Colloquium 2015.4-2016.3, Dept Astronomy, Kyoto University

題目Title:Using rapid variability to probe warped space-time around accreting black holes
講師Speaker:Magnus Axelsson 氏 (Tokyo Metropolitan University, JSPS fellow)
日時:3月10日(木) 午後4時 〜
Date: Thursday, March 10th, 2016 starting at 4:00 p.m.
Accretion provides one of the few ways to directly study black
holes. Because they vary on observable time scales, black hole X-ray
binaries are an interesting target for such studies. However, the
observed spectra are complex, with multiple components contributing to
the observed emission. Temporal variability is a powerful tool to
break this spectral degeneracy. In this talk I will focus on studies
of rapid (< 0.1s) variability in the form of the power spectrum, and
show how it changes with accretion rate in the canonical black hole
binary Cygnus X-1. Additionally, I will show how combining spectral
and temporal information in XTE J1550-564 and GX 339-4 allows us to
probe the geometry of the innermost regions of the accretion flow. The
results support the picture of quasi-periodic components arising due
to Lense-Thirring precession, a direct result of the warped space-time
close to the black hole.

講師Speaker:鈴木 竜二 氏 (国立天文台)
日時:2月23日(火) 午後3時 〜
Date: Tuesday, February 23th, 2016 starting at 3:00 p.m.
InfraRed Imaging Spectrograph (IRIS)はTMT第一期観測装置の一つで、0.84-
モードでは4, 9, 25, 50秒のピクセルスケールとR4,000,
 本談話会では、TMT, IRISの現状、IRISの期待される性能、及びアストロメト

講師Speaker:長倉 洋樹 氏 (京都大学基礎科学研究所、特任助教)
日時:2月19日(金) 午後4時 〜
Date: Friday, February 19th, 2016 starting at 4:00 p.m.
多次元輻射流体計算 は、天文、宇宙物理、計算科学のフロンティアである。近
研究が幅 広く行われるようになった。我々は、大質量星の重力崩壊における
ニュートリノ輻射流体計算を行い、超新星爆発やGRB、ブラックホール形成過 程
究では近似計算が主流であったが、我々はその支配方程式である 6次元ボルツ
本セミナーでは、超新 星爆発の研究業界の現状をレビューするとともに、我々

講師Speaker:久野 成夫 氏 (筑波大学)
日時:1月7日(木) 午後3時半 〜
Date: Thursday, January 7th, 2016 starting at 3:30 p.m.

題目Title:TW Hyaまわりの原始惑星系円盤のアルマ観測
講師Speaker:野村英子 氏 (東京工業大学)
日時:12月1日(火) 午後1時半 〜
Date: Tuesday, December 1st, 2015 starting at 1:30 p.m.
我々の太陽系から最も近傍に位置するTW Hya周りの原始惑星系

題目Title:The Cosmic Dawn : Physics of the First Luminous Objects
講師Speaker:Ken Chen  氏 (EACOA Fellow, NAOJ)
日時:11月20日(金) 午後16時 〜
Date: Friday, November 20th, 2015 starting at 4:00 p.m.
One of the paramount problems in modern cosmology is to elucidate how the first generation 
of luminous objects, stars, supernovae, accreting black holes, 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 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).

題目Title:High-z sources of Lyman Continuum from the SSA22 field
講師Speaker:Genoveva Micheva  氏 (Subaru Telescope, NAOJ)
日時:11月13日(金) 午後16時 〜
Date: Friday, November 13th, 2015 starting at 4:00 p.m.
The escape fraction of Lyman continuum (LyC) is the fraction of hydrogen 
ionizing radiation that escapes from a galaxy into the intergalactic 
medium (IGM) and contributes either to reionizing the Universe at redshifts 
z>6 or to keeping it ionized at lower redshifts. 
In this talk we will present the largest to date sample of LyC emitting galaxies 
at any redshift, with 18 Lyman Alpha Emitters (LAEs) and 7 Lyman Break Galaxies (LBGs),
 obtained from the SSA22 field with Subaru/Suprime-Cam. 
A spatial offset is often detected between the rest-frame non-ionizing 
ultraviolet (UV) detection and the LyC-emitting substructure or between 
the LyA emission and LyC. 
We show that statistically it is highly unlikely that all LyC candidates 
are foreground contaminants. 
From comparison to stellar evolutionary models (SEDs) both LAEs and LBGs 
hosting the LyC escape seem to require extremely metal-poor or 
even metal-free young (zero-age) populations. 
We further show that "standard" SED models cannot fully explain the observed 
LyC LAEs colors, and require exotic models instead, with a top-heavy initial 
mass function with an average stellar mass of ~100 M_sun and the "Lyman limit bump" model 
which postulates an escape of nebular recombination LyC. 
We find some evidence for a positive LyC/LyA correlation, suggesting that 
both LyC and LyA escape via a similar mechanism. 
The LyC emission seems to be bimodal - stacking non-detections reveals no
 significant LyC signal strength. 
From LyC detections we obtained estimates of LyC escape fraction of ~20% 
for LyC LBGs and ~30% for LyC LAEs, assuming an SMC dust law. 
From non-detections we obtain 3 sigma median upper limits on the flux density
 ratios as f(LyC)/f(UV)<0.08 from 143 non-LyC LAEs, and f(LyC)/f(UV)<0.02 
from 133 non-LyC LBGs. 
We will also introduce a new Subaru intensive program on the 
''Cosmic HydrOgen Reionization Unveiled with Subaru'' (CHORUS). 
The project will target the 3 central issues of Cosmic reionization: 
ionization sources, history, and topology.

題目Title:Black Hole Collider in Super-Eddington Disks
講師Speaker:Sergei Fabrika 氏 (Special Astrophysical Observatory, Russia)
日時:10月9日(金) 午後16時15分 〜
Date: Friday, October 9th, 2015 starting at 4:15 p.m.
SS 433 is the only known supercritical accretor in our Galaxy, 
a close binary system with a black hole. Owing to the super-Eddington 
regime of accretion, a strong wind and relativistic jets appear in the 
accretion disk. It was established that in SS 433 X-ray jets nickel is 
overabundant regarding to iron by a factor of 10--15 in solar units. We 
show that in the jet producing supercritical accretion disk, the nuclear 
reactions should occur. We developed a nuclear network and found the 
conditions where the Ni abundance met the observations. 
It is believed that the early growth of quasars at high redshifts 
occurs because of super-Eddington accretion with a powerful feedback 
on their host galaxies. The nuclear reactions in such disks
may provide a new channel of metal production and transportation of
these metals for big distances.

題目Title:Kinetic and Radiative Power of Supercritical Accreting Black Holes
講師Speaker:Roberto Soria 氏 (Curtin Institute of Radio Astronomy, Australia)
日時:10月9日(金) 午後15時 〜
Date: Friday, October 9th, 2015 starting at 3:00 p.m.
The relative fraction of power released by an accreting black hole
(BH) in the form of radiation (X-rays) and kinetic energy (winds,
jets) is a fundamental parameter for our understanding of accretion
flows, BH growth and feedback. It is already well known that at low
accretion rates, BHs are often dominated by a steady jet, while at
moderately high accretion rates they are dominated by radiative disk
emission. What happens at very high (super-Eddington) accretion rates
remains controversial. I present examples of candidate super-Eddington
BHs in nearby galaxies, in which there is observational evidence of
mechanical power comparable with the radiative power.

題目Title:An LBV gone SN in the "SN factory" NGC 2770?
講師Speaker:Christina Theone 氏 (Instituto de Astrofisica de Andalucia, IAA-CSIC)
日時:10月2日(金) 午後16時 〜
Date: Firday, October 2nd, 2015 starting at 4:00 p.m.
NGC 2770 got famous when a shock breakout was discovered for SN 2008D while
another SN only 2 weeks older, SN 2007uy, was being observed. NGC 2770 has
hosted another Type Ib SN previously, SN 1999eh, and became subsequently 
known as "SN factory". In Dec. 2013 and Feb. 2015, two outburst episodes of
an LBV in the same galaxy were observed and we decided to start some regular
observations of the star. On May 16 finally, the LBV had brightened several
magnitudes and possibly exploded into a SN IIn. We now monitored the
presumable explosion with several ground-based telescopes in imaging and
spectroscopy as well as with Swift/UVOT until the galaxy disappeared behind 
the sun in mid June.
In the years since the explosion of 2008D, our collaboration has obtained
several data covering NGC 2770 - one of them serendipitously covering the
outburst of late 2013 in spectroscopy. In this talk we  present one of the
most extensive monitorings of an LBV/SN outside the local group and discuss
its possible explosion as a IIn SN. Last but not least, we study the closer
and larger environment of the potential SN to obtain further information on
the possible progenitor star and the stellar population in this ever more
interesting galaxy.

題目Title:The W. M. Keck Observatory: Current Status and Future Plans
講師Speaker:Hilton Lewis 氏 (Director, W. M. Keck Observatory)
日時:9月7日(月) 午後15時 〜
Date: Monday, September 7th, 2015 starting at 3:00 p.m.
The W. M. Keck Observatory operates the largest, most scientifically
productive telescopes on Earth.  The two, 10-meter optical/infrared
telescopes near the summit of Maunakea on the Island of Hawaii feature a
suite of advanced instruments including imagers, multi-object
spectrographs, high-resolution spectrographs, integral-field
spectroscopy and world-leading laser guide star adaptive optics system.
The Director of Keck Observatory, Mr. Hilton Lewis, will present the
current status of the observatory along with plans for future upgrades
and new instrumentation.

題目Title:What Makes a Lyman-alpha Emitter?
講師Speaker:Alex Hagen 氏 (The Pennsylvania State University)
日時:6月29日(月) 午後2時 〜
Date: Monday, June 29th, 2015 starting at 2:00 p.m.
We compare the physical and morphological properties of z  2 Lyα emitting 
galaxies (LAEs) from the HETDEX Pilot Survey and narrow band studies with 
those of z  2 optical emission line galaxies (oELGs) identified via HSTWFC3
 infrared grism spectroscopy. Both sets of galaxies extend over the same wide
 range in stellar mass (7.5 < logM/M < 10.5), size (0.5 < R < 3.0 kpc), and 
star-formation rate ( 1 < SFR < 100M yr−1). Remarkably, in all physical and
 morphological parameters: stellar mass, half light radius, UV slope (β), star
 formation rate, ellipticity, nearest neighbor distance, star formation surface
 density (ΣSFR), and specific star formation rate, there are no statistically
 significant differences between these populations. In particular, in the case
 of the UV slope, which parametrizes reddening, the lack of difference suggests
 that Lyα emission is not significant modulated by dust, as is usually assumed.
 We develop a simple model of Lyα emission that connects LAEs to all 
high-redshift star forming galaxies where Lyman-α escapes through a fraction of
 the galaxy and is thus only observable on a fraction of sightlines. We find a
 average Lyman-α escape solid angle of ΩLyα = 2.4 ± 0.8 steradians, and find
 this value consistent with those we calculate from other studies. We then
 compare our models’ predictions with those of computational models. Furthermore,
 we find both oELGs and LAEs fall above a linear extrapolation of the main
 sequence of star forming galaxies, which could demonstrate that these
 galaxies are experiencing a starburst, or that there is a change in the main
 sequence slope at low stellar masses. This could demonstrate that both oELGs
 and LAEs are drawn from the same star-bursting subset of high-z star-forming

講師Speaker:鈴木建 氏 (名古屋大学)
日時:6月25日(木) 午後3時半 〜
Date: Thursday, June 25th, 2015 starting at 3:30 p.m.

題目Title:粒子的流体数値計算手法の最先端 スキーム開発と大規模化
講師Speaker:細野七月 氏 (理化学研究所)
日時:4月28日(火) 午後1時半 〜
Date: Tuesday, April 28th, 2015 starting at 1:30 p.m.
分野で開発された、Smoothed Particle Hydrodynamics (SPH)と呼ばれる手法が広く
近年提案された、新しい粒子法スキームであるWeighted Particle Hydrodynamics
Frameworkである、Framework for Developing Particle Simulator (FDPS)

2014(H26)年度談話会 abstract 2013(H25)年度談話会 abstract 2012(H24)年度談話会 abstract 2011(H23)年度談話会 abstract 2010(H22)年度談話会 abstract 2009(H21)年度談話会 abstract 2008(H20)年度談話会 abstract 2007(H19)年度談話会 abstract 2006(H18)年度談話会 2005(H17)年度談話会 2004(H16)年度談話会