Rotation of split cometary nuclei

A simple model for the rotational motion of split cometary nuclei is studied. A large-amplitude precession is easily excited due to the change of the moments of inertia even if the perturbation is small at the splitting. The damping timescale of the excited precession is widely ranged because of the uncertainty of the physical parameter of cometary nuclei. Another possibility for clarifying the evolution of the short period comets by studying the split cometary nuclei is also discussed

Lightcurve of comet Austin(1989c1) and its dust mantle development

Brightness variations of comet Austin(1989c1) were investigated in terms of the variations of water production rate. We translated the visual brightness data into water production rates using Newburn's semi-empirical law. The curve of the water production rates as a function of heliocentric distance was compared with the model calculations that assumed energy balance between the solar incident and vaporization of water. Thermal flow in a dust mantle at a surface of the nucleus is also included in the model. The model calculations including the dust mantle are more favorable for the observed rate than non-dust mantle cases. The extinction after the perihelion passage suggests that the dust mantle developed gradually

Meteor radiant mapping with MU radar

The radiant point mapping of meteor showers with the MU radar by using a modified mapping method originally proposed by Morton and Jones (1982) was carried out. The modification is that each meteor echo was weighted by using the beam pattern of the radar system. A preliminary result of the radiant point mapping of the Geminids meteor shower in 1989 is presented

Cloud reflection modelling for impact flashes on Jupiter: A new constraint on the bulk properties of the impact objects

We investigate optical characteristics of flashes caused by impacting meter- to decameter-sized outer solar system objects on Jupiter and contributions of reflected light from surface clouds at visible wavelengths to estimate more accurate bulk parameters such as the luminous energy of the flash, the kinetic energy, the mass, and the size of the impact object. Based on the results of recent reflectivity studies of the Jovian surface, we develop a cloud reflection model that calculates the contribution of the reflected light relative to that directly from the flash. We compare the apparent luminous energy of the previously reported flashes with the expected cloud reflection contributions to obtain their revised bulk parameters. We found that the cloud reflection contributions can be up to 200% of the flux directly from the flash and thus can be the most significant uncertainty in the measurement of the bulk parameters. The reflection contributions strongly depend on wavelength. With our cloud reflection correction, the revised bulk parameters of the previously reported flashes are obtained. Our cloud reflection correction provides a better understanding of the properties of impacting objects on Jupiter and is crucial for ongoing detailed investigations using high-sensitivity and multi-wavelength observation systems such as PONCOTS. It will also be useful for understanding other optical transients in Jupiter's upper atmosphere, such as the recently discovered sprite-like events.Comment: 6 pages, 4 figures, accepted for publication in Astronomy & Astrophysic

Modelling the optical energy profile of the 2021 October Jupiter impact flash

We have conducted numerical simulations to reproduce the observed optical energy profile of the 15 October 2021 (UT) impact flash on Jupiter, which was the largest and the most well-observed flash event detected by ground-based movie observations. The observed long-duration ($\sim 5.5~{\rm s}$) optical emission can be reproduced by an impact of an object with an exceptionally small angle of entry relative to the horizontal. The apparent lack of the impact debris feature despite the large impact object was possibly due to the shallower angle of entry ($\le 12^\circ$), which resulted in the lower ablation per unit volume at altitudes higher than $50 \, {\rm km}$, and the volume densities of the ablated materials were too low to allow the debris particulates to coagulate. The absence of temporal methane absorption change in the observed flash spectrum is consistent with the best-fit results. The model better fits the observed optical energy profile for weaker material (cometary and stony) cases than for metallic ones. Based on the simulation results, prospects for future observations of impact flashes are discussed.Comment: 6 pages, 5 figures, Accepted for publication in MNRA

Production of Scalar Higgs and Pseudoscalar Higgs in Multi-Higgs Doublet Models at γγ\gamma\gamma Colliders

We present the effects of heavy CP-even (H) and CP-odd (A) Higgs bosons on the production cross section of the process $\gamma\gamma$ $\to t\bar{t}$ at the energy around the mass poles of the Higgs bosons. It is found that the interference between H and A with the small mass gap, as well as the ones between Higgs bosons and the continuum, contributes to the cross section, if the photon beams are polarized and if we observe the helicity of the top quarks. It is demonstrated in the framework of the minimal supersymmetric extension of the standard model that the H and A contributions can be sizable at future $\gamma\gamma$ colliders for small value of $\tan\beta$. The methods to measure the CP-parity of the Higgs boson are also presented. The statistical significances of detecting the Higgs signals and measuring the Higgs CP-parity are evaluated.Comment: 23 pages, LATEX file with 8 PS figures, to be published in Eur.Phys.J.

Detection of an extremely large impact flash on Jupiter by high-cadence multiwavelength observations

木星で超大型の衝突閃光現象を発見 --京大のとある屋上の小さな望遠鏡による大発見--. 京都大学プレスリリース. 2022-09-13.We report the detection of an optical impact flash on Jupiter on 2021 October 15 by a dedicated telescope, Planetary ObservatioN Camera for Optical Transient Surveys, for the first time. Our temporally resolved three-band observations of the flash allowed investigations of its optical energy without the need for approximations on the impact brightness temperature. The kinetic energy of the impactor was equivalent to approximately two megatons of TNT, an order of magnitude greater than that of previously detected flashes on Jupiter and comparable with the Tunguska impact on Earth in 1908. This detection indicates that Tunguska-like impact events on Jupiter occur approximately once per year, two to three orders of magnitude more frequently than terrestrial impacts. The observed flash displayed a single-temperature blackbody spectrum with an effective temperature of approximately 8300 K without clear temporal variation, possibly representing common radiative features of terrestrial Tunguska-class superbolides