Precise determination of fundamental parameters of six exoplanet host stars and their planets

The aim of this paper is to determinate the fundamental parameters of six exoplanet host （EH） stars and their planets. Because techniques for detecting exo- planets yield properties of the planet only as a function of the properties of the host star, we must accurately determine the parameters of the EH stars first. For this rea- son, we constructed a grid of stellar models including diffusion and rotation-induced extra-mixing with given ranges of input parameters （i.e. mass, metallicity and initial rotation rate）. In addition to the commonly used observational constraints such as the effective temperature Tell, luminosity L and metallicity [Fe/H], we added two obser- vational constraints, the lithium abundance log N （Li） and the rotational period Prot. These two additional observed parameters can set further constraints on the model due to their correlations with mass, age and other stellar properties. Hence, our estimations of the fundamental parameters for these EH stars and their planets have a higher preci- sion than previous works. Therefore, the combination of rotational period and lithium helps us to obtain more accurate parameters for stars, leading to an improvement in knowledge about the physical state of EH stars and their planets.

Searching for exoplanets with HEPS:I.detection probability of Earth-like planets in multiple systems

The astrometry method has great advantages in searching for exoplanets in the habitable zone around solar-like stars. However, the presence of multiple planets may cause a problem with degeneracy when trying to compute accurate planet parameters from observation data and reduce detectability. The degeneracy problem is extremely critical, especially in a space mission which has limited observation time and cadence. In this series of papers, we study the detectability of habitable Earth-mass planets in different types of multi-planet systems, aiming to find the most favorable targets for the potential space mission–Habitable ExoPlanet Survey(HEPS). In the first paper, we present an algorithm to find planets in the habitable zone around solar-like stars using astrometry. We find the detectability can be well described by planets' signal-to-noise ratio(SNR) and a defined parameter S = M2/(T1-T2)2, where M2 and T2are the mass and period of the second planet, respectively. T1 is the period of the planet in the habitable zone. The parameter S represents the influence of planetary architectures. We fit the detectability as a function of both the SNR of the planet in the habitable zone and the parameter S. An Earth-like planet in a habitable zone is harder to detect(with detectability PHP< 80%) in a system with a hot Jupiter or warm Jupiter(within2 AU), in which the parameter S is large. These results can be used in target selections and to determine the priority of target stars for HEPS, especially when we select and rank nearby planet hosts with a single planet.

An Independent Degree-eight Mars Gravity Field Model and the Expected Results from the Tianwen-1 Mission

Tianwen-1 is China's first independent interplanetary exploration mission,targeting Mars,and includes orbiting,landing,and rover phases.Similar to previous Mars missions,the Tianwen-1 orbiter was designed for polar orbits during the scientific mission period but has an exceptional eccentricity of approximately 0.59.We provide the first independent eight-degree Martian gravity field model in this paper,which was developed exclusively by a team working in China with our independent software as well,based on about two months of radiometric Doppler and range data from only the Tianwen-1 mission.This model is independent from the models created by the groups at NASA Jet Propulsion Laboratory and Goddard Space Flight Center in the United States,as well as the Centre National d'Etudes Spatiales in France.Furthermore,in order to optimize the engineering and scientific benefits,we proposed a number of potential orbits for the extended Tianwen-1 mission.In order to solve a higher-degree independent Mars gravity field model,the viability of modifying the perigee height was investigated,with the priority considerations of fuel savings and implementation hazards being controlled.

From Solar System to Exoplanets:What can we learn from Planetary Spectroscopy?

The purpose of this paper is to address the question:Using our knowledge of infrared planetary spectroscopy,what can we learn about the atmospheres of exoplanets?In a first part,a simplified classification of exoplanets,assuming thermochemical equilibrium,is presented,based on their masses and their equilibrium temperatures,in order to propose some possible estimations about their atmospheric composition.In the second part,infrared spectra of planets are discussed,in order to see what lessons can be drawn for exoplanetary spectroscopy.In the last part,we consider the solar system as it would appear from a star located in the ecliptic plane.It first appears that the solar system(except in a few specific cases)would not be seen as a multiple system,because,contrary to many exoplanetary systems,the planets are too far from the Sun and the inclinations of their orbits with respect to the ecliptic plane are too high.Primary transit synthetic spectra of solar system planets are used to discuss the relative merits of transmission and direct emission spectroscopy for probing exoplanetary atmospheres.

A Search for Exoplanets in Open Clusters and Young Associations based on TESS Objects of Interest

We report the results of our search for planet candidates in open clusters and young stellar associations based on the Transiting Exoplanet Survey Satellite(TESS) Objects of Interest Catalog.We find one confirmed planet,one promising candidate,one brown dwarf and three unverified planet candidates in a sample of 1229 open clusters from the second Gaia data release.We discuss individual planet-star systems based on their basic parameters,membership probability and the observation notes from the ExoFOP-TESS website.We also find ten planet candidates(P> 95%) in young stellar associations by using the BANYAN ∑ Multivariate Bayesian Algorithm.Among the ten candidates,five are known planetary systems.We estimate the rotation periods of the host stars using the TESS light curves and estimate their ages based on gyrochronology.Two candidates with periodic variations are likely to be young planets,but their exact memberships to young stellar associations remain unknown.

Delay of planet formation at large radius and the outward decrease in mass and gas content of Jovian planets

A prominent observation of the solar system is that the mass and gas content of Jovian planets decrease outward with orbital radius, except that, in terms of these properties, Neptune is almost the same as Uranus. In previous studies, the solar nebula was assumed to preexist and the formation process of the solar nebula was not considered. It was therefore assumed that planet formation at different radii started at the same time in the solar nebula. We show that planet formation at different radii does not start at the same time and is delayed at large radii. We suggest that this delay might be one of the factors that causes the outward decrease in the masses of Jovian planets. The nebula starts to form from its inner part because of the inside-out collapse of its progenitorial molecular cloud core. The nebula then expands outward due to viscosity. Material first reaches a small radius and then reaches a larger radius, so planet formation is delayed at the large radius. The later the material reaches a planet＇s location, the less time it has to gain mass and gas content. Hence, the delay tends to cause the outward decrease in mass and gas content of Jovian planets. Our nebula model shows that the material reaches Jupiter, Saturn, Uranus and Neptune at t = 0.40, 0.57, 1.50 and 6.29 × 10^6 yr, respectively. We discuss the effects of time delay on the masses of Jovian planets in the framework of the core accretion model of planet formation. Saturn＇s formation is not delayed by much time relative to Jupiter so that they both reach the rapid gas accretion phase and become gas giants. However, the delay in formation of Uranus and Neptune is long and might be one of the factors that cause them not to reach the rapid gas accretion phase before the gas nebula is dispersed. Saturn has less time to go through the rapid gas accretion, so Saturn＇s mass and gas content are significantly less than those of Jupiter.

Effect of Orbital Characteristic of Inclined Third-body on Motion of Secondary-body for a Hierarchical Triple Systems

The influence of a third-body's orbital elements on the second-body's motion in a hierarchical triple system is a crucial problem in astrophysics.Most prolonged evaluation studies have focused on a distant zero-inclined thirdbody.This study presents a new perspective on second-body motion equations that addresses a perturbing-body in an elliptic orbit derived with consideration of the axial-tilt(obliquity)of the primary.The proposed model is compared by the dual-averaged method and the N-body problem algorithm.After validation,a generalized threebody model is derived to investigate the effects of the third-body's orbital elements on secondary-body motion behavior.The proposed model considers short-time oscillations that affect secular evaluation and applies to exoplanets with all the primary and third body eccentricities,inclinations,and mass ratios.It is shown that the obliquity of the primary(or third-body's inclination)must be considered for precise long-term assessment,even in highly-hierarchical systems.

Detection of TiO and VO in the Atmosphere of WASP-121b and Evidence For its Temporal Variation

We report the transit observations of the ultra-hot Jupiter WASP-121b using the Goodman High Throughput Spectrograph at the 4 m ground-based Southern Astrophysical Research Telescope,covering the wavelength range502-900 nm.By dividing the target and reference star into 19 spectroscopic passbands and applying differential spectrophotometry,we derive spectroscopic transit light curves and fit them using a Gaussian process framework to determine transit depths for every passband.The obtained optical transmission spectrum shows a steep increased slope toward the blue wavelength,which seems to be too steep to be accounted for by Rayleigh scattering alone.We note that the transmission spectrum from this work and other works differ obviously from each other,which was pointed out previously by Wilson et al.as evidence for temporal atmospheric variation.We perform a free chemistry retrieval analysis on the optical transmission spectra from this work and the literature HST/WFC3 NIR spectrum.We determine TiO,VO and H_(2)O with abundances of-5.95_(-0.42)^(+0.47)dex,-6.72_(-1.79)^(+0.51)dex and-4.13_(-0.46)^(+0.63)dex,respectively.We compare the abundances of all three of these molecules derived from this work and previous works,and find that they are not consistent with each other,indicating the chemical compositions of the terminator region may change over long timescales.Future multi-epoch and high-precision transit observations are required to further confirm this phenomenon.We note that when combining the transmission spectra in the optical and in NIR in retrieval analysis,the abundances of V and VO,the NIR-to-optical offset and the cloud deck pressure may be coupled with each other.

Everything Is a Circle: A New Universal Orbital Model

Based on measured astronomical position data of heavenly objects in the Solar System and other planetary systems, all bodies in space seem to move in some kind of elliptical motion with respect to each other. According to Kepler’s 1st Law, “orbit of a planet with respect to the Sun is an ellipse, with the Sun at one of the two foci.” Orbit of the Moon with respect to Earth is also distinctly elliptical, but this ellipse has a varying eccentricity as the Moon comes closer to and goes farther away from the Earth in a harmonic style along a full cycle of this ellipse. In this paper, our research results are summarized, where it is first mathematically shown that the “distance between points around any two different circles in three-dimensional space” is equivalent to the “distance of points around a vector ellipse to another fixed or moving point, as in two-dimensional space”. What is done is equivalent to showing that bodies moving on two different circular orbits in space vector-wise behave as if moving on an elliptical path with respect to each other, and virtually seeing each other as positioned at an instantaneously stationary point in space on their relative ecliptic plane, whether they are moving with the same angular velocity, or different but fixed angular velocities, or even with different and changing angular velocities with respect to their own centers of revolution. This mathematical revelation has the potential to lead to far reaching discoveries in physics, enabling more insight into forces of nature, with a formulation of a new fundamental model regarding the motions of bodies in the Universe, including the Sun, Planets, and Satellites in the Solar System and elsewhere, as well as at particle and subatomic level. Based on the demonstrated mathematical analysis, as they exhibit almost fixed elliptic orbits relative to one another over time, the assertion is made that the Sun, the Earth, and the Moon must each be revolving in their individual circular orbits of revolution in space. With this expectation, individual orbital parameters of the Sun, the Earth, and the Moon are calculated based on observed Earth to Sun and Earth to Moon distance data, also using analytical methods developed as part of this research to an approximation. This calculation and analysis process have revealed additional results aligned with observation, and this also supports our assertion that the Sun, the Earth, and the Moon must actually be revolving in individual circular orbits.

Ancient subsurface structure beneath crater Clavius:constraint by recent high-precision gravity and topography data

With the increasing precision of the GRAIL gravity field models and topography from LOLA, it is possible to investigate the substructure beneath crater Clavius. An admittance between gravity and topography data is commonly used to estimate selenophysical parameters, including load ratio, crustal thickness and density, and elastic thickness. Not only a surface load, but also a subsurface load is considered in estimation. The algorithm of particle swarm optimization(PSO) with a swarm size of 400 is employed as well.Results indicate that the observed admittance is best-fitted by the modeled admittance based on a spherical shell model, which was proved to be unsatisfactory in the previous study. The best-fitted load ratio f is around-0.194. Such a small load ratio conforms to the direct proportion between the nearly uncompensated topography and its corresponding negative gravity anomaly. It also indicates that a surface load dominates all the loads. Constrained within 2σSTD, a small crustal thickness(～30 km) and a crustal density of ～2587 kg m-3are found, quite close to the results from previous GRAIL research. Considering the well constrained crustal thickness and density, the best-fitted elastic thickness(～7 km) is rational. This result is slightly smaller than the previous study(～12 km). Such difference can be attributed to the difference in crustal density used and the precision of gravity and topography data. Considering that the small difference between the modeled gravity anomaly and observations is quite small, a parameter inversed here could be an indicator of the subsurface structure beneath Clavius.

Detecting exoplanets with FAST?

We briefly review the various proposed scenarios that may lead to nonthermal radio emissions from exoplanetary systems(planetary magnetospheres, magnetosphere-ionosphere and magnetospheresatellite coupling, and star-planet interactions), and the physical information that can be drawn from their detection. The latter scenario is especially favorable to the production of radio emission above 70 MHz. We summarize the results of past and recent radio searches, and then discuss FAST characteristics and observation strategy, including synergies. We emphasize the importance of polarization measurements and a high duty-cycle for the very weak targets that radio-exoplanets prove to be.

Strong Spatial Aggregation of Martian Surface Temperature Shaped by Spatial and Seasonal Variations in Meteorological and Environmental Factors

Spatio-temporal variation in the Martian surface temperature(MST)is an indicator of ground level thermal processes and hence a building block for climate models.However,the distribution of MST exhibits different levels of spatial aggregation or heterogeneity,and varies in space and time.Furthermore,the effect of regional differences in meteorological or environmental factors on the MST is not well understood.Thus,we investigated the degree of spatial autocorrelation of MST across the surface of Mars globally by Moran’s I,and identified the hot spots by GetisOrd G;*.We also estimated the regional differences in the influence of seasonally dominant factors including thermal inertia(TI),albedo,surface pressure,latitude,dust and slope on MST by a geographically weighted regression model.The results indicate(1)that MST is spatially aggregated and hot and cold spots varied over time and space.(2)Hemispheric differences in topography,surface TI and albedo were primarily responsible for the hemispheric asymmetry of hot spots.(3)The dominant factors varied by geographical locations and seasons.For example,the seasonal Hadley circulation dominates at the low-latitudes and CO;circulation at the high-latitudes.(4)Regions with extreme variations in topography and low TI were sensitive to meteorological and environmental factors such as dust and CO_(2)ice.We conclude that the spatial autocorrelation of MST and the spatial and seasonal heterogeneity of influencing factors must be considered when simulating Martian climate models.This work provides a reference for further exploration of Martian climatic processes.

The Investigation of the Dynamical Evolution of Extrasolar Three-planetary System GJ 3138

This article is devoted to studying the dynamical evolution and orbital stability of compact extrasolar threeplanetary system GJ 3138. In this system, all semimajor axes are less than 0.7 au. The modeling of planetary motion is performed using the averaged semi-analytical motion theory of the second order in planetary masses,which the authors construct. Unknown and known with errors orbital elements vary in allowable limits to obtain a set of initial conditions. Each of these initial conditions is applied for the modeling of planetary motion. The assumption about the stability of observed planetary systems allows to eliminate the initial conditions leading to excessive growth of the orbital eccentricities and inclinations and to identify those under which these orbital elements conserve moderate values over the whole modeling interval. Thus, it becomes possible to limit the range of possible values of unknown orbital elements and determine their most probable values in terms of stability.

Searching for exoplanets by HEPS II. detecting earth-like planets in habitable zone around planet hosts within 30 pc

HEPS(Habitable ExoPlanet Survey) is a planning astrometry satellite that aims to find Earth-like planets in the solar neighbourhood. In this paper, we selected 140 planet harboring stars within 30 pc of the solar system to be potential targets for HEPS. We calculate the detection probability of the planet in habitable zone(HZ) for each system using the simulated data of astrometry measurements. For those host stars without planets in HZ, we inject an additional planet of 10 M⊕ in their HZs and check the stability of the systems. Considering five observation modes of different sampling cadence and total observation time, we obtain a table containing the total detection probability of the planets in HZs for all of the 140 selected systems. This paper provides a potential ranked list of target stars for HEPS, or other astrometric mission to detect Earth-like planets in the future. We also calculate an empirical fitted expression of the detection probability as a function of both sampling cadence and total observation time. We conclude a quantitative method to estimate the detection probability for certain planet hosts and observation modes via the empirical expression. We show the minimum requirements of both sampling cadence and observation time for Proxima Centauri, HD 189733 and HD 102365, if the detection probability of habitable-zone planets of these three systems needs to be 90%.

Gap formation in a self-gravitating disk and the associated migration of the embedded giant planet

We present the results of our recent study on the interactions between a giant planet and a self-gravitating gas disk. We investigate how the disk＇s self-gravity affects the gap formation process and the migration of the giant planet. Two series of 1-D and 2-D hydrodynamic simulations are performed. We select several surface densities and focus on the gravitationally stable region. To obtain more reliable gravity torques exerted on the planet, a refined treatment of the disk＇s gravity is adopted in the vicinity of the planet. Our results indicate that the net effect of the disk＇s self- gravity on the gap formation process depends on the surface density of the disk. We notice that there are two critical values, ∑I and ∑n. When the surface density of the disk is lower than the first one,∑0 〈 ∑I, the effect of self-gravity suppresses the formation of a gap. When ∑0 〉 ∑I, the self-gravity of the gas tends to benefit the gap formation process and enlarges the width/depth of the gap. According to our 1-D and 2-D simulations, we estimate the first critical surface density to be ∑I ≈ 0.8 MMSN. This effect increases until the surface density reaches the second critical value ∑n- When ∑0 〉 ∑n, the gravitational turbulence in the disk becomes dominant and the gap formation process is suppressed again. Our 2-D simulations show that this critical surface density is around 3.5 MMSN. We also study the associated orbital evolution of a giant planet. Under the effect of the disk＇s self-gravity, the migration rate of the giant planet increases when the disk is dominated by gravitational turbulence. We show that the migration timescale correlates with the effective viscosity and can be up to 104 yr.

The Possibility of Detecting our Solar System through Astrometry

Searching for exoplanets with different methods has always been the focus of astronomers over the past few years.Among multiple planet detection techniques,astrometry stands out for its capability to accurately determine the orbital parameters of exoplanets.In this study,we examine the likelihood of extraterrestrial intelligent civilizations detecting planets in our solar system using the astrometry method.By conducting injection-recovery simulations,we investigate the detectability of the four giant planets in our solar system under different observing baselines and observational errors.Our findings indicate that extraterrestrial intelligence could detect and characterize all four giant planets,provided they are observed for a minimum of 90 yr with signal-noise ratios exceeding 1.For individual planets such as Jupiter,Saturn,and Neptune,a baseline that surpasses half of their orbital periods is necessary for detection.However,Uranus requires longer observing baselines since its orbital period is roughly half of that of Neptune.If the astrometry precision is equal to or better than 10μas,all 8707 stars located within30 pc of our solar system possess the potential to detect the four giant planets within 100 yr.Additionally,our prediction suggests that over 300 stars positioned within 10 pc from our solar system could detect our Earth if they achieve an astrometry precision of 0.3μas.

Inversion of Venus internal structure based on geodetic data

Understanding the internal structure of Venus promotes the exploration of the evolutionary history of this planet.However,the existing research concerning the internal structure of Venus has not used any inversion methods.In this work we employed an inversion method to determine the internal structure of Venus using observational or hypothetical geodetic data;these data include mass,mean radius,mean moment of inertia and second degree tidal Love number k2.To determine the core state of Venus,we created two models of Venus,an isotropic 3-layer model with entire liquid core and an isotropic 4-layer model with liquid outer core and a solid inner core,assuming that the interior of Venus is spherically symmetric and in hydrostatic equilibrium.A series of the sensitivity analysis of interior structure parameters to the geodetic data considered in here shows that not all of the parameters can be constrained by the geodetic data from Venus.On this basis,a Markov Chain Monte Carlo algorithm was used to determine the posterior probability distribution and the optimal values of the internal structure parameters of Venus with the geodetic data.We found that the 3-layer model is more credible than the 4-layer model via currently geodetic data.For the assumption of the 3-layer model with the k2=0.295±0.066,I/MR^2=0.33±0.0165,andρ=5242.7±2.6 kg m^-3,the liquid iron-rich core of Venus has a radius of 3294+215-261km,which suggests a larger core than previous research has indicated.The average density of the mantle and liquid core of Venus are 4101+325-375and 11885+955-1242kg m~^-3,respectively.

两个可能具有2:1平运动共振结构系统的稳定性研究

通过分析现有视向速度资料提供的轨道拟合解,发现HD 155358和24 Sextanis两系统都有可能处于2:1平运动共振状态.主要讨论了两系统共振结构的动力学稳定性问题,计算了两系统最优拟合值1σ置信区间内大量样本的混沌指标?emax.结果表明:HD155358系统长期稳定,不依赖于平运动共振的保护.但是,24 Sextanis系统如果要维持长期稳定,2:1平运动共振保护是必要条件.

Volatile Depletion in Planet-Forming Disks

Newly born stars are surrounded by gas and dust with a attened axisymmetric distribution termed protoplanetary disk,in which planets are formed.Observations of these objects are necessary for understanding the formation and early evolution of stars and planets,and for revealing the composition of the raw material from which planets are made.Numerical models can extract important parameters from the observational data,including the gas and dust mass of the disk.These parameters are used as input for further modeling,e.g.,to calculate the chemical composition of the disk.A consistent thermochemical model should be able to reproduce the abundances of di erent species in the disk.However,this good wish has been challenged for many disks:models over-predict the emission line intensity of some species;namely,they are depleted(with respect to expectations from canonical models).In this review we show how this disparity indicates that dust evolution has signi cant e ects on gas chemistry,and may indicate the earliest stages of planet formation.