• 천문학회보
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• 제37권2호
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• pp.75.2-75.2
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• 2012

SNe Ia are a well-known powerful distance indicator. Type Ia supernova (SN) 2011fe was discovered in the nearby spiral galaxy M101 in 2011. It was discovered in less than one day after its explosion and is one of the nearest SNe Ia. Therefore SN 2011fe plays a significant role for calibrating the luminosity of the SNe Ia as well as for studying the progenitors of SNe Ia. However, previous estimates of the distance to M101 based on various methods show a large range. We present a new determination of the distance to M101 using the tip of the red giant branch (TRGB) method. We measure the distance from the F555W and F814W images of nine fields taken with the HST/ACS and HST/WFPC2 available in the HST archive. We derive a distance estimate with much smaller errors than previous studies. We discuss the implication of our results in relation with the calibration of optical and near-infrared maximum magnitudes of SNe Ia and the Hubble Constant.

• 천문학회지
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• 제35권3호
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• pp.131-141
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• 2002

We present Near-IR photometry of the Arches cluster, a young and massive stellar cluster near the Galactic center. We have analyzed the high resolution (FWHM $\~$ 0.2") Hand K' band images in the Galactic Center Demonstration Science Data Set, which were obtained with the Gemini/Hokupa's adaptive optics (AO) system. We present the color-magnitude diagram, the luminosity function and the initial mass function (IMF) of the stars in the Arches cluster in comparison with the HST/NICMOS data. The IMF slope for the range of 1.0 < log (M/M$\bigodot$) < 2.1 is estimated to be ${\Gamma} = -0.79 {\pm} 0.16$, in good agreements with the earlier result based on the HST/NICMOS data [Figer et al. 1999, ApJ, 525, 750]. These results strengthen the evidence that the IMF of the bright. stars close to the Galactic center is much flatter than that for the solar neighborhood. This is also consistent with a recent finding that the IMFs of the bright stars in young clusters in M33 get flatter as the galactocentric distance decreases [Lee et al. 2001, astro-ph 0109258]. It is found that the power of the Gemini/ AO system is comparable, with some limits, to that of the HST/NICMOS.

• ETRI Journal
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• 제43권3호
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• pp.377-388
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• 2021

Owing to the difficulties associated with conducting millimeter-wave (mmWave) field measurements, especially in high-speed train (HST) environments, most propagation channels for mmWave HST have been studied using methods based on simulation rather than measurement. In this study, considering a linear cell layout in which base stations are installed along a railway, measurements were performed at 28 GHz with a speed up to 170 km/h in two prevalent HST scenarios: viaduct and tunnel scenarios. By observing the channel impulse responses, we could identify single- and double-bounced multipath components (MPCs) caused by railway static structures such as overhead line equipment. These MPCs affect the delay spread and Doppler characteristics significantly. Moreover, we observed distinct path loss behaviors for the two scenarios, although both are considered line-of-sight (LoS) scenarios. In the tunnel scenario, the path loss exponent (PLE) is 1.3 owing to the waveguide effect, which indicates that the path loss is almost constant with respect to distance. However, the LoS PLE in the viaduct scenario is 2.46, which is slightly higher than the free-space loss.

• 천문학회보
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• 제24권2호
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• pp.75-75
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• 1999

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 1999년도 제7회 수공학웍샵
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• pp.203-263
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• 1999

• 기계와재료
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• 제11권2호통권40호
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• pp.79-88
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• 1999

• 한국지구과학회:학술대회논문집
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• 한국지구과학회 2005년도 추계학술발표회 논문집
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• pp.187-189
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• 2005

1990년 궤도에 진입한 허블우주망원경(이하 HST)이 수년내에 그 수명을 다하여 임무를 마치게 되면, 2007에서 2011년을 전후로 하여 미국, 일본과 유럽 연합은 각각 차세대 우주 망원경을 발사할 예정이다. 2007년 유럽연합의 Herschel, 2011년 미국의 JWST (James Webb Space Telescope), 그리고 2012년 일본의 SPICA가 차례로 발사되어 예정된 관측을 수행하게 된다. 기존의 HST가 가시광선 영역과 근자외선 영역을 주로 관측 했던 것과는 달리 이들 차세대 우주망원경들은 주로 근적외선에서 원적외선 영역까지를 관측하는 것을 주된 임무로 하고 있다. 본 연구에서는 한국천문학자들이 이들 차세대 망원경의 제작에 참여하는 부분에 대해 소개하고, 이들 망원경을 활용한 적외선 천문학, 특히 항성의 형성과 관련된 부분에 관하여 소개하고자 한다.

• 천문학회보
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• 제39권2호
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• pp.48.2-48.2
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• 2014

We study the resolved stellar populations of ESO149-G003, a nearby dwarf irregular galaxy in the vicinity of the Sculptor group. We present F606W-F814W vs. F814W colour-magnitude diagrams (CMDs) obtained from HST/ACS archival data. We analyze the stellar content of ESO149-G003, as well as the spatial distribution of stars selected from stellar isochrone fitting analysis. Distance measurement using the tip of the red giant branch method, age measurement of various populations seen in the CMD, and isochrone fitting result will be shown and discussed.

• 천문학회보
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• 제42권2호
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• pp.41.3-42
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• 2017

The mass function of massive high-z clusters is extremely sensitive to the cosmological parameters. However, it is challenging to estimate their accurate masses. The "See Change" HST programme offers a rare opportunity to measure them using weak gravitational lensing. In this talk, we study SPT-CL J0205-5829 (z=1.322) and MOO1014+0038 (z=1.24) discovered in the SPT-SZ survey and MaDCoW Survey, respectively. We perform weak lensing analysis with the Advanced Camera for Surveys (ACS) and Wide Field Camera 3 (WFC3) images by carefully taking into account the instrumental effect. We successfully detect weak lensing signals which produce cluster masses consistent with those from non-lensing methods based on hydrostatic equilibrium.

• 천문학회보
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• 제42권1호
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• pp.50.3-51
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• 2017

Discovered in the South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) survey, the galaxy cluster SPT-CL J0205-5829 at z = 1.322 might be the most massive known SZ-selected galaxy cluster at z > 1.2. The SZ and X-ray combined mass estimate is $M500=(4.8{\pm}0.8){\times}10^{14}M_{\odot}$. To confirm this extreme mass, we perform weak lensing analysis of SPT-CL J0205-5829 using HST data. Our analysis produces a mass estimate consistent with the previous results obtained from non-lensing methods. In this poster, we describe details of the method including shape measurement, PSF correction, source selection, and mass estimation. We also present a two-dimensional mass map and compare this to the galaxy distribution.