Intrinsic Variability of Wolf-Rayet Stars from an Observational Point of View

1991 ◽  
pp. 109-124 ◽  
Author(s):  
Anthony F. J. Moffat ◽  
Carmelle Robert
Keyword(s):  
Point Of View ◽  
Intrinsic Variability ◽  
Observational Point

scholarly journals Intrinsic Variability of Wolf-Rayet Stars from an Observational Point of View

1991 ◽  
Vol 143 ◽  
pp. 109-124
Author(s):  
Anthony F. J. Moffat ◽  
Carmelle Robert
Keyword(s):  
Point Of View ◽  
Random Component ◽  
Common Phenomenon ◽  
Intrinsic Variability ◽  
Observational Point

Evidence is mounting that the dominant random component of variability in single WR stars can be explained by one common phenomenon: stochastic formation, propagation and decay of density enhancements in the winds.

scholarly journals Non-Radial Oscillations in δ Scuti Stars and Rapidly Oscillating AP Stars

1986 ◽  
Vol 7 ◽  
pp. 237-246
Author(s):  
D. W. Kurtz
Keyword(s):  
Present State ◽  
Point Of View ◽  
Observational Point ◽  
Stellar Seismology ◽  
Ap Stars ◽  
Scuti Stars ◽  
Complete Frequency ◽  
Δ Scuti Stars

AbstractThe present state of our knowledge of non-radial oscillations in δ Scuti stars and Rapidly Oscillating Ap stars is discussed primarily from an observational point of view. For the δ Scuti stars the need for complete frequency solutions for multi-periodic non-radial oscillating stars is emphasized in order for stellar seismology of these stars to be possible. An introduction to the Rapidly Oscillating Ap stars is given along with reference to a more complete recent review of those stars.

Introduction

2003 ◽  
Author(s):  
Yoram Rubin
Keyword(s):  
Epistemic Uncertainty ◽  
Wide Spectrum ◽  
Real Life ◽  
Mass Conservation ◽  
Point Of View ◽  
The Other ◽  
Intrinsic Variability ◽  
Stochastic Hydrogeology ◽  
Fundamental Point ◽  
Continuum Of States

Stochastic hydrogeology is the study of hydrogeology using physical and probabilistic concepts. It is an applied science because it is oriented toward applications. Its goal is to develop tools for analyzing measurements and observations taken over a sample region in space, and extract information which can then be used for evaluating and modeling the properties of physical processes taking place in this domain, and make risk-qualified predictions of their outcome. By invoking probabilistic concepts to deal with problems of physics, stochastic hydrogeology joins a well-established tradition followed in mining (Matheron, 1965; David, 1977; Journel and Huijbregts, 1978), turbulence (Kolmogorov, 1941; Batchelor, 1949), acoustics (Tatarski, 1961), atmospheric science (Lumley and Panofsky, 1964), composite materials and electrical engineering (Beran, 1968; Batchelor, 1974), and of course statistical mechanics. Stochastic hydrogeology broadens the scope of the deterministic approach to hydrogeology by considering the last as an end member to a wide spectrum of states of knowledge, stretching from deterministic knowledge at one end all the way to maximum uncertainty at the other, with a continuum of states, representing varying degrees of uncertainty in the hydrogeological processes, in between. It provides a formalism for addressing this continuum of states systematically. The departure from the confines of determinism is an important and intuitively appealing paradigm shift, representing the maturing of hydrogeology from an exploratory into an applied discipline. Deterministic knowledge of a site’s hydrogeology is a state we rarely, if ever, find ourselves in, although from a fundamental point of view there is no inherent element of chance in the hydrogeological processes. For example, we know that mass conservation is a deterministic concept, and we are also confident that Darcy’s law works under conditions which are fairly well understood. However, the application of these principles involves a fair amount of conjecture and speculation, and hence when dealing with real-life applications, determinism exists only in the fact that uncertainty and ambiguity are unavoidable, and might as well be studied and understood. The other end of the spectrum is where uncertainty is the largest. Generally speaking, two types of uncertainty exist: intrinsic variability and epistemic uncertainty.

scholarly journals Non-LTE Effects and Abundance Analyses of Halo Stars

1988 ◽  
Vol 132 ◽  
pp. 485-492
Author(s):  
Pierre Magain
Keyword(s):  
High Resolution ◽  
Model Atmosphere ◽  
Point Of View ◽  
Detailed Model ◽  
Observational Point ◽  
Halo Stars ◽  
Excitation Potential ◽  
Iron Abundance ◽  
The Impact ◽  
Echelle Spectrometer

The possible existence of departures from LTE affecting the abundance analyses of halo dwarfs and subgiants is analysed from the observational point of view, and illustrated by the case of the intermediate halo subgiant HD 76932. High resolution and high S/N Reticon and CCD spectra have been obtained with the ESO Coude Echelle Spectrometer. A detailed model atmosphere analysis has been carried out, which reveals a number of inconsistencies. In particular, the iron abundance derived from the neutral lines shows a very clear excitation potential dependence. Similar effects appear for oxygen and calcium and, possibly, for magnesium, chromium and ionized iron. Some overionization also seems to be present in a number of elements. The impact of these effects on the derived abundances may be rather large (some 0.2 to 0.6 dex). In particular, doubts might be raised about the reality of the oxygen overabundance and the odd-even effect in Na, Mg and Al.

Viscous effects in the dark sector of the Universe

2020 ◽  
Vol 35 (02n03) ◽  
pp. 2040041
Author(s):  
J. C. Fabris ◽  
T. R. P. Caramês ◽  
A. Wojnar ◽  
H. E. S. Velten
Keyword(s):  
Short Review ◽  
Point Of View ◽  
Accelerated Expansion ◽  
Viscous Effects ◽  
Dark Sector ◽  
Expansion Phase ◽  
Observational Point ◽  
Small Scales ◽  
Viscous Models ◽  
The Universe

Viscous properties are attributed to the dark sector of the Universe. They contribute to the accelerated expansion phase of the Universe and can alleviate existing tensions in the [Formula: see text]CDM model at small scales. We provide a short review of recent efforts on this topic. Different viscous models for the dark sector are analysed both from theoretical and observational point of view.

scholarly journals The Dynamical Evolution of Trapezium Systems

1974 ◽  
Vol 62 ◽  
pp. 239-246
Author(s):  
C. Allen ◽  
A. Poveda
Keyword(s):  
Equations Of Motion ◽  
Dynamical Evolution ◽  
Numerical Results ◽  
Point Of View ◽  
Observational Point

To study the dynamical evolution of trapezia, the equations of motion of the member stars in 30 different trapezia were integrated numerically. It was found that two-thirds of the trapezia still remain as such after 106 yr. Thus, the dynamical ages of trapezia containing O-stars are only slightly shorter than their nuclear ages. The properties of the binaries formed during the computations are studied. The numerical results are discussed from the observational point of view.

scholarly journals Magnetic fields in Proto Planetary Nebulae

2013 ◽  
Vol 9 (S302) ◽  
pp. 398-399
Author(s):  
L. Sabin ◽  
Q. Zhang ◽  
A. A. Zijlstra ◽  
N. A. Patel ◽  
R. Vázquez ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Planetary Nebulae ◽  
Point Of View ◽  
Late Type ◽  
Grain Alignment ◽  
Observational Point ◽  
The Magnetic Field

AbstractThe role of magnetic field in late type stars such as proto-planetary and planetary nebulae (PPNe/PNe), is poorly known from an observational point of view. We present submillimetric observations realized with the Submillimeter Array (SMA) which unveil the dust continuum polarization in the envelopes of two well known PPNe: CRL 618 and OH 231.8+4.2. Assuming the current grain alignment theory, we were then able to trace the geometry of the magnetic field.

scholarly journals CONSTRAINTS ON A-DECAYING COSMOLOGY FROM OBSERVATIONAL POINT OF VIEW

2005 ◽  
Vol 38 (2) ◽  
pp. 157-160 ◽  
Author(s):  
ZEN KOMIYA ◽  
KIYOSHI KAWABATA ◽  
KOICHI HIRANO ◽  
HIROSHI BUNYA ◽  
NAOTAKA YAMAMOTO
Keyword(s):  
Point Of View ◽  
Observational Point

scholarly journals The “discard problem” in Mediterranean fisheries, in the face of the European Union landing obligation: the case of bottom trawl fishery and implications for management

2018 ◽  
Vol 19 (3) ◽  
pp. 459 ◽  
Author(s):  
DIMITRIOS DAMALAS ◽  
ALESSANDRO LIGAS ◽  
KONSTANTINOS TSAGARAKIS ◽  
VASSILIKI VASSILOPOULOU ◽  
KONSTANTINOS I. STERGIOU ◽  
...  
Keyword(s):  
Scientific Evidence ◽  
Marine Species ◽  
Point Of View ◽  
Bottom Trawl ◽  
The European Union ◽  
Intrinsic Variability ◽  
Trawl Fishery ◽  
Management Plans ◽  
The Face ◽  
Business As Usual

Since the first introduction of the landing obligation (a.k.a. Discard ban) in 2015, the EU Mediterranean fisheries are facing some unforeseen challenges. The demersal bottom trawl fisheries, being the most significant contributors to the so-called 'discard problem', are confronted with the greatest challenges. Data from the Italian and the Greek fleet, spanning over two decades (1995–2015), were analysed with the intention of revealing the diversity and heterogeneity of the discard problem, especially for regulated species. Species composition of discards, as well as discarding rates, were shown to be irregular, fluctuating among areas, depth strata, seasons and years. Although fish dominated the discarded gross catch in weight, benthic invertebrates (other than commercial cephalopods and crustaceans) were the taxa discarded almost exclusively. The established minimum conservation reference size was largely ignored by fishers. From a management point of view, the present investigation suggests that the recently established Discard Management Plans lack scientific evidence (given the high intrinsic variability of the parameters and confusion regarding the rules) and provide exemptions from the landing obligation that will in practice allow the average Mediterranean bottom trawl vessel to continue business as usual. Moreover, detecting if these rules are actually respected is an almost impossible task for the Mediterranean control and enforcement authorities. Incentivizing the adoption of fishing technologies and practices that reduce pre-harvest mortality and post-harvest discards, while avoiding damage to sensitive marine species and habitats, seems the only way to move forward, rather than dealing with the problem after it has occurred.

scholarly journals The Co-Evolution of Supermassive Black Holes and Galaxies: Observational Constraints

2012 ◽  
Vol 8 (S295) ◽  
pp. 109-116
Author(s):  
Xian Zhong Zheng
Keyword(s):  
Black Holes ◽  
Galaxy Evolution ◽  
Recent Progress ◽  
Supermassive Black Holes ◽  
Point Of View ◽  
Observational Constraints ◽  
Host Galaxies ◽  
Observational Point ◽  
Evolution Understanding ◽  
Coherent Picture

AbstractThe connection between the growth of supermassive black holes (SMBHs) and the assembly of their host galaxies is termed ‘co-evolution’. Understanding co-evolution is one of the most fundamental issues in modern astrophysics. In this contribution, we review recent progress in addressing how the growth of SMBHs is linked to the properties of their host galaxies in the context of galaxy evolution, from the observational point of view. Although a coherent picture has not yet emerged, multiple pathways of co-evolution appear to be favored with a probable dependence on AGN luminosity and redshift.

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