Silicon and Nickel Enrichment in Planet Host Stars: Observations and Implications for the Core Accretion Theory of Planet Formation

2006 ◽  
Vol 643 (1) ◽  
pp. 484-500 ◽  
Author(s):  
Sarah E. Robinson ◽  
Gregory Laughlin ◽  
Peter Bodenheimer ◽  
Debra Fischer
Keyword(s):  
Planet Formation ◽  
The Core ◽  
Core Accretion ◽  
Host Stars ◽  
Nickel Enrichment

scholarly journals Composition of massive giant planets

2010 ◽  
Vol 6 (S276) ◽  
pp. 95-100
Author(s):  
Ravit Helled ◽  
Peter Bodenheimer ◽  
Jack J. Lissauer
Keyword(s):  
Large Range ◽  
Giant Planet ◽  
Giant Planets ◽  
Heavy Elements ◽  
Formation Model ◽  
The Core ◽  
Accretion Model ◽  
Low Mass ◽  
Core Accretion ◽  
Host Stars

AbstractThe two current models for giant planet formation are core accretion and disk instability. We discuss the core masses and overall planetary enrichment in heavy elements predicted by the two formation models, and show that both models could lead to a large range of final compositions. For example, both can form giant planets with nearly stellar compositions. However, low-mass giant planets, enriched in heavy elements compared to their host stars, are more easily explained by the core accretion model. The final structure of the planets, i.e., the distribution of heavy elements, is not firmly constrained in either formation model.

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 Metallicity effect and planet mass function in pebble-based planet formation models

2018 ◽  
Vol 619 ◽  
pp. A174 ◽  
Author(s):  
N. Brügger ◽  
Y. Alibert ◽  
S. Ataiee ◽  
W. Benz
Keyword(s):  
Internal Structure ◽  
Planet Formation ◽  
Large Fraction ◽  
Mass Function ◽  
Planetary Atmosphere ◽  
Population Synthesis ◽  
Core Accretion ◽  
Mass Functions ◽  
Synthesis Approach ◽  
Gaseous Envelope

Context. One of the main scenarios of planet formation is the core accretion model where a massive core forms first and then accretes a gaseous envelope. This core forms by accreting solids, either planetesimals or pebbles. A key constraint in this model is that the accretion of gas must proceed before the dissipation of the gas disc. Classical planetesimal accretion scenarios predict that the time needed to form a giant planet’s core is much longer than the time needed to dissipate the disc. This difficulty led to the development of another accretion scenario, in which cores grow by accretion of pebbles, which are much smaller and thus more easily accreted, leading to more rapid formation. Aims. The aim of this paper is to compare our updated pebble-based planet formation model with observations, in particular the well-studied metallicity effect. Methods. We adopt the Bitsch et al. (2015a, A&A, 575, A28) disc model and the Bitsch et al. (2015b, A&A, 582, A112) pebble model and use a population synthesis approach to compare the formed planets with observations. Results. We find that keeping the same parameters as in Bitsch et al. (2015b, A&A, 582, A112) leads to no planet growth due to a computation mistake in the pebble flux (2018b). Indeed a large fraction of the heavy elements should be put into pebbles (Zpeb∕Ztot = 0.9) in order to form massive planets using this approach. The resulting mass functions show a huge amount of giants and a lack of Neptune-mass planets, which are abundant according to observations. To overcome this issue we include the computation of the internal structure for the planetary atmosphere in our model. This leads to the formation of Neptune-mass planets but no observable giants. Furthermore, reducing the opacity of the planetary envelope more closely matches observations. Conclusions. We conclude that modelling the internal structure for the planetary atmosphere is necessary to reproduce observations.

How many suns are in the sky? Multiplicity surveys of exoplanet host stars

2018 ◽  
Vol 14 (S345) ◽  
pp. 316-317 ◽  
Author(s):  
M. Mugrauer ◽  
C. Ginski ◽  
N. Vogt ◽  
R. Neuhäuser ◽  
C. Adam
Keyword(s):  
Milky Way ◽  
Planet Formation ◽  
High Contrast ◽  
Contrast Imaging ◽  
Direct Imaging ◽  
High Contrast Imaging ◽  
Multiple Stars ◽  
First Results ◽  
Formation And Evolution ◽  
Host Stars

AbstractIn order to determine the true impact of stellar multiplicity on the formation and evolution of planets, we initiated direct imaging surveys to search for (sub)stellar companions of exoplanet host stars on close orbits, as their gravitational impact on the planet bearing disk at first and on formed planets afterwards is expected to be maximal. According to theory these are the most challenging environments for planet formation and evolution but might occur quite frequently in the milky way, due to the large number of multiple stars within our galaxy. On this poster we showed results, obtained so far in the course of our AO and Lucky-imaging campaigns of exoplanet host stars, conducted with NACO/ESO-VLT for southern and with AstraLux/CAHA2.2m for northern targets, respectively. In addition, we introduced our new high contrast imaging survey with SPHERE/ESO-VLT to search for close companions of southern exoplanet host stars, and presented some first results.

scholarly journals Deuterium burning in objects forming via the core accretion scenario

2012 ◽  
Vol 547 ◽  
pp. A105 ◽  
Author(s):  
P. Mollière ◽  
C. Mordasini
Keyword(s):  
The Core ◽  
Core Accretion

scholarly journals Characterisation of exoplanet host stars: A window into planet formation

2017 ◽  
Vol 12 (S330) ◽  
pp. 369-376 ◽  
Author(s):  
Nuno C. Santos
Keyword(s):  
Planet Formation ◽  
The Sun ◽  
The Future ◽  
The Galaxy ◽  
Crucial Information ◽  
Formation And Evolution ◽  
Host Stars

AbstractThe detection of thousands of planets orbiting stars other than the Sun has shown that planets are common throughout the Galaxy. However, the diversity of systems found has also raised many questions regarding the process of planet formation and evolution. Interestingly, but perhaps not unexpectedly, crucial information to constraint the planet formation models comes from the analysis of the planet-host stars. In this talk I will review why it is so important to study and understand the stars when finding and characterising exoplanets. I will then present some of the most relevant star-planet relations found to date, and how they are helping us to understand planet formation and evolution. I will end with a presentation of the future steps in this field, including what Gaia will bring to help constrain the properties of planet-host stars, as well as to the star-planet connection.

Planet Formation

2018 ◽  
Author(s):  
Morris Podolak
Keyword(s):  
Planet Formation ◽  
Giant Planet ◽  
Terrestrial Planet ◽  
Interstellar Space ◽  
Normal Density ◽  
Main Question ◽  
Primitive Form ◽  
The Core ◽  
Gas Giant ◽  
Time Required

Modern observational techniques are still not powerful enough to directly view planet formation, and so it is necessary to rely on theory. However, observations do give two important clues to the formation process. The first is that the most primitive form of material in interstellar space exists as a dilute gas. Some of this gas is unstable against gravitational collapse, and begins to contract. Because the angular momentum of the gas is not zero, it contracts along the spin axis, but remains extended in the plane perpendicular to that axis, so that a disk is formed. Viscous processes in the disk carry most of the mass into the center where a star eventually forms. In the process, almost as a by-product, a planetary system is formed as well. The second clue is the time required. Young stars are indeed observed to have gas disks, composed mostly of hydrogen and helium, surrounding them, and observations tell us that these disks dissipate after about 5 to 10 million years. If planets like Jupiter and Saturn, which are very rich in hydrogen and helium, are to form in such a disk, they must accrete their gas within 5 million years of the time of the formation of the disk. Any formation scenario one proposes must produce Jupiter in that time, although the terrestrial planets, which don’t contain significant amounts of hydrogen and helium, could have taken longer to build. Modern estimates for the formation time of the Earth are of the order of 100 million years. To date there are two main candidate theories for producing Jupiter-like planets. The core accretion (CA) scenario supposes that any solid materials in the disk slowly coagulate into protoplanetary cores with progressively larger masses. If the core remains small enough it won’t have a strong enough gravitational force to attract gas from the surrounding disk, and the result will be a terrestrial planet. If the core grows large enough (of the order of ten Earth masses), and the disk has not yet dissipated, then the planetary embryo can attract gas from the surrounding disk and grow to be a gas giant. If the disk dissipates before the process is complete, the result will be an object like Uranus or Neptune, which has a small, but significant, complement of hydrogen and helium. The main question is whether the protoplanetary core can grow large enough before the disk dissipates. A second scenario is the disk instability (DI) scenario. This scenario posits that the disk itself is unstable and tends to develop regions of higher than normal density. Such regions collapse under their own gravity to form Jupiter-mass protoplanets. In the DI scenario a Jupiter-mass clump of gas can form—in several hundred years which will eventually contract into a gas giant planet. The difficulty here is to bring the disk to a condition where such instabilities will form. Now that we have discovered nearly 3000 planetary systems, there will be numerous examples against which to test these scenarios.

Planetesimal Capture by an Evolving Giant Gaseous Protoplanet

2012 ◽  
Vol 8 (S293) ◽  
pp. 263-269
Author(s):  
Morris Podolak ◽  
Nader Haghighipour
Keyword(s):  
Mass Distribution ◽  
Total Mass ◽  
Size Composition ◽  
Giant Planets ◽  
The Core ◽  
Last Stage ◽  
Core Accretion ◽  
Gaseous Envelope ◽  
Gas Drag ◽  
Probability Of Capture

AbstractBoth the core-accretion and disk-instability models suggest that at the last stage of the formation of a gas-giant, the core of this object is surrounded by an extended gaseous envelope. At this stage, while the envelope is contracting, planetesimals from the protoplanetary disk may be scattered into the protoplanets atmosphere and deposit some or all of their materials as they interact with the gas. We have carried out extensive simulations of approximately 104 planetesimals interacting with a envelope of a Jupiter-mass protoplanet including effects of gas drag, heating, and the effect of the protoplanets extended mass distribution. Simulations have been carried out for different radii and compositions of planetesimals so that all three processes occur to different degrees. We present the results of our simulations and discuss their implications for the enrichment of ices in giant planets. We also present statistics for the probability of capture (i.e. total mass-deposition) of planetesimals as a function of their size, composition, and closest approach to the center of the protoplanetary body.

The galactic habitable zone in elliptical galaxies

2012 ◽  
Vol 11 (3) ◽  
pp. 157-161 ◽  
Author(s):  
Falguni Suthar ◽  
Christopher P. McKay
Keyword(s):  
Milky Way ◽  
Planet Formation ◽  
Elliptical Galaxies ◽  
Extrasolar Planet ◽  
Habitable Zone ◽  
Milky Way Galaxy ◽  
Habitable Zones ◽  
Nearby Stars ◽  
Host Stars ◽  
Metallicity Distribution

AbstractThe concept of a Galactic Habitable Zone (GHZ) was introduced for the Milky Way galaxy a decade ago as an extension of the earlier concept of the Circumstellar Habitable Zone. In this work, we consider the extension of the concept of a GHZ to other types of galaxies by considering two elliptical galaxies as examples, M87 and M32. We argue that the defining feature of the GHZ is the probability of planet formation which has been assumed to depend on the metallicity. We have compared the metallicity distribution of nearby stars with the metallicity of stars with planets to document the correlation between metallicity and planet formation and to provide a comparison to other galaxies. Metallicity distribution, based on the [Fe/H] ratio to solar, of nearby stars peaks at [Fe/H]≈−0.2 dex, whereas the metallicity distribution of extrasolar planet host stars peaks at [Fe/H]≈+0.4 dex. We compare the metallicity distribution of extrasolar planet host stars with the metallicity distribution of the outer star clusters of M87 and M32. The metallicity distribution of stars in the outer regions of M87 peaks at [Fe/H]≈−0.2 dex and extends to [Fe/H]≈+0.4 dex, which seems favourable for planet formation. The metallicity distribution of stars in the outer regions of M32 peaks at [Fe/H]≈−0.2 dex and extends to a much lower [Fe/H]. Both elliptical galaxies met the criteria of a GHZ. In general, many galaxies should support habitable zones.

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