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콜로퀴움

Total 641
30 2014-04
2014-04-30 16:00 ~ 17:15
  • Speaker : Dr. Tao An(Shanghai Observatory)
  • Location : JYS #331-2

I will briefly introduce the space-based radio astronomical missions suggested by SHAO, i.e., the Space mm-wavelength VLBI Array, and the Space Ultra-Low Frequency Radio Observatory. The overall concept design and progress will be presented.

29 2014-04
2014-04-29 11:00 ~ 12:00
  • Speaker : Dr. Willem Baan(Shanghai Observatory)
  • Location : JYS #331-2

Molecular emissions are tools for diagnosing the nature of the emitting regions. The interpretation of these emissions has become an essential key for understanding star-formation, the ISM, starburst and AGN activity, galaxy evolution, and cosmology. This talk will consider the interpretation of the signatures of thermal molecular line emissions and non-thermal maser emissions and what these mean for the emitting regions.

09 2014-04
2014-04-09 16:00 ~ 17:30
  • Speaker : Dr. Martin Bureau (Oxford University)
  • Location : JYS #331-2

I will demonstrate that, contrary to expectations, early-types galaxies contain a significant amount of cold molecular gas, and that the spatially-resolved kinematics of this gas can be used to establish its origin. More importantly, the molecular gas turns out to be an excellent, arguably the best tracer of the circular velocity in early-type galaxies, thus allowing accurate total/dynamical mass measurements. I will exploit this principally in two ways. First, to show that an accurate CO Tully-Fisher (luminosity-circular velocity) relation can easily be derived for early-type galaxies. This opens the way to probe the mass growth of galaxies of all types to significant redshits, with a unique and simple method. Second, to show that CO can be used to accurately measure the mass of the supermassive black holes lurking at galaxy centres. This opens the way for literaly hundreds of measurements across the Hubble sequence, potentially revolutionising our understanding of the co-evolution of galaxies and black holes.

31 2014-03
2014-03-31 16:00 ~ 17:00
  • Speaker : Dr. Sangwook Park (University of Texas at Arlington)
  • Location : JYS #331-2

Supernova remnants are an excellent laboratory to study many fundamental subjects of modern astronomy and astrophysics such as the nature of stellar evolution, explosion, interstellar chemical evolution, and cosmic-ray acceleration. With the emergence of modern X-ray observatories supernova remnant study has been revolutionized for the last decade. We briefly introduce recent results from deep X-ray observations of Type Ia supernova remnants, Kepler and G299.2-2.9. We detect Fe-peak ejecta elements Mn, Cr, Fe, and Ni in Kepler. Our estimated mass ratios among these elements show that Kepler's supernova was a thermonuclear explosion of a relatively young white dwarf with a supersolar metallicity. G299.2-2.9 apparently shows an elongated, strong outflow-like ejecta feature. This particular emission feature may suggest an asymmetric explosion or a significantly modified environment, unlike the traditional picture of Type Ia supernova.

24 2014-03
2014-03-24 16:00 ~ 17:30
  • Speaker : Dr. Emmanuel Momjian(NRAO)
  • Location : JYS #331-2

In recent years, various optical surveys revealed large samples of quasars out to z of 6. Studies have shown that at such high redshifts we are approaching the Epoch of Reionization, when the first stars and massive black holes were formed. High redshift quasars provide both interesting constraints on the growth of the first supermassive black holes, and light sources with which to probe the ionization history of the Universe. While observations at radio wavelengths show that only a few of these high-z quasars are radio-loud, (sub)mm studies reveal a significant fraction (20-30%) of these most distant sources to be copious emitters of far-IR radiation with FIR luminosities > 10^12 Lsun. VLBI, with its unprecedented resolving power, can be utilized to study the highest redshift quasars to 1) look at their physical structures at milliarcsecond resolution, 2) test for strong gravitational lensing to address the high mass values of their supermassive black holes, and 3) test, by direct imaging, whether the dominant power source at radio frequencies is an AGN or starburst, particularly in those sources that are strong FIR emitters. In this talk I will give an overview of the Very Long Baseline Array (VLBA) and the High Sensitivity Array (HSA), and present observational results obtained on various radio-loud and radio-quiet quasars at redshifts z > 4 with the VLBA and the HSA. I will also provide a summary on a similar work that targets sum-mm galaxies at z~2.

12 2014-02
2014-02-12 16:00 ~ 17:30
  • Speaker : Dr. Jeeseon Song (University of Michigan)
  • Location : JYS #331-2

Clusters of galaxies are great laboratories for many astrophysical processes on galaxy scale and have become one of the key probes in today's cosmology. Especially their mass function redshift distribution helps unveiling the effect of the mysterious driving force on the expansion of the universe - dark energy. In order to step forward to even higher precision cosmology using clusters, one not only needs to build good analysis tools, such as cluster finders, but also understands their systematics. In this talk, I will map out a round trip from understanding systemactics in large cluster samples to improving those tools for better cosmology. I will present a way to improve the understanding of the Universe as an interlocking element between real data and simulations. This will include, 1) building an empirically-motivated mock catalog using high-resolution N-body simulations to test various analysis tools, 2) understanding contamination and incompleteness using cross match of multi-wavelength cluster samples from large sky survey data. These projects are crucial in interpreting data from cluster surveys, such as South Pole Telescope (SPT), Dark Energy Survey (DES), as well as an upcoming survey from the Giant Magellan Telescope (GMT).

16 2014-01
2014-01-16 16:00 ~ 17:30
  • Speaker : Yim Kijeong(Kapteyn Astronomical Institute, University of Groningen, Netherlands)
  • Location : JYS #331-2

For understanding the relationship between star formation and the interstellar medium properties, measuring the disk thickness of a galaxy is very important since it allows us to derive the volume density, a quantity that may be better correlated with star formation rate (SFR) than surface density. In this talk, I present a study of the vertical structure of the gaseous and stellar disks in a sample of edge-on galaxies (NGC 891, 4157, 4565, and 5907) using BIMA/CARMA CO (J = 1-0), VLA HI, and Spitzer 3.6 micron data. In order to take into account projection effects when measuring the disk thickness as a function of radius, I obtain the inclination by modeling the radio data. Using the measurement of the disk thicknesses and the derived radial profiles of gas and stars, I estimate the corresponding volume densities and vertical velocity dispersions. Both stellar and gas disks have smoothly varying scale heights and velocity dispersions, contrary to assumptions of previous studies. Using these scale heights and velocity dispersions, the gravitational instability parameter Q follows a fairly uniform profile with radius and is greater than or similar to 1 across the star forming disk. The star formation law has a slope that is significantly different from those found in more face-on galaxy studies, both in deprojected and pixel-by-pixel plots and this is likely due to IR opacity. Midplane density appears to be a better predictor of molecular-to-atomic ratio than midplane gas pressure.

14 2014-01
2014-01-14 16:00 ~ 17:30
  • Speaker : Amol Upadye(IEU)
  • Location : JYS #331-2

New physics associated with the cosmic acceleration can be probed at cosmological scales as well as in laboratory experiments. I will begin by discussing the formation of large-scale cosmic structure, whose statistics will allow us to constrain cosmic expansion and new forces along with the masses of neutrinos. Using higher-order cosmological perturbation theories, I compute the power spectrum of large-scale structure, the Fourier transform of the two-point correlation function, for a universe with massive neutrinos and a cosmic acceleration driven by a time-varying dark energy density. Comparison with N-body dark matter simulations shows that perturbation theory is accurate to a few percent at distances of interest to upcoming galaxy surveys, and predicts a shift in the Baryon Acoustic Oscillations. Next, I will discuss laboratory constraints on couplings between dark energy and Standard Model particles, which are complementary to cosmological probes. Several models predict fifth forces at the dark energy scale, of order 100 microns, which are accessible to the next generation of laboratory experiments. Dark energy may also couple to photons, allowing for the production of dark energy particles in the Sun or the laboratory. The combination of information from the megaparsec and the micron scales will provide comprehensive constraints on dark energy over the next decade.

02 2014-01
2014-01-02 14:00 ~ 15:30
  • Speaker : Dr. Bindu Rani(MPIfR VLBI Group)
  • Location : JYS #331-2

The origin of high energy emission has always been a key question in AGN physics. The gamma-ray bright blazars constitute a unique laboratory to probe jet formation and its relation to radio-to-gamma-ray variability. A combination of high-resolution VLBI images associated with densely time sampled multi-frequency flux measurements of the extreme BL Lac object S5 0716+714 over the past four years allow us to study its broad-band variability, allowing us to probe the jet acceleration zone, with emphasis on the location and size of the emitting regions and the evolution with time. We study the characteristics of some prominent mm-/gamma-ray flares in the context of (1) the shock-in-jet models, (2) broadband spectral modeling, (3) and jet kinematics, to probe the location of the high energy emission region. Here, I will present and discuss the main results of the study.

04 2013-12
2013-12-04 16:00 ~ 17:30
  • Speaker : Dr. Mario Pasquato
  • Location : JYS #331-2

Globular Cluster (GC) cores have long been speculated to contain Intermediate-Mass Black Holes (IMBHs). Claims stemming from indirect detection methods abound, however there are still no definitive detections of radio or X-ray emission from accreting matter on IMBHs in GCs. Due to the high mass of IMBHs, an important criterium for distinguishing an IMBH candidate from other sources is based on how central the source is. I will briefly discuss analytical predictions and numerical simulation results about how far an IMBH can wander from the center of a typical GC, and the consequences in terms of potential false negatives in direct detection attempts.

27 2013-11
2013-11-27 16:00 ~ 17:00
  • Speaker : Dr. Kimitake Hayasaki
  • Location : JYS #331-2

Tidal disruption flares are thought to be evidences for quiescent supermassive black holes at the centers of inactive galaxies, because of those characteristic time variations with large luminosities. However, there is poorly known about tidal disruption and subsequent mass fallback process for stars approaching supermassive black holes on bound orbits. We perform three dimensional Smoothed Particle Hydrodynamics simulations of those processes with a pseudo-Newtonian potential. We find that the mass fallback rate decays with the expected -5/3 power of time for parabolic orbits, albeit with a slight deviation due to the self-gravity of the stellar debris. For eccentric orbits, however, there is a critical value of the orbital eccentricity, significantly below which all of the stellar debris is bound to the supermassive black hole. All the mass therefore falls back to the supermassive black hole in a much shorter time than in the standard, parabolic case. The resultant mass fallback rate considerably exceeds the Eddington accretion rate and substantially differs from the -5/3 power of time. We also show that general relativistic precession is crucial for accretion disk formation via circularization of stellar debris from stars on moderately eccentric orbits. We also discuss how a black hole spin affects the debris circularization by SPH simulations with Post-Newtonian corrections.

13 2013-11
2013-11-13 16:00 ~ 17:30
  • Speaker : Dr. Will Saunders(AAO)
  • Location : JYS #331-2

The AAO has always been a pioneer of innovative instrumentation for cosmology, and especially survey cosmology involving fiber-based massive multiplexing over large fields. I will review the instruments the AAO has developed, both for our own own use, and for other observatories including ESO, Subaru and GMT. I will also review the technologies under development by the Instrument Science group. I will also look forward to projects still in the future, and how AAO and KASI might be able to work together for mutual benefit.

07 2013-11
2013-11-07 16:00 ~ 17:30
  • Speaker : Dr. Vasyl Yurchyshyn (Big Bear Solar Observatory / New Jersey Institute of Technology)
  • Location : JYS #331-2

The New Solar Telescope (NST) in Big Bear is the first facility-class an off-axis solar telescope built in the US in a generation. The NST is in regular operation with adaptive optics (AO) correcting the light currently feeding photometric and near-IR polarimetric systems, as well as an imaging spectrograph. In this presentation I will review the existing and planned NST instrumentation and improvements. In the second part of my presentation I will review scientific results and findings based on the NST data.

23 2013-10
2013-10-23 16:00 ~ 17:30
  • Speaker : Dr. Kim, Kyoung Hee
  • Location : JYS #331-2

We present our investigation of the characteristics of Class II protoplanetary disks in Orion A star-forming region. Our major goal is to analyze a large sample of protoplanetary disks with near- and mid-IR spectra, by statistical approaches, to understand protoplanetary disk evolution in Orion A. For this work, 303 protoplanetary disks in Orion A region observed by IRS/Spitzer and the follow-up observation of 120 objects from SpeX/IRTF are used to reveal the characteristics of Class II disks in Orion A. For clues on environmental effects on disk evolution and planet formation, we compare the disk properties and dust properties of Orion A disks to that of Taurus disks and examine trends with respect to position within Orion A. We extract spectral indices, equivalent widths, and integrated fluxes from IRS spectra of Class II objects in Orion A which pertain to disk structure and dust composition. We measure mass accretion rates using hydrogen recombination lines in SpeX spectra of our targets. Utilizing the properties, we analyze the general distribution of properties of disks in ONC, L1641, and Taurus from their histograms. Our main findings are as follows. (1)Transitional disks ? those protoplanetary disks for which deficits of infrared excess signify sharp-edged gaps in the dust distribution ? are produced gravitationally by companions to the central star. (2) From the high frequency (>20%) of transitional disks and the similar vertical structure of the Orion A disks to those of Taurus, we infer that giant planet formation and dust sedimentation is well under way, if not complete, even in the youngest Class II objects. (3) Less grain processing ? crystallization and growth of grains to diameter of 1?10 μm ? has occurred among the dust grains in the Orion A disks than in Taurus. The time scales for dust processing must therefore lie in the range of ages of the nearby clouds like Orion, NGC 1333, Taurus, Ophiuchus and Chamaeleon. (4) We detected PAH emission at 6?14 μm from disks around low-mass and low-luminosity young stars, excited externally by UV from the Trapezium stars. (5) As others have found for the Trapezium region of Orion, the disks of the surrounding Orion Nebular Cluster suffer reduced emission at long infrared wavelengths. The reduction tracks distance from the most luminous Trapezium star, θ1 Ori C, so this appears to be the effect of UV oblation of the outer part of the disks.

16 2013-10
2013-10-16 16:00 ~ 17:30
  • Speaker : 이종익박사 (극지연구소)
  • Location : JYS #331-2

현재까지 인류가 소유한 운석의 약 80% 정도(60,000여개)가 1970년대 중반부터 자국 정부의 지원을 받는 운석탐사대에 의해 남극에서 회수되고 있다. 남극에서 운석탐사를 지속적으로 수행하는 나라는 미국, 일본, 이태리, 중국 등 4개국이고, 우리나라는 2006년부터 시작하였다. 2006년부터 현재까지 6 차례의 탐사를 통해 남극대륙의 청빙지대에서 달운석 1개를 포함 총 180여개의 운석을 확보하였다. 미국을 제외한 나머지 나라는 남극연구 전문기관에서 운석을 체계적으로 관리하고 있다. 남극운석은 연구용으로만 사용되기 때문에 남극운석을 회수한 기관은 일정기간 내에 정해진 기준에 의해 운석을 분류하고, 적절한 절차를 거쳐 전 세계 연구자들에게 분배하여야 한다. 현재 극지연구소는 남극운석 회수-보관-분류-등록-분배 임무를 총괄하는 큐레이션시스템(koreamet.kopri.re.kr)을 가동 중에 있고, 운석 연구 역량을 강화하기 위해 최신 분석장비 확보에 전력을 기울이고 있다. 극지연구소는 2009년부터 새로 건조한 쇄빙연구선 ‘아라온’을 매년 남극 탐사에 투입하고 있고, 2014년 2월 완공을 목표로 제2 남극기지 ‘장보고과학기지‘를 동남극 테라노바만에 건설하고 있다. 2014년 장보고과학기지 준공 원년부터 새로운 융복합 연구를 착수하고자 신규 정부 R&D 사업을 추진하고 있다. 신규 R&D 사업의 제2 세부과제는 운석학, 행성지질학, 우주생물학, 우주기상 연구의 기반 구축을 목표로 설정하고 다양한 산-학-연 협력연구를 추진할 예정이다. 또 이 세부과제는 남극내륙 고원에서 빙하시추와 천문/우주관측을 목표로 하는 제3 내륙기지 후보지를 탐색하는 임무도 수행할 예정이다. 이상에서와 같이 극지연구소는 현재 2020년 정부주도의 달 탐사 프로젝트 추진 동력을 뒷받침할 수 있는 기관 고유 임무를 남극에서 적극적으로 모색하는 단계에 있다. 따라서 문을 열고 출연연, 대학 등과 협력을 통해 발전을 도모해야 하는 중요한 전환기를 맞고 있다

02 2013-10
2013-10-02 14:30 ~ 16:00
  • Speaker : Dr. Min-Su Shin (University of Oxford)
  • Location : JYS #331-2

I will present new results of cosmological galaxy formation with cosmic magnetic fields. The new simulations are quite unique because of its usage of adaptive mesh refinement to cover a broad range of spatial/time scale and its tests of cosmological primordial magnetic fields. I will also introduce a new approach of stochastic models to incorporate sub-grid physics of astrophysical magnetic fields in cosmological galaxy formation simulation. Various applications of the new simulation results will be briefly explained in the talk, encouraging further usages of the results by the KASI people.

23 2013-09
2013-09-23 16:00 ~ 17:00
  • Speaker : Dr. Eric Linder(University of California, Berkeley)
  • Location : JYS #331-2

Dark energy and dark matter are fundamental mysteries in understanding our universe. With upcoming cosmic surveys they are ripe for advances. I highlight some new handles on dark energy and new cosmic probes that test both cosmic acceleration and the dark matter distribution. Time delays from strongly lensed active galactic nuclei give precision distances complementary to those from supernovae or large scale clustering. Redshift space distortions of the 3D pattern of galaxy clustering probe the matter growth rate and laws of gravity. Both require techniques and surveys that KASI is well positioned to contribute to, ready to make new discoveries in cosmology and astrophysics.

11 2013-09
2013-09-11 16:00 ~ 17:00
  • Speaker : Dr. Ed Fomalont JAO Santiago Chile and NRAO Charlottesville, USA
  • Location : Jang-Youngsil 331-2

Phase referencing is the main observational tool that is used by radio arrays in order to make high resolution images of extended radio sources, or to determine the precise position of celestial objects, natural and man-made. The fundamentals of phase referencing, examples of results, second-order corrections, and the problems when the phase stability is limited are discussed. Examples of projects that are in progress or ready-to-go will be outlined. Special phase referencing problems and possible solutions for high resolution ALMA observations at high frequencies are also discussed.

23 2013-08
2013-08-23 16:00 ~ 17:30
  • Speaker : Min-Young Lee (University of Wisconsin-Madison)
  • Location : Seminar room #331-2 in Jang Yeong-sil Hall

The formation of molecular gas is a critical step in the conversion of interstellar gas into stars, yet the physical processes involved still remain unclear. With a goal of providing observational constraints on the formation of molecular gas, I perform two high-resolution, multi-wavelength studies of the Perseus molecular cloud in the Milky Way. In the first study, I investigate the transition from atomic (HI) to molecular hydrogen (H2) on sub-parsec scales and find that the HI distribution is surprisingly uniform. As a result, the H2-to-HI ratio linearly increases with the total gas column density. These results are consistent with the theoretical model by Krumholz et al. (2009), where the formation and photodissociation of H2 are in balance and the abundance of H2 is controlled by the minimum HI column density required for H2 shielding. In the second study, I examine the relation between the H2 column density and the carbon monoxide (CO) integrated intensity and show that the ratio of the two, so called "X-factor", varies spatially by up to a factor of 100. I then compare the HI, H2, CO, and X-factor data with two contrasting theoretical models, i.e., PDR model by Wolfire et al. (2010) and MHD model by Shetty et al. (2011). I find that the steady state and equilibrium chemistry model (PDR) reproduces the observations very well but requires an extended halo around a dense core. While agreeing with the observations reasonably well, the macroturbulent and non-equilibrium chemistry model (MHD) shows interesting discrepancies, including a broader range of HI column density

14 2013-08
2013-08-14 16:00 ~ 17:30
  • Speaker : Chunglee Kim (Seoul National Univ.)
  • Location : Seminar room #331-2 in Jang Yeong-sil Hall

Radio pulsars are highly magnetized, rapidly rotating neutron stars that emit synchrotron radiation along the magnetic axes at their spin frequencies. A compact, strongly gravitating object that emits narrow, regular pulses 1-1000 times per second provides us with a laboratory to test Einstein’s general relativity by, for instance, long-term observations of pulse arrival times. Pulsars in tight binaries are of particular interests as they are important sources of gravitational waves. For example, NS-NS binaries are one of the prime targets for the advanced gravitational-wave detectors on Earth. Since the first discovery made by Jocelyn Bell Burnell and Antony Hewish in 1967, more than 2000 radio pulsars are known to-date in our Galaxy. Discoveries of new population and precision timings made in the past decade not only shed light on existing questions, but also arose new ones. Radio pulsar spectrum follows a power-law with a negative slope of -2. Hence, observations have often been done at low frequencies (MHz up to a few GHz). More recently, high-frequency pulsar observations (several GHz and above) have been practically possible, when a broad-band spectrometer and fast computers became available. The main driving force toward higher frequencies is to find pulsars in the vicinity of Sgr A*, which is one of the holy grails of pulsar astronomy. In this talk, I will overview the Galactic pulsar population and discuss how we can utilize the Korean VLBI Network for pulsar observations. I will also present the on-going efforts at KASI.

25 2013-06
2013-06-25 16:00 ~ 17:30
  • Speaker : Robert Wittenmyer (University of New South Wales)
  • Location : Seminar room #331-2 in Jang Yeong-sil Hall

I give an update on three major exoplanetary science initiatives being pursued by Australian-based planet-search teams. Further observations from the Anglo-Australian Planet Search (AAPS) have revealed that some systems previously thought to contain a single, moderate-eccentricity planet are better fit by two planets on nearly-circular orbits. We have investigated apparent single-planet systems to see if the available data can be better fit by two lower-eccentricity planets. We identify nine promising candidate systems and perform detailed dynamical tests to confirm the stability of the potential new multiple-planet systems. In addition to the AAPS, I describe the Pan-Pacific Planet Search, a radial-velocity survey of Southern hemisphere evolved, intermediate-mass stars using the 3.9m Anglo- Australian Telescope. We currently achieve velocity precisions of 3-6 m/s, and there are several planet candidates emerging as more data are obtained. I then describe a plan for Minerva: an installation of four 0.7m telescopes feeding a high-resolution spectrograph, sited at Mt Hopkins in Arizona. Minerva will give exoplanetary scientists the ability to pursue dedicated radial-velocity searches for planets orbiting the nearest bright stars. In addition, a Southern hemisphere Minerva could be used to follow up on objects of interest from Antarctic telescopes such as the Chinese AST-3. I will describe the diverse science cases for this highly cost-effective facility. Finally, I present results from our recent series of papers in which we have performed extensive suites of dynamical simulations to test the veracity of proposed multiple-planet systems. We show that some systems are strongly constrained by protected low-order resonances, while others are wildly unstable on short timescales. This work highlights the critical need to include dynamical stability analysis as an integral part of the discovery process for candidate multi-planet systems.

12 2013-06
2013-06-12 16:00 ~ 17:30
  • Speaker : Sang Hyun Lee (KASI)
  • Location :

We studied the structure of two old open clusters, NGC 1245 and NGC 2506, from a wide and deep VI photometry data acquired using the CFH12K CCD camera at Canada?France?Hawaii Telescope. We derived the physical parameters using detailed theoretical isochrone fittings using χ2 minimization. We devised a new method for assigning cluster membership probability to individual stars using both spatial positions and positions in the colour?magnitude diagram. From analyses of the luminosity functions at several cluster-centric radii and the radial surface density profiles derived from stars with different luminosity ranges, we found that the two clusters are dynamically relaxed to drive significant mass segregation and evaporation of some fraction of low-mass stars. There seems to be a signature of tidal tail in NGC 1245 but the signal is too low to be confirmed. We will discuss the halo and the tidal tail structure in the open cluster in this talk.

30 2013-05
2013-05-30 16:00 ~ 17:30
  • Speaker : Maurice Van Putten (Sejong Univ.)
  • Location :

We applied matched filtering to the light curves of 1491 long GRBs in the BATSE catalogue to search for evidence of spindown of rapidly rotating black holes and (proto-)neutron stars. On average, the results favor black hole spindown against high density matter at the ISCO. As a natural and common outcome of core-collapse of massive stars and mergers, this model accounts for GRBs in- and outside star forming regions. It also accounts for hyper-energetic GRB-SNe whose energy requirements exceed the maximal spin-energy of rapidly rotating neutron stars. Hyper-energetic CC-SNe hereby provide novel priors to LIGO-Virgo and KAGRA searches for long duration gravitational wave bursts up to tens of seconds with an anticipated negative chirp by expansion of the ISCO.

08 2013-05
2013-05-08 16:00 ~ 17:30
  • Speaker : Mario Pasquato (Yonsei university)
  • Location :

Currently, mass-loss in the late Red Giant Branch (RGB) phase of low-mass stars is still relatively poorly constrained by direct observations. Horizontal Branch (HB) colour distributions can provide quantitative constraints to an encounter-based mass-loss law, despite being indirect and model-dependent. Recent infrared observations of dusty RGB stars in Globular Clusters (GCs) suggest that mass-loss is episodic and weakly related to stellar properties. Stellar encounters in GCs cores are a candidate mechanism for producing RGB mass-loss with these characteristics, but a detailed quantitative treatment of the effect is yet lacking. This would be particularly important in GCs such as NGC 2808, where standard mass-loss prescriptions are unable to fully predict the HB morphology, even when helium-enhanced multipopulations are taken into account. I show that the maximum temperature along the HB for a sample of GCs follows a characteristic pattern with dynamical age (i.e. chronological age over relaxation time), suggestive of the high-density state reached during core-collapse playing a role in enhancing mass-stripping in the RGB phase. Moreover, simple, analytical assumptions for the mass-loss law in stellar encounters naturally result in a non-gaussian mass-loss distribution, with high skewness. I compare it to Hubble Space Telescope (HST) data of HB-mass over a sample of 71 GCs, and I briefly discuss the next step in modelling the mass-loss interaction, i.e. smoothed-particle hydrodynamics simulations.

30 2013-04
2013-04-30 16:00 ~ 17:30
  • Speaker : Valery Nakariakov (Univ. of Warwick)
  • Location :

The interest in long-period large-scale oscillations of solar coronal loops, confidently observed with the modern observational facilities is mainly connected with the diagnostics of the plasma, known as the method of magnetohydrodynamic (MHD) seismology. Typical periods of these oscillations range from a few seconds in flaring loops to several hours in prominences. Both rapidly decaying and undamped regimes have been revealed. Observed parameters of the oscillations give us unique information about the physical parameters of the plasma, that are either difficult or impossible to obtain by other methods, such as the magnetic field, fine structuring, effective transport coefficients and the empirical heating function. The basic theory used in the interpretation of the observations is based on the linear MHD perturbations of a straight plasma cylinder, that predict the existence of three main magnetoacoustic modes: kink, sausage and longitudinal. Observational manifestation of these modes in the EUV and microwave bands, and their seismological implications are discussed. The main emphasis is put on the kink mode.

02 2013-04
2013-04-02 16:00 ~ 17:30
  • Speaker : Patrick McCarthy (GMTO Director)
  • Location :

The Giant Magellan Telescope project is an international collaboration to design, build and operate a 25m telescope for research in astrophysics and cosmology. The consortium is composed of KASI and several US and Australian Universities and research institutes. The GMT primary mirror is comprised of seven 8.4m diameter segments, providing both a collecting area and diffraction-limited image concentration that are an order of magnitude better than those offered by current facilities. The telescope will be located at Las Campanas Observatory in Chile and will access the same region of the sky as the LSST, the Dark Energy Survey, ALMA and a number of other surveys and front-line facilities. The GMT will have the widest field of view of any of the proposed ELTs. Adaptive optics is integral to the telescope via a segmented adaptive secondary mirror. I will review the scientific goals of the project and the current technical status. Fabrication of 8.4m off-axis primary mirror segments, the largest technical challenge, has now been demonstrated. I will review the challenges associated with implementing a 20 arcminute diameter corrected field of view and approaches to spectroscopic follow-up of large imaging surveys. Diffraction-limited operations will be essential to the exploration of planetary systems and GMT offers unique opportunities as well as technical challenges. A roadmap for instrumentation development will closely interface with commissioning plans for the telescope and key scientific opportunities early in the next decade.

27 2013-03
2013-03-27 09:30 ~ 10:30
  • Speaker : Noriyuki Namiki (Chiba Institute of Technology)
  • Location :

Three topics will be discussed hopefully to give some clues for future Korean lunar and planetary missions. First topic is a scientific result of Japanese lunar exploration, Kaguya. Gravity measurement of the far side of the Moon by using a relay sub-satellite has revealed marked difference of mascon features between near and far sides indicating endogenic origin of lunar dichotomy. But there remains many unresolved issues in lunar sciences. The second topic is an introduction of ongoing asteroid mission, Hayabusa-2. Unlike big, well-planned missions of NASA and ESA, Japanese space scientists have been forced to achieve the most outcomes from the least budget and human resource because of the limit of our nation's economy and power. And Korean space scientists, maybe, face the similar problem with ours in the future. Then an experience of small mission like Hayabusa-2 will help designing future Korean missions. The third topic is a decadal survey activity in Japanese community of planetary scientists. Space programs can be initiated by a leadership of the government, however, the programs will not continue without strong supports of science community. Unfortunately, university researchers are very difficult to unite and share a common goal. An effort of Japanese community to organize a new mission by scientists, not JAXA, is reported.

13 2013-03
2013-03-13 16:00 ~ 17:30
  • Speaker : Wouter Vlemmings (Chalmers University of Technology)
  • Location :

Magnetic fields potentially play an important role during massive star-formation (MSF), especially in stabilizing disks and launching outflows. Currently, the only information on the magnetic field in the dense regions close to protostars comes from maser observations. In particular, it has recently been shown that methanol masers, the most abundant of the MSF maser species, are excellent probes of the magnetic field. I will present the status of our ongoing high angular resolution observations using the European VLBI Network (EVN). So far, these have revealed energetically dominant and large scale ordered fields in the majority of MSF regions. In particular, the observations reveal a likely relation between the magnetic field direction in and around disks and torii and the outflow, as predicted by recent models.

04 2013-02
2013-02-04 16:00 ~ 17:30
  • Speaker : Doug Simons & Daniel Devost (CFHT)
  • Location :

Title : CFHT Status Report and Future Plans Speaker : Dr. Doug Simons (CFHT) Abstract : After a brief summary of the nature of CFHT Corp. and recent metrics illustrating the scientific success of CFHT, the future of the Observatory is described through various initiatives designed to broaden the CFHT partnership, develop new capabilities, and take steps toward the replacement of CFHT with a powerful new facility dedicated to highly multiplexed wide-field spectroscopy. CFHT, in the context of the evolving landscape on Mauna Kea will also be discussed, as CFHT positions itself among a backdrop of some older facilities being decommissioned while new Mauna Kea facilities are on the planning horizon. Title : The CFHT Science Operations Speaker : Dr. Daniel Devost (CFHT) Abstract : I will review the Science operations at CFHT from the proposal submission all the way to the Archival of the data. CFHT Science Operations are essentially based on a Queue Scheduling system that optimizes the night time to maximize the Scientific return. I will describe each step in the process and show how we proceed to get the best possible observations for our Agencies.

23 2013-01
2013-01-23 16:00 ~ 17:30
  • Speaker : Rafael de Souza (KASI)
  • Location :

During the talk, I will give a brief review about my past and current projects related with the possibility to observe the first stars by looking their final fate as gamma-ray bursts or supernova. In special, I will discuss a current and still on going project explained bellow. With the next generation of optical and near-infrared (NIR) surveys, the possibility to observe primordial stars becomes real. A fraction of these first stars, with masses between ~ 140 and 260 solar mass, are expected to die as pair-instability supernovae (PISN). We use the state of art of cosmological simulations, to infer the predicted rate of PISN, and radiation hydrodynamical simulations, to model the spectral energy distribution of PISN in realistic circumstellar environments with Lyman absorption by the neutral intergalactic medium. We then constructed a synthetic survey of supernovae light curves as they should be observed by James Webb Space Telescope (JWST), including all important characteristic of the experiment. We are capable to provide a sample of FITS file that can be treated as the same way as a real data. Future supernova surveys are expected to observe much more supernovae than can be confirmed spectroscopically. Given the rare nature of these events, it’s imperative to rely in some good photometric predictor, in order to find suitable candidates for posterior spectroscopically confirmation. Thus, using our synthetic sample, we perform a comprehensive study of the best strategy capable to find these objects, estimate the redshift and identify them photometrically. To do so, we are using a combination of the best learning methods available, in special kernel principal components analysis (kpca), fuzzy logic and genetic algorithms. Our methodology based in KPCA already proved to have a higher accuracy only relying in photometric information in the problem of Type Ia identification (Ishida, E. and de Souza, R, MNRAS 2013,), with no need of redshift information. We are developing the most realistic and complex framework, from far, to study the best way to find the first supernovae. Being one of the most promising approaches to drive the future searches of these objects.

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