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Colloquium2015

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Colloquium

2015

Schedule & History

2010ǯ 2011ǯ 2012ǯ 2013ǯ 2014ǯ

ȯɽȥ/
4/1Rolf Kuiper (Univ of Tubingen)Protostellar Outflows and Radiative Feedback in Massive Star Formationֵ (Lecture Room) / 13:30׻
4/13Dimitris Stamatellos (Univ of Central Laucashire)Planet migration and gap opening in self-gravitating protoplanetary discsֵ (Lecture Room) / 13:30׻
4/15 ()ϻ¬ȥ¬زϤõŹʪо⥹ / 14:10
4/22ƻ۽ ()δĤμʽϥ¤⥹ / 14:10
5/13ʤ٤ߡ硼ȥ򣲤ͽ
5/20ʡл (󥻥󥿡)Precise and fast computation of generalized Fermi-Dirac integral by parameter polynomial approximation⥹ / 14:10
5/27͵ ()׷ȿʲ̤ۡˤäưץΣȼʽϱפι¤ˤĤ⥹ / 14:10
6/03ʤ٤ߡ3DTAݥŤΤ
6/10Hsi-An Pan ()What is a Giant Molecular Cloud? Are Observers and Simulators Discussing the Same Star-forming Clouds?⥹ / 13:30
6/10Alexander Pettitt ()Armed and/or dangerous: the sensitivity of galactic spiral generation in tidal encounters⥹ / 14:30
6/17Lukasz Stawarz (ISAS)Particle Acceleration in Astrophysical Sources of High Energy Radiation⥹ / 13:30
6/17 (KASI)On the origin of black hole outflows⥹ / 14:30
6/24ʤ٤ߡʪݥ೫ŤΤ
7/01ʤ٤ߡStar Formation WorkshopŤΤ
7/08 ¡μĹˤ⥹ / 14:10
7/15 ɡJAMSTECˡ֥饽եߥ졼ΤΥޥ⡼Ȱήˡ⥹ / 14:10
7/22Ĺë ɡˡPlanet Formation: from disks to the Solar System⥹ / 14:10
10/01Yutaka Komiya (Univ. of Tokyo)Chemical evolution of r-process elementsroom 313 / 16:00irregular
10/07Aleksander Sadowski (MIT)How not to lose photons when simulating radiative black hole accretion in general relativityֵ (Lecture Room) / 13:30
10/14Ken WongStrong Gravitational Lensing as a Probe of Galaxy Evolution and Cosmologyعּ (Rinkoh lecture Room) / 13:30
10/14Ken ChenThe Cosmic Dawn : Physics of the First Luminous Objectsعּ (Rinkoh lecture Room) / 14:30
10/21Hirotomo Noda (RISE project, NAOJ)Planetary laser altimeters⥹ (Conference Room, Cosmos Lodge) / 14:10
10/28ʤ٤ߡŷʸظΤ
11/04Yasunori Hori (NAOJ)How Does a Collision Sculpture a Super-Earth in the Proximity of Stars?ֵ (Lecture Room) / 14:10
11/11ʤ٤ߡ𤵤ֵΤ
11/18Kazem Ardaneh (U of Tsukuba) Collisionless Weibel shocks and electron acceleration in gamma-ray bursts⥹ (Conference Room, Cosmos Lodge) / 14:10
11/25Wing Kit Lee (Academia Sinica)Spiral Structure in Disksֵ (Lecture Room) / 14:10
12/02Tjarda, Boekholt (Leiden U)Chaos in N-body systems: Application to triple stars and Halley's cometֵ (Lecture Room) / 14:10
12/09Shingo Hirano (Univ. of Tokyo)Wide Mass Distribution of Primordial Stars: Various Star Formation in the Early Universeֵ (Lecture Room) / 15:00
12/16Lucie Jilkova (Leiden Observatory)Mass transfer between debris discs during close stellar encountersֵ (Lecture Room) / 13:30
12/17Thiem Hoang (CITA)Polarization of Anomalous Microwave Emission from Spinning Dust and Magnetic Dustseminar room (313) / 13:30irregular
1/13Alex Lazarian (U Wisconsin - Madison)Star Formation Mediated by Reconnection Diffusionֵ (Lecture Room) / 14:10
1/20Ronin Wu (Univ. of Tokyo)Spatially resolved physical conditions of molecular gas: a zoom-in from circumnuclear region of M83 to Carina nebula⥹ (Conference Room, Cosmos Lodge) / 14:10
1/27(no talk)(CfCA user's meeting)
2/03빾Τ(Mari Isoe)Exoplanetary System Architecture: Planetary Multiplicity and Mass Effectsֵ (Lecture Room) / 13:30
2/10Toshio FUKUSHIMA (NAOJ)Rotation curve of M33 explained by dark matter discֵ (Lecture Room) / 14:10
2/17Nobumitsu Yokoi (Univ. of Tokyo) Global flow induction by helicity: A closure approach to inhomogeneous turbulence⥹ (Conference Room, Cosmos Lodge) / 14:10
3/02Yichen Zhang(Chile/Yale)Star Formation across the Mass Spectrum and Environmentsֵ (Lecture Room) / 15:00

Confirmed speakers

  • ʸ㤵
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Abstract

4/1 Rolf Kuiper (Univ of Tubingen, Germany) Protostellar Outflows and Radiative Feedback in Massive Star Formation
During their formation and early evolution, massive protostars impact on their host cores via protostellar outflows and radiation pressure. We have performed radiation hydrodynamic simulations of the formation of massive stars, including the effect of protostellar outflows and radiative feedback, starting from a pre-stellar core of dusty gas. Therein, the evolution of the stellar environment is resolved down to the order of 1 AU and the stellar irradiation feedback is computed by use of a highly accurate frequency-dependent ray-tracing approach. In contrast to previous investigations, we follow the long-term evolution of the collapse until the cessation of accretion onto the protostar and its circumstellar disk, which enables us to quantitatively derive the final efficiencies of these feedback effects. To assess the net effects of protostellar outflows, we compare these results to simulations without outflows. Initially, protostellar outflows lower the accretion rate onto the disk and protostar. However, this decrease is compensated by a longer period of accretion. The bipolar cavity formed by the protostellar outflow enhances the flashlight effect and thus reduces radiative feedback during later evolutionary stages. We conclude that the combined effects of kinematic feedback from protostellar outflows and radiation pressure feedback by protostars are not simply additive. For the particular initial conditions chosen for this study (100 Msol cores with varying initial density slopes) we obtain final stellar masses in the range 42 – 55 Msol. When compared to equivalent cases without an outflow, those cases with a protostellar outflow had lower average accretion rates, longer accretion times, and slightly higher final masses. Furthermore, I can report on preliminary results of our ionization feedback studies and our recent studies on the effects of synchronously ongoing stellar evolution (with the aid of the STELLAR code by Harold Yorke) as well as on the shielding properties of the inner dust-free gas disk.
4/13 Dimitris Stamatellos (Univ of Central Laucashire) Planet migration and gap opening in self-gravitating protoplanetary discs
Gravitational torques between the planet and its host disc result in orbital migration of the planet and affect its subsequent evolution. Studies of migration of planets formed by core accretion (i.e. late during the disc evolution) have identified two main types of planet migration (fast/slow), depending on the mass of the planet. The discovery of massive planets orbiting at large distances from the host star suggests that at least some giant planets may form early-on during the disc evolution via disc fragmentation. Such planets will interact with a relatively massive (self- gravitating) disc. I will discuss how Jovian planets interact with self-gravitating discs, what are the effects of such interactions (inward migration, gap opening, and planetary mass growth), and how these depend on the disc thermodynamics. I will present global hydrodynamic simulations of planet-disc interaction and planet migration, and discuss whether signatures of such processes could be observed.
4/15 ()ϻ¬ȥ¬زϤõŹʪо
͡絬ŷʸ¬ɸŪʱϷǤϡߤαΥͥ륮Τ27%ŹʪȸƤФ̤ΤνϸǤޤʤƤȸƤ롣Źʪ¸ߤ͡ŷʸ¬ˤμ»뤵ƤΤΡʪŪˤĤƤ̤ޤƤ롣
ȯɽǤϡŹʪγŪΰĤǤоǸݡפκפõ׼ˡȤơϻ¬ȥ¬زϤҲ𤹤롣ϻ¬Ǥϡ˹ʪʬۤˤ鷺Ĥϥ󥺸̤¬롣ǡ¬ǤϡϷϳΥ륬طͤ¬롣ϥ󥺸̤ϡΰŹʪʬۤˤ졢ΰŹʪʬۤϡ⤷оǤƤСϳˤʤꤦ롣ʤŹʪоǤ¸ߤСϥ󥺸̤ȥطͤζʬۤˤشط뤳ȤԤ롣
桹ϡǽƼºݤδ¬ǡѤơϥ󥺸̤ȥطͤζؤ¬ꤷ¬̤ȤƳŹʪоǤؤ¡˾¬ؤŸ˾ˤĤȯɽ롣
4/22 ƻ۽ ()δĤμʽϥ¤
δĤˤϼʽϥ¤ȤФ٤ʱӹ¤¸ߤƤȹͤƤ롣ʽϥηˤϡ̵γҷϤǵƤ̩ᥫ˥()طƤȹͤƤܤϹԤƤʤäܸϥԥåѤܤȼʽϥδطǧ뤳ȤŪǤ롣ǸȤơ򤹤뤿ˡޤ̵ͷϤˤƱӷ¿Υߥ졼ȥưϤԤӤΥԥåѤĴ٤η̡ưϤ¿Υߥ졼󤬤褯פ뤳Ȥʬäϡ̵ͷϤαӷˤϥطƤ뤳Ȥ򼨺Ƥ롣ơʳȤơδĤˤƱͤ¿Υߥ졼ԤԥåѤĴ٤η̡ưϤͽۤʤ¸ǧ줿ϥδĤŬѤϡ긽Ūʥǥسĥɬפ뤳Ȥ̣Ƥ롣ȯɽǤϤθγפҲ𤹤롣ޤ֤С긽Ūǥ빽ۤ˸ΥǥҲ𤹤롣
5/20 ʡл (󥻥󥿡) Precise and fast computation of generalized Fermi-Dirac integral by parameter polynomial approximation
The generalized Fermi-Dirac integral, $F_k(\eta,\beta)$, is approximated by a group of polynomials of $\beta$ as $F_k(\eta,\beta) \approx \sum_{j=0}^J g_j \beta^j F_{k+j} (\eta)$ where $J=1(1)10$. Here $F_k(\eta)$ is the Fermi-Dirac integral of order $k$ while $g_j$ are the numerical coefficients of the single and double precision minimax polynomial approximations of the generalization factor as $\sqrt{1+x/2} \approx \sum_{j=0}^J g_j x^j$. If $\beta$ is not so large, an appropriate combination of these approximations computes $F_k(\eta,\beta)$ precisely when $\eta$ is too small to apply the optimally truncated Sommerfeld expansion (Fukushima, 2014, Appl. Math. Comp., 234, 417). For example, a degree 8 single precision polynomial approximation guarantees the 24 bit accuracy of $F_k(\eta,\beta)$ of the orders, $k=-1/2(1)5/2$, when $-\infty < \eta \le 8.92$ and $\beta \le 0.2113$. Also, a degree 7 double precision polynomial approximation assures the 15 digit accuracy of $F_k(\eta,\beta)$ of the same orders when $-\infty < \eta \le 29.33$ and $0 \le \beta \le 3.999 \times 10^{-3}$. Thanks to the piecewise minimax rational approximations of $F_k(\eta)$ (Fukushima, 2015, Appl. Math. Comp., 259, 708), the averaged CPU time of the new method is only 0.9--1.4 times that of the evaluation of the integrand of $F_k(\eta,\beta)$. Since most of $F_k(\eta)$ are commonly used in the approximation of $F_k(\eta,\beta)$ of multiple contiguous orders, the simultaneous computation of $F_k(\eta,\beta)$ of these orders is further accelerated by the factor 2--4. As a result, the new method runs 70-450 times faster than the direct numerical integration in practical applications requiring $F_k(\eta, \beta)$.
5/27 ͵ (ظ) ׷ȿʲ̤ۡˤäưץΣȼʽϱפι¤ˤĤ
ֱܹǤϣĤˤĤȯɽ롣 ȾǤϱ׷ˤ̤ۡαƶˤĤ𤹤롣ʬұΥϼΥץ饺ޤǤ뤿MHDΩ۸̡ʥ໶̡ۡξˤפ̤Τʤǡ̤ۡpoloidal줫troidalФpoloidalФƺͥ˥βžͶȤ̣롣ʤ顢̤ۡα׷ФƶˤĤƤϤޤޤǤۤȤĴ٤Ƥʤä ֱԤ3Ĥ۸̤ռ͢θ3Dߥ졼Ԥä˥̤ۡα׷ͿƶˤĤƸԤäη̡ʬұβž٥ȥȼ٥ȥ뤬ʿԤξ硢AU٤αפʤäΤФơȿʿԤξϣAU٤νŪ԰ʱפ뤳Ȥ狼äη̤ϲž٥ȥȼ٥ȥ뤬ʿԤȿʿԤȤޤޤǽ׻뤵Ƥʤä郎׷礭ѤȤˤƶˤƶ̣ޤ濴Dzž¥ʤ뤳ȤˤäƳѱư¸饨٥פղž븽ݤФ줿Τ褦ʵղž륨٥פϽʬ¬ǽǤꡢ⤷¬줿硢̤ۡפηʲˤƽפ̤ȤξڵȤʤȹͤ롣 ȾǤϡʽŪʱפι¤ˤĤƤռήϳإߥ졼ˤĤ𤹤롣ץǥͻ뤳Ȥǡʽϱפι¤ϲžץեȲ٥ץե뤫餭ޤ뤳Ȥ狼롣äƱռ͢򤭡ٹ¤ɤΤ褦ʥᥫ˥Ƿޤ뤫餫ˤɬפ롣ǡֱԤռήϳإߥ졼ˤäƼʽϱפι¤ˤĤĴ٤η̡٤㤤(100Kʲ)ΰǤư˳ȻŪήռ͢ˤäƲٹ¤ޤꡢפ̩١ͤϤβٹ¤ΤȤǤץǥǤ褯ҤǤ뤳Ȥ狼äΤ褦ʱץǥԸǤϹͻƤ餺̣̤ǤȹͤƤ롣 ʾ¾ˡ֤мʽ԰ˤʬ䤽ؤαѤˤĤƤ
6/10 Hsi-An Pan () What is a Giant Molecular Cloud? Are Observers and Simulators Discussing the Same Star-forming Clouds?
Observations and simulations have now reached the point where the giant molecular cloud (GMCs) populations can be studied over a whole galaxy. This is immensely helpful for understanding star formation, since the cloud properties set the conditions for new star birth. Yet, are these two groups really comparing the same objects? While simulators work in position-position-position (PPP) space, observers see projected properties along the line of sight, identifying clouds in position-position-velocity (PPV) space. If these methods do not identify the same objects, then the interpretation and comparisons between the data sets may be highly misleading. In this research we generated PPV and PPP data for a high-resolution simulated galaxy and compared the identified cloud properties in both data sets. Results show that the physical properties of molecular clouds in the individual galactic environments (bar, spiral, and outer disk) are highly similar among the two data structures. About 70% of clouds have single counterpart in each dataset, and their cloud properties scatter mostly within a factor of two. Therefore, comparing the simulated and the observed GMCs is practical, and it will be the trend in the ALMA era.
6/10 Alexander Pettitt () Armed and/or dangerous: the sensitivity of galactic spiral generation in tidal encounters
The nature of the spiral structure of disc galaxies is still somewhat of an open question. A number of different mechanism have been suggested to underpin spiral features; density waves, swing amplified transient spirals, bar driven arms and tidal encounters. The regimes where each of these mechanisms becomes dominant is an unknown, when does an interaction between a galaxy and a companion become strong enough to drown out the structure formed in isolation? We present the results of an investigation into the various morphologies created in the interaction between a disc galaxy and minor companion using numerous numerical simulations with stars, dark matter and gas. The primary goal of which is to discern the sensitivity of disc galaxies to tidal spiral structure. For what orbital paths, mass and velocity limits does the galaxy cease to feel the companion, and therefore any spiral generation is left to the galaxy itself? This also includes comparisons to transient spiral arm structures, those generated in simulations of isolated discs, and how the longevity, morphology and gas structure differs between the two mechanisms. By understanding the mechanisms driving different spiral morphologies we can better assess the origin of structure in external galaxies and the Milky Way.
6/17 Lukasz Stawarz (ISAS / Jagiellonian University, Poland)Particle Acceleration in Astrophysical Sources of High Energy Radiation
Strong shocks induced in the interstellar medium by supernova explosions are widely considered as the dominant production sites of cosmic ray particle detected on Earth with enormous energies reaching 10^15 eV. Relativistic, or instead weak by extremely extended shock waves encountered in various types of extragalactic object - predominantly active galaxies and clusters of galaxies - are on the other hand typically considered as the most likely sources of even higher energy cosmic rays, up to the ultra-high energy range of 10^21 eV. In this talk I will critically re-examine the current status of our understanding of particle acceleration in astrophysical environment in general, pointing out the most recent observational findings which challenge the shock paradigm for the cosmic ray production, and emphasizing important but often ignored differences between particle acceleration processes in non-relativistic and relativistic plasma.
6/17 (KASI)On the origin of black hole outflows
Understanding formation mechanism of relativistic jets in active galactic nuclei (AGN) is one of the biggest issues in astrophysics. To solve the problem, outstanding question is basic energetics in the vicinity of the central black holes which ultimately power the relativistic jets. The AGN jet Messier 87 (hereafter M87) is one of the closest (16Mpc from the Earth) example of relativistic jets and it is well known as the best source to explore a jet base close to ~10 Schwarzschild radii scale with VLBI (Very Long Baseline Interferometry) radio telescopes. Here I show highlights of VLBI observations of innermost part of the M87 jet. Then, I show the results of our estimate of magnetization degree at the base of M87 down to ISCO (innermost stable circular orbit) scale based on these observational data.
7/8 ¡μĹˤ
ɸŪǤϡϱǤޤȸƤФμפ졢˾͹Τ򷫤֤ȤǡǽŪ줿ȹͤƤ롣ηᥫ˥ȤƤϡϱפ濴̤ˤĤؤˤƼʽϤѤϷȤ⤬褫¿θԤˤ꿮Ƥʤ顢᡼˻ǤϼʽϤǤꡢ줬ֽפǺߤμȤʤäƤ롣桹Υ롼פǤϡȾͤΣοͥߥ졼ԤȤˤꡢ֥ߥγҤνΤǤȤι⤤¤η餫ˤƤˡȤΤ͡褷뤳Ȥ顢ĹǤĤ줿Ȥ󾧤Ƥ롣ֱܹǤϡ桹ΥȾͤΣοͥߥ졼̤Ҳ𤹤뤳ȤǡȾΥᥫ˥´򤷤ƤȤɸȤ롣
7/15 硡ɡJAMSTEC˥֥饽եߥ졼ΤΥޥ⡼Ȱήˡ
̵ͥץ饺ޤ¿ηϤλϡ̵ͥܥĥޥʥ֥饽ˤǤ롣츶׻ˡȤơġγҤαư饰󥸥Ūפγҥߥ졼󤬹ѤƤ롣γҥߥ졼ϡ르ꥺबץǥХȡ¤줿׻񸻤Ǥ¹ԤǤȤäͷ׻ˤƶˤƹޤĶϤʼˡǤ롣ǡγҥߥ졼ͭμä٤֥饽6־ľΥƥ顼Ū˲򤯥֥饽եߥ졼Ƥ졢äťץ饺ޤ伫ʽϷϤʤɤΥ֥饽-ݥϤˤƤ롣ʤ顢ܸоݤȤƤ뱧ץ饺ޤ񼧾ӤӤƤ롣ץ饺ޤΥ֥饽-ޥ륷ߥ졼󸦵ϡŪʤɤͳ顢̤ȯŸӾʬǤ롣ȯɽǤϡ֥饽եߥ졼󵻽Ѥȡä˥֥饽-ޥ륷ߥ졼ˤˤĤƾҲ𤷡ä٤桹ȯ³Ƥͷ׻ˡʥޥ⡼ȰήˡˤȡܼˡѤץ饺ޤΥ֥饽եߥ졼ˤĤƾҲ𤹤롣
7/22 Ĺë ɡPlanet Formation: from disks to the Solar System
Planet formation is one of the most ubiquitous processes in the Universe. As suggested by the ALMA images of HL Tau, it is currently recognized well that planet formation should be examined in the context of star formation. In addition, it is of fundamental importance to apply our understanding of planet formation to origins of the Solar system. In this talk, I will present some of the results of my recent projects that have been and are being developed with scientists at NAOJ. These include the observational and theoretical investigation of HL Tau, the stability analysis of protoplanetary disks by magnetorotational instabilities (MRIs), and formation of chondrules via planetesimal collisions. While many of these results are still preliminary, I will attempt to give some flavor of what I have done at NAOJ since last Sept.
10/1 Yutaka KomiyaUniv. of TokyoChemical evolution of r-process elements
The main astronomical source of the r-process element has not yet been identified. Two sites have been suggested, core-collapse supernovae and neutron star mergers (NSMs). From perspective of the Galactic chemical evolution, it has been pointed out that the NSM scenario is incompatible with observations, while nucleosynthetic studies favor the NSM scenario. Recently, however, Tsujimoto & Shigeyama (2014) pointed out that the NSM ejecta can spread into much larger volume than the ejecta from a supernova. We re-examine the chemical evolution of r-process elements under the NSM scenario considering this difference in propagation of the ejecta. We show results of our new chemical evolution model for the Milky Way and dwarf galaxies. We find that the NSM scenario can be compatible with the observed abundances of the Milky Way halo stars. We also discuss the difference of abundance patterns between galaxies.
10/7 Aleksander SadowskiMITHow not to lose photons when simulating radiative black hole accretion in general relativity
In this talk I will summarize the recent progress in simulating optically thick black hole accretion. In detail, I will describe simulations of super-critical black hole accretion disks applicable to ultra luminous X-ray sources and tidal disruption events. Special attention will be paid to their luminosities and mildly relativistic, radiative jets formed in such systems. I will introduce a photon-conserving method of treating Comptonization and show how it can be coupled with sophisticated radiation transfer solvers to obtain stets-of-art synthetic spectra of accretion disks.
10/14 Ken Wong (DTAStrong Gravitational Lensing as a Probe of Galaxy Evolution and Cosmology
Strong gravitational lensing is a useful probe for studying the evolution of galaxies over cosmic time, as well as the cosmological parameters of the universe. I will review a series of lensing projects that I am involved in, including 1) using galaxy cluster-scale lenses to magnify high-redshift galaxies, 2) studying the innermost mass distribution of a galaxy-scale lens and constraining the mass of its supermassive black hole, 3) using lensed quasars with measured time delays to constrain the Hubble constant, among other cosmological parameters, and 4) accounting for line-of-sight effects in time delay lenses, which can bias lens modeling results if not properly accounted for. These diverse projects demonstrate the application of using strong lensing at various scales as a tool to answer fundamental questions about extragalactic astronomy and cosmology.
10/14 Ken Chen (DTAThe Cosmic Dawn : Physics of the First Luminous Objects
One of the paramount problems in modern cosmology is to elucidate how the first generation of luminous objects, stars, accreting black holes (BHs) and galaxies, shaped the early universe at the end of the cosmic dark ages. According to the modern theory of cosmological structure formation, the hierarchical assembly of dark matter (DM) halos provided the gravitational potential wells that allowed gas to form stars and galaxies inside them. Modern large telescopes have pushed the detection of galaxies up to a redshift of z ~ 10. However, models of the first luminous objects still require considerable effort to reach the level of sophistication necessary for meaningful predictions. Due to the complexity of involved physical phenomena, this physical understanding may only come by the proper use of numerical simulations. Therefore, I have used state-of-the-art simulations on some of largest supercomputers to study these objects. In my talk, I will discuss the possible physics behind the formation of these first luminous objects by presenting the results from our simulations. I will also give possible observational signatures of the cosmic dawn that will be the prime targets for the future telescopes such as the James Webb Space Telescope (JWST).
10/21 Hirotomo Noda (RISE project, NAOJ) Planetary laser altimeters
I will review science outputs and hardware basics of the laser altimeters for lunar and planetary sciences which I have involved in. The laser altimeters aboard Kaguya, Hayabusa2 and JUICE will be mentioned.
11/4 Yasunori Hori (ABC, NAOJ) How Does a Collision Sculpture a Super-Earth in the Proximity of Stars?
The Kepler mission has revealed the prevalence of volatile-rich/poor low-mass planets in the proximity of host stars. Several post-formation processes have hitherto been proposed for explaining the origin of volatile inventory of those planets: a mass loss via a stellar XUV irradiation and Parker wind, degassing of accreted material, and in-situ accumulation of the disk gas. However, the compositional dissimilarity between neighboring planets on adjacent orbits such as Kepler-36 and Kepler-11 systems is puzzling for the three processes. We consider the possibility of a collisional origin for the coexistence of volatile-poor super-Earths and mini-Neptunes in a tightly-packed system. We performed three-dimensional hydrodynamic simulations of giant impacts on a super-Earth with a H/He atmosphere. A high-speed collision can strip off most of the original H/He atmosphere, as we expected. A hot and inflated planet after the giant impact cools down so slowly that a prolonged lifetime of the extended post-impact atmosphere enhances mass loss via a Parker wind and subsequent hydrodynamic escape driven by a stellar XUV irradiation. We also found that a low-speed head-on collision results in the appearance of a positive-compositional gradient deep inside the planet which leads to an inefficient heat transport via double-diffusive convection, whereas a high-speed one can homogenize a distribution of heavy elements above the core.
11/18 Kazem Ardaneh (U of Tsukuba) Collisionless Weibel shocks and electron acceleration in gamma-ray bursts
A study of collisionless external shocks in gamma-ray bursts is presented. The shock structure, electromagnetic fields, and process of electron acceleration are assessed by performing a self-consistent 3D particle-in-cell (PIC) simulation. In accordance with hydrodynamic shock systems, the shock consists of a reverse shock (RS) and forward shock (FS) separated by a contact discontinuity (CD). The development and structure are controlled by the ion Weibel instability. The ion filaments are sources of strong transverse electromagnetic fields at both sides of the double shock structure over a length of 30 - 100 ion skin depths. Electrons are heated up to a maximum energy E_ele = E_b**0.5, where E_ele is the energy normalized tothe total incoming energy. Jet electrons are trapped in the RS transition region due to the presence of an ambipolar electric field and reflection by the strong transverse magnetic fields in the shocked region. In a process similar to shock surfing acceleration (SSA) for ions, electrons experience drift motion and acceleration by ion filament transverse electric fields in the plane perpendicular to the shock propagation direction. Ultimately accelerated jet electrons are convected back into the upstream. The FS region shows the characteristic of a double layer plasma. In this region, acceleration of the electrons by the double layer electric fields creates a power-law distributed population in the electron distribution function. In the present work, the power-law index for the electron distribution function in the precursor region is =1.8, which can be associated to the radio afterglow emission.
11/25 Wing-Kit Lee (Academia Sinica) Spiral Structure in Disks
I will review some mechanisms for generating spiral structures in astrophysical disk systems such as galaxies and protoplanetary disks. In particular, I will talk about my research on instabilities of the galactic spiral arms, namely feathering instability. In addition, I will introduce some of my attempts to understand the three-dimensional spiral shocks in a protoplanetary disk.
12/2 Tjarda, Boekholt (Leiden U) Chaos in N-body systems: Application to triple stars and Halley's comet
N-body simulations are used to study the dynamical evolution of planetary systems, star clusters, galaxies and large scale structure. These systems are often chaotic, in the sense that they are highly sensitive to initial conditions. In the first part of my talk, I focus on the growth of small numerical errors, to determine the reliability of N-body results, specifically those of chaotic triple systems. In the second part I study the growth of a small, physical perturbation in order to study the stability of the orbit of comet Halley.
12/09 Shingo Hirano (Univ. of Tokyo) Wide Mass Distribution of Primordial Stars: Various Star Formation in the Early Universe
Primordial stars, so-called Population III stars, play vital roles in the early cosmic evolution. The stellar evolution and death, which regulate the dynamical, radiative, and chemical feedbacks to the surrounding medium, are largely determined by its stellar mass. The characteristic mass, or initial mass function, of Pop III stars is thus essential to understand the formation and evolution of the first galaxy. This talk introduces theoretical study on various formation paths of the first-generation stars and the distribution of their final masses. A series of numerical simulations from the formation of star-forming cloud to the end of the mass accretion onto the protostar are performed to determine the initial stellar mass. The simulation results show a certain dependence of the stellar masses on the initial state of star-forming clouds. By using such a correlation, a large sample of primordial star-forming clouds in the cosmological volume is converted to the mass distribution of the primordial stars. This is the first study to directly calculate the stellar mass distribution in the early universe theoretically. I will also introduce our recent study about formation of supermassive first star with 100,000 solar-masses which can become a seed of high-z quasar.
12/16 Lucie Jilkova (Leiden Observatory) Mass transfer between debris discs during close stellar encounters
Stars are born in clustered environment and planetary systems are born around stars. Stars in clusters gravitationally interact and experience close encounters that have a direct influence on their planetary systems. I will present results on simulations of mass transfer among debris (planetesimal) discs during close stellar encounters that happen in star clusters. We explored the parameter space of the encounters and mapped the orbits of the transferred planetesimals around their parent star as well as around their new host. Depending on encounter parameters, a substantial part of the disc can be captured by the other star and the captured objects have specific orbits. We expect that many stars experienced transfer among their debris discs and planetary systems in their birth environment and I will present the implications of this process for the Solar system.
12/17 Thiem Hoang (CITA) Polarization of Anomalous Microwave Emission from Spinning Dust and Magnetic Dust
Anomalous microwave emission (AME) in the 10-60 GHz frequency range is an important Galactic foreground component that contaminates the cosmic microwave background (CMB) radiation, which was discovered 20 years ago in the course of data analysis from COBE. With the explosion of CMB experiments hunting for primordial gravitational waves from the early universe through the CMB B-mode signal, a pressing issue is to have an accurate model of the AME polarization for reliable removal of CMB foregrounds and correct measurements of the B-mode signal. In this talk, I will first review two mechanisms suggested as origins of AME, including electric dipole emission from rapidly spinning tiny dust grains and magnetic dipole emission from ferromagnetic/ferrimagnetic nanoparticles. Then, I will discuss theoretical foundations for the polarization of AME and present our new results on quantifying the polarization of spinning dust emission and magnetic dust emission. I will compare the theoretical predictions with available observational data and discuss its implications for understanding the origin of AME.
1/13 Alexandre Lazarian (U. Wisconsin - Madison) Star Formation Mediated by Reconnection Diffusion
Turbulent reconnection entails violation of flux freezing in turbulent fluids. The whole paradigm of star formation was based on flux freezing and ambipolar diffusion as a way to circumvent the flux freezing constraint. Therefore this paradigm should be changed as reconnection induces a process that I term "reconnection diffusion". I shall provide evidence for turbulent reconnection being fast and violating flux conservation and will show the numerical studies of reconnection diffusion for diffuse media, molecular clouds and accretion disks. A comparison with observations will be provided.
1/20 Ronin Wu (Univ. of Tokyo) Spatially resolved physical conditions of molecular gas: a zoom-in from circumnuclear region of M83 to Carina nebula
Since the launch of the Herschel Space Observatory (Pilbratt et al. 2010), our understanding about the photodissociation regions (PDR) has taken a step forward. In the bandwidth of the Fourier Transform Spectrometer (FTS) of the Spectral and Photometric Imaging REceiver (SPIRE) on board Herschel, ten CO rotational transitions, including J = 4-3 to J = 13-12, and three fine structure lines, including [CI] 609, [CI] 370, and [NII] 250 m, are covered. This presentation focuses on the physical conditions of molecular gas probed by the Herschel SPIRE/FTS.
Based on the spatially resolved physical parameters derived from the CO spectral line energy distribution (SLED) map and the comparisons with the dust properties and starformation tracers, I will first present our findings at the circumnuclear region of M83 (Wu et al. 2015), and then zoom in toward the molecular cloud near a young open cluster, Trumpler 14, in Carina nebula. I will discuss (1) the potential of using [NII] 250 and [CI] 370 micron as star formation tracers; (2) the reliability of tracing molecular gas with CO (3) the excitation mechanisms of warm CO (4) the possibility of studying stellar feedback by tracing the thermal pressure of intersetllar molecular gas.
2/3 빾 Τ (DTA/Univ. of Tokyo) Exoplanetary System Architecture: Planetary Multiplicity and Mass Effects
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2/10 Toshio FUKUSHIMA (NAOJ) Rotation curve of M33 explained by dark matter disc
We developed a numerical method to compute the gravitational field of an infinitely-thin axisymmetric disc with an arbitrary profile of the surface mass density. We evaluate the gravitational potential by a split quadrature using the double exponential rule and obtain the acceleration vector by numerically differentiating the potential by Ridder's algorithm. The new method is of around 12 digit accuracy and sufficiently fast because requiring only one-dimensional integration. By using the new method, we show the rotation curve of some non-trivial discs: (i) truncated power-law discs, (ii) discs with a non-negligible center hole, (iii) truncated Mestel discs with edge-softening, (iv) double power-law discs, (v) exponentially-damped power-law discs, and (vi) an exponential disc with a sinusoidal modulation of the density profile. Also, we present a couple of model fittings to the observed rotation curve of M33: (i) the standard deconvolution by assuming a spherical distribution of the dark matter and (ii) a direct fit of infinitely-thin disc mass with a double power-law distribution of the surface mass density. Although the number of free parameters is a little larger, the latter model provides a significantly better fit. The determined profile of the surface mass density of the disc is significantly larger than those of the observed stars and gas. This hints a disc-like distribution of the dark matter.
2/17 Nobumitsu Yokoi (Institute of Industrial Science, University of Tokyo) Global flow induction by helicity: A closure approach to inhomogeneous turbulence
With accompanied by large-scale inhomogeneous fields, such as rotation, velocity strain, magnetic field, density stratification, radiation, astrophysical turbulence is not homogeneous isotropic, but highly inhomogeneous and anisotropic. Also due to these fields, some symmetry in turbulence is often broken. These conditions of astrophysical turbulence suggest that, in treating astrophysical turbulence, we have to incorporate the following two features: (i) nonlinear interactions between large-scale inhomogeneities and small-scale turbulence; (ii) dynamic balance between transport enhancement and suppression. In this talk, after a brief introduction to turbulence, a few closure approaches to inhomogeneous turbulence are outlined. Special references are made to turbulence modeling based on a renormalized perturbation theory with multiple-scale analysis. Among several interesting applications in the astrophysical context, turbulent vortex dynamo - global flow generation and sustainment mechanism through turbulence - is discussed as an illustrative example. In non-mirrorsymmetric turbulence, turbulent kinetic helicity (velocity--vorticity correlation) as well as turbulent energy represents the statistical properties of turbulence. In such a system, an enhanced momentum transport due to eddy viscosity coupled with the mean velocity strain can be counterbalanced by the helicity effect coupled with the mean absolute vorticity. This helicity effect may induce a global vortical flow structure without resorting to any baroclinicity (obliqueness between the density and pressure gradients) effect. Validation of the theoretical predictions through direct numerical simulations (DNSs) is also presented.
References: (1) http://arxiv.org/abs/1511.08983 (2) http://www.tandfonline.com/doi/abs/10.1080/03091929.2012.754022
3/2 Yichen Zhang(Chile/Yale) Star Formation across the Mass Spectrum and Environments
One of the major question in star formation is whether high and low-mass stars form in a similar way by accreting from pre-existing cores (core accretion). My talk will be around three aspects of this question. First, in the core accretion scenario, the outflow feedback is believed to be responsible for dispersing the core and regulating the core-to-star efficiency. I will present results of our recent ALMA observation of the low-mass HH 46/47 molecular outflow to understand the outflow feedback. Using 13CO and C18O emission to correct for the 12CO optical depth and trace denser and slower outflow material than 12CO only, we accurately estimated the mass, momentum and kinetic energy of the outflow. The estimated outflow properties indicate that the outflow is capable to disperse the parent core within the typical lifetime of the embedded phase of a low-mass protostar, and is regulating the core-to-star efficiency to about 1/4 to 1/3. This new observation also reveals a rotating/infalling envelope, a spinning outflow, and detailed outflow structures which help us to understand the outflow entrainment process. Second, through radiation transfer (RT) simulation, predictions of core accretion model and continuum observations of massive protostars are compared. I will introduce our evolutionary model of (massive) star formation based on the core accretion, which self-consistently includes protostellar evolution, collapse of the core, growth of the disk, and gradual opening-up of the outflow cavity. In such a framework, the evolutionary tracks are determined by the initial environmental conditions: the initial core mass, the mass surface density of the ambient clump, and the rotation of the core. Through RT simulations, we are able to produce temperature structures, SED, IR continuum images of protostars at different evolutionary stages under various initial conditions. I will show an example that such a model can interpret the multiwavelength observations of massive protostars. Third, the core accretion theory also predicts that the thermal/chemical evolution of protostellar cores can be strongly affected by the star-forming environment, e.g. a low-mass-surface-density region where low-mass stars form in relative isolation, like Taurus, vs. a crowded high-mass-surface-density region, like Orion. I will discuss this effect by combining the above RT model with simple chemical models.