“School of Astronomy”
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| Paper IPM / Astronomy / 14344 |
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NGC 147 and NGC 185, paired satellites of the Andromeda galaxy, possess the same order of mass
and analogous structures, but they show different star formation and different amounts of interstellar gas
and dust. Therefore, we present the first reconstruction of the star formation history of NGC 147 and
NGC 185. Asymptotic Giant Branch stars are highly evolved stars that are brightest in K-band. This
maximum K-band magnitude is related to the birth mass of stars. As a result, we have found a 9.9 Gyr
old single star formation epoch for NGC 185 followed by relatively continuous star formation. NGC 147,
however, has passed through two star formation episodes; one is as old as �?�6 Gyr and the other is as
recent as �?�850 Myr. Asymptotic Giant Branch stars are also important dust factories; by fitting Spectral
Energy Distributions to observed near and mid infrared data for each star, we were able to measure the
dust production rates of individual stars; on order of 10�??5M yr�??1
. Hence, we estimate the total mass
entering the interstellar medium to be 1.06 �? 10�??4M yr�??1 and 2.89 �? 10�??4M yr�??1
for NGC 147 and
NGC 185.
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