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Recent Colloquia

Special Seminar

Title:  Evolutionary Description of Giant Molecular Cloud Mass Functions on Galactic Disks

Masato Kobayashi (Nagoya University, Japan)

2pm-3pm, Monday, July 10 at GEN II R521

Abstract:

Recent radio observations show that giant molecular cloud (GMC) mass functions noticeably vary across galactic disks (e.g., Colombo et al. 2014). High-resolution magnetohydrodynamics simulations show that multiple episodes of compression are required for creating a molecular cloud in the magnetized interstellar medium (e.g., Inoue et al. 2012). To understand time evolution of GMC mass functions, we formulate the evolution equation for the GMC mass function to reproduce the observed profiles, for which multiple compressions are driven by a network of expanding shells due to H II regions and supernova remnants. We also introduce the cloud-cloud collision (CCC) terms in the evolution equation in contrast to previous work. In this seminar, I would like to present computed time evolutions and the following two suggestions:

(1) the GMC mass function slope is governed by the ratio of GMC formation timescale to its dispersal timescale whereas the CCC effect is limited only in the massive end of the profile,

(2) almost all of the dispersed gas contributes to the mass growth of pre-existing GMCs in arm regions whereas less than 60 percent contributes in inter-arm regions. Our results suggest that measurement of the GMC mass function slope provides a powerful method to constrain those GMC timescales and the gas resurrecting factor in various environments across galactic disks.

2017-06-27

Time Coordinate: 3:30 pm 9th June 2017 (Friday)

Space Coordinate: NTHU General Building II, R521

Speaker: He-Feng Hsieh and Ing-Guey Jiang (NTHU)

Title: Imaging the Exoplanets

Abstract:

Imaging method is a viable pathway to detect exoplanet and characterize the planetary atmosphere. However, imaging exoplanets is challenging due to the small angular separation and extreme intensity contrast between the exoplanet and its host star (~1e-4 for self-luminous giant planets and ~1e-10 for rocky planets). Collaborating with Nanjing Institute of Astronomical Optics & Technology, Chinese Academy of Sciences, we are developing next generation Adaptive Optic (AO) systems aiming to detect and characterize rocky exoplanets. The design of AO systems, the observation strategy, data reduction techniques, and the method for retrieving physical properties of imaged objects will be introduced in this talk.

 

2017-06-03

Time Coordinate: 3:30 pm 2nd June 2017 (Friday)

Space Coordinate: NTHU General Building II, R521

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Speaker A: Chia-Hsuan Cheng (NTHU)

Title: Variations of the x-ray flux from the globular cluster black hole

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Speaker B: Ren-Yi Deng (NTHU)

Title: Predicting the spectrum of ejection velocities of hypervelocity stars

2017-06-02