arXiv subjects

Jianghui Ji

Publications and source records attributed to Jianghui Ji.

At least 55 records · Page 3Linked to original sources

arXiv2019

The Observability Of Vortex-Driven Spiral Arms In Protoplanetary Disk: Basic Spiral Properties

Some circumstellar disks are observed to show prominent spiral arms in infrared scattered light or (sub-)millimeter dust continuum. The spirals might be formed from self-gravity, shadows, or planet-disk interactions. Recently, it was hypothesized that massive vortices can drive spiral arms in protoplanetary disks in a way analogous to planets. In this paper, we study the basic properties of vortex-driven spirals by the Rossby Wave Instability in 2D hydrodynamics simulations. We study how the surface density contrast, the number, and the shape of vortex-driven spirals depend on the properties of the vortex. We also compare vortex-driven spirals with those induced by planets. The surface density contrast of vortex-driven spirals in our simulations are comparable to those driven by a sub-thermal mass planet, typically a few to a few tens of Earth masses. In addition, different from the latter, the former is not sensitive to the mass of the vortex. Vortex-driven spiral arms are not expected to be detectable in current scattered light observations, and the prominent spirals observed in scattered light in a few protoplanetary disks, such as SAO 206462 (HD 135344B), MWC 758, and LkHa 330, are unlikely to be induced by the candidate vortices in them.

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arXiv2019

New constraints on the dust and gas distribution in the LkCa 15 disk from ALMA

We search a large parameter space of the LkCa 15's disk density profile to fit its observed radial intensity profile of $^{12}$CO (J = 3-2) obtained from ALMA. The best-fit model within the parameter space has a disk mass of 0.1 $M_{\odot}$ (using an abundance ratio of $^{12}$CO/H$_2$ $=$ 1.4 $\times 10^{-4}$ in mass), an inner cavity of 45 AU in radius, an outer edge at $\sim$ 600 AU, and a disk surface density profile follows a power-law of the form $ρ_r \propto r^{-4}$. For the disk density profiles that can lead to a small reduced $χ^2$ of goodness-of-fit, we find that there is a clear linear correlation between the disk mass and the power-law index $γ$ in the equation of disk density profile. This suggests that the $^{12}$CO disk of LkCa 15 is optically thick and we can fit its $^{12}$CO radial intensity profile using either a lower disk mass with a smaller $γ$ or a higher disk mass with a bigger $γ$. By comparing the $^{12}$CO channel maps of the best-fit model with disk models with higher or lower masses, we find that a disk mass of $\sim$ 0.1 $M_{\odot}$ can best reproduce the observed morphology of the $^{12}$CO channel maps. The dust continuum map at 0.87 mm of the LkCa 15 disk shows an inner cavity of the similar size of the best-fit gas model, but its out edge is at $\sim$ 200 AU, much smaller than the fitted gas disk. Such a discrepancy between the outer edges of the gas and dust disks is consistent with dust drifting and trapping models.

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arXiv2018

Dynamical evolution and stability maps of the Proxima Centauri system

Proxima Centauri was recently discovered to host an Earth-mass planet of Proxima b, and a 215-day signal which is probably a potential planet c. In this work, we investigate the dynamical evolution of the Proxima Centauri system with the full equations of motion and semi-analytical models including relativistic and tidal effects. We adopt the modified Lagrange-Laplace secular equations to study the evolution of eccentricity of Proxima b, and find that the outcomes are consistent with those from the numerical simulations. The simulations show that relativistic effects have an influence on the evolution of eccentricities of planetary orbits, whereas tidal effects primarily affects the eccentricity of Proxima b over long timescale. Moreover, using the MEGNO (the Mean Exponential Growth factor of Nearby Orbits) technique, we place dynamical constraints on orbital parameters that result in stable or quasi-periodic motions for coplanar and non-coplanar configurations. In the coplanar case, we find that the orbit of Proxima b is stable for the semi-major axis ranging from 0.02 au to 0.1 au and the eccentricity being less than 0.4. This is where the best-fitting parameters for Proxima b exactly fall. Additional simulations show that the robust stability of this system would favor an eccentricity of Proxima b less than 0.45 and that of Proxima c below 0.65. In the non-coplanar case, we find that mutual inclinations of two planets must be lower than $50^{\circ}$ in order to provide stability. Finally, we estimate the mass of Proxima c to be $3.13~{M_ \oplus } \le {m_c} \le 70.7~{M_ \oplus }$ when $1.27~{M_ \oplus } \le {m_b} \le 1.6~{M_ \oplus }$, if ${i_{mutual}} \le {50^{\circ}}$ and $ΔΩ= 0^{\circ}$.

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arXiv2018

Identifying Anticyclonic Vortex Features Produced by the Rossby Wave Instability in Protoplanetary Disks

Several nearby protoplanetary disks have been observed to display large scale crescents in the (sub)millimeter dust continuum emission. One interpretation is that these structures correspond to anticyclonic vortices generated by the Rossby wave instability within the gaseous disk. Such vortices have local gas over-densities and are expected to concentrate dust particles with Stokes number around unity. This process might catalyze the formation of planetesimals. Whereas recent observations showed that dust crescent are indeed regions where millimeter-size particles have abnormally high concentration relative to the gas and smaller grains, no observations have yet shown that the gas within the crescent region counter-rotates with respect to the protoplanetary disk. Here we investigate the detectability of anticyclonic features through measurement of the line-of-sight component of the gas velocity obtained with ALMA. We carry out 2D hydrodynamic simulations and 3D radiative transfer calculation of a protoplanetary disk characterized by a vortex created by the tidal interaction with a massive planet. As a case study, the disk parameters are chosen to mimic the IRS 48 system, which has the most prominent crescent observed to date. We generate synthetic ALMA observations of both the dust continuum and 12CO emission around the frequency of 345 GHz. We find that the anticyclonic features of vortex are weak but can be detected if both the source and the observational setup are properly chosen. We provide a recipe for maximizing the probability to detect such vortex features and present an analysis procedure to infer their kinematic properties.

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arXiv2018

Formation of S-type planets in close binaries: scattering induced tidal capture of circumbinary planets

Although several S-type and P-type planets in binary systems were discovered in past years, S-type planets have not yet been found in close binaries with an orbital separation not more than 5 au. Recent studies suggest that S-type planets in close binaries may be detected through high-accuracy observations. However, nowadays planet formation theories imply that it is difficult for S-type planets in close binaries systems to form in situ. In this work, we extensively perform numerical simulations to explore scenarios of planet-planet scattering among circumbinary planets and subsequent tidal capture in various binary configurations, to examine whether the mechanism can play a part in producing such kind of planets. Our results show that this mechanism is robust. The maximum capture probability is $\sim 10\%$, which can be comparable to the tidal capture probability of hot Jupiters in single star systems. The capture probability is related to binary configurations, where a smaller eccentricity or a low mass ratio of the binary will lead to a larger probability of capture, and vice versa. Furthermore, we find that S-type planets with retrograde orbits can be naturally produced via capture process. These planets on retrograde orbits can help us distinguish in situ formation and post-capture origin for S-type planet in close binaries systems. The forthcoming missions (PLATO) will provide the opportunity and feasibility to detect such planets. Our work provides several suggestions for selecting target binaries in search for S-type planets in the near future.

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arXiv2018

Investigation of Thermal Inertia and Surface Properties for Near-Earth Asteroid (162173) 1999 JU3

In order to obtain the substantial information about the surface physics and thermal property of the target asteroid (162173) 1999 JU3, which will be visited by Hayabusa 2 in a sample return mission, with the Advanced Thermal Physical Model (ATPM) we estimate the possible thermal inertia distribution over its surface, and infer the major material composition of its surface materials. In addition, the effective diameter and geometric albedo are derived to be $D_{\rm eff}=1.13\pm0.03\rm~km$, $p_{\rm v}=0.042\pm0.003$, respectively, and the average thermal inertia is estimated to be about $(300\pm50)\rm~J\cdot m^{-2}\cdot s^{-0.5}\cdot K^{-1}$. According to the derived thermal inertia distribution, we infer that the major area on the surface of the target asteroid may be covered by loose materials, such as rock debris, sands, and so on, but few bare rocks may exist in a very small region. In this sense, the sample return mission of Hayabusa 2 is feasible, when it is performed successfully, it will certainly bring significant scientific information to the research of asteroids.

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arXiv2018

Tidal Evolution of Kepler lower-mass Planets

The planets with a radius $<$ 4 $R$$_\oplus$ observed by the Kepler mission exhibit a unique feature, and propose a challenge for current planetary formation models. The tidal effect between a planet and its host star plays an essential role in reconfiguring the final orbits of the short-period planets. In this work, based on various initial Rayleigh distributions of the orbital elements, the final semi-major axis distributions of the planets with a radius $<$ 4 $R_\oplus$ after suffering tidal evolutions are investigated. Our simulations have qualitatively revealed some statistical properties: the semi-major axis and its peak value all increase with the increase of the initial semi-major axis and eccentricity. For the case that the initial mean semi-major axis is less than 0.1 au and the mean eccentricity is larger than 0.25, the results of numerical simulation are approximately consistent with the observation. In addition, the effects of other parameters, such as the tidal dissipation coefficient, stellar mass and planetary mass, etc., on the final semi-major axis distribution after tidal evolution are all relatively small. Based on the simulation results, we have tried to find some clues for the formation mechanism of low-mass planets. We speculate that these low-mass planets probably form in the far place of protoplanetary disk with a moderate eccentricity via the type I migration, and it is also possible to form in situ.

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arXiv2018

Photometric Follow-up Transit (Primary Eclipse) Observations of WASP-43 b and TrES-3b and A Study on Their Transit Timing Variations

Two photometric follow-up transit (primary eclipse) observations on WASP-43 b and four observations on TrES-3 b are performed using the Xuyi Near-Earth Object Survey Telescope. After differential photometry and light curve analysis, the physical parameters of the two systems are obtained and are in good match with the literature. Combining with transit data from a lot of literature, the residuals ($O-C$) of transit observations of both systems are fitted with the linear and quadratic functions. With the linear fitting, the periods and transit timing variations (TTVs) of the planets are obtained, and no obvious periodic TTV signal is found in both systems after an analysis. The maximum mass of a perturbing planet located at the 1:2 mean motion resonance (MMR) for WASP-43 b and TrES-3 b is estimated to be 1.826 and 1.504 Earth mass, respectively. By quadratic fitting, it is confirmed that WASP-43 b may have a long-term TTV which means an orbital decay. The decay rate is shown to be $\dot{P} =(-0.005248 \pm 0.001714)$~s$\cdot$yr$^{-1}$, and compared with the previous results. Based on this, the lower limit of the stellar tidal quality parameter of WASP-43 is calculated to be $Q'_{\rm *} \ge 1.5\times10^5$, and the remaining lifetimes of the planets are presented for the different $Q'_{\rm *}$ values of the two systems, correspondingly.

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arXiv2018

The formation mechanism of 4179 Toutatis' elongated bi-lobed structure in a close Earth encounter scenario

The optical images of near-Earth asteroid 4179 Toutatis acquired by Chang'e-2 spacecraft show that Toutatis has an elongated contact binary configuration, with the contact point located along the long axis. We speculate that such configuration may have resulted from a low-speed impact between two components. In this work, we performed a series of numerical simulations and compared the results with the optical images, to examine the mechanism and better understand the formation of Toutatis. Herein we propose an scenario that an assumed separated binary precursor could undergo a close encounter with Earth, leading to an impact between the primary and secondary, and the elongation is caused by Earth's tide. The precursor is assumed to be a doubly synchronous binary with a semi-major axis of 4 $R_p$ (radius of primary) and the two components are represented as spherical cohesionless self-gravitating granular aggregates. The mutual orbits are simulated in a Monte Carlo routine to provide appropriate parameters for our \emph{N}-body simulations of impact and tidal distortion. We employ the \emph{pkdgrav} package with a soft-sphere discrete element method (SSDEM) to explore the entire scenarios. The results show that contact binary configurations are natural outcomes under this scenario, whereas the shape of the primary is almost not affected by the impact of the secondary. However, our simulations further provide an elongated contact binary configuration best-matching to the shape of Toutatis at an approaching distance $r_p$ = 1.4 $\sim$ 1.5 $R_e$ (Earth radius), indicative of a likely formation scenario for configurations of Toutatis-like elongated contact binaries.

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arXiv2018

Limits on radio emission from meteors using the MWA

Recently, low frequency, broadband radio emission has been observed accompanying bright meteors by the Long Wavelength Array (LWA). The broadband spectra between 20 and 60 MHz were captured for several events, while the spectral index (dependence of flux density on frequency, with $S_ν\propto ν^α$) was estimated to be $-4\pm1$ during the peak of meteor afterglows. Here we present a survey of meteor emission and other transient events using the Murchison Widefield Array (MWA) at 72-103 MHz. In our 322-hour survey, down to a $5σ$ detection threshold of 3.5 Jy/beam, no transient candidates were identified as intrinsic emission from meteors. We derived an upper limit of -3.7 (95% confidence limit) on the spectral index in our frequency range. We also report detections of other transient events, like reflected FM broadcast signals from small satellites, conclusively demonstrating the ability of the MWA to detect and track space debris on scales as small as 0.1 m in low Earth orbits.

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arXiv2017

Near Mean-motion Resonances in the Systems Observed by Kepler: Affected by Mass Accretion and Type I Migration

The Kepler mission has released over 4496 planetary candidates, among which 3483 planets have been confirmed as of April 2017. The statistical results of the planets show that there are two peaks around 1.5 and 2.0 in the distribution of orbital period ratios. The observations indicate that a plenty of planet pairs could have firstly been captured into mean motion resonances (MMRs) in planetary formation. Subsequently, these planets depart from exact resonant locations to be near MMRs configurations. Through type I migration, two low-mass planets have a tendency to be trapped into first-order MMRs (2:1 or 3:2 MMRs), however two scenarios of mass accretion of planets and potential outward migration play an important role in reshaping their final orbital configurations. Under the scenario of mass accretion, the planet pairs can cross 2:1 MMRs and then enter into 3:2 MMRs, especially for the inner pairs. With such formation scenario, the possibility that two planets are locked into 3:2 MMRs can increase if they are formed in a flat disk. Moreover, the outward migration can make planets have a high likelihood to be trapped into 3:2 MMRs. We perform additional runs to investigate the mass relationship for those planets in three-planet systems, and we show that two peaks near 1.5 and 2.0 for the period ratios of two planets can be easily reproduced through our formation scenario. We further show that the systems in chain resonances (e.g., 4:2:1, 3:2:1, 6:3:2 and 9:6:4 MMRs), have been observed in our simulations. This mechanism can be applicable to understand the formation of systems of Kepler-48, Kepler-53, Kepler-100, Kepler-192, Kepler-297, Kepler-399, and Kepler-450.

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arXiv2017

The scattering outcomes of Kepler circumbinary planets: planet mass ratio

Recent studies reveal that the free eccentricities of Kepler-34b and Kepler-413b are much larger than their forced eccentricities, implying that the scattering events may take place in their formation. The observed orbital configuration of Kepler-34b cannot be well reproduced in disk-driven migration models, whereas a two-planet scattering scenario can play a significant role of shaping the planetary configuration. These studies indicate that circumbinary planets discovered by Kepler may have experienced scattering process. In this work, we extensively investigate the scattering outcomes of circumbinary planets focusing on the effects of planet mass ratio. We find that the planetary mass ratio and the the initial relative locations of planets act as two important parameters which affect the eccentricity distribution of the surviving planets. As an application of our model, we discuss the observed orbital configurations of Kepler-34b and Kepler-413b. We first adopt the results from the disk-driven models as the initial conditions, then simulate the scattering process occurred in the late evolution stage of circumbinary planets. We show that the present orbital configurations of Kepler-34b and Kepler-413b can be well reproduced when considering two unequal-mass planet ejection model. Our work further suggests that some of the currently discovered circumbinary single-planet systems may be the survivals of original multiple-planet systems. The disk-driven migration and the scattering events occurring in the late stage both play an irreplaceable role in sculpting the final systems.

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arXiv2017

Using Chebyshev polynomials interpolation to improve the computation efficiency of gravity near an irregular-shaped asteroid

In asteroid rendezvous missions, the dynamical environment near the asteroid's surface should be made clear prior to the mission launch. However, most of the asteroids have irregular shapes, which lower the efficiency of calculating their gravitational field by adopting the traditional polyhedral method. In this work, we propose a method to partition the space near the asteroid adaptively along three spherical coordinates and use Chebyshev polynomials interpolation to represent the gravitational acceleration in each cell. Moreover, we compare four different interpolation schemes to obtain the best precision with the identical initial parameters. An error-adaptive octree division is combined to improve the interpolation precision near the surface. As an example, we take the typical irregular-shaped near-Earth asteroid 4179 Toutatis to show the advantage of this method, as a result, we show that the efficiency can be increased by hundreds to thousands times with our method. In a word, this method can be applicable to other irregular-shaped asteroids and can greatly improve the evaluation efficiency.

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arXiv2017

Thermophysical characteristics of the large main-belt asteroid (349) Dembowska

(349) Dembowska, a large, bright main-belt asteroid, has a fast rotation and oblique spin axis. It may have experienced partial melting and differentiation. We constrain Dembowska's thermophysical properties, e.g., thermal inertia, roughness fraction, geometric albedo and effective diameter within 3$σ$ uncertainty of $Γ=20^{+12}_{-7}\rm~Jm^{-2}s^{-0.5}K^{-1}$, $f_{\rm r}=0.25^{+0.60}_{-0.25}$, $p_{\rm v}=0.309^{+0.026}_{-0.038}$, and $D_{\rm eff}=155.8^{+7.5}_{-6.2}\rm~km$, by utilizing the Advanced Thermophysical Model (ATPM) to analyse four sets of thermal infrared data obtained by IRAS, AKARI, WISE and Subaru/COMICS at different epochs. In addition, by modeling the thermal lightcurve observed by WISE, we obtain the rotational phases of each dataset. These rotationally resolved data do not reveal significant variations of thermal inertia and roughness across the surface, indicating the surface of Dembowska should be covered by a dusty regolith layer with few rocks or boulders. Besides, the low thermal inertia of Dembowska show no significant difference with other asteroids larger than 100 km, indicating the dynamical lives of these large asteroids are long enough to make the surface to have sufficiently low thermal inertia. Furthermore, based on the derived surface thermophysical properties, as well as the known orbital and rotational parameters, we can simulate Dembowska's surface and subsurface temperature throughout its orbital period. The surface temperature varies from $\sim40$ K to $\sim220$ K, showing significant seasonal variation, whereas the subsurface temperature achieves equilibrium temperature about $120\sim160$ K below $30\sim50$ cm depth.

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arXiv2017

Surface thermophysical properties investigation of the potentially hazardous asteroid (99942) Apophis

In this work, we investigate the surface thermophysical properties (thermal emissivity, thermal inertia, roughness fraction and geometric albedo) of asteroid (99942) Apophis, using the currently available thermal infrared observations of CanariCam on Gran Telescopio CANARIAS and far-infrared data by PACS of Herschel, on the basis of the Advanced thermophysical model. We show that the thermal emissivity of Apophis should be wavelength dependent from $8.70~μm$ to $160~μm$, and the maximum emissivity may arise around $20~μm$ similar to that of Vesta. Moreover, we further derive the thermal inertia, roughness fraction, geometric albedo and effective diameter of Apophis within a possible 1$σ$ scale of $Γ=100^{+100}_{-52}\rm~Jm^{-2}s^{-0.5}K^{-1}$, $f_{\rm r}=0.78\sim1.0$, $p_{\rm v}=0.286^{+0.030}_{-0.026}$, $D_{\rm eff}=378^{+19}_{-25}\rm~m$, and 3$σ$ scale of $Γ=100^{+240}_{-100}\rm~Jm^{-2}s^{-0.5}K^{-1}$, $f_{\rm r}=0.2\sim1.0$, $p_{\rm v}=0.286^{+0.039}_{-0.029}$, $D_{\rm eff}=378^{+27}_{-29}\rm~m$. The derived low thermal inertia but high roughness fraction may imply that Apophis could have regolith on its surface, and less regolith migration process has happened in comparison with asteroid Itokawa. Our results show that small-size asteroids could also have fine regolith on the surface, and further infer that Apophis may be delivered from the Main Belt by Yarkovsky effect.

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arXiv2017

Terrestrial Planets Formation under Migration: the Systems near 4:2:1 Mean Motion Resonance

In this work, we extensively investigate the formation of near 4:2:1 mean motion resonances (MMRs) configuration by performing two sets of N-body simulations. We model the eccentricity damping, gas drag, type I and type II planetary migration of planetesimals, planetary embryos and giant planets in the first sets. For the simulations of giant planets with type II migration, the massive terrestrial planets, with a mass up to several Earth masses, are likely produced in the systems. We further show that by shepherding and/or scattering mechanisms through Jovian planet's type II migration, the terrestrial planets and giant planets in the systems can be evolved into a near 4:2:1 MMRs. Moreover, the models are applicable to the formation of Kepler-238 and 302 systems. In the second set, we study the 4:2:1 MMRs formation in the terrestrial planetary systems, where the planets undergo type I migration and eccentricity damping. By considering type I migration, $\sim$ 17.1\% of the simulations indicate that terrestrial planets are evolved into 4:2:1 MMRs. However, this probability should depend on the initial conditions of planets. Hence, we conclude that both type I and type II migration can play a crucial role in close-in terrestrial planet formation.

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arXiv2016

Modeling Dust Emission of HL Tau Disk Based on Planet-Disk Interactions

We use extensive global two-dimensional hydrodynamic disk gas+dust simulations with embedded planets, coupled with three dimensional radiative transfer calculations, to model the dust ring and gap structures in the HL Tau protoplanetary disk observed with the Atacama Large Millimeter/Submillimeter Array (ALMA). We include the self-gravity of disk gas and dust components and make reasonable choices of disk parameters, assuming an already settled dust distribution and no planet migration. We can obtain quite adequate fits to the observed dust emission using three planets with masses 0.35, 0.17, and 0.26 $M_{Jup}$ at 13.1, 33.0, and 68.6 AU, respectively. Implications for the planet formation as well as the limitations of this scenario are discussed.

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arXiv2015

TianQin: a space-borne gravitational wave detector

TianQin is a proposal for a space-borne detector of gravitational waves in the millihertz frequencies. The experiment relies on a constellation of three drag-free spacecraft orbiting the Earth. Inter-spacecraft laser interferometry is used to monitor the distances between the test masses. The experiment is designed to be capable of detecting a signal with high confidence from a single source of gravitational waves within a few months of observing time. We describe the preliminary mission concept for TianQin, including the candidate source and experimental designs. We present estimates for the major constituents of the experiment's error budget and discuss the project's overall feasibility. Given the current level of technology readiness, we expect TianQin to be flown in the second half of the next decade.

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