• Journal of the Korean earth science society
• /
• v.38 no.3
• /
• pp.209-221
• /
• 2017

We investigate the star formation rate, stellar mass, and gas-phase metallicity of local starburst galaxies with different star formation time scales based on their optical spectra. The observation is made using the longslit spectrograph attached to the 4K CCD on the Bohyunsan Optical Astronomy Observatory 1.8m telescope, targeting 21 Wolf-Rayet galaxies as young starbursts and 13 UV excess galaxies as slightly older starbursts. A Baldwin-Phillips-Terlevich diagram analysis shows that 50% of the observed targets are pure star-forming galaxies while only 15% are classified as Active Galactic Nuclei. Fraction of galaxies that reside in composite region is higher in UV excess galaxies than in Wolf-Rayet galaxies, suggesting that the AGN development requires extra time after the onset of the star formation. Most of the observed starburst galaxies have stellar masses of $10^{9-11}M_{\odot}$ and stellar formation rates of $0.01-100M_{\odot}yr^{-1}$, and their star formation rates are consistent with that of the SDSS star forming main sequence galaxies of similar stellar mass. There is no significant difference between Wolf-Rayet galaxies and UV excess galaxies in terms of the stellar mass and star formation rate. We also see a mass-metallicity relation for local starbursts with slightly lower metallicity for a given stellar mass, which implies the existence of a strong feedback activity due to the star formation in these galaxies.

• The Bulletin of The Korean Astronomical Society
• /
• v.42 no.2
• /
• pp.38.2-38.2
• /
• 2017

별의 생성단계나 황혼기에는 성간운에 둘러싸여 있어 그 중심부에 별이 쌍을 이루고 있는지를 관측하기가 쉽지 않다. 항성계 통계 조사는 주로 별의 진화단계 상 장년기에 해당하는 주계열에서 이루어졌는데, 그 결과로 전체 항성계의 절반은 쌍성계 혹은 다성계임이 알려져있다. 한편, 대표적인 황혼기 현상인 행성상성운은 늙은 별 주변물질이 마지막 별빛을 받아 밝게 빛나는 것으로, 같은 종류의 천체 현상이라 믿기 어려울만큼 복잡다양한 모습들을 띄고 있다. 이와 같은 다양한 성운의 형태는 그 중심부 별이 하나 뿐일 경우로는 설명하기가 어렵다. 따라서 늙은 별 연구 커뮤니티는 최근 수 십년간 행성상성운을 바라보는 주 관점을 쌍성계로 돌리고 있다. 특히, 많은 행성상성운의 외각부분에 반복되는 고리 모양 구조(3차원으로는 나선구각구조)가 발견이 되었는데, 이를 분석하면 행성상성운에 이르기까지의 시기에 중심부 쌍성이 어떤 궤도운동을 해왔는지를 알아낼 수 있을 것으로 예상하고, 이론 및 관측으로 그 실효성을 따져보고 있다. 늙은별의 동반성을 직접 관측하고 그 궤도요소를 알아내는 것이 어려운 이유를 살펴보고, 나선구각구조를 이용함으로써 밝혀낼 수 있는 동반성의 범주를 알아본다.

• Journal of the Korean earth science society
• /
• v.32 no.4
• /
• pp.402-410
• /
• 2011

We present results of CO observations toward an infrared (IR) source, IRAS 07280-1829, and its possibly related molecular clouds. The physical parameters of this IR source such as its infrared slope (${\alpha}$=16) of the Spectral Energy Distribution and bolometric temperature (145 K) indicate that it is an embedded protostar. Its luminosity is ${\sim}2.9{\times}10^4L_{\odot}$, typical of a massive star. The CO profile toward IRAS 07280-1829 has broad wing components, implying a possible existence of CO outflow. The excitation temperature and mass of a molecular cloud (Cloud A) which is thought to harbor the IR source are estimated to be 9~22 K and ~180 $M_{\odot}$, respectively, indicating the Cloud A is a typical infrared-dark cloud. Its LTE mass is found to be much smaller than its virial mass by more than a factor of 10 which is inconsistent with the fact that a protostar recently formed exists in the Cloud A. This may suggest that the environment of the cloud where the IR source is forming is dominant of turbulence and/or magnetic filed, making its virial mass estimated unusually high.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.10 no.2
• /
• pp.159-167
• /
• 2022

The present study assessed the micro structure and durability characteristics of ternary blended cement with different types of alkali activators. Ground granulated blast furnace slag(GGBS) and ferronickel slag(FNS) was replaced until 50 % of the weight of cement. In addition, potassuim hydroxide and sodium hydroxide were used for comparing the properties of different type of alkali activator. Ternary blended cement with alkali activators showed higher peak portlandite peak than that of OPC(Ordinary Portlande Cement) and non activated ternary blended cement. Also, there was no new hydration products in ternary blended cement or/and alkali activators. Based on the mercury intrustion porosimetry(MIP) test result, ternary blended cement increased macro pore while alkali activated ternary blended cement modified pore structure and increased microp pore as compared to OPC as control. Combination with alkali activators is desirable to enhance the compressive strength and freeze thaw resistance.