• Title/Summary/Keyword: supergiant stars

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Near-IR TRGB Distance to Nearby Dwarf Irregular Galaxy NGC 6822

  • Sohn, Y.J.;Kang, A.;Han, W.;Park, J.H.;Kim, H.I.;Kim, J.W.;Shin, I.G.;Chun, S.H.
    • Journal of Astronomy and Space Sciences
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    • v.25 no.3
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    • pp.249-254
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    • 2008
  • We report the distance modulus of nearby dwarf irregular galaxy NGC 6822 estimated from the so-called Tip of Red-giant Branch (TRGB) method. To detect the apparent magnitudes of the TRGB we use the color-magnitude diagrams (CMDs) and luminosity functions (LFs) in the near-infrared JHK bands. Foreground stars, main-sequence stars, and supergiant stars have been classified on the (g - K, g) plane and removed on the near-infrared CMDs, from which only RGB and AGB stars are remained on the CMDs and LFs. By applying the Savitzky-Golay filter to the obtained LFs and detecting the peak in the second derivative of the observed LFs, we determined the apparent magnitudes of the TRGB. Theoretical absolute magnitudes of the TRGB are estimated from Yonsei-Yale isochrones with the age of 12Gyr and the metallicity range of -2.0 <[Fe/H]< -0.5. The derived values of distance modulus to NGC 6822 are (m - M) = $23.35{\pm}0.26$, $23.20{\pm}0.42$, and $23.27{\pm}0.50$ for J, H, and K bands, respectively. Distance modulus in bolometric magnitude is also derived as (m - M) = $23.41{\pm}0.17$. We compare the derived values of the TRGB distance modulus to NGC 6822 in the near-infrared bands with the previous results in other bands.

New challenges to stellar evolution theory from supernovae

  • Yoon, Sung-Chul
    • The Bulletin of The Korean Astronomical Society
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    • v.39 no.2
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    • pp.38-38
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    • 2014
  • Despite the great success that stellar evolution theory have enjoyed during the last 50 years, new challenges are emerging with recent observations of supernovae: many aspects of supernovae cannot be easily explained by the standard scenarios on supernova progenitors. A few examples include the red supergiant problem - the dearth of Type IIP supernova progenitors with masses higher than about 16 Msun, the non-detection of Type Ib/c supernova progenitors despite very deep searches in pre-supernova optical images, the unexpected blue colors of some Type IIn supernova progenitors, and the exotic stellar explosions of both ultra-faint and super-luminous types that have been only recently discovered. By confronting these observations with new stellar evolution models, we are making significnt progress in better understanding the role of metallicity, rotation and binary interactions for the pre-supernova evolution of massive stars. In this talk, I will give a brief review on the recent observational constraints on supernova progenitors and a progress report on several research projects that deal with pair-instability supernovae from the local Universe, type Ib/c supernovae from massive binary systems, and some peculiar stellar explosions like SN2012Z.

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X-ray observation of the shocked red supergiant wind of Cassiopeia A

  • Lee, Jae-Joon;Park, Sang-Wook
    • The Bulletin of The Korean Astronomical Society
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    • v.36 no.2
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    • pp.104.2-104.2
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    • 2011
  • We study X-ray characteristics of shocked ambient gas of the Galactic core-collapse supernova remnant Cas A. Using 1 Msec observation with Chandra X-ray Observatory, we identify thermal emissions from the shocked ambient gas along the outer boundary of the remnant. Our results show that Cas A is expanding into a circumstellar wind with a wind density n ~ 1 $cm^{-3}$ at the current outer radius of the remnant (~ 3 pc). We suggest that the progenitor star of Cas A, which exploded as a Type~IIb SN, had an initial mass ~16 Msun, and have lost ~10 Msun as a RSG wind. We discuss the implications of our results for the mass loss of massive stars and the resulting supernova type.

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PERIOD ANALYSIS FOR THE F COMPONENT OF THE ∈ AURIGAE SYSTEM USING WAVELETS (웨이블렛을 이용한 ∈ AURIGAE SYSTEM 주성 F별의 주기분석)

  • Kim, Hyouk
    • Journal of Astronomy and Space Sciences
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    • v.25 no.1
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    • pp.1-18
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    • 2008
  • We present a detailed period analysis for the F-type primary of ${\in}$ Aurigae by means of Fourier and wavelet algorithm. After collecting all available data which have been observed for around 160 years (1842 - 2006) from various international databases and published references we selected only data obtained during outside eclipse among them again. As a result of analysis using CLEANest and WWZ(weighted wavelet Z-transform) several frequencies including two clear periods ($67^d\;and\;123^d$) were found. In contrast to previous results that the periods vary irregularly it seems that the primary of ${\in}$ Aurigae is double mode or multiperiodic pulsator. The presence of the two periods and their ratio indicates that the high-mass interpretation of the variable could be valid. Also better understanding of the mechanisms driving the light variability of F-type supergiant stars requires continual series of photometric and radial velocity measurements in outside eclipse of this star.