115 research outputs found
Structure and evolution of protoplanetary disks
We present here a few thoughts on how high-angular resolution observations can give clues to some properties of protoplanetary disks that are fundamental to theories of planet formation. High-angular resolution infrared spectroscopy, either with a large single mirror telescope, or by using infrared interferometry, allows us to probe the abundance of thermally processed dust in the disk as a function of distance to the star. We show that this radial abundance profile can give information about the early evolution of the protoplanetary disk as well as about the nature of the turbulence. Since turbulence is one of the main ingredients in theories of planet formation, this latter result is particularly important. We also show that Nature itself provides an interesting way to perform high-angular resolution observations with intermediate-angular resolution telescopes: if a disk has a (nearly) edge-on orientation and is located in a low-density ambient dusty medium, the disk casts a shadow into this medium, as it blocks the starlight in equatorial direction. We argue how these shadows can be used to characterize the dust in the disk
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
Hidden Worlds: Dynamical Architecture Predictions of Undetected Planets in Multi-planet Systems and Applications to TESS Systems
Multi-planet systems produce a wealth of information for exoplanet science,
but our understanding of planetary architectures is incomplete. Probing these
systems further will provide insight into orbital architectures and formation
pathways. Here we present a model to predict previously undetected planets in
these systems via population statistics. The model considers both transiting
and non-transiting planets, and can test the addition of more than one planet.
Our tests show the model's orbital period predictions are robust to
perturbations in system architectures on the order of a few percent, much
larger than current uncertainties. Applying it to the multi-planet systems from
TESS provides a prioritized list of targets, based on predicted transit depth
and probability, for archival searches and for guiding ground-based follow-up
observations hunting for hidden planets.Comment: 24 pages, 14 figures, 3 tables, accepted to Astronomical Journa
High Contrast L' Band Adaptive Optics Imaging to Detect Extrasolar Planets
We are carrying out a survey to search for giant extrasolar planets around
nearby, moderate-age stars in the mid-infrared L' and M bands (3.8 and 4.8
microns, respectively), using the Clio camera with the adaptive optics system
on the MMT telescope. To date we have observed 7 stars, of a total 50 planned,
including GJ 450 (distance about 8.55pc, age about 1 billion years, no real
companions detected), which we use as our example here. We report the methods
we use to obtain extremely high contrast imaging in L', and the performance we
have obtained. We find that the rotation of a celestial object over time with
respect to a telescope tracking it with an altazimuth mount can be a powerful
tool for subtracting telescope-related stellar halo artifacts and detecting
planets near bright stars. We have carried out a thorough Monte Carlo
simulation demonstrating our ability to detect planets as small as 6 Jupiter
masses around GJ 450. The division of a science data set into two independent
parts, with companions required to be detected on both in order to be
recognized as real, played a crucial role in detecting companions in this
simulation. We mention also our discovery of a previously unknown faint stellar
companion to another of our survey targets, HD 133002. Followup is needed to
confirm this as a physical companion, and to determine its physical properties.Comment: 8 pages, 4 figure
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