New CCD photometric observations of ten short-period LMB (Low Mass Binaries) were carried out. Data were obtained using 65 cm telescope in Ondřejov in the filters I, R and V from 2014 to 2016. Light curves were analysed using the program PHOEBE. The obtained masses and radii of the stars were compared with the theoretical mass-radii relation. There arises that the short-period binaries have the radii of about 4 % larger than the theoretical prediction from the stellar evolution models. Powered by TCPDF (www.tcpdf.org)

Η μελέτη των διπλών εκλειπτικών συστημάτων παραμένει ένα από τα πιο ενδιαφέροντα ερευνητικά πεδία της αστροφυσικής γιατί παρέχει την πιο ακριβή μέθοδο υπολογισμού των βασικών αστρικών μεγεθών (μαζών, ακτίνων, θερμοκρασιών) αλλά και κάθε μορφής αστρικής δραστηριότητας που αναπτύσσεται (κηλίδες, δίσκοι προαύξησης ύλης, αναπάλσεις) μέσα από τη μακρόχρονη μεταβολή της περιόδου τους. Επιπλέον επιτρέπει τον έλεγχο των θεωριών αστρικής εξέλιξης μέσα από την αλληλεπίδρασή τους αλλά και την πρόβλεψη παρουσίας τρίτων σωμάτων αστρικής ή μη φύσης. Σε αυτήν τη διατριβή μελετάται μία ιδιαίτερη κατηγορία διπλών εκλειπτικών συστημάτων σε επαφή, τα W UMa τα οποία αποτελούνται από αστέρες κύριας ακολουθίας οι οποίοι βρίσκονται σε υπερεπαφή, και χαρακτηρίζονται από τις μικρότερες περιόδους κι άρα από τη μικρότερη στροφορμή. Σκοπός της είναι τόσο η παρατηρησιακή μελέτη και ανάλυση συστημάτων W UMa που παρουσιάζουν ιδιαίτερο ενδιαφέρον όσο και η ανάγκη ανάπτυξης μεθοδολογίας μοντελοποίησης για την εξαγωγή της μέγιστης πληροφορίας και ελέγχου των εξαγόμενων φυσικών παραμέτρων κάτω από την εφαρμογή σύγχρονων στατιστικών μεθόδων. Το πρώτο μέρος της επικεντρώνεται στη σκιαγράφηση του θεωρητικού επιστημονικού πλαισίου περιγραφής των διπλών εκλειπτικών αστρικών συστημάτων σε επαφή. Το Κεφάλαιο1 αναφέρεται στη γεωμετρία των τροχιών και στη φυσική των αστέρων του συστήματος, στην περιγραφή του μοντέλου Roche και στην αλληλεπίδραση των μελών καθώς και στη δυναμική των συστημάτων όπως αυτή εκδηλώνεται από την παρατηρούμενη μεταβολή της περιόδου του. Το Κεφάλαιο 2 αναφέρεται στις φωτομετρικές παρατηρήσεις που έγιναν κατά την διάρκεια της παρούσας διατριβής καθώς και στις αυτοματοποιημένες μεθόδους επεξεργασίας και ανάλυσης των παρατηρησιακών αστρονομικών δεδομένων οι οποίες αναπτύχθηκαν. Το Κεφάλαιο 3 περιγράφει τις σύγχρονες τεχνικές μοντελοποίησης και τα προγράμματα ανάλυσης για τηλύση του αντίστροφου προβλήματος. Το Κεφάλαιο 4 περιγράφει την αναζήτηση, εξόρυξη και αυτόματη ανάλυση δεδομένων από παρατηρησιακές αστρονομικές επισκοπήσεις και την εφαρμογή του κώδικα τεχνητών νευρωνικών δικτύων EBAI. Το δεύτερο μέρος επικεντρώνεται στην αναλυτική μελέτη επιλεγμένων στενών διπλών συστημάτων W UMa με ιδιαίτερο ενδιαφέρον. Σε όλα τα επιλεγμένα συστήματα παρουσιάζεται η φωτομετρική τους μελέτη κάτω από το φως νέων BV RcIc παρατηρήσεων, η μελέτη της περιόδου, το εξαγόμενο μοντέλο σε συνδυασμό με φασματοσκοπικά δεδομένα, ο προσδιορισμός τροχιακών και φυσικών παραμέτρων και η θέση τους σε εξελικτικά διαγράμματα. Επίσης γίνεται η διερεύνηση του προτεινόμενου μοντέλου για μοναδικότητα στο χώρο των λύσεων μέσα από σάρωση με εισαγωγή διαταραχών ή άλλων στατιστικών μεθόδων και ο στατιστικός προσδιορισμός των σφαλμάτων των παραμέτρων. Συγκεκριμένα στο Κεφάλαιο5 παρουσιάζεται το ενοποιημένο μοντέλο του συστήματος TY Boo δύο κηλίδων που ερμηνεύει τη συμπεριφορά του την περίοδο 1969-2011 και τη μελέτη της περιόδου του. Σύμφωνα με αυτό το σύστημα TY Boo ανήκει στην υποκατηγορία W των W UMa με μικρό βαθμό επαφής f = (7.6 ±0.8)% και η μακρόχρονη μελέτη της περιόδου του δείχνει μακροχρόνια μείωση (dP/dt = −3.65x10^−8 d yr^−1 ) και μία περιοδικότητα (P3 = 58.9yrs, A = 0.0254 days)η οποία, χωρίς να αποκλείεται η παρουσία τρίτου σώματος, ερμηνεύεται με ενεργό μαγνητικό κύκλο που προκαλεί την εμφάνιση κηλίδων.Στο Κεφάλαιο 6 παρουσιάζεται για πρώτη φορά η λεπτομερής ανάλυση του συστήματος WUMa, FI Boo το οποίο ταξινομείται στην υποκατηγορία W, με βαθμό επαφής f = (50.15 ±8.10) %, κάτω από την παρουσία τρίτου σώματος το οποίο μπορεί να παίζει σημαντικό ρόλο στη δημιουργία και την εξέλιξή του. Σύμφωνα με το προτεινόμενο μοντέλο προσδιορίζονται οι μάζες Mh =0.40 ± 0.05 Msun , Mc =1.07 ± 0.05 Msun , και οι θερμοκρασίες Th = 5746±33Κ, Tc = 5420±46 Κ των αστέρων-μελών του καθώς και των προγεννητόρων τους (1.71 ±0.10 Msun και 0.63 ± 0.01 Msun , αντίστοιχα) και διερευνάται το εξελικτικό στάδιο του αστέρα με τη μεγαλύτερη μάζα μέσα από ισόχρονες.Στο Κεφάλαιο 7 διερευνάται σε βάθος το σύστημα σε επαφή V1003 Her, το οποίο χαρακτηρίζεται από μεταβολή μικρού πλάτους, με πολλαπλά μοντέλα για τα οποία ελέγχεται η σταθερότητα των με ανεξάρτητες μεθόδους. Το επικρατέστερο από αυτά δείχνει ότι το σύστημα είναι W UMa με βαθμό επαφής f = (36±10) %, με ασυνήθιστα άνισες θερμοκρασίες μεταξύ των αστέρων του 550 Κ, και λόγο μαζών q = 0.373. Η μικρή του κλίση i = 38^o ±1^ο το καθιστά ένα από τα μεγαλύτερης μάζας στην υποκατηγορίας W.Στο Κεφάλαιο 8 εξετάζεται η φύση του διπλού συστήματος HI Dra, η λεπτομερής ανάλυση του οποίου δείχνει ότι είναι W UMa με μικρό βαθμό επαφής f = (24 ± 4) % και διαφορά θερμοκρασίας μεταξύ των αστέρων του 330 Κ. Προτείνονται και διερευνώνται εξονυχιστικά δύο μοντέλα με κηλίδες από τα οποία επικρατέστερο, με ψυχρή κηλίδα πάνω στον μικρότερης μάζας και ψυχρότερο αστέρα- τον τοποθετεί στην υποκατηγορία Α. Προσδιορίζονται οι φυσικές παράμετροι των μελών του (M = 1.72 ± 0.08Msun , Mc = 0.43 ± 0.02 Msun , Rh =1.98 ± 0.03Rsun , Rc = 1.08 ± 0.02 Rsun , Lh = 9.6 ± 0.1 Lsun , Lc = 2.4 ± 0.1 Lsun ) και των προγεννητόρων τους (1.11 ± 0.03 Msun και 2.25 ± 0.07 Msun, αντίστοιχα) και προσεγγίζεται η ηλικία του συστήματος σε 2.4 Gyr .Τέλος στο Κεφάλαιο 8 παρουσιάζονται τα πρώτα αποτελέσματα από τις φωτομετρικές παρατηρήσεις με το τηλεσκόπιο Αρίσταρχος 2.3 m, διπλών εκλειπτικών συστημάτων με ιδιαίτερο ενδιαφέρον που ανακαλύφθηκαν ή παρατηρήθηκαν από την διαστημική αποστολή Kepler με περιόδους περιφοράς < 0.45 d, τα οποία παρουσιάζουν ασυμμετρίες στην καμπύλη φωτός, χρονικές μεταβολές των εκλείψεων των μελών τους ή είναι εν δυνάμει τριπλά συστήματα. Τα πρώτα αποτελέσματα αφορούν τα συστήματα KIC 11246163 και KIC 4563150τα οποία ταξινομούνται ως συστήματα τύπου W UMa, W υποκατηγορίας με πιθανό τριτο συνοδό. / The study of eclipsing binary systems remains one of the most powerful research fields in stellar astrophysics because it provides the primary source of calculating fundamentals properties of stars (masses, radii, temperatures) and every form of stellar activity (spots, accreting discs, pulsations) through photometry and spectroscopy or/and through the study of long-term variability of their period. Additionally it allows testing of stellar structure and evolution theories and the prediction of third body companions of stellar or sub-stellar origin. This thesis is focused on the study of W UMa type eclipsing binaries containing main sequence stars in overcontact configuration with short periods and,therefore the small angular momentum. The aim is both the multiband observational study, analysis and investigation of WUMa systems of particular interest but also the development of modeling methodology in order to extract the maximum information and to determine a detailed assessment of the parameter uncertainties through the application of modern statistical methods. The first part of the Doctoral Thesis outlines the theoretical framework for describing eclipsing binary stars. Chapter 1 refers to the physics and geometry of orbits and components, the description of the Roche model that led to the classification based on equipotential surfaces, the computation of the total radiated flux in the direction of the observer by including all the corrections needed and the description of systems dynamics as manifested by the observed change of their period. Chapter2 presents the photometric observations made during this research and the automated methods of processing and analysis (pipelines) which were developed. Chapter 3 sketches the modern modeling and analysis software techniques for the solution of inverse problem(Differential Corrections, Levenberg-Marquardt, Downhill Simplex, Genetic Algorithms,Heuristic Scanning, Bootstrap resampling, Metropolis –Hasting Markov Chain MonteCarlo), their implementation to programs developed as part of the present thesis and their application to real data. These also represent the methodology of the analyses implemented for the study of the WUMa systems, described in Part 2. Finally, Chapter4 describes the development of a pipeline for the exploration, extraction and automatic analysis of data from astronomical surveys and its application to ASAS database. In the same chapter the first results from the training and validation of the Artificial Neural Network (ANN), EBAI, and the best topology for the ANN are presented.The second part focuses on the detailed study of selected W UMa systems with particular interest. This includes: the new multiband photometric observations, the longterm period variation, the exported model from photometric and spectroscopic data (from the literature), the determination of orbital and physical parameters and their position in evolutionary diagrams, the investigation of the proposed model for uniqueness in the parameter space through heuristic scanning with parameter kicking or other statistical methods- and the statistical determination of the uncertainties of the derived parameters.In Chapter 5, new CCD four-color light curves of TY Boo made on eight nights over2010–2011 were analyzed in comparison with historical light curves obtained from 1969through 2011. The light curves could all be represented by a unique geometry and by wavelength consistent phototometric parameters of a two-spot model on either stellar component. It is confirmed that TY Boo is a shallow W-type contact binary system with a degree of contact factor of f = 7.6 ± 0.8%. A period investigation based on all available data shows a long-term decrease (dP/dt = −3.65 ×10−8 days yr−1 ) and an oscillation (P3 = 58.9 yr, A = 0.0254 days). Without ruling out the presence of a tertiary companion, the weight of evidence points to an active cyclic magnetic activity that causes spot formation rather than an unseen companion. Mass transfer between the components and angular momentum loss are also considered as possible mechanisms.In Chapter 6, a detailed analysis of the interesting W UMa binary FI Boo in view of the spectroscopic signature of a third body through photometry, period variation, and a thorough investigation of solution uniqueness is presented. We obtained new BVRcIc photometric data that, when combined with spectroscopic data, enable us to analyze the system FI Boo and determine its basic orbital and physical properties through PHOEBE,as well as the period variation by studying the times of the minima. This combined approach allows us to study the long-term period changes in the system for the first time in order to investigate the presence of a third body and to check extensively the solution uniqueness and the uncertainties of derived parameters. Our modeling indicates that FIBoo is a W-type moderate (f = 50.15% ± 8.10%) overcontact binary with component masses of Mh = 0.40 ± 0.05 M and Mc =1.07 ± 0.05 M , temperatures of Th = 5746 ±33 K and Tc = 5420 ± 56 K, and a third body, which may play an important role in the formation and evolution. The results were tested by heuristic scanning and parameter kicking to provide the consistent and reliable set of parameters that was used to obtain the initial masses of the progenitors (1.71 ± 0.10 M and 0.63 ± 0.01 M , respectively). We also investigated the evolutionary status of massive components with several sets of widely used isochrones.In Chapter 7, an extensive analysis of the low amplitude, contact binary V1003 Her is presented, based on the new VRc Ic , CCD photometric light curves in combination with published radial velocity (RV) curves. We investigate the stable configurations for the system with two independent methods and modeling tools: PHOEBE, ROCHE, via heuristic scanning and genetic algorithms, although the very low inclination of the system can place limitations. All methods indicate that V1003 Her is most likely in overcontact state with unequal components with temperature difference of 550 K, a mass ratio of q= 0.373 and a contact degree of 36 ± 10 %. As it is viewed at the very low inclination of i ∼ 38^◦ ± 1^◦ , if its configuration is confirmed, it will be among the most massive W-subtype of W UMa systems. This conclusion is also supported by other published models.However, in order to conclude reliable physical properties of the system, the high-precise based-ground photometry (or satellite photometry) and spectroscopic follow-up of V1003Her is required.In Chapter 8, a detailed investigation of the low-amplitude contact binary HI Dra is presented, based on the new VRc Ic CCD photometric light curves (LCs) combined with published radial velocity (RV) curves. Our completely covered LCs were analyzed using PHOEBE and revealed that HI Dra is an overcontact binary with low fill-out factor f = 24 ± 4 (%) and temperature difference between the components of 330 K.Two spotted models are proposed to explain the LC symmetry, between which the A subtype of W UMa type eclipsing systems, with a cool spot on the less massive and cooler component, proves to be more plausible on evolutionary grounds. The results and stability of the solutions were explored by heuristic scan and parameter perturbation to provide a consistent and reliable set of parameters and their errors. Our photometric modeling and RV curve solution give the following absolute parameters of the hot and cool components, respectively: Mh = 1.72 ± 0.08 Msun and Mc = 0.43 ± 0.02 Msun , Rh =1.98 ± 0.03 Rsun and Rc = 1.08 ± 0.02 Rsun , and Lh = 9.6 ± 0.1 Lsun and Lc = 2.4 ± 0.1Lsun . Based on these results the initial masses of the progenitors (1.11 ± 0.03 Msun and2.25 ± 0.07 Msun , respectively) and a rough estimate of the age of the system of 2.4 Gyr are discussed.Finally, in Chapter 9, our first results from ground based follow up photometric observation of interesting eclipsing binary systems (EBs) from Kepler field are presented.The program was launched in 2013 with the 2.3 m Aristarchos telescope at Helmos Observatory, Greece including eclipsing binary systems with periods < 0.45d and Kp (mag)=12.6-16 mag. The included targets in this program show light curve asymmetries,Eclipse Timings Variation or they are third body candidates. Modern analysis techniques such as heuristic scanning with parameter perturbation and genetic algorithm(PIKAIA), enable to reveal and optimize the astrophysical parameters of selected EBs.The results from BVRI photometry for the third body candidates, WUMa eclipsing binary systems of W-subtype, KIC11246163 and KIC4563150, are presented for the first time, as well as conclusions derived so far.

Made available in DSpace on 2015-03-03T15:16:25Z (GMT). No. of bitstreams: 1 SauloCM_TESE.pdf: 2950789 bytes, checksum: d10187bfbd3f161c4305c3a9fa050100 (MD5) Previous issue date: 2011-08-18 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Sessenta e cinco sistemas bin?rios eclipsantes, identificados nos objetivos da miss?o espacial CoRoT, foram selecionados para a an?lise. Destes, cinquenta e nove curvas de luz fotom?tricas que foram analisadas e processadas neste estudo s?o curvas crom?ticas (simultaneamente observadas nos tr?s filtros azul, verde e vermelho do sat?lite), fornecendo uma importante informa??o que ajuda a distinguir falsos positivos e genu?nos sistemas bin?rios eclipsantes. Neste sentido, este estudo fornece um cat?logo de sistemas bin?rios eclipsantes com suas respectivas solu??es fotom?tricas, baseadas nas curvas de luz CoRoT. Os sistemas selecionados incluem ambos, sistemas de n?o contato e de contato para os quais s?o apresentados uma variedade de par?metros f?sicos, incluindo per?odo orbital, o ?ngulo de inclina??o da orbita, raz?o de temperaturas, raz?o de raios e raz?o de luminosidades. Em adicional, e poss?vel estimar, aproximadamente, os par?metros absolutos de tais sistemas tomando como refer?ncia os valores t?picos a partir dos tipos espectrais conhecidos. O trabalho contribui para um aumento significativo no n?mero e na diversidade de sistemas bin?rios eclipsantes estudados a partir da base de dados CoRoT

Magnetic fields are important for multiple physical processes in and around stars, for these reasons improving the understanding of how they are generated and maintained is of great value. In this work the magnetic field structure of the eclipsing binary UV Piscium is investigated. This is done by utilising the Zeeman-Doppler Imaging technique that reconstructs stellar magnetic maps by combining the information of how the magnetic field affects spectral lines with the rotational modulation of spectral lines. In order to improve the signal-to-noise ratio the least squares deconvolution technique was used to combine multiple spectral lines into an average line profile. The high resolution circular polarisation observations analysed in this work were taken by the ESPaDOnS spectograph at the Canada-France-Hawaii Telescope during August and September of 2016. We reconstructed detailed magnetic field maps and obtained the average magnetic field strengths of 137G for the primary and 88G for the secondary, which is not unusual values for stars of this type. The methods used are however likely to underestimate the magnetic field strengths. This is because the lack of linear polarisation profiles likely results in systematic underestimation of magnetic field strengths, especially meridional components. Another issue that became apparent in this work is that in eclipsing binaries, without linear polarisation observations, there is a degeneracy between the different hemispheres, resulting in further uncertainties in the determination of surface magnetic field geometry. We also found that there is indication of surface evolution on the time scale of months as some observations taken around fifty days earlier were could not be phased with the main data set.

The presence of a magnetic field is shown to affect the evolution and properties of stars. Hence, it is necessary to observe different types of stars to explore these effects. The detached eclipsing binary UV Piscium is the object of interest in this study, where a first step of analyzing its global magnetic field is done. The observational data was collected during 2016, at the 3.6-m Canada-France-Hawaii Telescope at Mauna Kea, Hawaii. The analysis of the magnetic field is based on the line-addition technique least-squares deconvolution (LDS) of the polarisation signatures, and the aim is to search for circular polarisation signals produced by the Zeeman effect. The result shows a strong circular polarisation signature for the primary star of the binary, which is a direct evidence for the presence of a magnetic field. In contrast to this, the secondary star only shows a weak signal of circular polarisation in one of the analysed observations and further analysis of its magnetic field is needed. The secondary goal of the project was to calculate the stellar masses of the binary. This is done by measuring the radial velocities of the two stars via the line profiles, and preforming an orbital fit. The results gave: M1= 1.0211 ± 0.0040 Msol and M2 = 0.7728 ± 0.0028 Msol.

In my PhD, I advanced the scientific exploration of the Next Generation Transit Survey (NGTS), a ground-based wide-field survey operating at ESO’s Paranal Observatory in Chile since 2016. My original contribution to knowledge is the development of novel methods to 1) estimate NGTS’ yield of planets and false positives; 2) disentangle planets from false positives; and 3) accurately characterise planets. If an exoplanet passes (transits) in front of its host star, we can measure a periodic decrease in brightness. The study of transiting exoplanets gives insight into their size, formation, bulk composition and atmospheric properties. Transit surveys are limited by their ability to identify false positives, which can mimic planets and out-number them by a hundredfold. First, I designed a novel yield simulator to optimise NGTS’ observing strategy and identification of false positives (published in Günther et al., 2017a). This showed that NGTS’ prime targets, Neptune- and Earth-sized signals, are frequently mimicked by blended eclipsing binaries, allowing me to quantify and prepare strategies for candidate vetting and follow-up. Second, I developed a centroiding algorithm for NGTS, achieving a precision of 0.25 milli-pixel in a CCD image (published in Günther et al., 2017b). With this, one can measure a shift of light during an eclipse, readily identifying unresolved blended objects. Third, I innovated a joint Bayesian fitting framework for photometry, centroids, and radial velocity cross-correlation function profiles. This allows to disentangle which object (target or blend) is causing the signal and to characterise the system. My method has already unmasked numerous false positives. Most importantly, I confirmed that a signal which was almost erroneously rejected, is in fact an exoplanet (published in Günther et al., 2018). The presented achievements minimise the contamination with blended false positives in NGTS candidates by 80%, and show a new approach for unmasking hidden exoplanets. This research enhanced the success of NGTS, and can provide guidance for future missions.

The theory of stellar evolution and stellar structure relies on the observation of stars in di erent phases of their evolutionary cycle. The relation between observations and theory can be strengthened by obtaining observational data of a large sample of stars in a particular evolutionary phase. The search for Cephei stars, as conducted in this study, can contribute to the sample of known Cephei stars, where these interesting stars are massive non-supergiant early B-type stars, displaying pulsating behaviour which is not well understood. Stars tend to form in clusters where it can therefore be expected that young massive stars can be found in open clusters. For this reason two young southern open clusters were observed in order to search for B-type pulsating stars. The region of NGC 6204 and Hogg 22 was observed over a period of thirteen nights in Johnson B, V and I bands. NGC 6204 is believed to be the oldest cluster of the two at a distance of 0.8 kpc while the much younger Hogg 22 is more distant at 2.8 kpc. These two open clusters are located 6 arcminutes apart which made it possible to observe them simultaneously with a 12.8 12.8 arcminute eld of view. The observations were done with the newly installed 1600 telescope of the North-West University, South Africa. In order to do a variability search, periodic stars need to be identi ed from the cluster data, where a typical data set may contain thousands of scienti c images. In addition to the main motivation for this study, a pipeline was created in order to automate the photometry and data reduction processes. A Lomb-Scargle transform was applied to the stellar light curves in order to identify periodic sources. 354 signi cantly periodic stars were identi ed from the 3182 observed stars. Amongst them, two new possible Cephei stars were found together with a possible slowly pulsating B star (SPB), and numerous eclipsing binary systems. By using photometry of this region obtained by Forbes & Short (1996), instrumental magnitudes were transformed to a standard system in order to compare photometry results. From the constructed colour magnitude diagram of the two clusters, it could be seen that some stars, indicated by Forbes & Short (1996) to be cluster members, were in fact eld stars belonging to neither cluster. The reduction and photometry pipeline was implemented successfully on the data set, which also highlighted the importance of instrumentation and correct data analysis procedures. Possible improvements were identi ed in order to overcome di culties experienced during this study. / Thesis (MSc (Space Physics))--North-West University, Potchefstroom Campus, 2013

The theory of stellar evolution and stellar structure relies on the observation of stars in di erent phases of their evolutionary cycle. The relation between observations and theory can be strengthened by obtaining observational data of a large sample of stars in a particular evolutionary phase. The search for Cephei stars, as conducted in this study, can contribute to the sample of known Cephei stars, where these interesting stars are massive non-supergiant early B-type stars, displaying pulsating behaviour which is not well understood. Stars tend to form in clusters where it can therefore be expected that young massive stars can be found in open clusters. For this reason two young southern open clusters were observed in order to search for B-type pulsating stars. The region of NGC 6204 and Hogg 22 was observed over a period of thirteen nights in Johnson B, V and I bands. NGC 6204 is believed to be the oldest cluster of the two at a distance of 0.8 kpc while the much younger Hogg 22 is more distant at 2.8 kpc. These two open clusters are located 6 arcminutes apart which made it possible to observe them simultaneously with a 12.8 12.8 arcminute eld of view. The observations were done with the newly installed 1600 telescope of the North-West University, South Africa. In order to do a variability search, periodic stars need to be identi ed from the cluster data, where a typical data set may contain thousands of scienti c images. In addition to the main motivation for this study, a pipeline was created in order to automate the photometry and data reduction processes. A Lomb-Scargle transform was applied to the stellar light curves in order to identify periodic sources. 354 signi cantly periodic stars were identi ed from the 3182 observed stars. Amongst them, two new possible Cephei stars were found together with a possible slowly pulsating B star (SPB), and numerous eclipsing binary systems. By using photometry of this region obtained by Forbes & Short (1996), instrumental magnitudes were transformed to a standard system in order to compare photometry results. From the constructed colour magnitude diagram of the two clusters, it could be seen that some stars, indicated by Forbes & Short (1996) to be cluster members, were in fact eld stars belonging to neither cluster. The reduction and photometry pipeline was implemented successfully on the data set, which also highlighted the importance of instrumentation and correct data analysis procedures. Possible improvements were identi ed in order to overcome di culties experienced during this study. / Thesis (MSc (Space Physics))--North-West University, Potchefstroom Campus, 2013

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