• 천문학회지
• /
• 제56권1호
• /
• pp.11-22
• /
• 2023

We report the result of a high-resolution spectroscopic study on seven magnesium (Mg) enhanced stars. The high Mg abundances in these stars imply that they were born in an environment heavily affected by the nucleosynthesis products of massive stars. We measure abundances of 16 elements including Mg and they show various abundance patterns implying their diverse origin. Three of our program stars show a very high Mg to Si ratio ([Mg/Si] ≈ 0.18-0.25), which might be well explained by fall-back supernovae or by supernovae with rapid rotating progenitors having an initial mass higher than about 20 M_⊙. Another three of our program stars have high light to heavy s-process element ratios ([Y/Ba] ≈ 0.30-0.44), which are consistent with the theoretical prediction of the nucleosynthesis in rapidly rotating massive stars with an initial mass of about M = 40 M_⊙. We also report a star having both high Y ([Y/Fe] = 0.2) and Ba ([Ba/Fe] = 0.28) abundance ratios, and it also shows the highest Zn abundance ratio ([Zn/Fe] = 0.27) among our sample, implying the nucleosynthesis by asymmetric supernova explosion induced by very rapid rotation of a massive progenitor having an initial mass between 20 M_⊙ ≲ M ≲ 40 M_⊙. A relative deficiency of odd-number elements, which would be a signature of the pair-instability nucleosynthesis, is not found in our sample.

• 천문학회보
• /
• 제40권1호
• /
• pp.46.2-46.2
• /
• 2015

Modern methods in determining the value of the Hubble constant are divided into two main ways: the classical distance ladder method and the inverse distance ladder method. The classical distance ladder method is based on Cepheid calibrated Type Ia supernovae (SNe Ia), which are known as powerful distance indicator. The inverse distance ladder method uses cosmic microwave background radiation, which emitted from the high-z universe, and the cosmological model. Recent estimations of the Hubble constant based on these two methods show a $2{\sim}3{\sigma}$ difference, which called the "Hubble tension". It is currently an issue in the modern cosmology. We have been working on the luminosity calibration of SNe Ia based on the Tip of the Red Giant Branch (TRGB), which is a precise population I distance indicator. We present the TRGB distance estimates of 5 SNe Ia host galaxies with the archival Hubble Space Telescope image data. We derive the mean absolute maximum magnitude of 5 SNe Ia and the value of the Hubble constant. Cosmological implications of our estimate will be discussed.

• 천문학회보
• /
• 제40권1호
• /
• pp.56.1-56.1
• /
• 2015

We are at the initial performance-verification phase of our KMTNet Supernova Project (KSP) using the three wide-field telescopes of the KMTNet in the southern hemisphere. The primary science objectives of KSP, which take advantage of its unique 24-hour continuous sky coverage, are to study early (i.e., within a few hours from explosion) and rare/peculiar (e.g. fast decay) supernovae (SNe), SN progenitors, explosion mechanisms, as well as other exotic optical transients. We present the initial status/results of the program, along with the program strategy, science objectives, target fields, and future plan. While the target field selection will be made based on the performance of the system and consideration of various scientific merits, the initial target fields are focused on nearby galaxies with increased cadence and filter coverage.

• 천문학논총
• /
• 제27권4호
• /
• pp.225-230
• /
• 2012

Supernovae (SN) and supernova remnants (SNRs) play a major role in the life-cycle of interstellar dusts. Fast shock waves generated by SN explosions sweep out the interstellar space destroying dust grains and modifying their physical and chemical properties. The dense, cooling SN ejecta, on the other hand, provide an environment for dusts to condense. Recent space-infrared telescopes have revealed the hidden universe related to these fascinating microscopic processes. In this paper, I introduce the results on stardusts in young core-collapse supernova remnants obtained by AKARI. The AKARI results show diverse infrared characteristics of stardusts associated with SNRs, implying diverse physical/chemical stellar structures and circumstellar environments at the time of explosion.

• 천문학회보
• /
• 제40권2호
• /
• pp.40.2-40.2
• /
• 2015

In our recent investigation (Lim et al. 2015), we have shown that the combination of narrow-band Ca photometry and low-resolution spectroscopy can effectively search for globular clusters (GCs) with supernovae (SNe) enrichments. We apply this technique to the metal-poor bulge GC NGC 6273 and find two distinct subpopulations having different light and heavy element abundances. Our result suggests that NGC 6273 was massive enough to retain SNe ejecta, which would place this cluster in the growing group of GCs with Galactic building block characteristics, such as ${\omega}$ Centauri and M22.

• 천문학회보
• /
• 제38권2호
• /
• pp.74.1-74.1
• /
• 2013

We have performed new narrow-band calcium photometry for Milky Way globular clusters (GCs) and detected multiple red giant branches (RGBs) in some massive GCs. Our new calcium filter was designed to avoid the CN contamination below $3883{\AA}$ and to measure only Ca II H&K lines. The fact that we are detecting multiple RGBs from the new filter is suggesting that they are indeed different in calcium abundance, which can only be produced by supernovae (SNe). Therefore, the presence of the multiple RGBs for the peculiar GCs in the calcium photometry is best understood if the later generation of stars are enhanced in some SNe products. In this talk, we will present our progress in the calcium photometry for the peculiar GCs showing the multiple RGBs.

• 천문학회보
• /
• 제38권2호
• /
• pp.62.2-62.2
• /
• 2013

Recent spectroscopic observations have provided evidence for complex chemical evolution by supernovae and/or asymptotic giant branch (AGB) stars in the two metal-poor globular clusters (GCs) NGC2419 and M15. In particular, the horizontal branches (HBs) of these metal-poor GCs are very extended in the Hertzsprung-Russell diagram. The origin of these peculiar features, as well as that for the Sandage period-shift effect observed in these clusters, are yet to be understood. Here we show, by constructing population models including the Nitrogen enhanced subpopulation, that the second generation populations in these clusters would be enhanced not only in Helium, but also in Nitrogen. This working hypothesis can simultaneously explain the observed extended feature on the HB and the period-shift of RR Lyrae variables.

• 천문학논총
• /
• 제15권spc1호
• /
• pp.61-71
• /
• 2000

The emission line objects such as planetary nebulae, symbiotics, gaseous nebulae, HII regions, novae, supernovae, SNRs, nearby spiral galaxies, dIrr, dE, and nearby active galactic nuclei, would be goldmines for us to dig with the 1.8m bohyunsan optical (BOAO) telescope. We discussed the importance of strategically important diagnostic lines and atomic constant calculation for a study of Galactic and extragalactic emission objects. The scientific background on a spectrometer development history is briefly presented and spectroscopic research areas other than the emission objects are also summarized.

• 천문학회보
• /
• 제39권2호
• /
• pp.104.2-104.2
• /
• 2014

The RGB Bayer filter system consists of mosaic R, G, and B filters on the grid of photo sensors with which typical commercial DSLR (Digital Single Lens Reflex) cameras and CCD/CMOS cameras are taken. Many unique astronomical data taken with RGB Bayer filter systems are available, including transient objects, e.g., supernovae, variable stars, and solar system bodies. The utilization of such data in scientific research strongly requires reliable photometry transformation methods. In this work, we develop a series of formulae to derive magnitudes in the Johnson-Cousins BVR filter system from those in the RGB Bayer filter system.

• 천문학회보
• /
• 제41권2호
• /
• pp.53.3-54
• /
• 2016

We combine a semi-analytic model of galaxy evolution with constraints on circumstellar habitable zones and the distribution of terrestrial planets in order to probe the suitability of galaxies of different mass and type to host habitable planets, and how it evolves with time. We find that the fraction of stars with terrestrial planets in their habitable zone (known as habitability) depends only weakly on galaxy mass, with a maximum around $4{\times}10^{10}M_{\odot}$. We estimate that 0.7% of all stars in Milky Way-type galaxies to host a terrestrial planet within their habitable zone, consistent with the value derived from Kepler observations. On the other hand, the habitability of passive galaxies is slightly but systematically higher, unless we assume an unrealistically high sensitivity of planets to supernovae. We find that the overall habitability of galaxies has not changed significantly in the last ~8 Gyr, with most of the habitable planets in local disk galaxies having formed ~1.5 Gyr before our own solar system. Finally, we expect that ${\sim}1.4{\times}10^9$ planets similar to present-day Earth have existed so far in our galaxy.