• 천문학회보
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• 제37권1호
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• pp.70.2-70.2
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• 2012

The night sky in Mongolia is known to be one of the darkest and clearest in Asia. The seasonal dust winds from the Gobi desert, however, might degrade the transparency of the night sky and affect the photometrical quality for astronomical research. In this poster, we present the preliminary results of the first transparency measurement of the night sky in Monglia. The observations are done at Zuunmod located at 25 km south from Ulaanbaatar in 2011 October 26-31. We used a CCD camera (QSI 583s) attached to an 80 mm aperture refractor telescope (William Optics Zentih Star 80 II ED APO). A new supernova, SN2011fe, and a young stellar object, HBC 722, were monitored in order to measure the extinction coefficients. These values in Mongolia are compared with those in other astronomical observatory.

• 천문학회지
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• 제40권4호
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• pp.187-188
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• 2007

This contribution to the IV Korea-Mexico meeting deals with the hydrodynamics of the matter reinserted within super star clusters (SSCs) by both stellar winds and supernova explosions, results recently printed in The Astrophysical Journal (Silich et al. 2007). The motivation of such a project arose from the persistent presence of the small mass and compact HII regions that sit right on top of many massive and compact SSCs, from which one expects a large mechanical energy power. The data used for our calculations appear only recently (see Smith et al. 2006) for the massive and compact SSC M82-A1. We presented in our paper the calculated flow, derived through analytical and semi-analytical methods, which led to almost identical results. We have found out that the only way of accommodating a compact HII region (4.5 pc in radius, in the case of M82-A1) on top of a 6.3 Myr old and massive (> $10^6M_{\bigodot}$) SSC with a half light radius of 3 pc, requires of two assumptions: a very low heating efficiency (< 10%) within the cluster, what leads to a bimodal solution (see Tenorio-Tagle et al. 2007) and a high pressure in the surrounding medium.

• 천문학회지
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• 제27권2호
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• pp.147-158
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• 1994

We have obtained high angular resolution maps toward a molecular cloud associated with an HII region S287 and studied mainly kinematics of the cloud. The mapped region is 1.5 square degrees of the cloud in the transitions of $^{12}CO\;and\;^{13}CO\;J=1-0$. We have obtained a large range of mass, $1.3\times10^4M_\bigodot$, to $7.2{\times}10^4M_{\bigodot}$ using three different techniques. The S287 molecular cloud shows a very disturbed feature: velocity field of the cloud is very complicated, and shows several arcs. It is likely that the southern part of cloud is being disrupted by the residing HII region S287 as well as external perturbing sources. In addition to an HII region, five bipolar outflows are also disturbing the molecular gas significantly. The large virial mass and the very disturbed morphology may reflect the fact that the cloud is not gravitationally bound system, as in the case of nearby giant molecular cloud (GMC) G216-2.5. The several arc structure and the filamentary features are possibly driven by external strong stellar winds, and these external perturbing sources may be driving the second generation of star-forming activities on the edges of the S287 molecular cloud.

• 천문학회보
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• 제37권2호
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• pp.140.2-140.2
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• 2012

The silicate carbon star IRAS 09425-6040 shows very conspicuous crystalline silicate dust features and excessive emission at far infrared. To investigate properties of dusty envelopes around the object, we use radiative transfer models for axisymmetric and sphericallly symmetric dust distributions. We perform model calculations for various possible combinations of dust shells and disks with various dust species. We compare the model results with the observed spectral energy distributions (SEDs) including the IRAS, ISO, AKARI, MSX and 2MASS data. We find that a model with multiple disks of amorphous and crystalline silicate and multiple spherical shells of carbon dust can reproduce the observed SED fairly well. This supports the scenario for the origin of silicate carbon stars that oxygen-rich material was shed by mass loss when the primary star was an M giant and the O-rich material is stored in a circumbinary disk. Highly (about 75 %) crystallized forsterite dust in the disk can reproduce the conspicuous crystalline features of the ISO observational data. This object looks to have a detached silicate and H2O ice shell with a much higher mass-loss rate. It could be a remnant of the chemical transition phase. The last phase of stellar winds of O-rich materials looks to be a superwind.

• 천문학회보
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• 제44권1호
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• pp.67.2-67.2
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• 2019

We present the results of KVN and ALMA observations toward WX Psc (IRC+10011) which is a long-period variable OH/IR star. The SiO masers of v=1 and v=2, J=5-4, and the SiO thermal emission of v=0, J=5-4 were observed together with H2O v2=1 (232.6 GHz) and continuum emission at ALMA Band 6 in October 2017 (Cycle 5). This observation aims to investigate the physical association between the inner and outer parts of the circumstellar envelope (CSE) swept by the stellar winds, which is very crucial to understand the asymmetric outward motions developed during the evolutionary phases from the asymptotic giant branch (AGB) stars to the planetary nebulae (PNe). The strong SiO maser features and thermal emissions are detected together with the continuum emission in ALMA observation, which imply the elongated morphology of the CSE of WX Psc. While the spatial resolution of about 20 mas in ALMA observation cannot clearly resolve the detailed characteristics of the inner part of the CSE, the Korean VLBI Network (KVN) observations show the spatial distributions of the v=1 J=1-0, J=2-1, J=3-2 SiO masers emitted from the inner regions of CSE, which are the complementary to the ALMA results. Therefore, we expect these results reveal how the bipolar features of the 22 GHz H2O maser are connected to the innermost region of CSE through the dust condensation region, which is closely related to the enormous mass ejection of the evolved stars.