The evolved asymptotic giant branch stars in the central bar of the dwarf irregular galaxy NGC 6822

A. Kang, Young-Jong Sohn, H. I. Kim, J. Rhee, J. W. Kim, N. Hwang, M. G. Lee, Yong Cheol Kim, M. S. Chun

Research output: Contribution to journalArticle

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Abstract

Images of JHK and gi obtained with the Canada-France-Hawaii Telescope are used to investigate the stellar contents of the resolved asymptotic giant branch (AGB) population in the area of 3′6×6′3 on the central bar of the dwarf irregular galaxy NGC 6822. The upper envelope of near-infrared (J - K, K) and (H - K, K) color-magnitude diagrams (CMDs) shows four components of main-sequence stars, foreground stars, massive supergiants, and AGB stars. These components are also noticeable in the bright part of (g - i, g) CMD. We select AGB stars in NGC 6822 from the (g - K, g) CMD, which has a long spectral wavelength base line in the color index. There are 141 C stars with a mean absolute magnitude of 〈MK〉 = -7.60 ± 0.50, and with mean colors of 〈(J - K)0〉 = 1.77 ± 0.41, and 〈(H - K)0〉 = 0.75 ± 0.28. The number ratio of C stars to M-giants (C/M) is estimated as 0.27 ± 0.03, while the northern part of the bar has a somewhat lower C/M ratio than the southern part. The (J - K) and (H - K) color distributions of AGB stars contain a main peak of M-giant stars and a red tail of C stars. The broad color distributions for M-giants indicate that NGC 6822 has a wide range of intermediate ages with a peak at log(tyr) ∼ 9.0. The MK luminosity function (LF) for C stars in the central bar of NGC 6822 is likely to be a Gaussian distribution, while the LF of C stars in the southern part is slightly skewed to the brighter side than in northern part. The mean bolometric magnitude of 141 C stars in NGC 6822 is 〈Mbol〉 = -4.36 ± 0.54. The bolometric LF for M-giants extends up to Mbol = -6.5, while the one for C stars spans -5.8 < Mbol < -3.5.

Original languageEnglish
Pages (from-to)717-727
Number of pages11
JournalAstronomy and Astrophysics
Volume454
Issue number3
DOIs
Publication statusPublished - 2006 Aug 1

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irregular galaxies
carbon stars
asymptotic giant branch stars
dwarf galaxies
color-magnitude diagram
color
diagram
luminosity
giant stars
M stars
main sequence stars
massive stars
France
Canada
normal density functions
near infrared
envelopes
telescopes
wavelength
wavelengths

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Kang, A. ; Sohn, Young-Jong ; Kim, H. I. ; Rhee, J. ; Kim, J. W. ; Hwang, N. ; Lee, M. G. ; Kim, Yong Cheol ; Chun, M. S. / The evolved asymptotic giant branch stars in the central bar of the dwarf irregular galaxy NGC 6822. In: Astronomy and Astrophysics. 2006 ; Vol. 454, No. 3. pp. 717-727.
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abstract = "Images of JHK and gi obtained with the Canada-France-Hawaii Telescope are used to investigate the stellar contents of the resolved asymptotic giant branch (AGB) population in the area of 3′6×6′3 on the central bar of the dwarf irregular galaxy NGC 6822. The upper envelope of near-infrared (J - K, K) and (H - K, K) color-magnitude diagrams (CMDs) shows four components of main-sequence stars, foreground stars, massive supergiants, and AGB stars. These components are also noticeable in the bright part of (g - i, g) CMD. We select AGB stars in NGC 6822 from the (g - K, g) CMD, which has a long spectral wavelength base line in the color index. There are 141 C stars with a mean absolute magnitude of 〈MK〉 = -7.60 ± 0.50, and with mean colors of 〈(J - K)0〉 = 1.77 ± 0.41, and 〈(H - K)0〉 = 0.75 ± 0.28. The number ratio of C stars to M-giants (C/M) is estimated as 0.27 ± 0.03, while the northern part of the bar has a somewhat lower C/M ratio than the southern part. The (J - K) and (H - K) color distributions of AGB stars contain a main peak of M-giant stars and a red tail of C stars. The broad color distributions for M-giants indicate that NGC 6822 has a wide range of intermediate ages with a peak at log(tyr) ∼ 9.0. The MK luminosity function (LF) for C stars in the central bar of NGC 6822 is likely to be a Gaussian distribution, while the LF of C stars in the southern part is slightly skewed to the brighter side than in northern part. The mean bolometric magnitude of 141 C stars in NGC 6822 is 〈Mbol〉 = -4.36 ± 0.54. The bolometric LF for M-giants extends up to Mbol = -6.5, while the one for C stars spans -5.8 < Mbol < -3.5.",
author = "A. Kang and Young-Jong Sohn and Kim, {H. I.} and J. Rhee and Kim, {J. W.} and N. Hwang and Lee, {M. G.} and Kim, {Yong Cheol} and Chun, {M. S.}",
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The evolved asymptotic giant branch stars in the central bar of the dwarf irregular galaxy NGC 6822. / Kang, A.; Sohn, Young-Jong; Kim, H. I.; Rhee, J.; Kim, J. W.; Hwang, N.; Lee, M. G.; Kim, Yong Cheol; Chun, M. S.

In: Astronomy and Astrophysics, Vol. 454, No. 3, 01.08.2006, p. 717-727.

Research output: Contribution to journalArticle

TY - JOUR

T1 - The evolved asymptotic giant branch stars in the central bar of the dwarf irregular galaxy NGC 6822

AU - Kang, A.

AU - Sohn, Young-Jong

AU - Kim, H. I.

AU - Rhee, J.

AU - Kim, J. W.

AU - Hwang, N.

AU - Lee, M. G.

AU - Kim, Yong Cheol

AU - Chun, M. S.

PY - 2006/8/1

Y1 - 2006/8/1

N2 - Images of JHK and gi obtained with the Canada-France-Hawaii Telescope are used to investigate the stellar contents of the resolved asymptotic giant branch (AGB) population in the area of 3′6×6′3 on the central bar of the dwarf irregular galaxy NGC 6822. The upper envelope of near-infrared (J - K, K) and (H - K, K) color-magnitude diagrams (CMDs) shows four components of main-sequence stars, foreground stars, massive supergiants, and AGB stars. These components are also noticeable in the bright part of (g - i, g) CMD. We select AGB stars in NGC 6822 from the (g - K, g) CMD, which has a long spectral wavelength base line in the color index. There are 141 C stars with a mean absolute magnitude of 〈MK〉 = -7.60 ± 0.50, and with mean colors of 〈(J - K)0〉 = 1.77 ± 0.41, and 〈(H - K)0〉 = 0.75 ± 0.28. The number ratio of C stars to M-giants (C/M) is estimated as 0.27 ± 0.03, while the northern part of the bar has a somewhat lower C/M ratio than the southern part. The (J - K) and (H - K) color distributions of AGB stars contain a main peak of M-giant stars and a red tail of C stars. The broad color distributions for M-giants indicate that NGC 6822 has a wide range of intermediate ages with a peak at log(tyr) ∼ 9.0. The MK luminosity function (LF) for C stars in the central bar of NGC 6822 is likely to be a Gaussian distribution, while the LF of C stars in the southern part is slightly skewed to the brighter side than in northern part. The mean bolometric magnitude of 141 C stars in NGC 6822 is 〈Mbol〉 = -4.36 ± 0.54. The bolometric LF for M-giants extends up to Mbol = -6.5, while the one for C stars spans -5.8 < Mbol < -3.5.

AB - Images of JHK and gi obtained with the Canada-France-Hawaii Telescope are used to investigate the stellar contents of the resolved asymptotic giant branch (AGB) population in the area of 3′6×6′3 on the central bar of the dwarf irregular galaxy NGC 6822. The upper envelope of near-infrared (J - K, K) and (H - K, K) color-magnitude diagrams (CMDs) shows four components of main-sequence stars, foreground stars, massive supergiants, and AGB stars. These components are also noticeable in the bright part of (g - i, g) CMD. We select AGB stars in NGC 6822 from the (g - K, g) CMD, which has a long spectral wavelength base line in the color index. There are 141 C stars with a mean absolute magnitude of 〈MK〉 = -7.60 ± 0.50, and with mean colors of 〈(J - K)0〉 = 1.77 ± 0.41, and 〈(H - K)0〉 = 0.75 ± 0.28. The number ratio of C stars to M-giants (C/M) is estimated as 0.27 ± 0.03, while the northern part of the bar has a somewhat lower C/M ratio than the southern part. The (J - K) and (H - K) color distributions of AGB stars contain a main peak of M-giant stars and a red tail of C stars. The broad color distributions for M-giants indicate that NGC 6822 has a wide range of intermediate ages with a peak at log(tyr) ∼ 9.0. The MK luminosity function (LF) for C stars in the central bar of NGC 6822 is likely to be a Gaussian distribution, while the LF of C stars in the southern part is slightly skewed to the brighter side than in northern part. The mean bolometric magnitude of 141 C stars in NGC 6822 is 〈Mbol〉 = -4.36 ± 0.54. The bolometric LF for M-giants extends up to Mbol = -6.5, while the one for C stars spans -5.8 < Mbol < -3.5.

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