scholarly journals A metal-line strength indicator for damped Lyman alpha (DLA) systems at low signal-to-noise

2018 ◽  
Vol 481 (3) ◽  
pp. 3921-3934 ◽  
Author(s):  
Andreu Arinyo-i-Prats ◽  
Lluís Mas-Ribas ◽  
Jordi Miralda-Escudé ◽  
Ignasi Pérez-Ràfols ◽  
Pasquier Noterdaeme
Keyword(s):  
Line Strength ◽  
Signal To Noise ◽  
Metal Line ◽  
Lyman Alpha

scholarly journals The cosmological bias factor of damped Lyman alpha systems: dependence on metal line strength

2018 ◽  
Vol 480 (4) ◽  
pp. 4702-4709 ◽  
Author(s):  
Ignasi Pérez-Ràfols ◽  
Jordi Miralda-Escudé ◽  
Andreu Arinyo-i-Prats ◽  
Andreu Font-Ribera ◽  
Lluís Mas-Ribas
Keyword(s):  
Line Strength ◽  
Metal Line ◽  
Lyman Alpha ◽  
Bias Factor ◽  
Damped Lyman Alpha Systems

scholarly journals A correlation between SN II metal line strength and host H ii region oxygen abundance

2015 ◽  
Vol 11 (A29B) ◽  
pp. 272-273
Author(s):  
Joseph P. Anderson ◽  
Claudia P. Gutiérrez ◽  
Luc Dessart
Keyword(s):  
Emission Line ◽  
Line Strength ◽  
Type Ii ◽  
Metal Line ◽  
Oxygen Abundance ◽  
Large Sample ◽  
H Ii Region

AbstractDessart et al., demonstrated that type II supernova (SN II) model spectra present increasing metal line strength with increasing progenitor metallicity. To confront these models with observations, we obtained a large sample of SN II host H ii region emission line spectroscopy. We show that inferred SN II host H ii region metallicities have a statistically significant correlation with the strength of SN II metal lines, specifically Fe ii 5018Å.

scholarly journals The Overall Abundances of Globular Clusters

1988 ◽  
Vol 126 ◽  
pp. 79-92
Author(s):  
R. A. Bell
Keyword(s):  
Globular Clusters ◽  
Line Strength ◽  
The Other ◽  
Metal Line ◽  
Metal Abundance

At a meeting on globular clusters held five years ago, Zinn (1981) made the following comments:“In summary, there are clearly large differences in metal line strength between 47 Tuc giants and the giants in the other clusters. These differences suggest that there are substantial differences in metal abundance, which conflicts with the measurements obtained from echelle spectrograms, and there appears to be no simple way of reconciling these results. Until this is done, the metallicity scale for globular clusters hangs in limbo.”

scholarly journals Getting the model right: an information criterion for spectroscopy

2020 ◽  
Vol 501 (2) ◽  
pp. 2268-2278
Author(s):  
John K Webb ◽  
Chung-Chi Lee ◽  
Robert F Carswell ◽  
Dinko Milaković
Keyword(s):  
Line Strength ◽  
Detection Threshold ◽  
Information Criterion ◽  
Optimal Number ◽  
Information Criteria ◽  
High Signal ◽  
Model Parameters ◽  
Signal To Noise ◽  
Data Set ◽  
Noise Data

ABSTRACT Robust model-fitting to spectroscopic transitions is a requirement across many fields of science. The corrected Akaike and Bayesian information criteria (AICc and BIC) are most frequently used to select the optimal number of fitting parameters. In general, AICc modelling is thought to overfit (too many model parameters) and BIC underfits. For spectroscopic modelling, both AICc and BIC lack in two important respects: (a) no penalty distinction is made according to line strength such that parameters of weak lines close to the detection threshold are treated with equal importance as strong lines and (b) no account is taken of the way in which a narrow spectral line impacts only on a very small section of the overall data. In this paper, we introduce a new information criterion that addresses these shortcomings, the Spectral Information Criterion (SpIC). Spectral simulations are used to compare performances. The main findings are (i) SpIC clearly outperforms AICc for high signal-to-noise data, (ii) SpIC and AICc work equally well for lower signal-to-noise data, although SpIC achieves this with fewer parameters, and (iii) BIC does not perform well (for this application) and should be avoided. The new method should be of broader applicability (beyond spectroscopy), wherever different model parameters influence separated small ranges within a larger data set and/or have widely varying sensitivities.

scholarly journals Line-Strength Profiles in Early-Type Galaxies

1995 ◽  
Vol 164 ◽  
pp. 453-453
Author(s):  
David Fisher ◽  
Garth Illingworth ◽  
Marijn Franx
Keyword(s):  
Stellar Population ◽  
Velocity Dispersion ◽  
Line Strength ◽  
Strong Correlations ◽  
Metal Line ◽  
Cluster Galaxies ◽  
Brightest Cluster Galaxies ◽  
The Mean ◽  
S0 Galaxies ◽  
Line Strengths

Line-strengths and their gradients in Mg, Fe, and Hβ have been determined for a sample of 9 brightest cluster (BCG), 7 elliptical, and 15 S0 galaxies in order to study their stellar populations and investigate their relationship to one another. We find that BCGs follow the same relationship between central Mgb line-strength and central velocity dispersion found for ellipticals while the S0 galaxies show significant scatter with respect to this relation. Brightest cluster galaxies are in agreement with the known trend towards more massive ellipticals having larger [Mg/Fe] ratios while the internal gradients within our BCG and E galaxies are consistent with a roughly constant [Mg/Fe] ratio. We find that a correlation exists between the central [Mg/Fe] ratio and average Hβ line-strength in the sense that BCG and E galaxies with larger [Mg/Fe] ratios have lower Hβ strengths. For our BCG and E galaxies, Hβ is the best predictor of [Mg/Fe] ratio. The Mgb metallicity gradients for BCGs and ellipticals are similar and consistent with a reduction in the mean metallicity of the stellar population by about a factor of 2 over a factor of ten in radius. No strong correlations are found between the metallicity gradient sizes and either kinematic or line-strength parameters of the E and BCG galaxies. The S0 disks display roughly constant Mg, Fe, and Hβ line-strengths with radius indicating that they have uniform age and metallicity throughout. S0 galaxy minor axes ‘bulge’ metal line-strength gradients are similar to elliptical gradients and fall to values lower than those found in the disks.

scholarly journals Power spectrum of the flux in the Lyman-alpha forest from high-resolution spectra of 87 QSOs

2019 ◽  
Vol 489 (2) ◽  
pp. 2536-2554 ◽  
Author(s):  
Aaron Day ◽  
David Tytler ◽  
Bharat Kambalur
Keyword(s):  
High Resolution ◽  
Power Spectrum ◽  
Systematic Errors ◽  
Metal Line ◽  
Spectral Leakage ◽  
Lyman Alpha ◽  
Spectrum Measurement ◽  
Lyman Alpha Forest ◽  
Hydrogen Lines ◽  
First Time

Abstract We measure and calibrate the power spectrum of the flux in the Ly α forest at 1.8 < z < 4.6 for wavenumbers 0.003 ≤ k ≤ 0.1 s km−1 from the spectra of 87 QSOs obtained with HIRES on the Keck-I telescope. This is the largest sample using high-resolution spectra, yielding the smallest statistical errors, and we have applied calibrations to reduce new systematic errors. We fit Voigt profiles to the damped Ly α absorbers and we remove them. We subtract metal lines statistically based on metal absorption on the red side of the Ly α emission peak. We find that when performing a statistical subtraction of metal lines, a systematic offset due to the blending of metal and hydrogen lines must be taken into account. This offset was not accounted for in previous analyses, and requires up to a $3 {{\ \rm per\ cent}}$ reduction in the BOSS Ly α forest flux power spectrum, increasing the allowed neutrino mass. For the first time in a Ly α forest power spectrum measurement from high-resolution spectra, we correct for spectral leakage by applying Welch’s window function. Our treatment of metal line removal as well as our elimination of errors due to spectral leakage leads to a more accurate measurement of the Ly α forest power spectrum at the smallest scales. We find evidence that previously published values of the power are systematically too high at scales log k ≥ −1.3 (k ≥ 0.05) s km−1, which implies that the intergalactic medium is hotter than previously deduced from the Ly α forest flux power spectrum.

Photo-electric Hβ and uvby photometry

1966 ◽  
Vol 24 ◽  
pp. 170-180
Author(s):  
D. L. Crawford
Keyword(s):  
Narrow Band ◽  
Line Strength ◽  
Interference Filter ◽  
B Stars ◽  
Relative Line ◽  
The Mean ◽  
F Stars ◽  
Two Parameters ◽  
Filter Photometry ◽  
The Continuum

Early in the 1950's Strömgren (1, 2, 3, 4, 5) introduced medium to narrow-band interference filter photometry at the McDonald Observatory. He used six interference filters to obtain two parameters of astrophysical interest. These parameters he calledlandc, for line and continuum hydrogen absorption. The first measured empirically the absorption line strength of Hβby means of a filter of half width 35Å centered on Hβand compared to the mean of two filters situated in the continuum near Hβ. The second index measured empirically the Balmer discontinuity by means of a filter situated below the Balmer discontinuity and two above it. He showed that these two indices could accurately predict the spectral type and luminosity of both B stars and A and F stars. He later derived (6) an indexmfrom the same filters. This index was a measure of the relative line blanketing near 4100Å compared to two filters above 4500Å. These three indices confirmed earlier work by many people, including Lindblad and Becker. References to this earlier work and to the systems discussed today can be found in Strömgren's article inBasic Astronomical Data(7).

Radiation Damage, Contrast and Statistics in High Resolution Biological Electron Microscopy

1970 ◽  
Vol 28 ◽  
pp. 260-261
Author(s):  
Robert M. Glaeser
Keyword(s):  
High Resolution ◽  
Particle Flux ◽  
Unit Area ◽  
Signal To Noise ◽  
Resolution Image ◽  
High Resolution Image ◽  
Pass Through ◽  
Counting Statistics ◽  
The Relationship ◽  
Picture Element

It is well known that a large flux of electrons must pass through a specimen in order to obtain a high resolution image while a smaller particle flux is satisfactory for a low resolution image. The minimum particle flux that is required depends upon the contrast in the image and the signal-to-noise (S/N) ratio at which the data are considered acceptable. For a given S/N associated with statistical fluxtuations, the relationship between contrast and “counting statistics” is s131_eqn1, where C = contrast; r2 is the area of a picture element corresponding to the resolution, r; N is the number of electrons incident per unit area of the specimen; f is the fraction of electrons that contribute to formation of the image, relative to the total number of electrons incident upon the object.

Determination of the Best Emulsion for the Microscopy of Crystals

1981 ◽  
Vol 39 ◽  
pp. 32-33
Author(s):  
David A. Grano ◽  
Kenneth H. Downing
Keyword(s):  
Spatial Frequency ◽  
Information Transfer ◽  
Signal To Noise Ratio ◽  
Experimental Situation ◽  
Photographic Emulsion ◽  
Modulation Transfer ◽  
Signal To Noise ◽  
Frequency Space ◽  
Noise Ratio

The retrieval of high-resolution information from images of biological crystals depends, in part, on the use of the correct photographic emulsion. We have been investigating the information transfer properties of twelve emulsions with a view toward 1) characterizing the emulsions by a few, measurable quantities, and 2) identifying the “best” emulsion of those we have studied for use in any given experimental situation. Because our interests lie in the examination of crystalline specimens, we've chosen to evaluate an emulsion's signal-to-noise ratio (SNR) as a function of spatial frequency and use this as our critereon for determining the best emulsion.The signal-to-noise ratio in frequency space depends on several factors. First, the signal depends on the speed of the emulsion and its modulation transfer function (MTF). By procedures outlined in, MTF's have been found for all the emulsions tested and can be fit by an analytic expression 1/(1+(S/S0)2). Figure 1 shows the experimental data and fitted curve for an emulsion with a better than average MTF. A single parameter, the spatial frequency at which the transfer falls to 50% (S0), characterizes this curve.

Experiments in Bright-Field Imaging with Hollow-Cone Illumination

1981 ◽  
Vol 39 ◽  
pp. 226-227
Author(s):  
W. Kunath ◽  
K. Weiss ◽  
E. Zeitler
Keyword(s):  
Signal To Noise Ratio ◽  
Carbon Support ◽  
Electronic System ◽  
Optic Axis ◽  
Hollow Cone ◽  
Signal To Noise ◽  
Bright Field ◽  
Noise Ratio ◽  
Single Field ◽  
Field Imaging

Bright-field images taken with axial illumination show spurious high contrast patterns which obscure details smaller than 15 ° Hollow-cone illumination (HCI), however, reduces this disturbing granulation by statistical superposition and thus improves the signal-to-noise ratio. In this presentation we report on experiments aimed at selecting the proper amount of tilt and defocus for improvement of the signal-to-noise ratio by means of direct observation of the electron images on a TV monitor.Hollow-cone illumination is implemented in our microscope (single field condenser objective, Cs = .5 mm) by an electronic system which rotates the tilted beam about the optic axis. At low rates of revolution (one turn per second or so) a circular motion of the usual granulation in the image of a carbon support film can be observed on the TV monitor. The size of the granular structures and the radius of their orbits depend on both the conical tilt and defocus.

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