• 천문학회지
• /
• 제29권spc1호
• /
• pp.183-186
• /
• 1996

We report the results of H I 21-cm and molecular line studies of the shocked interstellar gas in the W51 complex. We present convincing evidences suggesting that the shocked gas has been produced by the interaction of the W51C supernova remant (SNR) with a large molecular cloud, Our results show that W51C is the second SNR with direct evidences for the shocked cloud material.

• 천문학회보
• /
• 제42권2호
• /
• pp.64.3-64.3
• /
• 2017

For the detection of transient sources in optical wide field surveys like KMTNet Supernova Project, difference imaging technique is commonly used. As this method produces a fair amount of false positives, it is also common to utilize machine learning algorithms to screen likely true positives. While deep learning methods such as a convolutional neural network has been successfully applied recently, its application can be limited if the size of the training sample is small. I will discuss a variation of more conventional method that adopts the wavelet transform for feature engineering and its performance.

• 천문학회보
• /
• 제42권1호
• /
• pp.36.1-36.1
• /
• 2017

A major goal of the proposed Korean Neutrino Detector and Telescope is to detect neutrino burst from core-collapse supernova (SN) explosions in the Milky Way, which will provide an unprecedented opportunity to look into the core of an exploding massive star. Detection with high statistics would give important information for the explosion physics. It can also detect neutrino signals from SN events in the Local Group and trigger alert of the event for the astronomical community. In this talk, I will review the SN rates of the Milky Way and the Local Group, and will discuss the implications for the proposed neutrino telescope.

• 천문학회보
• /
• 제45권1호
• /
• pp.53.1-53.1
• /
• 2020

We present Herschel Space Observatory far-IR observations of the supernova remnant(SNR) G21.5-0.9. We search PACS-IFU data for 63um [O I], 88um [O III], 157um [C II] emission lines and detect the [O II] and the [C II]. We then produce emission line maps to check the spatial distribution of the elements. We compare the maps to Radio, IR-photometrics, and X-ray images in order to understand interaction of the ejecta with the Pulsar Wind Nebula(PWN) and physical environment in the SNR.

• 천문학회지
• /
• 제1권1호
• /
• pp.51-60
• /
• 1968

• 천문학회지
• /
• 제52권5호
• /
• pp.181-205
• /
• 2019

There is evidence that the luminosities of Type Ia supernova (SN Ia) depend on their environments. While the impact of this trend on estimating cosmological parameters is widely acknowledged, the origin of this correlation is still under debate. In order to explore this problem, we first construct the YONSEI (YOnsei Nearby Supernova Evolution Investigation) SN catalog. The catalog consists of 1231 spectroscopically confirmed SNe Ia over a wide redshift range (0.01 < z < 1.37) from various SN surveys and includes light-curve fit data from two independent light-curve fitters, SALT2 and MLCS2k2. For a sample of 674 host galaxies, we use the stellar mass and the star formation rate data in Kim et al. (2018). We find that SNe Ia in low-mass and star-forming host galaxies are $0.062{\pm}0.009mag$ and $0.057{\pm}0.010mag$ fainter than those in high-mass and passive hosts, after light-curve corrections with SALT2 and MLCS2k2, respectively. When only local environments of SNe Ia (e.g., locally star-forming and locally passive) are considered, this luminosity difference increases to $0.081{\pm}0.018mag$ for SALT2 and $0.072{\pm}0.018mag$ for MLCS2k2. Considering the significant difference in the mean stellar population age between the two environments, this result suggests that the luminosity evolution of SNe Ia with redshift is most likely the origin of the environmental dependence.

• 천문학회보
• /
• 제45권1호
• /
• pp.43.1-43.1
• /
• 2020

Cassiopeia A (Cas A) is a young supernova remnant (SNR) where we observe the interaction of SNR blast wave with circumstellar medium. From the early optical studies, dense, slowly-moving, N-rich "quasi-stationary flocculi" (QSF) have been known. These are probably dense CNO-processed circumstellar knots that have been engulfed by the SNR blast wave. We have carried out near-infrared, high-resolution (R=45,000) spectroscopic observations of ~40 QSF, and here we present the result on a QSF knot (hereafter 'Knot 24') near the SNR boundary of Cas A. The average [Fe II] 1.644 um spectrum of Knot 24 has a remarkable shape with a narrow (~8 km/s) line superposed on the broad (~200 km/s) line emitted from shocked gas. The spatial morphology and the line parameters indicate that Knot 24 has been partially destroyed by a shock wave and that the narrow line is emitted from the unshocked material heated/ionized by the shock radiation. This is the first detection of the emission from the pristine circumstellar material of the Cas A supernova progenitor. We also detected H Br gamma and other [Fe II] lines corresponding to the narrow [Fe II] 1.644 um line. For the main clump where we can clearly identify the shock emission associated with the unshocked material, we analyze the observed line ratios using a shock model that includes radiative precursor. The analysis indicates that the majority of Fe in the unshocked material is in the gas phase, not depleted onto dust grains as in the general interstellar medium. We discuss the non-depletion of Fe in QSF and its implications on the immediate progenitor of the Cas A supernova.

• 천문학회지
• /
• 제46권1호
• /
• pp.49-63
• /
• 2013

Nonthermal radiation from supernova remnants (SNRs) provides observational evidence and constraints on the diffusive shock acceleration (DSA) hypothesis for the origins of Galactic cosmic rays (CRs). Recently it has been recognized that a variety of plasma wave-particle interactions operate at astrophysical shocks and the detailed outcomes of DSA are governed by their complex and nonlinear interrelationships. Here we calculate the energy spectra of CR protons and electrons accelerated at Type Ia SNRs, using time-dependent, DSA simulations with phenomenological models for magnetic field amplification due to CR streaming instabilities, Alf$\acute{e}$enic drift, and free escape boundary. We show that, if scattering centers drift with the Alf$\acute{e}$en speed in the amplified magnetic fields, the CR energy spectrum is steepened and the acceleration efficiency is significantly reduced at strong CR modified SNR shocks. Even with fast Afv$\acute{e}$nic drift, DSA can still be efficient enough to develop a substantial shock precursor due to CR pressure feedback and convert about 20-30% of the SN explosion energy into CRs. Since the high energy end of the CR proton spectrum is composed of the particles that are injected in the early stages, in order to predict nonthermal emissions, especially in X-ray and ${\gamma}-ray$ bands, it is important to follow the time dependent evolution of the shock dynamics, CR injection process, magnetic field amplification, and particle escape. Thus it is crucial to understand the details of these plasma interactions associated with collisionless shocks in successful modeling of nonlinear DSA.

• 천문학논총
• /
• 제13권1호
• /
• pp.135-147
• /
• 1998

We have simulated the interaction of supernova remnants with constant ambient medium to explore the dynamics of Type Ia supernova remnant. We assumed the supernova ejecta density distribution of the central constant and the outer power-law density distribution$({\rho}{\propto}{\gamma}^{-n})$. We have calculated four different cases with different n. By scaling the length and time scales from the initial parameters-ejecta mass, ejecta energy, the ambient density, we could compare effects of the different density distribution of the ejecta on the dynamics of the SNRs. The radius of the outer forward shock converges the Sedov-Talyor solution at t' = 2.3 when the swept-up mass is 8 times of the ejecta mass. On the other hand, the motion of the reverse shock are largely affected by n. The ejecta with smaller n takes comparably long time to thermalize the whole ejecta at $t'{\simeq}5.3,\;M_{sw}{\simeq}18M_{ej}$. We have applied our calculated results to obtain the ejecta density distributions of Tycho and SN1006 with $n{\simeq}6$.

• 천문학회지
• /
• 제51권2호
• /
• pp.37-48
• /
• 2018

Massive stars blow powerful stellar winds throughout their evolutionary stages from the main sequence to Wolf-Rayet phases. The amount of mechanical energy deposited in the interstellar medium by the wind from a massive star can be comparable to the explosion energy of a core-collapse supernova that detonates at the end of its life. In this study, we estimate the kinetic energy deposition by massive stars in our Galaxy by considering the integrated Galactic initial mass function and modeling the stellar wind luminosity. The mass loss rate and terminal velocity of stellar winds during the main sequence, red supergiant, and Wolf-Rayet stages are estimated by adopting theoretical calculations and observational data published in the literature. We find that the total stellar wind luminosity due to all massive stars in the Galaxy is about ${\mathcal{L}}_w{\approx}1.1{\times}10^{41}erg\;s^{-1}$, which is about 1/4 of the power of supernova explosions, ${\mathcal{L}}_{SN}{\approx}4.8{\times}10^{41}erg\;s^{-1}$. If we assume that ~ 1 - 10 % of the wind luminosity could be converted to Galactic cosmic rays (GCRs) through collisonless shocks such as termination shocks in stellar bubbles and superbubbles, colliding-wind shocks in binaries, and bow-shocks of massive runaway stars, stellar winds might be expected to make a significant contribution to GCR production, though lower than that of supernova remnants.