8 research outputs found
Disentangling 2:1 resonant radial velocity orbits from eccentric ones and a case study for HD 27894
In radial velocity observations, a pair of extrasolar planets near a 2:1
orbital resonance can be misinterpreted as a single eccentric planet, if data
are sparse and measurement precision insufficient to distinguish between these
models. We determine the fraction of alleged single-planet RV detected systems
for which a 2:1 resonant pair of planets is also a viable model and address the
question of how the models can be disentangled. By simulation we quantified the
mismatch arising from applying the wrong model. Model alternatives are
illustrated using the supposed single-planet system HD 27894 for which we also
study the dynamical stability of near-2:1 resonant solutions. From the data
scatter around the fitted single-planet Keplerians, we find that for of
the putative single-planet systems, a 2:1 resonant pair cannot be
excluded as a viable model, since the error due to the wrong model is smaller
than the scatter. For stars -probabilities can be used to reject
the Keplerian models with a confidence of for of the stars and
with for of the stars. For HD 27894 a considerable fit
improvement is obtained when adding a low-mass planet near half the orbital
period of the known Jovian planet. Dynamical analysis demonstrates that this
system is stable when both planets are initially placed on circular orbits. For
fully Keplerian orbits a stable system is only obtained if the eccentricity of
the inner planet is constrained to . A large part of the allegedly RV
detected single-planet systems should be scrutinized in order to determine the
fraction of systems containing near-2:1 resonant pairs of planets. Knowing the
abundance of such systems will allow us to revise the eccentricity distribution
for extrasolar planets and provide direct constraints for planetary system
formation.Comment: 12 pages, 8 figures, one of them composed by two files, accepted by
A&A, citations may appear in a non-standard way (double brackets) due to
reformatting needs. Abstract slightly adjuste
Can 1D radiative equilibrium models of faculae be used for calculating contamination of transmission spectra?
The reliable characterization of planetary atmospheres with transmission
spectroscopy requires realistic modeling of stellar magnetic features, since
features that are attributable to an exoplanet atmosphere could instead stem
from the host star's magnetic activity. Current retrieval algorithms for
analysing transmission spectra rely on intensity contrasts of magnetic features
from 1D radiative-convective models. However, magnetic features, especially
faculae, are not fully captured by such simplified models. Here we investigate
how well such 1D models can reproduce 3D facular contrasts, taking a G2V star
as an example. We employ the well established radiative magnetohydrodynamic
code MURaM to obtain three-dimensional simulations of the magneto-convection
and photosphere harboring a local small-scale-dynamo. Simulations without
additional vertical magnetic fields are taken to describe the quiet solar
regions, while simulations with initially 100 G, 200 G and 300 G vertical
magnetic fields are used to represent different magnetic activity levels.
Subsequently, the spectra emergent from the MURaM cubes are calculated with the
MPS-ATLAS radiative transfer code. We find that the wavelength dependence of
facular contrast from 1D radiative-convective models cannot reproduce facular
contrasts obtained from 3D modeling. This has far reaching consequences for
exoplanet characterization using transmission spectroscopy, where accurate
knowledge of the host star is essential for unbiased inferences of the
planetary atmospheric properties.Comment: 7 pages, 2 figures, submitted to APJ
A roadmap to the efficient and robust characterization of temperate terrestrial planet atmospheres with JWST
Ultra-cool dwarf stars are abundant, long-lived, and uniquely suited to
enable the atmospheric study of transiting terrestrial companions with JWST.
Amongst them, the most prominent is the M8.5V star TRAPPIST-1 and its seven
planets, which have been the favored targets of eight JWST Cycle 1 programs.
While Cycle 1 observations have started to yield preliminary insights into the
planets, they have also revealed that their atmospheric exploration requires a
better understanding of their host star. Here, we propose a roadmap to
characterize the TRAPPIST-1 system -- and others like it -- in an efficient and
robust manner. We notably recommend that -- although more challenging to
schedule -- multi-transit windows be prioritized to constrain stellar
heterogeneities and gather up to 2 more transits per JWST hour spent.
We conclude that in such systems planets cannot be studied in isolation by
small programs, thus large-scale community-supported programs should be
supported to enable the efficient and robust exploration of terrestrial
exoplanets in the JWST era
Recommended from our members
The effect of stellar contamination on low-resolution transmission spectroscopy: needs identified by NASA’s Exoplanet Exploration Program Study Analysis Group 21
Study Analysis Group 21 (SAG21) of NASA’s Exoplanet Exploration Program Analysis Group was organized to study the effect of stellar contamination on space-based transmission spectroscopy, a method for studying exoplanetary atmospheres by measuring the wavelength-dependent radius of a planet as it transits its star. Transmission spectroscopy relies on a precise understanding of the spectrum of the star being occulted. However, stars are not homogeneous, constant light sources but have temporally evolving photospheres and chromospheres with inhomogeneities like spots, faculae, plages, granules, and flares. This SAG brought together an interdisciplinary team of more than 100 scientists, with observers and theorists from the heliophysics, stellar astrophysics, planetary science, and exoplanetary atmosphere research communities, to study the current research needs that can be addressed in this context to make the most of transit studies from current NASA facilities like Hubble Space Telescope and JWST. The analysis produced 14 findings, which fall into three science themes encompassing (i) how the Sun is used as our best laboratory to calibrate our understanding of stellar heterogeneities (‘The Sun as the Stellar Benchmark’), (ii) how stars other than the Sun extend our knowledge of heterogeneities (‘Surface Heterogeneities of Other Stars’), and (iii) how to incorporate information gathered for the Sun and other stars into transit studies (‘Mapping Stellar Knowledge to Transit Studies’). In this invited review, we largely reproduce the final report of SAG21 as a contribution to the peer-reviewed literature
Accurate Short-Characteristics Radiative Transfer in A Numerical Tool for Astrophysical RESearch (ANTARES)
We aim to improve the accuracy of radiative energy transport in three-dimensional radiation hydrodynamical simulations in ANTARES (A Numerical Tool for Astrophysical RESearch). We implement in the ANTARES short-characteristics numerical schemes a modification of the Bezier interpolant solver. This method yields a smoother surface structure in simulations of solar convection and reduces the artifacts appearing due to the limited number of rays along which the integration is done. Reducing such artifacts leads to increased stability of the code. We show that our new implementation achieves a better agreement of the temperature structure and its gradient with a semi-empirical model derived from observations, as well as of synthetic spectral-line profiles with the observed solar spectrum
A roadmap to the efficient and robust characterization of temperate terrestrial planet atmospheres with JWST
Ultra-cool dwarf stars are abundant, long-lived, and uniquely suited to enable the atmospheric study of transiting terrestrial companions with JWST. Amongst them, the most prominent is the M8.5V star TRAPPIST-1 and its seven planets, which have been the favored targets of eight JWST Cycle 1 programs. While Cycle 1 observations have started to yield preliminary insights into the planets, they have also revealed that their atmospheric exploration requires a better understanding of their host star. Here, we propose a roadmap to characterize the TRAPPIST-1 system -- and others like it -- in an efficient and robust manner. We notably recommend that -- although more challenging to schedule -- multi-transit windows be prioritized to constrain stellar heterogeneities and gather up to 2 more transits per JWST hour spent. We conclude that in such systems planets cannot be studied in isolation by small programs, thus large-scale community-supported programs should be supported to enable the efficient and robust exploration of terrestrial exoplanets in the JWST era