It has recently been shown that stellar clustering plays an important role in shaping the properties of planetary systems. We investigate how the multiplicity distributions and orbital periods of planetary systems depend on the 6D phase space density of stars surrounding planet host systems. We find that stars in high stellar phase space density environments (overdensities) have a factor 1.6 - 2.0 excess in the number of single planet systems compared to stars in low stellar phase space density environments (the field). The multiplicity distribution of planets around field stars is much flatter (i.e. there is a greater fraction of multi-planet systems) than in overdensities. This result is primarily driven by the combined facts that: (i) `hot Jupiters' (HJs) are almost exclusively found in overdensities; (ii) HJs are predominantly observed to be single-planet systems. Nevertheless, we find that the difference in multiplicity is even more pronounced when only considering planets in the Kepler sample, which contains few HJs. This suggests that the Kepler dichotomy -- an apparent excess of systems with a single transiting planet -- plausibly arises from environmental perturbations. In overdensities, the orbital periods of single-planet systems are smaller than orbital periods of multiple-planet systems. As this difference is more pronounced in overdensities, the mechanism responsible for this effect may be enhanced by stellar clustering. Taken together, the pronounced dependence of planetary multiplicity and orbital period distributions on stellar clustering provides a potentially powerful tool to diagnose the impact of environment on the formation and evolution of planetary systems.
In recent years a correlation between mass accretion rates onto new-born stars and their proto-planetary disc masses was detected in nearby young star-forming regions. Although such a correlation can be interpreted as due to viscous-diffusion processes in the disc, highly-accreting sources with low disc masses in more evolved regions remain puzzling. In this paper, we hypothesise that the presence of a stellar companion truncating the disc can explain these outliers. Firstly, we searched the literature for information on stellar multiplicity in Lupus, Chamaeleon~I and Upper Sco, finding that r…
The Kepler mission has discovered thousands of exoplanets around various stars with different spectral types (M, K, G, and F) and thus different masses and effective temperatures. Previous studies have shown that the planet occurrence rate, in terms of average number of planets per star, drops with increasing stellar effective temperature (Teff). In this paper, with the final Kepler Data Release (DR25) catalog, we revisit the relation between stellar effective temperature (as well as mass) and planet occurrence, but in terms of the fraction of stars with planets and the number of planets per p…
Planet formation is generally described in terms of a system containing the host star and a protoplanetary disc, of which the internal properties (e.g. mass and metallicity) determine the properties of the resulting planetary system. However, (proto)planetary systems are predicted and observed to be affected by the spatially-clustered stellar formation environment, either through dynamical star-star interactions or external photoevaporation by nearby massive stars. It is challenging to quantify how the architecture of planetary systems is affected by these environmental processes, because stel…
Multiplicity of young isolated planetary mass objects in Taurus and Upper Scorpius
Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS（波尔多大学天体物理实验室）；Institut universitaire de France (IUF)（法国高等研究院）；Univ. Grenoble Alpes, CNRS, IPAG（格勒诺布尔阿尔卑斯大学）；Astronomy Department, University of California Berkeley（加州大学伯克利分校天文系）；Space Telescope Science Institute（太空望远镜科学研究所）；Departamento de Inteligencia Artificial, Universidad Nacional de Educación a Distancia (UNED)（西班牙国立远程教育大学人工智能系）；Universidad Nacional Autónoma de México, Instituto de Radioastronomía y Astrofísica（墨西哥国立自治大学无线电天文学与天体物理学研究所）；Centro de Astrobiología (CAB), CSIC-INTA（西班牙国家航空航天技术研究所/西班牙国家科学研究委员会天体生物学中心）；Department of Astronomy, Gr（天文学系）
Planets orbiting intermediate and low-mass stars are in jeopardy as their stellar hosts evolve to white dwarfs (WDs) because the dynamics of the planetary system changes due to the increase of the planet:star mass ratio after stellar mass-loss. In order to understand how the planet multiplicity affects the dynamical stability of post-main sequence (MS) systems, we perform thousands of N-body simulations involving planetary multiplicity as the variable and with a controlled physical and orbital parameter space: equal-mass planets; the same orbital spacing between adjacent planet's pairs; and or…
An HST survey of photometry and multiplicity of brown dwarfs and planetary-mass objects in the field of Taurus
Institute for Astronomy, University of Edinburgh（爱丁堡大学天文研究所）；Centre for Exoplanet Science, University of Edinburgh（爱丁堡大学系外行星科学中心）；Leiden Observatory, Leiden University（莱顿大学莱登天文台）；Department of Astronomy, School of Science, Westlake University（西湖大学理学院天文学系）；Institute of Natural Sciences, Westlake Institute for Advanced Study（西湖高等研究院自然科学院）；Department of Astronomy, Indiana University（印第安纳大学天文学系）；Département de Physique and Observatoire du Mont-Mégantic, Université de Montréal（蒙特利尔大学物理系与蒙梅加尼克天文台）
The orbit eccentricities of the Solar System planets are unusually low compared to the average of known exoplanetary systems. A power law correlation has previously been found between the multiplicity of a planetary system and the orbital eccentricities of its components, for systems with multiplicities above two. In this study we investigate the correlation for an expanded data sample, by focusing on planetary systems as units (unlike previous studies that have focused on individual planets). Our full data sample contains 1171 exoplanets, in 895 systems, and the correlation between eccentrici…
A recent study suggests that the observed multiplicity of super-Earth (SE) systems is correlated with stellar overdensities: field stars in high phase-space density environments have an excess of single-planet systems compared to stars in low density fields. This correlation is puzzling as stellar clustering is expected to influence mostly the outer part of planetary systems. Here we examine the possibility that stellar flybys indirectly excite the mutual inclinations of initially coplanar SEs, breaking their co-transiting geometry. We propose that flybys excite the inclinations of exterior su…
Population studies of the orbital characteristics of exoplanets in multi-planet systems have highlighted the existence of an anticorrelation between the average orbital eccentricity of planets and the number of planets of their host system, that is, its multiplicity. This effect was proposed to reflect the varying levels of violence in the dynamical evolution of planetary systems. Previous work suggested that the relative violence of the dynamical evolution of planetary systems with similar orbital architectures can be compared through the computation of their angular momentum deficit (AMD). W…
We investigate the origin of close-in planets and related phenomena orbiting white dwarfs (WDs), which are thought to originate from orbits more distant from the star. We use the planetary architectures of the 75 multiple-planet systems (four, five and six planets) detected orbiting main-sequence stars to build 750 dynamically analogous templates that we evolve to the WD phase. Our exploration of parameter space, although not exhaustive, is guided and restricted by observations and we find that the higher the multiplicity of the planetary system, the more likely it is to have a dynamical insta…
Recent work has demonstrated that exoplanetary system properties correlate strongly with ambient stellar clustering in six-dimensional stellar position-velocity phase space, quantified by dividing planetary systems into sub-samples with high or low phase space densities (`overdensity' and `field' systems, respectively). We investigate the physical origins of the phase space overdensities and, thereby, which environmental mechanisms may have impacted the planetary systems. We consider the galactic-scale kinematic structure of the Milky Way observed with Gaia and show that the overdensities corr…
Revealing the mechanisms shaping the architecture of planetary systems is crucial for our understanding of their formation and evolution. In this context, it has been recently proposed that stellar clustering might be the key in shaping the orbital architecture of exoplanets. The main goal of this work is to explore the factors that shape the orbits of planets. We used a homogeneous sample of relatively young FGK dwarf stars with RV detected planets and tested the hypothesis that their association to phase space (position-velocity) over-densities ('cluster' stars) and under-densities ('field' …
The dynamical influence of binary companions is expected to profoundly influence planetary systems. However, the difficulty of identifying planets in binary systems has left the magnitude of this effect uncertain; despite numerous theoretical hurdles to their formation and survival, at least some binary systems clearly host planets. We present high-resolution imaging of 382 Kepler Objects of Interest (KOIs) obtained using adaptive-optics imaging and nonredundant aperture-mask interferometry (NRM) on the Keck-II telescope. Among the full sample of 506 candidate binary companions to KOIs, we sup…
Extrasolar planets with sizes between that of the Earth and Neptune ($R_{\rm p}=1{-}4~{\rm R}_\oplus$) have a bimodal radius distribution. This 'planet radius valley' separates compact, rocky super-Earths ($R_{\rm p}=1.0{-}1.8~{\rm R}_\oplus$) from larger sub-Neptunes ($R_{\rm p}=1.8{-}3.5~{\rm R}_\oplus$) hosting a gaseous hydrogen-helium envelope around their rocky core. Various hypotheses for this radius valley have been put forward, which all rely on physics internal to the planetary system: photoevaporation by the host star, long-term mass loss driven by the cooling planetary core, or the…
The angular momentum deficit (AMD) of a planetary system is a measure of its orbital excitation and a predictor of long-term stability. We adopt the AMD-stability criteria to constrain the orbital architectures for exoplanetary systems. Previously, He, Ford, & Ragozzine (2019) (arXiv:1907.07773v2) showed through forward modelling (SysSim) that the observed multiplicity distribution can be well reproduced by two populations consisting of a low and a high mutual inclination component. Here, we show that a broad distribution of mutual inclinations arising from systems at the AMD-stability limit c…
A planetary system with gas giants and super-Earths around the nearby M dwarf GJ 676A. Optimizing data analysis techniques for the detection of multi-planetary systems
We perform a detailed study of six transiting planetary systems with relatively bright stars close enough to affect observations of these systems. Light curves are analysed taking into account the contaminating light and its uncertainty. We present and apply a method to correct the velocity amplitudes of the host stars for the presence of contaminating light. We determine the physical properties of six systems (WASP-20, WASP-70, WASP-8, WASP-76, WASP-2 and WASP-131) accounting for contaminating light. In the case of WASP-20 the measured physical properties are very different for the three scen…
We present a study on the effect of undetected stellar companions on the derived planetary radii for the Kepler Objects of Interest (KOIs). The current production of the KOI list assumes that the each KOI is a single star. Not accounting for stellar multiplicity statistically biases the planets towards smaller radii. The bias towards smaller radii depends on the properties of the companion stars and whether the planets orbit the primary or the companion stars. Defining a planetary radius correction factor $X_R$, we find that if the KOIs are assumed to be single, then, {\it on average}, the pla…
We use simulated planetary systems to model the planet multiplicity of Kepler stars. Previous studies have underproduced single planet systems and invoked the so called Kepler dichotomy, where the planet forming ability of a Kepler star is dichotomous, producing either few or many transiting planets. In this paper we show that the Kepler dichotomy is only required when the inner part of planetary disks are just assumed to be flared. When the inner part of planetary disks are flat, we reproduce the observed planet multiplicity of Kepler stars without the need to invoke a dichotomy. We find that…
Revisiting Planetary Systems in Okayama Planet Search Program: A new long-period planet, RV astrometry joint analysis, and multiplicity-metallicity trend around evolved stars
The known population of exoplanets exhibits a much wider range of orbital eccentricities than Solar System planets and has a much higher average eccentricity. These facts have been widely interpreted to indicate that the Solar System is an atypical member of the overall population of planetary systems. We report here on a strong anti-correlation of orbital eccentricity with multiplicity (number of planets in the system) among catalogued radial velocity (RV) systems. The mean, median and rough distribution of eccentricities of Solar System planets fits an extrapolation of this anti-correlation …
Due to the high stellar densities in young clusters, planetary systems formed in these environments are likely to have experienced perturbations from encounters with other stars. We carry out direct $N$-body simulations of multi-planet systems in star clusters to study the combined effects of stellar encounters and internal planetary dynamics. These planetary systems eventually become part of the Galactic field population the parental cluster dissolves, which is where most presently-known exoplanets are observed. We show that perturbations induced by stellar encounters lead to distinct signatu…
It is a truism within the exoplanet field that "to know the planet, you must know the star." This pertains to the physical properties of the star (i.e. mass, radius, luminosity, age, multiplicity), the activity and magnetic fields, as well as the stellar elemental abundances which can be used as a proxy for planetary composition. In this white paper, we discuss important stellar characteristics that require attention in upcoming ground- and space-based missions, such that their processes can be understood and either detangled from that of the planet, correlated with the presence of a planet, o…
Observational advances over the last decade have enabled high-resolution, interferometric studies of forming multiple systems, statistical surveys of multiplicity in star-forming regions, and new insights into disk evolution and planetary architectures in these systems. In this review, we compile the results of observational and theoretical studies of stellar multiplicity. We summarize the population statistics spanning system evolution from the protostellar phase through the main-sequence phase and evaluate the influence of the local environment. In short, most stars are born in multiple stel…
We explore the multiplicity of exoplanet host stars with high-resolution images obtained with VLT/SPHERE. Two different samples of systems were observed: one containing low-eccentricity outer planets, and the other containing high-eccentricity outer planets. We find that 10 out of 34 stars in the high-eccentricity systems are members of a binary, while the proportion is 3 out of 27 for circular systems. Eccentric-exoplanet hosts are, therefore, significantly more likely to have a stellar companion than circular-exoplanet hosts. The median magnitude contrast over the 68 data sets is 11.26 and 9…
We explore the impact of outer stellar companions on the occurrence rate of giant planets detected with radial velocities. We searched for stellar and planetary companions to a volume-limited sample of solar-type stars within 25 pc. Using adaptive optics imaging from the Lick 3m and Palomar 200" Telescopes, we characterized the multiplicity of our sample stars, down to the bottom of the main sequence. With these data, we confirm field star multiplicity statistics from previous surveys. We combined three decades of radial velocity data from the California Planet Search with new RV data from Kec…
Recent studies have shown that the radii and masses of adjacent planets within a planetary system are correlated. It is unknown how this 'peas-in-a-pod' phenomenon originates, whether it is in place at birth or requires evolution, and whether it (initially) applies only to neighboring planets or to all planets within a system. Here we address these questions by making use of the recent discovery that planetary system architectures strongly depend on ambient stellar clustering. Based on Gaia's second data release, we divide the sample of planetary systems hosting multiple planets into those res…
The majority of stars have one or more stellar companions. As exoplanets continue to be discovered, it is crucial to examine planetary systems to identify their stellar companions. By observing a change in proper motion, companions can be detected by the acceleration they induce on their host stars. We selected 701 stars from the Hipparcos-Gaia Catalog of Accelerations (HGCA) that have existing adaptive optics imaging data gathered with Gemini/NIRI. Of these, we examined 21 stars known to host planet candidates and reduced their archival NIRI data with Gemini's DRAGONS software. We assessed th…
High-multiplicity Kepler systems (referred to as Kepler multis) are often tightly packed and may be on the verge of instability. Many systems of this type could have experienced past instabilities, where the compact orbits and often low densities make physical collisions likely outcomes. We use numerical simulations to study the dynamical instabilities and planet-planet interactions in a synthetically generated sample of closely-packed, high-multiplicity systems. We focus specifically on systems resembling Kepler-11, a Kepler multi with six planets, and run a suite of dynamical integrations, s…
Planetary Architectures of Kepler Compact Multis with Binary Star Companions
University of California Santa Cruz（加州大学圣克鲁兹分校）；Mullard Space Science Laboratory, University College London（伦敦大学学院穆拉德空间科学实验室）；California Institute of Technology（加州理工学院）
Evolved stars, multiplicity and planets: Shaping and Being Shaped by Stellar Evolution
Chalmers University of Technology（查尔姆斯理工大学）；Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天体物理中心）；University of Newcastle（纽卡斯尔大学）；Anton Pannekoek Institute for Astronomy, University of Amsterdam（阿姆斯特丹大学安东·潘内库克天文学研究所）；University College Dublin（都柏林大学学院）；Macquarie University（麦考瑞大学）；University of Virginia（弗吉尼亚大学）；Virginia Institute for Theoretical Astronomy, University of Virginia（弗吉尼亚大学理论天文研究所）；Univ. of Bordeaux（波尔多大学）；Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；Centro de Astrobiologia (CAB), CSIC/INTA（西班牙国家航空航天技术研究所/西班牙高等科学研究委员会天体生物学中心）；Observatorio Astronómico Nacional, IGN/GNIG, MITMS（西班牙国家地理研究所国家天文台）；Institute of Fundamental Physics (IFF), CSIC（西班牙高等科学研究委员会基础物理研究所）；KU Leuven（荷语鲁汶大学）；LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Universit（巴黎天文台，PSL大学，索邦大学，巴黎西岱大学，CY塞吉-蓬图瓦兹大学）
The Kepler mission observed thousands of transiting exoplanet candidates around hundreds of thousands of FGK dwarf stars. He, Ford, & Ragozzine (2019) (arXiv:1907.07773) applied forward modeling to infer the distribution of intrinsic architectures of planetary systems, developed a clustered Poisson point process model for exoplanetary systems (SysSim) to reproduce the marginal distributions of the observed Kepler population, and they showed that orbital periods and planet radii are clustered within a given planetary system. Here, we extend the clustered model to explore correlations between pl…
Using the updated exoplanet population parameters of our previous study, which includes the planetary radius updates from Gaia DR2 and an inferred multiplicity distribution, we provide a revised $η_{\oplus}$ calculation. This is achieved by sampling planets from our derived population model and determining which planets meet our criterion for habitability. To ensure robust results, we provide probabilities calculated over a range of upper radius limits. Our most optimistic criterion for habitability provides an $η_{\oplus}$ value of $0.34\pm 0.02 \frac{\rm planets}{\rm star}$. We also consider…
Influence of Stellar Multiplicity On Planet Formation. I. Evidence of Suppressed Planet Formation Due to Stellar Companions Within 20 AU and Validation of Four Planets From the Kepler Multiple Planet Candidates
Planet multiplicities are useful in constraining the formation and evolution of planetary systems but usually difficult to constrain observationally. Here, we develop a general method that can properly take into account the survey incompleteness and recover the intrinsic planet multiplicity distribution. We then apply it to the radial velocity (RV) planet sample from the California Legacy Survey (CLS). Within the $1\,$au ($10\,$au) region, we find $21 \pm 4\%$ ($19.2 \pm 2.8\%$) of Sun-like stars host planets with masses above $10\,M_\oplus$ ($0.3\,M_{\rm J}$), about 30\% (40\%) of which are m…
Most stars form in star clusters and stellar associated. To understand the roles of star cluster environments in shaping the dynamical evolution of planetary systems, we carry out direct $N$-body simulations of four planetary systems models in three different star cluster environments with respectively N=2k, 8k and 32k stars. In each cluster, an ensemble of initially identical planetary systems are assigned to solar-type stars with $\sim 1 M_{\odot}$ and evolved for 50~Myr. We found that following the depletion of protoplanetary disks, external perturbations and planet-planet interactions are …
NASA's Kepler Mission uncovered a wealth of planetary systems, many with planets on short-period orbits. These short-period systems reside around 50% of Sun-like stars and are similarly prevalent around M dwarfs. Their formation and subsequent evolution is the subject of active debate. In this paper, we simulate late-stage, in-situ planet formation across a grid of planetesimal disks with varying surface density profiles and total mass. We compare simulation results with observable characteristics of the Kepler sample. We identify mixture models with different primordial planetesimal disk prop…
A major outstanding question regarding the formation of planetary systems is whether wide-orbit giant planets form differently than close-in giant planets. We aim to establish constraints on two key parameters that are relevant for understanding the formation of wide-orbit planets: 1) the relative mass function and 2) the fraction of systems hosting multiple companions. In this study, we focus on systems with directly imaged substellar companions, and the detection limits on lower-mass bodies within these systems. First, we uniformly derive the mass probability distributions of known companion…
We study the multiplicity of host stars to known transiting extra-solar planets to test competing theories on the formation mechanisms of hot Jupiters. We observed 45 exoplanet host stars using VLT/SPHERE/IRDIS to search for potential companions. For each identified candidate companion we determined the probability that it is gravitationally bound to its host by performing common proper motion checks and modelling of synthetic stellar populations around the host. We detected new candidate companions around K2-38, WASP-72, WASP-80, WASP-87, WASP-88, WASP-108, WASP-118, WASP-120, WASP-122, WASP1…
The Intrinsic Multiplicity Distribution of Exoplanets Revealed from the Radial Velocity Method. II. Constraints on Giant Planet Multiplicity from Different Surveys
We consider planetary systems evolving under the effect of a Stokes-type dissipative force mimicking the outcome of a type II migration process. As inward migration proceeds and the planets follow the circular family (they start on circular orbits) and even though they are initially almost coplanar, resonance capture can be realized. Then, at the \textit{vertical critical orbits} (VCOs), that the circular family possesses, the inclination excitation can abruptly take place. The planets are now guided by the spatial elliptic families, which bifurcate from those critical orbits. We herein, perfo…
We present independent and self-consistent metallicities for a sample of 807 planet-hosting stars from the California-Kepler Survey from an LTE spectroscopic analysis using a selected sample of Fe I and Fe II lines. Correlations between host-star metallicities, planet radii, and planetary architecture (orbital periods - warm or hot - and multiplicity - single or multiple), were investigated using non-parametric statistical tests. In addition to confirming previous results from the literature, e.g., that overall host star metallicity distributions differ between hot and warm planetary systems o…
This paper presents combined ${\it Spitzer}$ IRAC and ${\it Hubble}$ COS results for a double-blind survey of 195 single and 22 wide binary white dwarfs for infrared excesses and atmospheric metals. The selection criteria include cooling ages in the range 9 to 300 Myr, and hydrogen-rich atmospheres so that the presence of atmospheric metals can be confidently linked to ongoing accretion from a circumstellar disc. The entire sample has infrared photometry, whereas 168 targets have corresponding ultraviolet spectra. Three stars with infrared excesses due to debris discs are recovered, yielding a…
