http://sedici.unlp.edu.ar:80/handle/10915/167659 2026-04-11T20:55:51Z 2026-04-11T20:55:51Z Christen, Alejandra http://sedici.unlp.edu.ar:80/handle/10915/167767 2024-07-04T20:02:25Z 2021-01-01T00:00:00Z

Objeto de conferencia VIII La Plata International School: Pulsations Along Stellar Evolution (La Plata, 11 al 22 de noviembre de 2019); Pulsations Along Stellar Evolution: Proceedings of the VIII La Plata International School Wavelet analysis has been widely used to analyze time series and has countless applications in astronomy. Because of its characteristics it is a method that is well suited to approximate functions, eliminate noise, detect points of change, discontinuities and periodicities. In this article an introduction to the wavelet theory and its use in time series is presented. Numerical simulations and some real examples are developed in the software R.

2021-01-01T00:00:00Z Wavelet analysis has been widely used to analyze time series and has countless applications in astronomy. Because of its characteristics it is a method that is well suited to approximate functions, eliminate noise, detect points of change, discontinuities and periodicities. In this article an introduction to the wavelet theory and its use in time series is presented. Numerical simulations and some real examples are developed in the software R. Glatzel, Wolfgang http://sedici.unlp.edu.ar:80/handle/10915/167766 2024-07-04T20:02:29Z 2021-01-01T00:00:00Z

Objeto de conferencia VIII La Plata International School: Pulsations Along Stellar Evolution (La Plata, 11 al 22 de noviembre de 2019); Pulsations Along Stellar Evolution: Proceedings of the VIII La Plata International School As an introduction to the subject basic properties of stellar pulsations are derived using simple intuitive estimates. With respect to a theoretical description of pulsating stars the physical principles governing stellar structure and dynamics are discussed. The associated equations are simplified by the assumption of spherical symmetry thus providing the basis for the study of radial pulsations.

2021-01-01T00:00:00Z As an introduction to the subject basic properties of stellar pulsations are derived using simple intuitive estimates. With respect to a theoretical description of pulsating stars the physical principles governing stellar structure and dynamics are discussed. The associated equations are simplified by the assumption of spherical symmetry thus providing the basis for the study of radial pulsations. Kraus, Michaela http://sedici.unlp.edu.ar:80/handle/10915/167765 2024-07-04T20:02:33Z 2021-01-01T00:00:00Z

Objeto de conferencia VIII La Plata International School: Pulsations Along Stellar Evolution (La Plata, 11 al 22 de noviembre de 2019); Pulsations Along Stellar Evolution: Proceedings of the VIII La Plata International School The post-main sequence evolution of massive stars still bears many unknowns. In particular, the physical processes involved in triggering enhanced mass-loss or eruptions are yet to be established. In this Chapter, the post-main sequence evolution of massive stars, and the various phases which are well-known for their mass ejections, are briefly touched upon. Amongst those transition phases, two classes of objects are discussed in more detail: the B-type supergiants and the Yellow Hypergiants. Their ability to perform pulsations is presented based on observational and theoretical evidences. Moreover, the possibility of a pulsation-mass-loss relation in these two classes of objects is delineated.

2021-01-01T00:00:00Z The post-main sequence evolution of massive stars still bears many unknowns. In particular, the physical processes involved in triggering enhanced mass-loss or eruptions are yet to be established. In this Chapter, the post-main sequence evolution of massive stars, and the various phases which are well-known for their mass ejections, are briefly touched upon. Amongst those transition phases, two classes of objects are discussed in more detail: the B-type supergiants and the Yellow Hypergiants. Their ability to perform pulsations is presented based on observational and theoretical evidences. Moreover, the possibility of a pulsation-mass-loss relation in these two classes of objects is delineated. Romero, Alejandra Daniela http://sedici.unlp.edu.ar:80/handle/10915/167764 2024-07-04T20:02:40Z 2021-01-01T00:00:00Z

Objeto de conferencia VIII La Plata International School: Pulsations Along Stellar Evolution (La Plata, 11 al 22 de noviembre de 2019); Pulsations Along Stellar Evolution: Proceedings of the VIII La Plata International School Hot subdwarf stars are core helium-burning objects, located at the hot end of the horizontal branch, and therefore, they are also known as Extreme Horizontal Branch stars. We can divide them into two large groups, of spectral types B and O, depending on their effective temperature. Each spectroscopic class has subgroups showing luminosity variations due to pulsations, opening the possibility to study these compact objects through Asteroseismology. In this notes I will briefly review the main characteristics of hot subdwarfs B and O stars and the different pulsating subgroups.

2021-01-01T00:00:00Z Hot subdwarf stars are core helium-burning objects, located at the hot end of the horizontal branch, and therefore, they are also known as Extreme Horizontal Branch stars. We can divide them into two large groups, of spectral types B and O, depending on their effective temperature. Each spectroscopic class has subgroups showing luminosity variations due to pulsations, opening the possibility to study these compact objects through Asteroseismology. In this notes I will briefly review the main characteristics of hot subdwarfs B and O stars and the different pulsating subgroups. Sánchez Arias, Julieta Paz http://sedici.unlp.edu.ar:80/handle/10915/167762 2024-07-04T20:02:44Z 2021-01-01T00:00:00Z

Objeto de conferencia VIII La Plata International School: Pulsations Along Stellar Evolution (La Plata, 11 al 22 de noviembre de 2019); Pulsations Along Stellar Evolution: Proceedings of the VIII La Plata International School This Chapter provides a brief description of the different classes of pulsating A-F stars emphasising hybrids δ Sct-γ Dor stars. A modelling technique for hybrid δ Sct-γ Dor stars is presented along with the typical features that these stars “print” on their light curves and frequency spectra. Finally, we present a very different family of pulsating stars overlapping the region where pulsating A-F stars usually lie, the precursors of the so-called extremely low mass white dwarf stars. These stars have very similar atmospheric characteristics and their oscillation periods partially overlap making them difficult to discern. We discuss tools based on their seismic oscillation properties to distinguish them.

2021-01-01T00:00:00Z This Chapter provides a brief description of the different classes of pulsating A-F stars emphasising hybrids δ Sct-γ Dor stars. A modelling technique for hybrid δ Sct-γ Dor stars is presented along with the typical features that these stars “print” on their light curves and frequency spectra. Finally, we present a very different family of pulsating stars overlapping the region where pulsating A-F stars usually lie, the precursors of the so-called extremely low mass white dwarf stars. These stars have very similar atmospheric characteristics and their oscillation periods partially overlap making them difficult to discern. We discuss tools based on their seismic oscillation properties to distinguish them. Kraus, Michaela http://sedici.unlp.edu.ar:80/handle/10915/167722 2024-07-03T20:01:44Z 2021-01-01T00:00:00Z

Objeto de conferencia VIII La Plata International School: Pulsations Along Stellar Evolution (La Plata, 11 al 22 de noviembre de 2019); Pulsations Along Stellar Evolution: Proceedings of the VIII La Plata International School Stellar pulsations can cause variability in the brightness of the star as well as in the shape and radial velocity of photospheric lines. To determine the periods and modes of pulsations, two different but complementary observational techniques are in use: photometric light curves to measure the brightness variations, and spectroscopic time series to analyze the time-dependent motions at the stellar surface. In the first part of this Chapter, both observing techniques and their sources of errors and limitations are presented. In the second part, an overview of the various space and ground-based missions for both photometry and spectroscopy is given. Considering all the currently available and newly planned instruments, the future for research in variable and pulsating stars is bright.

2021-01-01T00:00:00Z Stellar pulsations can cause variability in the brightness of the star as well as in the shape and radial velocity of photospheric lines. To determine the periods and modes of pulsations, two different but complementary observational techniques are in use: photometric light curves to measure the brightness variations, and spectroscopic time series to analyze the time-dependent motions at the stellar surface. In the first part of this Chapter, both observing techniques and their sources of errors and limitations are presented. In the second part, an overview of the various space and ground-based missions for both photometry and spectroscopy is given. Considering all the currently available and newly planned instruments, the future for research in variable and pulsating stars is bright. Glatzel, Wolfgang http://sedici.unlp.edu.ar:80/handle/10915/167721 2024-07-03T20:01:52Z 2021-01-01T00:00:00Z

Objeto de conferencia VIII La Plata International School: Pulsations Along Stellar Evolution (La Plata, 11 al 22 de noviembre de 2019); Pulsations Along Stellar Evolution: Proceedings of the VIII La Plata International School The linear stability analysis of stellar models poses a linear fourth or sixth order boundary eigenvalue problem. Methods for its numerical solution are reviewed, most of which face severe problems, if the ratio of the thermal and dynamical timescale falls below unity for a significant fraction of the stellar envelope considered. The extremely robust and highly accurate Riccati method is introduced and shown to be applicable to stellar stability problems with success even in these cases of strong deviations from adiabaticity. Numerical simulations of the evolution of a stellar instability into the nonlinear regime are still restricted to spherical geometry. We address the basic requirements for and problems connected with the simulation of radial pulsations. How violent artificial initial perturbations may be avoided and the extremely high accuracy requirements posed by the differences between the various energy forms can be met by strictly conservative numerical schemes is discussed.

2021-01-01T00:00:00Z The linear stability analysis of stellar models poses a linear fourth or sixth order boundary eigenvalue problem. Methods for its numerical solution are reviewed, most of which face severe problems, if the ratio of the thermal and dynamical timescale falls below unity for a significant fraction of the stellar envelope considered. The extremely robust and highly accurate Riccati method is introduced and shown to be applicable to stellar stability problems with success even in these cases of strong deviations from adiabaticity. Numerical simulations of the evolution of a stellar instability into the nonlinear regime are still restricted to spherical geometry. We address the basic requirements for and problems connected with the simulation of radial pulsations. How violent artificial initial perturbations may be avoided and the extremely high accuracy requirements posed by the differences between the various energy forms can be met by strictly conservative numerical schemes is discussed. Benvenuto, Omar Gustavo http://sedici.unlp.edu.ar:80/handle/10915/167720 2024-07-03T20:01:55Z 2021-01-01T00:00:00Z

Objeto de conferencia VIII La Plata International School: Pulsations Along Stellar Evolution (La Plata, 11 al 22 de noviembre de 2019); Pulsations Along Stellar Evolution: Proceedings of the VIII La Plata International School We present the problem of low amplitude, adiabatic non-radial oscillations starting from first principles. We describe the perturbations imposed to the models, assuming that its non-perturbed structure is spherical. Then, we restrict ourselves to the case of adiabatic oscillations, presenting the equations written in terms of the Dziem- bowski variables. We describe a numerical method for solving these equations based on finite differences and apply it for the simple case of polytropic spheres. A computer code based on this algorithm is available at the web page of the school. This method can be easily generalised for computing the case of low amplitude, non-adiabatic, non-radial pulsations.

2021-01-01T00:00:00Z We present the problem of low amplitude, adiabatic non-radial oscillations starting from first principles. We describe the perturbations imposed to the models, assuming that its non-perturbed structure is spherical. Then, we restrict ourselves to the case of adiabatic oscillations, presenting the equations written in terms of the Dziem- bowski variables. We describe a numerical method for solving these equations based on finite differences and apply it for the simple case of polytropic spheres. A computer code based on this algorithm is available at the web page of the school. This method can be easily generalised for computing the case of low amplitude, non-adiabatic, non-radial pulsations. Glatzel, Wolfgang http://sedici.unlp.edu.ar:80/handle/10915/167719 2024-07-03T20:01:59Z 2021-01-01T00:00:00Z

Objeto de conferencia VIII La Plata International School: Pulsations Along Stellar Evolution (La Plata, 11 al 22 de noviembre de 2019); Pulsations Along Stellar Evolution: Proceedings of the VIII La Plata International School We discuss the general strategy of the theoretical description of stellar stability and pulsations. The initial construction of a spherically symmetric stellar model in hydrostatic equilibrium is followed by considering small perturbations around the equilibrium. Both for radial and nonradial disturbances the linear equations governing these small perturbations are derived. The influence of the thermal and the dynamical timescale on the properties of linear pulsations is discussed in detail. For unstable stellar models the last step of the general approach consists of following the evolution of an instability into the nonlinear regime by numerical simulation.

2021-01-01T00:00:00Z We discuss the general strategy of the theoretical description of stellar stability and pulsations. The initial construction of a spherically symmetric stellar model in hydrostatic equilibrium is followed by considering small perturbations around the equilibrium. Both for radial and nonradial disturbances the linear equations governing these small perturbations are derived. The influence of the thermal and the dynamical timescale on the properties of linear pulsations is discussed in detail. For unstable stellar models the last step of the general approach consists of following the evolution of an instability into the nonlinear regime by numerical simulation. Carpintero, Daniel Diego http://sedici.unlp.edu.ar:80/handle/10915/167718 2024-07-03T20:02:03Z 2021-01-01T00:00:00Z

Objeto de conferencia VIII La Plata International School: Pulsations Along Stellar Evolution (La Plata, 11 al 22 de noviembre de 2019); Pulsations Along Stellar Evolution: Proceedings of the VIII La Plata International School Fourier’s traditional signal analysis does not work when observations are not equispaced in time, as is usually the case in Astronomy. The Lomb Scargle periodogram is the favorite substitute. We will study the basics of this technique and some care that needs to be taken for its practical application and its interpretation.

2021-01-01T00:00:00Z Fourier’s traditional signal analysis does not work when observations are not equispaced in time, as is usually the case in Astronomy. The Lomb Scargle periodogram is the favorite substitute. We will study the basics of this technique and some care that needs to be taken for its practical application and its interpretation. Benvenuto, Omar Gustavo http://sedici.unlp.edu.ar:80/handle/10915/167717 2024-07-03T20:02:09Z 2021-01-01T00:00:00Z

Objeto de conferencia VIII La Plata International School: Pulsations Along Stellar Evolution (La Plata, 11 al 22 de noviembre de 2019); Pulsations Along Stellar Evolution: Proceedings of the VIII La Plata International School With the aim of providing a reference frame for the study of stellar pulsations we describe the process known as stellar evolution. Evolution and pulsations are deeply related and the knowledge gained in one of them has an immediate impact on the other. First we describe the observational basis, presenting the Hertzsprung-Russell Diagram and other fundamental concepts. Then we describe the physical context of stellar evolution in which, quite fortunately, matter is very close to (but not in) thermodynamic equilibrium. This allows for a simplification of the problem of paramount importance. We describe the equation of state of stellar matter, paying attention on when we should expect the occurrence of partial and full ionization (fundamental for pulsations), and electron degeneracy. Then, we present the concept of hydrostatic equilibrium. As a natural consequence we consider barotropic structures, like polytropic spheres and cold white dwarfs, discussing the existence of the Chandrasekhar’s mass limit. As realistic stars are not cold but at finite temperature (they radiate energy in space!), in general they are nonbarotropic. So, we need to consider the conservation of energy and also its transport by radiation, convection and conduction. As it is well known, the engine of stars is nuclear reactions. We present the proton-proton and carbon-nitrogen-oxygen cycles of hydrogen burning and also the main helium burning reactions. Then, we make some brief comments on the methods for solving the full set of non-linear, partial differential equations of stellar evolution and also those needed for computing the changes of chemical composition. At this point we are in conditions to present stellar evolution as a direct consequence of these physical ingredients. We discuss the main stages of stellar evolution for a variety of objects: pre-main sequence, low and intermediate mass, white dwarfs, and finally massive stars. In this paper we restricted ourselves to the case of isolated and nonrotating objects evolving during their long lived stages. In our opinion, this provides a general basis for most of the usually considered pulsating stars.

2021-01-01T00:00:00Z With the aim of providing a reference frame for the study of stellar pulsations we describe the process known as stellar evolution. Evolution and pulsations are deeply related and the knowledge gained in one of them has an immediate impact on the other. First we describe the observational basis, presenting the Hertzsprung-Russell Diagram and other fundamental concepts. Then we describe the physical context of stellar evolution in which, quite fortunately, matter is very close to (but not in) thermodynamic equilibrium. This allows for a simplification of the problem of paramount importance. We describe the equation of state of stellar matter, paying attention on when we should expect the occurrence of partial and full ionization (fundamental for pulsations), and electron degeneracy. Then, we present the concept of hydrostatic equilibrium. As a natural consequence we consider barotropic structures, like polytropic spheres and cold white dwarfs, discussing the existence of the Chandrasekhar’s mass limit. As realistic stars are not cold but at finite temperature (they radiate energy in space!), in general they are nonbarotropic. So, we need to consider the conservation of energy and also its transport by radiation, convection and conduction. As it is well known, the engine of stars is nuclear reactions. We present the proton-proton and carbon-nitrogen-oxygen cycles of hydrogen burning and also the main helium burning reactions. Then, we make some brief comments on the methods for solving the full set of non-linear, partial differential equations of stellar evolution and also those needed for computing the changes of chemical composition. At this point we are in conditions to present stellar evolution as a direct consequence of these physical ingredients. We discuss the main stages of stellar evolution for a variety of objects: pre-main sequence, low and intermediate mass, white dwarfs, and finally massive stars. In this paper we restricted ourselves to the case of isolated and nonrotating objects evolving during their long lived stages. In our opinion, this provides a general basis for most of the usually considered pulsating stars. Kraus, Michaela Torres, Andrea F. http://sedici.unlp.edu.ar:80/handle/10915/167660 2024-07-05T17:44:51Z 2021-01-01T00:00:00Z

Libro Kraus, Michaela; Torres, Andrea F. The VIII La Plata International School was successfully held in the period 2019 November 11 - 22 on the campus of the Universidad Nacional de La Plata. The school was organized by the research group Modelos de Estrellas Peculiares (MEP) of the Facultad de Ciencias Astronómicas y Geofísicas (FCAG). The subject of this school was Pulsations Along Stellar Evolution. The offered lectures covered a wide range of topics such as stellar evolution, theoretical concepts of stellar pulsations, observing and data analysis techniques, along with practical courses for the analysis of selected pulsating stars. The ultimate goal of the Summer School was that the participants deepen their understanding of the physics of stellar pulsations and learn relevant techniques to analyze and properly interpret observational data of pulsating stars. This was achieved by the active participation in a number of courses dealing with theoretical exercises and practical computer-based exercises. This volume provides a comprehensive summary of the lectures that were presented during the school. Asociación Argentina de Astronomía,

2021-01-01T00:00:00Z The VIII La Plata International School was successfully held in the period 2019 November 11 - 22 on the campus of the Universidad Nacional de La Plata. The school was organized by the research group Modelos de Estrellas Peculiares (MEP) of the Facultad de Ciencias Astronómicas y Geofísicas (FCAG). The subject of this school was Pulsations Along Stellar Evolution. The offered lectures covered a wide range of topics such as stellar evolution, theoretical concepts of stellar pulsations, observing and data analysis techniques, along with practical courses for the analysis of selected pulsating stars. The ultimate goal of the Summer School was that the participants deepen their understanding of the physics of stellar pulsations and learn relevant techniques to analyze and properly interpret observational data of pulsating stars. This was achieved by the active participation in a number of courses dealing with theoretical exercises and practical computer-based exercises. This volume provides a comprehensive summary of the lectures that were presented during the school.