• Journal of Astronomy and Space Sciences
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• 제25권4호
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• pp.329-334
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• 2008

We investigate the spectral energy distributions (SEDs) of Massive Young Stellar Objects (MYSOs) using the various infrared observational data including the Infrared Space Observatory (ISO) data. We model the dust envelopes around the stars using a radiative transfer model for spherically symmetric geometry. Comparing the model results with the observed SEDs of the two MYSOs (AFGL 4176 and AFGL 2591), we derive the relevant dust shell parameters including the dust opacity, the dust density distribution, and dust temperature distribution. We find that the spherical model can produce the SEDs roughly similar to the observations. We expect that the results would be helpful for making more realistic non-spherical dust envelope models for MYSOs.

• 천문학논총
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• 제8권1호
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• pp.243-263
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• 1993

One hundred forty two digital spectra of 110 standard stars with 1 A resolution in ${\lambda}{\lambda}\;3000\;A\;{\sim}4150\;A$ region were analyzed to determine the spectral indices sensitive to the atmospheric parameters. The standard stars cover the temperature in the range of $T_eff$ from ${\sim}4000^{\circ}$ to ${\sim}7000^{\circ}\;K$ and the surface gravity in the range of log g from 0 to 5 and the metal abundance [Fe/H] from -2.7 to 0.4. We have derived physical parameters, theta(=T/5040), log g, and [Fe/H] for the standard stars using indices, P(38/93), Fe I(A), Fe I(B), SrII, and $H{\delta}$, with overall accuracies of 0.067, 0.617, and 0.466, respectively. However for some region of spectral type and metallicity, those can be obtained with better accuracies. Those indices are found to be useful especially for stellar gravity determination.

• 천문학회보
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• 제36권2호
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• pp.146.2-146.2
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• 2011

In this study, we have derived the abundances of several elements ? Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni - for the six F G K type stars in IC 2391 and the seven stars in NGC 6475. The spectra of those stars are taken from UVES POP archive data, of which resolution is 80,000. To derive the abundances of those elements, TAME (Tools for Automatic Measurement of Equivalent-widths), Kurucz stellar atmospheric model, and MOOG code are used. The stellar parameters (effective temperature, log g, metallicity, microturbulent velocity) are determined from the iron lines. The results provide the abundance differences of chemical elements between two open clusters, IC 2391 (a member of Gould Belt) and NGC 6475 (non-member of it), which would lead to better understanding about Gould Belt.

• 천문학회보
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• 제39권1호
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• pp.58.2-58.2
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• 2014

The Arches cluster is a young (2-4 Myr), compact (~1 pc), and massive (${\sim}2{\times}10^4M_{\odot}$) star cluster located ~30 pc away from the Galactic center (GC) in projection. Being exposed to the extreme environment of the GC such as elevated temperature and turbulent velocities in the molecular clouds, strong magnetic fields, and larger tidal forces, the Arches cluster is an excellent target for understanding the effects of star-forming environment on the initial mass function (IMF) of the star cluster. However, resolving stars fainter than ~1 $M_{\odot}$ in the Arches cluster partially will have to wait until an extremely large telescope with adaptive optics in the infrared is available. Here we devise a new method to estimate the shape of the low-end mass function where the individual stars are not resolved, and apply it to the Arches cluster. This method involves histograms of pixel intensities in the observed images. We find that the initial mass function of the Arches cluster should not be too different from that for the Galactic disk such as the Kroupa IMF.

• Journal of Astronomy and Space Sciences
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• 제17권1호
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• pp.39-44
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• 2000

lUE 저분산 자로플 가지고 44i Boo, W UMa, AW UMa및 VW Cep에서 나오는 자외선 방출선들의 특징을 조사하였다 단파장영역과 장파장영역에서의 방출선 선세기를 구하여, 이를 자$\boxUl$선 등급으로 변환하여 광도곡선을 얻었다 단파장 영ff에서 나오는 방출선인 C I, C II, C IV, SiIV, N V에 대한 선세기를 구한 결파, C IV가 모든 별에서 가장 센 방출을 보였으며. Si IV와 NV는 비교적 작은 양의 선세기를 나타내었다. 4개의 W UMa 별 쿵에근 44i Boo가 가장 높은 선세기를 보였으며, 단과장 영역에서는 위상 0.2와 0 8부근에서 자외선 팡도가 maximup을 보이는 변광을 확인하였다 또한, 전이영역에서 나오는 C IV, Si IV, N V 방출선을 합하여 이를 극소기의 태양값과 비교하여 태양보다 최대40배의 높은 활동성을 가지고 있음을 알았다. 짧은 주기를 갖는 별,즉 44i Boo, W UMa, AW UMa순으로 전이영역의 헐동성이 감소하는 것으로 나타났다. 장 파장 영역에서는 AW UMa와 VW Cep의 Mg ll 방출선을 조사하였는데, 단파장의 방출선 보다 뚜렷한 주기적 변광을 보였으며, 이를 이응하여 두 별의 유효온도를 추정하였다..

• 천문학회보
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• 제36권2호
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• pp.151.2-151.2
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• 2011

IGRINS (Immersion GRating INfrared Spectrometer) will provide the spectra with high-resolution and an instantaneous spectral coverage of H and K band in NIR region. Therefore, it is expected that the wide coverage of wavelength would make a production of an extensive NIR high-resolution spectra of standard stars as a prior program of IGRINS. As a counter part of these NIR spectra, we have planned to obtain the high-resolution spectra of those standard stars in optical band. These optical high-resolution spectra would give us an opportunity to produce the library of high-resolution stellar spectra covering from optical to NIR band, and to confirm the method to determine the stellar parameters and chemical abundances from the NIR high-resolution spectra. Before using the NIR high-resolution spectra, we have tested the method to determine the stellar parameters by comparing between the observed spectra and the synthetic spectra in optical band. In order to make the synthetic spectra, we have used the Kurucz ATLAS9 model grids and the SYNTH code described by Fiorella Castelli (http://wwwuser.oat.ts.astro.it/castelli/). For the cross-check against the parameters that would be derived from the NIR spectra, the stellar parameters such as effective temperature and surface gravity were determined using the optical spectra of the solar-like stars, as preliminary results.

• 천문학회보
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• 제38권1호
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• pp.59.2-59.2
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• 2013

Wilson and Bappu found a tight correlation between the stellar absolute visual magnitude (MV) and the width of the Ca II K emission line for late-type stars in 1957. Here, we revisit the Wilson-Bappu relationship (hereafter, WBR) to claim that WBR can be an excellent indicator of stellar surface gravity of late-type stars as well as a distance indicator. We have measured the width (W) of the Ca II K emission line in high resolution spectra of 125 late-type stars, which were obtained with Bohyunsan Optical Echelle Spectrograph (BOES) and adopted from the UVES archive. Based on our measurement of the emission line width (W), we have obtained a WBR of $M_V=33.76-18.00{\log}W$. In order to extend the WBR to be a surface gravity indicator, the stellar atmospheric parameters such as effective temperature ($T_{eff}$), surface gravity (logg), metallicity ([Fe/H]), and micro-turbulence (${\xi}_{tur}$) have been derived from the self-consistent detailed analysis using the Kurucz stellar atmospheric model and the abundance analysis code, MOOG. Using these stellar parameters and logW, we found that ${\log}g=-5.85\;{\log}W+9.97\;{\log}T_{eff}-23.48$ for late-type stars.

• Journal of Astronomy and Space Sciences
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• 제11권1호
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• pp.31-40
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• 1994

The IUE low dispersion spectra of AZ Cas have been analyzed for line identifications and energy distribution in ultraviolet region. Highly ionized atoms, SiIV and CIV are identified. We could infer a temperature range of the B star between 15,000K and 20,000K. The energy density distribution shows a hump between IUE short wavelength and long wavelength regions. Photometric and spectroscopic elements were revised based on the Florkowisk photeelectric observations and collected radial velocities. The temperature of both stars were reduced as 16,000K and 3,800K. The radii of both stars are $10 R_{\odot}\;and\;320R_{\odot}$. The eccentricity and longitude of periastron are 0.61 and $10.5^{\circ}$, respectively.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 1997년도 한국우주과학회보 제6권2호
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• pp.11.1-11
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• 1997

No Abstract.See Full-text

• 천문학회지
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• 제38권2호
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• pp.283-287
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• 2005

The slow evolution of global magnetic fields and other dynamical processes in atmospheres of CP magnetic stars lead to the development of induced electric currents in all conductive atmospheric layers. The Lorentz force, which results from the interaction between a magnetic field and the induced currents, may modify the atmospheric structure and provide insight into the formation and evolution of stellar magnetic fields. This modification of the pressure-temperature structure influences the formation of absorption spectral features producing characteristic rotational variability of some spectral lines, especially the Balmer lines (Valyavin et al., 2004 and references therein). In order to study these theoretical predictions we began systematic spectroscopic survey of Balmer line variability in spectra of brightest CP magnetic stars. Here we present the first results of the program. A0p star $\Theta$ Aur revealed significant variability of the Balmer profiles during the star's rotation. Character of this variablity corresponds to that classified by Kroll (1989) as a result of an impact of significant Lorentz force. From the obtained data we estimate that amplitudes of the variation at H$\alpha$, H$\beta$, H$\gamma$ and H$\delta$ profiles reach up to $2.4\%$during full rotation cycle of the star. Using computation of our model atmospheres (Valyavin et al., 2004) we interpret these data within the framework of the simplest model of the evolution of global magnetic fields in chemically peculiar stars. Assuming that the field is represented by a dipole, we estimate the characteristic e.m.f. induced by the field decay electric current (and the Lorentz force as the result) on the order of $E {\~} 10^{-11}$ cgs units, which may indicate very fast (< < $10^{10}$ years) evolution rate of the field. This result strongly contradicts the theoretical point of view that global stellar magnetic fields of CP stars are fossil and their the characteristic decay time of about $10^{10}$ yr. Alternatively, we briefly discuss concurring effects (like the ambipolar diffusion) which may also lead to significant atmospheric currents producing the observable Lorentz force.