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Title: Exploring the final stages of stars in our Milky Way using large sky surveys
Author: Greiss, Sandra
ISNI:       0000 0004 5357 7487
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2014
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Multi-wavelength astronomical surveys have revolutionised the field. They have dramatically changed the way we search for sources, as well as the way we analyse their data. In this thesis, we focus on the search for compact objects using different photometric surveys, from X-rays to near-infrared, including the optical bands. Compact sources are the end points of stellar evolution. They consist of white dwarfs, neutron stars and black holes. This thesis consists of two key parts. The first concerns the exploitation of three near-infrared surveys of the Galactic Bulge in order to find the counterparts of 1658 X-ray sources detected with NASA’s Chandra satellite. These sources are the focus of the Galactic Bulge Survey (GBS), which has a main goal to find low-mass X-ray binaries, composed of neutron stars or stellar-mass black holes accreting material from a low-mass companion. We present all viable counterpart candidates and associate a false alarm probability (FAP) to each near-infrared match in order to identify the most likely counterparts. The FAP takes into account a statistical study involving a chance alignment test, as well as considering the positional accuracy of the individual X-ray sources. We find that although the star density in the Bulge is very high, ∼90% of our sources have a FAP < 10%, indicating that for most X-ray sources, viable near-infrared counterparts candidates can be identified. In addition to the FAP, we provide positional and photometric information for candidate counterparts to ∼95% of the GBS X-ray sources. This information in combination with optical photometry, spectroscopy and variability constraints will be crucial to characterize and classify secure counterparts. We also present the available GBS optical photometry, near-infrared as well as optical variability data, and some initial spectroscopic results. In the second part, we search for white dwarfs in a region of the sky known as the Kepler field. The Kepler mission provides superior time series photometry of a 116 deg2 field. In order to search for white dwarfs, we carried out our own survey, the Kepler- INT Survey (KIS), using the U, g, r, i and Hα filters, reaching down to ∼ 20th mag. Our second data release catalogue contained ∼14.5 million sources and covered ∼97% of the field. Using KIS, we selected white dwarf candidates on the basis of their colours, which were then confirmed via optical spectroscopy. We discovered 43 new white dwarfs, including six pulsating hydrogen-atmosphere white dwarfs. Asteroseismology is the only way to probe the interiors of the stars thus finding more pulsators is crucial. We obtained short-cadence Kepler observations of four of our pulsating white dwarfs: KIC11911480, KIC10132702, KIC0435037 and KIC07594781. All four have pulsation periods within the expected range for this type of variable white dwarfs. They also all confirm that white dwarfs are slow rotators, with rotation periods in the order of days. We end this Thesis with the full asteroseismic analysis of KIC11911480, our first ZZCeti in the Kepler field.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QB Astronomy