  
Interesting Correlation ◽  
Effective Temperatures ◽  
Expanding Atmospheres

Stratified non-LTE models for expanding atmospheres have become available in the recent years. They are based on the idealized assumptions of spherical symmetry, stationarity and radiative equilibrium. The satisfactory agreement between calculated and observed Wolf-Rayet spectra suggests that this “standard model” is basically adequate for describing real WR atmospheres and hence can be applied for their quantitative spectral analyses. By the application of these models, the fundamental parameters have been determined meanwhile for the majority of the known Galactic WR stars. Most WN stars populate a vertical strip in the Hertzspung-Russell diagram at effective temperatures of ≈35 kK, the luminosities ranging from 104.5 to 105.9L⊙. Only three WN stars of earliest subtype, other early-type WN stars if they have strong lines, and the WC stars are hotter. The chemical compositions of the WR atmospheres correspond to nuclear-processed material (WN: hydrogen burning in the CNO cycle; WC: helium burning). Hydrogen is depleted but still detectable in the cooler members of the WN subclass. Quantitatively, the hydrogen abundances show an interesting correlation with the luminosity which can be compared with the predictions from evolutionary calculations.

scholarly journals A spectroscopic study of RCB stars in the Galaxy and the LMC

1993 ◽  
Vol 139 ◽  
pp. 215-215
Author(s):  
Karen Pollard ◽  
P.L. Cottrell ◽  
W.A. Lawson
Keyword(s):  
Model Atmosphere ◽  
Large Magellanic Cloud ◽  
Atmospheric Parameters ◽  
Physical Processes ◽  
Convective Mixing ◽  
Cno Cycle ◽  
Wide Range ◽  
The Galaxy ◽  
Key Indicators ◽  
Nuclear Processes

AbstractHigh resolution échelle spectra have been obtained of two Large Magellanic Cloud (LMC) and one galactic R Coronae Borealis (RCB) star with the Anglo-Australian Telescope. An analysis of these data using He- and C-rich models and the model atmosphere code WIDTH6 of Kurucz indicates that the galactic RCB star SU Tau and the two LMC stars, W Men and HV12842, have similar atmospheric parameters to the warmer galactic RCB and hydrogen-deficient Carbon (HdC) stars e.g., R CrB and XX Cam. Specifically, the new stars have Teff ∼7000 K, log g = 0.5-1.0, microturbulent velocities between 6 and 8 km.s-1 and C/He ratios from 0.004 to 0.006.An abundance analysis has been performed on these stars for a wide range of species. Special emphasis has been placed on particular elements H, He, Li, C, N, O, & Fe (see figure 1), which are key indicators of the extent and relative importance of nuclear processes such as the CNO cycle and triple-alpha process, and also of the physical processes such as convective mixing and mass loss. Specific values for the abundances of [H/He], [Li/Fe] and [Fe/total] (expressed relative to the total abundance of all species) in SU Tau and HV12842 are -5.4 & -6.4, +2.5 & +2.4, -0.4 & -0.8.

scholarly journals A spectroscopic analysis of the Trapezium Cluster stars

2003 ◽  
Vol 212 ◽  
pp. 749-750
Author(s):  
Sergio Simón-Díaz ◽  
Artemio Herrero ◽  
César Esteban
Keyword(s):  
Spectral Analysis ◽  
Spectral Type ◽  
Spectroscopic Analysis ◽  
Massive Stars ◽  
The Other ◽  
Orion Nebula ◽  
Metal Line ◽  
Synthetic Spectra ◽  
H Ii Region

We consider the Orion Nebula (M 42) within a project aimed at studying the interaction between massive stars and their surrounding ISM. This is an H ii region ionized by θ1 Ori C, one of the four massive stars in the Trapezium Cluster. θ1 Ori C has the earliest spectral type (O7Vp) among them, emitting an ionizing flux several orders of magnitude larger than those of the other stars. We present a spectral analysis of the Trapezium Cluster stars to determine their stellar parameters. We use spectra between 4250 – 4750 Å and compare them with synthetic spectra obtained by means of an updated version of fastwind that includes an approximated treatment of metal-line blanketing.

scholarly journals Systematic differences in the spectroscopic analysis of red giants

2019 ◽  
Vol 622 ◽  
pp. A111 ◽  
Author(s):  
D. Slumstrup ◽  
F. Grundahl ◽  
V. Silva Aguirre ◽  
K. Brogaard
Keyword(s):  
Chemical Composition ◽  
Equivalent Width ◽  
Spectroscopic Analysis ◽  
Spectroscopic Method ◽  
Quality Data ◽  
High Signal ◽  
Red Giants ◽  
Atmospheric Parameters ◽  
Optical Telescope ◽  
Atomic Parameters

Aims. A spectroscopic analysis of stellar spectra can be carried out using multiple approaches such as different methods, line lists, atmospheric models, atomic parameters, and solar abundances. The resulting atmospheric parameters from these choices can vary beyond the quoted uncertainties in the literature. We characterize these differences by systematically comparing some of the commonly adopted ingredients such as line lists, equivalent width measurements, and atomic parameters. Methods. High-resolution and high signal-to-noise (S/N) spectroscopic data of one helium-core-burning red giant star in each of the three open clusters, NGC 6819, M67, and NGC 188 were obtained with the FIES spectrograph at the Nordic Optical Telescope. The M67 target was used to benchmark the analysis, as it is a well-studied cluster with asteroseismic data from the K2 mission. For the other two clusters we obtained higher quality data than had been analyzed before, which allows us to establish their chemical composition more securely. Using a line by line analysis, we tested several different combinations of line lists and programs to measure equivalent widths of stellar absorption lines to characterize systematic differences within the same spectroscopic method. Results. The obtained parameters for the benchmark star in M67 vary up to ~170 K in effective temperature, ~0.4 dex in log g and ~0.25 dex in [Fe/H] between the tested setups. Using the combination of an equivalent width measurement program and line list that best reproduce the inferred surface gravity from asteroseismology, we determined the atmospheric parameters for the three stars and securely established the chemical composition of NGC 6819 to be close to solar, [Fe/H] = −0.02 ± 0.01 dex. Conclusions. We highlighted the significantly different results obtained with different combinations of line lists, programs, and atomic parameters. The results emphasize the importance of benchmark stars studied with several methods to anchor spectroscopic analyses.

scholarly journals Carbon-rich (DQ) white dwarfs in the Sloan Digital Sky Survey

2019 ◽  
Vol 628 ◽  
pp. A102 ◽  
Author(s):  
D. Koester ◽  
S. O. Kepler
Keyword(s):  
White Dwarfs ◽  
Sloan Digital Sky Survey ◽  
Significant Fraction ◽  
Atmospheric Parameters ◽  
Spectral Evolution ◽  
Large Sample ◽  
Synthetic Spectra ◽  
Sky Survey ◽  
Data Release

Context. Among the spectroscopically identified white dwarfs, a fraction smaller than 2% have spectra dominated by carbon lines, mainly molecular C2, but also a smaller group dominated by C I and C II lines. These are together called DQ white dwarfs. Aims. We want to derive atmospheric parameters Teff, log g, and carbon abundances for a large sample of these stars and discuss implications for their spectral evolution. Methods. Sloan Digital Sky Survey spectra and ugriz photometry were used, together with Gaia Data Release 2 parallaxes and G band photometry. These were fitted to synthetic spectra and theoretical photometry derived from model atmospheres. Results. We found that the DQ hotter than Teff ~ 10 000 K have masses ~ 0.4 M⊙ larger than the classical DQ, which have masses typical for the majority of white dwarfs (~ 0.6 M⊙). We found some evidence that the peculiar DQ below 10 000 K also have significantly larger masses and may thus be the descendants of the hot and warm DQ above 10 000 K. A significant fraction of the hotter objects with Teff > 14 500 K have atmospheres dominated by carbon.

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