S-process nucleosynthesis in massive stars and the weak component. I - Evolution and neutron captures in a 25 solar mass star

1991 ◽  
Vol 367 ◽  
pp. 228 ◽  
Author(s):  
C. M. Raiteri ◽  
M. Busso ◽  
G. Picchio ◽  
R. Gallino ◽  
L. Pulone
Keyword(s):  
Massive Stars ◽  
Mass Star ◽  
Solar Mass ◽  
Weak Component

scholarly journals MRI-active inner regions of protoplanetary discs. I. A detailed model of disc structure

2021 ◽  
Vol 504 (1) ◽  
pp. 280-299
Author(s):  
Marija R Jankovic ◽  
James E Owen ◽  
Subhanjoy Mohanty ◽  
Jonathan C Tan
Keyword(s):  
Energy Transport ◽  
Threshold Temperature ◽  
Mass Star ◽  
Dust Grains ◽  
Solar Mass ◽  
Detailed Model ◽  
Short Period ◽  
Pressure Maximum ◽  
Ion Emission ◽  
Protoplanetary Discs

ABSTRACT Short-period super-Earth-sized planets are common. Explaining how they form near their present orbits requires understanding the structure of the inner regions of protoplanetary discs. Previous studies have argued that the hot inner protoplanetary disc is unstable to the magnetorotational instability (MRI) due to thermal ionization of potassium, and that a local gas pressure maximum forms at the outer edge of this MRI-active zone. Here we present a steady-state model for inner discs accreting viscously, primarily due to the MRI. The structure and MRI-viscosity of the inner disc are fully coupled in our model; moreover, we account for many processes omitted in previous such models, including disc heating by both accretion and stellar irradiation, vertical energy transport, realistic dust opacities, dust effects on disc ionization, and non-thermal sources of ionization. For a disc around a solar-mass star with a standard gas accretion rate ($\dot{M}\, \sim \, 10^{-8}$ M⊙ yr−1) and small dust grains, we find that the inner disc is optically thick, and the accretion heat is primarily released near the mid-plane. As a result, both the disc mid-plane temperature and the location of the pressure maximum are only marginally affected by stellar irradiation, and the inner disc is also convectively unstable. As previously suggested, the inner disc is primarily ionized through thermionic and potassium ion emission from dust grains, which, at high temperatures, counteract adsorption of free charges on to grains. Our results show that the location of the pressure maximum is determined by the threshold temperature above which thermionic and ion emission become efficient.

scholarly journals Growth after the streaming instability

2019 ◽  
Vol 624 ◽  
pp. A114 ◽  
Author(s):  
Beibei Liu ◽  
Chris W. Ormel ◽  
Anders Johansen
Keyword(s):  
Dynamical Evolution ◽  
Bimodal Distribution ◽  
Stokes Number ◽  
Volume Density ◽  
Mass Star ◽  
Type I ◽  
Solar Mass ◽  
Streaming Instability ◽  
Two Component ◽  
Self Gravity

Context. Streaming instability is a key mechanism in planet formation, clustering pebbles into planetesimals with the help of self-gravity. It is triggered at a particular disk location where the local volume density of solids exceeds that of the gas. After their formation, planetesimals can grow into protoplanets by feeding from other planetesimals in the birth ring as well as by accreting inwardly drifting pebbles from the outer disk. Aims. We aim to investigate the growth of planetesimals into protoplanets at a single location through streaming instability. For a solar-mass star, we test the conditions under which super-Earths are able to form within the lifetime of the gaseous disk. Methods. We modified the Mercury N-body code to trace the growth and dynamical evolution of a swarm of planetesimals at a distance of 2.7 AU from the star. The code simulates gravitational interactions and collisions among planetesimals, gas drag, type I torque, and pebble accretion. Three distributions of planetesimal sizes were investigated: (i) a mono-dispersed population of 400 km radius planetesimals, (ii) a poly-dispersed population of planetesimals from 200 km up to 1000 km, (iii) a bimodal distribution with a single runaway body and a swarm of smaller, 100 km size planetesimals. Results. The mono-dispersed population of 400 km size planetesimals cannot form protoplanets of a mass greater than that of the Earth. Their eccentricities and inclinations are quickly excited, which suppresses both planetesimal accretion and pebble accretion. Planets can form from the poly-dispersed and bimodal distributions. In these circumstances, it is the two-component nature that damps the random velocity of the large embryo through the dynamical friction of small planetesimals, allowing the embryo to accrete pebbles efficiently when it approaches 10−2 M⊕. Accounting for migration, close-in super-Earth planets form. Super-Earth planets are likely to form when the pebble mass flux is higher, the disk turbulence is lower, or the Stokes number of the pebbles is higher. Conclusions. For the single site planetesimal formation scenario, a two-component mass distribution with a large embryo and small planetesimals promotes planet growth, first by planetesimal accretion and then by pebble accretion of the most massive protoplanet. Planetesimal formation at single locations such as ice lines naturally leads to super-Earth planets by the combined mechanisms of planetesimal accretion and pebble accretion.

scholarly journals A Starspot Model for the RS CVn Stars

1980 ◽  
Vol 88 ◽  
pp. 389-396
Author(s):  
Steven N. Shore ◽  
Douglas S. Hall
Keyword(s):  
Essential Feature ◽  
Rotational Velocity ◽  
Active Regions ◽  
Dynamo Model ◽  
Evolutionary Status ◽  
Mass Star ◽  
Solar Mass ◽  
Orbital Parameters ◽  
Rs Cvn Stars ◽  
Synchronous Rotation

We employ a simplified dynamo model to describe the long term photometric spectroscopic behavior of the RS CVn stars. The essential feature of the model is that the stars are in nearly synchronous rotation, with the differential rotation slower and the rotational velocity higher than for a single evolved 1 to 2 solar mass star. The spot groups are formed by eruption of enhanced toroidal fields, which have areas at the photosphere of several tenths of the surface area; the sizes of these regions are shear limited. Estimates of the lifetimes of active regions and of flare energetics are presented. The RS CVn phenomenon is then related to both the evolutionary status and the orbital parameters of the binary system.

scholarly journals The history of KZ Hya and its unseen companions

2008 ◽  
Vol 4 (S252) ◽  
pp. 421-422
Author(s):  
S. Y. Jiang
Keyword(s):  
Effective Temperature ◽  
White Dwarf ◽  
Main Sequence ◽  
Absolute Magnitude ◽  
High Amplitude ◽  
Mass Star ◽  
Solar Mass ◽  
Short Period ◽  
Outer Atmosphere ◽  
Rich Material

AbstractKZ Hya is a short-period high amplitude metal pool population II pulsating variable. Its spectral type is B9-A7 III/IV. Its average effective temperature is 7640K. But its mass is only 0.97 solar mass. From normal stellar evolution and H-R diagram, we can not get such a solar mass star at post main sequence stage with so high effective temperature and so early type spectra. We observe this star since 1984 till now, 23years past. Finally we prove it is inside a binary with at least 2 unseen companions. The most massive companion has mass larger than 0.76 solar mass, mostly may be 0.99 to 3.99 solar mass. That means this companion must be a massive white dwarf. The distance between tow companions is about 10 AU. If the companion is white dwarf, this binary are fairly inside the nebula. This system is very old, older than 7.59 billion years. The nebula should be already diluted to very low density so that we can see the nebula directly. As its spectra type is B9III/VI at some time of maximum light and the visual absolute magnitude is 2.78, about 2 magnitudes higher than our sun. We can image that at the end of AGB stage of the companion, the strong fast winds from hot central core push away the outer atmosphere of KZ Hya. Later KZ Hya absorbed a part of Helium rich material from the companion. This will cause hydrogen content X decrease from 0.75 to about 0.62. Then KZ Hya looks like a hot post main sequence star

scholarly journals Exploring the formation by core accretion and the luminosity evolution of directly imaged planets

2019 ◽  
Vol 624 ◽  
pp. A20 ◽  
Author(s):  
Gabriel-Dominique Marleau ◽  
Gavin A. L. Coleman ◽  
Adrien Leleu ◽  
Christoph Mordasini
Keyword(s):  
Mass Star ◽  
Population Synthesis ◽  
Direct Imaging ◽  
Solar Mass ◽  
High Eccentricity ◽  
Body Dynamics ◽  
Low Mass ◽  
Open Question ◽  
Core Accretion ◽  
First Time

Context. A low-mass companion to the two-solar mass star HIP 65426 has recently been detected by SPHERE at around 100 au from its host. Explaining the presence of super-Jovian planets at large separations, as revealed by direct imaging, is currently an open question. Aims. We want to derive statistical constraints on the mass and initial entropy of HIP 65426 b and to explore possible formation pathways of directly imaged objects within the core-accretion paradigm, focusing on HIP 65426 b. Methods. Constraints on the planet’s mass and post-formation entropy are derived from its age and luminosity combined with cooling models. For the first time, the results of population synthesis are also used to inform the results. Then a formation model that includes N-body dynamics with several embryos per disc is used to study possible formation histories and the properties of possible additional companions. Finally, the outcomes of two- and three-planet scattering in the post-disc phase are analysed, taking tides into account for small-pericentre orbits. Results. The mass of HIP 65426 b is found to be mp = 9.9−1.8+1.1 MJ using the hot population and mp = 10.9−2.0+1.4 MJ with the cold-nominal population. We find that core formation at small separations from the star followed by outward scattering and runaway accretion at a few hundred astronomical units succeeds in reproducing the mass and separation of HIP 65426 b. Alternatively, systems having two or more giant planets close enough to be on an unstable orbit at disc dispersal are likely to end up with one planet on a wide HIP 65426 b-like orbit with a relatively high eccentricity (≳ 0.5). Conclusions. If this scattering scenario explains its formation, HIP 65426 b is predicted to have a high eccentricity and to be accompanied by one or several roughly Jovian-mass planets at smaller semi-major axes, which also could have a high eccentricity. This could be tested by further direct-imaging as well as radial-velocity observations.

scholarly journals The Status of Multi-Dimensional Core-Collapse Supernova Models

2016 ◽  
Vol 33 ◽  
Author(s):  
B. Müller
Keyword(s):  
Initial Conditions ◽  
Massive Stars ◽  
Core Collapse ◽  
Solar Mass ◽  
Convective Boundary ◽  
3D Simulations ◽  
Core Collapse Supernova ◽  
Wide Range ◽  
Supernova Explosions ◽  
The Impact

AbstractModels of neutrino-driven core-collapse supernova explosions have matured considerably in recent years. Explosions of low-mass progenitors can routinely be simulated in 1D, 2D, and 3D. Nucleosynthesis calculations indicate that these supernovae could be contributors of some lighter neutron-rich elements beyond iron. The explosion mechanism of more massive stars remains under investigation, although first 3D models of neutrino-driven explosions employing multi-group neutrino transport have become available. Together with earlier 2D models and more simplified 3D simulations, these have elucidated the interplay between neutrino heating and hydrodynamic instabilities in the post-shock region that is essential for shock revival. However, some physical ingredients may still need to be added/improved before simulations can robustly explain supernova explosions over a wide range of progenitors. Solutions recently suggested in the literature include uncertainties in the neutrino rates, rotation, and seed perturbations from convective shell burning. We review the implications of 3D simulations of shell burning in supernova progenitors for the ‘perturbations-aided neutrino-driven mechanism,’ whose efficacy is illustrated by the first successful multi-group neutrino hydrodynamics simulation of an 18 solar mass progenitor with 3D initial conditions. We conclude with speculations about the impact of 3D effects on the structure of massive stars through convective boundary mixing.

scholarly journals Definitions, Summary, and Some Issues

2002 ◽  
Vol 12 ◽  
pp. 179-181
Author(s):  
Peter S. Conti
Keyword(s):  
Spectral Type ◽  
Massive Star ◽  
Massive Stars ◽  
Mass Star ◽  
Mass Limit ◽  
Physical Processes ◽  
Intermediate Mass ◽  
Observable Quantity ◽  
Low Mass ◽  
Final Evolution

This Joint Discussion has been titled Massive Star Birth. Perhaps it is appropriate here to define what we mean by a massive star. The very word massive suggests we consider aminimummassMbelow which one would speak of low (or intermediate) mass evolution, and above which is the realm of massive stars. It is natural to take this mass limit as that in which a (single) star will end its life as a supernova: 8M⊙. This corresponds to a (minimum) luminosityLof a few × 103L⊙, a (minimum)Teff of 20000 K, and a ZAMS spectral type of about B1.5V. Note that this mass division refers to the final evolution of a star, and might well have nothing to do with difference in physical processes between massive and low mass starbirth. For example, the minimumTeff for a star to produce an UCHII region, a readily observable quantity, corresponds to aTeffcloser to 30000 K and a mass of 15M⊙.

scholarly journals Carina High-contrast Imaging Project for massive Stars (CHIPS)

2020 ◽  
Vol 640 ◽  
pp. A15
Author(s):  
A. Rainot ◽  
M. Reggiani ◽  
H. Sana ◽  
J. Bodensteiner ◽  
C. A. Gomez-Gonzalez ◽  
...  
Keyword(s):  
Main Sequence ◽  
Massive Stars ◽  
Imaging Techniques ◽  
Mass Function ◽  
Local Source ◽  
High Contrast ◽  
Contrast Imaging ◽  
Solar Mass ◽  
Low Mass ◽  
Spectral Channels

Context. Massive stars like company. However, low-mass companions have remained extremely difficult to detect at angular separations (ρ) smaller than 1″ (approx. 1000–3000 au, considering the typical distance to nearby massive stars) given the large brightness contrast between the companion and the central star. Constraints on the low-mass end of the companions mass-function for massive stars are needed, however, for helping, for example, to distinguish among the various scenarios that describe the formation of massive stars. Aims. With the aim of obtaining a statistically significant constraint on the presence of low-mass companions beyond the typical detection limit of current surveys (Δmag ≲ 5 at ρ ≲ 1″), we initiated a survey of O and Wolf-Rayet stars in the Carina region using the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) coronagraphic instrument on the Very Large Telescope (VLT). In this, the first paper of the series, we aim to introduce the survey, to present the methodology and to demonstrate the capability of SPHERE for massive stars using the multiple system QZ Car. Methods. We obtained VLT-SPHERE snapshot observations in the IRDIFS_EXT mode, which combines the IFS and IRDIS sub-systems and simultaneously provides us four-dimensional (4D) data cubes in two different fields-of-view: 1.73″ × 1.73″ for IFS (39 spectral channels across the YJH bands) and 12″ × 12″ for IRDIS (two spectral channels across the K band). Angular- and spectral-differential imaging techniques as well as PSF-fitting were applied to detect and measure the relative flux of the companions in each spectral channel. The latter were then flux-calibrated using theoretical SED models of the central object and compared to a grid of ATLAS9 atmosphere model and (pre-)main-sequence evolutionary tracks, providing a first estimate of the physical properties of the detected companions. Results. Detection limits of 9 mag at ρ >  200 mas for IFS, and as faint as 13 mag at ρ > 1.​″8 for IRDIS (corresponding to sub-solar masses for potential companions), can be reached in snapshot observations of only a few minutes integration times, allowing us to detect 19 sources around the QZ Car system. All but two are reported here for the first time. With near-IR magnitude contrasts in the range of 4 to 7.5 mag, the three brightest sources (Ab, Ad, and E) are most likely to be physically bound. They have masses in the range of 2 to 12 M⊙ and are potentially co-eval with QZ Car central system. The remaining sources have flux contrast of 1.5 × 105 to 9.5 × 106 (ΔK ≈ 11 to 13 mag). Their presence can be explained by the local source density and they are, thus, likely to be chance alignments. If they were members of the Carina nebula, they would be sub-solar-mass pre-main sequence stars. Conclusions. Based on this proof of concept, we show that the VLT/SPHERE allows us to reach the sub-solar mass regime of the companion mass function. It paves the way for this type of observation with a large sample of massive stars to provide novel constraints on the multiplicity of massive stars in a region of the parameter space that has remained inaccessible so far.

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