Blue horizontal branch stars using the VVV survey
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2018
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en
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Universidad Andrés Bello
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Licencia CC
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The VISTA Variables in the V a L actea (VVV) is an ESO Public Survey,
part of the Paranal Observatory. The VVV Survey is targeting the central
parts of our galaxy, covering an area of 540 square degrees. Its main goal
is to study our galaxy's bulge and southern plane, in order to reveal the
corresponding 3D structure through variable stars. This survey detects the
emission of stars in ve near-IR bands (ZYJHKs), and uses it to solve the
problem of high interstellar dust extinction and high stellar density in that
area.
In this thesis project, we aim to search and characterize the population
of Blue Horizontal Branch (BHB) stars, taking a census of these old and
numerous objects in the bulge-halo transition region of the Milky Way, which
corresponds to the VVV tiles b201 - b228 (10o & ` & 350o and 10o . b .
8o). Using the globular cluster M22 as a standard and constructing colorcolor
diagrams with speci c cuts in color, we were able to nd our targets.
According to this, a total of 12554 BHB stars were detected.
In order to detect and characterize overdensities of stars in sizes similar
to those of old clusters or streams, Montecarlo simulations were performed.
The main simulation was made using the same number of stars that the total
of tiles contain. More simulations were made for each of the 28 tiles and their
respective stars. By plotting and comparing real and simulated data, and
using the appropiate bin size, we detected some overdensities, mostly of low
signi cance.
Using data from VSA (VISTA Science Archive) and doing a crossmatch
with our targets, we constructed lightcurves for BHB stars to study their
variability properties in the Ks band. We took an average of 52 epochs to
calculate periods and amplitudes, and also identi ed eclipsing binaries that
were present in our data. We obtained a total of 7665 variable star lightcurves
with an average period of 0.53 [days], of which 336 correspond to bonadife
eclipsing binaries. These results allow comparisons with other old stellar
populations such as RR Lyrae variable stars.
Notas
Tesis (Magíster en Ciencias Físicas)
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