多普勒成像使用高色散光谱技术生成旋转物体的2D全球地图。当应用于褐矮星和太阳系外行星时，这种技术可以以前所未有的细节约束全球大气动力学和/或磁场对这些物体的影响。我提出了第一个定量评估的前景多普勒成像的亚恒星物体与现有的设施和未来的巨型地面望远镜。K波段的观测灵敏度最高，但H和L波段也可用于这些目的。为了评估目标的数量和可用性，我还提出了一个汇编的光度变化，旋转周期（P）和投影旋转速度（v sin i）的棕矮星和系外行星的所有测量。几个明亮的物体已经可以用现有的仪器进行多普勒成像。随着巨大的地面望远镜的发展，多普勒成像将成为可行的几十个棕矮星和少数最明亮的直接成像的太阳系外行星（如β Pic b）。目前对P、v sin i和变异性的测量对于许多天体来说是不完整的，并且样本强烈地偏向于早期类型的天体（< L5）。因此，测量晚型物体的这些量的调查将特别有助于扩大通过多普勒成像进行全球天气监测的候选样本。
英文摘要：
Doppler Imaging produces 2D global maps of rotating objects using high-dispersion spectroscopy. When applied to brown dwarfs and extrasolar planets, this technique can constrain global atmospheric dynamics and/or magnetic effects on these objects in un- precedented detail. I present the first quantitative assessment of the prospects for Doppler Imaging of substellar objects with current facilities and with future giant ground-based telescopes. Observations will have the greatest sensitivity in K band, but the H and L bands will also be useful for these purposes. To assess the number and availability of targets, I also present a compilation of all measurements of photometric variability, rotation period (P), and projected rotational velocity (v sin i) for brown dwarfs and exoplanets. Several bright objects are already accessible to Doppler Imaging with currently available instruments. With the development of giant ground-based telescopes, Doppler Imaging will become feasible for many dozens of brown dwarfs and for the few brightest directly imaged extrasolar planets (such as beta Pic b). The present set of measurements of P, v sin i, and variability are incomplete for many objects, and the sample is strongly biased toward early-type objects (< L5). Thus, surveys to measure these quantities for later-type objects will be especially helpful in expanding the sample of candidates for global weather monitoring via Doppler Imaging.
The Unrealised Interdisciplinary Advantage of Observing High Mass Transiting Exoplanets and Brown Dwarfs -- Strategic Exoplanet Initiatives with HST and JWST White Paper
High-resolution Doppler spectroscopy is a powerful tool for identifying molecular species in the atmospheres of both transiting and non-transiting exoplanets. Currently, such data is analysed using cross-correlation techniques to detect the Doppler shifting signal from the orbiting planet. In this paper we demonstrate that, compared to cross-correlation methods currently used, the technique of Doppler tomography has improved sensitivity in detecting the subtle signatures expected from exoplanet atmospheres. This is partly due to the use of a regularizing statistic, which acts to suppress noise…
The third Gaia data release includes a catalog of exoplanets and exoplanet candidates identified via the star's astrometric motion. This paper reports on tests for consistency between the Gaia two-body orbital solutions and precise Doppler velocities, for the stars currently amenable to such a comparison. For BD 17-0063, HD 81040, and HD 132406, the Gaia orbital solution and the Doppler data were found to be consistent, and were fitted jointly to obtain the best possible constraints on the planets' orbits and masses. Inconsistencies were found for 4 stars: HD 111232, probably due to additional…
Recent and upcoming stabilized spectrographs are pushing the frontier for Doppler spectroscopy to detect and characterize low-mass planets. Specifications for these instruments are so impressive that intrinsic stellar variability is expected to limit their Doppler precision for most target stars (Fischer et al. 2016). To realize their full potential, astronomers must develop new strategies for distinguishing true Doppler shifts from intrinsic stellar variability. Stellar variability due to star spots, faculae and other rotationally-linked variability are particularly concerning, as the stellar…
We present an auto-differentiable spectral modeling of exoplanets and brown dwarfs. This model enables a fully Bayesian inference of the high--dispersion data to fit the ab initio line-by-line spectral computation to the observed spectrum by combining it with the Hamiltonian Monte Carlo in recent probabilistic programming languages. An open source code, exojax, developed in this study, was written in Python using the GPU/TPU compatible package for automatic differentiation and accelerated linear algebra, JAX (Bradbury et al. 2018). We validated the model by comparing it with existing opacity c…
In order to understand the atmospheres as well as the formation mechanism of giant planets formed outside our solar system, the next decade will require an investment in studies of isolated young brown dwarfs. In this white paper we summarize the opportunity for discovery space in the coming decade of isolated brown dwarfs with planetary masses in young stellar associations within 150 pc. We suggest that next generation telescopes and beyond need to invest in characterizing young brown dwarfs in order to fully understand the atmospheres of sibling directly imaged exoplanets as well as the tail…
The precise radial velocity technique is a cornerstone of exoplanetary astronomy. Astronomers measure Doppler shifts in the star's spectral features, which track the line-of/sight gravitational accelerations of a star caused by the planets orbiting it. The method has its roots in binary star astronomy, and exoplanet detection represents the low-companion-mass limit of that application. This limit requires control of several effects of much greater magnitude than the signal sought: the motion of the telescope must be subtracted, the instrument must be calibrated, and spurious Doppler shifts "ji…
Prioritizing High-Precision Photometric Monitoring of Exoplanet and Brown Dwarf Companions with JWST -- Strategic Exoplanet Initiatives with HST and JWST White Paper
Line-profile tomography of exoplanet transits I: The Doppler shadow of HD 189733b
我们提出了一个直接的方法隔离的星光的组成部分，被行星阻挡，因为它的过境其宿主恒星，并将其应用到光谱的明亮过境行星HD 189733b。我们模拟的恒星交叉关联函数的全球形状的边缘变暗的旋转配置文件和高斯代表的多普勒核心的平均光球线轮廓的卷积。在凌日期间被行星阻挡的光是具有相同固有宽度的高斯，其穿过线轮廓的轨迹产生失准角的精确测量和v sin I的独立测量。我们表明，即使当v sin我是小于内在的线轮廓的宽度，旅行多普勒“阴影”的行星投下创建一个可识别的扭曲的线轮廓，这是服从直接建模。直接测量丢失的星光的轨迹产生自洽的措施，预计恒星旋转速率，平均本地光球线轮廓的固有宽度，预计自旋轨道失调角，和系统的质心速度。结合光度旋转周期，结果给出了一个几何测量的恒星半径，这与从高精度的过境测光得到的值，如果少量的差分旋转存在于恒星光球。
We present optimal survey strategies for the upcoming NIX imager, part of the ERIS instrument to be installed on the Very Large Telescope (VLT). We will use a custom 2.2 micron K-peak filter to optimise the efficiency of a future large-scale direct imaging survey, aiming to detect brown dwarfs and giant planets around nearby stars. We use the results of previous large scale imaging surveys (primarily SPHERE SHINE and Gemini GPIES) to inform our choice of targets, as well as improved planet population distributions. We present four possible approaches to optimise survey target lists for the hig…
The Polar Vortex Hypothesis: Evolving, Spectrally Distinct Polar Regions Explain Short- and Long-term Light Curve Evolution and Color-Inclination Trends in Brown Dwarfs and Giant Exoplanets
A planetary atmosphere is the outer gas layer of a planet. Besides its scientific significance among the first and most accessible planetary layers observed from space, it is closely connected with planetary formation and evolution, surface and interior processes, and habitability of planets. Current theories of the planetary atmosphere were primarily obtained through the studies of eight large planets, Pluto and three large moons (Io, Titan, and Triton) in the Solar System. Outside the Solar System, more than four thousand extra-solar planets (exoplanets) and two thousand brown dwarfs have be…
Tempawral: A Time-Resolved Retrieval Framework for Variable Brown Dwarfs and Exoplanets
University of Hertfordshire（赫特福德大学）；University of Sheffield（谢菲尔德大学）；Université de Montréal（蒙特利尔大学）；National Astronomical Observatory of Japan（日本国立天文台）；SOKENDAI（综合研究大学院大学）；American Museum of Natural History（美国自然历史博物馆）；The Graduate Center City University of New York（纽约市立大学研究生中心）；Trinity College Dublin, The University of Dublin（都柏林三一学院，都柏林大学）
PICASO 4.0: Clouds and Photochemistry in Climate Models of Brown Dwarfs and Exoplanets
University of Texas at Austin（德克萨斯大学奥斯汀分校）；NASA Ames Research Center（美国国家航空航天局艾姆斯研究中心）；SETI Institute（搜寻地外文明研究所）；Arizona State University（亚利桑那州立大学）；Dordt University（多尔特大学）；Space Science Institute（空间科学研究所）；University of Arizona（亚利桑那大学）；University of California Santa Cruz（加州大学圣克鲁兹分校）；University of St Andrews（圣安德鲁斯大学）；University of Bristol（布里斯托大学）；Carnegie Institution for Science（卡内基科学机构）；California Institute of Technology（加州理工学院）
Lightning is an important electrical phenomenon, known to exist in several Solar System planets. It carries information on convection and cloud formation, and may be important for pre-biotic chemistry. Exoplanets and brown dwarfs have been shown to host environments appropriate for the initiation of lightning discharges. In this PhD project, I aim to determine if lightning on exoplanets and brown dwarfs can be more energetic than it is known from Solar System planets, what are the most promising signatures to look for, and if these "exo-lightning" signatures can be detected from Earth. This th…
Satellites around substellar companions are a heterogeneous class of objects with a variety of different formation histories. Focusing on potentially detectable satellites around exoplanets and brown dwarfs, we might expect to find objects belonging to two main populations: planet-like satellites similar to Titan or the Galileian Satellites - likely formed within the scope of core accretion; and binary-like objects, formed within different scenarios, such as disk instability. The properties of these potential satellites would be very different from each other. Additionally, we expect that thei…
Observations and models suggest that the conditions to develop lightning may be present in cloud-forming extrasolar planetary and brown dwarf atmospheres. Whether lightning on these objects is similar to or very different from what is known from the Solar System awaits answering as lightning from extrasolar objects has not been detected yet. We explore terrestrial lightning parameterisations to compare the energy radiated and the total radio power emitted from lightning discharges for Earth, Jupiter, Saturn, extrasolar giant gas planets and brown dwarfs. We find that lightning on hot, giant ga…
Bridging the Gap: Using Brown Dwarfs to Examine Silicate Clouds in Giant Exoplanet Atmospheres
American Museum of Natural History（美国自然历史博物馆）；Dordt University（多尔特大学）；Center for Exoplanetary Systems, Space Science Institute（系外行星系统中心，空间科学研究所）；The Graduate Center, City University of New York（纽约市立大学研究生中心）
Young brown dwarfs are analogs to giant exoplanets, as they share effective temperatures, near-infrared colors, and surface gravities. Thus, the detailed characterization of young brown dwarfs might shed light on the study of giant exoplanets, that we are currently unable to observe with sufficient signal-to-noise to allow precise characterization of their atmospheres. 2MASS J22081363+2921215 is a young L3 brown dwarf, member of the beta-Pictoris young moving group (23 +/-3 Myr), that shares its effective temperature and mass with the beta Pictoris b giant exoplanet. We performed a ~2.5 hr spe…
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 5-100 AU using hierarchical Bayesian modeling. Orbit fits are performed in a uniform manner for companions with short orbital arcs; this typically results in …
We explore the prospects for the detection of giant circumbinary exoplanets and brown dwarfs (BDs) orbiting Galactic double white dwarfs binaries (DWDs) with the Laser Interferometer Space Antenna (LISA). By assuming an occurrence rate of 50%, motivated by white dwarf pollution observations, we built a Galactic synthetic population of P-type giant exoplanets and BDs orbiting DWDs. We carried this out by injecting different sub-stellar populations, with various mass and orbital separation characteristics, into the DWD population used in the LISA mission proposal. We then performed a Fisher matr…
The study of the composition of brown dwarf atmospheres helped to understand their formation and evolution. Similarly, the study of exoplanet atmospheres is expected to constrain their formation and evolutionary states. We use results from 3D simulations, kinetic cloud formation and kinetic ion-neutral chemistry to investigate ionisation processes which will affect their atmosphere chemistry: The dayside of super-hot Jupiters is dominated by atomic hydrogen, and not H$_2$O. Such planetary atmospheres exhibit a substantial degree of thermal ionisation and clouds only form on the nightside where…
The relative abundance of deuterium and hydrogen is a potent tracer of planet formation and evolution. Jupiter and Saturn have protosolar atmospheric D/H ratios, a relic of substantial gas accretion from the nebula, while the atmospheres of Neptune and Uranus are enhanced in D by accretion of ices into their envelopes. For terrestrial planets, D/H ratios are used to determine the mechanisms of volatile delivery and subsequent atmosphere loss over the lifetime of the planet. Planets and brown dwarfs more massive than 13 M_J quickly fuse their initial D reservoir. Here, we simulate spectra for g…
We present an improved, hybrid CPU-GPU atmospheric retrieval code, Helios-r2, which is applicable to medium-resolution emission spectra of brown dwarfs, in preparation for precision atmospheric spectroscopy in the era of the James Webb Space Telescope. The model is available as open-source code on the Exoclimes Simulation Platform. We subject Helios-r2 to a battery of tests of varying difficulty. The simplest test involves a mock retrieval on a forward model generated using the same radiative transfer technique, the same implementation of opacities, and the same chemistry model. The least triv…
Brown dwarfs and exoplanets provide unique atmospheric regimes that hold information about their formation routes and evolutionary states. Modelling mineral cloud particle formation is key to prepare for missions and instruments like CRIRES+, JWST and ARIEL as well as possible polarimetry missions like {\sc PolStar}. The aim is to support more detailed observations that demand greater understanding of microphysical cloud processes. We extend our kinetic cloud formation model that treats nucleation, condensation, evaporation and settling of mixed material cloud particles to consistently model c…
The last few years has seen a dramatic increase in the number of exoplanets known and in the range of methods for characterising their atmospheric properties. At the same time, new discoveries of increasingly cooler brown dwarfs have pushed down their temperature range which now extends down to Y-dwarfs of <300 K. Modelling of these atmospheres has required the development of new techniques to deal with the molecular chemistry and clouds in these objects. The atmospheres of brown dwarfs are relatively well understood, but some problems remain, in particular the behavior of clouds at the L/T tr…
Young, rapidly-rotating M dwarfs exhibit prominent starspots, which create quasiperiodic signals in their photometric and Doppler spectroscopic measurements. The periodic Doppler signals can mimic radial velocity (RV) changes expected from orbiting exoplanets. Exoplanets can be distinguished from activity-induced false positives by the chromaticity and long-term incoherence of starspot signals, but these qualities are poorly constrained for fully-convective M stars. Coherent photometric starspot signals on M dwarfs may persist for hundreds of rotations, and the wavelength dependence of starspo…
The cloud formation process starts with the formation of seed particles, after which, surface chemical reactions grow or erode the cloud particles. We investigate which materials may form cloud condensation seeds in the gas temperature and pressure regimes (T$_{\rm gas}$ = 100-2000 K, p$_{\rm gas}$ = 10$^{-8}$-100 bar) expected to occur in planetary and brown dwarf atmospheres. We apply modified classical nucleation theory which requires surface tensions and vapour pressure data for each solid species, which are taken from the literature. We calculate the seed formation rates of TiO$_{2}$[s] a…
While scattering of light by atoms and molecules yields large amount of polarization at the B-band of both T- and L-dwarfs, scattering by dust grains in cloudy atmosphere of L-dwarfs gives rise to significant polarization at the far-optical and infra-red wavelengths where these objects are much brighter. However, the observable disk averaged polarization should be zero if the clouds are uniformly distributed and the object is spherically symmetric. Therefore, in order to explain the observed large polarization of several L-dwarfs, rotation-induced oblateness or horizontally inhomogeneous cloud…
Mass is one of the most important parameters for determining the true nature of an astronomical object. Yet, many published exoplanets lack a measurement of their true mass, in particular those detected thanks to radial velocity (RV) variations of their host star. For those, only the minimum mass, or $m\sin i$, is known, owing to the insensitivity of RVs to the inclination of the detected orbit compared to the plane-of-the-sky. The mass that is given in database is generally that of an assumed edge-on system ($\sim$90$^\circ$), but many other inclinations are possible, even extreme values clos…
Young giant planets and brown dwarf companions emit near-infrared radiation that can be linearly polarized up to several percent. This polarization can reveal the presence of a circumsubstellar accretion disk, rotation-induced oblateness of the atmosphere, or an inhomogeneous distribution of atmospheric dust clouds. We measured the near-infrared linear polarization of 20 known directly imaged exoplanets and brown dwarf companions with the high-contrast imager SPHERE-IRDIS at the VLT. We reduced the data using the IRDAP pipeline to correct for the instrumental polarization and crosstalk with an…
The \textit{Nancy Grace Roman Space Telescope} (\textit{ Roman}) will provide an enormous number of microlensing light curves with much better photometric precisions than ongoing ground-based observations. Such light curves will enable us to observe high-order microlensing effects which have been previously difficult to detect. In this paper, we investigate \textit{Roman}'s potential to detect and characterize short-period planets and brown dwarfs (BDs) in source systems using the orbital motion of source stars, the so-called xallarap effect. We analytically estimate the measurement uncertaint…
Clouds form on extrasolar planets and brown dwarfs where lightning could occur. Lightning is a tracer of atmospheric convection, cloud formation and ionization processes as known from the Solar System, and may be significant for the formation of prebiotic molecules. We study lightning climatology for the different atmospheric environments of Earth, Venus, Jupiter and Saturn. We present lightning distribution maps for Earth, Jupiter and Saturn, and flash densities for these planets and Venus, based on optical and/or radio measurements from the WWLLN and STARNET radio networks, the LIS/OTD satel…
Brown dwarfs and directly imaged exoplanets exhibit observational evidence for active atmospheric circulation, raising critical questions about mechanisms driving the circulation, its fundamental nature, and time variability. Our previous work demonstrated the crucial role of cloud radiative feedback on driving a vigorous atmospheric circulation using local models that assume a Cartesian geometry and constant Coriolis parameters. In this study, we explore the properties of the global dynamics. We show that, under relatively strong dissipation in the bottom layers of the model, horizontally iso…
Mass, radius, and age are three of the most fundamental parameters for celestial objects, enabling studies of the evolution and internal physics of stars, brown dwarfs, and planets. Brown dwarfs are hydrogen-rich objects that are unable to sustain core fusion reactions but are supported from collapse by electron degeneracy pressure. As they age, brown dwarfs cool, reducing their radius and luminosity. Young exoplanets follow a similar behaviour. Brown dwarf evolutionary models are relied upon to infer the masses, radii and ages of these objects. Similar models are used to infer the mass and ra…
Upcoming James Webb Space Telescope (JWST) observations will allow us to study exoplanet and brown dwarf atmospheres in great detail. The physical interpretation of these upcoming high signal-to-noise observations requires precise atmospheric models of exoplanets and brown dwarfs. While several one-dimensional and three-dimensional atmospheric models have been developed in the past three decades, these models have often relied on simplified assumptions like chemical equilibrium and are also often not open-source, which limits their usage and development by the wider community. We present a pyt…
We present a catalog of cool dwarf targets ($V-J>2.7$, $T_{\rm eff} \lesssim 4000 K$) and their stellar properties for the upcoming Transiting Exoplanet Survey Satellite (TESS), for the purpose of determining which cool dwarfs should be observed using two-minute observations. TESS has the opportunity to search tens of thousands of nearby, cool, late K and M-type dwarfs for transiting exoplanets, an order of magnitude more than current or previous transiting exoplanet surveys, such as {\it Kepler}, K2 and ground-based programs. This necessitates a new approach to choosing cool dwarf targets. Co…
