Planet seminar is held at 14:00 every Tuesday (Organizers: Yuichi Ito, Kenji Furuya)
| Date | Speaker | Title | Remarks | Person in charge |
|---|---|---|---|---|
| 7/20 | Huan-Yu Teng | Exploring Planetary Systems around Evolved Stars through the Radial Velocity Method — The latest results from EAPS-Net | Yuichi Ito | |
| 7/27 | Kei Tanaka | Hot Disks in Massive Star Formation | Kenji Furuya | |
| 8/3 | Yukihiko Hasegawa | Collisional Growth and Fragmentation of Dust Aggregates | Given in Japanese | Kenji Furuya |
| 10/24 | Yuhito Shibaike | Constraints on PDS70 b and c with the dust continuum emission from the circumplanetary discs | Kenji Furuya | |
| 11/14 | Sota Arakawa | Numerical investigations on collisional behaviors of dust aggregates | Kenji Furuya | |
| 11/21 | Yuki Nakamura | Impacts of solar energetic particles on the Martian atmosphere | Yuichi Ito | |
| 11/28 | Takahiro Ueda | A Comprehensive Model of Gravitationally Self-Regulated Protoplanetary Disks Supported by Multiple Observations of the IM Lup Disk | Kenji Furuya | |
| 1/8 | Xiaoyi Ma | Vortex-induced substructures in protoplanetary disks | Akimasa Kataoka Yuichi Ito |
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| 1/15 | Xinting Yu | Unlocking the Nature of Sub-Neptunes -Atmospheric Characterization in the JWST era | Monday from 14:00 | Kazumasa Ohno Kenji Furuya |
| 1/16 | Nicolas Kaufmann | Population level study of the influence of planetesimal fragmentation on planet formation | Yuhito Shibaike Yuichi Ito |
|
| 2/6 | Yoshiharu Shinnaka | Comet observations | Kenji Furuya | |
Huan-Yu Teng (Tokyo Institute of Technology),
Exploring Planetary Systems around Evolved Stars through the Radial Velocity Method — The latest results from EAPS-Net
The formation of giant planets is debated, with observational evidence needed to refine and augment the theories. In this study, we conduct the continuation of our radial velocity planet survey, the Okayama Planet Search Program (OPSP) and its collaborative East Asian Planet Search Network (EAPS-Net), to search for and characterize planets targeting evolved stars. We have validated diverse planet populations orbiting stars with wide mass range, investigated the correlation between planetary and stellar properties, and discussed planet formation and migration theories for specific planetary systems within OPSP and EAPS-Net framework. In the presentation, I will mainly introduce the latest planet discovery status from EAPS-Net, and focus on the correlation between planetary characteristics and stellar properties, as well as the inference on planet formation from our observations.
Kei Tanaka (Tokyo Institute of Technology),
Hot Disks in Massive Star Formation
Recent high-resolution observations have revealed detailed structures and chemistry in protoplanetary disks around low-mass stars. However, these observations are mostly limited to regions outside the water snowlines with temperatures of <200K. In contrast, accretion disks around massive stars have been found to reach temperatures as high as ~200-1000 K or even hotter due to the intense stellar radiation and high accretion heating. These conditions provide unique opportunities to investigate the physics and chemistry of gas and dust at such high temperatures (e.g., the collisional growth of silicate grains, sublimation of refractory materials, and evaporation of photoionized gas. In this talk, I will introduce our theoretical and observational studies on “hot disks” around massive stars and also discuss some future perspectives for this research in the ngVLA era.
Yukihiko Hasegawa (Tohoku University),
Collisional Growth and Fragmentation of Dust Aggregates
The dust grains grow and fragment through collisions between dust grains in protoplanetary disks. To clarify the evolution process of dust grains, we need to know the detailed physical properties of collisions between dust grains. In this seminar, I’ll talk about collisional outcomes of water-ice dust aggregates with various mass ratios; we particularly focus on unequal-mass offset collisions. We carried out three-dimensional numerical N-body simulations of collisions between two dust aggregates in a wide range of the mass ratio 1-64. First, we found that the mass transfer from a larger target to a smaller projectile is a dominant process in collisions with a mass ratio higher than 3. As a result, the critical velocity for fragmentation of the largest body is considerably reduced due to the mass transfer for such unequal-mass collisions; the critical velocity of collisions with a mass ratio of 3 is about half of that obtained from equal-mass collisions. Next, we derived analytic expressions of the mass distribution of large remnants and small fragments by numerical fitting to the simulation results. Our analytic formulae for masses of the large remnants can reproduce the contribution of mass transfer from a larger target to a smaller projectile. Our fragment model can roughly reproduce the results of our simulations and be applied to statistical simulations of the dust evolution.
Yuhito Shibaike (NAOJ),
Constraints on PDS70 b and c with the dust continuum emission from the circumplanetary discs
A young T Tauri star PDS70 has two gas accreting planets sharing one large gap in a pre-transitional disc. Dust continuum emission from PDS70 c has been detected by Atacama Large Millimeter/submillimeter Array (ALMA) Band 7, considered as the evidence of the circumplanetary disc (CPDs). However, there has been no detection of the dust emission from the CPD of PDS70 b. We constrained the planet mass and the gas accretion rates of the planets by introducing a dust evolution model to the CPDs and reproducing the observations, which is the first case to succeed in obtaining the constraints on the planet properties with the dust continuum emission from CPDs. Summarizing the obtained constraints, I will also discuss a possible scenario for the two planets explaining consistently their observations.
Sota Arakawa (JAMSTEC),
Numerical investigations on collisional behaviors of dust aggregates
Understanding the collisional behavior of dust aggregates is essential in the context of planet formation. It is known that low-velocity collisions of dust aggregates result in bouncing rather than sticking when the filling factor of colliding dust aggregates is higher than a threshold value. However, a large discrepancy between numerical and experimental results on the threshold filling factor was reported so far. In this study, we perform numerical simulations using soft-sphere discrete element methods and demonstrate that the sticking probability decreases with increasing aggregate radius. Our results suggest that the large discrepancy in the threshold filling factor may reflect the difference in the size of dust aggregates in earlier numerical simulations and laboratory experiments.
Yuki Nakamura(The University of Tokyo),
Impacts of solar energetic particles on the Martian atmosphere
Solar energetic particles (SEPs) are high-energy (from a few tens of keV to GeV) charged particles consisting mainly of electrons and protons ejected from the Sun associated with solar flares and coronal mass ejections. Precipitation of SEPs into planetary atmospheres causes changes in atmospheric chemical composition through ionization, dissociation, and excitation of atmospheric molecules. In contrast to the Earth’s atmosphere, where the destruction of ozone by SEPs in the polar mesosphere has been studied by observations and models for decades, the effect of SEPs on the atmospheric composition on Mars is far from understood. Understanding the effects of solar energetic particles (SEPs) on the atmospheric chemistry on Mars is of astrobiological interest because the precipitation of SEPs into the early Martian atmosphere could have facilitated the prebiotic chemistry. In this talk, I will introduce recent updates on the impacts of SEPs on the Martian atmosphere.
Takahiro Ueda (MPIA),
A Comprehensive Model of Gravitationally Self-Regulated Protoplanetary Disks Supported by Multiple Observations of the IM Lup Diskgetic particles on the Martian atmosphere
Protoplanetary disk, a birthplace of planets, is believed to be gravitationally unstable in its early phase of evolution. We develop a theoretical model of the gravitationally self-regulated disk around IM Lup, comprehensively explaining multiple observations of the disk. Our findings indicate that dust particles need to be fragile in order to maintain a sufficient amount responsible for the observed millimeter emission. Preferably, the dust should be moderately porous to account for the observed millimeter polarization. Another key finding is that the inner region is likely heated by gas accretion. The accretion heating naturally accounts for the bright millimeter emission within 20 au around IM Lup. The actively-heated inner region cast a 100-au-scale shadow, which is in good agreement with the previous near-infrared scattered light observation. The fragile dust is also preferred to maintain enough optical thickness for accretion heating to be the dominant source of heating. The fragile dust makes it unlikely for a giant planet to form beyond 50 au within IM Lup’s age, suggesting that any giant planet responsible for the substructures seen in the ALMA observations, if present, likely formed via gravitational instability. Conversely, the less turbulent inner region with abundant pebbles is favorable for the formation of planetesimals/planets within 1 Myr.
Xiaoyi Ma (University of Victoria),
Vortex-induced substructures in protoplanetary disks
The presence of both crescents and rings has been observed in protoplanetary disks through dust continuum emission. The crescents in continuum emission have been proposed to be dust-trapping vortices produced by the Rossby Wave Instability (RWI). Our hypothesis suggests that these RWI vortices may induce rings and gaps by driving density waves, analogous to those induced by planets. To explore this, we investigate the properties of density waves and substructures generated by the vortices through 2D hydrodynamic simulations conducted with Athena++ for a shearing box. Our work successfully confirms that the vortices can produce rings and gaps in the disk, comparable to ALMA dust continuum observations.
Xinting Yu (University of Texas San Antoni),
Unlocking the Nature of Sub-Neptunes: Atmospheric Characterization in the JWST era
In the upcoming era of the James Webb Space Telescope (JWST), the field of exoplanet research is poised for transformative discoveries. This talk will delve into my recent work on leveraging atmospheric characterization techniques to identify surface conditions on sub-Neptunes. These enigmatic worlds, which defy easy classification, offer a unique opportunity to study planetary formation, evolution, and even habitability. I will discuss the methodologies employed in transmission spectroscopy to probe the atmospheres of sub-Neptunes and how these data can be used to infer surface conditions. I will also touch on some experimental works on planetary hazes that support exoplanet characterization in the JWST era.
Nicolas Kaufmann (University of Bern),
Population level study of the influence of planetesimal fragmentation on planet formation
The size distribution of solids in the protoplanetary disk is still ill constrained and evolves significantly throughout plant formation by various processes. As the planets grow, they excite the mutual random velocities among planetesimals, making collisions between them destructive. This leads to their fragmentation changing the typical size of solids accreted by protoplanets. I will show the impact planetesimal collisional fragmentation has on planet formation employing a population synthesis approach. The synthesis is performed by varying the initial conditions based on observations of disks to generate synthetic exoplanet populations. Our results show that planetesimal fragmentation, in conjunction with radial drift and the interactions with the gas disk, can either promote or hinder planet formation, depending on the typical size of fragments produced in collisions. In addition, the enhanced radial drift of the smaller fragments also changes the typical origin of accreted solids affecting the composition of the forming planets.
Shinnaka Yoshiharu (Kyoto Sangyo University),
Comet observations: science background and open questions
Comets are thought to be one of the pristine objects in our solar system, holding crucial clues about its early stages. In this presentation, I will introduce recent advancements in cometary science, primarily based on our observational results. The focus will be on exploring the relationship between derived physical parameters (such as chemical compositions, isotopic ratios, mineral compositions, and more) and the conditions under which comets formed in the solar nebula. Additionally, I will highlight recent studies on interstellar objects, which represent potential pristine objects beyond our solar system.