Dissertations / Theses on the topic 'Binary stellar evolution'

The effective use of statistical techniques is one of the cornerstones of modern astrophysics. In this thesis we use sophisticated statistical methodology to expand our understanding of astrophysics. In particular, we focus on the physics of coalescing binary black holes, and the observation of these events using gravitational-wave astronomy. We use Fisher matrices to explore how much we expect to learn from gravitational-wave observations, and then use machine learning techniques, including random forests and Gaussian processes, to facilitate an otherwise intractable Bayesian comparison of real observations to our model. Finally, we develop a technique based on Gaussian processes for characterising stochastic variability in time series data.

We report on a search for short -period binary systems composed of pairs of evolved stars. The search is being carried out concurrently with a program to characterize the kinematical properties of two different samples of stars. Each sample has produced one close binary candidate for which further spectroscopic observations are planned. We also recapitulate the discovery of a close detached binary system composed of two cool DA white dwarfs, and we discuss the null results of Ha observations of the suspected white dwarf /brown dwarf system G 29-38.

Les nébuleuses planétaires (NP) sont le produit de l'évolution d'étoiles de masses intermédiaires après leur expansion sphérique à la fin de leurs vies. Il a été estimé observationnellement que 80 % des NP ont des formes non-sphériques. Une fraction si élevée est déroutante et a mobilisé la communauté de recherche sur les NP pendant plus de trente ans. Un scénario qui permettrait de justifier les formes observées serait que les étoiles progénitrices de noyaux de NP (NNP) ne sont pas simples, mais possèdent un compagnon. Les formes des nébuleuses seraient ainsi le résultat de l'interaction avec le compagnon. La fraction si élevée de NP non-sphériques impliquerait donc une fraction élevée de NNP binaires, faisant de la parité stellaire un canal de formation privilégié pour les NP. Après avoir présenté l'état de connaissance actuelle concernant la formation et la mise en forme des NP, je présente mes travaux visant à détecter un excès infrarouge qui serait la signature de la présence d'un compagnon orbitant le NNP. La première partie de ce projet consiste en l'analyse de données et photométrie acquises par moi-même. Dans la deuxième partie je présente une tentative d'utilisation de jeux de données d'archives : la campagne optique Sloan Digital Sky Survey Data Release 7 et la version étendue de la base de données assemblée par Frew (2008). Je présente aussi les résultats d'une analyse de vitesses radiales de spectres VLT/UVES pour 14 NNP dans le but de détecter des compagnons spectroscopiques. Finalement j'expose les détails d'une analyse de photométrie de données optiques dans le but de détecter des compagnons orbitant autour de NNP en utilisant la technique de variabilité photométrique. Le résultat principal de cette thèse réside dans les analyses d'excès infrarouge proche que je combine avec des données publiées précédemment. Je conclus que si la fraction détectée d'excès infrarouge proche est attribuée à la présence de compagnons stellaires, alors la fraction binaire de NNP est plus grande que celle attendue en se basant sur la population binaire de progéniteurs de la séquence principale et ainsi conclus que la multiplicité stellaire est un canal de formation privilégié pour la formation des NP. Je clos en soulignant la nécessité d'un échantillon d'étude d'environ 150 objets pour réduire l'incertitude sur la fraction binaire et appuyer les conclusions statistiques de ce résultat
Planetary nebulae (PNe) are the products of the evolution of intermediate mass stars that have expanded spherically at the end of their lives. Observationally, it has been estimated that 80% of them have non-spherical shapes. Such a high fraction is puzzling and has occupied the PN community for more than 30 years. One scenario that would allow to justify the observed shapes is that a comparable fraction of the progenitors of central stars of PN (CSPN) are not single, but possess a companion. The shape of the nebulae would then be the result of an interaction with this companion. The high fraction of non-spherical PNe would thus imply a high fraction of binary CSPN, making binarity a preferred channel for PN formation. After presenting the current state of knowledge regarding PN formation and shaping and reviewing the diverse efforts to find binaries in PNe, I present my work to detect a near-infrared excess that would be the signature of the presence of cool companions. The first part of the project consists in the analysis of data and photometry acquired and conducted by myself. The second part details an attempt to make use of archived datasets: the Sloan Digital Sky Survey Data Release 7 optical survey and the extended database assembled by Frew (2008). I also present results from a radial velocity analysis of VLT/UVES spectra for 14 objects aiming to the detection of spectroscopic companions. Finally I give details of the analysis of optical photometry data from our observations associated to the detection of companions around CSPN using the photometric variability technique. The main result of this thesis is from the near-infrared excess studies which I combine with previously-published data. I conclude that the if the detected red and NIR flux excess is indicative of a stellar companion then the binary fraction is larger than what we may expect based on the main-sequence progenitor population binary fraction and therefore conclude that binarity is a preferential channel for the formation of PN. I finish by underlining the need for a sample size of ∼ 150 objects to decrease the uncertainty on the PN population binary fraction and increase the statistical significance of this result

Despite being observed since the XVIIIth century, Algol systems and related objects are

still rather poorly understood. We know that they are composed by a generally B-A main sequence

star and a lighter but more evolved companion star. This paradox is explained by the transfer of mass

between the two stars, but new problems arose. In particular, I studied the mass-transfer driven spin-

up of the accreting star that drives the star to critical rotation and the puzzling, indirectly observed, non-conservative evolution.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

The Solar Twin Planet Search program is an unprecedented eort that aimed to procure extrasolar planets in more than 70 stars extremely similar to the Sun. In the course of this program, hundreds of high-quality optical spectra were obtained for these stars using the HARPS spectrograph, which is fed by the ESO La Silla 3.6 m telescope. Beyond the search for exoplanets, the data are invaluable to study the physical properties of Sun-like stars. Particularly in this dissertation, we are interested in verifying if the Sun possesses a regular rotation for its age among stars that are strictly similar to it, how the rotation of solar twins evolve with age and if the rotation of Sun-like stars is influenced by the presence of stellar mass companions. Previous conclusions on the regularity of the Suns rotation have been conflicting, and this is the first time such a large sample of solar twins with high quality spectroscopic data is used to clarify this puzzle. Our results suggest that the Sun is indeed a regular rotator for its age, which favors the use of the solar rotation to calibrate gyrochronology -- the estimation of stellar ages from their rotation. However, these results also imply a rotational evolution process that saturates after the solar age, constituting a departure from the widely used Skumanich relation and posing a challenge for gyrochronology. We securely identified 18 binary or multiple systems in the solar twin sample, of which only three display enhanced rotation for their ages. I estimated the orbital parameters of the binaries from their radial velocity variations, and the results show that their spectroscopic companions lie at orbital periods varying from a few to several years. I conclude that the presence of red or brown dwarf companions at moderate to long orbital periods do not influence the evolution of rotation in these systems, and therefore the main stars should evolve as single in this regard. The peculiarities in HIP 19911, HIP 67620 and HIP 103983 can be fully explained by spectral contamination from their companions.
O programa The Solar Twin Planet Search é um esforço sem precedentes na procura de planetas extra-solares em mais de 70 estrelas extremamente similares ao Sol. Ao longo desse programa, centenas de espectros ópticos de alta qualidade foram obtidos com o espectrógrafo HARPS, que está instalado no telescópio de 3,6 m do Observatório de La Silla. Além da busca de exoplanetas, estes dados são úteis para estudar as propriedades físicas de estrelas como o Sol. Estamos interessados em verificar se o Sol possui uma rotação regular para sua idade quando comparado com estrelas estritamente similares a ele, como que a rotação de gêmeas solares evolui com o tempo e se a rotação dessas estrelas é influenciada pela presença de companheiras estelares. Conclusões anteriores na regularidade da rotação solar são conflitantes, e esta é a primeira vez que uma amostra grande de gêmeas solares com dados espectroscópicos de alta qualidade é usada para esclarecer essa questão. Nossos resultados sugerem que o Sol de fato rota regularmente para sua idade, o que favorece o uso da rotação solar para calibrar a girocronologia -- a estimativa de idades estelares a partir de sua rotação. No entanto, tais resultados também implicam em um processo de evolução rotacional que satura depois da idade solar, constituindo um desvio da amplamente usada relação de Skumanich e apresentando um desafio para a girocronologia. Nós identificamos 18 sistemas binários na amostra de gêmeas solares, das quais apenas três mostram rotações elevadas para suas idades. Os parâmetros orbitais das binárias foram estimados a partir da variação de suas velocidades radiais, e os resultados mostram que suas companheiras espectroscópicas possuem períodos orbitais variando de alguns poucos até muitos anos. Concluimos que a presença de companheiras do tipo anãs vermelhas ou marrons em períodos orbitais moderados não influenciam a evolução rotacional desses sistemas. As peculiaridades de HIP 19911, HIP 67620 e HIP 103983 podem ser completamente explicadas por contaminação espectral de suas companheiras.

Etude d'etoiles de type a-f au voisinage solaire, de noyaux brillants de nebuleuses planetaires et des sous naines les plus brillantes. On s'interesse plus specialement a leur repartition galactique: jeune disque, vieux disque, halo. Les relations theoriques entre binarite, rotation, pulsation et structure d'enveloppe chez les etoiles a-f ont ete confirmees par analyse statistique. Un noyau a spectre composite a ete decouvert dans la nebuleuse planetaire lts et des variations d'eclat periodiques decelees dans le noyau abell 35. Six nouvelles binaires spectroscopiques ont par ailleurs ete decouvertes parmi les sous naines brillantes du halo

In this thesis I present the search for ultracool dwarf companions to main sequence stars, subgiants and white dwarfs. The ultracool dwarfs identified here are benchmark objects, with known ages and distances. The online data archives, the two micron all sky survey (2MASS) and SuperCOSMOS were searched for ultracool companions to white dwarfs, where one M9 1 companion to a DA white dwarf is spectroscopically confirmed as the widest separated system of its kind known to date. The age of the M9 1 is constrained to a minium age of 1.94Gyrs, based on the estimated age of the white dwarf from a spectroscopically derived Teff and log g and an initial-final mass relation. This search was extended using the next generation surveys, the sloan digital sky survey (SDSS) and the UK infrared deep sky survey (UKIDSS), where potential white dwarf + ultracool dwarf binary systems from this search are presented. A handful of these candidate systems were followed-up with second epoch near infrared (NIR) imaging. A new white dwarf with a spectroscopic M4 companion and a possible wide tertiary ultracool component is here confirmed. Also undertaken was a pilot imaging survey in the NIR, to search for ultracool companions to subgiants in the southern hemisphere using the Anglo-Australian telescope. The candidates from that search, as well as the subsequent follow-up of systems through second epoch NIR/optical imaging and methane imaging are presented. No systems are confirmed from the current data but a number of good candidates remain to be followed-up and look encouraging. A search for widely separated ultracool objects selected from 2MASS as companions to Hipparcos main-sequence stars was also undertaken. 16 candidate systems were revealed, five of which had been previously identified and two new L0 2 companions are here confirmed, as companions to the F5V spectroscopic system HD120005 and the M dwarf GD 605. The properties of HD120005C were calculated using the DUSTY and COND models from the Lyon group, and the age of the systems were inferred from the primary members. For GD 605B no age constraint could be placed due to the lack of information available about the primary, but HD120005C has an estimated age of 2-4Gyr. In the final part of this thesis I investigate correlations with NIR broadband colours (J - H, H - K and J - K) with respect to properties, Teff , log g and [Fe/H] for the benchmark ultracool dwarfs, both confirmed from the searches undertaken in this work and those available from the literature. This resulted in an observed correlation with NIR colour and Teff, which is presented here. I find no correlation however with NIR colours and log g or [Fe/H], due in part to a lack of suitable benchmarks. I show that despite the current lack of good benchmark objects, this work has the potential to allow UCD properties to be measured from observable characteristics, and suggest that expanding this study should reveal many more benchmarks where true correlation between properties and observables can be better investigated.

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 common envelope (CE) interaction is a still poorly understood, yet critical phase of evolution in binary systems that is responsible for various astrophysical classes and phenomena. In this thesis, we use various approaches and techniques to investigate different aspects of this interaction, and compare our models to observations. We start with a semi-empirical analysis of post-CE systems to predict the outcome of a CE interaction. Using detailed stellar evolutionary models, we revise the α equation and calculate the ejection efficiency, α, both from observations and simulations consistently. We find a possible anti-correlation between α and the secondary-to- primary mass ratio, suggesting that the response of the donor star might be important for the envelope ejection. Secondly, we present a survey of three-dimensional hydrodynamical simulations of the CE evolution using two different numerical techniques, and find very good agreement overall. However, most of the envelope of the donor is still bound at the end of the simulations and the final orbital separations are larger than the ones of young observed post-CE systems. Despite these two investigations, questions remain about the nature of the extra mechanism required to eject the envelope. In order to study the dynamical response of the donor, we perform one-dimensional stellar evolution simulations of stars evolving with mass loss rates from 0.001 up to a few M⊙/yr. For mass-losing giant stars, the evolution is dynamical and not adiabatic, and we find no significant radius increase in any case. Finally, we investigate whether the substellar companions recently observed in close orbits around evolved stars could have survived the CE interaction, and whether they might have been more massive prior to their engulfment. Using an analytical prescription for the disruption of gravitationally bound objects by ram pressure stripping, we find that the Earth-mass planets around KIC 05807616 could be the remnants of a Jovian-mass planet, and that the other substellar objects are unlikely to have lost significant mass during the CE interaction.
Graduate

This dissertation describes a new detailed abundance study of field red horizontal branch stars, RR Lyrae stars and blue horizontal branch stars. To carry out this study, we obtained high-resolution and high signal-to-noise ratio echelle spectra at the McDonald observatory and Las Campanas Observatory. In addition, new pulsational emphemerides were derived to analyze the spectra of RR Lyrae stars throughout the pulsational cycles. We find that the abundance ratios are generally consistent with those of field stars of similar metallicity in different evolutionary stages and throughout the pulsational cycles for RR Lyrae stars. We also estimated the red and blue edges of the RR Lyrae instability strip using the derived effective temperatures of RHB and BHB stars. New variations between microturbulence and effective temperature are found among the HB population. For the first time the variation of microturbulence as a function of phase is empirically shown to be similar to the theoretical calculations. Finally, through the study of a rare eclipsing sdB and M dwarf binary, we discovered an unusually low mass for this type of HB star, which observationally proved the existence of a new group of low-mass sdB stars that was theoretically predicted in the past.
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In this thesis I investigate the population of X-ray binaries (XRB) and ultraluminous X-ray sources (ULX) in order to approach several contemporary astrophysical conundrums. My main method of analysis is the population synthesis, which allows for a comprehensive comparison of theoretical models and observations. I provide an introduction with fundamental knowledge concerning XRBs and ULXs. Firstly, I approach a problem of the mass gap, i.e., the lack of compact objects with masses between 2 5 M . I show that the rapid supernova explosion mechanism can provide a natural explanation for the observed separation between neutron stars and black holes. Afterwards, I investigate the common envelope. This important phase of evolution of binaries still escapes the grasp of our understanding. I show that, although the common envelope phase is essential for the formation of XRB, none of currently available models is able to reproduce the observations. I analyse also the formation of the most luminous ULXs. I show that it is possible to obtain mass transfer rates high enough to power such a source in regular XRBs. The phase of powerful emission will be very short but present in the evolution of numerous systems. Finally, I present the preliminary results of the investigation of accretion models in the context of the ULX population. I compare the synthetic population, which is based on our best knowledge of astrophysical processes, with the observations in order to understand the nature and formation processes of these systems.

Tesis (Doctor en Astronomía)--Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía, Física y Computación, 2020.
Se han descubierto discos de gas en un grupo de enanas blancas con discos de polvo, a través de la detección en sus espectros de lineas de emisión inusuales del triplete de Ca II en 8600 Å. En este contexto, se han obtenido espectros ópticos GMOS/GEMINI para 13 enanas blancas con excesos IR, seleccionados de nuestra muestra de 29 estrellas con discos “debris”, con el objetivo de encontrar la contraparte gaseosa a los discos de polvo. Se presenta además un estudio comparativo de las principales propiedades físicas y de parámetros relacionados al disco de polvo de las enanas blancas con y sin discos de gas detectados. Adicionalmente, se aplicó la técnica de “Eclipse Timing Variation” en una muestra de 8 sistemas binarios eclipsantes formados por enana blanca+estrella de secuencia principal con el objetivo de detectar planetas circumbinarios. Para ello, se obtuvieron observaciones propias con los telescopios argentinos localizados en la Estación Astrofísica de Bosque Alegre y el telescopio Jorge Sahade en el Complejo Astronómico El Leoncito. Las curvas de luz obtenidas, fueron complementadas con las disponibles en las bases de datos del “Catalina Sky Survey” y Kepler+K2. Los tiempos de mínimo fueron obtenidos con el código Wilson & Devinney.
Gas disks have been discovered in a group of white dwarfs with dust disks, through the detection in their spectra of unusual emission lines of the triplet of Ca II at 8600 Å. In this context, GMOS/GEMINI optical spectra have been obtained for 13 white dwarfs with IR excesses, selected from our sample of 29 stars with debris disks, with the aim to find the gaseous counterpart to the dusty disks. We also present a comparative study of the main physical properties and parameters related to the dusty disk of white dwarfs with and without gas disks detected. Additionally, the Eclipse Timing Variation technique was applied in a sample of 8 eclipsing binary systems formed by white dwarf + main sequence star, with the aim to detect circumbinary planets. For this, own observations were obtained with the Argentine telescopes located in the Estación Astrofísica de Bosque Alegre and the Jorge Sahade telescope in the Complejo Astronómico El Leoncito. The light curves obtained were complemented with those available in the databases "Catalina Sky Survey" and Kepler+K2. Minimum times were obtained with the Wilson & Devinney code.
Fil: Saker, Leila Yamila. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.

Niniejsza praca opisuje, jak własności gwiazd pulsujących typu RR Lutni oraz cefeid mogą zostać zmienione w wyniku obecności towarzysza w układzie podwójnym. Studium to jest wieloaspektowe i składa się z trzech projektów z możliwością ich rozwinięcia oraz włączenia kolejnych projektów w przyszłości. Pierwszy projekt ma na celu pokazanie, że gwiazdy pulsujące typu RR Lutni (RRL) są wiarygodnymi i precyzyjnymi świecami standardowymi, które spełniają zależność okresjasność-metaliczność w bliskiej podczerwieni. Ta zależność jest wykorzystana do wyznaczenia odległości do dwóch galaktyk Grupy Lokalnej: Carina i Fornax. Wyniki są zgodne z istniejącymi w literaturze wyznaczeniami odległości, ale charakteryzują się większą precyzją, na poziomie 5%. Za ten stan rzeczy odpowiada zredukowanie wpływu błędów systematycznych i statystycznych. Między innymi, obserwacje w bliskiej podczerwieni charakteryzują się mniejszą czułością na ekstynkcję międzygwiazdową niż obserwacje w zakresie widzialnym. Ponadto, wpływ metaliczności na jasność gwiazd RRL w bliskiej podczerwieni jest mniejszy niż w zakresie widzialnym. Te cechy czynią zależność okres-jasność-metaliczność w bliskiej podczerwieni dla gwiazd RRL cennym narzędziem do wyznaczania odległości, w szczególności do pobliskich galaktyk, których moduł odległości jest nie większy niż około 22 mag, a w których nie ma cefeid. Odległości wyznaczone do galaktyk Carina i Fornax zgadzają się z wyznaczeniami dokonanymi w ramach projektu Araucaria za pomocą innych świec standardowych, takich jak gwiazdy red clump lub gwiazdy na wierzchołku gałęzi czerwonych olbrzymów. Ewentualna znaczna rozbieżność osiągniętych wyników z innymi wyznaczeniami oznaczałaby, że dodatkowe i do tej pory nie uwzględnione efekty mogły zakłócić pomiar odległości. Jeden z tych efektów – obecność towarzysza w układzie podwójnym – został omówiony w dalszej części pracy. Kolejne dwa projekty mają charakter teoretyczny i wykorzystują kod do syntezy populacji układów podwójnych StarTrack, stworzony przez Belczynski et al. (2002, 2008) i nieustannie od tego czasu rozwijany. Praca z syntetyczną populacją umożliwia opisanie w sposób statystyczny właściwości układów podwójnych, prześledzenie etapów ich ewolucji oraz stopnia i charakteru interakcji między składnikami. Oba projekty badają układy podwójne z przynajmniej jednym składnikiem w pasie niestabilności, przy czym jeden projekt skupia się na układach, w których między składnikami nastąpiła interakcja w postaci transferu masy, podczas gdy drugi projekt bada własności gwiazd związanych jedynie grawitacyjnie, w których nie nastąpił transfer masy. Badania nad syntetyczną populacją, w której gwiazdy doświadczają transferu masy, prowadzą do potwierdzenia istnienia nowej klasy gwiazd pulsujących, tzw. BEP (ang. Binary Evolution Pulsator ). Pierwszą i do tej pory jedyną gwiazdą BEP jest OGLEBLG-RRLYR-02792, obiekt o którego odkryciu donosi publikacja Soszyński et al. (2010a) i który został opisany obszerniej przez autorów Pietrzyński et al. (2012) oraz Smolec et al. (2013). BEP wykazuje pulsacje podobne do gwiazd RRL, lecz różni się od nich masą i ścieżką ewolucji, właśnie dlatego, że znajduje się w układzie podwójnym, w którym interakcja między składnikami przebiegła pod postacią transferu masy. Projekt poświęcony BEP-om pokazuje, że gwiazdy te powinny istnieć wewnątrz pasa niestabilności, w obszarze małych jasności, charakterystycznych dla gwiazd RRL, ale także w wyższych partiach pasa niestabilności, w którym znajdują się cefeidy. Obiekty te mogą być błędnie klasyfikowane ze względu na kształt krzywych zmian blasku jako gwiazdy RRL lub cefeidy. Najskuteczniejszym sposobem ich detekcji jest zaobserwowanie zaćmień w krzywej zmian blasku lub zmian związanych z ruchem orbitalnym w krzywej prędkości radialnych. Nierozpoznanych BEP-ów powinno być na tyle mało, by ich obecność nie zaburzała pomiarów odległości opartych na zależnościach okres-jasność dla cefeid i gwiazd RRL. Niemniej, interesujące właściwości oraz ścieżki ewolucji tych obiektów zachęcają do poszukiwania kolejnych gwiazd należących do tej nowej klasy oraz do dalszego studiowania znanych już kandydatek. Projekt potwierdza, że interakcje w układach podwójnych są kluczowe dla wytłumaczenia zaobserwowanych własności niektórych gwiazd pulsujących w układach podwójnych. Kolejny projekt poświęcony jest układom podwójnym, w których nie doszło do transferu masy i ma na celu sprawdzić, czy gwiazdy w pasie niestabilności – konkretnie cefeidy klasyczne – realizują zależność okres-jasność w sposób niezaburzony obecnością towarzysza, czy raczej dodatkowe światło od towarzysza powoduje systematyczne zawyżenie zależności okres-jasność. Temat ten był wielokrotnie poruszany w literaturze i dyskutowany w sposób jakościowy. Odosobnione przypadki cefeid w układach podwójnych, które znajdują się znacząco ponad zależnością okres-jasność zostały opisane w publikacjach autor- stwa Pietrzyński et al. (2010) oraz Pilecki et al. (2018). Natomiast przedstawiony w niniejszej pracy projekt po raz pierwszy realizuje temat w ujęciu nie tylko jakościowym, ale i ilościowym. Dla trzech syntetycznych populacji gwiazd podwójnych o metalicznościach Drogi Mlecznej, Małego i Wielkiego Obłoku Magellana oszacowano, jak poważne jest zagrożenie zawyżenia pomiarów odległości za pomocą zależności okres-jasność dla cefeid dla różnych długości fali i różnego odsetka układów podwójnych. Wnioski płynące z pracy uspokajają, że wyznaczenia odległości z zależności okres-jasność dla mieszanej próbki cefeid (pojedynczych i podwójnych) obarczone są tylko nieznacznym błędem systematycznym wynikającym z obecności towarzysza i mogą być dodatkowo minimalizowane, jeśli obserwacje prowadzone są na większych długościach fali. Niniejsza praca składa się z trzech głównych rozdziałów, prezentujących opisane powyżej projekty, poprzedzającego je wstępu oraz następującego po nich podsumowania. W dwóch dodatkach kończących pracę znajdują się zestawienie dostępnych w literaturze zależności okres-jasność-metaliczność dla gwiazd RRL w bliskiej podczerwieni oraz szczegółowy opis działania programu do syntezy populacji StarTrack. Wstęp poprzedza spis wykorzystywanych w pracy jednostek fizycznych wraz z ich wartościami wyrażonymi w układzie jednostek miar SI lub cgs oraz spis wykorzystywanych w pracy skrótowców wraz z ich rozwinięciem i polskim tłumaczeniem. W całej pracy liczby niecałkowite zapisane w systemie dziesiętnym posiadają jako separator dziesiętny kropkę, a nie – zgodny z polskim zwyczajem typograficznym – przecinek. Konwencja oddzielenia części całkowitej od dziesiętnej kropką jest powszechnie stosowana w fachowej literaturze anglojęzycznej na całym świecie, a także we wszystkich cytowanych pracach. Aby zachować konsekwencję zapisu cytowanych publikacji, w niniejszej pracy także stosowana jest kropka. W pracy stosowane są przedrostki do jednostki czasu, na przykład 5 Gyr czyli 5 mld lat lub 28 kyr czyli 28 tys. lat. Obie formy stosowane są wymiennie, chociaż na rysunkach pojawiają się tylko formy Gyr, kyr, natomiast w tekście dołożono starań, by dominowała forma polska. Słowo „ jasność” jest najczęściej używane jako synonim dzielności promieniowania gwiazdy, L. Gdy opisywana jest jasność gwiazdy w konkretnych filtrach, podana jest nazwa filtra i jednostka magnitudo. W pojedynczych przypadkach, gdy jasności w formie jasności w filtrze i dzielności promieniowania są opisywane razem, występuje rozdzielenie terminów „ jasność” i „dzielność promieniowania”.
This doctoral dissertation describes how the properties of pulsating stars, exemplified by RR Lyrae stars and classical Cepheids, can be changed as a result of the presence of a companion in a binary system. The study consists of three diverse projects which can be further developed and extended in the future. The first project aims to show that RR Lyrae (RRL) pulsating stars are reliable and precise standard candles that follow the period-brightness-metallicity relation in the nearinfrared. This relation is then used to determine the distance to two galaxies in the Local Group: Carina and Fornax. The results are consistent with the distances existing in the literature, but are of greater precision, at a level of 5%. The reason behind such precision is smaller contribution of systematic and statistical errors. For example, near-infrared observations are less affected by the interstellar extinction than observations in the visible domain. Also, the effect of metallicity on the brightness of RRL stars in the near-infrared is smaller than in the visible regime. These assets make the near-infrared period-brightnessmetallicity relation for RRL stars a valuable tool for determining distances, in particular to nearby galaxies (distance module not larger than about 22 mag) which do not host classical Cepheid. The results agree with the distances determined using other standard candles, such as red clump stars or stars on the tip of the red giant branch, in the course of the Araucaria Project. A significant discrepancy between obtained results and other distance determinations would mean that additional and not yet addressed effects could alter the distance measurements. One of these effects – the presence of a companion in a binary system – will have been discussed in the next chapters of this doctoral dissertation. The next two projects are of theoretical nature and use a binary population synthesis code StarTrack, created by Belczynski et al. (2002, 2008) and constantly developed since. The population synthesis method allows for statistical description of properties of binary systems as well as for the analysis of the interaction between the components on different evolutionary stages. Both projects examine binary systems with at least one star inside the instability strip, but one project focuses on systems that undergo the mass transfer, whereas the other project investigates the systems that are only gravitationally bound, without mass transfer episodes. A study of a synthetic population of binary stars which experience mass transfer episodes leads to the confirmation of the existence of a new class of pulsating stars, so-called BEP (Binary Evolution Pulsator ). The first and so far the only BEP star is OGLE-BLGRRLYR-02792, the object discovered by Soszyński et al. (2010a) and further studied by Pietrzyński et al. (2012) and Smolec et al. (2013). BEP mimics the pulsational pattern of RRL stars but – due to the mass transfer episode that it has experienced – its mass and evolutionary path are utterly different from RRL’s. This project shows that BEPs are expected to populate the instability strip, in the areas of both RRL stars and Cepheids. Moreover, BEPs can be misclassified as RRLs or Cepheids due to the shape of their light curves. The most effective way to detect BEPs is to observe eclipses in their light curves or fluctuations in their radial velocity curves associated with the orbital motion. Unrecognized BEPs should not be abundant and therefore their presence should not alter the distance measurements based on the period-brightness relation for Cepheids and RRL stars. Nevertheless, the interesting properties and evolutionary paths of BEPs encourage to search for more stars belonging to this new class and to continue to study already known candidates. The project reaffirms that the interactions in binary systems are crucial for explaining the observed properties of some binary pulsating stars. A study of binary stars with no mass transfer episodes was performed in order to check whether the components residing in the instability strip – particularly Cepheids – follow the period-luminosity relation undisturbed by the presence of companions, or rather an additional light from the companions systematically shifts the period-luminosity relation. This issue has appeared frequently in the literature and discussed in a qualitative way. Isolated cases of Cepheid in binary systems that lay significantly above the periodluminosity relation are described by Pietrzyński et al. (2010) and Pilecki et al. (2018). The project, which is presented in this doctoral dissertation, for the first time addresses the issue of the excess light of Cepheids’ companions in both qualitative and quantitative way. Three synthetic populations of binary stars with metallicities of Milky Way, Small and Large Magellanic Clouds were used to determine the change in the accuracy of distance determinations calculated from period-luminosity relations for a mixed sample of Cepheids (single and binary stars) at different wavelengths and for different percentage of binary systems in the sample. The results reassure that distance determinations from the periodluminosity relation for a mixed sample are only slightly shifted due to the excess light from the companion, which can be further minimised if the observations are carried out at larger wavelengths. This dissertation consists of three main chapters, presenting the projects described above, the introduction which precedes them and the summary that follows them. The two appendices include: a collection of near-infrared period-luminosity-metallicity relations for RRL stars that are available in the literature and a detailed description of the StarTrackpopulation synthesis code. The introduction is preceded by a list of physical units used in this thesis together with their values expressed in the SI or cgs systems, and by a list of abbreviations used in this thesis together with their long form and the Polish translation. Every non-integer number written in the decimal system has a decimal separator which is a period, and not a comma, as would Polish typographic practise recommend. This convention is widely used in the literature around the world, as well as in all publications cited here. In order to preserve the consistency with the cited publications, a period symbol is used as a decimal separator also in this dissertation. The thesis uses prefixes to a unit of time, for example 5 Gyr or 5 billion years, 28 kyr or 28 thousand years. Both forms are used interchangeably, although only Gyr, kyr forms appear in the figures, whereas the long form dominates in the text. The word ’brightness’ is most often used as a synonym for the ’luminosity’, L. Whenever star’s brightness is expressed a in specific passband, the filter name and the magnitude unit are given. In individual cases, when the brightness and luminosity appear together in the text, there is a clear distinction between the brightness and the luminosity.