2019/7/17 (水)

UTAPwiki/セミナー/planet lunch
担当者:Hayashi, Toshinori
時間 :12:15-13:00
場所 :理学部1号館908室
内容: We here revisit the essential problem of dynamical stability of planetary orbits around stellar binaries. We build on the coplanar three-body system of the Dvorak(1986), extending his stability diagram to both corotation and counter rotation of P-type orbits. His stability diagram express the change of stability across the gap between upper(UCO) and lower(LCO) critical orbits. By radius, this gap has a width of about 8% in the corotation case and 24% in the counter rotation case. As the gap of the second lies below the first, counter rotation is more stable, yet by width it is more chaotic. The gap between UCO and LCO follows a transition radius r+g=2.39+2.53e−1.40e2 and r−g=0.92−2.47e for corotation and respectively, counter rotation of the third body (the planet). Our r+g agrees with the same of Dvorak to within 0.35%. As a result, we discover r+g/r−g≲2.57 for all e. Around dim binaries, therefore, a relatively close in habitable zone may still be populated with planets on counter rotating orbits. The accurate numerical results presented here based on adaptive integration using MATLAB ODE45 may also serve as a novel benchmark of accurate \textit{N}-body integrators of exosolar systems more generally.

Author(s)TitleYear,JournalLink
Chaelin Hong and Maurice H.P.M. van PuttenOn the stability of corotating and counter rotating P-type orbits around stellar binaries: a numerical study2019, 8 May, arXiv:1905.03605doi


2019/7/10 (水)

UTAPwiki/セミナー/planet lunch
担当者:Hayashi, Toshinori
時間 :12:15-13:00
場所 :理学部1号館908室
内容:Exomoons orbiting terrestrial or super-terrestrial exoplanets have not yet been discovered; their possible existence and properties are therefore still an unresolved question. Here we explore the collisional formation of exomoons through giant planetary impacts. We make use of smooth particle hydrodynamical (SPH) collision simulations and survey a large phase-space of terrestrial/super-terrestrial planetary collisions. We characterize the properties of such collisions, including the debris mass, the long-term tidal-stability and the expected properties of the formed exomoons. We find our giant-impact models to generate relatively iron-rich massive disks, however even under the most optimistic assumptions these disks would not form exomoons exceeding ~Mars mass. Most of the modelled exomoons are likely to form beyond the synchronous radius of the planet, and would tidally evolve outward rather than be destroyed. We also find one rare case in which an exomoon forms through a graze \& capture scenario between a super-Earth and an Earth-sized planet. The result is an intact, planet-sized exomoon, containing about half the mass of the Earth. Our results suggest that it is extremely difficult to collisionally form currently-detectable exomoons orbiting super-terrestrial planets, through single giant impacts. It might be possible to form more massive, detectable exomoons through several mergers of smaller exomoons, formed by multiple impacts, however more studies are required in order to reach a conclusion. Given the current observational initiatives, the search should focus on more massive planet categories. However, typical exomoons predicted by our models are very likely to be detectable, given an order of magnitude improvement in the detection capability of future instruments.

Author(s)TitleYear,JournalLink
Uri Malamud, Hagai B. Perets, Christoph Schaefer and Christoph BurgerCollisional formation of detectable exomoons of super-terrestrial exoplanets2019, 29 Apr, arXiv:1904.12854doi


2019/7/3 (水)

UTAPwiki/セミナー/planet lunch
担当者:Wang,Shijie
時間 :12:15-13:00
場所 :理学部1号館908室
内容:
The Galactic center is dominated by the gravity of a super-massive black hole (SMBH), Sagittarius A*, and is suspected to contain a sizable population of binary stars. Such binaries form hierarchical triples with the SMBH, undergoing Eccentric Kozai–Lidov (EKL) evolution, which can lead to high-eccentricity excitations for the binary companions' mutual orbit. This effect can lead to stellar collisions or Roche-lobe crossings, as well as orbital shrinking due to tidal dissipation. In this work we investigate the dynamical and stellar evolution of such binary systems, especially with regards to the binaries' post-main-sequence evolution. We find that the majority of binaries (~75%) is eventually separated into single stars, while the remaining binaries (~25%) undergo phases of common-envelope evolution and/or stellar mergers. These objects can produce a number of different exotic outcomes, including rejuvenated stars, G2-like infrared-excess objects, stripped giant stars, Type Ia supernovae (SNe), cataclysmic variables, symbiotic binaries, or compact object binaries. We estimate that, within a sphere of 250 Mpc radius, about 7.5–15 SNe Ia per year should occur in galactic nuclei due to this mechanism, potentially detectable by the Zwicky Transient Facility and ASAS-SN. Likewise, we estimate that, within a sphere of 1 Gpc3 volume, about 10–20 compact object binaries form per year that could become gravitational wave sources. Based on results of EKL-driven compact object binary mergers in galactic nuclei by Hoang et al., this compact object binary formation rate translates to about 15–30 events per year that are detectable by Advanced LIGO.

Author(s)TitleYear,JournalLink
Alexander P. Stephan et al.The Fate of Binaries in the Galactic Center: The Mundane and the Exotic2019 June 13, APJdoi


2019/6/26 (水)

UTAPwiki/セミナー/planet lunch
担当者:Aizawa, Masataka
時間 :12:15-13:00
場所 :理学部1号館908室

Author(s)TitleYear,JournalLink
Sebastián Pérez et al.Long baseline observations of HD100546 with ALMA: a possible circumplanetary disk detected in dust continuum and gas kinematics2019, arXiv:1906.06305link
Andrea Isella et al.Submillimeter emission associated with candidate protoplanets2019, arXiv:1906.06308link


2019/6/19 (水)

UTAPwiki/セミナー/planet lunch
担当者:Nakagawa, Yuta
時間 :12:15-13:00
場所 :理学部1号館908室
内容:Thermal light-curve analysis is a powerful approach to probe the thermal structures of exoplanetary atmospheres, which are greatly influenced by the planetary obliquity and eccentricity. Here we investigate the thermal light curves of eccentric-tilted exoplanets across various radiative timescales, eccentricities, obliquities, and viewing geometries using results of shallow-water simulations presented in Ohno & Zhang. We also achieve an analytical theory of the thermal light curve that can explain general trends in the light curves of tilted exoplanets. For tilted planets in circular orbits, the orbital phase of the flux peak is largely controlled by either the flux from the hot spot projected onto the orbital plane or the pole heated at the summer solstice, depending on the radiative timescale τ rad, planetary day P orb, and obliquity θ. We find that tilted planets potentially produce the flux peak after the secondary eclipse when obliquity is θ gsim 90° for the hot regime τ rad Lt P rot or θ gsim 18° for the cool regime τ rad Gt P rot. For tilted planets in eccentric orbits, the shape of the light curve is considerably influenced by the heating at the periapse. The flux peak occurring after the secondary eclipse can be used to distinguish tilted planets from nontilted planets when the periapse takes place before the secondary eclipse. Our results could help to constrain exoplanet obliquities in future observations.

Author(s)TitleYear,JournalLink
Kazumasa Ohno and Xi ZhangAtmospheres on Nonsynchronized Eccentric-tilted Exoplanets. II. Thermal Light Curves2019 March 15, APJdoi


2019/6/12 (水)

UTAPwiki/セミナー/planet lunch
担当者:Mori, Shoji
時間 :12:15-13:00
場所 :理学部1号館908室
内容 :
The poor stickiness of silicate dust grains is a major obstacle to the formation of rocky planetesimals. In this study, we examine the possibility that silicate grains with an organic mantle, which we call Organic-mantled Grains (OMGs), form planetesimals through direct coagulation. Organic mantles are commonly found in interplanetary dust particles, and laboratory experiments show that they are softer than silicates, in particular in warm environments. This, combined with the theory of particle adhesion, implies that OMGs are stickier than bare silicate grains. Because organic mantles can survive up to 400 K, silicate grains inside the water snow line in protoplanetary disks can in principle hold such mantles. We construct a simple grain adhesion model to estimate the threshold collision velocity below which aggregates of OMGs can grow. The model shows that aggregates of 0.1 μm-sized OMGs can overcome the fragmentation barrier in protoplanetary disks if the mantles are as thick as those in interplanetary dust particles and if the temperature is above ∼200 K. We use this adhesion model to simulate the global evolution of OMG aggregates in the inner part of a protoplanetary disk, demonstrating that OMG aggregates can indeed grow into planetesimals under favorable conditions. Because organic matter is unstable at excessively high temperatures, rocky planetesimal formation by the direct sticking of OMGs is expected to occur in a disk annulus corresponding to the temperature range ∼200–400 K. The organic-rich planetesimals may grow into carbon-poor rocky planetesimals by accreting a large amount of carbon-poor chondrules.

Author(s)TitleYear,JournalLink
Homma, Kazuaki A.; Okuzumi, Satoshi; Nakamoto, Taishi; Ueda, YutaRocky Planetesimal Formation Aided by Organics2019 April 28, ApJlink


2019/6/5 (水)

UTAPwiki/セミナー/planet lunch
担当者:Kanagawa, Kazuhiro
時間 :12:15-13:00
場所 :理学部1号館908室
内容 :
The composition of gas and solids in protoplanetary discs sets the composition of planets that form out of them. Recent chemical models have shown that the composition of gas and dust in discs evolves on Myr time-scales, with volatile species disappearing from the gas phase. However, discs evolve due to gas accretion and radial drift of dust on time-scales similar to these chemical time-scales. Here we present the first model coupling the chemical evolution in the disc mid-planes with the evolution of discs due to accretion and radial drift of dust. Our models show that transport will always overcome the depletion of CO2 from the gas phase, and can also overcome the depletion of CO and CH4 unless both transport is slow (viscous α ≲ 10−3) and the ionization rate is high (ζ ≈ 10−17). Including radial drift further enhances the abundances of volatile species because they are carried in on the surface of grains before evaporating left at their ice lines. Due to large differences in the abundances within 10 au for models with and without efficient radial drift, we argue that composition can be used to constrain models of planet formation via pebble accretion.

Author(s)TitleYear,JournalLink
R A Booth, J D IleePlanet-forming material in a protoplanetary disc: the interplay between chemical evolution and pebble drift31 May 2019, MNRASdoi


2019/5/29 (水)

UTAPwiki/セミナー/planet lunch
担当者:Suto, Yasushi
時間 :12:15-13:00
場所 :理学部1号館908室

Author(s)TitleYear,JournalLink
Toshinori Hayashi, Shijie Wang, Yasushi SutoA strategy to search for an inner binary black hole from the motion of the tertiary star I: a perturbative analytic approach to a coplanar and near-circular three-body system and its application to 2M05215658+43592202019, arXiv:1905.07100link
Katelyn Breivik, Sourav Chatterjee, Jeff J. AndrewsConstraining Compact Object Formation with 2M05212018, arXiv:1810.08206link
Stephen R. Kane et al.Discovery of a Compact Companion to a Nearby Star2019, arXiv:1903.04529link


2019/5/15 (水)

UTAPwiki/セミナー/planet lunch
担当者:Hayashi, Toshinori
時間 :12:15-13:00
場所 :理学部1号館908室
内容:To date more than 3500 exoplanets have been discovered orbiting a large variety of stars. Due to the sensitivity limits of the currently used detection techniques, these planets populate zones restricted either to the solar neighbourhood or towards the Galactic bulge. This selection problem prevents us from unveiling the true Galactic planetary population and is not set to change for the next two decades. Here we present a new detection method that overcomes this issue and that will allow us to detect gas giant exoplanets using gravitational wave astronomy. We show that the Laser Interferometer Space Antenna (LISA) mission can characterise hundreds of new circumbinary exoplanets orbiting white dwarf binaries everywhere in our Galaxy - a population of exoplanets so far completely unprobed - as well as detecting extragalactic bound exoplanets in the Magellanic Clouds. Such a method is not limited by stellar activity and, in extremely favourable cases, will allow LISA to detect super-Earths down to 10 Earth masses.

Author(s)TitleYear,JournalLink
Nicola Tamanini and Camilla DanielskiListening to the gravitational wave sound of circumbinary exoplanets2018, 12 Dec, arXiv:1812.04330doi


2019/5/8 (水)

UTAPwiki/セミナー/planet lunch
担当者:Nakagawa, Yuta
時間 :12:15-13:00
場所 :理学部1号館908室
内容 :Relatively long-period, nonsynchronized planets—such as warm Jupiters—potentially retain the primordial rotation, eccentricity, and obliquity that might encapsulate information on planetary climate and formation processes. To date, there has not been a systematic study on climate patterns on these planets that will significantly influence their observations. Here we investigate the atmospheric dynamics of nonsynchronized, fast-rotating exoplanets across various radiative timescales, eccentricities, and obliquities using a shallow water model. The dynamical pattern can be demarcated into five regimes in terms of radiative timescale τ rad and obliquity θ. An atmosphere with τ rad shorter than a planetary day usually exhibits a strong day–night temperature contrast and a day-to-night flow pattern. In the intermediate τ rad regime between a planetary day and a year, the atmosphere is dominated by steady temperature and eastward jet patterns for θ ≤ 18° but shows a strong seasonal variation for θ ≥ 18° because the polar region undergoes an intense heating at around the summer solstice. If τ rad is larger than a year, seasonal variation is very weak. In this regime, eastward jets are developed for θ ≤ 54° and westward jets are developed for θ ≥ 54°. These dynamical regimes are also applicable to planets in eccentric orbits. The large effects of exoplanetary obliquities on circulation patterns might offer observational signatures, which will be investigated in Paper II of this study.

Author(s)TitleYear,JournalLink
Kazumasa Ohno and Xi ZhangAtmospheres on Nonsynchronized Eccentric-tilted Exoplanets. I. Dynamical Regimes2019 March 15, APJdoi


2019/4/24 (水)

UTAPwiki/セミナー/planet lunch
担当者:Aizawa, Masataka
時間 :12:15-13:00
場所 :理学部1号館908室
内容 :Numerous exoplanets have been detected around Sun-like stars. These stars end their lives as white dwarfs, which should inherit any surviving planetary systems. Manser et al. found periodic shifts in emission lines from a disc of gas orbiting around a white dwarf (see the Perspective by Fossati). They used numerical simulations to show that the most likely explanation for the spectral shifts is a low-mass planet orbiting within the disc. The planet must be unusually small and dense to avoid being ripped apart by tidal forces. The authors speculate that it may be the leftover core of a planet whose outer layers have been removed.

Author(s)TitleYear,JournalLink
Christopher J. Manser et al.A planetesimal orbiting within the debris disc around a white dwarf star2019 April 8, APJdoi


2019/4/17 (水)

UTAPwiki/セミナー/planet lunch
担当者:Wang,Shijie
時間 :12:15-13:00
場所 :理学部1号館908室
内容:

Author(s)TitleYear,JournalLink
Susanne Pfalzner and Michele T. BannisterA Hypothesis for the Rapid Formation of Planets2019 April 8, APJdoi



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Last-modified: 2019-04-16 (火) 11:22:14 (157d)