• Title, Summary, Keyword: stars: AGB

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INFRARED TWO-COLOR DIAGRAMS OF AGB STARS AND PLANETARY NEBULAE USING WISE DATA

  • Suh, Kyung-Won
    • Journal of The Korean Astronomical Society
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    • v.51 no.5
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    • pp.155-164
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    • 2018
  • We present various infrared two-color diagrams (2CDs) using WISE data for asymptotic giant branch (AGB) stars and Planetary Nebulae (PNe) and investigate possible evolutionary tracks. We use the sample of 5036 AGB stars, 660 post-AGB stars, and 2748 PNe in our Galaxy. For each object, we cross-identify the IRAS, AKARI, WISE, and 2MASS counterparts. To investigate the spectral evolution from AGB stars to PNe, we compare the theoretical model tracks of AGB stars and post-AGB stars with the observations on the IR 2CDs. We find that the theoretical dust shell model tracks can roughly explain the observations of AGB stars, post-AGB stars, and PNe on the various IR 2CDs. WISE data are useful in studying the evolution of AGB stars and PNe, especially for dim objects. We find that most observed color indices generally increase during the evolution from AGB stars to PNe. We also find that $Fe_{0.9}Mg_{0.1}O$ dust is useful to fit the observed WISE W3-W4 colors for O-rich AGB stars with thin dust shells.

ASTROPHYSICS OF DUSTY STELLAR WINDS FROM AGB STARS

  • Suh, Kyung-Won
    • Journal of The Korean Astronomical Society
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    • v.47 no.6
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    • pp.219-233
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    • 2014
  • The main site of dust formation is believed to be the cool envelopes around AGB stars. Nearly all AGB stars can be identified as long-period variables (LPVs) with large amplitude pulsation. Shock waves produce by the strong pulsation and radiation pressure on newly formed dust grains drive dusty stellar winds with high mass-loss rates. IR observations of AGB stars identify various dust species in different physical conditions. Radio observations of gas phase materials are helpful to understand the overall properties of the stellar winds. In this paper, we review (i) classification of AGB stars; (ii) IR two-color diagrams of AGB stars; (iii) pulsation of AGB stars; (iv) dust around AGB stars including dusty stellar winds; (v) dust envelopes around AGB stars; (vi) mass-loss and evolution of AGB stars; and (vii) contribution of AGB dust to galactic environments. We discuss various observational evidences and their theoretical interpretations.

A NEW CATALOG OF AGB STARS BASED ON INFRARED TWO-COLOR DIAGRAMS

  • Suh, Kyung-Won;Hong, Jinju
    • Journal of The Korean Astronomical Society
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    • v.50 no.4
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    • pp.131-138
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    • 2017
  • We present a new catalog of AGB stars based on infrared two-color diagrams (2CDs) and known properties of the pulsations and spectra. We exclude some misclassified objects from previous catalogs. We identify color areas in two IR 2CDs where most O-rich and C-rich objects listed in previous catalogs of AGB stars are found. By collecting new objects in these color selection areas in the two IR 2CDs, we find candidate objects for AGB stars. By using the color selection method, we identify 3996 new objects in the O-rich areas, 1487 new objects in the C-rich areas, and 295 new objects in the overlap areas of the two 2CDs simultaneously. We have found that 470 O-rich and 9 C-rich objects are Mira variables with positive spectral identification and they are newly identified AGB stars. We present a new catalog of 3828 O-rich AGB stars and 1168 C-rich AGB stars excluding misclassified objects and adding newly identified objects.

INFRARED COLOR-COLOR DIAGRAMS FOR AGB STARS

  • Suh, kyung-Won
    • Journal of Astronomy and Space Sciences
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    • v.24 no.3
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    • pp.197-202
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    • 2007
  • We present infrared color-color diagrams of AGB stars from the observations at near and mid infrared bands. We compile the observations for hundreds of OH/IR stars and carbon stars using the data from the Midcourse Space Experiment (MSX), the two micron sky survey (2MASS), and the IRAS point source catalog (PSC). We compare the observations with the theoretical evolutionary tracks of AGB stars. From the new observational data base and the theoretical evolution tracks, we discuss the meaning of the infrared color-color diagrams at different wavelengths.

DUST GRAINS IN AGB STARS AS SOURCES OF INTERSTELLAR DUST

  • SUH KYUNG- WON
    • Journal of The Korean Astronomical Society
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    • v.37 no.4
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    • pp.289-294
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    • 2004
  • The main sources of interstellar dust are believed to be dust envelopes around AGB stars. The outflowing envelopes around the long period pulsating variables are very suitable place for massive dust formation. Oxygen-rich silicate dust grains or carbon-rich dust grains form in the envelopes around AGB stars depending on the chemical composition of the stellar surface. The dust grains expelled from AGB stars get mixed up and go through some physical and chemical changes in interstellar medium. There are similarities and differences between interstellar dust and dust grains in AGB stars. The mass cycle in the Galaxy may be best manifested by the fact that the dust grains at various regions have many similarities and understandable differences.

Simultaneous observations of SiO and $H_2O$ masers toward AGB and post-AGB stars

  • Yoon, Dong-Hwan;Cho, Se-Hyung;Kim, Jaeheon;Cho, Chi-Young;Yun, Youngjoo;Park, Yong-Sun
    • The Bulletin of The Korean Astronomical Society
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    • v.37 no.2
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    • pp.237.2-237.2
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    • 2012
  • We performed simultaneous observations of SiO v=1, 2, $^{29}SiO$ v=0, J=1-0 and $H_2O$ $6_{16}-5_{23}$ maser lines toward 132 AGB and 183 post-AGB stars in order to investigate how evolutionary characteristics from AGB to post-AGB stars appear in these two maser emissions. The observations were carried out from 2011 February to 2012 March using the Korean VLBI Network 21-m radio telescopes. We have detected SiO and/or $H_2O$ maser emission from 29 sources out of 183 post-AGB stars including 19 new detections. Of 132 AGB stars which are mainly selected based on the IRAS Point Source Catalog, we detected SiO and/or $H_2O$ maser emission from 38 stars including 18 newly detected sources. An evolutionary characteristic from AGB to post-AGB stars is discussed in IRAS two-color diagram. It is found that SiO v=2, J=1-0 maser emission without SiO v=1 maser detections was detected from 8 sources among 21 SiO detected post-AGB stars and the intensity of SiO v=2, J=1-0 maser tends to be much stronger than that of SiO v=1. We also found that for the post-AGB stars the maser detection rate of blue group sources (which have higher outflow velocities than red group) are higher than that of red group. Especially, only $H_2O$ maser emission was detected from 7 sources among 94 red group sources without SiO maser detections.

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ASPHERICAL DUST ENVELOPES AROUND OXYGEN-RICH AGB STARS

  • Suh, Kyung-Won
    • Journal of Astronomy and Space Sciences
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    • v.23 no.4
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    • pp.303-310
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    • 2006
  • We model the aspherical dust envelopes around O-rich AGB stars. We perform the radiative transfer model calculations for axisymmetric dust distributions. We simulate what could be observed from the aspherical dust envelopes around O-rich AGB stars by presenting the model spectral energy distributions and images at various wave-lengths for different optical depths and viewing angles. The model results are very different from the ones with spherically symmetric geometry.

A CATALOG OF AGB STARS IN IRAS PSC

  • Suh, Kyung-Won;Kwon, Young-Joo
    • Journal of The Korean Astronomical Society
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    • v.42 no.4
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    • pp.81-91
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    • 2009
  • We make a new catalog of AGB stars in our Galaxy from the sources listed in the Infrared Astronomical Satellite (IRAS) point source catalog (PSC) compiling the lists of previous works with verifying processes. We verify the class identification of AGB stars into oxygen-rich and carbon-rich stars using the information from recent investigations. For the large sample of AGB stars, we present infrared two-color diagrams from the observations at near infrared bands and IRAS PSC. On the two-color diagrams, we plot the tracks of theoretical radiative transfer model results with increasing dust shell optical depths. Comparing the observations with the theoretical tracks, we discuss the meaning of the infrared two-color diagrams.

THE EVOLUTION OF AGB STARS ON INFRARED 2-COLOR DIAGRAMS

  • Suh, Kyung-Won;Lee, Jae-Woo;Kim, Hak-Youn
    • Journal of Astronomy and Space Sciences
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    • v.18 no.1
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    • pp.15-20
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    • 2001
  • We present infrared 2-color diagrams of AGB stars from the observations at near infrared and IRAS point source catalog (PSC) data. We compile the observations for thousands of newly identified OH/IR stars and carbon stars. We compare the observations with the theoretical evolutionary tracks of AGB stars. From the new observational data base and theoretical tracks, we discuss the meaning of the infrared 2-color diagrams.

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