A study of the global magnetic activity of the star Kepler-17 using light curve inversion with bipartite regularization     

Tao Luo  Yan-Yan Liang  Wing-Huen Ip  Hao-Zhi Huang  Xu-Xin Lin 《天文和天体物理学研究(英文版)》2021,(4):95-114

A new method of light curve inversion with bipartite regularization(LIBR),which is complementary to the previous treatments by Bonomo and Lanza and Estrela and Valio,is used to reconstruct the physical properties of star spots on the solar-type star Kepler-17 by using the full Q1-Q17 data set.The Markov Chain Monte Carlo(MCMC) method was applied to find the best profile of the reconstructed surface.The known value of the rotation inclination of Kepler-17 allows the generation of a star spot model in a sequence of stellar rotation with a period of 12.26 d.Because of the nature of the light curve inversion,the spot model is limited to the equatorial region.We also investigated the starspot lifetimes of Kepler-17 utilizing the MCMC method.Combined with the LIBR inversion results,it was found that the star spots typically last from one to several stellar rotations.From the time evolution of the spot size,a magnetic cycle period of 437 d can be derived.This value is comparatively shorter than the solar cycle which might be a consequence of the younger age(～1.78 Gyr) of Kepler-17.The light curve of Kepler-17 is characterized by the presence of large-amplitude variation caused by star spots but no superflare activity.An interesting possibility is that the magnetic energy stored in the star spot regions could have been constantly dissipated by electrodynamic interaction between the central star and the hot Jupiter,Kepler-17 b,via a lower-level energy release process.  相似文献   

Chinese records on the correlation of heliocentric planetary alignments and earthquake activities     

W.-H. Ip 《Icarus》1976,29(3):435-436

A short account of the correlation of heliocentric planetary alignments and the earthquake activities in Northern China is given. It appears that such arrangement of planetary orbital positions has no effect on the triggering of earthquakes.  相似文献   

The neutral atmospheres of comets     

D. A. Mendis  W. -H. Ip 《Astrophysics and Space Science》1976,39(2):335-385

In this paper we have endeavored to critically evaluate our present understanding of cometary atmospheres. Following a brief introduction of the significance of the study of cometary atmospheres (Section 1), the relevant photometric and spectroscopic observations are summarized in Section 2.The interaction with the solar radiation, with regard to both the excitation of the observed species as well as the dissociation of stable molecules evaporating from the nucleus, is considered in Sections 3 and 4. The gas phase chemistry likely to take place in the dense inner coma is next considered in Section 5.The exospheric and hydrodynamic models of the expanding cometary atmosphere are considered in detail in Section 6, and both their limitations as well as possible improvements are discussed.The observed chemical composition of the neutral atmosphere and the inferred chemical composition of the volatile component of the nucleus, together with possible variations between different classes of comets is next considered in Section 7, and their possible cosmogonic significance is discussed.In conclusion, some of the important directions in which future research should progress, in order to provide more complete and secure knowledge of cometary atmospheres, are stressed (Section 8).Astrophysics and Space Science Review Paper.  相似文献   

Numerical investigation of wave propagation in the Liverpool Bay, NW England     

LI Ming  RAYMOND Ip  WOLF Judith  CHEN Xueen  BURROWS Richard 《海洋学报(英文版)》2011,30(5):1-13

The computer model for near shore wave propagation,SWAN,was used to study wave climates in Liverpool Bay,northwest England with various input parameters,including bottom friction factor,white capping,wind drag formulation and effects of tidal modulations.Results were compared with in-situ measurements and reveal the impacts from these inputs on the predictions of wave height and propagation distributions.In particular,the model results were found very sensitive to different input formulations,and tend to underestimate the wave parameters under storm conditions in comparison with the observations.It is therefore important to further validate the model against detailed field measurements,particularly under large storms that are often of the primary concern.  相似文献   

A dawn-to-dusk electric field in the Jovian magnetosphere     

C.K. Goertz  W.-H. Ip 《Planetary and Space Science》1984,32(2):179-185

We show that if Io-injected plasma is lost via a planetary wind a sun-fixed Birkeland current system may result. This is due to the fact that a current flows across a density gradient produced by the loss of plasma through the planetary wind in the tail. The divergent current is connected to field-aligned Birkeland currents which flow into the ionosphere at dawn and out of it at dusk. The closure currents in the ionosphere require a dawn-to-dusk electric field which at the orbit of Io is estimated to have a strength of a few mV m^?1. Independent estimates derived from the local time asymmetry of the torus u.v. emission indicate a field of 1.5mVm^?1.  相似文献   

On the structure of the Io torus     

C.K. Goertz  W.-H. Ip 《Planetary and Space Science》1982,30(9):855-864

It is now recognized that a number of neutral-plasma interaction processes are of great importance in the formation of the Io torus. One effect not yet considered in detail is the charge exchange between fast torus ions and the atmospheric neutrals producing fast neutrals energetic enough to escape from Io. Since near Io the plasma flow is reduced, the neutrals of charge exchange origin are not energetic enough to leave the Jovian system; these neutrals are therefore distributed over an extensive region as indicated by the sodium cloud. It is estimated here that the total neutral injection rate can reach 10²⁷ s^?1 if not more. New ions subsequently created in the distributed neutral atomic cloud as a result of charge exchange or electron impact ionization are picked up by the corotating magnetic field. The pick-up ions are hot with initial gyration speed near the corotation speed. The radial current driven by the pickup process cannot close in the torus but must be connected to the planetary ionosphere by field-aligned currents. These field-aligned currents will flow away from the equator at the outer edge of the neutral cloud and towards it at the inner edge. We find that the Jovian ionospheric photoelectrons alone cannot supply the current flowing away from the equator, and torus ions accelerated by a parallel electric field could be involved. The parallel potential drop is estimated to be several kV which is large enough to push the torus ions into the Jovian atmosphere. This loss could explain the sharp discontinuous change of flux tube content and ion temperature at L = 5.6 as well as the generation of auroral type hiss there. Finally we show that the inner torus should be denser at system III longitudes near 240° as a result of the enhanced secondary electron flux in this region. This effect may be related to the longitudinal brightness variation observed in the SII optical emissions.  相似文献   

Collisional interactions of ring particles: The ballistic transport process     

W.-H. Ip 《Icarus》1983,54(2):253-262

As the erosion rate of the Saturnian rings resulting from meteoroid bombardment can be quite significant in the evolutionary history of the ring system, a simple model is constructed to study the relevant dynamics of ballistic transport of the impact ejecta. The combined process of collision with the ring plane particles, with the impact probability related to the optical depth and inelastic rebound from the ring plane until the random motion of the particle is effectively damped, is traced by using the Monte Carlo method. The numerical results indicate that the final distribution of the ejecta depends very much on the initial ejection velocity. For high-velocity fragments, their distribution tends to follow the optical depth variation of the rings. But for low-velocity fragments, pronounced edge effect with ejected particles accumulated at the boundaries of optical depth discontinuities could result. Therefore, in a global scale, the large increase of optical depth near the inner edge of the B ring, for example, as well as the depletion of micrometer-sized particles in the B ring and the Cassini division may be interpreted by the mechanism of ballistic transport. The edge effect found in the calculations might also be closely related to the formation of sharp edges and double peaks in a number of narrow ringlets. (The simultaneous operation of ballistic transport diffusion and gravitational resonant effects of satellites remains to be investigated.)  相似文献   

A note on the cosmogony of the asteroidal belt     

W. -H. Ip 《Astrophysics and Space Science》1976,39(1):235-241

Several arguments based on the orbital dynamics of the asteroids are used to support the idea that the original solar nebula might not necessarily be the Laplacian type of thin disk-like structure. The orbital distribution of the large asteroids is suggested to be a direct result of their accretions of condensed grains in eccentric orbits via the jet stream process.  相似文献   

Neutral atmospheres of comets: A distributed source model     

W. -H. Ip  D. A. Mendis 《Astrophysics and Space Science》1974,26(1):153-166

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Evidence for methane and ammonia in the coma of comet P/Halley     

Allen M  Delitsky M  Huntress W  Yung Y  Ip WH  Schwenn R  Rosenbauer H  Shelley E  Balsiger H  Geiss J 《Astronomy and Astrophysics》1987,187(1-2):502-512

Methane and ammonia abundances in the coma of Halley are derived from Giotto IMS data using an Eulerian model of chemical and physical processes inside the contact surface to simulate Giotto HIS ion mass spectral data for mass-to-charge ratios (m/q) from 15 to 19. The ratio m/q = 19/18 as a function of distance from the nucleus is not reproduced by a model for a pure water coma. It is necessary to include the presence of NH3, and uniquely NH3, in coma gases in order to explain the data. A ratio of production rates Q(NH3)/Q(H2O) = 0.01-0.02 results in model values approximating the Giotto data. Methane is identified as the most probable source of the distinct peak at m/q = 15. The observations are fit best with Q(CH4)/Q(H2O) = 0.02. The chemical composition of the comet nucleus implied by these production rate ratios is unlike that of the outer planets. On the other hand, there are also significant differences from observations of gas phase interstellar material.  相似文献