scholarly journals The Detection of Ionized Helium and Carbon in the Pulsating DB Degenerate GD358

1989 ◽  
Vol 114 ◽  
pp. 354-358 ◽  
Author(s):  
Edward M. Sion ◽  
James Liebert ◽  
Gerard Vauclair ◽  
Gary Wegner
Keyword(s):  
High Resolution ◽  
Mass Loss ◽  
Thermal Diffusion ◽  
White Dwarfs ◽  
Current Understanding ◽  
Physical Processes ◽  
Complex Interplay ◽  
Ion Absorption ◽  
Fundamental Challenge ◽  
Absorption Features

Spectroscopic observations of hot white dwarfs utilizing the Explorer (IUE) high resolution spectrograph have led to the important discovery of ion absorption features (undetectable at low resolution) which have been ascribed to wind outflow in some cases (cf. Bruhweiler and Kondo 1983) and formation at the photosphere (cf. Sion and Guinan 1983; Bruhweiler and Kondo 1983; Dupree and Raymond 1982) in others. These line features, often weak and sharp, have presented a fundamental challenge to current understanding of the complex interplay of physical processes which control observed surface abundances in white dwarfs: gravitational/thermal diffusion, selective radiative support of ions, mass loss, convective dilution and mixing, and accretion (cf. the review by Vauclair, this volume and references therein).

scholarly journals Terminal Velocities for a Large Sample of O Stars, B Supergiants, and Wolf-Rayet Stars

1991 ◽  
Vol 143 ◽  
pp. 317-317
Author(s):  
R. K. Prinja ◽  
M. J. Barlow ◽  
I. D. Howarth
Keyword(s):  
High Resolution ◽  
Mass Loss ◽  
Early Type ◽  
Nuclear Mass ◽  
Ob Stars ◽  
Residual Intensity ◽  
The Mean ◽  
Effective Temperatures ◽  
Early Type Stars ◽  
Absorption Features

We argue that easily measured, reliable estimates of terminal velocities for early-type stars are provided (1) by the central velocity asymptotically approached by narrow absorption features in unsaturated UV P Cygni profiles, and (2) by the violet limit of zero residual intensity in saturated P Cygni profiles. We use these estimators and high resolution IUE data to determine terminal velocities, v∞, for 181 O stars, 70 early B supergiants, and 35 Wolf-Rayet stars. For OB stars our values are typically 15-20% smaller than the extreme violet edge velocities, vedge, while for WR stars v∞ = 0.76vedge on average. We give new mass-loss rates for WR stars which are thermal radio emitters, taking into account our new terminal velocities and recent revisions to estimates of distances and to the mean nuclear mass per electron. We examine the relationships between v∞, the surface escape velocities, and effective temperatures.

scholarly journals Stromgren Trails of Hot White Dwarfs

1984 ◽  
Vol 81 ◽  
pp. 311-314
Author(s):  
John C. Raymond
Keyword(s):  
High Resolution ◽  
White Dwarfs ◽  
Significant Contribution ◽  
Ionization Zone ◽  
Ionization Time ◽  
B Stars ◽  
Crossing Time ◽  
The Galaxy ◽  
Stellar Velocity ◽  
Absorption Features

AbstractHigh resolution IUE spectra of Feige 24 reveal sharp C IV absorption features at both the stellar velocity and the velocity of the interstellar lines. Dupree and Raymond have shown that the ionization zone created by Feige 24 itself accounts for the interstellar components of C IV and Si IV, and that the density of hot white dwarfs in the galaxy implies that similar ionized zones around hot white dwarfs make a significant contribution to the C IV column densities observed toward distant O and B stars. Typical white dwarf velocities of around 30 km/s and C IV ionization zone diameters less than 1 pc imply that the crossing time is comparable to the ionization time, so that non-equilibrium ionization models are required. Models of the resulting elongated trails are presented.

scholarly journals The Formation and Evolution of ONe White Dwarfs: Prospects for Accretion Induced Collapse

2011 ◽  
Vol 7 (S281) ◽  
pp. 52-59
Author(s):  
Enrique García–Berro
Keyword(s):  
Chemical Composition ◽  
Mass Loss ◽  
Electron Capture ◽  
White Dwarfs ◽  
Stellar Mass ◽  
Asymptotic Giant Branch ◽  
Current Understanding ◽  
Convective Mixing ◽  
Formation And Evolution ◽  
Carbon Burning

AbstractI review our current understanding of the evolution of stars which experience carbon burning under conditions of partial electron degeneracy and ultimately become thermally pulsing “super” asymptotic giant branch (SAGB) stars with electron-degenerate cores composed primarily of oxygen and neon. The range in stellar mass over which this occurs is very narrow and the interior evolutionary characteristics vary rapidly over this range. Consequently, while those stars with larger masses (~11 M⊙) are likely to undergo electron-capture accretion induced collapse, those models with smaller masses (8.5 ≲ M/M⊙ ≲ 10.5) will presumably form massive (M ≳ 1.1 M⊙) white dwarfs. The final outcome depends sensitively on the adopted mass-loss rates, the chemical composition of the massive envelopes, and on the adopted prescription for convective mixing.

Beam induced mass loss in high resolution biological microanalysis

1986 ◽  
Vol 144 (3) ◽  
pp. 317-327 ◽  
Author(s):  
M. E. Cantino ◽  
L. E. Wilkinson ◽  
M. K. Goddard ◽  
D. E. Johnson
Keyword(s):  
High Resolution ◽  
Mass Loss

scholarly journals What Should Be Considered When Simulating Doppler Velocities Measured by Ground-Based Weather Radars?

2008 ◽  
Vol 47 (8) ◽  
pp. 2256-2262 ◽  
Author(s):  
Olivier Caumont ◽  
Véronique Ducrocq
Keyword(s):  
High Resolution ◽  
Atmospheric Model ◽  
Physical Processes ◽  
Model Sensitivity ◽  
Sensitivity Experiments ◽  
Weather Radars ◽  
Vertical Beam ◽  
Beam Broadening

Abstract A sophisticated and flexible simulator of Doppler velocities measured by ground-based weather radars is appended to a high-resolution nonhydrostatic atmospheric model. Sensitivity experiments are conducted by using different configurations for each of the physical processes that is modeled by the simulator. It is concluded that neglecting the vertical beam broadening effect or the weighting by reflectivities yields errors of the same order on the simulated reflectivities. Neglecting hydrometeor fall speeds has a much smaller impact. It is also shown that neglecting both the beam broadening effect and the weighting by reflectivities yields errors of the same order as occur when only one of these effects is neglected.

scholarly journals Large spatial variations in the flux balance along the front of a Greenland tidewater glacier

2019 ◽  
Vol 13 (3) ◽  
pp. 911-925 ◽  
Author(s):  
Till J. W. Wagner ◽  
Fiamma Straneo ◽  
Clark G. Richards ◽  
Donald A. Slater ◽  
Laura A. Stevens ◽  
...  
Keyword(s):  
High Resolution ◽  
Spatial Variability ◽  
Ocean Model ◽  
Complex Interplay ◽  
Flux Balance ◽  
Tidewater Glacier ◽  
Glacier Front ◽  
The Individual ◽  
High Spatial Variability ◽  
Frontal Ablation

Abstract. The frontal flux balance of a medium-sized tidewater glacier in western Greenland in the summer is assessed by quantifying the individual components (ice flux, retreat, calving, and submarine melting) through a combination of data and models. Ice flux and retreat are obtained from satellite data. Submarine melting is derived using a high-resolution ocean model informed by near-ice observations, and calving is estimated using a record of calving events along the ice front. All terms exhibit large spatial variability along the ∼5 km wide ice front. It is found that submarine melting accounts for much of the frontal ablation in small regions where two subglacial discharge plumes emerge at the ice front. Away from the subglacial plumes, the estimated melting accounts for a small fraction of frontal ablation. Glacier-wide, these estimates suggest that mass loss is largely controlled by calving. This result, however, is at odds with the limited presence of icebergs at this calving front – suggesting that melt rates in regions outside of the subglacial plumes may be underestimated. Finally, we argue that localized melt incisions into the glacier front can be significant drivers of calving. Our results suggest a complex interplay of melting and calving marked by high spatial variability along the glacier front.

scholarly journals Ionisation fractions and mass-loss in O stars

1987 ◽  
Vol 122 ◽  
pp. 449-450
Author(s):  
Raman K. Prinja ◽  
Ian D. Howarth
Keyword(s):  
High Resolution ◽  
Mass Loss ◽  
Column Density ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Terminal Velocity ◽  
Stellar Radius ◽  
Left Part ◽  
Hr Diagram

The most sensitive indicators of mass-loss for stars in the upper left part of the HR diagram are the UV P Cygni profiles observed in the resonance lines of common ions such as N V, Si IV, and C IV. We present here some results from a study of these lines in the high resolution IUE spectra of 197 Ï stars. Profile fits were carried out in the manner described by Prinja & Howarth (1986) for all unsaturated P Cygni resonance doublets. The parameterisations adopted enable the product of mass-loss rate (Ṁ) and ion fraction (qi) to be determined at a given velocity, such that Ṁ qi°C Ni R* v∞, where Ni is the column density of the observed ion i, v∞ is the terminal velocity, and R⋆ is the stellar radius. The accompanying figures illustrate the behaviour of Ṁ qi (evaluated at 0.5 v∞) for N V and C IV.

scholarly journals The runaway supergiant HD 188209 (O9.5Iab): a binary or a pulsating star?

1999 ◽  
Vol 193 ◽  
pp. 69-70
Author(s):  
Garik Israelian ◽  
Artemio Herrero ◽  
E. Santolaya-Rey ◽  
A. Kaufer ◽  
F. Musaev ◽  
...  
Keyword(s):  
Time Series ◽  
High Resolution ◽  
Mass Loss ◽  
Radial Velocity ◽  
Loss Rate ◽  
State Of The Art ◽  
Mass Loss Rate ◽  
Fundamental Parameters ◽  
Binary Nature ◽  
Period 2

We report radial velocity studies of photospheric absorption lines from spectral time series of the late O-type runaway supergiant HD 188209. Radial velocity variations with a quasi-period ∼ 2 days have been detected in high-resolution echelle spectra and most probably indicate that the supergiant is pulsating. Night-to-night variations in the position and strength of the central emission reversal of the Hα profile have been observed. The fundamental parameters of the star have been derived using state-of-the-art plane-parallel and unified non-LTE model atmospheres, these last including the mass-loss rate. The binary nature of this star is not suggested either from Hipparcos photometry or from radial-velocity curves.

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