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 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.

Registration of the rotation axis in X-ray tomography

2015 ◽  
Vol 22 (2) ◽  
pp. 452-457 ◽  
Author(s):  
Yimeng Yang ◽  
Feifei Yang ◽  
Ferdinand F. Hingerl ◽  
Xianghui Xiao ◽  
Yijin Liu ◽  
...  
Keyword(s):  
Rotation Axis ◽  
Signal To Noise Ratio ◽  
Geological Samples ◽  
Signal To Noise ◽  
High Demand ◽  
X Ray ◽  
Data Registration ◽  
Reconstruction Quality ◽  
Tomographic Data

There is high demand for efficient, robust and automated routines for tomographic data reduction, particularly for synchrotron data. Registration of the rotation axis in data processing is a critical step affecting the quality of the reconstruction and is not easily implemented with automation. Existing methods for calculating the center of rotation have been reviewed and an improved algorithm to register the rotation axis in tomographic data is presented. The performance of the proposed method is evaluated using synchrotron-based microtomography data on geological samples with and without artificial reduction of the signal-to-noise ratio. The proposed method improves the reconstruction quality by correcting both the tilting error and the translational offset of the rotation axis. The limitation of this promising method is also discussed.

scholarly journals The Effect of Noise and Finite Sampling on the Line Profile Variations of m = 0 Modes

2000 ◽  
Vol 176 ◽  
pp. 383-383
Author(s):  
M. H. Montgomery
Keyword(s):  
Phase Shift ◽  
Signal To Noise Ratio ◽  
Mode Frequency ◽  
Line Profiles ◽  
Signal To Noise ◽  
A Value ◽  
Scuti Star ◽  
Finite Sampling ◽  
Sampling Times ◽  
Synthetic Line

Figure 1 is of the same form as Fig. 3 in Schrijvers et al. (1997): the upper part of each panel is the amplitude of the variation across the line at the mode frequency and the lower part is the phase shift of these two components across the line (in units of Φ). The parameters {Vavg, k, Ω/ω0, W} were chosen to have values representative of the δ Scuti star 4 CVn. Each panel in this array of plots has m=0, with a value of ∓ of 0, 1, or 2, and an inclination angle θi between 10° and 80°. In order to generate the synthetic line profiles, we use sampling times taken from the last week of the 1996 δ Scuti campaign on 4 CVn, and we assume that the signal-to-noise ratio of the spectrum is 250.

scholarly journals Low-latency time-of-flight non-line-of-sight imaging at 5 frames per second

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Ji Hyun Nam ◽  
Eric Brandt ◽  
Sebastian Bauer ◽  
Xiaochun Liu ◽  
Marco Renna ◽  
...  
Keyword(s):  
Signal To Noise Ratio ◽  
Time Of Flight ◽  
Motion Blur ◽  
Line Of Sight ◽  
Low Latency ◽  
Imaging Method ◽  
Signal To Noise ◽  
Array Detectors ◽  
Noise Ratio ◽  
Non Line Of Sight

AbstractNon-Line-Of-Sight (NLOS) imaging aims at recovering the 3D geometry of objects that are hidden from the direct line of sight. One major challenge with this technique is the weak available multibounce signal limiting scene size, capture speed, and reconstruction quality. To overcome this obstacle, we introduce a multipixel time-of-flight non-line-of-sight imaging method combining specifically designed Single Photon Avalanche Diode (SPAD) array detectors with a fast reconstruction algorithm that captures and reconstructs live low-latency videos of non-line-of-sight scenes with natural non-retroreflective objects. We develop a model of the signal-to-noise-ratio of non-line-of-sight imaging and use it to devise a method that reconstructs the scene such that signal-to-noise-ratio, motion blur, angular resolution, and depth resolution are all independent of scene depth suggesting that reconstruction of very large scenes may be possible.

scholarly journals A phantom study to contrast and compare polymer and gold fiducial markers in radiotherapy simulation imaging

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Daryl Lim Joon ◽  
Drew Smith ◽  
Mark Tacey ◽  
Michal Schneider ◽  
Benjamin Harris ◽  
...  
Keyword(s):  
Signal To Noise Ratio ◽  
Fiducial Markers ◽  
Line Profiles ◽  
Signal To Noise ◽  
Gray Scale ◽  
Tissue Equivalent ◽  
Tissue Equivalent Phantom ◽  
Noise Ratio ◽  
Prostate Cancer Radiotherapy ◽  
Ct And Mri

AbstractTo assess visibility and artifact characteristics of polymer fiducials compared to standard gold fiducials for radiotherapy CT and MRI simulation. Three gold and three polymer fiducials were inserted into a CT and MRI tissue-equivalent phantom that approximated the prostate cancer radiotherapy configuration. The phantom and fiducials were imaged on CT and MRI. Images were assessed in terms of fiducial visibility and artifact. ImageJ was employed to quantify the pixel gray-scale of each fiducial and artifact. Fiducial gray-scale histograms and profiles were generated for analysis. Objective measurements of the contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR), and artifact index (AI) were calculated. The CT images showed that the gold fiducials are visually brighter, with greater contrast than the polymer. The higher peak values illustrate this in the line profiles. However, they produce bright radiating and dark shadowing artifacts. This is depicted by the greater width of line profiles and the disruption of phantom area profiles. Quantitatively this results in greater percentile ranges of the histograms. Furthermore, for CT, gold had a higher CNR than polymer, relative to the phantom. However, the gold CNR and SNR were degraded by the greater artifact and thus AI. Both fiducials were visible on MRI and had similar histograms and profiles that were also reflected in comparable CNR, SNR and AI. Polymer fiducials were well visualized in a phantom on CT and MR and produce less artifact than the gold fiducials. Polymer markers could enhance the quality and accuracy of radiotherapy co-registration and planning but require clinical confirmation.

High-signal-to-noise-ratio laser technique for accurate measurements of spectral line parameters

2012 ◽  
Vol 85 (2) ◽  
Author(s):  
A. Cygan ◽  
D. Lisak ◽  
S. Wójtewicz ◽  
J. Domysławska ◽  
J. T. Hodges ◽  
...  
Keyword(s):  
Spectral Line ◽  
Signal To Noise Ratio ◽  
High Signal ◽  
Laser Technique ◽  
Signal To Noise ◽  
Noise Ratio

scholarly journals NGC 3992 – A Galaxy without a Massive Halo

1983 ◽  
Vol 100 ◽  
pp. 93-94
Author(s):  
S. T. Gottesman ◽  
J. H. Hunter ◽  
J. R. Ball
Keyword(s):  
Velocity Distribution ◽  
Observational Data ◽  
Signal To Noise Ratio ◽  
Rotational Velocity ◽  
Signal To Noise ◽  
Gas Density ◽  
The Galaxy ◽  
Circular Flows ◽  
Noise Ratio

As a continuation of our earlier work (Gottesman and Hunter, 1982), we have reobserved the HI emission from the galaxy NGC 3992. We have combined all the data and produced new maps, at a significantly improved signal-to-noise ratio, of the gas density and velocity distribution with resolutions of ~ 22″ and 25 km s−1. The resultant, angle averaged, HI rotational velocity is shown in Figure 1 for the symmetric and nearly circular flows for r ≤ 3.35′ from the center (r ≤ 14.0 kpc, assuming de Vaucouleurs' (1979) distance of 14.2 mpc for NGC 3992). Shown, also, in Figure 1 is a fit to the observations provided by a Toomre disk of index n = o. No attempt was made to fit the observational data within 1′, in view of the low signal to noise.

scholarly journals [C II] 158 μm self-absorption and optical depth effects

2020 ◽  
Vol 636 ◽  
pp. A16 ◽  
Author(s):  
C. Guevara ◽  
J. Stutzki ◽  
V. Ossenkopf-Okada ◽  
R. Simon ◽  
J. P. Pérez-Beaupuits ◽  
...  
Keyword(s):  
Optical Depth ◽  
Column Density ◽  
Signal To Noise Ratio ◽  
Far Infrared ◽  
Emission Lines ◽  
High Spectral Resolution ◽  
Line Of Sight ◽  
High Signal ◽  
Line Profiles ◽  
Star Forming

Context. The [C II] 158 μm far-infrared fine-structure line is one of the most important cooling lines of the star-forming interstellar medium (ISM). It is used as a tracer of star formation efficiency in external galaxies and to study feedback effects in parental clouds. High spectral resolution observations have shown complex structures in the line profiles of the [C II] emission. Aims. Our aim is to determine whether the complex profiles observed in [12C II] are due to individual velocity components along the line-of-sight or to self-absorption based on a comparison of the [12C II] and isotopic [13C II] line profiles. Methods. Deep integrations with the SOFIA/upGREAT 7-pixel array receiver in the sources of M43, Horsehead PDR, Monoceros R2, and M17 SW allow for the detection of optically thin [13C II] emission lines, along with the [12C II] emission lines, with a high signal-to-noise ratio. We first derived the [12C II] optical depth and the [C II] column density from a single component model. However, the complex line profiles observed require a double layer model with an emitting background and an absorbing foreground. A multi-component velocity fit allows us to derive the physical conditions of the [C II] gas: column density and excitation temperature. Results. We find moderate to high [12C II] optical depths in all four sources and self-absorption of [12C II] in Mon R2 and M17 SW. The high column density of the warm background emission corresponds to an equivalent Av of up to 41 mag. The foreground absorption requires substantial column densities of cold and dense [C II] gas, with an equivalent Av ranging up to about 13 mag. Conclusions. The column density of the warm background material requires multiple photon-dominated region surfaces stacked along the line of sight and in velocity. The substantial column density of dense and cold foreground [C II] gas detected in absorption cannot be explained with any known scenario and we can only speculate on its origins.

scholarly journals Effective Temperatures and Gravities for O-Type Stars Determined from High Precision Line Profiles and Wind-Blanketed Model Atmospheres

1988 ◽  
Vol 132 ◽  
pp. 127-130 ◽  
Author(s):  
B. Bohannan ◽  
S. A. Voels ◽  
D. C. Abbott ◽  
D. G. Hummer
Keyword(s):  
Spectral Type ◽  
Massive Stars ◽  
Signal To Noise Ratio ◽  
High Signal ◽  
Line Profiles ◽  
Astronomical Instrumentation ◽  
Signal To Noise ◽  
Effective Temperatures ◽  
Stellar Properties

Analysis of line profiles obtained with astronomical instrumentation capable of high signal-to-noise ratio spectroscopy have contributed significant new precision to the determination of the basic stellar parameters of hot, luminous, mass-loosing stars. Accurate measurement of such stellar properties as effective temperature and helium abundance for stars of spectral type O and early B is important not only to the physics of these stars but also to the environment in which they are located. The overall goals of the work we summarize here are to refine the spectral-type vs. temperature calibration for the most massive stars and to determine helium abundances for stars that are loosing mass at a rate sufficiently high to affect their evolution. Details of our procedures are described in the analysis of ξ Puppis by Bohannan et al. (1986).

scholarly journals linestacker: a spectral line stacking tool for interferometric data

2020 ◽  
Vol 499 (3) ◽  
pp. 3992-4010
Author(s):  
Jean-Baptiste Jolly ◽  
Kirsten K Knudsen ◽  
Flora Stanley
Keyword(s):  
Signal To Noise Ratio ◽  
Simulated Data ◽  
Spectral Lines ◽  
Emission Lines ◽  
Data Sets ◽  
Large Array ◽  
Line Profiles ◽  
Signal To Noise ◽  
Very Large Array ◽  
Simulated Data Sets

ABSTRACT linestacker is a new open access and open source tool for stacking of spectral lines in interferometric data. linestacker is an ensemble of casa tasks, and can stack both 3D cubes or already extracted spectra. The algorithm is tested on increasingly complex simulated data sets, mimicking Atacama Large Millimeter/submillimeter Array, and Karl G. Jansky Very Large Array observations of [C ii] and CO(3–2) emission lines, from z ∼ 7 and z ∼ 4 galaxies, respectively. We find that the algorithm is very robust, successfully retrieving the input parameters of the stacked lines in all cases with an accuracy ≳90 per cent. However, we distinguish some specific situations showcasing the intrinsic limitations of the method. Mainly that high uncertainties on the redshifts (Δz > 0.01) can lead to poor signal-to-noise ratio improvement, due to lines being stacked on shifted central frequencies. Additionally, we give an extensive description of the embedded statistical tools included in linestacker: mainly bootstrapping, rebinning, and subsampling. Velocity rebinning is applied on the data before stacking and proves necessary when studying line profiles, in order to avoid artificial spectral features in the stack. Subsampling is useful to sort the stacked sources, allowing to find a subsample maximizing the searched parameters, while bootstrapping allows to detect inhomogeneities in the stacked sample. linestacker is a useful tool for extracting the most from spectral observations of various types.

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