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. 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
arcmin×6.3 arcmin 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(t_yr)˜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 <
M_bol>=-4.36±0.54. The bolometric LF for M-giants extends up
to M_bol=-6.5, while the one for C stars spans -5.8
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
arcmin×6.3 arcmin 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(t_yr)˜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 <
M_bol>=-4.36±0.54. The bolometric LF for M-giants extends up
to M_bol=-6.5, while the one for C stars spans -5.8
KW - galaxies: individual: NGC 6822
KW - galaxies: stellar content
KW - stars: AGB and post-AGB
U2 - 10.1051/0004-6361:20054763
DO - 10.1051/0004-6361:20054763
M3 - Article
VL - 454
SP - 717
EP - 727
JO - Astronomy & Astrophysics
JF - Astronomy & Astrophysics
SN - 0004-6361
IS - 3
ER -