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Description
Using the CFH12K camera, we apply the four-band photometric technique to identify 904 carbon stars in an area 28'x42' centered on NGC 6822. A few C stars outside of this area were also discovered with the Las Campanas Swope Telescope. The NGC 6822 survey employs two sets of observations obtained by rather different telescopes and with different procedures: the Swope Telescope on Las Campanas was used in 1999 October to secure images of NGC 6822 in Kron-Cousins R_KC_, CN (810nm), and TiO (770nm) filters. The 2048x2048 SITe No. 1 CCD yields a field of view of 23.7'x23.7'; NGC 6822 was also observed with the CFH12K at the beginning of one night in 2000 September. The camera consists of a 12Kx8K pixel mosaic covering a field of 42'x28', with each pixel corresponding to 0.206". Images were obtained through Mould I and R filters and through the CN and TiO filters. The NGC 6822 C star population has <I>=19.26 leading to an <M_I_>=-4.70, value essentially identical to the mean magnitude obtained for the C stars in IC 1613. Contrary to stars highlighting the optical image of NGC 6822, C stars are seen at large radial distances and trace a huge, slightly elliptical halo, which does not coincide with the huge H I cloud surrounding NGC 6822. The previously unknown stellar component of NGC 6822 has a exponential scale length of 3.0+/-0.1' and can be traced to 5 scale lengths. The C/M ratio of NGC 6822 is evaluated to be 1.0+/-0.2.
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