This thesis reports photometric and spectroscopic studies of three close binary systems; BP Velorum, V392 Carinae and V752 Centauri. BP Velorum, a W UMa-type binary, was observed photometrically in February 2007. The light curves in four filters were fitted simultaneously with a model generated in the eclipsing binary modeling software package PHOEBE. The best model was one with a cool star spot on the secondary larger component. The light curves showed additional cycle-to-cycle variations near the times of maximum light which may indicate the presence of star spots that vary in strength and/or location on a time scale comparable with the orbital period, (P = 0.265 d). The system was confirmed to belong to the W-type subgroup of W UMa binaries for which the deeper primary minimum is due to an occultation. V392 Carinae, a detached binary with an orbital period of 3.147 d, was observed photometrically by Michael Snowden in 1997. These observations were reduced and combined with the published light curve from Debernardi and North (2001). High resolution spectroscopic images were taken using the University of Canterbury's HERCULES spectrograph. The radial velocities measured from these observations were combined with velocities from Debernardi and North (2001). The radial velocity and light curves were fit simultaneously, confirming that V392 Car is a detached system of two main sequence A stars with a mass-ratio of 0.95. The derived systematic velocity is consistent with V392 Car being a member of the open cluster NGC 2516. The W UMa-type binary V752 Centauri was observed photometrically and spectroscopically during 2007. The high resolution spectra displayed weak sharp lined features superimposed over the strong broad lined spectrum expected from the 0.370 d contact binary. Fourier methods were used to separate the broad and sharp spectral features and radial velocities for each were measured by cross-correlation. A fit to the photometry and radial velocities for the contact binary implied a system of two late F stars with a mass-ratio of 3.38 in an over-contact configuration. The derived systematic velocity (−13.8km/s), has changed significantly from the 1972 value (29.2km/s). The third (sharp lined) component's radial velocities were measured and found to have a period of 5.147 d, semi-amplitude of 43.4km/s and systematic velocity of −7.3km/s. The likely configuration of the entire system is that of a contact binary in a long period orbit about a lower mass detached binary. V752 Cen is thus a triple lined spectroscopic quadruple.

Περίπου το 70% των αστέρων που παρατηρούνται στο σύμπαν είναι μέλη πολλαπλών συστημάτων και η μελέτη τους είναι υψίστης σημασίας για τους αστρονόμους τις τελευταίες δεκαετίες. Τα διπλά εκλειπτικά συστήματα προσφέρουν μοναδικές δυνατότητες μελέτης των αστρικών παραμέτρων και κατ’ επέκταση των θεωριών εξέλιξης εξαιτίας της γεωμετρίας τους και αποτελούν τη βάση της μεθόδου προσδιορισμού αστρονομικών αποστάσεων ως «πρότυπα κεριά» (standard candles). Στην παρούσα εργασία πραγματοποιείται η μοντελοποίηση των καμπυλών φωτός 36 λαμπρών αποχωρισμένων διπλών εκλειπτικών συστημάτων που παρατηρήθηκαν κατά την τρίτη φάση του προγράμματος OGLE στο Μεγάλο Νέφος του Μαγγελάνου και εξάγονται οι φωτομετρικές τους παράμετροι, ώστε τα πιο ενδιαφέροντα από αυτά να επιλεχθούν για περαιτέρω φασματοσκοπικές παρατηρήσεις ως υποψήφιοι δείκτες απόστασης. Στο πρώτο κεφάλαιο πραγματοποιείται μία εισαγωγή στους μεταβλητούς αστέρες, μία αναφορά στην ταξινόμηση των διπλών εκλειπτικών συστημάτων σύμφωνα με το μοντέλο Roche και με τη μορφή της καμπύλης φωτός τους καθώς και στοιχεία που αφορούν τη γεωμετρία τους και τις εξισώσεις της τροχιάς τους. Στο δεύτερο κεφάλαιο περιγράφεται το πρόγραμμα OGLE (Optical Gravitational Lensing Experiment) σκοπός του οποίου είναι η ανίχνευση συμβάντων βαρυτικής μικροεστίασης με κύριους στόχους τα Νέφη του Μαγγελάνου, το Γαλαξιακό Δίσκο και την Κεντρική Περιοχή του Γαλαξία. Ως αποτέλεσμα της χαρτογράφησης των πεδίων αυτών είναι η δημιουργία μίας μεγάλης βάσης δεδομένων μεταβλητών αστέρων για περεταίρω μελέτη. Στο τρίτο κεφάλαιο περιγράφεται αναλυτικά το πρόγραμμα PHOEBE (PHysics Of Eclipsing BinariEs) με το οποίο πραγματοποιήθηκε η μελέτη των καμπυλών φωτός των 36 συστημάτων. Το πρόγραμμα αυτό αποτελεί μία βελτιωμένη έκδοση του προγράμματος WD (Wilson & Devinney 1979) που στηρίζεται στη μέθοδο των διαφορικών διορθώσεων για της εξαγωγή των φωτομετρικών παραμέτρων των συστημάτων. Τέλος στο τέταρτο κεφάλαιο παρουσιάζεται η μέθοδος επιλογής των 36 διπλών εκλειπτικών συστημάτων που μελετήθηκαν, ο προσδιορισμός των βασικών παραμέτρων που εισήχθησαν στο πρόγραμμα, οι φωτομετρικές παράμετροι που διεξήχθησαν καθώς και τα επιστημονικά συμπεράσματα της μελέτης. / Over 70% of the stars in the universe are components of multiple systems. The study of these systems is crucial for the astronomers over the last decades because their parameters can be derived due to their geometry and assumptions can be made about stellar evolution. Moreover these systems are very promising for measuring distances in the universe as “standard candles”. In the present work 36 DEBs were chosen from the third phase of OGLE program from the Large Magellanic Cloud and Light Curve modeling was held via PHOEBE program which is an improved version of WD code (Wilson & Devinney 1979). Photometric parameters of these systems were derived so that the most interesting of these would be potential targets for further spectroscopic observations as distance indicators for the Large Magellanic Cloud.

Starspots are not well understood for contact binary star systems. The following properties of spots were systematically investigated: temperature, radius, colatitude, and longitude. Spots were modeled on an AE Phe like contact binary system. The spots were changed in a systematic manner. The light curve phases of primary minimum and primary maximum were affected by these parameter changes in a systematic manner, as well as the secondary minimum and maximum. It will be shown that it is possible to use the shift in these phases to study starspots over time. This information can also be used to identify the presence of spots in binary star systems.Starspots on contact binary systems are not commonly found at a longitude near 180°. The results of this study show that starspots near 180° should be the easiest to detect using photometric techniques. This is the most significant result from this study. Either there is an unknown physical reason why contact binary stars do not have starspots near a longitude of 180°, or the starspots are there and the photometric data has been misinterpreted. / Department of Physics and Astronomy

This thesis reports photometric and spectroscopic studies of three close binary systems; BP Velorum, V392 Carinae and V752 Centauri. BP Velorum, a W UMa-type binary, was observed photometrically in February 2007. The light curves in four filters were fitted simultaneously with a model generated in the eclipsing binary modeling software package PHOEBE. The best model was one with a cool star spot on the secondary larger component. The light curves showed additional cycle-to-cycle variations near the times of maximum light which may indicate the presence of star spots that vary in strength and/or location on a time scale comparable with the orbital period, (P = 0.265 d). The system was confirmed to belong to the W-type subgroup of W UMa binaries for which the deeper primary minimum is due to an occultation. V392 Carinae, a detached binary with an orbital period of 3.147 d, was observed photometrically by Michael Snowden in 1997. These observations were reduced and combined with the published light curve from Debernardi and North (2001). High resolution spectroscopic images were taken using the University of Canterbury's HERCULES spectrograph. The radial velocities measured from these observations were combined with velocities from Debernardi and North (2001). The radial velocity and light curves were fit simultaneously, confirming that V392 Car is a detached system of two main sequence A stars with a mass-ratio of 0.95. The derived systematic velocity is consistent with V392 Car being a member of the open cluster NGC 2516. The W UMa-type binary V752 Centauri was observed photometrically and spectroscopically during 2007. The high resolution spectra displayed weak sharp lined features superimposed over the strong broad lined spectrum expected from the 0.370 d contact binary. Fourier methods were used to separate the broad and sharp spectral features and radial velocities for each were measured by cross-correlation. A fit to the photometry and radial velocities for the contact binary implied a system of two late F stars with a mass-ratio of 3.38 in an over-contact configuration. The derived systematic velocity (−13.8km/s), has changed significantly from the 1972 value (29.2km/s). The third (sharp lined) component's radial velocities were measured and found to have a period of 5.147 d, semi-amplitude of 43.4km/s and systematic velocity of −7.3km/s. The likely configuration of the entire system is that of a contact binary in a long period orbit about a lower mass detached binary. V752 Cen is thus a triple lined spectroscopic quadruple.

No description available.

W Ursae Majoris-type (W UMa-type) variable stars are contact eclipsing binary stars whose evolution is unknown. Modelling to determine the physical parameters of as many W UMa-type variable stars as possible might provide some insight as to how these contact binaries form and evolve. The All Sky Automated Survey (ASAS) has discovered over ve thousand of these systems. Using data from the ASAS and from the Wide Angle Search for Planets (SuperWASP) project, models of selected ASAS contact binaries are being created to determine their physical parameters. Some W UMa-type variable stars are known to undergo changes in orbital period. For selected ASAS contact binaries, a period analysis has been performed using SuperWASP data to determine if the systems are undergoing changes in orbital period. Results of the modelling and period analyses of selected systems are presented. / Thesis (M. Sc. (Astronomy))

In this investigation of near-contact binary stars, the author fit a synthetic light, computer generated, curve model to observations by adjusting various parameters of two near-contact binary pairs, CN Andromeda and TZ Draconis. By fitting asymmetries in the light curves using spotting parameters, the spotting activity for both stars can be determined. From the spotting parameters it is possible to compare the spotting activity of these two near-contact binaries to the spotting activity of 47 contact binaries (Csizmadia et al., 2004). The author determined that, for both TZ Dra and CN And, spots are located at positions that were previously not seen in other observations of contact binaries (Hill, 2007). / Department of Physics and Astronomy

Η παρούσα εργασία έχει ως θέμα τη φωτομετρική μελέτη δύο διπλών εκλειπτικών συστημάτων: της V380 Cas και του TZ Boo, με το 14΄΄ τηλεσκόπιο του Εργαστηρίου Αστρονομίας του Τμήματος Φυσικής του Πανεπιστημίου Πατρών μέσα από την κατασκευή της καμπύλης φωτός σε πολλά φίλτρα αλλά και την κατασκευή και τη μελέτη των O-C διαγραμμάτων τους. Τα πρώτα τρία κεφάλαια αναφέρονται σε γενικότερα θέματα που αφορούν στη φυσική των διπλών αστρικών συστημάτων, τις τεχνικές παρατήρησης τους καθώς και την ανάλυση μέσω των διαγραμμάτων O-C. Τα επόμενα δύο κεφάλαια αναφέρονται στην ανάλυση των δυο παρατηρηθέντων συστημάτων: της V380 Cas, που είχε ταξινομηθεί ως Algol type και του ΤΖ Βοο, τύπου W-Ma. Το κάθε κεφάλαιο περιέχει : τις παρατηρήσεις, την ανάλυση, τα μοντέλα και τις εξαγόμενες παραμέτρους αυτού του συστήματος καθώς και την ανάλυση του διαγράμματος O-C. Τα νέα φωτομετρικά δεδομένα του 2010 στα φίλτρα BVRI του TZ Boo -ενός εκλειπτικού διπλού συστήματος σε επαφή τύπου W UMa-σε συνδυασμό με δημοσιευμένες φασματοσκοπικές παρατηρήσεις, οδήγησαν στην πρώτη φωτομετρική λύση του με το πρόγραμμα PHOEBE. Οι συνθετικές καμπύλες, που δημιουργήθηκαν για να ταιριάξουν στα ιδιαίτερα χαρακτηριστικά των φωτομετρικών καμπύλων περιλαμβάνουν μια ψυχρή κηλίδα στον πρωτεύοντα αστέρα και η μικρή αναλογία των μαζών του συστήματος δείχνει ότι το σύστημα είναι σε στενή επαφή με f=52.5% και ανήκει στην Α-υποκατηγορία.. Με βάση τα 7 νέα ελάχιστα και όλα τα προηγούμενα της βιβλιογραφίας σε σύνολο 70 ετών, μελετήθηκε η μακρόχρονη μεταβολή της τροχιακής του περιόδου από το O-C διάγραμμα. Παρατηρήθηκε μια κυκλική μεταβολή της περιόδου 31,2 ετών, με πλάτος 0,033 ημερών και επιπρόσθετα μια μείωση με ρυθμό dP/dt = -2,1 x 10-8 ημέρες /έτος. Η κυκλική αλλαγή της περιόδου πιθανόν υποδηλώνει ότι το διπλό εκλειπτικό σύστημα TZ Boo είναι τριπλό ή τετραπλό σύστημα, σε συμφωνία με τα τελευταία φασματοσκοπικά δεδομένα. Η μακροχρόνια μείωση της περιόδου με την απώλεια μάζας και στροφορμής έχει ως αποτέλεσμα την αύξηση του βαθμού επαφής και τελικά την εξέλιξη του συστήματος σε έναν ταχέως περιστρεφόμενο αστέρα. Ο μεταβλητός αστέρας V0380 Cas παρατηρήθηκε από τον Ιούνιο του 2009 έως τον Ιούλιο του 2010 και οι πλήρεις καμπύλες φωτός στα φίλτρα BVRI παρουσιάζονται για πρώτη φορά μαζί με νέα ελάχιστα για την εύρεση της περιόδου του. Κανένα δευτερεύον ελάχιστο δεν παρατηρήθηκε. Με το πρόγραμμα PHOEBE δημιουργήθηκε για πρώτη φορά φωτομετρική λύση. Το σύστημα πιθανόν να είναι αποχωρισμένο με διπλάσια περίοδο από την αναφερόμενη στη βιβλιογραφία και τα δύο μέλη να έχουν την ίδια θερμοκρασία. Παρουσιάζεται το πρώτο O-C διάγραμμα με την ανανεωμένη εφημερίδα του συστήματος βασισμένο σε 11 νέα ελάχιστα και 11 παλαιότερα της βιβλιογραφία μόνο από CCD παρατηρήσεις. Επίσης εξετάζεται η πιθανότητα ύπαρξης τρίτου σώματος και από την φωτομετρική λύση αλλά και από το διάγραμμα O-C. / The thesis reports photometric studies of two eclipsing binaries V380 Cas and TZ Boo Cas with the 14΄΄ telescope of the Astronomical Laboratoy of the University of Patras, Observatory and longterm analysis of their O-C diagrams. The first three chapters of the thesis are devoted to acquainting a general science background to eclipsing binaries, observational techniques and modeling of light curves. The subsequent two are each devoted to the analysis of two systems, V380 Cas, a previous classified as Algol type and ΤΖ Βοο , a W-Ma type with each chapter arranged as follows : observations, analysis, collected data, models and derived parameteters for each system are discussed in context to previous reseachers. The light curves of TZ Boo, a W UMa type binary, in BVRI filters were fitted simultaneously with a model generated in the eclipsing binary modeling software package PHOEBE and the first modern photometric solution is deduced from new photometric observations and published spectroscopic data. This low mass ratio binary turns out to be a deep overcontact system with f=52.5% of A-subtype. A conservative spot model has been applied to fit the particular features of light curves. Based on our 7 new light minimum times and all others compiled from the literature over 70 years, we studied the orbital period from the O-C curve. It is found that there exists a 31.2 yr cyclic variation with an amplitude of 0.033 days, overlaying a secular decrease at a rate of dP/dt = -2.1 x 10-8 days/year. The cyclic period change may indicate that TZ Boo is a triple or a quadruple system as suggested from the published spectroscopic data. The long term orbital period decrease, accompanying mass and angular momentum loss would cause the overcontact degree to increase and finally the binary will evolve into a single rapid -rotation star V380 Cas was observed photometrically in June-July 2009 -2010 and its complete light curves are presented for the first time in BVRI filters along with new minima and its period investigation. No secondary minimum has been detected. The PHOEBE program is used to provide the first photometric solution. The system is probably a detached one with equal components and double period. The first O-C analysis of the system based on timings of minima up to date, is presented and a new ephemeris is estimated. Also the probability of third light is excluded from both the O-C and photometric solution.

W Ursae Majoris-type (W UMa-type) variable stars are contact eclipsing binary stars whose evolution is unknown. Modelling to determine the physical parameters of as many W UMa-type variable stars as possible might provide some insight as to how these contact binaries form and evolve. The All Sky Automated Survey (ASAS) has discovered over ve thousand of these systems. Using data from the ASAS and from the Wide Angle Search for Planets (SuperWASP) project, models of selected ASAS contact binaries are being created to determine their physical parameters. Some W UMa-type variable stars are known to undergo changes in orbital period. For selected ASAS contact binaries, a period analysis has been performed using SuperWASP data to determine if the systems are undergoing changes in orbital period. Results of the modelling and period analyses of selected systems are presented. / Thesis (M. Sc. (Astronomy))

La mesure des distances aux galaxies proches de notre Voie Lactée a révolutionné notre compréhension de l'échelle de distance et a fourni la preuve de l'expansion de l'univers. Notamment les distances aux Petit et Grand Nuages de Magellan sont deux échelons essentiels de l'échelle des distances cosmiques. De nombreuses méthodes indépendantes (comme celle des RR Lyrae, des Céphéides ou des étoiles Red clump) ont été utilisées pour déterminer ces distances. Le but de mon travail de thèse est d'améliorer notre compréhension de la relation BSC grâce à l'interférométrie optique. Pour cela, j'ai utilisé l'instrument VEGA installé sur l'interféromètre CHARA. Cet instrument fonctionne dans le visible et bénéficie de la plus longue base du monde. VEGA a une résolution spatiale de 0.3 mas, ce qui en fait un outil idéal pour une détermination précise des diamètres des étoiles. Dans un premier temps j'ai déterminé le diamètre de huit étoiles de type OBA avec une précision moyenne de 1.5%. Ensuite j'ai combiné ces diamètres avec d'autres mesures collectées dans la littérature pour ainsi donner une nouvelle relation BSC pour ce type d'étoiles. Dans un second temps, une étude théorique de l'impact de rotation sur la relation BSC a été faite pour comprendre les effets physiques influant sur la précision de cette relation de manière à compenser la dispersion existant actuellement et ce dans le but d'améliorer encore la précision sur les distances extragalactiques. / Measuring distances separating our own Galaxy from nearby ones revolutionized our understanding of the distance scale and provided the evidence for the expansion of the universe. The distances to the Small and Large Magellanic Clouds are critical steps of the cosmic distance ladder, and they have been determined using numerous independent methods (as, RR Lyrae stars, Cepheids and "red clump" stars). The aim of my thesis work is to improve our understanding of the Surface Brightness-Color relation (SBC) using optical interferometry. For this, we use the interferometer VEGA on CHARA. This instrument operates in the visible and benefits from the baselines of the CHARA interferometer. It has a spatial resolution of 0.3 mas, which makes it an ideal tool to determine diameters of stars. At first I determined the diameter of eight OBA-type stars with an average accuracy of 1.5%. Then I combined these diameters with others collected from the literature, to determine a new SBC relation for this type of stars. In a second step, a theoretical study of the impact of the rotation on the SBC relation was made to understand the physical effects affecting the accuracy of this relation and suppress the currently existing dispersion in order to further improve the accuracy of extragalactic distances.