scholarly journals The magnetic early B-type stars – IV. Breakout or leakage? H α emission as a diagnostic of plasma transport in centrifugal magnetospheres

2020 ◽  
Vol 499 (4) ◽  
pp. 5379-5395
Author(s):  
M E Shultz ◽  
S Owocki ◽  
Th Rivinius ◽  
G A Wade ◽  
C Neiner ◽  
...  
Keyword(s):  
Mass Loss Rate ◽  
Continuous Process ◽  
Intrinsic Variability ◽  
Scale Invariant ◽  
Corotation Radius ◽  
Leakage Mechanism ◽  
Wide Range ◽  
Magnetically Confined ◽  
Early Type Stars ◽  
Emission Strength

ABSTRACT Rapidly rotating early-type stars with strong magnetic fields frequently show H α emission originating in centrifugal magnetospheres (CMs), circumstellar structures in which centrifugal support due to magnetically enforced corotation of the magnetically confined plasma enables it to accumulate to high densities. It is not currently known whether the CM plasma escapes via centrifugal breakout (CB), or by an unidentified leakage mechanism. We have conducted the first comprehensive examination of the H α emission properties of all stars currently known to display CM-pattern emission. We find that the onset of emission is dependent primarily on the area of the CM, which can be predicted simply by the value BK of the magnetic field at the Kepler corotation radius RK. Emission strength is strongly sensitive to both CM area and BK. Emission onset and strength are not dependent on effective temperature, luminosity, or mass-loss rate. These results all favour a CB scenario; however, the lack of intrinsic variability in any CM diagnostics indicates that CB must be an essentially continuous process, i.e. it effectively acts as a leakage mechanism. We also show that the emission profile shapes are approximately scale-invariant, i.e. they are broadly similar across a wide range of emission strengths and stellar parameters. While the radius of maximum emission correlates closely as expected to RK, it is always larger, contradicting models that predict that emission should peak at RK.

scholarly journals The X-ray properties of magnetic massive stars

2014 ◽  
Vol 9 (S307) ◽  
pp. 437-442
Author(s):  
Yaël Nazé ◽  
Véronique Petit ◽  
Melanie Rinbrand ◽  
David Cohen ◽  
Stan Owocki ◽  
...  
Keyword(s):  
Massive Stars ◽  
Mass Loss Rate ◽  
High Energy ◽  
Strongly Correlated ◽  
X Rays ◽  
X Ray ◽  
Magnetically Confined ◽  
Higher Temperature ◽  
Early Type Stars ◽  
High Energy Emission

AbstractEarly-type stars are well-known to be sources of soft X-rays. However, this high-energy emission can be supplemented by bright and hard X-rays when magnetically confined winds are present. In an attempt to clarify the systematics of the observed X-ray properties of this phenomenon, a large series of Chandra and XMM observations was analyzed, over 100 exposures of 60% of the known magnetic massive stars listed recently by Petit et al. (2013). It is found that the X-ray luminosity is strongly correlated with mass-loss rate, in agreement with predictions of magnetically confined wind models, though the predictions of higher temperature are not always verified. We also investigated the behaviour of other X-ray properties (absorption, variability), yielding additional constraints on models. This work not only advances our knowledge of the X-ray emission of massive stars, but also suggests new observational and theoretical avenues to further explore magnetically confined winds.

scholarly journals Observed Periodic Phenomena

2000 ◽  
Vol 175 ◽  
pp. 178-191 ◽  
Author(s):  
D. Baade
Keyword(s):  
Circumstellar Disks ◽  
Be Stars ◽  
Early Type ◽  
Late Type ◽  
Intrinsic Variability ◽  
Wide Range ◽  
Early Type Stars ◽  
Nonradial Pulsation

AbstractThe wide range of periodic and cyclic variabilities commonly observed in Be stars and their circumstellar disks is reviewed. Many of them are related to the basic nonradial pulsation, the effects of which may range from the photosphere to the disk. Through pulsation-triggered outbursts, some stars may owe their Be characteristics largely to their intrinsic variability. However, because late-type Be stars do not normally show detectable short-periodic variability, this is probably not true of all Be stars. Comparisons are made with other variable early-type stars.

scholarly journals Measurement and Implications of the Cosmic Microwave Background Spectrum

1996 ◽  
Vol 168 ◽  
pp. 17-29
Author(s):  
John C. Mather
Keyword(s):  
Background Radiation ◽  
Far Infrared ◽  
Big Bang ◽  
Scale Invariant ◽  
Background Spectrum ◽  
Nasa Goddard Space ◽  
Wide Range ◽  
Infrared Background ◽  
Microwave Radiometers ◽  
The Big Bang

The Cosmic Background Explorer (COBE) was developed by NASA Goddard Space Flight Center to measure the diffuse infrared and microwave radiation from the early universe. It also measured emission from nearby sources such as the stars, dust, molecules, atoms, ions, and electrons in the Milky Way, and dust and comets in the Solar System. It was launched 18 November 1989 on a Delta rocket, carrying one microwave instrument and two cryogenically cooled infrared instruments. The Far Infrared Absolute Spectrophotometer (FIRAS) mapped the sky at wavelengths from 0.01 to 1 cm, and compared the CMBR to a precise blackbody. The spectrum of the CMBR differs from a blackbody by less than 0.03%. The Differential Microwave Radiometers (DMR) measured the fluctuations in the CMBR originating in the Big Bang, with a total amplitude of 11 parts per million on a 10° scale. These fluctuations are consistent with scale-invariant primordial fluctuations. The Diffuse Infrared Background Experiment (DIRBE) spanned the wavelength range from 1.2 to 240 μm and mapped the sky at a wide range of solar elongation angles to distinguish foreground sources from a possible extragalactic Cosmic Infrared Background Radiation (CIBR). In this paper we summarize the COBE mission and describe the results from the FIRAS instrument. The results from the DMR and DIRBE were described by Smoot and Hauser at this Symposium.

scholarly journals The theory of winds in early type stars

1981 ◽  
Vol 59 ◽  
pp. 125-130 ◽  
Author(s):  
A.G. Hearn
Keyword(s):  
Mass Loss ◽  
Spectral Type ◽  
Stellar Evolution ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Optical Measurements ◽  
Early Type ◽  
Large Uncertainty ◽  
Early Type Stars ◽  
Loss Rates

I assume that the purpose of this review of the theory of winds from early type stars is to summarize the way in which the mass loss rate of a star may be included in a calculation of stellar evolution. Let me summarize my conclusions. It is not possible. One can only use estimates of mass loss rates obtained from the observations. Even these give a large uncertainty. The observed mass loss rates for different stars of the same spectral type vary. Further the mass loss rates obtained by different methods for the same star differ. An extreme example of this is 9 Sgr. The mass loss rate derived from the radio observations is forty times greater than that derived from the U.V. and optical measurements (Abbott et al. 1980).

Devulcanization of Waste Tire Rubber by Powerful Ultrasound

1996 ◽  
Vol 69 (1) ◽  
pp. 92-103 ◽  
Author(s):  
A. Tukachinsky ◽  
D. Schworm ◽  
A. I. Isayev
Keyword(s):  
Crosslink Density ◽  
Continuous Process ◽  
Operating Parameter ◽  
Rubber Crumb ◽  
Screw Extruder ◽  
Tire Rubber ◽  
Rubber Tire ◽  
Treatment Conditions ◽  
Wide Range ◽  
Devulcanized Rubber

Abstract Ground rubber tire (GRT) is devulcanized in a continuous process where the rubber crumb is conveyed by a screw extruder to a thin gap between a stationary die and a vibrating horn. Ultrasound amplitude, gap thickness and the duration of the treatment are varied, and their effect on the rubber properties is studied. The degree of devulcanization is characterized by the crosslink density and gel fraction of the devulcanized rubber. These characteristics are found to correlate uniquely with each other over a wide range of the treatment conditions. The specific energy of ultrasound consumed per unit mass of the rubber is found to be the operating parameter correlating with the properties of the devulcanized rubber. The mechanical properties of the re-vulcanized samples reach a maximum with an increasing degree of devulcanization, and then drop as a result of excessive degradation. Even without optimization of cure recipes, tensile strength and ultimate elongation of re-vulcanized tire rubber as high as 10.5 MPa and 250%, respectively, are achieved.

High Power Gyrotrons

1994 ◽  
Vol 347 ◽  
Author(s):  
R. J. Temkin ◽  
K. E. Kreischer
Keyword(s):  
High Power ◽  
Plasma Heating ◽  
Industrial Applications ◽  
Continuous Operation ◽  
Materials Processing ◽  
Pulse Operation ◽  
Wide Range ◽  
Magnetically Confined ◽  
The Status ◽  
Long Pulse

ABSTRACTHigh power gyrotrons have been developed for application to plasma heating in the program of magnetically confined nuclear fusion research. Gyrotron power levels of up to 1 MW in long pulse operation (>ls) and up to 200 kW in true continuous operation (CW) have been demonstrated at frequencies in the 8 to 140 GHz range. The status of high power gyrotron development is reviewed. One current goal of the worldwide gyrotron effort is the development of 1 MW,CW gyrotrons at a frequency of about 170 GHz for heating the proposed international tokamak ITER to ignition. Gyrotrons are also now being used in a variety of other applications including materials processing. Improved gyrotrons with features such as wide range tuning could be developed for industrial applications.

scholarly journals TESS Data for Asteroseismology: Light-curve Systematics Correction

2021 ◽  
Vol 257 (2) ◽  
pp. 53
Author(s):  
Mikkel N. Lund ◽  
Rasmus Handberg ◽  
Derek L. Buzasi ◽  
Lindsey Carboneau ◽  
Oliver J. Hall ◽  
...  
Keyword(s):  
Light Curves ◽  
Intrinsic Variability ◽  
Space Telescopes ◽  
Noise Sources ◽  
Full Spectrum ◽  
Stellar Oscillations ◽  
Science Operations ◽  
Wide Range ◽  
Noise Statistics ◽  
Operations Center

Abstract Data from the Transiting Exoplanet Survey Satellite (TESS) have produced of the order of one million light curves at cadences of 120 s and especially 1800 s for every ∼27 day observing sector during its two-year nominal mission. These data constitute a treasure trove for the study of stellar variability and exoplanets. However, to fully utilize the data in such studies a proper removal of systematic-noise sources must be performed before any analysis. The TESS Data for Asteroseismology group is tasked with providing analysis-ready data for the TESS Asteroseismic Science Consortium, which covers the full spectrum of stellar variability types, including stellar oscillations and pulsations, spanning a wide range of variability timescales and amplitudes. We present here the two current implementations for co-trending of raw photometric light curves from TESS, which cover different regimes of variability to serve the entire seismic community. We find performance in terms of commonly used noise statistics meets expectations and is applicable to a wide range of intrinsic variability types. Further, we find that the correction of light curves from a full sector of data can be completed well within a few days, meaning that when running in steady state our routines are able to process one sector before data from the next arrives. Our pipeline is open-source and all processed data will be made available on the websites of the TESS Asteroseismic Science Operations Center and the Mikulski Archive for Space Telescopes.

scholarly journals PROBLEM MENDASAR YANG MUNCUL DARI PERKEMBANGAN ILMU DI BIDANG HUKUM

2018 ◽  
Vol 15 (2) ◽  
pp. 123-139
Author(s):  
Wawan Irawan
Keyword(s):  
History Of Science ◽  
Nature Of Science ◽  
General Problem ◽  
Continuous Process ◽  
Distinctive Character ◽  
Wide Range ◽  
New Knowledge ◽  
History Of ◽  
Science Problem ◽  
Historical Necessity

Recording the history of science can be traced back to thousands of years before Christ until now. Historical necessity gave birth to a wide range of concepts about the nature of science. Law as science has a distinctive character (suigeneris), that it is normative. Those characteristics caused some law scholars that do not understand the characteristics of jurisprudence have doubted law as a science. Doubt it caused more normative jurisprudence rather than empirical and his study object with respect to the guidance of behavior in a way that compliance is not entirely dependent on free will is concerned, but can be imposed by a public authority.Through science we generate new knowledge. Since the beginning of human civilization, Law has progressed in a continuous process. Progress toward understanding and managing the law-science problem seems to require disaggregating the questions. If we look carefully at what kind of "science" and what kind of "law," then perhaps we can get some analytic leverage. If we cut the general problem into little pieces, we can atleast ask more precisely what is problematic at which particular law-science interface.

scholarly journals Inflation without a trace of lambda

2020 ◽  
Vol 80 (9) ◽  
Author(s):  
John D. Barrow ◽  
Spiros Cotsakis
Keyword(s):  
General Relativity ◽  
Scalar Field ◽  
Cosmological Constant ◽  
Conformal Transformation ◽  
Vacuum Energy ◽  
Einstein Equations ◽  
Scale Invariant ◽  
Field Source ◽  
Scale Theory ◽  
Wide Range

AbstractWe generalise Einstein’s formulation of the traceless Einstein equations to f(R) gravity theories. In the case of the vacuum traceless Einstein equations, we show that a non-constant Weyl tensor leads via a conformal transformation to a dimensionally homogeneous (‘no-scale’) theory in the conformal frame with a scalar field source that has an exponential potential. We then formulate the traceless version of f(R) gravity, and we find that a conformal transformation leads to a no-scale theory conformally equivalent to general relativity and a scalar field $$\phi $$ ϕ with a potential given by the scale-invariant form: $$V(\phi )=\frac{D-2}{4D}Re^{-\phi }$$ V ( ϕ ) = D - 2 4 D R e - ϕ , where $$\phi =[2/(D-2)]\ln f^{\prime }(R)$$ ϕ = [ 2 / ( D - 2 ) ] ln f ′ ( R ) . In this theory, the cosmological constant is a mere integration constant, statistically distributed in a multiverse of independent causal domains, the vacuum energy is another unrelated arbitrary constant, and the same is true of the height of the inflationary plateau present in a huge variety of potentials. Unlike in the conformal equivalent of full general relativity, flat potentials are found to be possible in all spacetime dimensions for polynomial lagrangians of all orders. Hence, we are led to a novel interpretation of the cosmological constant vacuum energy problem and have accelerated inflationary expansion in the very early universe with a very small cosmological constant at late times for a wide range of no-scale theories. Fine-tunings required in traceless general relativity or standard non-traceless f(R) theories of gravity are avoided. We show that the predictions of the scale-invariant conformal potential are completely consistent with microwave background observational data concerning the primordial tilt and the tensor-to-scalar ratio.

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