1,067 research outputs found
Extrasolar planet population synthesis IV. Correlations with disk metallicity, mass and lifetime
Context. This is the fourth paper in a series showing the results of planet
population synthesis calculations.
Aims. Our goal in this paper is to systematically study the effects of
important disk properties, namely disk metallicity, mass and lifetime on
fundamental planetary properties.
Methods. For a large number of protoplanetary disks we calculate a population
of planets with our core accretion formation model including planet migration
and disk evolution.
Results. We find a large number of correlations: Regarding the planetary
initial mass function, metallicity, disk mass and disk lifetime have different
roles: For high [Fe/H], giant planets are more frequent. For high disk masses,
giant planets are more massive. For long disk lifetimes, giant planets are both
more frequent and massive. At low metallicities, very massive giant planets
cannot form, but otherwise giant planet mass and metallicity are uncorrelated.
In contrast, planet masses and disk gas masses are correlated. The sweet spot
for giant planet formation is at 5 AU. In- and outside this distance, higher
planetesimals surface densities are necessary. Low metallicities can be
compensated by high disk masses, and vice versa, but not ad infinitum. At low
metallicities, giant planets only form outside the ice line, while at high
metallicities, giant planet formation occurs throughout the disk. The extent of
migration increases with disk mass and lifetime and usually decreases with
metallicity. No clear correlation of metallicity and the semimajor axis of
giant planets exists because in low [Fe/H] disks, planets start further out,
but migrate more, whereas for high [Fe/H] they start further in, but migrate
less. Close-in low mass planets have a lower mean metallicity than Hot
Jupiters.
Conclusions. The properties of protoplanetary disks are decisive for the
properties of planets, and leave many imprints.Comment: 23 pages, 16 figures. Accepted for A&
A Comparison of the Interiors of Jupiter and Saturn
Interior models of Jupiter and Saturn are calculated and compared in the
framework of the three-layer assumption, which rely on the perception that both
planets consist of three globally homogeneous regions: a dense core, a metallic
hydrogen envelope, and a molecular hydrogen envelope. Within this framework,
constraints on the core mass and abundance of heavy elements (i.e. elements
other than hydrogen and helium) are given by accounting for uncertainties on
the measured gravitational moments, surface temperature, surface helium
abundance, and on the inferred protosolar helium abundance, equations of state,
temperature profile and solid/differential interior rotation.Comment: 25 pages, 6 tables, 10 figures Planetary and Space Science, in pres
Hydrogen-Helium Mixtures at High Pressure
The properties of hydrogen-helium mixtures at high pressure are crucial to
address important questions about the interior of Giant planets e.g. whether
Jupiter has a rocky core and did it emerge via core accretion? Using path
integral Monte Carlo simulations, we study the properties of these mixtures as
a function of temperature, density and composition. The equation of state is
calculated and compared to chemical models. We probe the accuracy of the ideal
mixing approximation commonly used in such models. Finally, we discuss the
structure of the liquid in terms of pair correlation functions.Comment: Proceedings article of the 5th Conference on Cryocrystals and Quantum
Crystals in Wroclaw, Poland, submitted to J. Low. Temp. Phys. (2004
The HARPS search for southern extra-solar planets XXXV. Super-Earths around the M-dwarf neighbors Gl433 and Gl667C
M dwarfs have been found to often have super-Earth planets with short orbital
periods. Such stars are thus preferential targets in searches for rocky or
ocean planets in the solar neighbourhood. In a recent paper (Bonfils et al.
2011), we announced the discovery of respectively 1 and 2 low mass planets
around the M1.5V stars Gl433 and Gl667C. We found those planets with the HARPS
spectrograph on the ESO~3.6-m telescope at La Silla Observatory, from
observations obtained during the Guaranteed Time Observing program of that
instrument. We have obtained additional HARPS observations of those two stars,
for a total of respectively 67 and 179 Radial Velocity measurements for Gl433
and Gl667C, and present here an orbital analysis of those extended data sets
and our main conclusion about both planetary systems. One of the three planets,
Gl667Cc, has a mass of only M2.sin(i)~4.25 M_earth and orbits in the central
habitable zone of its host star. It receives just 10% less stellar energy from
Gl667C than the Earth receives from the Sun. However planet evolution in
habitable zone can be very different if the host star is a M dwarf or a
solar-like star, without necessarily questioning the presence of water. The two
other planets, Gl433b and Gl667Cb, both have M2.sin(i) of ~5.5 M_earth and
periods of ~7 days. The Radial Velocity measurements of both stars contain
longer time scale signals, which we fit as longer period Keplerians. For Gl433
that signal probably originates in a Magnetic Cycle, while a longer time span
will be needed to conclude for Gl667C. The metallicity of Gl433 is close to
solar, while Gl667C is metal poor with [Fe/H] ~ -0.6. This reinforces the
recent conclusion that the occurence of Super-Earth planets does not strongly
correlate with stellar metallicity.Comment: 14 pages, 8 figures, submitted to A&
The Deep Water Abundance on Jupiter: New Constraints from Thermochemical Kinetics and Diffusion Modeling
We have developed a one-dimensional thermochemical kinetics and diffusion
model for Jupiter's atmosphere that accurately describes the transition from
the thermochemical regime in the deep troposphere (where chemical equilibrium
is established) to the quenched regime in the upper troposphere (where chemical
equilibrium is disrupted). The model is used to calculate chemical abundances
of tropospheric constituents and to identify important chemical pathways for
CO-CH4 interconversion in hydrogen-dominated atmospheres. In particular, the
observed mole fraction and chemical behavior of CO is used to indirectly
constrain the Jovian water inventory. Our model can reproduce the observed
tropospheric CO abundance provided that the water mole fraction lies in the
range (0.25-6.0) x 10^-3 in Jupiter's deep troposphere, corresponding to an
enrichment of 0.3 to 7.3 times the protosolar abundance (assumed to be H2O/H2 =
9.61 x 10^-4). Our results suggest that Jupiter's oxygen enrichment is roughly
similar to that for carbon, nitrogen, and other heavy elements, and we conclude
that formation scenarios that require very large (>8 times solar) enrichments
in water can be ruled out. We also evaluate and refine the simple time-constant
arguments currently used to predict the quenched CO abundance on Jupiter, other
giant planets, and brown dwarfs.Comment: 42 pages, 7 figures, 4 tables, with note added in proof. Accepted for
publication in Icarus [in press
Planet Populations as a Function of Stellar Properties
Exoplanets around different types of stars provide a window into the diverse
environments in which planets form. This chapter describes the observed
relations between exoplanet populations and stellar properties and how they
connect to planet formation in protoplanetary disks. Giant planets occur more
frequently around more metal-rich and more massive stars. These findings
support the core accretion theory of planet formation, in which the cores of
giant planets form more rapidly in more metal-rich and more massive
protoplanetary disks. Smaller planets, those with sizes roughly between Earth
and Neptune, exhibit different scaling relations with stellar properties. These
planets are found around stars with a wide range of metallicities and occur
more frequently around lower mass stars. This indicates that planet formation
takes place in a wide range of environments, yet it is not clear why planets
form more efficiently around low mass stars. Going forward, exoplanet surveys
targeting M dwarfs will characterize the exoplanet population around the lowest
mass stars. In combination with ongoing stellar characterization, this will
help us understand the formation of planets in a large range of environments.Comment: Accepted for Publication in the Handbook of Exoplanet
Circumstellar disks and planets. Science cases for next-generation optical/infrared long-baseline interferometers
We present a review of the interplay between the evolution of circumstellar
disks and the formation of planets, both from the perspective of theoretical
models and dedicated observations. Based on this, we identify and discuss
fundamental questions concerning the formation and evolution of circumstellar
disks and planets which can be addressed in the near future with optical and
infrared long-baseline interferometers. Furthermore, the importance of
complementary observations with long-baseline (sub)millimeter interferometers
and high-sensitivity infrared observatories is outlined.Comment: 83 pages; Accepted for publication in "Astronomy and Astrophysics
Review"; The final publication is available at http://www.springerlink.co
A chemical survey of exoplanets with ARIEL
Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planetβs birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25β7.8 ΞΌm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10β100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed β using conservative estimates of mission performance and a full model of all significant noise sources in the measurement β using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL β in line with the stated mission objectives β will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.Peer reviewedFinal Published versio
Jet energy measurement with the ATLAS detector in proton-proton collisions at root s=7 TeV
The jet energy scale and its systematic uncertainty are determined for jets measured with the ATLAS detector at the LHC in proton-proton collision data at a centre-of-mass energy of βs = 7TeV corresponding to an integrated luminosity of 38 pb-1. Jets are reconstructed with the anti-kt algorithm with distance parameters R=0. 4 or R=0. 6. Jet energy and angle corrections are determined from Monte Carlo simulations to calibrate jets with transverse momenta pTβ₯20 GeV and pseudorapidities {pipe}Ξ·{pipe}<4. 5. The jet energy systematic uncertainty is estimated using the single isolated hadron response measured in situ and in test-beams, exploiting the transverse momentum balance between central and forward jets in events with dijet topologies and studying systematic variations in Monte Carlo simulations. The jet energy uncertainty is less than 2. 5 % in the central calorimeter region ({pipe}Ξ·{pipe}<0. 8) for jets with 60β€pT<800 GeV, and is maximally 14 % for pT<30 GeV in the most forward region 3. 2β€{pipe}Ξ·{pipe}<4. 5. The jet energy is validated for jet transverse momenta up to 1 TeV to the level of a few percent using several in situ techniques by comparing a well-known reference such as the recoiling photon pT, the sum of the transverse momenta of tracks associated to the jet, or a system of low-pT jets recoiling against a high-pT jet. More sophisticated jet calibration schemes are presented based on calorimeter cell energy density weighting or hadronic properties of jets, aiming for an improved jet energy resolution and a reduced flavour dependence of the jet response. The systematic uncertainty of the jet energy determined from a combination of in situ techniques is consistent with the one derived from single hadron response measurements over a wide kinematic range. The nominal corrections and uncertainties are derived for isolated jets in an inclusive sample of high-pT jets. Special cases such as event topologies with close-by jets, or selections of samples with an enhanced content of jets originating from light quarks, heavy quarks or gluons are also discussed and the corresponding uncertainties are determined. Β© 2013 CERN for the benefit of the ATLAS collaboration
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