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تسجيل مستخدم جديدFrom evolved stars to the evolution of IC 1613
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IC 1613 is a Local Group dwarf irregular galaxy at a distance of 750 kpc. In this work, we present an analysis of the star formation history (SFH) of a field of $sim200$ square arcmin in the central part of the galaxy. To this aim, we use a novel method based on the resolved population of more highly evolved stars. We identify 53 such stars, 8 of which are supergiants and the remainder are long period variables (LPV), large amplitude variables (LAV) or extreme Asymptotic Giant Branch (x-AGB) stars. Using stellar evolution models, we find the age and birth mass of these stars and thus reconstruct the SFH. The average rate of star formation during the last Gyr is $sim3times10^{-4}$ M$_odot$ yr$^{-1}$ kpc$^{-2}$. The absence of a dominant epoch of star formation over the past 5 Gyr, suggests that IC 1613 has evolved in isolation for that long, spared harrassment by other Local Group galaxies (in particular M 31 and the Milky Way). We confirm the radial age gradient, with star formation currently concentrated in the central regions of IC 1613, and the failure of recent star formation to have created the main HI supershell. Based on the current rate of star formation at $(5.5pm2)times10^{-3}$ M$_odot$ yr$^{-1}$, the interstellar gas mass of the galaxy of $9times10^7$ M$_odot$ and the gas production rate from AGB stars at $sim6times10^{-4}$ M$_odot$ yr$^{-1}$, we conclude that the star formation activity of IC 1613 can continue for $sim18$ Gyr in a closed-box model, but is likely to cease much earlier than that unless gas can be accreted from outside.
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We are going to apply AGB stars to find star formation history for IC,1613 galaxy, this a new and simple method that works well for nearby galaxies. IC,1613 is a Local Group dwarf irregular galaxy that is located at distance of 750 kpc, a gas rich an
d isolated dwarf galaxy that has a low foreground extinction. We use the long period variable stars (LPVs) that represent the very final stage of evolution of stars with low and intermediate mass at the AGB phase and are very luminous and cool so that they emit maximum brightness in near--infrared bands. Thus near--infrared photometry with using stellar evolutionary models help us to convert brightness to birth mass and age and from this drive star formation history of the galaxy. We will use the luminosity distribution of the LPVs to reconstruct the star formation history--a method we have successfully applied in other Local Group galaxies. Our analysis shows that the IC 1613 has had a nearly constant star formation rate, without any dominant star formation episode.
Determining the star formation history (SFH) is key to understand the formation and evolution of dwarf galaxies. Recovering the SFH in resolved galaxies is mostly based on deep colour--magnitude diagrams (CMDs), which trace the signatures of multiple
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