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

A. Kang, Y. J. Sohn, H. I. Kim, J. Rhee, J. W. Kim, N. Hwang, M. G. Lee, Y. C. 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, Y. J. ; Kim, H. I. ; Rhee, J. ; Kim, J. W. ; Hwang, N. ; Lee, M. G. ; Kim, Y. C. ; 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.",
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The evolved asymptotic giant branch stars in the central bar of the dwarf irregular galaxy NGC 6822. / Kang, A.; Sohn, Y. J.; Kim, H. I.; Rhee, J.; Kim, J. W.; Hwang, N.; Lee, M. G.; Kim, Y. C.; 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, Y. J.

AU - Kim, H. I.

AU - Rhee, J.

AU - Kim, J. W.

AU - Hwang, N.

AU - Lee, M. G.

AU - Kim, Y. C.

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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