scholarly journals Uncertainties in the Position of the β Cephei Instability Strip in the HR Diagram

1995 ◽  
Vol 155 ◽  
pp. 291-292
Author(s):  
A.A. Pamyatnykh ◽  
W.A. Dziembowski ◽  
P. Mikołaj
Keyword(s):  
Heavy Element ◽  
Element Abundance ◽  
Instability Strip ◽  
Metal Mixture ◽  
Hr Diagram

AbstractWe discuss the sensitivity of the theoretical B star instability domains to the heavy element abundance Z, the adopted metal mixture, the assumed overshooting from stellar convective cores and the choice of the opacity data.

scholarly journals A Spectroscopic Survey in the EUV of the “Coolest” Hot DA Stars

1996 ◽  
Vol 152 ◽  
pp. 217-222
Author(s):  
Jean Dupuis ◽  
Stéphane Vennes
Keyword(s):  
Effective Temperature ◽  
White Dwarfs ◽  
Heavy Element ◽  
Extreme Ultraviolet ◽  
Diffusion Theory ◽  
Hydrogen Atmosphere ◽  
Element Abundance ◽  
Pure Hydrogen ◽  
Element Abundances ◽  
The One

We present an analysis of the extreme ultraviolet (EUV) spectroscopy of a sample of 10 DA white dwarfs observed by the Extreme Ultraviolet Explorer (EUVE). We have selected white dwarfs cooler than about 50,000 K and with presumably low heavy element abundances. The goal of this study is to determine the fundamental atmospheric parameters, namely the effective temperature and chemical composition, of these stars by fitting their continua with synthetic spectra computed from pure hydrogen LTE/line-blanketed model atmospheres. The question of the presence (or absence) of trace elements is explored by comparing EUV-determined effective temperatures to the one obtained from a fit of hydrogen balmer lines. It is found that the majority of the DA in the sample are consistent with having a pure hydrogen atmosphere. One of the star, MCT0027-634, is another possible example of a HZ 43-type white dwarf, having an effective temperature above 50000 K and a low heavy element abundance, i.e., much lower than predicted by diffusion theory.

scholarly journals Element Abundance Analyses of Novae

1977 ◽  
Vol 42 ◽  
pp. 242-273 ◽  
Author(s):  
Robert E. Williams
Keyword(s):  
Temperature Distribution ◽  
Emission Line ◽  
Heavy Element ◽  
Element Abundance ◽  
Element Abundances ◽  
Maximum Light ◽  
Growth Studies ◽  
Nova Shells

AbstractThe different methods by which element abundances in novae have been determined are reviewed. Curve of growth studies of novae at maximum light have indicated CNO nuclei to be greatly enhanced with respect to hydrogen in certain objects. These results are questionable because they depend upon an assumed temperature distribution in the photosphere which is probably too steep to be realistic. Emission line analyses of novae, generally obtained in the period of early decline, also indicate possible heavy element enhancement, however these results are tentative because of uncertainties in the parameters of the emitting gas. It is suggested that useful abundance determinations of nova ejecta might be obtained from studies of old, extended nova shells.

scholarly journals Population Models for Massive Globular Clusters

2012 ◽  
Vol 10 (H16) ◽  
pp. 247-248 ◽  
Author(s):  
Young-Wook Lee ◽  
Seok-Joo Joo ◽  
Sang-Il Han ◽  
Chongsam Na ◽  
Dongwook Lim ◽  
...  
Keyword(s):  
Parameter Space ◽  
Globular Clusters ◽  
Heavy Element ◽  
Milky Way ◽  
Population Modeling ◽  
Stellar Populations ◽  
Population Models ◽  
Horizontal Branch ◽  
Element Abundances ◽  
Hr Diagram

Increasing number of massive globular clusters (GCs) in the Milky Way are now turned out to host multiple stellar populations having different heavy element abundances enriched by supernovae. Recent observations have further shown that [CNO/Fe] is also enhanced in metal-rich subpopulations in most of these GCs, including ω Cen and M22 (Marino et al. 2011, 2012). In order to reflect this in our population modeling, we have expanded the parameter space of Y2 isochrones and horizontal-branch (HB) evolutionary tracks to include the cases of normal and enhanced nitrogen abundances ([N/Fe] = 0.0, 0.8, and 1.6). The observed variations in the total CNO content were reproduced by interpolating these nitrogen enhanced stellar models. Our test simulations with varying N and O abundances show that, once the total CNO sum ([CNO/Fe]) is held constant, both N and O have almost identical effects on the HR diagram (see Fig. 1).

Helioseismic models of the sun with a low heavy element abundance

2017 ◽  
Vol 61 (10) ◽  
pp. 901-913 ◽  
Author(s):  
S. V. Ayukov ◽  
V. A. Baturin
Keyword(s):  
Heavy Element ◽  
Element Abundance ◽  
The Sun

The Lyman limit absorption system in the spectrum of PKS 2126-158 - Heavy-element abundance at high redshift

1990 ◽  
Vol 351 ◽  
pp. 364 ◽  
Author(s):  
Wallace L. W. Sargent ◽  
Charles C. Steidel ◽  
A. Boksenberg
Keyword(s):  
Heavy Element ◽  
High Redshift ◽  
Element Abundance ◽  
Absorption System

scholarly journals Photospheric Activity among Early F-Type Stars

1993 ◽  
Vol 137 ◽  
pp. 651-653 ◽  
Author(s):  
L. Mantegazza ◽  
E. Poretti ◽  
E. Antonello ◽  
F. Zerbi
Keyword(s):  
Instability Strip ◽  
Scuti Stars ◽  
Secondary Results ◽  
Hr Diagram

In the last decade stars showing variability of unclear origin have been detected among early F-type stars mainly as secondary results in the context of observational programmes devoted to the study of δ-Scuti and CP stars.For this reason only a small number of these objects has been thoroughly studied: their positions in HR diagram is shown in fig.l.Figure 1: HR diagram of the observed stars.The stars in NGC 2516 have been singled out in a survey work by Antonello and Mantegazza (1986), HD 164615 has been studied by Abt et al.(1983), the variability in 9 Aur has been discovered by Krischinas et al.(1990,1991) and HD 23375 in Pleiades has been pointed out by Breger (1972). The solid line in Fig. 1 is the ZAMS and the dashed lines are the borders of the i-Scuti stars instability strip.

The Main Sequence Evolution of Inhomogeneous Stars

1982 ◽  
Vol 4 (4) ◽  
pp. 396-400 ◽  
Author(s):  
J. Lattanzio
Keyword(s):  
Gravitational Collapse ◽  
Heavy Element ◽  
Main Sequence ◽  
Element Abundance ◽  
Sequence Evolution ◽  
Interstellar Gas ◽  
Convective Mixing ◽  
The Core ◽  
Gas Cloud

Duley (1974) has shown that, at the temperatures usually associated with interstellar gas clouds, we would expect CNO grains to be present. During gravitational collapse these grains migrate to the centre of the gas cloud, leading to an enhancement of the heavy-element abundance in the core (Prentice 1976, 1978). It was Krautschneider (1977) who verified such a scenario, by considering the dynamical collapse of gas and grain clouds. If such an initial radial abundance inhomogeneity existed, Prentice (1976a) showed that this configuration may well survive the later convective mixing phase and thus approach the zero-age main-sequence (ZAMS) with a small (-v 3% by mass) metal enhanced core.

scholarly journals Helioseismic limit on heavy element abundance

2002 ◽  
Vol 393 (3) ◽  
pp. L95-L98 ◽  
Author(s):  
H. M. Antia ◽  
S. M. Chitre
Keyword(s):  
Heavy Element ◽  
Element Abundance
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