scholarly journals Microturbulent velocities and abundances for A and F dwarfs in open clusters

2006 ◽  
Vol 2 (S239) ◽  
pp. 160-162
Author(s):  
M. Gebran ◽  
R. Monier
Keyword(s):  
Main Sequence ◽  
Chemical Elements ◽  
Open Clusters ◽  
Current Status ◽  
High Signal ◽  
Signal To Noise ◽  
Synthetic Spectra ◽  
Noise Spectroscopy ◽  
Microturbulent Velocity ◽  
Alpha Persei

AbstractThe current status of microturbulent velocity and abundance determinations for A and F dwarfs in open clusters is reviewed. A programme to observe several tens of A and F dwarfs in open clusters of various ages was initiated several years ago. We have performed high resolution high signal-to-noise spectroscopy of stars well distributed in mass along the Main Sequence. Microturbulent velocities and abundances of several chemical elements have been derived iteratively by fitting grids of synthetic spectra calculated in LTE to the observed spectra. Curve of growths were used in a few instances as well. The results obtained are reviewed for Coma Berenices, the Pleiades, Alpha Persei and the Ursa Major moving group.The microturbulent velocities exhibit a broad maximum in the range A5V to about F0V as indicated in Smalley (2004).

scholarly journals Model atmosphere analysis of two new early–type O4 dwarfs stars

2017 ◽  
Vol 2 (2) ◽  
pp. 559-564 ◽  
Author(s):  
D.A. Fouda ◽  
M. Hamdy ◽  
M. Nouh ◽  
M. Beheary ◽  
Abdelaziz Bakrey ◽  
...  
Keyword(s):  
Signal To Noise Ratio ◽  
Rotational Velocity ◽  
Model Atmosphere ◽  
Surface Gravity ◽  
High Signal ◽  
Early Type ◽  
Atmospheric Models ◽  
Signal To Noise ◽  
Dwarf Stars ◽  
Synthetic Spectra

AbstractWe present a synthetic spectra study of two new galactic early-type O4 dwarf stars(ALS 19618 and BD+50886) with high signal-to-noise ratio, typically S/N ∼ 300, medium-rosalution R ∼ 2500 optical spectra of O4 dwarfs stars from Galactic O-Stars Spectroscopic Survey (GOSSS), The main stellar parameters (Teff, surface gravity, rotational velocity) have been established using non-LTE, line-blanketed, atmospheric models calculated by TLUSTY204 and SYNSPEC49.

scholarly journals High Signal-To-Noise Ratio - the Spectroscopic Key to Algol Systems

1989 ◽  
Vol 107 ◽  
pp. 245-255
Author(s):  
Jocelyn Tomkin
Keyword(s):  
Main Sequence ◽  
Near Infrared ◽  
Signal To Noise Ratio ◽  
Large Fraction ◽  
High Signal ◽  
Signal To Noise ◽  
Algol System ◽  
Low Mass ◽  
Noise Ratio ◽  
Cno Abundances

AbstractThe usefulness of high signal-to-noise-ratio spectra for both radial-velocity and abundance studies of Algol systems is emphasised. It is shown that division by a hot star is a worthwhile step in pursuit of this objective. A preliminary analysis of high signal-to-noise-ratio, red and near-infrared, Reticon observations of R CMa shows that its primary has solar CNO abundances within the 0.3 dex observational error. The low-mass (0.17 m⊙) secondary of this Algol system must have lost a large fraction of its original mass. Some of this material would have been extensively processed during the secondary’s main-sequence lifetime and would therefore have had a highly non-solar CNO-abundance distribution. The lack of serious contamination of the primary’s abundances is consistent with most, but not all, plausible mass-transfer scenarios.

scholarly journals Beryllium abundances along the evolutionary sequence of the open cluster IC 4651

2009 ◽  
Vol 5 (S268) ◽  
pp. 357-358 ◽  
Author(s):  
Rodolfo Smiljanic ◽  
L. Pasquini ◽  
C. Charbonnel ◽  
N. Lagarde
Keyword(s):  
Main Sequence ◽  
Open Cluster ◽  
High Signal ◽  
Evolutionary Sequence ◽  
Main Sequence Stars ◽  
Signal To Noise ◽  
Mixing Processes ◽  
Hydrodynamical Models ◽  
Spectrum Synthesis ◽  
Hertzsprung Gap

AbstractThe simultaneous investigation of Li and Be in stars is a powerful tool in the study of the evolutionary mixing processes. Here, we present beryllium abundances in stars along the whole evolutionary sequence of the open cluster IC 4651. This cluster has a metallicity of [Fe/H] = +0.11 and an age of 1.2 or 1.7 Gyr. Abundances have been determined from high-resolution, high signal-to-noise UVES spectra using spectrum synthesis and model atmospheres. Lithium abundances for the same stars were determined in a previous work. Confirming previous results, we find that the Li dip is also a Be dip. For post-main-sequence stars, the Be dilution starts earlier within the Hertzsprung gap than expected from classical predictions, as does the Li dilution. Theoretical hydrodynamical models are able to reproduce well all the observed features.

scholarly journals Internal Rotation, Mixing and Lithium Abundances

1998 ◽  
Vol 185 ◽  
pp. 25-36
Author(s):  
Brian Chaboyer
Keyword(s):  
Internal Rotation ◽  
Transport Process ◽  
Main Sequence ◽  
Convection Zone ◽  
Nuclear Reactions ◽  
Open Clusters ◽  
Current Status ◽  
The Sun ◽  
Rotation Rates ◽  
Destruction Zone

Lithium is an excellent tracer of mixing in stars as it is destroyed (by nuclear reactions) at a temperature around ~ 2.5 × 106 K. The lithium destruction zone is typically located in the radiative region of a star. If the radiative regions are stable, the observed surface value of lithium should remain constant with time. However, comparison of the meteoritic and photospheric Li abundances in the Sun indicate that the surface abundance of Li in the Sun has been depleted by more than two orders of magnitude. This is not predicted by solar models and is a long standing problem. Observations of Li in open clusters indicate that Li depletion is occurring on the main sequence. Furthermore, there is now compelling observational evidence that a spread of lithium abundances is present in nearly identical stars. This suggests that some transport process is occurring in stellar radiative regions. Helioseismic inversions support this conclusion, for they suggest that standard solar models need to be modified below the base of the convection zone. There are a number of possible theoretical explanations for this transport process. The relation between Li abundances, rotation rates and the presence of a tidally locked companion along with the observed internal rotation in the Sun indicate that the mixing is most likely induced by rotation. The current status of non-standard (particularly rotational) stellar models which attempt to account for the lithium observations are reviewed.

scholarly journals On High Signal to Noise Spectroscopy with CCDs

1988 ◽  
Vol 132 ◽  
pp. 49-53
Author(s):  
Bernard Fort
Keyword(s):  
High Signal ◽  
Signal To Noise ◽  
Noise Spectroscopy

This communication presents a very quick overview of major trends in CCD development and somes ideas on how to use a CCD for spectroscopy with H.S.N. ratio.

scholarly journals New Homogeneous v sin i Determinations for B Stars in Galactic Open Clusters

2004 ◽  
Vol 215 ◽  
pp. 69-70 ◽  
Author(s):  
P. North ◽  
F. Royer ◽  
C. Melo ◽  
J. R. de Medeiros ◽  
J. D. do Nascimento ◽  
...  
Keyword(s):  
Least Squares ◽  
Main Sequence ◽  
Open Clusters ◽  
B Stars ◽  
Synthetic Spectra ◽  
Least Squares Fit ◽  
Galactic Clusters

We present new observations of projected rotational velocities of main sequence B stars in the galactic clusters NGC 2439, NGC 3293, NGC 3766, NGC 4755, NGC 7160 and h & χ Persei. 257 stars have been observed with three instruments, 207 of which are presented here. Projected rotational velocities have been determined by least-squares fit to synthetic spectra. Our v sin i scale is compared with that of Slettebak et al. (1975).

scholarly journals 12C/13C ratios in giants of open clusters

2006 ◽  
Vol 2 (S239) ◽  
pp. 298-300
Author(s):  
Rodolfo Smiljanic ◽  
R. Gauderon ◽  
P. North ◽  
B. Barbuy ◽  
C. Charbonnel ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Isotopic Ratio ◽  
Open Clusters ◽  
High Signal ◽  
Signal To Noise ◽  
Hydrogen Burning ◽  
Carbon Isotopic Ratio ◽  
Carbon Isotopic ◽  
Spectrum Synthesis ◽  
Convective Layer

AbstractThe carbon isotopic ratio,12C/13C, is a tracer of the mixing events during the evolution along the giant branch, due to the conversion of12C into13C (and14N) via the CN cycle. A decrease of this ratio from 90, the solar value, to 20–25, is expected due to the first dredge-up. However, ratios down to 3–4, the CN cycle equilibrium value, have been observed in giants of the field, of globular and of open clusters. Observations seem to indicate a non-standard mixing in the RGB, probably beginning in the luminosity bump, when the outward moving hydrogen burning shell crosses the molecular weight barrier left by the convective layer in its maximum extent. We are currently analyzing a sample of 24 giants in 8 open clusters for which we determined12C/13C from high resolution, high signal to noise spectra using spectrum synthesis. In this work we discuss the general characteristics of our results in comparison to previous analyses of giants in open clusters available in the literature.

A compact guided-wave EMAT with pulsed electromagnet for ferromagnetic tube inspection

2020 ◽  
Vol 64 (1-4) ◽  
pp. 951-958
Author(s):  
Tianhao Liu ◽  
Yu Jin ◽  
Cuixiang Pei ◽  
Jie Han ◽  
Zhenmao Chen
Keyword(s):  
Power Plants ◽  
Signal To Noise Ratio ◽  
Small Diameter ◽  
Performance Testing ◽  
Guided Wave ◽  
High Signal ◽  
Receiver Coil ◽  
Signal To Noise ◽  
Corrosion Defects

Small-diameter tubes that are widely used in petroleum industries and power plants experience corrosion during long-term services. In this paper, a compact inserted guided-wave EMAT with a pulsed electromagnet is proposed for small-diameter tube inspection. The proposed transducer is noncontact, compact with high signal-to-noise ratio and unattractive to ferromagnetic tubes. The proposed EMAT is designed with coils-only configuration, which consists of a pulsed electromagnet and a meander pulser/receiver coil. Both the numerical simulation and experimental results validate its feasibility on generating and receiving L(0,2) mode guided wave. The parameters for driving the proposed EMAT are optimized by performance testing. Finally, feasibility on quantification evaluation for corrosion defects was verified by experiments.

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