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1968년 ~ 2024년까지 1,211 건의 한국천문학회지를 격월간 확인하실 수 있습니다.
- The Korean Astronomical Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-4614 (ISSN : 1225-4614)
1225-4614
- DB구축현황 : 1,211건 (DB Construction : 1,211 Articles)
총 게시글 1,211건
페이지 43/122
421
- Kim, Sang-Chul
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.115-123
- 2006
- 원문 바로보기
We present <TEX>$JHK_S$</TEX> near-infrared CCD photometric study for the Galactic open clusters NGC 1641 and NGC 2394. These clusters have never been studied before, and we provide, for the first time the cluster parameters; reddening, distance, metallicity and age. NGC 1641 is an old open cluster with age <TEX>$1.6{\pm}0.2$</TEX> Gyr, metallicity <TEX>$[Fe/H]=0.0{\pm}0.2$</TEX> dex, distance modulus<TEX>$(m-M)_0=10.4{\pm}0.3\;mag(d=1.2{\pm}02\;kpc)$</TEX>, and reddening <TEX>$E(B-V)=0.10{\pm}0.05$</TEX> mag. The parameters for the other old open cluster NGC 2394 are estimated to be <TEX>$age=1.1{\pm}0.2$</TEX> Gyr, <TEX>$[Fe/H]=0.0{\pm}0.2$</TEX> dex, <TEX>$(m-M)_0=9.1{\pm}0.4\;mag(d=660{\pm}120\;pc)$</TEX>, and <TEX>$E(B-V)=0.05{\pm}0.10$</TEX> mag. The metallicities and distance values for these two old open clusters are consistent with the relation between the metallicities and the Galactocentric distances of other old open clusters. We find the metallicity gradient of 53 old open clusters including NGC 1641 and NGC 2394 to be <TEX>${\Delta}[Fe/H]/{\Delta}R_{gc}=-0.067{\pm}0.009\;dex\;kpc^{-1}$</TEX>.
422
- Kim, Kyoo-Hyun
- Journal of the Korean astronomical society = 천문학회지
- 39, n.3
- pp.57-71
- 2006
- 원문 바로보기
We investigated the structural parameters of a sample of 30 dwarf galaxies(15 dEs and 15 dS0s) in the Virgo Cluster using i-band images from the Sloan Digital Sky Survey Data Release 4. Among 28 galaxies for which surface brightness profiles were derived from ellipse fittings, 23 galaxies had a single component that was adequately described by a generalized <TEX>$S\acute{e}rsic$</TEX> function with a shape parameter ranging from n=0.5 to 2, while 5 galaxies(2 dEs and 3 dS0s) had bulge and disk components that were fitted by a generalized <TEX>$S\acute{e}rsic$</TEX> function and an exponential function, respectively. Since the majority of dwarf galaxies in the present sample had a single component, it seems likely that genuine dS0 galaxies that have disk and bulge components are quite rare in the Virgo Cluster. The similarity in structural parameters of genuine dS0 galaxies in the Virgo Cluster with those of Magellanic-type galaxies implies that the progenitors of dwarf lenticular galaxies in the Virgo Cluster were most likely Magellanic-type galaxies if dS0s are harassed late-type spirals.
423
- Chi Seung-Youp
- Journal of the Korean astronomical society = 천문학회지
- 39, n.1
- pp.9-17
- 2006
- 원문 바로보기
In an attempt to investigate star formation activity and statistical properties of clumps of high Galactic latitude clouds (HLCs), we mapped the Polaris Flare region, PF121.3+25.5, in <TEX>$^{12}CO\;and\;^{13}CO$</TEX> J = 1 - 0 using SRAO 6-m telescope and also observed its 12 <TEX>$^{13}CO$</TEX> peak positions in CS J = 2 - 1 with TRAO 14-m telescope. <TEX>$^{13}CO$</TEX> integrated intensity map shows clearly its clumpy structure and the locations of clumps well agree with <TEX>$^{12}CO$</TEX>morphology. CS line is not detected toward the 12 <TEX>$^{13}CO$</TEX> peak positions, so we can conclude there are no dense <TEX>$(\sim10^4\;cm^{-3})$</TEX> in this region. We decomposed 105 clumps from <TEX>$^{13}CO$</TEX> map using GAUSSCLUMPS algorithm. The mass of clumps ranges from <TEX>$7.8\;M_{\odot}\;to\;7.4{\times}10^{-2}\;M_{\odot}$</TEX> with a total mass of <TEX>$66.4\;M_{\odot}$</TEX> The mass spectrum follows a power law, dN/dM <TEX>${\propto}\;M^{-\alpha}$</TEX> with a power index of <TEX>${\alpha}=1.91{\pm}0.13$</TEX>. The virial masses of clumps are in the range of <TEX>$10{\sim}100M_{LTE}$</TEX> and so these clumps are considered to be gravitationally unbound.
424
- Lee, Sung-Ho
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.151-155
- 2006
- 원문 바로보기
Long slit spectrometers are widely used in optical and infrared bands in astronomy. Absolute flux calibration for extended sources, however, is not straightforward, because a portion of the radiation energy from a flux calibration star is blocked by the narrow slit width. Assuming that the point spread function(PSF) of the star is circularly symmetric, we develop a robust method to extrapolate the detected stellar flux to the unobscured flux using the measured PSF along the slit-length direction. We apply this method to our long slit data and prove that the uncertainty of the absolute flux calibration is less than a few percents.
425
- Lee Min-Young
- Journal of the Korean astronomical society = 천문학회지
- 39, n.1
- pp.1-7
- 2006
- 원문 바로보기
We present the results of a highly sensitive (<TEX>${\sim}10$</TEX> mK rms) survey toward the central parts of 22 barred spiral galaxies in <TEX>$^{12}CO(1-0)$</TEX> line using the NRAO 12m telescope at Kitt Peak. Seven of the target galaxies were detected in CO; NGC 3686 has been detected with CO for the first time. We estimated central CO fluxes of <TEX>$50{\sim}1000\;Jy\;km\;s^{-1}$</TEX> and molecular gas masses of <TEX>$10^7{\sim}10^8\;M_{\odot}$</TEX> for those galaxies.
426
- Kim, Chul-Hee
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.125-128
- 2006
- 원문 바로보기
In order to determine the precise effective temperature and surface gravity of warm stars, all synthetic spectral lines in the wavelength range of <TEX>$4000-5700{\AA}$</TEX> with T=6000-7750 K, and log g=3.5, 4.0, and 4.5 for [M/H]=0.0, <TEX>$V_{rot}$</TEX>=10 km <TEX>$s^{-1}$</TEX>, and <TEX>$V_{tubl}$</TEX>=2 km <TEX>$s^{-1}$</TEX> were calculated using the SYNSPEC package(Hubeny, et al., 1995) and the Kurucz(1995) model. Then, the depth-ratios for all line pairs were investigated and we selected two and six depth-ratios appropriate for the surface gravity and temperature indicators, respectively. We plotted six grids with X- and Y-axes for the depth-ratios of surface gravity and temperature, respectively, for the simultaneous estimation of these two atmospheric parameters. This method was applied to the spectum of <TEX>$\delta$</TEX> Scu for the determination of its temperature and surface gravity simultaneously.
427
- Lee Jae-Woo
- Journal of the Korean astronomical society = 천문학회지
- 39, n.2
- pp.41-50
- 2006
- 원문 바로보기
We present the results of new multi-color CCD photometry for the contact binary XZ Leo, together with reasonable explanations for the period and light variations. Six new times of minimum light have been determined. A period study with all available timings confirms Qian's (2001) finding that the O-C residuals have varied secularly according to <TEX>$dP/dt\;=\;+8.20{\times}10^{-8}\;d\;yr^{-l}$</TEX>. This trend could be interpreted as a conservative mass transfer from the less massive cool secondary to the more massive hot primary in the system with a mass flow rate of about <TEX>$5.37{\times}10^{-8}\;M_{\odot}\;yr^{-l}$</TEX>. By simultaneous analysis of our light curves and the previously published radial-velocity data, a consistent set of light and velocity parameters for XZ Leo is obtained. The small differences between the observed and theoretical light curves are modelled by a blue third light and by a hot spot near the neck of the primary component. Our period study does not support the tertiary light but the hot region which may be formed by gas streams from the cool secondary. The solution indicates that XZ Leo is a deep contact binary with the values of q=0.343, <TEX>$i=78^{\circ}.8$</TEX>, <TEX>${\Delta}(T_1-T_2)=126\;K$</TEX>, and f=33.6 %, differing much from those of Niarchos et al. (1994). Absolute parameters of XZ Leo are determined as follows: <TEX>$M_1=1.84\;M_{\odot},\;M_2=0.63\;M_{\odot},\;R_1=1.75\;R_{\odot},\;R_2=1.10\;R_{\odot},\;L_1=7.19\;L_{\odot},\;and\;L_2=2.66\;L_{\odot}$</TEX>.
428
- Lee Chung-Uk
- Journal of the Korean astronomical society = 천문학회지
- 39, n.1
- pp.25-30
- 2006
- 원문 바로보기
We completed four color light curves of the near-contact binary CN And during three nights from September to December 2004 using the 61-cm reflector and BV RI filters at Sobaeksan Observatory. We determined four new times of minimum light (two timings for primary eclipse, two for secondary). Newly obtained BV RI light curves and the radial velocity curves from Rucinski et a1. (2000) were simultaneously analyzed to derive the system parameters of CN And. We used the semi-detached mode 4 of the 2003-version of the Wilson-Devinney binary model, and interpreted the asymmetry of the light curve by introducing two spots; a cool spot on the primary component and a hot spot on the secondary component. New photometric parameters are not much different from those of Cicek et a1. (2005), and it is considered that the system is in the era of broken contact. From the orbital period study with all available timings including our data, we found a continous period decrease with a rate of <TEX>$P_{obs}=--1.82{\times}10^{-7}\;d\;yr^{-1}$</TEX> that can be explained with two possible mechanisms. We think the most likely cause of the period decrease is a thermal mass transfer from the primary to the secondary component, rather than angular momentum loss due to a magnetic stellar wind.
429
- Kyeong, Jae-Mann
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.89-94
- 2006
- 원문 바로보기
We present JHK-band near-infrared photometry of the star clusters in the dwarf irregular galaxy IC 5152. After excluding possible foreground stars, a number of candidate star clusters are identified in the near-infrared images of IC 5152, which include young populations. Especially, five young star clusters are identified in the(J-H, H-K) two color diagram and the total extinction values toward these clusters are estimated to be <TEX>$A_v=2-6$</TEX> from the comparison with the theoretical values given by the Leitherer et al.(1999)'s theoretical star cluster model.
430
- Chi Seung-Youp
- Journal of the Korean astronomical society = 천문학회지
- 39, n.1
- pp.19-24
- 2006
- 원문 바로보기
We carried out CO survey toward IR-excess clouds using SRAO 6-m telescope in search of molecular <TEX>$H_2$</TEX>. These clouds, which show far-infrared excess over what is expected from HI column density, are considered to be candidates of molecular clouds. In order to find new high Galactic latitude clouds, we made mapping observations for 14 IR-excess clouds selected from Reach et al.(1998) in <TEX>$^{12}CO$</TEX> J = 1 - 0 line, supplementing the similar survey in southern hemisphere (Onishi et al. 2001). <TEX>$^{12}CO$</TEX> emission is detected from three IR-excess clouds among 14 objects. Three newly detected clouds exhibit somewhat clumpy morphology and column densities amount to <TEX>${\sim}10^{21}\;cm^{-2}$</TEX>. One of three clouds, DIR120-28, show discrepancy between IR-excess center and CO emission center. It seems that IR-excess may not be an effective tracer of molecular gas. Instead, optical depth<TEX>$(\tau)$</TEX> excess, i.e., IR-excess corrected for temperature dependence, may be more effective tracer of molecular clouds, since, by combining statistics from both hemispheres, we found that the detection rate is higher for IR-excess clouds with lower dust temperature.