Volume 418, Number 1, April IV 2004
|Page(s)||33 - 40|
|Published online||02 April 2004|
Carbon star survey in the Local Group*
VIII. Probing the stellar halo of NGC 147
INAF, Osservatorio Astronomico di Roma, Viale del Parco Mellini 84, 00136 Roma, Italia
2 Département de Physique, Université de Montréal, C.P.6128, Succursale Centre-Ville, Montréal, Québec, H3C 3J7, Canada e-mail: email@example.com
Corresponding author: P. Battinelli, firstname.lastname@example.org
Accepted: 12 January 2004
We have imaged a 42 field centered on the spheroidal galaxy NGC 147 to study its AGB population and determine the main structural properties of this M 31 companion. This field was observed through two broadband (R and I) and two narrowband (CN and TiO) filters, following the standard approach of our systematic survey of C stars in nearby galaxies. We identified 288 C stars in NGC 147. The average I-magnitude of such sample of C stars is with . If we adopt a distance modulus , derived from the luminosity of both the tip of the red giant branch (TRGB) and the horizontal branch (HB) by Han et al., we conclude that the average absolute I-magnitude of C stars is = –4.39, thus slightly under luminous with respect to what was found for other galaxies in our survey. From the radial surface profile we derive a scale length of 4.1 ± and a tidal radius rt = 33.9 ± , a value quite larger than previous estimates. The C star population shows a scale length remarkably similar, thus suggesting that intermediate-age stars in NGC 147 are well mixed with the older population. Finally, the overall ratio is 0.24 ± 0.02 and its local values increase monotonically from the center up to 3.5 scale lengths (beyond which counts become too low to yield reliable ratios). Such radial behaviour implies a corresponding decrease of about 0.4 dex in [Fe/H], confirming a well defined metallicity gradient in NGC 147.
Key words: galaxies: individual: NGC 147 / galaxies: stellar content / galaxies: structure
© ESO, 2004
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