天文学教室談話会

last-update:2017/06/25

本談話会より、談話会の開始時刻が、火曜日の16:00に変更になります。ご注意下さい。

  次回 第1628回 2017年6月27日(火)

High Energy, Cool Transients: Investigating Infrared-Luminous Outbursts with Spitzer
Ryan M. Lau (NASA JPL)
The Spitzer Space Telescope is pioneering the exploration of infrared (IR) luminous transients. In our Spitzer InfraRed Intensive Transients Survey (SPIRITS), we are conducting a systematic search of 200 nearby galaxies for IR-luminous outbursts that elude detection in traditional optical surveys. In this talk, I will present two puzzling discoveries from SPIRITS and discuss open questions and the plans to address them.
SPIRITS has revealed a new class of obscured, red transients with mid-IR luminosities between novae and supernovae that do not exhibit optical counterparts. We call them SPRITEs (eSPecially Red Intermediate-luminosity Transient Events). The key to disentangling the various possible physical origins of SPRITEs is IR spectroscopy, which can only be obtained with the unprecedented sensitivity of the upcoming James Webb Space Telescope (JWST). I will discuss possible SPRITE origins and the JWST Guaranteed Time Observation (GTO) program I am leading to determine their nature.
In SPIRITS, we serendipitously discovered variable mid-IR counterparts of ultraluminous X-ray sources (ULXs). A ULX is an off-nuclear point source showing extreme, super-Eddington X-ray luminosities thought to be driven by accretion onto a compact object in a close binary undergoing Roche Lobe overflow. We attribute the mid-IR emission to a circumbinary dust disk produced by the outflow from the supergiant donor star, but the nature of the variability is still uncertain. I will discuss the work I have lead on dusty ULXs and highlight the importance of coordinated multi-wavelength observations.
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  第1629回 2017年7月4日(火)

Neutrino Oscillations in Core Collapse Supernovae
Yamaç Pehlivan Deliduman (Mimar Sinan University)
Neutrinos are the second most abundant particle species in the universe after
the photons. Their sheer numbers make them major players in many astrophysical
phenomena despite their minuscule properties. Neutrinos also hold a great
potential as a new observational window to the Universe since, due to their
small cross sections, their last point of scattering (and hence their memory)
lies deep within dense astrophysical objects.
In this talk, I will focus on the neutrinos emitted by a proto-neutron star
which forms at the center of a core collapse supernovae. Here, in the deep
regions, self interactions of neutrinos turn their flavor evolution into a
nonlinear many-body phenomenon. Tiny neutrino properties such as their mass
hierarchy and magnetic dipole moments, can be amplified by emergent many-body
effects. I will discuss the consequences of these many-body effects on
supernova dynamics, and various nucleosynthesis processes that take place in
the outer layers of the supernova.
PDF

  第1630回 2017年7月11日(火)

(Sub)millimeter Observations for the Study of Star Formation and the Formation and Evolution of Dust Through Cosmic Times
Johannes Staguhn (The Johns Hopkins University/NASA’s Goddard Space Flight Center)
Understanding the emergence and evolution of star formation, the interstellar medium (ISM) in galaxies, as traced by dust emission, and how these two quantities relate to the underlying dark matter and larger scale structures is a major stated goal of extragalactic astronomy in the US Astronomy 2010 decadal survey. The primary tracers of star formation and the ISM are observable at FIR through (sub)millimeter wavelengths, yet most analysis on early Universe galaxy evolution has been done using optical/near­infrared studies because comparably sensitive Far­Infrared (FIR) through millimeter survey instruments have not existed, so few constraints exist on the rest-frame FIR properties of z>3 galaxies. To bridge this and other gaps in our understanding, the US decadal survey recommended building the CCAT observatory, which was not realized due to funding constraints. In order to compensate for this lack of observational capabilities, we are planning to install our millimeter continuum cameras GISMO and GISMO­2 at the LMT in Mexico, which will allow us to carry out a large fraction of the high­redshift survey science proposed for CCAT.
We will illustrate the anticipated scientific capabilities of our instruments by presenting scientific results we have already obtained from observations with GISMO at the IRAM 30 m telescope in Spain. These observations include deep millimeter surveys and spatially resolved Sunyaev-Zel’dovich effect observations of a high-redshift galaxy cluster.
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  第1631回 2017年7月18日(火)

Astrophysics with Weyl Gravity
Cemsinan Deliduman (Mimar Sinan University)
This talk will introduce an attempt to describe the diverse astrophysical phenomena via Weyl gravity.
In the first part I will review my work on the resolution of the flat galactic rotation curve problem via geometry instead of assuming the existence of dark matter. Motivation for this work came from the observation that the scale independence of the rotational velocity in the outer region of galaxies could point out to a possible existence of local scale symmetry and therefore the gravitational phenomena inside such regions should be described by the unique local scale symmetric theory, namely Weyl’s theory of gravity. Solution to field equations of Weyl gravity determines the special geometry of the outer region of galaxies.
In the second part of the talk it will be conjectured that this special geometry could be valid up to the scale of galaxy clusters. Then one challenge of this approach will be to explain gravitational lens characteristics of galaxy clusters by Weyl geometry without assuming existence of dark matter. Research in this direction will be summarized.
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  今後の予定

2017年6月19日(月) Haining Li (NAOC)

2017年6月27日(火) Ryan M. Lau (NASA JPL)

2017年7月4日(火) Yamac Deliduman (Mimar Sinan University)

2017年7月11日(火) Johannes Staguhn (The Johns Hopkins University/NASA’s Goddard Space Flight Center)

2017年7月18日(火) Cemsinan Deliduman (Mimar Sinan University)

2017年7月25日(火) 廿日出文洋 (東京大学 天文学教育研究センター)

 

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