scholarly journals Connecting substellar and stellar formation: the role of the host star’s metallicity

2019 ◽  
Vol 624 ◽  
pp. A94 ◽  
Author(s):  
J. Maldonado ◽  
E. Villaver ◽  
C. Eiroa ◽  
G. Micela
Keyword(s):  
Formation Mechanism ◽  
Formation Process ◽  
Planet Formation ◽  
Maximum Efficiency ◽  
Stellar Formation ◽  
Wide Range ◽  
Solar Type ◽  
Low Metallicity ◽  
Low Mass ◽  
Core Accretion

Context. Most of our current understanding of the planet formation mechanism is based on the planet metallicity correlation derived mostly from solar-type stars harbouring gas-giant planets. Aims. To achieve a more extensive grasp on the substellar formation process, we aim to analyse in terms of their metallicity a diverse sample of stars (in terms of mass and spectral type) covering the whole range of possible outcomes of the planet formation process (from planetesimals to brown dwarfs and low-mass binaries). Methods. Our methodology is based on the use of high-precision stellar parameters derived by our own group in previous works from high-resolution spectra by using the iron ionisation and equilibrium conditions. All values were derived in an homogeneous way, except for the M dwarfs where a methodology based on the use of pseudo equivalent widths of spectral features was used. Results. Our results show that as the mass of the substellar companion increases the metallicity of the host star tends to lower values. The same trend is maintained when analysing stars with low-mass stellar companions and a tendency towards a wide range of host star’s metallicity is found for systems with low-mass planets. We also confirm that more massive planets tend to orbit around more massive stars. Conclusions. The core-accretion formation mechanism for planet formation achieves its maximum efficiency for planets with masses in the range 0.2–2 MJup. Substellar objects with higher masses have higher probabilities of being formed as stars. Low-mass planets and planetesimals might be formed by core-accretion even around low-metallicity stars.

scholarly journals Constraining the entropy of formation from young transiting planet

2020 ◽  
Vol 498 (4) ◽  
pp. 5030-5040
Author(s):  
James E Owen
Keyword(s):  
Lower Bound ◽  
Mass Loss ◽  
Upper Bound ◽  
Early Evolution ◽  
Mass Measurements ◽  
Transiting Planets ◽  
Wide Range ◽  
Entropy Of Formation ◽  
Low Mass ◽  
Core Accretion

ABSTRACT Recently, K2 and TESS have discovered transiting planets with radii between ∼5 and 10 R⊕ around stars with ages <100 Myr. These young planets are likely to be the progenitors of the ubiquitous super-Earths/sub-Neptunes, which are well studied around stars with ages ≳1 Gyr. The formation and early evolution of super-Earths/sub-Neptunes are poorly understood. Various planetary origin scenarios predict a wide range of possible formation entropies. We show how the formation entropies of young (∼20–60 Myr), highly irradiated planets can be constrained if their mass, radius, and age are measured. This method works by determining how low-mass an H/He envelope a planet can retain against mass-loss, this lower bound on the H/He envelope mass can then be converted into an upper bound on the entropy. If planet mass measurements with errors ≲20 per cent can be achieved for the discovered young planets around DS Tuc A and V1298 Tau, then insights into their origins can be obtained. For these planets, higher measured planet masses would be consistent with the standard core-accretion theory. In contrast, lower planet masses (≲6–7 M⊕) would require a ‘boil-off’ phase during protoplanetary disc dispersal to explain.

scholarly journals Pebble accretion in self-gravitating protostellar discs

2019 ◽  
Vol 485 (4) ◽  
pp. 4465-4473
Author(s):  
D H Forgan
Keyword(s):  
Time Scales ◽  
Planet Formation ◽  
Density Ratio ◽  
Streaming Instability ◽  
Planetary Cores ◽  
Low Mass ◽  
Spiral Structures ◽  
Protostellar Discs ◽  
Core Accretion ◽  
Solid Bodies

Abstract Pebble accretion has become a popular component to core accretion models of planet formation, and is especially relevant to the formation of compact, resonant terrestrial planetary systems. Pebbles initially form in the inner protoplanetary disc, sweeping outwards in a radially expanding front, potentially forming planetesimals and planetary cores via migration and the streaming instability. This pebble front appears at early times, in what is typically assumed to be a low-mass disc. We argue this picture is in conflict with the reality of young circumstellar discs, which are massive and self-gravitating. We apply standard pebble accretion and streaming instability formulae to self-gravitating protostellar disc models. Fragments will open a gap in the pebble disc, but they will likely fail to open a gap in the gas, and continue rapid inward migration. If this does not strongly perturb the pebble disc, our results show that disc fragments will accrete pebbles efficiently. We find that in general the pebble-to-gas-density ratio fails to exceed 0.01, suggesting that the streaming instability will struggle to operate. It may be possible to activate the instability if 10 cm grains are available, and spiral structures can effectively concentrate them in regions of low gravito-turbulence. If this occurs, lunar mass cores might be assembled on time-scales of a few thousand years, but this is likely to be rare, and is far from proven. In any case, this work highlights the need for study of how self-gravitating protostellar discs define the distribution and properties of solid bodies, for future planet formation by core accretion.

scholarly journals Understanding exoplanet formation, structure and evolution in 2010

2010 ◽  
Vol 6 (S276) ◽  
pp. 171-180
Author(s):  
Gilles Chabrier ◽  
Jérémy Leconte ◽  
Isabelle Baraffe
Keyword(s):  
Planet Formation ◽  
Large Fraction ◽  
Brown Dwarfs ◽  
Short Review ◽  
Transiting Planets ◽  
The Core ◽  
Theoretical Mass ◽  
Low Mass ◽  
Core Accretion ◽  
Present Understanding

AbstractIn this short review, we summarize our present understanding (and non-understanding) of exoplanet formation, structure and evolution, in the light of the most recent discoveries. Recent observations of transiting massive brown dwarfs seem to remarkably confirm the predicted theoretical mass-radius relationship in this domain. This mass-radius relationship provides, in some cases, a powerful diagnostic to distinguish planets from brown dwarfs of same mass, as for instance for Hat-P-20b. If confirmed, this latter observation shows that planet formation takes place up to at least 8 Jupiter masses. Conversely, observations of brown dwarfs down to a few Jupiter masses in young, low-extinction clusters strongly suggests an overlapping mass domain between (massive) planets and (low-mass) brown dwarfs, i.e. no mass edge between these two distinct (in terms of formation mechanism) populations. At last, the large fraction of heavy material inferred for many of the transiting planets confirms the core-accretion scenario as been the dominant one for planet formation.

scholarly journals Giant planet formation — a theoretical timeline

2004 ◽  
Vol 202 ◽  
pp. 167-174 ◽  
Author(s):  
Günther Wuchterl
Keyword(s):  
Star Formation ◽  
Solar System ◽  
Formation Process ◽  
Planet Formation ◽  
Giant Planet ◽  
Circumstellar Disks ◽  
Giant Planets ◽  
Low Mass ◽  
Star Formation Regions ◽  
Observational Techniques

Low mass circumstellar disks are a result of the star formation process. The growth of dust and solid planets in such pre-planetary disks determines many properties of our solar system. Models of the Solar System giant planets indicate an enrichment of heavy elements and imply heavy element cores. Detailed models therefore describe giant planet formation as a consequence of the formation of solid planets that have grown sufficiently large to permanently bind gas from the protoplanetary nebula. The diversity of Solar System and extrasolar giant planets is explained by variations in the core growth rates caused by a coupling of the dynamics of planetesimals and the contraction of the massive envelopes they dive into, as well as by changes in the hydrodynamical accretion behavior of the envelopes resulting from differences in nebula density, temperature and orbital distance. Detailed formation models are able to determine observables as luminosities, radii and effective temperatures of young giant planets. Present observational techniques do now allow to probe star formation regions at ages covering all evolutionary stages of the giant planet formation process.

scholarly journals A giant exoplanet orbiting a very-low-mass star challenges planet formation models

Science ◽  
2019 ◽  
Vol 365 (6460) ◽  
pp. 1441-1445 ◽  
Author(s):  
J. C. Morales ◽  
A. J. Mustill ◽  
I. Ribas ◽  
M. B. Davies ◽  
A. Reiners ◽  
...  
Keyword(s):  
Near Infrared ◽  
Planet Formation ◽  
Giant Planet ◽  
Mass Star ◽  
Low Mass Stars ◽  
Migration Rates ◽  
Low Mass ◽  
And Migration ◽  
Core Accretion ◽  
Planet Accretion

Surveys have shown that super-Earth and Neptune-mass exoplanets are more frequent than gas giants around low-mass stars, as predicted by the core accretion theory of planet formation. We report the discovery of a giant planet around the very-low-mass star GJ 3512, as determined by optical and near-infrared radial-velocity observations. The planet has a minimum mass of 0.46 Jupiter masses, very high for such a small host star, and an eccentric 204-day orbit. Dynamical models show that the high eccentricity is most likely due to planet-planet interactions. We use simulations to demonstrate that the GJ 3512 planetary system challenges generally accepted formation theories, and that it puts constraints on the planet accretion and migration rates. Disk instabilities may be more efficient in forming planets than previously thought.

scholarly journals Planet formation around M dwarfs via disc instability

2020 ◽  
Vol 633 ◽  
pp. A116
Author(s):  
Anthony Mercer ◽  
Dimitris Stamatellos
Keyword(s):  
Planet Formation ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
Dwarf Stars ◽  
Low Mass ◽  
Protostellar Discs ◽  
Stellar Masses ◽  
M Dwarf Stars ◽  
Core Accretion ◽  
M Dwarf

Context. Around 30 per cent of the observed exoplanets that orbit M dwarf stars are gas giants that are more massive than Jupiter. These planets are prime candidates for formation by disc instability. Aims. We want to determine the conditions for disc fragmentation around M dwarfs and the properties of the planets that are formed by disc instability. Methods. We performed hydrodynamic simulations of M dwarf protostellar discs in order to determine the minimum disc mass required for gravitational fragmentation to occur. Different stellar masses, disc radii, and metallicities were considered. The mass of each protostellar disc was steadily increased until the disc fragmented and a protoplanet was formed. Results. We find that a disc-to-star mass ratio between ~0.3 and ~0.6 is required for fragmentation to happen. The minimum mass at which a disc fragment increases with the stellar mass and the disc size. Metallicity does not significantly affect the minimum disc fragmentation mass but high metallicity may suppress fragmentation. Protoplanets form quickly (within a few thousand years) at distances around ~50 AU from the host star, and they are initially very hot; their centres have temperatures similar to the ones expected at the accretion shocks around planets formed by core accretion (up to 12 000 K). The final properties of these planets (e.g. mass and orbital radius) are determined through long-term disc-planet or planet–planet interactions. Conclusions. Disc instability is a plausible way to form gas giant planets around M dwarfs provided that discs have at least 30% the mass of their host stars during the initial stages of their formation. Future observations of massive M dwarf discs or planets around very young M dwarfs are required to establish the importance of disc instability for planet formation around low-mass stars.

scholarly journals Isotopic Compositions of Ruthenium Predicted from the NuGrid Project

2022 ◽  
Vol 924 (2) ◽  
pp. 88
Author(s):  
Seonho Kim ◽  
Kwang Hyun Sung ◽  
Kyujin Kwak
Keyword(s):  
Stellar Wind ◽  
Asymptotic Giant Branch ◽  
Lower Mass ◽  
Low Mass Stars ◽  
Isotopic Compositions ◽  
Carbon Abundance ◽  
Wide Range ◽  
Low Metallicity ◽  
Low Mass

Abstract The isotopic compositions of ruthenium (Ru) are measured from presolar silicon carbide (SiC) grains. In a popular scenario, the presolar SiC grains formed in the outskirt of an asymptotic giant branch (AGB) star, left the star as a stellar wind, and joined the presolar molecular cloud from which the solar system formed. The Ru isotopes formed inside the star, moved to the stellar surface during the AGB phase, and were locked into the SiC grains. Following this scenario, we analyze the Nucleosynthesis Grid (NuGrid) data, which provide the abundances of the Ru isotopes in the stellar wind for a set of stars in a wide range of initial masses and metallicities. We apply the C > O (carbon abundance larger than the oxygen abundance) condition, which is commonly adopted for the condition of the SiC formation in the stellar wind. The NuGrid data confirm that SiC grains do not form in the winds of massive stars. The isotopic compositions of Ru in the winds of low-mass stars can explain the measurements. We find that lower-mass stars (1.65 M ☉ and 2 M ☉) with low metallicity (Z = 0.0001) can explain most of the measured isotopic compositions of Ru. We confirm that the abundance of 99 Ru inside the presolar grain includes the contribution from the in situ decay of 99 Tc. We also verify our conclusion by comparing the isotopic compositions of Ru integrated over all the pulses with those calculated at individual pulses.

scholarly journals Modelling Planet Formation by Capture-Theory Interactions

2004 ◽  
Vol 202 ◽  
pp. 244-246
Author(s):  
Michael M. Woolfson ◽  
Stephen Oxley
Keyword(s):  
Smoothed Particle Hydrodynamics ◽  
Planet Formation ◽  
Open Cluster ◽  
Brown Dwarfs ◽  
Low Mass Stars ◽  
Capture Theory ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Solar Type ◽  
Low Mass

Diffuse low-mass stars and brown dwarfs coexist with condensed solar-type stars in the embedded stage of a developing open cluster. It is shown by smoothed-particle-hydrodynamics modelling that interactions between stars and protostars leads to disruption of the protostar to form protoplanets that can then be captured by the star.

scholarly journals Nucleosynthetic yields of Z = 10−5 intermediate-mass stars

2020 ◽  
Vol 645 ◽  
pp. A10
Author(s):  
P. Gil-Pons ◽  
C. L. Doherty ◽  
J. Gutiérrez ◽  
S. W. Campbell ◽  
L. Siess ◽  
...  
Keyword(s):  
Galactic Halo ◽  
Intermediate Mass ◽  
Intermediate Mass Stars ◽  
Wide Range ◽  
Low Metallicity ◽  
Low Mass ◽  
Stellar Models ◽  
Massive Models ◽  
Uncertain Input ◽  
The Impact

Context. Observed abundances of extremely metal-poor stars in the Galactic halo hold clues for understanding the ancient universe. Interpreting these clues requires theoretical stellar models in a wide range of masses in the low-metallicity regime. The existing literature is relatively rich with extremely metal-poor massive and low-mass stellar models. However, relatively little information is available on the evolution of intermediate-mass stars of Z ≲ 10−5, and the impact of the uncertain input physics on the evolution and nucleosynthesis has not yet been systematically analysed. Aims. We aim to provide the nucleosynthetic yields of intermediate-mass Z = 10−5 stars between 3 and 7.5 M⊙, and quantify the effects of the uncertain wind rates. We expect these yields could eventually be used to assess the contribution to the chemical inventory of the early universe, and to help interpret abundances of selected C-enhanced extremely metal-poor (CEMP) stars. Methods. We compute and analyse the evolution of surface abundances and nucleosynthetic yields of Z = 10−5 intermediate-mass stars from their main sequence up to the late stages of their thermally pulsing (Super) AGB phase, with different prescriptions for stellar winds. We use the postprocessing code MONSOON to compute the nucleosynthesis based on the evolution structure obtained with the Monash-Mount Stromlo stellar evolution code MONSTAR. By comparing our models and others from the literature, we explore evolutionary and nucleosynthetic trends with wind prescriptions and with initial metallicity (in the very low-Z regime). We also compare our nucleosynthetic yields to observations of CEMP-s stars belonging to the Galactic halo. Results. The yields of intermediate-mass extremely metal-poor stars reflect the effects of very deep or corrosive second dredge-up (for the most massive models), superimposed with the combined signatures of hot-bottom burning and third dredge-up. Specifically, we confirm the reported trend that models with initial metallicity Zini ≲ 10−3 give positive yields of 12C, 15N, 16O, and 26Mg. The 20Ne, 21Ne, and 24Mg yields, which were reported to be negative at Zini ≳ 10−4, become positive for Z = 10−5. The results using two different prescriptions for mass-loss rates differ widely in terms of the duration of the thermally pulsing (Super) AGB phase, overall efficiency of the third dredge-up episode, and nucleosynthetic yields. We find that the most efficient of the standard wind rates frequently used in the literature seems to favour agreement between our yield results and observational data. Regardless of the wind prescription, all our models become N-enhanced EMP stars.

Study on the Modes of Operation of a Multi-Machine Installations with Mechanical Reduction

2019 ◽  
pp. 12-22
Author(s):  
A. M. Oleynikov ◽  
L. N. Kanov
Keyword(s):  
Mathematical Description ◽  
Reactive Power ◽  
Maximum Efficiency ◽  
Wind Flow ◽  
System Of Equations ◽  
Mechanical Equilibrium ◽  
Synchronous Generators ◽  
Electromagnetic Excitation ◽  
Number Of Generators ◽  
Wide Range

The paper gives the description of the original wind electrical installation with mechanical reduction in which the output of vertical axis wind turbine with rather low rotation speed over multiplicator is distributed to a certain number of generators. The number of acting generators is determined by the output of actual operating wind stream at each moment. According to this constructive scheme, it is possible to provide effective and with maximum efficiency installation work in a wide range of wind speeds and under any schedule issued to the consumer of electricity. As there are no any experience in using such complexes, mathematical description of its main elements is given, namely windwheels, generators with electromagnetic excitation of magnetic electrical type, then their interaction with windwheel, and also the results of mathematical modeling of work system regimes under using the offered system of equations. The basis for the mathematical description of the main elements of the installation – synchronous generators – are the system of equations of electrical and mechanical equilibrium in relative units in rotating coordinates without considering saturation of the magnetic circuit. The equation of mechanical equilibrium systems includes torque and brake windwheel electromagnetic moments of generators with taking into account the reduction coefficients and friction. In addition, we specify the alternator rotor dynamics resulting from continuous torque of windwheel fluctuations under the influence of unsteady wind flow and wind speed serving as the original variable is modeled by a set of sinusoids. Model simplification is achieved by equivalization of similar generators and by disregarding these transitions with a small time constant. Calculation the installation with synchronous generators of two types of small and medium capacity taking into account the operational factors allowed us to demonstrate the logic of interactions in the main elements of the reported complex in the process of converting wind flow into the generated active and reactive power. We have shown the possibility of stable system work under changeable wind stream condition by regulating of the plant blade angle and with simultaneous varying of generator number of different types. All these are in great interest for project organizations and power producers.

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