scholarly journals Understanding Saturn’s interior from the Cassini Grand Finale gravity measurements

2020 ◽  
Vol 639 ◽  
pp. A10 ◽  
Author(s):  
Dongdong Ni
Keyword(s):  
Rotation Rate ◽  
Mass Fraction ◽  
Heavy Element ◽  
Equations Of State ◽  
Layer Structure ◽  
Element Abundance ◽  
Structure Model ◽  
Core Mass ◽  
Induced Gravity ◽  
Gravity Measurements

Context. Measurements of Saturn’s gravity field by Cassini Grand Finale have been acquired with high precision. It has been demonstrated that the even gravitational harmonics J6–J10 have larger absolute values than the predictions by typical rigid-body interior models. A four-layer structure model, proposed to interpret Juno’s gravity measurements for Jupiter, has been applied to Saturn, but great attention was paid to the depth of zonal flows in order to interpret the large absolute values of J6–J10. Aims. We aim to understand the internal structure and interior composition of Saturn with a similar model for Jupiter. The additional uncertainties in Saturn’s structure and composition are investigated in detail, such as rotation periods, atmospheric helium mass fractions, and flow-induced gravity corrections. Also, we investigate the effect of equations of state for hydrogen and helium on the predictions of the core mass and heavy element abundance. Methods. In the four-layer structure model, we adjusted the heavy element abundances in the outer two envelopes and the mass of the compact core in order to reproduce Saturn’s equatorial radius as well as the Cassini Grand Finale gravity measurements corrected by the flow-induced gravity signals. Different four-layer interior models are specified in terms of the rotation period, the atmospheric helium mass fraction, and the flow-induced gravity corrections. Two different ab initio equations of state for hydrogen and helium were used in interior structure calculations. Optimized calculations were then performed to explore Saturn’s internal structure and composition. Results. It is found that the absolute values of J6–J10 tend to increase with increasing deep rotation rate and depend on the equations of state adopted in interior calculations. Saturn’s deep rotation rate and atmospheric helium mass fraction are important to determine the distribution of helium and heavy elements in the outer envelopes. We also show that the core mass and heavy element abundance in Saturn are dependent upon the deep rotation rate, the atmospheric helium mass fraction, the flow-induced gravity corrections, and the equations of state for hydrogen and helium.

scholarly journals Understanding Jupiter’s deep interior: the effect of a dilute core

2019 ◽  
Vol 632 ◽  
pp. A76
Author(s):  
Dongdong Ni
Keyword(s):  
Heavy Element ◽  
Equations Of State ◽  
Layer Structure ◽  
Core Region ◽  
Element Abundance ◽  
Interior Structure ◽  
Core Mass ◽  
The Core ◽  
Two Envelopes ◽  
Structure Calculations

Context. The Juno spacecraft has significantly improved the accuracy of low-order even gravitational harmonics. It has been demonstrated that a dilute core is helpful to interpret Juno’s gravity measurements. However, introducing a dilute core adds a new degree of freedom to Jupiter’s interior models in addition to the uncertainties in the equations of state for hydrogen and helium. Aims. We present four-layer structure models for Jupiter where a dilute core region is added above a central compact core of rocks. The effect of the dilute core on the structure and composition of Jupiter is investigated in detail. Combined with current knowledge of Jupiter’s composition and thermal state, we aim to obtain information on the dilute core. Also, we investigate the effect of equations of state for hydrogen and helium on the predictions of the core mass and heavy element abundance. Methods. In the four-layer structure model, the heavy element abundances in the outer two envelopes and the mass of the compact core were adjusted to reproduce Jupiter’s equatorial radius as well as Juno’s gravity observations. Different dilute core configurations were constructed in terms of its size and composition and different equations of state for hydrogen and helium were used in interior structure calculations. Optimized calculations were then performed to investigate the effect of dilute cores and equations of state on Jupiter’s internal structure and composition. Results. It is found that the absolute values of J6 and J8 tend to decrease as helium becomes more depleted in the dilute core region. Most interior structure calculations seem to prefer an inward decrease of the helium mass fraction from the metallic envelope to the dilute core region. We also show that the core mass and heavy element abundance in Jupiter are dependent upon the rock-to-ice ratio in the dilute core region, the temperature jump from the molecular to metallic envelope, and the equations of state for hydrogen and helium. The resulting heavy-element mass in the core is generally larger than the three-layer structure models owing to the heavy elements dissolved in the dilute core region, and the global heavy-element abundance is in good agreement with the available dilute-core predictions.

scholarly journals Simulations of the IMF in Clusters

2010 ◽  
Vol 6 (S270) ◽  
pp. 151-158
Author(s):  
Ralph E. Pudritz
Keyword(s):  
Equations Of State ◽  
Stellar Dynamics ◽  
Mass Function ◽  
Initial Mass Function ◽  
Core Mass ◽  
Numerical Work ◽  
Computational Approaches ◽  
The Core ◽  
The Imf

AbstractWe review computational approaches to understanding the origin of the Initial Mass Function (IMF) during the formation of star clusters. We examine the role of turbulence, gravity and accretion, equations of state, and magnetic fields in producing the distribution of core masses - the Core Mass Function (CMF). Observations show that the CMF is similar in form to the IMF. We focus on feedback processes such as stellar dynamics, radiation, and outflows can reduce the accreted mass to give rise to the IMF. Numerical work suggests that filamentary accretion may play a key role in the origin of the IMF.

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 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 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.

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

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.

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