Go to the main menu
Skip to content
Go to bottom
REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
> Journal Vol & Issue
Journal of The Korean Astronomical Society
Journal Basic Information
Journal DOI :
The Korean Astronomical Society
Editor in Chief :
Volume & Issues
Volume 37, Issue 5 - Dec 2004
Volume 37, Issue 4 - Dec 2004
Volume 37, Issue 3 - Sep 2004
Volume 37, Issue 2 - Jun 2004
Volume 37, Issue 1 - Mar 2004
Selecting the target year
) ] OBSERVATIONS TOWARD THE SGR B2 REGION
MINH Y. C. ; IRVINE W. M. ; KIM S.-J. ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 131~135
DOI : 10.5303/JKAS.2004.37.4.131
line emission is observed to be strongly localized toward Sgr B2(M), and emissions from other positions in the more extended SgrB2 region are almost negligible.
is thought to form effectively by the passage of the C-type shocks but to be quickly transformed to
or other sulfur species (Pineau des Forets et al. 1993). Such a shock may have enhanced the
abundance in Sgr B2(M), where massive star formation is taking place. But the negligible emission of
from other observed positions may indicate that these positions have not been affected by shocks enough to produce
, or if they have experienced shocks,
may have transformed already to other sulfur-containing species. The
line was also observed to be detectable only toward the (M) position. The line intensity ratios of these two molecules appear to be very similar at Sgr B2(M) and IRAS 16239-2422, where the latter is a region of low-mass star formation. This may suggest that the shock environment in these two star-forming regions is similar and that the shock chemistry also proceeds in a similar fashion in these two different regions, if we accept shock formation of these two species.
FRACTAL DIMENSIONS OF INTERSTELLAR MEDIUM: I. THE MOLECULAR CLOUDS IN THE ANTIGALACTIC CENTER
LEE YOUNGUNG ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 137~141
DOI : 10.5303/JKAS.2004.37.4.137
We have estimated the fractal dimension of the molecular clouds in the Antigalactic Center based on the
(J = 1- 0) and
(J = 1- 0) database obtained using the 14m telescope at Taeduk Radio Astronomy Observatory. Using a developed code within IRAF, we were able to identify slice-clouds, and determined the dispersions of two spatial coordinates as well as perimeters and areas. The fractal dimension of the target region was estimated to be D = 1.34 for low resolution
(J = 1 - 0) database, and D = 1.4 for higher resolution
(J = 1 - 0) and
(J = 1 - 0) database, where
. The sampling rate (spatial resolution) of observed data must be an important parameter when estimating fractal dimension. Our database with higher resolution of 1 arcminute, which is corresponding to 0.2 pc at a distance of 1.1 kpc, gives us the same estimate of fractal dimension to that of local dark clouds. Fractal dimension is apparently invariant when varying the threshold temperatures applied to cloud identification. According to the dispersion pattern of longitudes and latitudes of identified slice-clouds, there is no preference of elongation direction.
PHOTOMETRIC PROPERTIES OF FOUR NEW VARIABLE STARS IN THE VICINITY OF BR CAM
KIM S.-L. ; LEE C.-D. ; LEE J. W. ; LEE J. A. ; KANG Y.B. ; KOO J.-R. ; VAUCLAIR G. ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 143~149
DOI : 10.5303/JKAS.2004.37.4.143
We present photometric results for four new variable stars discovered in the vicinity of the ZZ Ceti-type pulsating white dwarf BR Cam. Observations were performed on 5 nights in November 2003 using the 1.8m telescope at Bohyunsan Optical Astronomy Observatory with no filter, on 3 nights in December 2003 using the 0.61m telescope at Sobaeksan Optical Astronomy Observatory with V, I filters, and on 3 nights in October 2004 using the 1.0m telescope at Mt. Lemmon Optical Astronomy Observatory with V, I filters. We estimated their periods from the phase-match technique for one eclipsing binary and the multiple frequency analysis for three pulsating stars. By considering the light curve shape, period and amplitude difference between two passbands, we classified the objects by their variability types as follows: V1 (USNO-A2.0 1425-05691757) is a W UMa-type eclipsing binary with an orbital period of
; V2 (USNO-A2.0 1425-05703335) is a multi-periodic
Set-type pulsating star with a dominant period of
; V3 (USNO-A2.0 1425-05699659) is also a
Set-type pulsating star with a period of
; and V 4 (USNO-A2.0 1425-05707705) is a RR Lyr-type pulsating star with a period of
RELATIONSHIPS OF THE SOLAR WIND PARAMETERS WITH THE MAGNETIC STORM MAGNITUDE AND THEIR ASSOCIATION WITH THE INTERPLANETARY SHOCK
OH SU YEON ; YI YU ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 151~157
DOI : 10.5303/JKAS.2004.37.4.151
It is investigated quantitative relations between the magnetic storm magnitude and the solar wind parameters such as the Interplanetary Magnetic Field (hereinafter, IMF) magnitude (B), the southward component of IMF (Bz), and the dynamic pressure during the main phase of the magnetic storm with focus on the role of the interplanetary shock (hereinafter, IPS) in order to build the space weather fore-casting model in the future capable to predict the occurrence of the magnetic storm and its magnitude quantitatively. Total 113 moderate and intense magnetic storms and 189 forward IPSs are selected for four years from 1998 to 2001. The results agree with the general consensus that solar wind parameter, especially, Bz component in the shocked gas region plays the most important role in generating storms (Tsurutani and Gonzales, 1997). However, we found that the correlations between the solar wind parameters and the magnetic storm magnitude are higher in case the storm happens after the IPS passing than in case the storm occurs without any IPS influence. The correlation coefficients of B and
are specially over 0.8 while the magnetic storms are driven by IPSs. Even though recently a Dst prediction model based on the real time solar wind data (Temerin and Li, 2002) is made, our correlation test results would be supplementary in estimating the prediction error of such kind of model and in improving the model by using the different fitting parameters in cases associated with IPS or not associated with IPS rather than single fitting parameter in the current model.
RETRIEVAL OF LOCAL INTERPLANETARY DUST EMISSIVITY BY ASTRO-F
HONG S. S. ; KWON S. M. ; PYO J. ; UENO M. ; ISHIGURO M. ; USUI F. ; WEINBERG J. L. ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 159~169
DOI : 10.5303/JKAS.2004.37.4.159
This is a proposal to probe local part of the interplanetary dust (IPD) cloud complex and retrieve mean volume emissivity of the local IPDs at mid-infrared wavelengths. This will be done by monitoring, with Infrared Camera (IRC) aboard the ASTRO-F, the annual modulation of the zodiacal emission. In pointing mode of the ASTRO-F mission the spacecraft can make attitude maneuvering over approximately
range centered at solar elongation
in the ecliptic plane. The attitude maneuvering combined with high sensitivity of the IRC will provide us with a unique opportunity observationally to take derivatives of the zodiacal emission brightness with respect to the solar elongation. From the resulting differential of the brightness over the
range, one can directly determine the mean volume emissivity of the local IPDs with a sufficient accuracy to de-modulate the annual emissivity variations due to the Earth's elliptical motion and the dis-alignment of the maximum IPD density plane with respect to the ecliptic. The non-zero eccentricity (
= 0.0167) of the Earth's orbit combined with the sensitive temperature dependence of the Planck function would bring modulations of amplitude at least
to the zodiacal emission brightness at mid-infrared wavelengths, with which one may determine the IPD temperature T(r) and mean number density n(r) as functions of heliocentric distance r. This will in turn fix the power-law exponent
in the relation
for the dust temperature and v in
for the density. We discuss how one may de-couple the notorious degeneracy of cross-section, density, reference temperature
STUDY OF FLARE-ASSOCIATED X-RAY PLASMA EJECTIONS : II. MORPHOLOGICAL CLASSIFICATION
KIM YEON-HAN ; MOON Y.-J. ; CHO K.-S. ; BONG SU-CHAN ; PARK Y.-D. ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 171~177
DOI : 10.5303/JKAS.2004.37.4.171
X-ray plasma ejections often occurred around the impulsive phases of solar flares and have been well observed by the SXT aboard Yohkoh. Though the X-ray plasma ejections show various morphological shapes, there has been no attempt at classifying the morphological groups for a large sample of the X-ray plasma ejections. In this study, we have classified 137 X-ray plasma ejections according to their shape for the first time. Our classification criteria are as follows: (1) a loop type shows ejecting plasma with the shape of loops, (2) a spray type has a continuous stream of plasma without showing any typical shape, (3) a jet type shows collimated motions of plasma, (4) a confined ejection shows limited motions of plasma near a flaring site. As a result, we classified the flare-associated X-ray plasma ejections into five groups as follows: loop-type (60 events), spray-type (40 events), jet-type (11 events), confined ejection (18 events), and others (8 events). As an illustration, we presented time sequence images of several typical events to discuss their morphological characteristics, speed, CME association, and magnetic field configuration. We found that the jet-type events tend to have higher speeds and better association with CMEs than those of the loop-type events. It is also found that the CME association (11/11) of the jet-type events is much higher than that (5/18) of the confined ejections. These facts imply that the physical characteristics of the X-ray plasma ejections are closely associated with magnetic field configurations near the reconnection regions.
DEVELOPMENT OF WIDE-FIELD IMAGING CAMERA FOR ZODIACAL LIGHT OBSERVATION
KWON S. M. ; HONG S. S. ; SHIN K. J. ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 179~184
DOI : 10.5303/JKAS.2004.37.4.179
We have developed a wide-field imaging camera system, called WICZO, to monitor light of the night sky over extended period. Such monitoring is necessary for studying the morphology of interplanetary dust cloud and also the time and spatial variations of airglow emission. The system consists of an electric cooler a CCD camera with
quantum efficiency at 500nm, and a fish-eye lens with
field of view. Wide field imaging is highly desired in light of the night sky observations in general, because the zodiacal light and the airglow emission extend over the entire sky. This paper illustrates the design of WICZO, reports the result of its laboratory performance test, and presents the first night sky image, which was taken, under collaboration with Byulmaro Observatory, on top of Mt. Bongrae at Yongweol in January, 2004.
CHARACTERISTICS AND PERFORMANCE OF A FAST CCD CAMERA: DALSTA IM30P
SEO YOUNG-MIN ; PARK KI-WOONG ; CHAE JONGCRUL ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 185~191
DOI : 10.5303/JKAS.2004.37.4.185
We have been developing a solar observing system based on a fast CCD camera 1M30P made by the DALSA company. Here we examine and present the characteristics and performance of the camera. For this we have analyzed a number of images of a flat wall illuminated by a constant light source. As a result we found that in the default operating mode 1) the mean bias level is 49 ADU/pix, 2) the mean dark current is about 8 ADU /s/pix, 3) the readout noise is 1.3 ADU, and 4) the gain is about 42 electrons/ ADU. The CCD detector is found to have a linearity with a deviation smaller than
, and a uniform sensitivity better than
. These parameters will be used as basic inputs in the analysis of data to be taken by the camera.
FAR-INFRARED [C II] EMISSION FROM THE CENTRAL REGIONS OF SPIRAL GALAXIES
MOCHIZUKI KENJI ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 193~197
DOI : 10.5303/JKAS.2004.37.4.193
Anomalies in the far-infrared [C II] 158
line emission observed in the central one-kiloparsec regions of spiral galaxies are reviewed. Low far-infrared intensity ratios of the [C II] line to the continuum were observed in the center of the Milky Way, because the heating ratio of the gas to the dust is reduced by the soft interstellar radiation field due to late-type stars in the Galactic bulge. In contrast, such low line-to-continuum ratios were not obtained in the center of the nearby spiral M31, in spite of its bright bulge. A comparison with numerical simulations showed that a typical column density of the neutral interstellar medium between illuminating sources at
in the region; the medium is translucent for photons sufficiently energetic to heat the grains but not sufficiently energetic to heat the gas. This interpretation is consistent with the combination of the extremely high [C Il]/CO J = 1-0 line intensity ratios and the low recent star-forming activity in the region; the neutral interstellar medium is not sufficiently opaque to protect the species even against the moderately intense incident UV radiation. The above results were unexpected from classical views of the [C II] emission, which was generally considered to trace intense interstellar UV radiation enhanced by active star formation.
ON THE GALACTIC SPIRAL PATTERNS: STELLAR AND GASEOUS
MARTOS MARCO ; YANEZ MIGUEL ; HERNANDEZ XAVIER ; MORENO EDMUNDO ; PICHARDO BARBARA ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 199~203
DOI : 10.5303/JKAS.2004.37.4.199
The gas response to a proposed spiral stellar pattern for our Galaxy is presented here as calculated via 2D hydrodynamic calculations utilizing the ZEUS code in the disk plane. The locus is that found by Drimmel (2000) from emission profiles in the K band and at 240
. The self-consistency of the stellar spiral pattern was studied in previous work (see Martos et al. 2004). It is a sensitive function of the pattern rotation speed,
p, among other parameters which include the mass in the spiral and its pitch angle. Here we further discuss the complex gaseous response found there for plausible values of
p in our Galaxy, and argue that its value must be close to
from the strong self-consistency criterion and other recent, independent studies which depend on such parameter. However, other values of
p that have been used in the literature are explored to study the gas response to the stellar (K band) 2-armed pattern. For our best fit values, the gaseous response to the 2-armed pattern displayed in the K band is a four-armed pattern with complex features in the interarm regions. This response resembles the optical arms observed in the Milky Way and other galaxies with the smooth underlying two-armed pattern of the old stellar disk populations in our interpretation. The complex gaseous response appears to be related to resonances in stellar orbits. Among them, the 4:1 resonance is paramount for the axisymmetric Galactic model employed, and the set of parameters explored. In the regime seemingly proper to our Galaxy, the spiral forcing appears to be marginally strong in the sense that the 4:1 resonance terminates the stellar pattern, despite its relatively low amplitude. In current work underway, the response for low values of
p tends to remove most of the rich structure found for the optimal self-consistent model and the gaseous pattern is ring-like. For higher values than the optimal, more features and a multi-arm structure appears.
ARE GALACTIC WARPS INDUCED BY INTERGALACTIC FLOWS?
SANCHEZ-SALCEDO F. J. ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 205~210
DOI : 10.5303/JKAS.2004.37.4.205
The interaction of disk galaxies with intergalactic winds has been invoked as a possible mechanism of the generation of galactic warps. Here we discuss conditions under which intergalactic flows can be relevant for warping field galaxies. Constraints include the heating of the outer disk, the level of asymmetry in the vertical distribution of the volume gas density, the angular frequency of the warp, the symmetry of galactic warps amplitude between the approaching and receding sides of the galaxy, and the speed of the intergalactic flow whether subsonic or supersonic. These constraints are discussed in this paper in reference to the proposal of Lopez-Corredoira et al. that warps can be a natural consequence of accretion flows onto the disk.
INTERSTELLAR ENVIRONMENTS IN THE LARGEMAGELLANIC CLOUD
KIM SUNGEUN ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 211~216
DOI : 10.5303/JKAS.2004.37.4.211
We present the results of an H I aperture synthesis mosaic of the Large Magellanic Cloud (LMC), made by combining data from 1344 separate pointing centers using the Australia Telescope Compact' Array (ATCA) and the Parkes multibeam receiver. The resolution of the mosaiced images is 50" (<15 pc, using a distance to the LMC of 55kpc). This mosaic, with a spatial resolution .15 times higher than that which had been previously obtained, emphasises the turbulent and fractal structure of the ISM on the small scale, resulting from the dynamical feedback of the star formation processes with the ISM. We also have done a widefield panoramic survey of H
emission from the Magellanic Clouds with an imager mounted on the 16-inch telescope at Siding Spring Observatory. This survey produced H
images which are equal to the ATCA survey in area coverage and resolution. This survey allows us to produce a continuum-subtracted image of the entire LMC. In contrast with its appearance in the H
image, the LMC is remarkably symmetric in H I on the largest scales, with the bulk of the H I residing in a disk of diameter 8.
(7.3 kpc) and a spiral structure is clearly seen. The structure of the neutral atomic ISM in the LMC is dominated by H I filaments combined with numerous shells and holes.
SUPERBUBBLES AS SPACE BAROMETERS
GARCIA-SEGURA G. ; OEY M. S. ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 217~222
DOI : 10.5303/JKAS.2004.37.4.217
High ambient interstellar pressure is suggested as a possible factor to explain the ubiquitous ob-served growth-rate discrepancy for supernova-driven super bubbles and stellar wind bubbles. Pressures of P / k
K are plausible for regions with high star formation rates, and these values are intermediate between the estimated Galactic mid-plane pressure and those observed in starburst galaxies. High-pressure components also are commonly seen in Galactic ISM localizations. We demonstrate the sensitivity of shell growth to the ambient pressure, and suggest that super bubbles ultimately might serve as ISM barometers.
THE ENVIRONMENT OF TYCHO: POSSIBLE INTERACTION WITH A MOLECULAR CLOUD
LEE J.-J. ; KOO B.-C. ; TATEMATSU K. ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 223~224
DOI : 10.5303/JKAS.2004.37.4.223
The Tycho supernova remnant (SNR), as one of the few historical SNRs, has been widely studied in various wavebands and previous observations have shown evidence that Tycho is interacting with a dense ambient medium toward the northeast direction, In this paper, we report our high-resolution (16')
observation of the remnant using the Nobeyama 45m radio telescope. The Nobeyama data shows that a large molecular cloud surrounds the SNR along the northeastern boundary. We suggest that the Tycho SNR and the molecular cloud are both located in the Perseus arm and that the dense medium interacting with the SNR is possibly the molecular cloud. We also discuss the possible connection between the molecular cloud and the Balmer-dominated optical filaments, and suggest that the preshock gas may be accelerated within the cosmic ray and/or fast neutral precursor.
NUMERICAL STUDIES OF COSMIC RAY ACCELERATION AT COSMIC SHOCKS
KANG HYESUNG ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 225~232
DOI : 10.5303/JKAS.2004.37.4.225
Shocks are ubiquitous in astrophysical environments and cosmic-rays (CRs) are known to be accelerated at collisionless shocks via diffusive shock acceleration. It is believed that the CR pressure is important in the evolution of the interstellar medium of our galaxy and most of galactic CRs with energies up to
eV are accelerated by supernova remnant shocks. In this contribution we have studied the CR acceleration at shocks through numerical simulation of 1D, quasi-parallel shocks for a wide range of shock Mach numbers and shock speeds. We show that CR modified shocks evolve to time-asymptotic states by the time injected particles are accelerated to moderately relativistic energies, and that two shocks with the same Mach number, but with different shock speeds, evolve qualitatively similarly when the results are presented in terms of a characteristic diffusion length and diffusion time. We find that
of the particles passed through the shock are accelerated to form the CR population, and the injection rate is higher for shocks with higher Mach number. The time asymptotic value for the CR acceleration efficiency is controlled mainly by shock Mach number, and high Mach number shocks all evolve towards efficiencies
, regardless of the injection rate and upstream CR pressure. We conclude that the injection rates in strong quasi-parallel shocks are sufficient to lead to significant nonlinear modifications to the shock structures, implying the importance of the CR acceleration at astrophysical shocks.
INTERACTION OF HIGH VELOCITY CLOUDS WITH MAGNETIZED DISKS: THREE-DIMENSIONAL NUMERICAL SIMULATIONS
SANTILLAN ALFREDO ; FRANCO JOSE ; KIM JONGSOO ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 233~235
DOI : 10.5303/JKAS.2004.37.4.233
High-velocity clouds are flows of neutral hydrogen, located at high galactic latitudes, with large velocities (
) that do not match a simple model of circular rotation for our Galaxy. Numerical simulations have been performed for the last 20 years to study the details of their evolution, and their possible interaction with the Galactic disk. Here we present a brief review of the models that have been already published, and describe newly performed three-dimensional magnetohydrodynamic simulations.
THE VELOCITY FIELD OF SUPERNOVA-DRIVEN TURBULENCE IN THE INTERSTELLAR MEDIUM
KIM JONGSOO ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 237~241
DOI : 10.5303/JKAS.2004.37.4.237
We perform numerical experiments on supernova-driven turbulent flows in order to see whether or not supernovae playa major role in driving turbulence in the interstellar medium. In a
computational box, we set up, as initial conditions, uniformly magnetized gas distributions with different pairs of hydrogen number densities and magnetic field strengths, which cover the observed values in the Galactic midplane. We then explode supernovae at randomly chosen positions at a Galactic explosion rate and follow up the evolution of the supernova-driven turbulent flows by integrating numerically the ideal MHD equations with cooling and heating terms. From the numerical experiments we find that the density-weighted velocity dispersions of the flows are in the range of 5-10 km
, which are consistent with the observed velocity dispersions of cold and warm neutral media. Additionally, we find that strong compressible flows driven by supernova explosions quickly change into solenoidal flows.
FORMATION OF INTERMEDIATE-SCALE STRUCTURES IN SPIRAL GALAXIES
KIM WOONG-TAE ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 243~248
DOI : 10.5303/JKAS.2004.37.4.243
Disk galaxies abound with intermediate-scale structures such as OB star complexes, giant clouds, and dust spurs in a close geometrical association with spiral arms. Various mechanisms have been proposed as candidates for their origin, but a comprehensive theory should encompass fundamental physical agents such as self-gravity, magnetic fields, galactic differential rotation, and spiral arms, all of which are known to exist in disk galaxies. Recent numerical simulations incorporating all these physical processes show that magneto-Jeans instability (MJI), in which magnetic tension resists the stabilizing Coriolis force of galaxy rotation, is much more powerful than swing-amplification or the Parker instability in forming self-gravitating intermediate-scale structures. The MJI occurring in shearing and expanding flows off spiral arms rapidly forms structures elongated along the direction perpendicular to the arms, remarkably similar to dust spurs seen in HST images of spiral galaxies. In highly nonlinear stages, these spurs fragment to form bound clumps, possibly evolving into bright arm and interarm H II regions, suggesting that all these intermediate-scale structures in spiral galaxies probably share a common dynamical origin.
PARKER-JEANS INSTABILITY IN THE GALACTIC GASEOUS DISK. I. LINEAR STABILITY ANALYSIS AND TWO-DIMENSIONAL MHD SIMULATIONS
LEE S. M. ; KIM JONGSOO ; FRANCO J. ; HONG S. S. ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 249~255
DOI : 10.5303/JKAS.2004.37.4.249
Here we present a linear stability analysis and an MHD 2D model for the Parker-Jeans instability in the Galactic gaseous disk. The magnetic field is assumed parallel to a Galactic spiral arm, and the gaseous disk is modelled as a multi-component, magnetized, and isothermal gas layer. The model employs the observed vertical stratifications for the gas density and the gravitational acceleration in the Solar neighborhood, and the self-gravity of the gas is also included. By solving Poisson's equation for the gas density stratification, we determine the vertical acceleration due to self-gravity as a function of z. Subtracting it from the observed gravitational acceleration, we separate the total acceleration into self and external gravities. The linear stability analysis provides the corresponding dispersion relations. The time and length scales of the fastest growing mode of the Parker-Jeans instability are about 40 Myr and 3.3 kpc, respectively. In order to confirm the linear stability analysis, we have performed two-dimensional MHD simulations. These show that the Parker-Jeans instability under the self and external gravities evolves into a quasi-equilibrium state, creating condensations on the northern and southern sides of the plane, in an alternate manner.
INWARD MOTIONS IN STARLESS CORES TRACED WITH CS (3-2) and (2-1) LINES
LEE CHANG WON ; MYERS PHILIP C. ; PLUME RENE ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 257~259
DOI : 10.5303/JKAS.2004.37.4.257
We compare the results of the surveys of starless cores performed with CS (2-1) and (3-2) lines to study inward motions in the cores. The velocity shifts of the CS(3-2) and (2-1) lines with respect to
are found to correlate well with each other and to have similar number distributions, implying that, in many cores, systematic inward motions of gaseous material may occur over a range of density of at least a factor
4. Fits of the CS spectra to a 2-layer radiative transfer model in ten infall candidates suggest that the median effective line-of-sight speed of the inward-moving gas is
for CS (3-2) and
for CS(2-1). Considering that the optical depth obtained from the fits is usually smaller in CS(3-2) than in (2-1) line, this may indicate that CS(3-2) usually traces inner, denser gas with greater inward motions than CS(2-1) implying that many of the infall candidates have faster infall toward the center. However, this conclusion may not be representative of all starless core infall candidates, due to the statistically small number analyzed here. Further line observations will be useful to test this conclusion.
HCN(1-0) OBSERVATIONS OF STARLESS CORES
SOHN J, ; LEE C, W, ; LEE H, M. ; PARK Y.-S. ; MYERS P. C. ; LEE Y. ; TAFALLA M. ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 261~263
DOI : 10.5303/JKAS.2004.37.4.261
We present a progress report on HCN(1-0) line observations toward starless cores to probe inward motions. We have made a single pointing survey toward the central regions of 85 starless cores and performed mapping observations of 6 infall candidate starless cores. The distributions of the velocity difference between HCN(1-0) hyperfine lines and the optically thin tracer
(1-0) are significantly skewed to the blue, meaning that HCN(1-0) frequently detects inward motions. Their skewness to the blue is even greater than that of CS(2-1) Lee et al., possibly implying more infall occurrence than CS(1-0). We identify 19 infall candidates by using several characteristics illustrating spectral infall asymmetry seen in HCN(1-0) hyperfine lines, CS(3-2), CS(2-1),
observations. The HCN(1-0) F(O-l) with the least optical depth usually shows a similar intensity distribution to that of
which closely traces the density distribution of the cores, indicating that HCN(1-0) is less chemically affected and so believed to reflect kinematics occurring in rather inner regions of the cores. Detailed radiative transfer model fits of the spectra are underway to analyze central infall kinematics in starless cores.
HOT, WARM, AND COLD CORES: GOLDILOCKS MEETS MASSIVE STAR FORMATION
KURTZ S. ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 265~268
DOI : 10.5303/JKAS.2004.37.4.265
Molecular clouds present many levels of structure, including clumps and cores of varying size and density. We present a brief summary of these cores, describing their observed physical properties and their place in the star formation process. We conclude with some speculation about pre-proto-stellar stages of molecular cores and the observational challenges in their observation.
A WIDE FIELD SURVEY OF PLANETARY NEBULAE IN M31: A PROGRESS REPORT
RICHER M. G. ; LEE M. G. ; HWANG N. ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 269~272
DOI : 10.5303/JKAS.2004.37.4.269
We present the first results of a wide field survey for planetary nebulae throughout M31 undertaken at the KPNO 0.9m telescope with the Mosaic camera. So far, images in [O III]
5007 and its continuum filter have been analyzed. Our survey appears to be at least
complete to about 2 mag below the peak of the planetary nebula luminosity function. Over 900 planetary nebulae candidates have been found within a 12 square degree area.
HIGH DISPERSION OPTICAL SPECTROSCOPY OF PLANETARY NEBULAE
HYUNG SIEK ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 273~279
DOI : 10.5303/JKAS.2004.37.4.273
Chemical compositions of planetary nebulae are of interest for a study of the late stage of stellar evolution and for elemental contributions to the interstellar medium of reprocessed elements since possibly a large fraction of stars in 0.8 - 8
range go through this stage. One of the methods for getting chemical composition is a construction of theoretical photoionization models, which involves geometrical complexities and a variety of physical processes. With modelling effort, one can analyze the high dispersion and find the elemental abundances for a number of planetary nebulae. The model also gives the physical parameter of planetary nebula and its central star physical parameter along with the knowledge of its evolutionary status. Two planetary nebulae, NGC 7026 and Hu 1-2, which could have evolved from about one solar mass progenitor stars, showed radically different chemical abundances: the former has high chemical abundances in most elements, while the latter has extremely low abundances. We discuss their significance in the light of the evolution of our Galaxy.
PHYSICAL PROPERTIES OF THE GIANT H II REGION G353.2+0.9 IN NGC 6357
BOHIGAS JOAQUIN ; TAPIA MAURICIO ; ROTH MIGUEL ; RUlZ MARIA TERESA ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 281~284
DOI : 10.5303/JKAS.2004.37.4.281
Optical imaging and spectroscopy of G353.2+0.9, the brightest part of the giant H II region NGC 6357, shows that this H II region is optically thin, contains
of ionized gas and is probably expanding into the surrounding medium. Its chemical composition is similar to that found in other H II regions at similar galactocentric distances if temperature fluctuations are significant. The inner regions are probably made of thin shells and filaments, whereas extended slabs of material, maybe shells seen edge-on, are found in the periphery. The radio continuum and H
emission maps are very similar, indicating that most of the optical nebula is not embedded in the denser regions traced by molecular gas and the presence of IR sources. About
UV photons per second are required to produce the H
flux from the 1l.3'
10' region surrounding the Pis 24 cluster that is south of G353.2+0.9. Most of the energy powering this region is produced by the 03-7 stars in Pis 24. Most of the 2MASS sources in the field with large infrared excesses are within G353.2+0.9, indicating that the most recent star forming process occured within it. The formation of Pis 24 preceded and caused the formation of this new generation of stars and may be responsible for the present-day morphology of the entire NGC 6357 region.
SH 2-128, AN H II AND STAR FORMING REGION IN AN UNLIKELY PLACE
BOHIGAS JOAQUIN ; TAPIA MAURICIO ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 285~288
DOI : 10.5303/JKAS.2004.37.4.285
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
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
show the presence of a small cluster of B-type stars, mainly associated with S 128N. The
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
years respectively. No molecular hydrogen emission was detected at 2.12
. The origin of this remote star forming region is an open problem.
DUST GRAINS IN AGB STARS AS SOURCES OF INTERSTELLAR DUST
SUH KYUNG- WON ;
Journal of The Korean Astronomical Society, volume 37, issue 4, 2004, Pages 289~294
DOI : 10.5303/JKAS.2004.37.4.289
The main sources of interstellar dust are believed to be dust envelopes around AGB stars. The outflowing envelopes around the long period pulsating variables are very suitable place for massive dust formation. Oxygen-rich silicate dust grains or carbon-rich dust grains form in the envelopes around AGB stars depending on the chemical composition of the stellar surface. The dust grains expelled from AGB stars get mixed up and go through some physical and chemical changes in interstellar medium. There are similarities and differences between interstellar dust and dust grains in AGB stars. The mass cycle in the Galaxy may be best manifested by the fact that the dust grains at various regions have many similarities and understandable differences.