1,444 research outputs found
The Exoplanet Population Observation Simulator. I - The Inner Edges of Planetary Systems
The Kepler survey provides a statistical census of planetary systems out to
the habitable zone. Because most planets are non-transiting, orbital
architectures are best estimated using simulated observations of ensemble
populations. Here, we introduce EPOS, the Exoplanet Population Observation
Simulator, to estimate the prevalence and orbital architectures of multi-planet
systems based on the latest Kepler data release, DR25. We estimate that at
least 42% of sun-like stars have nearly coplanar planetary systems with 7 or
more exoplanets. The fraction of stars with at least one planet within 1 au
could be as high as 100% depending on assumptions about the distribution of
single transiting planets. We estimate an occurrence rate of planets in the
habitable zone around sun-like stars of eta_earth=36+-14%. The innermost
planets in multi-planet systems are clustered around an orbital period of 10
days (0.1 au), reminiscent of the protoplanetary disk inner edge or could be
explained by a planet trap at that location. Only a small fraction of planetary
systems have the innermost planet at long orbital periods, with fewer than ~8%
and ~3% having no planet interior to the orbit of Mercury and Venus,
respectively. These results reinforce the view that the solar system is not a
typical planetary system, but an outlier among the distribution of known
exoplanetary systems. We predict that at least half of the habitable zone
exoplanets are accompanied by (non-transiting) planets at shorter orbital
periods, hence knowledge of a close-in exoplanet could be used as a way to
optimize the search for Earth-size planets in the Habitable Zone with future
direct imaging missions.Comment: Accepted in AAS journals, code available on githu
The Onset of Planet Formation in Brown Dwarf Disks
The onset of planet formation in protoplanetary disks is marked by the growth
and crystallization of sub-micron-sized dust grains accompanied by dust
settling toward the disk mid-plane. Here we present infrared spectra of disks
around brown dwarfs and brown dwarf candidates. We show that all three
processes occur in such cool disks in a way similar or identical to that in
disks around low- and intermediate-mass stars. These results indicate that the
onset of planet formation extends to disks around brown dwarfs, suggesting that
planet formation is a robust process occurring in most young circumstellar
disks.Comment: Published in Science 2005, vol 310, 834; 3 pages in final format, 4
figures + 8 pages Supporting Online Material. For final typeset, see
http://www.sciencemag.org/cgi/content/abstract/310/5749/834?eto
Earths in Other Solar Systems N-body simulations: the Role of Orbital Damping in Reproducing the Kepler Planetary Systems
The population of exoplanetary systems detected by Kepler provides
opportunities to refine our understanding of planet formation. Unraveling the
conditions needed to produce the observed exoplanets will sallow us to make
informed predictions as to where habitable worlds exist within the galaxy. In
this paper, we examine using N-body simulations how the properties of planetary
systems are determined during the final stages of assembly. While accretion is
a chaotic process, trends in the ensemble properties of planetary systems
provide a memory of the initial distribution of solid mass around a star prior
to accretion. We also use EPOS, the Exoplanet Population Observation Simulator,
to account for detection biases and show that different accretion scenarios can
be distinguished from observations of the Kepler systems. We show that the
period of the innermost planet, the ratio of orbital periods of adjacent
planets, and masses of the planets are determined by the total mass and radial
distribution of embryos and planetesimals at the beginning of accretion. In
general, some amount of orbital damping, either via planetesimals or gas,
during accretion is needed to match the whole population of exoplanets.
Surprisingly, all simulated planetary systems have planets that are similar in
size, showing that the "peas in a pod" pattern can be consistent with both a
giant impact scenario and a planet migration scenario. The inclusion of
material at distances larger than what Kepler observes has a profound impact on
the observed planetary architectures, and thus on the formation and delivery of
volatiles to possible habitable worlds.Comment: Resubmitted to ApJ. Planet formation models available online at
http://eos-nexus.org/genesis-database
Cross-Sector Partnerships and the Co-creation of Dynamic Capabilities for Stakeholder Orientation
This is the final version of the article. Available from Springer Verlag via the DOI in this record.This paper explores the relationship between business experience in cross-sector partnerships (CSPs) and the co-creation of what we refer to as âdynamic capabilities for stakeholder orientation,â consisting of the four dimensions of (1) sensing, (2) interacting with, (3) learning from and (4) changing based on stakeholders. We argue that the co-creation of dynamic capabilities for stakeholder orientation is crucial for CSPs to create societal impact, as stakeholder-oriented organizations are more suited to deal with âwicked problems,â i.e., problems that are large, messy, and complex (Rittel and Webber, Policy Sciences 4:155â169, 1973; Waddock, Paper presented at the 3rd international symposium on cross sector social interactions, 2012). By means of a grounded theory approach of inductive research, we collected and interpreted data on four global agri-food companies which have heterogeneous experience in participating in CSPs. The results of this paper highlight that only companiesâ capability of interacting with stakeholders continually increases, while their capabilities of sensing, learning from, and changing based on stakeholders first increase and then decrease as companies gain more experience in CSP participation. To a large extent, this can be attributed to the development of corporate strategies on sustainability after a few years of CSP participation, which entails a shift from a reactive to a proactive attitude towards sustainability issues and which may decrease the need or motivation for stakeholder orientation. These findings open up important issues for discussion and for future research on the impact of CSPs in a context of wicked problems
The Exoplanet Population Observation Simulator. II -- Population Synthesis in the Era of Kepler
The collection of planetary system properties derived from large surveys such
as Kepler provides critical constraints on planet formation and evolution.
These constraints can only be applied to planet formation models, however, if
the observational biases and selection effects are properly accounted for. Here
we show how epos, the Exoplanet Population Observation Simulator, can be used
to constrain planet formation models by comparing the Bern planet population
synthesis models to the Kepler exoplanetary systems. We compile a series of
diagnostics, based on occurrence rates of different classes of planets and the
architectures of multi-planet systems, that can be used as benchmarks for
future and current modeling efforts. Overall, we find that a model with 100
seed planetary cores per protoplanetary disk provides a reasonable match to
most diagnostics. Based on these diagnostics we identify physical properties
and processes that would result in the Bern model more closely matching the
known planetary systems. These are: moving the planet trap at the inner disk
edge outward; increasing the formation efficiency of mini-Neptunes; and
reducing the fraction of stars that form observable planets. We conclude with
an outlook on the composition of planets in the habitable zone, and highlight
that the majority of simulated planets smaller than 1.7 Earth radii have
substantial hydrogen atmospheres.
The software used in this paper is available online for public scrutiny at
https://github.com/GijsMulders/eposComment: Accepted in Ap
Geographic analysis of multiple sensor data from the NASA/USGS earth resources program
Qualitative and quantitative analyses were made of multi-sensor data acquired during aircraft missions. While the principal analysis effort was concentrated on imagery taken over test sites in Southern California, data were also studied from records acquired on missions over test sites at Phoenix, Chicago, Asheville, and New Orleans. The objectives of the analyses were: (1) to determine the capabilities of ten remote sensors in identifying the elements of information necessary in conducting geographic investigations in land use analysis, urban problems, surface energy budget, and soil moisture; (2) to determine the feasibility of using these sensors for these purposes at orbital altitudes; and (3) to collate and analyze ground and air data previously collected and assemble it in a format useful in the accomplishment of cost effectiveness studies
The Photoevaporative Wind from the Disk of TW Hya
Photoevaporation driven by the central star is expected to be a ubiquitous
and important mechanism to disperse the circumstellar dust and gas from which
planets form. Here, we present a detailed study of the circumstellar disk
surrounding the nearby star TW Hya and provide observational constraints to its
photoevaporative wind. Our new high-resolution (R ~ 30,000) mid-infrared
spectroscopy in the [Ne II] 12.81 {\mu}m line confirms that this gas diagnostic
traces the unbound wind component within 10AU from the star. From the blueshift
and asymmetry in the line profile, we estimate that most (>80%) of the [Ne II]
emission arises from disk radii where the midplane is optically thick to the
redshifted outflowing gas, meaning beyond the 1 or 4AU dust rim inferred from
other observations. We re-analyze high-resolution (R ~ 48, 000) archival
optical spectra searching for additional transitions that may trace the
photoevaporative flow. Unlike the [Ne II] line, optical forbidden lines from
OI, SII, and MgI are centered at the stellar velocity and have symmetric
profiles. The only way these lines could trace the photoevaporative flow is if
they arise from a disk region physically distinct from that traced by the [Ne
II] line, specifically from within the optically thin dust gap. However, the
small (~10 km/s) FWHM of these lines suggest that most of the emitting gas
traced at optical wavelengths is bound to the system rather than unbound. We
discuss the implications of our results for a planet-induced versus a
photoevaporation-induced gap.Comment: Accepted for publication in Ap
Deserts and pile-ups in the distribution of exoplanets due to photoevaporative disc clearing
We present models of giant planet migration in evolving protoplanetary discs.
We show that disc clearing by EUV photoevaporation can have a strong effect on
the distribution of giant planet semi-major axes. During disc clearing planet
migration is slowed or accelerated in the region where photoevaporation opens a
gap in the disc, resulting in "deserts" where few giant planets are found and
corresponding "pile-ups" at smaller and larger radii. However, the precise
locations and sizes of these features are strong functions of the efficiency of
planetary accretion, and therefore also strongly dependent on planet mass. We
suggest that photoevaporative disc clearing may be responsible for the pile-up
of ~Jupiter-mass planets at ~1AU seen in exoplanet surveys, and show that
observations of the distribution of exoplanet semi-major axes can be used to
test models of both planet migration and disc clearing.Comment: 5 pages, 3 figures. Accepted for publication in MNRAS Letter
The Inner Rim of YSO Disks: Effects of dust grain evolution
Dust-grain growth and settling are the first steps towards planet formation.
An understanding of dust physics is therefore integral to a complete theory of
the planet formation process. In this paper, we explore the possibility of
using the dust evaporation front in YSO disks (`the inner rim') as a probe of
the dust physics operating in circumstellar disks. The geometry of the rim
depends sensitively on the composition and spatial distribution of dust. Using
radiative transfer and hydrostatic equilibrium calculations we demonstrate that
dust growth and settling can curve the evaporation front dramatically (from a
cylindrical radius of about 0.5 AU in the disk mid-plane to 1.2 AU in the disk
upper layers for an A0 star). We compute synthetic images and interferometric
visibilities for our representative rim models and show that the current
generation of near-IR long-baseline interferometers (VLTI, CHARA) can strongly
constrain the dust properties of circumstellar disks, shedding light on the
relatively poorly understood processes of grain growth, settling and turbulent
mixing.Comment: 26 pages, 9 figures. Accepted for publication in Ap
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