200 research outputs found
Characterization of exoplanets from their formation III: The statistics of planetary luminosities
This paper continues a series in which we predict the main observable
characteristics of exoplanets based on their formation. In Paper I we described
our global planet formation and evolution model. In Paper II we studied the
planetary mass-radius relationship. Here we present an extensive study of the
statistics of planetary luminosities during both formation and evolution. Our
results can be compared with individual directly imaged (proto)planets as well
as statistical results from surveys. We calculated three synthetic planet
populations assuming different efficiencies of the accretional heating by gas
and planetesimals. We describe the temporal evolution of the planetary
mass-luminosity relation. We study the shock and internal luminosity during
formation. We predict a statistical version of the post-formation mass versus
entropy "tuning fork" diagram. We find high nominal post-formation luminosities
for hot and cold gas accretion. Individual formation histories can still lead
to a factor of a few spread in the post-formation luminosity at a given mass.
However, if the gas and planetesimal accretional heating is unknown, the
post-formation luminosity may exhibit a spread of as much as 2-3 orders of
magnitude at a fixed mass covering cold, warm, and hot states. As a key result
we predict a flat log-luminosity distribution for giant planets, and a steep
increase towards lower luminosities due to the higher occurrence rate of
low-mass planets. Future surveys may detect this upturn. During formation an
estimate of the planet mass may be possible for cold gas accretion if the gas
accretion rate can be estimated. Due to the "core-mass effect" planets that
underwent cold gas accretion can still have high post-formation entropies. Once
the number of directly imaged exoplanets with known ages and luminosities
increases, the observed distributions may be compared with our predictions.Comment: 44 pages, 26 figures (journal format). A&A in print. Language
correction only relative to V
Global Models of Planet Formation and Evolution
Despite the increase in observational data on exoplanets, the processes that
lead to the formation of planets are still not well understood. But thanks to
the high number of known exoplanets, it is now possible to look at them as a
population that puts statistical constraints on theoretical models. A method
that uses these constraints is planetary population synthesis. Its key element
is a global model of planet formation and evolution that directly predicts
observable planetary properties based on properties of the natal protoplanetary
disk. To do so, global models build on many specialized models that address one
specific physical process. We thoroughly review the physics of the sub-models
included in global formation models. The sub-models can be classified as models
describing the protoplanetary disk (gas and solids), the (proto)planet (solid
core, gaseous envelope, and atmosphere), and finally the interactions
(migration and N-body interaction). We compare the approaches in different
global models and identify physical processes that require improved
descriptions in future. We then address important results of population
synthesis like the planetary mass function or the mass-radius relation. In
these results, the global effects of physical mechanisms occurring during
planet formation and evolution become apparent, and specialized models
describing them can be put to the observational test. Due to their nature as
meta models, global models depend on the development of the field of planet
formation theory as a whole. Because there are important uncertainties in this
theory, it is likely that global models will in future undergo significant
modifications. Despite this, they can already now yield many testable
predictions. With future global models addressing the geophysical
characteristics, it should eventually become possible to make predictions about
the habitability of planets.Comment: 30 pages, 16 figures. Accepted for publication in the International
Journal of Astrobiology (Cambridge University Press
petitRADTRANS: a Python radiative transfer package for exoplanet characterization and retrieval
We present the easy-to-use, publicly available, Python package petitRADTRANS,
built for the spectral characterization of exoplanet atmospheres. The code is
fast, accurate, and versatile; it can calculate both transmission and emission
spectra within a few seconds at low resolution ( = 1000;
correlated-k method) and high resolution (;
line-by-line method), using only a few lines of input instruction. The somewhat
slower correlated-k method is used at low resolution because it is more
accurate than methods such as opacity sampling. Clouds can be included and
treated using wavelength-dependent power law opacities, or by using optical
constants of real condensates, specifying either the cloud particle size, or
the atmospheric mixing and particle settling strength. Opacities of amorphous
or crystalline, spherical or irregularly-shaped cloud particles are available.
The line opacity database spans temperatures between 80 and 3000 K, allowing to
model fluxes of objects such as terrestrial planets, super-Earths, Neptunes, or
hot Jupiters, if their atmospheres are hydrogen-dominated. Higher temperature
points and species will be added in the future, allowing to also model the
class of ultra hot-Jupiters, with equilibrium temperatures K. Radiative transfer results were tested by cross-verifying the low- and
high-resolution implementation of petitRADTRANS, and benchmarked with the
petitCODE, which itself is also benchmarked to the ATMO and Exo-REM codes. We
successfully carried out test retrievals of synthetic JWST emission and
transmission spectra (for the hot Jupiter TrES-4b, which has a of
1800 K). The code is publicly available at
http://gitlab.com/mauricemolli/petitRADTRANS, and its documentation can be
found at https://petitradtrans.readthedocs.io.Comment: 17 pages, 7 figures, published in A&
Detecting isotopologues in exoplanet atmospheres using ground-based high-dispersion spectroscopy
Cross-correlation is a well-tested method for exoplanet characterization. A
new, potentially powerful application is the measurement of atmospheric isotope
ratios. In particular D/H can give unique insights into a planet's formation
and evolution. Here we aim to study the detectability of isotopologues in the
high-dispersion spectra of exoplanets, to identify the optimal wavelengths
ranges, and to predict the required observational efforts with current and
future ground-based instruments. High-dispersion (R=10) thermal emission
(and sometimes reflection) spectra were simulated by self-consistently modeling
exoplanet atmospheres over a wide range of temperatures. These were
synthetically observed with telescopes equivalent to the VLT or ELT, and
analyzed with cross-correlation, resulting in S/N predictions for the detection
of CO, HDO, and CHD. For the best observable exoplanets, CO
is in range of current telescopes. It will be most favorably detected at 2.4
microns, just longward of the spectral range probed by several high-dispersion
observations in the literature. CHD can best be seen at 4.7 microns, using
40m-class telescopes for planets with below 600 K. In this case,
sky emission is often dominating the noise. HDO can be targeted at 3.7 microns,
where sky emission is smaller. 40m-class telescopes may detect it in planets
with below 900~K, potentially even 8m-class telescopes in the
case of methane quenching. If Proxima Cen b is water-rich, HDO could be
detected with the ELT in 1 night in reflected light. Isotopologues will soon
belong to the exoplanet characterisation tools. Measuring D/H, and ratios of
other isotopes, could be a prime science case for the METIS instrument on the
ELT, especially for nearby rocky and ice giant planets. This can give unique
insights in their history of ice enrichment and atmospheric evaporation.Comment: 22 pages, 12 figures, updated version, accepted for publication in A
&
Evolutionary models of cold and low-mass planets: Cooling curves, magnitudes, and detectability
Future instruments like NIRCam and MIRI on JWST or METIS at the ELT will be
able to image exoplanets that are too faint for current direct imaging
instruments. Evolutionary models predicting the planetary intrinsic luminosity
as a function of time have traditionally concentrated on gas-dominated giant
planets. We extend these cooling curves to Saturnian and Neptunian planets. We
simulate the cooling of isolated core-dominated and gas giant planets with
masses of 5 Earthmasses to 2 Jupitermasses. The luminosity includes the
contribution from the cooling and contraction of the core and of the H/He
envelope, as well as radiogenic decay. For the atmosphere we use grey,
AMES-Cond, petitCODE, and HELIOS models. We consider solar and non-solar
metallicities as well as cloud-free and cloudy atmospheres. The most important
initial conditions, namely the core-to-envelope ratio and the initial
luminosity are taken from planet formation simulations based on the core
accretion paradigm. We first compare our cooling curves for Uranus, Neptune,
Jupiter, Saturn, GJ 436b, and a 5 Earthmass-planet with a 1% H/He envelope with
other evolutionary models. We then present the temporal evolution of planets
with masses between 5 Earthmasses and 2 Jupitermasses in terms of their
luminosity, effective temperature, radius, and entropy. We discuss the impact
of different post formation entropies. For the different atmosphere types and
initial conditions magnitudes in various filter bands between 0.9 and 30
micrometer wavelength are provided. Using black body fluxes and non-grey
spectra, we estimate the detectability of such planets with JWST. It is found
that a 20 (100) Earthmass-planet can be detected with JWST in the background
limit up to an age of about 10 (100) Myr with NIRCam and MIRI, respectively.Comment: Language corrected version and improved arrangements of figures,
online data at:
http://www.space.unibe.ch/research/research_groups/planets_in_time/numerical_data/index_eng.htm
The 12CO/13CO isotopologue ratio of a young, isolated brown dwarf: possibly distinct formation pathways of super-Jupiters and brown dwarfs
Stars and planetary system
Search for gas from the disintegrating rocky exoplanet K2-22b
[Abridged] Aims. We searched for circumplanetary sodium and ionized calcium
gas around the disintegrating rocky exoplanet K2-22 b to constrain its gas-loss
and sublimation processes.
Methods. We observed four transits of K2-22 b with X-shooter on ESO's Very
Large Telescope to obtain time-series of intermediate-resolution (R
11400) spectra. Our analysis focused on the two sodium D lines (588.995 nm and
589.592 nm) and the Ca triplet (849.802 nm, 854.209 nm and 866.214 nm).
Planet-related absorption is searched for in the velocity rest frame of the
planet, which changes from 66 kms during the transit.
Results. Since K2-22 b exhibits highly variable transit depths, we analyzed
the individual nights and their average. By injecting signals we reached
5 upper-limits on the individual nights that ranged from 11% - 13% and
1.7% - 2.0% for the tail's sodium and ionized calcium absorption, respectively.
Night 1 was contaminated by its companion star so we considered weighted
averages with and without Night 1 and quote conservative 5 limits
without Night 1 of 9% and 1.4%, respectively. Assuming their mass fractions to
be similar to those in the Earth's crust, these limits correspond to scenarios
in which 0.04% and 35% of the transiting dust is sublimated and observed as
absorbing gas. However, this assumes the gas to be co-moving with the planet.
We show that for the high irradiation environment of K2-22 b, sodium and
ionized calcium could be quickly accelerated to 100s of km s due to
radiation pressure and entrainment by the stellar wind, making them much more
difficult to detect. No evidence for such possibly broad and blue-shifted
signals are seen in our data.
Conclusions. Future observations aimed at observing circumplanetary gas
should take into account the possible broad and blue-shifted velocity field of
atomic and ionized species.Comment: Accepted on 7 June 2019 for publication in Astronomy and Astrophysics
(A&A). 17 pages, 11 figures. Submission updated after language editing by A&
Atmospheric retrievals for LIFE and other future space missions: the importance of mitigating systematic effects
Atmospheric retrieval studies are essential to determine the science
requirements for future generation missions, such as the Large Interferometer
for Exoplanets (LIFE). The use of heterogeneous absorption cross-sections might
be the cause of systematic effects in retrievals, which could bias a correct
characterization of the atmosphere. In this contribution we quantified the
impact of differences in line list provenance, broadening coefficients, and
line wing cut-offs in the retrieval of an Earth twin exoplanet orbiting a
Sun-like star at 10 pc from the observer, as it would be observed with LIFE. We
ran four different retrievals on the same input spectrum, by varying the
opacity tables that the Bayesian retrieval framework was allowed to use. We
found that the systematics introduced by the opacity tables could bias the
correct estimation of the atmospheric pressure at the surface level, as well as
an accurate retrieval of the abundance of some species in the atmosphere (such
as CO and NO). We argue that differences in the line wing cut-off might
be the major source of errors. We highlight the need for more laboratory and
modeling efforts, as well as inter-model comparisons of the main radiative
transfer models and Bayesian retrieval frameworks. This is especially relevant
in the context of LIFE and future generation missions, to identify issues and
critical points for the community to jointly work together to prepare for the
analysis of the upcoming observations.Comment: 24 pages, 12 figures. Proceedings SPIE Volume 12180, Space Telescopes
and Instrumentation 2022: Optical, Infrared, and Millimeter Wave; 121803L
(2022
MIRACLES: atmospheric characterization of directly imaged planets and substellar companions at 4-5 m. II. Constraints on the mass and radius of the enshrouded planet PDS 70 b
The circumstellar disk of PDS 70 hosts two forming planets, which are
actively accreting gas from their environment. In this work, we report the
first detection of PDS 70 b in the Br and filters with VLT/NACO, a
tentative detection of PDS 70 c in Br, and a reanalysis of archival
NACO and SPHERE and imaging data. The near side of the disk is
also resolved with the Br and filters, indicating that scattered
light is non-negligible at these wavelengths. The spectral energy distribution
of PDS 70 b is well described by blackbody emission, for which we constrain the
photospheric temperature and photospheric radius to K and . The relatively low bolometric
luminosity, , in combination with the large
radius, is not compatible with standard structure models of fully convective
objects. With predictions from such models, and adopting a recent estimate of
the accretion rate, we derive a planetary mass and radius in the range of
and
, independently of the age and post-formation entropy of the
planet. The blackbody emission, large photospheric radius, and the discrepancy
between the photospheric and planetary radius suggests that infrared
observations probe an extended, dusty environment around the planet, which
obscures the view on its molecular composition. Finally, we derive a rough
upper limit on the temperature and radius of potential excess emission from a
circumplanetary disk, K and
, but we do find weak evidence that the current data favors a
model with a single blackbody component.Comment: 19 pages, 7 figures, accepted for publication in A&
ELT-METIS: estimating the constraining power of high-resolution exoplanet spectra with Bayesian inference
Stars and planetary system
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