79 research outputs found
The Demographics and Atmospheres of Giant Planets with the ELTs
Gas giants are the most readily detectable exoplanets but fundamental
questions about their system architectures, formation, migration, and
atmospheres have been unanswerable with the current generation of ground- and
space-based facilities. The dominant techniques to detect and characterize
giant planets radial velocities, transits, direct imaging, microlensing,
and astrometry are each isolated to a limited range of planet masses,
separations, ages, and temperatures. These windows into the arrangement and
physical properties of giant planets have spawned new questions about the
timescale and location of their assembly; the distributions of planet mass and
orbital separation at young and old ages; the composition and structure of
their atmospheres; and their orbital and rotational angular momentum
architectures. The ELTs will address these questions by building bridges
between these islands of mass, orbital distance, and age. The angular
resolution, collecting area, all-sky coverage, and novel instrumentation suite
of these facilities are needed to provide a complete map of the orbits and
atmospheric evolution of gas giant planets (0.310 ) across
space (0.1100 AU) and time (1 Myr to 10 Gyr). This white paper highlights
the scientific potential of the GMT and TMT to address these outstanding
questions, with a particular focus on the role of direct imaging and
spectroscopy of large samples of giant planets that will soon be made available
with .Comment: White paper for the Astro2020 decadal surve
ELemental abundances of Planets and brown dwarfs Imaged around Stars (ELPIS): I. Potential Metal Enrichment of the Exoplanet AF Lep b and a Novel Retrieval Approach for Cloudy Self-luminous Atmospheres
AF Lep A+b is a remarkable planetary system hosting a gas-giant planet that
has the lowest dynamical mass among directly imaged exoplanets. We present an
in-depth analysis of the atmospheric composition of the star and planet to
probe the planet's formation pathway. Based on new high-resolution spectroscopy
of AF Lep A, we measure a uniform set of stellar parameters and elemental
abundances (e.g., [Fe/H] = dex). The planet's dynamical mass
( M) and orbit are also refined using published
radial velocities, relative astrometry, and absolute astrometry. We use
petitRADTRANS to perform chemically-consistent atmospheric retrievals for AF
Lep b. The radiative-convective equilibrium temperature profiles are
incorporated as parameterized priors on the planet's thermal structure, leading
to a robust characterization for cloudy self-luminous atmospheres. This novel
approach is enabled by constraining the temperature-pressure profiles via the
temperature gradient , a departure from previous studies
that solely modeled the temperature. Through multiple retrievals performed on
different portions of the m spectrophotometry, along with
different priors on the planet's mass and radius, we infer that AF Lep b likely
possesses a metal-enriched atmosphere ([Fe/H] dex). AF Lep b's
potential metal enrichment may be due to planetesimal accretion, giant impacts,
and/or core erosion. The first process coincides with the debris disk in the
system, which could be dynamically excited by AF Lep b and lead to planetesimal
bombardment. Our analysis also determines K,
dex, and the presence of silicate clouds and
dis-equilibrium chemistry in the atmosphere. Straddling the L/T transition, AF
Lep b is thus far the coldest exoplanet with suggested evidence of silicate
clouds.Comment: AJ, in press. Main text: Pages 1-32, Figures 1-15, Tables 1-6. All
figures and tables after References belong to the Appendix (Pages 32-58,
Figures 16-20, Table 7). For supplementary materials, please refer to the
Zenodo repository https://doi.org/10.5281/zenodo.826746
Masses, Radii, and Cloud Properties of the HR 8799 Planets
The near-infrared colors of the planets directly imaged around the A star HR
8799 are much redder than most field brown dwarfs of the same effective
temperature. Previous theoretical studies of these objects have concluded that
the atmospheres of planets b, c, and d are unusually cloudy or have unusual
cloud properties. Some studies have also found that the inferred radii of some
or all of the planets disagree with expectations of standard giant planet
evolution models. Here we compare the available data to the predictions of our
own set of atmospheric and evolution models that have been extensively tested
against observations of field L and T dwarfs, including the reddest L dwarfs.
Unlike some previous studies we require mutually consistent choices for
effective temperature, gravity, cloud properties, and planetary radius. This
procedure thus yields plausible values for the masses, effective temperatures,
and cloud properties of all three planets. We find that the cloud properties of
the HR 8799 planets are not unusual but rather follow previously recognized
trends, including a gravity dependence on the temperature of the L to T
spectral transition--some reasons for which we discuss. We find the inferred
mass of planet b is highly sensitive to whether or not we include the H and K
band spectrum in our analysis. Solutions for planets c and d are consistent
with the generally accepted constraints on the age of the primary star and
orbital dynamics. We also confirm that, like in L and T dwarfs and solar system
giant planets, non-equilibrium chemistry driven by atmospheric mixing is also
important for these objects. Given the preponderance of data suggesting that
the L to T spectral type transition is gravity dependent, we present an
exploratory evolution calculation that accounts for this effect. Finally we
recompute the the bolometric luminosity of all three planets.Comment: 52 pages, 12 figures, Astrophysical Journal, in press. v2 features
minor editorial updates and correction
The geography of biodiversity change in marine and terrestrial assemblages
This work was supported by funding to the sChange working group through sDiv, the synthesis center of iDiv, the German Centre for Integrative Biodiversity Research Halle-Jena-Leipzig, funded by the German Research Foundation (FZT 118). S.A.B., H.B., J.M.C., J.H., and M.W. were supported by the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig. S.R.S. was supported by U.S. National Science Foundation grant 1400911. LHA was supported by Fundação para a Ciência e Tecnologia, Portugal (POPH/FSE SFRH/BD/90469/2012), and by the Jane and Aatos Erkko Foundation. M.D. was supported by a Leverhulme Trust Fellowship. A.E.M., F.M., and M.D. were supported by ERC AdG BioTIME 250189 and PoC BioCHANGE 727440. A.G. is supported by the Liber Ero Chair in Biodiversity Conservation.Human activities are fundamentally altering biodiversity. Projections of declines at the global scale are contrasted by highly variable trends at local scales, suggesting that biodiversity change may be spatially structured. Here, we examined spatial variation in species richness and composition change using more than 50,000 biodiversity time series from 239 studies and found clear geographic variation in biodiversity change. Rapid compositional change is prevalent, with marine biomes exceeding and terrestrial biomes trailing the overall trend. Assemblage richness is not changing on average, although locations exhibiting increasing and decreasing trends of up to about 20% per year were found in some marine studies. At local scales, widespread compositional reorganization is most often decoupled from richness change, and biodiversity change is strongest and most variable in the oceans.PostprintPostprintPeer reviewe
The Demographics and Atmospheres of Giant Planets with the ELTs
Gas giants are the most readily detectable exoplanets but fundamental questions about their system architectures, formation, migration, and atmospheres have been unanswerable with the current generation of ground- and space-based facilities. The dominant techniques to detect and characterize giant planets − radial velocities, transits, direct imaging, microlensing, and astrometry − are each isolated to a limited range of planet masses, separations, ages, and temperatures. These windows into the arrangement and physical properties of giant planets have spawned new questions about the timescale and location of their assembly; the distributions of planet mass and orbital separation at young and old ages; the composition and structure of their atmospheres; and their orbital and rotational angular momentum architectures. The ELTs will address these questions by building bridges between these islands of mass, orbital distance, and age. The angular resolution, collecting area, all-sky coverage, and novel instrumentation suite of these facilities are needed to provide a complete map of the orbits and atmospheric evolution of gas giant planets (0.3−10 M_(Jup)) across space (0.1−100 AU) and time (1 Myr to 10 Gyr). This white paper highlights the scientific potential of the GMT and TMT to address these outstanding questions, with a particular focus on the role of direct imaging and spectroscopy of large samples of giant planets that will soon be made available with Gaia
<i>TESS</i> Spots a Compact System of Super-Earths around the Naked-eye Star HR 858
Transiting Exoplanet Survey Satellite (TESS) observations have revealed a compact multiplanet system around the sixth-magnitude star HR 858 (TIC 178155732, TOI 396), located 32 pc away. Three planets, each about twice the size of Earth, transit this slightly evolved, late F-type star, which is also a member of a visual binary. Two of the planets may be in mean motion resonance. We analyze the TESS observations, using novel methods to model and remove instrumental systematic errors, and combine these data with follow-up observations taken from a suite of ground-based telescopes to characterize the planetary system. The HR 858 planets are enticing targets for precise radial velocity observations, secondary eclipse spectroscopy, and measurements of the Rossiter–McLaughlin effect
A planet within the debris disk around the pre-main-sequence star AU Microscopii
AU Microscopii (AU Mic) is the second closest pre main sequence star, at a
distance of 9.79 parsecs and with an age of 22 million years. AU Mic possesses
a relatively rare and spatially resolved3 edge-on debris disk extending from
about 35 to 210 astronomical units from the star, and with clumps exhibiting
non-Keplerian motion. Detection of newly formed planets around such a star is
challenged by the presence of spots, plage, flares and other manifestations of
magnetic activity on the star. Here we report observations of a planet
transiting AU Mic. The transiting planet, AU Mic b, has an orbital period of
8.46 days, an orbital distance of 0.07 astronomical units, a radius of 0.4
Jupiter radii, and a mass of less than 0.18 Jupiter masses at 3 sigma
confidence. Our observations of a planet co-existing with a debris disk offer
the opportunity to test the predictions of current models of planet formation
and evolution.Comment: Nature, published June 24th [author spelling name fix
The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems II: A 1 to 20 Micron Spectrum of the Planetary-Mass Companion VHS 1256-1257 b
We present the highest fidelity spectrum to date of a planetary-mass object.
VHS 1256 b is a 20 M widely separated (8\arcsec, a =
150 au), young, planetary-mass companion that shares photometric colors and
spectroscopic features with the directly imaged exoplanets HR 8799 c, d, and e.
As an L-to-T transition object, VHS 1256 b exists along the region of the
color-magnitude diagram where substellar atmospheres transition from cloudy to
clear. We observed VHS 1256~b with \textit{JWST}'s NIRSpec IFU and MIRI MRS
modes for coverage from 1 m to 20 m at resolutions of 1,000 -
3,700. Water, methane, carbon monoxide, carbon dioxide, sodium, and potassium
are observed in several portions of the \textit{JWST} spectrum based on
comparisons from template brown dwarf spectra, molecular opacities, and
atmospheric models. The spectral shape of VHS 1256 b is influenced by
disequilibrium chemistry and clouds. We directly detect silicate clouds, the
first such detection reported for a planetary-mass companion.Comment: Accepted ApJL Iterations of spectra reduced by the ERS team are
hosted at this link:
https://github.com/bemiles/JWST_VHS1256b_Reduction/tree/main/reduced_spectr
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