The evolved asymptotic giant branch stars in the central bar of the dwarf irregular galaxy NGC 6822
1
Department of Astronomy, Yonsei University, Seoul 120-749, Korea e-mail: sohnyj@yonsei.ac.kr;breeze82@galaxy.yonsei.ac.kr
2
Center for Space Astrophysics, Yonsei University, Seoul 120-749, Korea
3
Korea Astronomy and Space Science Institute, Daejeon 305-348, Korea
4
Astronomy Division, Department of Physics and Astronomy, Seoul National University, Seoul 151-742, Korea
Received:
23
December
2005
Accepted:
26
January
2006
Images of 
and 
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 
on the central bar of the dwarf irregular galaxy NGC 6822.
The upper envelope of near-infrared 
and 
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
CMD. We select AGB stars in NGC 6822 from the 
CMD, which has a long spectral
wavelength base line in the color index. There are 141 C stars with a mean absolute magnitude of
, and with mean colors of 
, and 
.
The number ratio of C stars to M-giants (C/M) is estimated as 
, while the northern part
of the bar has a somewhat lower C/M ratio than the southern part.
The 
and 
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
.
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 
. The bolometric LF for M-giants
extends up to 
, while the one for C stars spans 
.
Key words: galaxies: individual: NGC 6822 / galaxies: stellar content / stars: AGB and post-AGB
© ESO, 2006