scholarly journals ASCA observations of clusters of galaxies

1996 ◽  
Vol 175 ◽  
pp. 363-366
Author(s):  
Koujun Yamashita
Keyword(s):  
High Resolution Spectroscopy ◽  
Atomic Processes ◽  
Spectral Fitting ◽  
Elemental Abundances ◽  
Hot Plasma ◽  
Emission Models ◽  
Formation And Evolution ◽  
Collisional Ionization ◽  
Intracluster Gas

X-ray emissions from clusters are most likely originated from a thin hot plasma in a collisional ionization equilibrium. The optical depth of continuum component is order of 10–3, whereas that of emission lines is around unity. Present emission models used for spectral fitting can not estimate this effect, so that the determination of elemental abundances seems to include large uncertainty. The high resolution spectroscopy with ASCA gives a clue to investigate the physical state of hot intracluster gas and a impact to reconsider the basic atomic processes. This is important issue to deeply understand the structure, formation and evolution of clusters, and the origin of intracluster gas.

scholarly journals How well can we determine ages and chemical abundances from spectral fitting of integrated light spectra?

2020 ◽  
Vol 499 (2) ◽  
pp. 2327-2339
Author(s):  
Geraldo Gonçalves ◽  
Paula Coelho ◽  
Ricardo Schiavon ◽  
Christopher Usher
Keyword(s):  
High Resolution ◽  
Wavelength Range ◽  
Globular Clusters ◽  
Stellar Population ◽  
High Resolution Spectroscopy ◽  
Chemical Abundances ◽  
Spectral Fitting ◽  
Light Spectra ◽  
The Ideal

ABSTRACT The pixel-to-pixel spectral fitting technique is often used in studies of stellar populations. It enables the user to infer several parameters from integrated light spectra such as ages and chemical abundances. In this paper, we examine the question of how the inferred parameters change with the choice of wavelength range used. We have employed two different libraries of integrated light spectra of globular clusters (GCs) from the literature and fitted them to stellar population models using the code Starlight. We performed tests using different regions of the spectra to infer reddening, ages, [Fe/H], and [α/Fe]. Comparing our results to age values obtained from isochrone fitting and chemical abundances from high-resolution spectroscopy, we find that: (1) the inferred parameters change with the wavelength range used; (2) the method in general retrieves good reddening estimates, specially when a wider wavelength range is fitted; (3) the ideal spectral regions for determination of age, [Fe/H], and [α/Fe] are 4170–5540, 5280–7020, and 4828–5364 Å, respectively; (4) the retrieved age values for old metal-poor objects can be several Gyr younger than those resulting from isochrone fitting. We conclude that, depending on the parameter of interest and the accuracy requirements, fitting the largest possible wavelength range may not necessarily be the best strategy.

scholarly journals Astrometric Tests of Galactic Evolution

1995 ◽  
Vol 166 ◽  
pp. 251-258
Author(s):  
Gerard Gilmore
Keyword(s):  
Phase Space ◽  
Three Dimensional ◽  
Galactic Evolution ◽  
Critical Test ◽  
Current Standard ◽  
High Quality ◽  
Stellar Velocity ◽  
Formation And Evolution ◽  
Standard Models

There are many fundamental aspects of Galactic structure and evolution which can be studied best or exclusively with high quality three dimensional kinematics. Amongst these we note as examples determination of the orientation of the stellar velocity ellipsoid, and the detection of structure in velocity-position phase space. The first of these is the primary limitation at present to reliable and accurate measurement of the Galactic gravitational potential. The second is a critical test of current standard models of Galactic formation and evolution.

Instrumentation for wet steam

2004 ◽  
Vol 218 (8) ◽  
pp. 811-842 ◽  
Author(s):  
A Kleitz ◽  
J M Dorey
Keyword(s):  
Liquid Phase ◽  
Liquid Film ◽  
Direct Determination ◽  
Dispersed Phase ◽  
Wet Steam ◽  
Turbine Performance ◽  
Chemical Measurements ◽  
Formation And Evolution

This paper is devoted to the measuring methods and instrumentation used in the wet-steam area for both aerodynamics measurements (pressure, temperature and velocity) taking into account the interaction between the vapour and the liquid phase, and the characterization of the liquid phase itself (dispersed phase and liquid film). The development of suitable instrumentation is an important part in understanding the formation and evolution of the liquid phase but is now more and more oriented towards practical industrial concerns, such as the direct determination of turbine performance by measuring exhaust wetness or chemical measurements relating to erosion in the transition zone inside the turbine. Emphasis has been given to techniques suitable for use in actual turbines.

scholarly journals Clusters of Galaxies

1980 ◽  
Vol 5 ◽  
pp. 699-714 ◽  
Author(s):  
Neta A. Bahcall
Keyword(s):  
Large Scale ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Clusters Of Galaxies ◽  
Groups Of Galaxies ◽  
Formation And Evolution ◽  
The Rich ◽  
The Many ◽  
The Universe

AbstractClusters and groups of galaxies contain the majority of galaxies in the universe. The rich clusters, while less numerous than the many poor groups, are the densest and largest systems known, and can be easily recognized and studied even at relatively large distances. Their study is important for understanding the formation and evolution of clusters and galaxies, and for a determination of the large-scale structure in the universe.

scholarly journals Measuring relative abundances in the solar corona with optimised linear combinations of spectral lines

2019 ◽  
Vol 632 ◽  
pp. A20
Author(s):  
Natalia Zambrana Prado ◽  
Éric Buchlin
Keyword(s):  
Good Accuracy ◽  
Emission Measure ◽  
Spectral Lines ◽  
Linear Combinations ◽  
Elemental Abundances ◽  
Heliospheric Physics ◽  
Small Set ◽  
First Ionization Potential ◽  
Coronal Structures

Context. Elemental abundances in some coronal structures differ significantly from photospheric abundances, with a dependence on the first ionization potential (FIP) of the element. Measuring these FIP-dependent abundance biases is important for coronal and heliospheric physics. Aims. We aim to build a method for optimal determination of FIP biases in the corona from spectroscopic observations in a way that is in practice independent from differential emission measure (DEM) inversions. Methods. We optimised linear combinations of spectroscopic lines of low-FIP and high-FIP elements so that the ratio of the corresponding radiances yields the relative FIP bias with good accuracy for any DEM in a small set of typical DEMs. Results. These optimised linear combinations of lines allow retrieval of a test FIP bias map with good accuracy for all DEMs in the map. The results also compare well with a FIP bias map obtained from observations using a DEM-dependent method. Conclusions. The method provides a convenient, fast, and accurate way of computing relative FIP bias maps. It can be used to optimise the use of existing observations and the design of new observations and instruments.

scholarly journals Atomic Data Needed for X-ray and EUV Astronomy

1992 ◽  
Vol 9 ◽  
pp. 573-574
Author(s):  
John C. Raymond
Keyword(s):  
Spectral Resolution ◽  
Atomic Data ◽  
Ionization State ◽  
Crystal Spectrometer ◽  
X Ray ◽  
Transmission Grating ◽  
Elemental Abundances ◽  
The Past ◽  
Accurate Temperature

AbstractThe astronomical X-ray and EUV satellites of the past generally had low enough spectral resolution that atomic data of modest quality was sufficient for most interpretation of the data. Typical proportional counter resolution Δ E/E ~ 1 permits a determination of the spectral shape sufficient for an estimate of the temperature of the emitting gas, but only the Fe K feature at 6.7 keV stands out as a distinct emission line. The higher spectral resolution Einstein Transmission Grating, Solid State Spectrometer, and Focal Plane Crystal Spectrometer instruments measured a score of emission lines or line blends, permitting determinations of the elemental abundances, temperature, and ionization state of the emitting gas. The higher spectral resolution and throughput of the BBXRT aboard the ASTRO mission and the instruments planned for EUVE, ASTRO-D, AXAF, and XMM will make possible a far more detailed analysis of the data. It should be possible to derive better abundances for more elements, accurate temperature distributions, electron densities, and accurate ionization states.

An Essay on the History and Hermeneutics of Naslhat al-Muluk by Ghazali, Abu HamidMuhammad Ibn Muhammad Al-Tusi: semic analysis

Servis plus ◽  
10.12737/6463 ◽  
2014 ◽  
Vol 8 (4) ◽  
pp. 21-29 ◽  
Author(s):  
Марклен Конурбаев ◽  
Marklen Konurbaev ◽  
Салават Конурбаев ◽  
Salavat Konurbaev
Keyword(s):  
Methodological Approach ◽  
Roland Barthes ◽  
Literary Critic ◽  
Plain Language ◽  
History Of ◽  
Unique Approach ◽  
Formation And Evolution ◽  
Theological Study ◽  
History Of Formation

The series of articles entitled «An Essay on the History and Hermeneutics ofphilosophy ofFalsafa» is dedicated to the studies of Abu Hamid Muhammad Ibn Muhammad Al- TusT´s work «NasihatAl-Muluk». The Persian philosopher of lth century Al-Ghazali went down in history as one of the brightest representatives of medieval Muslim apologetics. The study of his works allows turning to different aspects of life of the medieval Muslim East. One of´his mostfamousworks, «NasihatAl-Muluk», which is part of his fundamental theological study «The Elixir of Bliss», belongs to the genre of medieval Arabic-Muslim literature — so-called «Mirrors for princes» which are simplified retellings of fundamental philosophical views on state and politics of a certain thinker in plain language. These retellings help to comprehend in practice the essence of government by series of allegories and narratives. The conducted hermeneutical analysis of«Nasihat Al-Muluk» reveals the unique approach of a brilliant Persian philosopher to determination of complicated ethical questions that underlie the art of governing. The methodological approach of the French philosopher and literary critic Roland Barthes was taken as the analysis basis. The first and the second part of the essay contain the history of formation and evolution ofphilosophy ofFalsafa and the exposition of the fundamentals of the hermeneutical teaching of Roland Barthes which underlies the instrumental basis of the analysis.

scholarly journals Confronting expansion distances of planetary nebulae with Gaia DR2 measurements

2019 ◽  
Vol 625 ◽  
pp. A137 ◽  
Author(s):  
D. Schönberner ◽  
M. Steffen
Keyword(s):  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Precise Determination ◽  
Asymptotic Giant Branch ◽  
Correction Factors ◽  
Trigonometric Parallaxes ◽  
Formation And Evolution ◽  
Hydrodynamical Simulations ◽  
Good Agreement

Context. Individual distances to planetary nebulae are of the utmost relevance for our understanding of post-asymptotic giant-branch evolution because they allow a precise determination of stellar and nebular properties. Also, objects with individual distances serve as calibrators for the so-called statistical distances based on secondary nebular properties. Aims. With independently known distances, it is possible to check empirically our understanding of the formation and evolution of planetary nebulae as suggested by existing hydrodynamical simulations. Methods. We compared the expansion parallaxes that have recently been determined for a number of planetary nebulae with the trigonometric parallaxes provided by the Gaia Data Release 2. Results. Except for two out of 11 nebulae, we found good agreement between the expansion and the Gaia trigonometric parallaxes without any systematic trend with distance. Therefore, the Gaia measurements also prove that the correction factors necessary to convert proper motions of shocks into Doppler velocities cannot be ignored. Rather, the size of these correction factors and their evolution with time as predicted by 1D hydrodynamical models of planetary nebulae is basically validated. These correction factors are generally greater than unity and are different for the outer shell and the inner bright rim of a planetary nebula. The Gaia measurements also confirm earlier findings that spectroscopic methods often lead to an overestimation of the distance. They also show that even modelling of the entire system of star and nebula by means of sophisticated photoionisation modelling may not always provide reliable results. Conclusions. The Gaia measurements confirm the basic correctness of the present radiation-hydrodynamics models, which predict that both the shell and the rim of a planetary nebula are two independently expanding entities, created and driven by different physical processes, namely thermal pressure (shell) or wind interaction (rim), both of which vary differently with time.

scholarly journals A Review of High-Redshift Merger Observations

1999 ◽  
Vol 186 ◽  
pp. 11-22
Author(s):  
R.G. Abraham
Keyword(s):  
Direct Measurement ◽  
Hierarchical Models ◽  
High Redshift ◽  
Space Density ◽  
Evolution Of Galaxies ◽  
Morphological Studies ◽  
Redshift Surveys ◽  
Formation And Evolution ◽  
Merger Rate

Evolution in the merger rate as a function of redshift isin principlethe key observable testing hierarchical models for the formation and evolution of galaxies. However,in practice, direct measurement of this quantity has proven difficult. In this opening review I outline the current best estimates for the merger rate as a function of cosmic epoch, focusing mostly upon recent advances made possible by deep ground-based redshift surveys and morphological studies undertaken withHST.I argue that a marriage of these techniques, in an attempt to determine the space density of mergers amongst the abundant morphologically peculiar population at high redshifts, is probably the most promising currently-available avenue for determining the prevalence of mergers at high redshifts. However, resolved kinematical studies, which seem set to become available in the next few years, are probably the best hope for a definitive determination of the space density of mergers at high redshifts.

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