• 천문학회보
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• 제44권1호
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• pp.58.1-58.1
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• 2019

Gravitational-wave (GW) sources for the next decades would be in majority binaries consisting of neutron stars and/or black holes reside in the extragalactic environment. For example, GW170817 was the first extragalactic neutron star - neutron star binary found by GW observations and it was proved the power of multi-messenger astronomy (MMA) including the KMTNet observations. With the ever increased sensitivity, the $3^{rd}$ observation run (O3) led by the advanced LIGO and advanced Virgo this year aims to search for more 'standard' populations as well as 'exotic' ones expected by stellar evolution. I will present highlights of on-going efforts by researchers in Korea and those in abroad for estimating physical parameters of a source. Mass, spin, distance, and location are prerequisite information to constrain theoretical understanding of the source formation and evolution. Furthermore, these information are to be shared with the international community for follow-up multi-messenger observations. I will present the observational accuracy expected for the future GW observations and discuss their implications. If time allows, I will make a few remarks on prospects of O3 with KAGRA collaborations, which many domestic researchers are closely involved in.

• 천문학회보
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• 제45권1호
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• pp.39.2-39.2
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• 2020

Based upon the previous heritage in the complete development of the infrared imaging spectrometer, NISS (Near-infrared Imaging Spectrometer for Star formation history) onboard NEXTSat-1, we are participating in the NASA MIDEX mission (PI Institute: Caltech), the all-sky infrared spectro-photometric surveyor SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer). The SPHEREx will provide us the first all-sky infrared spectro-photometric data set to probe the origin of our Universe, to explore the origin and evolution of galaxies, and to explore whether planets around other stars could harbor life. After the SPEHREx have passed the PDR (Preliminary Design Review) on this September, the fabrication of flight hardware will be started soon. As an international partner, KASI takes part in the hardware development, the operation and the science for the SPHEREx. Here, we report the status of the SPHEREx project and the progress in the Korean participation.

• 천문학회보
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• 제46권1호
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• pp.29.2-29.2
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• 2021

Intracluster light (ICL) is composed of the stars diffused throughout the galaxy cluster but does not bound to any galaxy. The ICL is a ubiquitous feature of galaxy clusters and occupies a significant fraction of the total stellar mass in the cluster. Therefore, the ICL components are believed to help understand the formation and evolution of the clusters. However, in the numerical study, one needs to perform the high-resolution cosmological hydrodynamic simulations, which require an expensive calculation, to trace these low-surface brightness structures (LSB). Here, we introduce the Galaxy Replacement Technique (GRT) that focuses on implementing the gravitational evolution of the diffused ICL structures without the expensive baryonic physics. The GRT reproduces the ICL structures by a multi-resolution cosmological N-body re-simulation using a full merger tree of the cluster from a low-resolution DM-only cosmological simulation and an abundance matching model. Using the GRT, we show the preliminary results about the evolution of the ICL in the on-going simulations for the various clusters.

• 천문학회보
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• 제46권2호
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• pp.42.2-42.2
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• 2021

Intraclusterlight (ICL) is diffuse light from stars that are bound to the clusterpotential, not to individual member galaxies. Understanding the formationmechanism of ICL provides critical information on the assembly and evolution ofthe galaxy cluster. Although there exist several competing models, the dominantproduction mechanism is still in dispute. The ICL measurement between z=1 and 2strongly constrains the formation scenario of the ICL because the epoch is whenthe first mature clusters begin to appear. However, the number of high-redshiftICL studies is small mainly because of observational challenges. In this study, based on deep HST WFC3/IR data, we measured ICL of 10 galaxy clusters atredshift beyond unity, which nearly doubles the sample size in this redshiftregime. With careful handling of systematics including object masking, skyestimation, flatfielding, dwarf galaxy contamination, etc., we quantified thetotal amount of ICL, measured the color profile, and examined the transitionbetween BCG and ICL.

• 천문학회보
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• 제46권1호
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• pp.57.1-57.1
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• 2021

The icy mantles of interstellar grains are developed by the freeze-out of interstellar molecules and atoms onto grain surfaces. The ice molecules become more complex by surface chemistry induced directly by high energy photons or by the thermal energy diffused over heated grain surface. Therefore, the ice composition is an important tracer of physical conditions where the ices form. Ices have been studied via their absorption features against continuum sources, such as young stellar objects or evolved background stars, in infrared wavelengths. The Spitzer IRS was the most sensitive spectrometer for the observations of infrared ice absorption features. We has been developing an automated analysis tool for the Spitzer IRS spectra, especially for the 15 ㎛ CO₂ bending mode. The 15 ㎛ CO₂ absorption feature is very useful for the study of accretion process in star formation since its spectral shape varies with thermal condition of the dust grains. Eventually, this tool will cover the whole range of the Spitzer IRS spectrum (5~20 ㎛).

• 천문학회지
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• 제38권2호
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• pp.249-252
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• 2005

We present results of the velocity-resolved spectroscopy of the [Fe II] $\lambda$1.644${\mu}m$ emission toward outflow sources with the Subaru Telescope at the angular resolution of 0.apos;16 ${\~}$ 0.apos;5 arcseconds. The observed sources are L1551 IRS 5, DG Tau, HL Tau and RW Aur, which are located in the Taurus-Aurigae Molecular Cloud, one of the closest star forming regions (0.apos;1 = 14 AU). We were able to resolve outflow structure in the vicinity of the sources at a scale of a few tens of AU. The position-velocity diagram of each object shows two velocity components: the high velocity component (HVC: 200 - 400 km $s^{-l}$) and the low velocity component (LVC: 50 - 150 km $s^{-l}$), which are clearly distinct in space and velocity. The HVC may be a highly collimated jet presumed from its narrow velocity width and high velocity. The LVC, on the other hand, may be a widely opened disk wind inferred from its broad velocity width and low velocity. The spectrum taken perpendicular to the L1551 IRS 5 outflow at its base shows that the LVC has a spatially wide subcomponent, supporting the above interpretation. We demonstrated that the [Fe II] 1.644 $\mu$ spectroscopy is a very powerful tool for the studies of fast jets and winds that directly emanate from star-disk systems.

• 천문학회보
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• 제39권2호
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• pp.95-95
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• 2014

The mass measurement of neutron stars or black holes is of fundamental importance in our understanding of the evolution of massive stars and core-collapse supernova explosions as well as some exotic physics of the extreme conditions. Despite the importance, however, it's very difficult to measure mass of these objects directly. One way to do this, if they are in binary systems, to measure their binary motions (i.e., Doppler shifts) which can give us direct information on their mass. Recently many new highly-obscured massive X-ray binaries have been discovered by new hard X-ray satellites such as INTEGRAL and NuSTAR. The new highly-obscured massive X-ray binaries are faint in the optical, but bright in the infrared with many emission lines. Based on the near-infrared spectroscopy, one can first understand the nature of stellar companions to the compact objects, determining its spectral types and luminosity classes as well as mass losses and conditions of (potential) circumstellar material. Next, spectroscopic monitoring of these objects can be used to estimate the mass of compact objects via measuring the Doppler shifts of the lines. For the former, broad-band spectroscopy is essential; for the latter, high-resolution spectroscopy is critical. Therefore, IGRINS appears to be an ideal instrument to study them. An IGRINS survey of these new highly-obscured massive X-ray binaries can give us a rare opportunity to carry out population analyses for understanding the evolution of massive binary systems and formation of compact objects and their mass ranges. In this talk, we will present a sample near-infrared high resolution spectra of HMXB, IGR J19140+0951 and discuss about its spectral feature. These spectra are obtained on 13th July, 2014 from IGRINS commissioning run at McDonald 2.7m telescope. And at final, we will introduce the upgrade plan of IGRINS Operation Software (IGOS), to gather the input from IGRINS observer.

• 천문학회보
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• 제41권2호
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• pp.38.2-38.2
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• 2016

How dense cores and filaments in molecular clouds form is one of key questions in star formation. To challenge this issue we started to make a systematic mapping survey of nearby molecular clouds in various environments with TRAO 14m telescope equipped with 16 beam array, in high ($N_2H^+$, $HCO^+$ 1-0) and low ($C^{18}O$, $^{13}CO$ 1-0) density tracers (TRAO Multi-beam Legacy Survey of Nearby Filamentary Molecular Clouds, PI: C. W. Lee). We pursue to dynamically and chemically understand how filaments, dense cores, and stars form under different environments. We have performed On-The-Fly (OTF) mapping observations toward L1251, southern part of Perseus molecular cloud, and Serpens main molecular cloud from January to May, 2016. In total, ~3.5 square degree area map of $^{13}CO$ and $C^{18}O$ was simultaneously obtained with S/N of >10 in a velocity resolution of ~0.2 km/s. Dense core regions of ~1.7 square degree area where $C^{18}O$ 1-0 line is strongly detected were also mapped in $N_2H^+$ 1-0 and $HCO^+$ 1-0. The L1251 and Perseus MC are known to be low- to intermediate-mass star-forming clouds, while the Serpens MC is an active low-mass star-forming cloud. The observed molecular filaments will help to understand how the filaments, cores and eventually stars form in a low- and/or intermediate-mass star-forming environment. In this talk, I'll give a brief report on the observation and show preliminary results of Perseus MC.

• 천문학회지
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• 제37권4호
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• pp.285-288
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• 2004

Near-infrared imaging photometry supplemented by optical spectroscopy and narrow-band imaging of the H II region Sh 2-128 and its environment are presented. This region contains a developed H II region and the neighboring compact H II region S 128N associated with a pair of water maser sources. Midway between these, the core of a CO cloud is located. The principal ionizing source of Sh 2-128 is an 07 star close to its center. A new spectroscopic distance of 9.4 kpc is derived, very similar to the kinematic distance to the nebula. This implies a galactocentric distance of 13.5 kpc and z = 550 pc. The region is optically thin with abundances close to those predicted by galactocentric gradients. The $JHK_s$ images show that S 128N contains several infrared point sources and nebular emission knots with large near-infrared excesses. One of the three red Ks knots coincides with the compact H II region. A few of the infrared-excess objects are close to known mid- and far-infrared emission peaks. Star counts in J and $K_s$ show the presence of a small cluster of B-type stars, mainly associated with S 128N. The $JHK_s$ photometric properties together with the characteristics of the other objects in the vicinity suggest that Sh 2-128 and S 128N constitute a single complex formed from the same molecular cloud, with ages ${\~}10^6$ and < $3 {\times} 10^5$ years respectively. No molecular hydrogen emission was detected at 2.12 ${\mu}m$. The origin of this remote star forming region is an open problem.

• 천문학회보
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• 제36권2호
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• pp.61.2-61.2
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• 2011

Low-ionization nuclear emission-line regions (LINERs) have been generally regarded to be powered by active galactic nuclei (AGNs), yet still a number of alternative explanations on the origin of LINER emission are suggested; for example, planetary nebulae nuclei of massive stars, supernovae shocks from death of massive stars, and old stellar populations. Interestingly, a majority of recent star formation early-type galaxies (ETGs) in local universe presents such LINER emission lines. Given that situation, revealing the true nature of LINERs is a crucial step to constrain the evolution path to quiescent ETGs. To resolve the issue, we use Keck/LRIS to obtain spatially resolved spectra on a carefully selected ETG. The ETG SDSS J091628.05+420818.7 at redshift z ~ 0.024 shows modest LINER emission line features without any detection of 21 cm radio continuum nor X-ray emission. We perform a stellar continuum subtraction and measure emission line strengths and their uncertainties for each spectrum from five apertures along the slit with size of 1 arcsecond (~0.5 kpc). We find that extended spatial distributions of four emission lines $H{\alpha}$, $H{\beta}$, [OIII]${\lambda}5007$, and [NII]${\lambda}6583$, and they can be explained by central emission blurring effect. We conclude that the emissions seem to be centrally concentrated, indicating the AGN-nature of LINERs.