More than 60 years ago, in the optical color-magnitude diagram of the Galactic Globular Cluster M3 a new type of star was discovered: the blue straggler stars. Since then, these objects have been found in all types of stellar systems and environments, from the dense core of globular clusters to the low-density environment of the Galactic field. Understanding their formation has fascinated both observers and theorists, and today it is widely accepted that they have formed through the interaction with other stars. Among the multiple formation mechanisms proposed, two are the main scenarios: collision-induced stellar mergers and mass transfer in binary systems. Both scenarios, however, can be easily modified by the presence of a third (or more) star. What is still partially unclear is how much each mechanism contributes to the straggler population currently observed. With many authors proposing different pathways that dominate in different environments, it is not easy to identify the exact pathway without information about their BSS properties. To do so we require first having large and homogeneous compilations of these stars, suitable to find pathological cases on which these formation scenarios can be further tested. This thesis presents an observational effort made to contribute to a better understanding of the properties of blue straggler stars in open clusters (OCs), improve membership-driven BS statistics, and shed light on which formation mechanism is the most predominant from a macro scale point of view. Two are the sides that define this thesis. From one side, this work presents the most comprehensive and homogeneous catalog of the BSS population in a sample of more than 400 OCs. After having compiled the catalog, we have revisited the most famous relations between the straggler numbers and the cluster environment (age, mass, integrated magnitude, binary fraction) ruling out previous claims and providing invaluable information about the BSS environments, which is crucial to building realistic models of their evolution. Yellow straggler stars (YSS) are much less sampled and studied than BSS. Their importance, however, relies on the suggestion of these stars as possible evolved-BSS. As part of this thesis, we present the first and largest systematic search of YSS in OCs, where nearly 80 have been found in 45 OCs. This is the first time these systems are reported as part of a catalog, their properties are important to have a complete picture of the formation and evolution of BSS stars. After our internally consistent and accurate straggler selection, we have ranked the host clusters in terms of their internal dynamical evolution by using the so-called Ar+ parameter, which measures the central concentration of BSS within the cluster. This thesis has extrapolated the calculation of Ar+ from 10 Ocs (previously reported in the literature) to ~40. Moreover, by estimating the parameter Nrelax (indicative of the dynamical state of the cluster) we showed the OCs distribution is completely different from that of the globular clusters. From the other side and going more into detail, we tried to assess the binary nature of a few blue stragglers to investigate their origin. We managed to identify both, long and short-period binary stars, and we also obtained their rotational velocities. We showed most of them are fast-rotators stars with Vsini > 30 km/s and some of them up to 150 km/s. One unexpected finding is the large short-period binary fractions we found for a sample of 10 OCs. For all of them, we derived their periods between 5 hours and 3 days. Among them, we found more than 50 eclipsing-BSS binaries, where nearly 90 % are new discoveries.
More than 60 years ago, in the optical color-magnitude diagram of the Galactic Globular Cluster M3 a new type of star was discovered: the blue straggler stars. Since then, these objects have been found in all types of stellar systems and environments, from the dense core of globular clusters to the low-density environment of the Galactic field. Understanding their formation has fascinated both observers and theorists, and today it is widely accepted that they have formed through the interaction with other stars. Among the multiple formation mechanisms proposed, two are the main scenarios: collision-induced stellar mergers and mass transfer in binary systems. Both scenarios, however, can be easily modified by the presence of a third (or more) star. What is still partially unclear is how much each mechanism contributes to the straggler population currently observed. With many authors proposing different pathways that dominate in different environments, it is not easy to identify the exact pathway without information about their BSS properties. To do so we require first having large and homogeneous compilations of these stars, suitable to find pathological cases on which these formation scenarios can be further tested. This thesis presents an observational effort made to contribute to a better understanding of the properties of blue straggler stars in open clusters (OCs), improve membership-driven BS statistics, and shed light on which formation mechanism is the most predominant from a macro scale point of view. Two are the sides that define this thesis. From one side, this work presents the most comprehensive and homogeneous catalog of the BSS population in a sample of more than 400 OCs. After having compiled the catalog, we have revisited the most famous relations between the straggler numbers and the cluster environment (age, mass, integrated magnitude, binary fraction) ruling out previous claims and providing invaluable information about the BSS environments, which is crucial to building realistic models of their evolution. Yellow straggler stars (YSS) are much less sampled and studied than BSS. Their importance, however, relies on the suggestion of these stars as possible evolved-BSS. As part of this thesis, we present the first and largest systematic search of YSS in OCs, where nearly 80 have been found in 45 OCs. This is the first time these systems are reported as part of a catalog, their properties are important to have a complete picture of the formation and evolution of BSS stars. After our internally consistent and accurate straggler selection, we have ranked the host clusters in terms of their internal dynamical evolution by using the so-called Ar+ parameter, which measures the central concentration of BSS within the cluster. This thesis has extrapolated the calculation of Ar+ from 10 Ocs (previously reported in the literature) to ~40. Moreover, by estimating the parameter Nrelax (indicative of the dynamical state of the cluster) we showed the OCs distribution is completely different from that of the globular clusters. From the other side and going more into detail, we tried to assess the binary nature of a few blue stragglers to investigate their origin. We managed to identify both, long and short-period binary stars, and we also obtained their rotational velocities. We showed most of them are fast-rotators stars with Vsini > 30 km/s and some of them up to 150 km/s. One unexpected finding is the large short-period binary fractions we found for a sample of 10 OCs. For all of them, we derived their periods between 5 hours and 3 days. Among them, we found more than 50 eclipsing-BSS binaries, where nearly 90 % are new discoveries.
Stelle blue straggler in ammassi aperti galattici / RAIN SEPULVEDA, MARIA JOSE DEL PILAR. - (2022 Jun 24).
Stelle blue straggler in ammassi aperti galattici
RAIN SEPULVEDA, MARIA JOSE DEL PILAR
2022
Abstract
More than 60 years ago, in the optical color-magnitude diagram of the Galactic Globular Cluster M3 a new type of star was discovered: the blue straggler stars. Since then, these objects have been found in all types of stellar systems and environments, from the dense core of globular clusters to the low-density environment of the Galactic field. Understanding their formation has fascinated both observers and theorists, and today it is widely accepted that they have formed through the interaction with other stars. Among the multiple formation mechanisms proposed, two are the main scenarios: collision-induced stellar mergers and mass transfer in binary systems. Both scenarios, however, can be easily modified by the presence of a third (or more) star. What is still partially unclear is how much each mechanism contributes to the straggler population currently observed. With many authors proposing different pathways that dominate in different environments, it is not easy to identify the exact pathway without information about their BSS properties. To do so we require first having large and homogeneous compilations of these stars, suitable to find pathological cases on which these formation scenarios can be further tested. This thesis presents an observational effort made to contribute to a better understanding of the properties of blue straggler stars in open clusters (OCs), improve membership-driven BS statistics, and shed light on which formation mechanism is the most predominant from a macro scale point of view. Two are the sides that define this thesis. From one side, this work presents the most comprehensive and homogeneous catalog of the BSS population in a sample of more than 400 OCs. After having compiled the catalog, we have revisited the most famous relations between the straggler numbers and the cluster environment (age, mass, integrated magnitude, binary fraction) ruling out previous claims and providing invaluable information about the BSS environments, which is crucial to building realistic models of their evolution. Yellow straggler stars (YSS) are much less sampled and studied than BSS. Their importance, however, relies on the suggestion of these stars as possible evolved-BSS. As part of this thesis, we present the first and largest systematic search of YSS in OCs, where nearly 80 have been found in 45 OCs. This is the first time these systems are reported as part of a catalog, their properties are important to have a complete picture of the formation and evolution of BSS stars. After our internally consistent and accurate straggler selection, we have ranked the host clusters in terms of their internal dynamical evolution by using the so-called Ar+ parameter, which measures the central concentration of BSS within the cluster. This thesis has extrapolated the calculation of Ar+ from 10 Ocs (previously reported in the literature) to ~40. Moreover, by estimating the parameter Nrelax (indicative of the dynamical state of the cluster) we showed the OCs distribution is completely different from that of the globular clusters. From the other side and going more into detail, we tried to assess the binary nature of a few blue stragglers to investigate their origin. We managed to identify both, long and short-period binary stars, and we also obtained their rotational velocities. We showed most of them are fast-rotators stars with Vsini > 30 km/s and some of them up to 150 km/s. One unexpected finding is the large short-period binary fractions we found for a sample of 10 OCs. For all of them, we derived their periods between 5 hours and 3 days. Among them, we found more than 50 eclipsing-BSS binaries, where nearly 90 % are new discoveries.File | Dimensione | Formato | |
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PhdThesis_MariaJose-RainS.pdf
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