scholarly journals Analysis of High Resolution Stellar Line Profiles

1980 ◽  
Vol 51 ◽  
pp. 75-84
Author(s):  
David F. Gray
Keyword(s):  
High Resolution ◽  
Spectral Line ◽  
Spectral Resolution ◽  
Signal To Noise Ratio ◽  
Physical Phenomenon ◽  
Velocity Fields ◽  
Line Profiles ◽  
Late Type ◽  
Signal To Noise ◽  
Line Shapes

High resolution implies that we obtain some information on spectral line shapes. In late-type stars, we need to measure velocities of a few km/sec to accomplish this. Increasing the spectral resolution and the signal to noise ratio allows us to progress step by step toward deeper physical understanding. The steps we take often lead to good debate and “stimulate” our lives. I am sometimes amused at the urgency we feel to press on to the next step. We rarely seem to pause and enjoy the completion of previous steps. Perhaps this is because we always see shortcomings in completed work. Quite typically one will “discover” the importance of some physical phenomenon (It makes little difference how many others already know about it.), and in his eyes everything done previously becomes wrong because this phenomenon was not included. We used to hear how Milne-Eddington or Schuster-Schwarzschild model atmospheres were inadequate -we had to use instead properly computed depth dependence. We used to hear how LTE models were no good - we had to use more detailed physics. Now we talk about line analyses being inadequate because it has not included velocity fields. The curious thing is that we believe that including our pet phenomenon gives the correct models. We ignore all those other phenomena as yet unseen! (Is this a mechanism for maintaining sanity?) I think it really amounts to a statement of what we are able to measure, compute, or understand.

scholarly journals Computed Spectral Line Variations for Oblique Nonradial Pulsators

1986 ◽  
Vol 90 ◽  
pp. 234-234
Author(s):  
Dietrich Baade ◽  
Werner W. Weiss
Keyword(s):  
Spectral Line ◽  
Observational Data ◽  
Rotation Axis ◽  
Signal To Noise Ratio ◽  
Line Of Sight ◽  
Pulsation Velocity ◽  
Line Profiles ◽  
Signal To Noise ◽  
Velocity Amplitude ◽  
Mode Order

AbstractSpectral line profiles are computed for nonradially pulsating CP2 stars. For a range which currently is thought to be typical for these stars, the influence of six parameters on the line profiles is considered: mode order ℓ and degree m, pulsation velocity amplitude, the angle between the rotation and pulsation axis, the angle between the rotation axis and the line-of-sight, and the phase angle of the rotation. In view of the expected low signal-to-noise ratio of observational data it is investigated to what extent easily measurable, simple quantities can still be useful in discriminating between different modes.

scholarly journals Space Observations of Chemically Peculiar and Related Normal Stars

1986 ◽  
Vol 90 ◽  
pp. 109-119
Author(s):  
David S. Leckrone
Keyword(s):  
High Resolution ◽  
Spectroscopic Study ◽  
Spectral Resolution ◽  
Hubble Space Telescope ◽  
Signal To Noise Ratio ◽  
Signal To Noise ◽  
Space Telescope ◽  
Ultraviolet Spectra ◽  
Chemically Peculiar ◽  
Quantitative Analyses

AbstractProgress in the spectroscopic study of CP stars and related sharp-lined normal stars from the IUE is briefly reviewed as a preamble to a discussion of the potential for research with the Hubble Space Telescope. The substantial gains in spectral resolution, signal-to-noise ratio and photometric accuracy that will be realized with the High Resolution Spectrograph on the HST will dramatically increase our ability to disentangle the complex ultraviolet spectra of these stars and to carry out accurate quantitative analyses.

Non-LTE model atmosphere analyses of faint PN central stars observed with Keck HIRES

1997 ◽  
Vol 180 ◽  
pp. 120-121
Author(s):  
James K. McCarthy ◽  
Roberto H. Méndez ◽  
R.-P. Kudritzki
Keyword(s):  
High Resolution ◽  
Signal To Noise Ratio ◽  
Model Atmosphere ◽  
Helium Abundance ◽  
Line Profiles ◽  
Signal To Noise ◽  
Echelle Spectrograph ◽  
First Results ◽  
Central Stars ◽  
Temperature Surface

We are engaged in using the HIRES echelle spectrograph (Vogt et al. 1994) on the 10 m Keck I Telescope to significantly increase the number of central stars of planetary nebulae (CSPN) studied spectroscopically at high resolution and signal-to-noise ratio. With Keck we are able to extend our previous work (Méndez et al. 1988, 1992; McCarthy 1988) to much fainter magnitudes. In short, comparisons of the observed HI Balmer, HeI, and He II line profiles to the Munich grid of plane-parallel non-LTE model atmosphere line profiles provide distance- and nebula-independent determinations of CSPN effective temperature, surface gravity, and helium abundance. For CSPN showing wind emission, the comparisons are made to new “unified” models (reviewed by Kudritzki et al., this meeting) which include radiation-driven winds. The first results of this on-going program are shown below.

scholarly journals On cross-correlations, averages and noise in electron microscopy

2019 ◽  
Vol 75 (1) ◽  
pp. 12-18 ◽  
Author(s):  
Michael Radermacher ◽  
Teresa Ruiz
Keyword(s):  
High Resolution ◽  
Cross Correlation ◽  
Signal To Noise Ratio ◽  
3D Structure ◽  
Signal To Noise ◽  
High Resolution Structure ◽  
Multiple Copies ◽  
High Level ◽  
2D Images ◽  
Resolution Structure

Biological samples are radiation-sensitive and require imaging under low-dose conditions to minimize damage. As a result, images contain a high level of noise and exhibit signal-to-noise ratios that are typically significantly smaller than 1. Averaging techniques, either implicit or explicit, are used to overcome the limitations imposed by the high level of noise. Averaging of 2D images showing the same molecule in the same orientation results in highly significant projections. A high-resolution structure can be obtained by combining the information from many single-particle images to determine a 3D structure. Similarly, averaging of multiple copies of macromolecular assembly subvolumes extracted from tomographic reconstructions can lead to a virtually noise-free high-resolution structure. Cross-correlation methods are often used in the alignment and classification steps of averaging processes for both 2D images and 3D volumes. However, the high noise level can bias alignment and certain classification results. While other approaches may be implicitly affected, sensitivity to noise is most apparent in multireference alignments, 3D reference-based projection alignments and projection-based volume alignments. Here, the influence of the image signal-to-noise ratio on the value of the cross-correlation coefficient is analyzed and a method for compensating for this effect is provided.

Fizeau interferometer system for fast high resolution studies of spectral line shapes

2011 ◽  
Vol 82 (2) ◽  
pp. 023105 ◽  
Author(s):  
O. Novák ◽  
I. S. Falconer ◽  
R. Sanginés ◽  
M. Lattemann ◽  
R. N. Tarrant ◽  
...  
Keyword(s):  
High Resolution ◽  
Spectral Line ◽  
Fizeau Interferometer ◽  
Line Shapes

Ca II Emission from Late-type Stars

1983 ◽  
Vol 5 (2) ◽  
pp. 152-157 ◽  
Author(s):  
L. E. Cram
Keyword(s):  
Line Profile ◽  
Strong Correlation ◽  
Velocity Fields ◽  
Line Profiles ◽  
Late Type ◽  
Wide Range ◽  
Cool Stars ◽  
Visual Magnitude ◽  
The Absolute ◽  
Emission Core

Two recent observational surveys of the Ca II resonance lines (Zarro and Rodgers 1983; Linsky et al. 1979) illustrate the great diversity of line profile shapes found in the spectra of cool stars. This diversity reflects a corresponding wide range in the underlying chromospheric properties of the stars. There are, however, three well-marked systematic trends in the shapes of Ca II line profiles which presumably reflect systematic trends in chromospheric properties. One of these, the Wilson-Bappu effect (Wilson and Bappu 1957), describes the strong correlation betweeen the width of the emission core (see Figure 1) and the absolute visual magnitude of the star. Despite much work, it is still not clear whether this is due primarily to systematic changes of velocity fields (e.g. Hoyle and Wilson 1958) or optical depths (e.g. Jefferies and Thomas 1959) in stellar chromospheres.

The impact theory of spectral line shapes: a paradigm shift

2013 ◽  
Vol 91 (11) ◽  
pp. 879-895 ◽  
Author(s):  
A.D. May ◽  
W.-K. Liu ◽  
F.R.W. McCourt ◽  
R. Ciuryło ◽  
J. Sanchez-Fortún Stoker ◽  
...  
Keyword(s):  
Spectral Line ◽  
Line Shape ◽  
Paradigm Shift ◽  
Wigner Distribution ◽  
Kinetic Equations ◽  
Line Profiles ◽  
Line Shapes ◽  
Experimental Line ◽  
Impact Theory ◽  
The Impact

An overview of the binary collision impact theory of spectral line shapes has been given to provide a unified statistical mechanical approach to line-shape theory, laser theory, nonlinear optics, and transport phenomena in dilute gases. The computation of spectral line profiles corresponding to those obtained from ultra-high-resolution spectral line-shape measurements requires numerical ab initio calculation of scattering amplitudes directly from the underlying dynamics of collisions between radiatively active molecules and their perturbers. The Wigner distribution function–density matrix is utilized to describe the kinetic theory of spectral line shapes and to discuss the various collisional processes that contribute to the kernel of kinetic equations. The influence of features of the potential energy surface on spectral parameters is also discussed, and the importance of comparing experimental line profiles directly with numerically computed line shapes obtained from reliable interaction potentials is emphasized. This contrasts sharply with the universal practice of comparing experimental line widths and shifts using some average or approximate theoretical scattering cross-sections and it contrasts sharply with fitting experimental profiles to some convenient analytical line-shape model; hence the phrase “a paradigm shift” in the title of this work.

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