Tesis
A relationship between iron spread and variability in giant stars of globular clusters = Una relación entre dispersión de hierro y variabilidad en estrellas gigantes de cúmulos globulares.
Autor
Llancaqueo Albornoz, Álvaro Ignacio
Institución
Resumen
The work presented here is the results from an analysis of 34 light curves, 17 in the
V filter and 17 in the I filter of 17 giant stars of NGC 3201, spanning 4 nights of
observation carried out on March 20-23, 2013.
The objective of this work was to check and prove if there is a relationship between the variability of a giant star and its iron abundance. To analyze the light
curves the Generalized Lomb-Scargle periodogram and the Phase Dispersion Minimization method were computed, and used in order to check if each giant was a
variable star. Then a revision of the [Fe/H] values of each variable star from the
literature was carried out.
From the period analysis made in the sample of 17 stars, 8 were non-variable,
3 were considered as possible variables and 6 stars were variable. From the sample of the discovered variable stars, they displayed different periods ranging from
0.0881±0.0001 to 0.5418±0.0027 days. These 6 variable stars showed distinct values
of [Fe I/H], the 3 most metal-rich stars being RGB, one star with [Fe I/H] = −1.37
and two with [Fe I/H] = −1.31 dex. The two most metal-poor variables have
[Fe I/H] = −1.61 and [Fe I/H] = −1.62 dex and are AGB stars and one variable
showed [Fe I/H] = −1.50 dex also being an AGB star. Meanwhile stars that were
non-variables showed −1.56 ≤ [Fe I/H] ≤ −1.40.
The conclusion brought from this work is that there is a relationship between the
iron abundance and variability of giant stars, where stars that are variable present
extreme values [Fe/H] compared with the stars that are non-variable and that variability affects somehow the spectroscopic determination of the iron content of giant
stars in globular clusters.
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