386 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
Weather on Other Worlds. IV. H emission and photometric variability are not correlated in L0T8 dwarfs
Recent photometric studies have revealed that surface spots that produce flux
variations are present on virtually all L and T dwarfs. Their likely magnetic
or dusty nature has been a much-debated problem, the resolution to which has
been hindered by paucity of diagnostic multi-wavelength observations. To test
for a correlation between magnetic activity and photometric variability, we
searched for H emission among eight L3T2 ultra-cool dwarfs with
extensive previous photometric monitoring, some of which are known to be
variable at 3.6 m or 4.5 m. We detected H only in the
non-variable T2 dwarf 2MASS J125453930122474. The remaining seven objects do
not show H emission, even though six of them are known to vary
photometrically. Combining our results with those for 86 other L and T dwarfs
from the literature show that the detection rate of H emission is very
high (94) for spectral types between L0 and L3.5 and much smaller (20)
for spectral types L4, while the detection rate of photometric variability
is approximately constant (3055) from L0 to T8 dwarfs. We conclude
that chromospheric activity, as evidenced by H emission, and
large-amplitude photometric variability are not correlated. Consequently, dust
clouds are the dominant driver of the observed variability of ultra-cool dwarfs
at spectral types at least as early as L0.Comment: 12 pages, 4 figures, accepted for publication in Ap
Crystalline silicates as a probe of disk formation history
We present a new perspective on the crystallinity of dust in protoplanetary
disks. The dominant crystallization by thermal annealing happens in the very
early phases of disk formation and evolution. Both the disk properties and the
level of crystallinity are thereby directly linked to the properties of the
molecular cloud core from which the star+disk system was formed. We show that,
under the assumption of single star formation, rapidly rotating clouds produce
disks which, after the main infall phase (i.e. in the optically revealed class
II phase), are rather massive and have a high accretion rate but low
crystallinity. Slowly rotating clouds, on the other hand, produce less massive
disks with lower accretion rate, but high levels of crystallinity. Cloud
fragmentation and the formation of multiple stars complicates the problem and
necessitates further study. The underlying physics of the model is
insufficiently understood to provide the precise relationship between
crystallinity, disk mass and accretion rate. But the fact that with `standard'
input physics the model produces disks which, in comparison to observations,
appear to have either too high levels of crystallinity or too high disk masses,
demonstrates that the comparison of these models to observations can place
strong contraints on the disk physics. The question to ask is not why some
sources are so crystalline, but why some other sources have such a low level of
crystallinity.Comment: Accepted for publication in ApJ
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
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
Hubble Space Telescope astrometry of the closest brown dwarf binary system -- I. Overview and improved orbit
Located at ~2pc, the L7.5+T0.5 dwarfs system WISE J104915.57-531906.1
(Luhman16AB) is the third closest system known to Earth, making it a key
benchmark for detailed investigation of brown dwarf atmospheric properties,
thermal evolution, multiplicity, and planet-hosting frequency. In the first
study of this series -- based on a multi-cycle Hubble Space Telescope (HST)
program -- we provide an overview of the project and present improved estimates
of positions, proper motions, annual parallax, mass ratio, and the current best
assessment of the orbital parameters of the A-B pair. Our HST observations
encompass the apparent periastron of the binary at 220.5+/-0.2 mas at epoch
2016.402. Although our data seem to be inconsistent with recent ground-based
astrometric measurements, we also exclude the presence of third bodies down to
Neptune masses and periods longer than a year.Comment: 19 pages, 9 figures, 9 tables. Accepted for publication in MNRAS on
2017 May
The young stellar population of Lynds 1340. An infrared view
We present results of an infrared study of the molecular cloud Lynds 1340,
forming three groups of low and intermediate-mass stars. Our goals are to
identify and characterise the young stellar population of the cloud, study the
relationships between the properties of the cloud and the emergent stellar
groups, and integrate L1340 into the picture of the star-forming activity of
our Galactic environment. We selected candidate young stellar objects from the
Spitzer and WISE data bases using various published color criteria, and
classified them based on the slope of the spectral energy distribution. We
identified 170 Class II, 27 Flat SED, and Class 0/I sources. High angular
resolution near-infrared observations of the RNO 7 cluster, embedded in L1340,
revealed eight new young stars of near-infrared excess. The surface density
distribution of young stellar objects shows three groups, associated with the
three major molecular clumps of L1340, each consisting of less than 100
members, including both pre-main sequence stars and embedded protostars. New
Herbig--Haro objects were identified in the Spitzer images. Our results
demonstrate that L1340 is a prolific star-forming region of our Galactic
environment in which several specific properties of the intermediate-mass mode
of star formation can be studied in detail.Comment: 73 pages, 33 figures, 15 tables. Accepted for publication in ApJ
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