arXiv subjects

Seong-Jae Lee

Publications and source records attributed to Seong-Jae Lee.

9 recordsLinked to original sources

arXiv2026

Simulation of advective accretion flows around black holes under various outer boundary conditions

We simulated various accretion disc structures with viscous hydrodynamic (HD) flow around a black hole (BH). We found that the structure of the accretion disc is significantly influenced by changes in the physical parameters of the initial inflowing gases. These physical parameters can be called outer boundary conditions (OBCs) at the outer-accretion boundary and represented on an OBC plane, which is primarily divided into hot-mode and cold-mode inflowing gases. We found smooth and shocked flows in the simulation, which follow the semi-analytical solutions with their OBCs. Interestingly, we observed that certain types of OBCs can produce shocks with jet-like features in the accretion flow. However, other OBCs can produce smooth or shock-free accretion flow, which may or may not have outflows. The smooth flows can display both the lowest and highest angular momentum distributions among the advective flows, depending on the OBCs. Additionally, the nature of the accretion flows can be either steady or quasi-steady, also influenced by the OBCs. We also observed that solutions corresponding to hot-mode gases have a greater tendency to generate outflows compared to those with the cold-mode. Therefore, this qualitative study of OBCs is crucial for understanding accretion physics, which can aid in modeling accretion discs, similar to the quantitative studies (which involve only changing mass accretion rates) of the inflowing gases. Thus, we assert that an accretion model should be based on both the qualitative and quantitative aspects of the initial inflowing gases.

astro-ph.HE↗

arXiv2022

The [S II] Spectral Images of the Planetary Nebula NGC 7009: II. Major Axis

We derived position-velocity density distribution diagrams along the major (PA = 77$^{\circ}$) axis of the elliptical planetary nebula NGC 7009 with the Keck HIRES [SII] 6716/6731 \A, doublet spectral images. The average densities of the main shell and knots of NGC 7009 derived from the [SII] 6716/673 \A, fluxes integrated over the line of sight indicate a density range of $N_{\rm e}$ = $10^{3.4}$ to 10$^{3.9}$ $cm^{-3}$, while the local densities from the volume fraction resolved in radial velocities along the line of sight show a considerably large range of about 10$^{2.8}$ -- 10$^{4.7}$ $cm^{-3}$. The derived projection angle of the major axis of the main shell is about $ψ\sim$18.3($\pm$2)$^{\circ}$. Assuming that the main shell is an ellipsoidal shell with $a \simeq$16$''$ and $b \simeq 6''$, we found the range of expansion velocity, radius, and latitude of four knots and a hot bubble. The four knots at the points in symmetrical positions are roughly aligned with the same axis of expansion of latitudes $ϕ\sim \pm 34.5(\pm 0.6)^{\circ}$: One pair expands at about 35 $kms^{-1}$ close to the main ellipsoidal shell, and the other expands rapidly at about 60 $kms^{-1}$ at a distance of $r \sim 16''$. In the latitude range $ϕ= $65 -- 75$^{\circ}$, the hot bubble of a relatively large structure expands rapidly with a velocity of 130 -- 150 $kms^{-1}$. Four knots and hot bubble points that expand faster than the main shell appear to have been formed by two to three eruptions at a different epoch than the primary structure formation.

astro-ph.SR↗

arXiv2022

Double Shells of the Planetary Nebula NGC 7009 Minor Axis

We analyzed the minor axis spectra of the elliptical planetary nebula (PN) NGC 7009 observed with the Keck HIRES with a 0.862$"$ $\times$ 10$"$ slit placed at about $\sim$7.5$"$ and 10$"$ away from the center and a 0.862$"$ $\times$ 14$"$ slit at the center. The mean densities derived from the integrated [SII] 6716/6731Å, fluxes along the Keck HIRES slit length indicate a density range of 10$^{3.7}$ to 10$^{4.1}$ cm$^{-3}$, while the local densities derived from the slit spectral images show a large local density variation of about 10$^{2.8}$ - 10$^{4.6}$ cm$^{-3}$: local densities vary substantially more than values integrated over the line of sight. The expansion rates of the main and outer shells obtained by [SII] are about 21.7 and 30.0 kms$^{-1}$, respectively. The kinematic results of the [SII] spectral lines correspond to the outermost regions of the two shells and are not representative of the whole PN but are closely related to the other emission lines observed in the shell gas. We conclude that the density contrast leads to the formation of the inner shell, while the change in ionization state leads to the formation of the outer shell. We suggest that the inner main and outer shells result from two successive major ejections. The physical conditions of the central star must have been different when these shells first formed.

astro-ph.SR↗

arXiv2020

Development of Open Informal Dataset Affecting Autonomous Driving

This document is a document that has written procedures and methods for collecting objects and unstructured dynamic data on the road for the development of object recognition technology for self-driving cars, and outlines the methods of collecting data, annotation data, object classifier criteria, and data processing methods. On-road object and unstructured dynamic data were collected in various environments, such as weather, time and traffic conditions, and additional reception calls for police and safety personnel were collected. Finally, 100,000 images of various objects existing on pedestrians and roads, 200,000 images of police and traffic safety personnel, 5,000 images of police and traffic safety personnel, and data sets consisting of 5,000 image data were collected and built.

cs.CV↗

arXiv2020

The Formation of the Double Gaussian Line Profiles of the Symbiotic Star AG Peg

We analyze high dispersion emission lines of the symbiotic nova AG Peg, observed in 1998, 2001, and 2002. The H$α$ and H$β$ lines show three components, two narrow and one underlying broad line components, but most other lines, such as HI, HeI, and HeII lines, show two blue- and red-shifted components only. A recent study by Lee & Hyung (2018) suggested that the double Gaussian lines emitted from a bipolar conic shell is likely to form Raman scattering lines observed in 1998. In this study, we show that the bipolar cone with an opening angle of 74$^{o}$, which expands at a velocity of 70 kms$^{-1}$ along the polar axis of the white dwarf, can accommodate the observed double line profiles in 1998, 2001, and 2002. We conclude that the emission zone of the bipolar conic shell, which formed along the bipolar axis of the white dwarf due to the collimation by the accretion disk, is responsible for the double Gaussian profiles.

astro-ph.SR↗

arXiv2018

The H$α$ and H$β$ Raman-scattering line profiles of the symbiotic star AG Peg

The H$α$ and H$β$ line profiles of the symbiotic star AG Peg observed on 1998 September (phase $ϕ$ = 10.24), display the top narrow double Gaussian and bottom broad (FWHM of 200 -- 400 kms$^{-1}$) components. The photo-ionization model indicated that the ionized zone, responsible for the hydrogen Balmer and Lyman lines, is radiation-bounded, with a hydrogen gas number density of $n_{\rm H} \sim 10^{9.85}$ cm$^{-3}$ and a gas temperature of T$_e$ = 12\,000 -- 15\,000~K. We carried out Monte Carlo simulations to fit the Raman scattering broad wings, assuming that the hydrogen Ly$β$ and Ly$γ$ lines emitted within the radiation-bounded HII zone around a white dwarf have the same double Gaussian line profile shape as the hydrogen Balmer lines. The simulation shows that the scattering HI zones are attached to (or located just outside of) the inner HII shells. The best fit to the observed broad HI line profiles indicates that the column density of the scattering neutral zone is $N_{\rm H} \simeq $ 3 -- 5 $\times$ 10$^{19}$ cm$^{-2}$. We examined whether the geometrical structure responsible for the observed H$α$ and H$β$ line profiles is a bipolar conical shell structure, consisting of the radiation-bounded ionized zone and the outer material bounded neutral zone. The expanding bipolar structure might be two opposite regions of the common envelope or the outer shell of the Roche lobe around the hot white dwarf, formed through the mass inflows from the giant star and pushed out by the fast winds from the hot white dwarf.

astro-ph.SR↗

arXiv2016

Simulations of Viscous Accretion Flow around Black Holes in Two-Dimensional Cylindrical Geometry

We simulate shock-free and shocked viscous accretion flow onto a black hole in a two dimensional cylindrical geometry, where initial conditions were chosen from analytical solutions. The simulation code used the Lagrangian Total Variation Diminishing (LTVD) and remap routine, which enabled us to attain high accuracy in capturing shocks and to handle the angular momentum distribution correctly. Inviscid shock-free accretion disk solution produced a thick disk structure, while the viscous shock-free solution attained a Bondi-like structure, but in either case, no jet activity nor any QPO-like activity developed. The steady state shocked solution in the inviscid, as well as, in the viscous regime, matched theoretical predictions well. However, increasing viscosity renders the accretion shock unstable. Large amplitude shock oscillation is accompanied by intermittent, transient inner multiple shocks. Such oscillation of the inner part of disk is interpreted as the source of QPO in hard X-rays observed in micro-quasars. Strong shock oscillation induces strong episodic jet emission. The jets also showed existence of shocks, which are produced as one shell hits the preceding one. The periodicity of jets and shock oscillation were similar. The jets for higher viscosity parameter are evidently stronger and faster.

astro-ph.HE↗

arXiv2010

Quasi-Spherical, Time-Dependent Viscous Accretion Flow: One-Dimensional Results

We investigated the instability of advective accretion flow as a consequence of angular momentum transfer in one-dimensional, quasi-spherical transonic accretion flow around a non-rotating black hole. The code is designed to include the effects of viscosity; the hydrodynamics component preserves angular momentum strictly with Lagrangian and remap method in absence of viscosity, while the viscosity component updates viscous angular momentum transfer through the implicit method. We performed two tests to demonstrate the suitability of the code for accretion study. First, we simulated the inviscid, low angular momentum, transonic accretion flow with shocks around a black hole, and then the subsonic, self-similar ADAF solution around a Newtonian object. Both simulations fitted the corresponding analytical curves extremely well. We then simulated a rotating, viscous, transonic fluid with shocks. We showed that for low viscosity parameter, stable shocks at larger distance are possible. For higher viscosity parameter, more efficient angular momentum transfer in the post-shock disk makes the shock structure oscillatory. Moreover, as the shock drifts to larger distances, a secondary inner shock develops. We showed that the inner shock is the direct consequence of expansion of the outer shock, as well as creation of regions with $\partial l / \partial r < 0$ due to more efficient angular momentum transfer near the inner sonic point. We showed that all disk parameters, including emissivity, oscillate with the same period as that of the shock oscillation. Our simulation may have implication for low frequency QPOs, e.g., GRO J1655-40 and XTE J1550-564.

astro-ph.CO↗

arXiv2001

The electron temperature of the inner halo of the Planetary Nebula NGC 6543

We investigate the electron temperature of the inner halo and nebular core regions of NGC 6543, using archival Hubble Space Telescope (HST) Wide Field Planetary Camera 2 (WFPC2) images taken through narrow band [O III] filters. Balick et al. (2001) showed that the inner halo consists of a number of spherical shells. We find the temperature of this inner halo to be much higher (~15000 K) than that of the bright core nebula (~8500 K). Photo-ionization models indicate that hardening of the UV radiation from the central star cannot be the main source of the higher temperature in the halo region. Using a radiation hydrodynamic simulation, we show that mass loss and velocity variations in the AGB wind can explain the observed shells, as well as the higher electron temperature.

astro-ph↗