scholarly journals Dust Scattering of Emission Lines in HiiRegions. I. Plane‐parallel Models and Application to the Orion Nebula (M42)

1998 ◽  
Vol 503 (2) ◽  
pp. 760-779 ◽  
Author(s):  
W. J. Henney
Keyword(s):  
Emission Lines ◽  
Orion Nebula ◽  
Plane Parallel ◽  
Parallel Models

scholarly journals Spectroscopic studies of OB stars in the Magellanic Clouds with VLT-UVES

2003 ◽  
Vol 212 ◽  
pp. 176-177
Author(s):  
Christopher J. Evans ◽  
Paul A. Crowther ◽  
Alexander W. Fullerton ◽  
D. John Hillier
Keyword(s):  
Mass Loss ◽  
Model Atmosphere ◽  
Spectroscopic Studies ◽  
Magellanic Clouds ◽  
Ob Stars ◽  
Plane Parallel ◽  
Parallel Models ◽  
Cno Abundances ◽  
Loss Rates

We present results from optical and ultraviolet analysis of nine LMC/SMC supergiants. Temperatures, mass-loss rates and CNO abundances are obtained using the non-LTE, line-blanketed model atmosphere code of Hillier & Miller (1998). In general, the derived temperatures are significantly lower than those determined from unblanketed, plane-parallel models.

Faint emission lines in the spectrum of the Orion Nebula and the abundances of some of the rarer elements

1992 ◽  
Vol 389 ◽  
pp. 305 ◽  
Author(s):  
Donald E. Osterbrock ◽  
Hien D. Tran ◽  
Sylvain Veilleux
Keyword(s):  
Emission Lines ◽  
Orion Nebula

scholarly journals Commemorating John Dyson

2012 ◽  
Vol 10 (H16) ◽  
pp. 626-627
Author(s):  
Julian M. Pittard
Keyword(s):  
Early Life ◽  
Oral Examination ◽  
Emission Lines ◽  
Orion Nebula ◽  
Hii Region ◽  
Broad Emission ◽  
The University ◽  
University Of Manchester

John Dyson was born on the 7th January 1941 in Meltham Mills, West Yorkshire, England, and later grew up in Harrogate and Leeds. The proudest moment of John's early life was meeting Freddie Trueman, who became one of the greatest fast bowlers of English cricket. John used a state scholarship to study at Kings College London, after hearing a radio lecture by D. M. McKay. He received a first class BSc Special Honours Degree in Physics in 1962, and began a Ph.D. at the University of Manchester Department of Astronomy after being attracted to astronomy by an article of Zdenek Kopal in the semi-popular journal New Scientist. John soon started work with Franz Kahn, and studied the possibility that the broad emission lines seen from the Orion Nebula were due to flows driven by the photoevaporation of neutral globules embedded in a HII region. John's thesis was entitled “The Age and Dynamics of the Orion Nebula“ and he passed his oral examination on 28th February 1966.

Emission Lines in the Orion Nebula Near 8500 Å

1974 ◽  
Vol 86 ◽  
pp. 208 ◽  
Author(s):  
I. J. Danziger ◽  
Marc Aaronson
Keyword(s):  
Emission Lines ◽  
Orion Nebula

scholarly journals The Helium λ 10830 Line in Planetary Nebulae and the Orion Nebula

1968 ◽  
Vol 34 ◽  
pp. 74-75
Author(s):  
Arthur H. Vaughan
Keyword(s):  
Planetary Nebulae ◽  
Frame Of Reference ◽  
Emission Lines ◽  
Orion Nebula ◽  
Absorption Component ◽  
Frequency Redistribution ◽  
Upper Limit ◽  
Line Widths ◽  
And Shifts ◽  
Absorption Edges

Interferometric observations of profiles of He I λ 10830 emission lines in 11 planetary nebulae, and in selected regions of the Orion Nebula, are presented. In common with the Orion Nebula, the planetaries are shown to emit a P Cygni-like λ 10830 line, with the absorption component shifted toward the violet with respect to the laboratory wavelength in a frame of reference at rest in the centre of expansion of the gas. The emission components are shifted toward the red. In planetaries, the negative displacements of the absorption edges are, in general, approximately equal to the widths, β, of the emission components which, in turn, range from about 12 km/sec in IC 418 to about 28 km/sec in NGC 6210. The emission red-shift is about 0·7 β on the average, but individual shifts vary from 0·5 β in IC 2149 to 1·05 β in NGC 6826. The line widths and shifts tend to increase in nebulae with larger expansion velocities. In Orion, the absorption edges in the λ 10830 line coincide in velocity with those in the line He I λ 3888 observed against the spectra of the Trapezium stars. In planetaries, the absorption edges in the λ 10830 line appear qualitatively similar to those in the line He I λ 3888, but a coincidence in velocity could not be demonstrated.The observed profiles indicate that the nebulae are expanding, or that they contain expanding globules or filaments. Some form of circumnebular absorbing zone may be indicated. However, it is suggested that frequency redistribution associated with resonance-like scattering in a homogeneous expanding medium might in principle (even in the absence of stratification) account for the shifted λ 10830 profiles. (See Hummer, D.G. and Rybicki, G.B. (1968), Astrophys. J. Letters (in press), for a further discussion of this point.)No trace of He3 is evident from the profiles. Quantitative conclusions are uncertain without a model which reproduces most of the phenomena, but an upper limit of He3/He4 ≤ 0·05 or even 0·01 is suggested on the basis of conservative assumptions.

High‐Resolution Spectroscopy of Faint Emission Lines in the Orion Nebula

2000 ◽  
Vol 129 (1) ◽  
pp. 229-246 ◽  
Author(s):  
J. A. Baldwin ◽  
E. M. Verner ◽  
D. A. Verner ◽  
G. J. Ferland ◽  
P. G. Martin, ◽  
...  
Keyword(s):  
High Resolution ◽  
Emission Lines ◽  
High Resolution Spectroscopy ◽  
Orion Nebula

scholarly journals Comparison of Limb-Darkening Laws from Plane-Parallel and Spherically-Symmetric Model Stellar Atmospheres

2011 ◽  
Vol 7 (S282) ◽  
pp. 243-246
Author(s):  
Hilding R. Neilson
Keyword(s):  
Stellar Atmospheres ◽  
Stellar Disk ◽  
Symmetric Model ◽  
Spherically Symmetric ◽  
Linear Quadratic ◽  
Plane Parallel ◽  
Curve Fit ◽  
Parallel Models ◽  
Spherically Symmetric Model ◽  
Limb Darkening

AbstractLimb-darkening is a fundamental constraint for modeling eclipsing binary and planetary transit light curves. As observations, for example from Kepler, CoRot, and Most, become more precise then a greater understanding of limb-darkening is necessary. However, limb-darkening is typically modeled as simple parameterizations fit to plane-parallel model stellar atmospheres that ignores stellar atmospheric extension. In this work, I compute linear, quadratic and four-parameter limb-darkening laws from grids of plane-parallel and spherically-symmetric model stellar atmospheres in a temperature and gravity range representing stars evolving on the Red Giant branch. The limb-darkening relations for each geometry are compared and are found to fit plane-parallel models much better than the spherically-symmetric models. Assuming that limb-darkening from spherically-symmetry model atmospheres are more physically representative of actual stellar limb-darkening than plane-parallel models, then these limb-darkening laws will not fit the limb of a stellar disk leading to errors in a light curve fit. This error will increase with a star's atmospheric extension.

Long-term Cyclic Variations of Prominences, Green and Red Coronae over Solar Cycles

2000 ◽  
Vol 179 ◽  
pp. 201-204
Author(s):  
Vojtech Rušin ◽  
Milan Minarovjech ◽  
Milan Rybanský
Keyword(s):  
Emission Lines ◽  
High Latitudes ◽  
Green Line ◽  
Solar Cycles ◽  
The South ◽  
Coronal Emission ◽  
Local Maxima ◽  
The North ◽  
Cyclic Variations

AbstractLong-term cyclic variations in the distribution of prominences and intensities of green (530.3 nm) and red (637.4 nm) coronal emission lines over solar cycles 18–23 are presented. Polar prominence branches will reach the poles at different epochs in cycle 23: the north branch at the beginning in 2002 and the south branch a year later (2003), respectively. The local maxima of intensities in the green line show both poleward- and equatorward-migrating branches. The poleward branches will reach the poles around cycle maxima like prominences, while the equatorward branches show a duration of 18 years and will end in cycle minima (2007). The red corona shows mostly equatorward branches. The possibility that these branches begin to develop at high latitudes in the preceding cycles cannot be excluded.

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