• 천문학회보
• /
• 제39권1호
• /
• pp.63.1-63.1
• /
• 2014

We present a study on the parsec-scale jets from young stellar objects using long-slit spectroscopic data obtained from Bohyunsan Optical Astronomy Observatory on 2012 - 2014. Through the position-velocity diagrams, we show the radial velocity variation, peak velocity and velocity width of the outflow from several T Tauri stars and Herbig Ae/Be star. $H{\alpha}$, [OI] 6300/6363, [NII] 6548/6584 and [SII] 6716/6731 emission lines are obtained and they show various velocity features. We also compare our result with other data from literatures.

• 천문학회지
• /
• 제34권4호
• /
• pp.251-254
• /
• 2001

To examine the structure and dynamics of thick accretion disks, we use a two-dimensional viscous hydrodynamic code coupled with radiation transport. The $\alpha$-model and the full viscous stress-tensor description for the kinematic viscosity are used. The radiation transport is treated in the gray, flux-limited diffusion approximation. The finite difference methods used are based on an explicit-implicit method. We apply the numerical code to the Super-Eddington black-hole model for SS 433.@The result for a very small viscosity parameter a reproduces well the characteristic features of SS 433, such as the relativistic jets with $\~$0.26c, the small collimation degree of the jets, the mass-outflow rate of ${\ge}5{\times}10^{-7}M{\bigodot}yr^{-1}$, and the formation of the X-ray iron emission lines.

• 대한수의학회지
• /
• 제57권1호
• /
• pp.63-66
• /
• 2017

A 6-month-old mature intact female Siamese cat presented with exertional dyspnea. Diagnostic studies revealed pleural effusion, grade 4/6 left basal systolic murmur, deep S-wave in electrocardiograph leads I, II, and III, cardiomegaly with pleural effusion on radiography, pulmonic systolic (~5.8 m/sec) and tricuspid (3.6 m/sec) regurgitant jets, atrial septal defect, and a hypoplastic right outflow tract. Based on these results, the case was diagnosed as pulmonic stenosis with atrial septal defect. To the best of our knowledge, this is the first case report describing pulmonic stenosis with atrial septal defect in a cat in Korea.

• 천문학논총
• /
• 제30권2호
• /
• pp.453-455
• /
• 2015

In this paper we introduce the Plasma Physics of Active Galactic Nuclei project, which is an ongoing experiment with Korean VLBI Network (KVN) and KVN and VERA Array (KaVA) to study multi-frequency polarimetric properties on parsec scales of active galaxies. The goal of the project is to improve our understanding of fundamental jet physics, especially evolution of the relativistic outflow coupled with the large-scale magnetic field. We selected six radio-loud AGN as our targets. So far we (i) detected resolved emissions regions at 86 and 129 GHz on VLBI scales, (ii) constructed 2D spectral index maps of the outflows, and (iii) found polarizations at 22 and 43 GHz for a few targets. Here we present spectral index distributions of 3C 120 between 22 and 43 GHz and a linear polarization map of BL Lac at 43 GHz obtained with KVN.

• 천문학회보
• /
• 제40권2호
• /
• pp.37.1-37.1
• /
• 2015

It is suggested that relativistic jets associated with active galactic nuclei (AGNs) can have great impacts on the evolution of the host galaxy. However, the physical properties of AGN jets including the formation mechanism are not well known to date, and hence the AGN feedback on the host galaxy is yet poorly understood. OVV 1633+382 as a highly variable AGN source (a.k.a. blazer) with a compact core and very well developed jet components is an excellent laboratory to study the jet formation mechanism of radio-loud AGN. Near 2002, a major flare was reported at mm wavelength with a dramatic increase of the flux, which is likely to be followed by a dense and bright outflow. In order to probe the evolution of the innermost region of this radio-loud AGN, we have monitored using the Very Large Baseline Array (VLBA) and the Effelsberg 100m single-dish radio telescope in 12 epochs from 2002 and 2005. The observations were conducted at 22, 43 and 86 GHz in full polarization mode. In this work, we present the intensity and spectral index maps at 22 and 43 GHz from our monitoring observations. We probe the kinematics and geometry of individual jet components to discuss the evolution of the jet.

• 천문학논총
• /
• 제30권2호
• /
• pp.113-114
• /
• 2015

Recent high-resolution, high-sensitivity observations of protostellar jets have shown many to possess an underlying 'wiggle' structure. HH 211 is one such example where recent sub-mm observations revealed a clear reflection-symmetric wiggle. An explanation for this is that the HH211 jet source is moving as part of a protobinary system. Here we test this assumption by simulating HH211 through 3D hydrodynamic simulations using the pluto code with a molecular chemistry and cooling module, and initial conditions based on an analytical model derived from SMA observations. Molecular chemistry allows us to accurately plot synthetic molecular emission maps and position-velocity diagrams for direct comparison to observations, enabling us to test the observational assumptions and put constraints on the physical parameters of HH211. Our preliminary results show that the reflection-symmetric wiggle can be recreated through the assumption of a jet source being part of a binary system.

• 천문학회보
• /
• 제37권1호
• /
• pp.74.2-74.2
• /
• 2012

We present [Fe II] 1.64 ${\mu}m$ imaging observations for jets and outflows from young stellar objects over the northern part (-24'${\times}$45') of the Carina Nebula, a typical evolved massive star forming region. The observations were performed with IRIS2 of Anglo-Autralian Telescope and the seeing was -1.5". Several jets and outflows features are detected at seven different regions, and one new Herbig-Haro Object is identified. The [Fe II] features have knotty and elongated shapes, and distribute around the triangular area formed by the star clusters Tr 14, Tr 15, and Tr 16, which contain many massive stars. The [Fe II] feature shows a highest detection rate (3.2 %) for the earliest stage YSOs, and the rate decreases as the stage evolves. The low detection rate (1.5 %) of [Fe II] features from the numerous YSOs seem to be related with the severe radiation environment of the Carina Nebula. The outflow rate shows reasonable relations with the physical parameters of the corresponding YSOs-derived from the SED fitting-such as the accretion luminosity, the stellar mass, the stellar age, the disk accretion rate, etc.

• 천문학회지
• /
• 제48권6호
• /
• pp.365-380
• /
• 2015

We map 6 massive young stellar objects (YSOs) in the CO J=2-1 line and survey 18 massive YSOs, including the six, in the HCO⁺ J=1−0, SiO J=2−1, H₂O 6₁₆ − 5₂₃ maser, and CH₃OH 7₀ − 6₁ A⁺ maser lines. We detect CO bipolar outflows in all the six mapped sources. Four of them are newly discovered (07299−1651, 21306+5540, 22308+5812, 23133+6050), while 05490+2658 is mapped in the CO J=2-1 line for the first time. The detected outflows are much more massive and energetic than outflows from low-mass YSOs with masses >20 M_⊙ and momenta >300 M_⊙ km s⁻¹. They have mass outflow rates (3−6)×10⁻⁴ M_⊙ yr⁻¹, which are at least one order of magnitude greater than those observed in low-mass YSOs. We detect HCO⁺ and SiO line emission in 18 (100%) and 4 (22%) sources, respectively. The HCO⁺ spectra show high-velocity wings in 11 (61%) sources. We detect H₂O maser emission in 13 (72%) sources and 44 GHz CH₃OH maser emission in 8 (44%) sources. Of the detected sources, 5 H₂O and 6 CH₃OH maser sources are new discoveries. 20081+3122 shows high-velocity (>30 km s⁻¹) H₂O maser lines. We find good correlations of the bolometric luminosity of the central (proto)star with the mechanical force, mechanical luminosity, and mass outflow rate of molecular outflow in the bolometric luminosity range of 10⁻¹−10⁶ L_⊙, and identified 3 intermediate- or high-mass counterparts of Class O objects.

• 천문학회보
• /
• 제44권2호
• /
• pp.51.3-51.3
• /
• 2019

Its ability to measure the polarization of light at four frequencies makes the KVN a "plasma physics observatory" that can probe the internal physics (e.g., magnetic fields, outflow geometries) of AGN radio jets and cores. We initiated a Key Science Program, the Plasma-physics of Active Galactic Nuclei (PAGaN) project, dedicated to polarimetric monitoring of 14 radio-bright AGN. We have been able to measure the Faraday rotation measure of the cores of our targets as function of frequency; the observed scaling relation is in good agreement with conically expanding outflows to first order. We are further probing a polarized hotspot in the jet of 3C84 and possible systematic differences in the Faraday rotation in BL Lacertae objects and flat spectrum radio quasars.

• Wind and Structures
• /
• 제26권3호
• /
• pp.147-161
• /
• 2018

For wind engineering applications downbursts are, presently, almost exclusively modeled, both experimentally and numerically, as transient impinging momentum jets (IJ), even though that model contains none of the physics of real events. As a result, there is no connection between the IJ-simulated downburst wind fields and the conditions of formation of the event. The cooling source (CS) model offers a significant improvement since it incorporates the negative buoyancy forcing and baroclinic vorticity generation that occurs in nature. The present work aims at using large-scale numerical simulation of downburst-producing thunderstorms to develop a simpler model that replicates some of the key physics whilst maintaining the relative simplicity of the IJ model. Using an example of such a simulated event it is found that the non-linear scaling of the velocity field, based on the peak potential temperature (and, hence, density) perturbation forcing immediately beneath the storm cloud, produces results for the radial location of the peak radial outflow wind speeds near the ground, the magnitude of that peak and the time at which the peak occurs that match well (typically within 5%) of those produced from a simple axi-symmetric constant-density dense source simulation. The evolution of the downdraft column within the simulated thunderstorm is significantly more complex than in any axi-symmetric model, with a sequence of downdraft winds that strengthen then weaken within a much longer period (>17 minutes) of consistently downwards winds over almost all heights up to at least 2,500 m.