135 research outputs found
RadVel: The Radial Velocity Modeling Toolkit
RadVel is an open source Python package for modeling Keplerian orbits in
radial velocity (RV) time series. RadVel provides a convenient framework to fit
RVs using maximum a posteriori optimization and to compute robust confidence
intervals by sampling the posterior probability density via Markov Chain Monte
Carlo (MCMC). RadVel allows users to float or fix parameters, impose priors,
and perform Bayesian model comparison. We have implemented realtime MCMC
convergence tests to ensure adequate sampling of the posterior. RadVel can
output a number of publication-quality plots and tables. Users may interface
with RadVel through a convenient command-line interface or directly from
Python. The code is object-oriented and thus naturally extensible. We encourage
contributions from the community. Documentation is available at
http://radvel.readthedocs.io.Comment: prepared for resubmission to PAS
Population-level Eccentricity Distributions of Imaged Exoplanets and Brown Dwarf Companions: Dynamical Evidence for Distinct Formation Channels
The orbital eccentricities of directly imaged exoplanets and brown dwarf companions provide clues about their formation and dynamical histories. We combine new high-contrast imaging observations of substellar companions obtained primarily with Keck/NIRC2 together with astrometry from the literature to test for differences in the population-level eccentricity distributions of 27 long-period giant planets and brown dwarf companions between 5 and 100 au using hierarchical Bayesian modeling. Orbit fits are performed in a uniform manner for companions with short orbital arcs; this typically results in broad constraints for individual eccentricity distributions, but together as an ensemble, these systems provide valuable insight into their collective underlying orbital patterns. The shape of the eccentricity distribution function for our full sample of substellar companions is approximately flat from e = 0–1. When subdivided by companion mass and mass ratio, the underlying distributions for giant planets and brown dwarfs show significant differences. Low mass ratio companions preferentially have low eccentricities, similar to the orbital properties of warm Jupiters found with radial velocities and transits. We interpret this as evidence for in situ formation on largely undisturbed orbits within massive extended disks. Brown dwarf companions exhibit a broad peak at e ≈ 0.6–0.9 with evidence for a dependence on orbital period. This closely resembles the orbital properties and period-eccentricity trends of wide (1–200 au) stellar binaries, suggesting that brown dwarfs in this separation range predominantly form in a similar fashion. We also report evidence that the "eccentricity dichotomy" observed at small separations extends to planets on wide orbits: the mean eccentricity for the multi-planet system HR 8799 is lower than for systems with single planets. In the future, larger samples and continued astrometric orbit monitoring will help establish whether these eccentricity distributions correlate with other parameters such as stellar host mass, multiplicity, and age
Population-level Eccentricity Distributions of Imaged Exoplanets and Brown Dwarf Companions: Dynamical Evidence for Distinct Formation Channels
The orbital eccentricities of directly imaged exoplanets and brown dwarf companions provide clues about their formation and dynamical histories. We combine new high-contrast imaging observations of substellar companions obtained primarily with Keck/NIRC2 together with astrometry from the literature to test for differences in the population-level eccentricity distributions of 27 long-period giant planets and brown dwarf companions between 5 and 100 au using hierarchical Bayesian modeling. Orbit fits are performed in a uniform manner for companions with short orbital arcs; this typically results in broad constraints for individual eccentricity distributions, but together as an ensemble, these systems provide valuable insight into their collective underlying orbital patterns. The shape of the eccentricity distribution function for our full sample of substellar companions is approximately flat from e = 0–1. When subdivided by companion mass and mass ratio, the underlying distributions for giant planets and brown dwarfs show significant differences. Low mass ratio companions preferentially have low eccentricities, similar to the orbital properties of warm Jupiters found with radial velocities and transits. We interpret this as evidence for in situ formation on largely undisturbed orbits within massive extended disks. Brown dwarf companions exhibit a broad peak at e ≈ 0.6–0.9 with evidence for a dependence on orbital period. This closely resembles the orbital properties and period-eccentricity trends of wide (1–200 au) stellar binaries, suggesting that brown dwarfs in this separation range predominantly form in a similar fashion. We also report evidence that the "eccentricity dichotomy" observed at small separations extends to planets on wide orbits: the mean eccentricity for the multi-planet system HR 8799 is lower than for systems with single planets. In the future, larger samples and continued astrometric orbit monitoring will help establish whether these eccentricity distributions correlate with other parameters such as stellar host mass, multiplicity, and age
Obliquity Constraints on an Extrasolar Planetary-Mass Companion
We place the first constraints on the obliquity of a planetary-mass companion outside of the solar system. Our target is the directly imaged system 2MASS J01225093–2439505 (2M0122), which consists of a 120 Myr 0.4 M⊙ star hosting a 12–27 M_J companion at 50 au. We constrain all three of the system's angular-momentum vectors: how the companion spin axis, the stellar spin axis, and the orbit normal are inclined relative to our line of sight. To accomplish this, we measure projected rotation rates (v sin i) for both the star and the companion using new near-infrared high-resolution spectra with NIRSPEC at Keck Observatory. We combine these with a new stellar photometric rotation period from TESS and a published companion rotation period from Hubble Space Telescope to obtain spin-axis inclinations for both objects. We also fitted multiple epochs of astrometry, including a new observation with NIRC2/Keck, to measure 2M0122b's orbital inclination. The three line-of-sight inclinations place limits on the true de-projected companion obliquity and stellar obliquity. We find that while the stellar obliquity marginally prefers alignment, the companion obliquity tentatively favors misalignment. We evaluate possible origin scenarios. While collisions, secular spin–orbit resonances, and Kozai–Lidov oscillations are unlikely, formation by gravitational instability in a gravito-turbulent disk—the scenario favored for brown dwarf companions to stars—appears promising
Dynamical orbital evolution scenarios of the wide-orbit eccentric planet HR 5183b
The recently-discovered giant exoplanet HR5183b exists on a wide,
highly-eccentric orbit (\,au, ). Its host star possesses a common
proper-motion companion which is likely on a bound orbit. In this paper, we
explore scenarios for the excitation of the eccentricity of the planet in
binary systems such as this, considering planet-planet scattering, Lidov-Kozai
cycles from the binary acting on a single-planet system, or Lidov-Kozai cycles
acting on a two-planet system that also undergoes scattering. Planet-planet
scattering, in the absence of a binary companion, has a probability
of pumping eccentricities to the observed values in our simulations, depending
on the relative masses of the two planets. Lidov-Kozai cycles from the binary
acting on an initially circular orbit can excite eccentricities to the observed
value, but require very specific orbital configurations for the binary and
overall there is a low probability of catching the orbit at the high observed
high eccentricity (). The best case is provided by planet-planet
scattering in the presence of a binary companion: here, the scattering provides
the surviving planet with an initial eccentricity boost that is subsequently
further increased by Kozai cycles from the binary. We find a success rate of
for currently observing in this set-up. The single-planet
plus binary and two-planet plus binary cases are potentially distinguishable if
the mutual inclination of the binary and the planet can be measured, as the
latter permits a broader range of mutual inclinations. The combination of
scattering and Lidov-Kozai forcing may also be at work in other wide-orbit
eccentric giant planets, which have a high rate of stellar binary companions.Comment: Accepted to MNRAS. A simple board game based on the paper may be
found at http://filestore.astro.lu.se/research/alex/HR5183b.pd
As chapeuzinhos vermelhos: uma análise histórica e intertextual da representação do feminino na literatura infantil
Investiga narrativas pertencentes ao gênero Contos de Fadas através da análise de textos. De que forma temáticas do contexto social são representadas pelos autores em suas obras e qual papel desse conteúdo na formação identitária do público infantojuvenil dentro do contexto escolar. Para isso será analisada a personagem Chapeuzinho Vermelho através das obras de Perrault, Grimm, Dahl e Pennart
Signs of Similar Stellar Obliquity Distributions for Hot and Warm Jupiters Orbiting Cool Stars
Transiting giant planets provide a natural opportunity to examine stellar
obliquities, which offer clues about the origin and dynamical histories of
close-in planets. Hot Jupiters orbiting Sun-like stars show a tendency for
obliquity alignment, which suggests that obliquities are rarely excited or that
tidal realignment is common. However, the stellar obliquity distribution is
less clear for giant planets at wider separations where realignment mechanisms
are not expected to operate. In this work, we uniformly derive line-of-sight
inclinations for 47 cool stars ( 6200 K) harboring
transiting hot and warm giant planets by combining rotation periods, stellar
radii, and measurements. Among the systems that show signs of
spin-orbit misalignment in our sample, three are identified as being misaligned
here for the first time. Of particular interest are Kepler-1654, one of the
longest-period (1047 d; 2.0 AU) giant planets in a misaligned system, and
Kepler-30, a multi-planet misaligned system. By comparing the reconstructed
underlying inclination distributions, we find that the inferred minimum
misalignment distributions of hot Jupiters spanning = 3-20 (
0.01-0.1 AU) and warm Jupiters spanning = 20-400 ( 0.1-1.9
AU) are in good agreement. With 90 confidence, at least 24 of
warm Jupiters and 14 of hot Jupiters around cool stars are
misaligned by at least 10. Most stars harboring warm Jupiters are
therefore consistent with spin-orbit alignment. The similarity of hot and warm
Jupiter misalignment rates suggests that either the occasional misalignments
are primordial and originate in misaligned disks, or the same underlying
processes that create misaligned hot Jupiters also lead to misaligned warm
Jupiters.Comment: AJ, accepte
No difference in orbital parameters of RV-detected giant planets between 0.1 and 5 au in single vs multi-stellar systems
Our Keck/NIRC2 imaging survey searches for stellar companions around 144
systems with radial velocity (RV) detected giant planets to determine whether
stellar binaries influence the planets' orbital parameters. This survey, the
largest of its kind to date, finds eight confirmed binary systems and three
confirmed triple systems. These include three new multi-stellar systems (HD
30856, HD 86081, and HD 207832) and three multi-stellar systems with newly
confirmed common proper motion (HD 43691, HD 116029, and HD 164509). We combine
these systems with seven RV planet-hosting multi-stellar systems from the
literature in order to test for differences in the properties of planets with
semimajor axes ranging between 0.1-5 au in single vs multi-stellar systems. We
find no evidence that the presence or absence of stellar companions alters the
distribution of planet properties in these systems. Although the observed
stellar companions might influence the orbits of more distant planetary
companions in these systems, our RV observations currently provide only weak
constraints on the masses and orbital properties of planets beyond 5 au. In
order to aid future efforts to characterize long period RV companions in these
systems, we publish our contrast curves for all 144 targets. Using four years
of astrometry for six hierarchical triple star systems hosting giant planets,
we fit the orbits of the stellar companions in order to characterize the
orbital architecture in these systems. We find that the orbital plane of the
secondary and tertiary companions are inconsistent with an edge-on orbit in
four out of six cases.Comment: 34 pages, 10 figures, 16 tables, including 4 tables in machine
readable format and 7 tables with online supplemental dat
The Impact of Bayesian Hyperpriors on the Population-Level Eccentricity Distribution of Imaged Planets
Orbital eccentricities directly trace the formation mechanisms and dynamical
histories of substellar companions. Here, we study the effect of hyperpriors on
the population-level eccentricity distributions inferred for the sample of
directly imaged substellar companions (brown dwarfs and cold Jupiters) from
hierarchical Bayesian modeling (HBM). We find that the choice of hyperprior can
have a significant impact on the population-level eccentricity distribution
inferred for imaged companions, an effect that becomes more important as the
sample size and orbital coverage decrease to values that mirror the existing
sample. We reanalyse the current observational sample of imaged giant planets
in the 5-100 AU range from Bowler et al. (2020) and find that the underlying
eccentricity distribution implied by the imaged planet sample is broadly
consistent with the eccentricity distribution for close-in exoplanets detected
using radial velocities. Furthermore, our analysis supports the conclusion from
that study that long-period giant planets and brown dwarf eccentricity
distributions differ by showing that it is robust to the choice of hyperprior.
We release our HBM and forward modeling code in an open-source Python package,
ePop!, and make it freely available to the community.Comment: 18 pages, 11 figures. Accepted for publication in The Astronomical
Journa
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