P. Patsis - Academia.edu (original) (raw)

Papers by P. Patsis

Astronomy & Astrophysics

Aims. Periodic orbits (POs) have been exhaustively studied. On the contrary, to our knowledge, no... more Aims. Periodic orbits (POs) have been exhaustively studied. On the contrary, to our knowledge, no complete and systematic study of higher-multiplicity (ℳ) POs, that is, orbits that close after more than one revolution in phase space, exists. Here, we fill this gap and also extend the standard tools used for studies of the x1 POs to studies of higher multiplicity POs. Methods. We adopted a multi-aspect approach, using surfaces of section, stability diagrams, characteristic diagrams, studies of the shapes of individual orbits, and other properties of the POs. We modified and extended the standard tools used for ℳ = 1, to ℳ > 1 cases, allowing them to use the snapshot information more fully. Our potential is more realistic than those of most previous studies, as it is obtained directly from a snapshot of a fully self-consistent, high-resolution numerical simulation. Results. We find five main pairs of PO families with ℳ = 2. Two of these bifurcate from the x1 family and are direct r...

Monthly Notices of the Royal Astronomical Society, 2018

Astrophysics and Space Science Proceedings, 2008

1 Research Center for Astronomy, Academy of Athens, Soranou Efessiou 4, GR-11527, Athens, Greece ... more 1 Research Center for Astronomy, Academy of Athens, Soranou Efessiou 4, GR-11527, Athens, Greece mkatsan@yahoo.gr, patsis@academyofathens.gr 2 Department of Economic Studies, University of Thessaly, Volos, Greece zachilas@uth.gr ... Summary. In order to ...

… Astronomy with the …, 2008

Communicating Astronomy with the Public 2007: Proceedings from the IAU/National Observatory of At... more Communicating Astronomy with the Public 2007: Proceedings from the IAU/National Observatory of Athens/ESA/ESO Conference, Athens, Greece, 8-11 October 2007, Christensen LL, Zoulias M. & Robson, I. (eds.). Published by Eugenides Foundation. ... The Society for Space and ...

The flow in the arms of spiral galaxies is qualitatively different among different morphological ... more The flow in the arms of spiral galaxies is qualitatively different among different morphological types. The stars that reinforce the spiral arms can be either participating in an ordered or in a chaotic flow. Ordered flows are typically described by precessing ellipses corresponding to stable periodic orbits at successive energies (Jacobi constants). Contrarily, there are spiral arms in barred-spiral systems which may be supported by stars in chaotic motion "along" the arms. The trajectories of these stars are associated with the invariant manifolds of unstable periodic orbits at corotations region. We find that the spirals and the outer parts of the bars share the same orbital content. However, there also barredspiral systems with spirals inside corotation, consisting mainly by chaotic orbits, or by ordered flows. The talk will present models where various dynamical mehanisms coexits and will compare them with structures that are possible the result of the concerted actio...

It has proven very difficult to estimate the amplitudes of spiralperturbations in disk galaxies f... more It has proven very difficult to estimate the amplitudes of spiralperturbations in disk galaxies from observations due to the variation ofmass-to-light ratio and extinction across spiral arms. Deep, near-infraredimages of grand-design spiral galaxies obtained with HAWK-I/VLT were used toanalyze the azimuthal amplitude and shape of arms, which, even in the K-bandmay,be significantly biased by the presence of young stellar populations. Severaltechniques were applied to evaluate the relative importance of young starsacross the arms, such as surface brightness of the disk with light fromclusters subtracted, number density of clusters detected, and texture of thedisk. The modulation of the texture measurement,which correlates with the numberdensity of faint clusters, yields amplitudes of the spiral perturbation in therange 0.1-0.2. This estimate gives a better estimate of the mass perturbationin the spiral arms, since it is dominated by old clusters.

International Journal of Bifurcation and Chaos, 1994

The problems encountered in the study of three-dimensional Hamiltonian systems by means of the Po... more The problems encountered in the study of three-dimensional Hamiltonian systems by means of the Poincare cross-sections are reviewed. A new method to overcome these problems is proposed. In order to visualize the four-dimensional “space” of section we introduce the use of color and rotation. We apply this method to the case of a family of simple periodic orbits in a three-dimensional potential and we describe the differences in the orbital behavior between regions close to stable and unstable periodic orbits. We outline the differences between the transition from stability to simple instability and the transition from stability to complex instability. We study the changes in the structure of the 4D “spaces” of section, which occur when the family becomes complex unstable after a DU →Δ or a S →Δ transition. We conclude that the orbital behavior after the transition depends on the orbital behavior before it.

Monthly Notices of the Royal Astronomical Society, 2005

Using N-body simulations we study the structures induced on a galactic disc by repeated flybys of... more Using N-body simulations we study the structures induced on a galactic disc by repeated flybys of a companion in decaying eccentric orbit around the disc. Our system is composed by a stellar disc, bulge and live dark matter halo, and we study the system's dynamical response to a sequence of a companion's flybys, when we vary i) the disc's temperature (parameterized by Toomre's Q-parameter) and ii) the companion's mass and initial orbit. We use a new 3D Cartesian grid code: MAIN (Mesh-adaptive Approximate Inverse N-body solver). The main features of MAIN are reviewed, with emphasis on the use of a new Symmetric Factored Approximate Sparse Inverse (SFASI) matrix in conjunction with the multigrid method that allows the efficient solution of Poisson's equation in three space variables. We find that: i) companions need to be assigned initial masses in a rather narrow window of values in order to produce significant and more long-standing non-axisymmetric structure...

The Opacity of Spiral Disks, 1995

Monthly Notices of the Royal Astronomical Society, 2010

International Journal of Bifurcation and Chaos, 2011

We study the orbital behavior at the neighborhood of complex unstable periodic orbits in a 3D aut... more We study the orbital behavior at the neighborhood of complex unstable periodic orbits in a 3D autonomous Hamiltonian system of galactic type. At a transition of a family of periodic orbits from stability to complex instability (also known as Hamiltonian Hopf Bifurcation) the four eigenvalues of the stable periodic orbits move out of the unit circle. Then the periodic orbits

Monthly Notices of the Royal Astronomical Society, 2016

I will review the dynamical mechanisms that have been found to shape the observed structures of d... more I will review the dynamical mechanisms that have been found to shape the observed structures of disk galaxies, such as the spirals and the bars. The morphological properties of the spiral arms will be described in association with different dynamical mechanisms that have been proposed to build them. Differences are expected due to the fact that the spirals can be reinforced by stars in regular or in chaotic motion. Also in bars chaos may contribute to the observed morphologies in percentages that vary from case to case. I will also discuss the vertical structure of disk galaxies and the possible contribution of chaotic orbits to their density profiles away from the equatorial plane.

The spiral structure of five ordinary spiral galaxies was studied using deep BVIK' surface ph... more The spiral structure of five ordinary spiral galaxies was studied using deep BVIK' surface photometry maps obtained at the 2.2m ESO/MPI telescope. The detailed shape of the arms was analyzed in terms of the spiral density wave theory. Grand design spirals were found on the K' maps in all five galaxies although at least two would be classified as flocculent

Deep K-band surface photometry of 12 spiral galaxies was used to analyze the spiral structure in ... more Deep K-band surface photometry of 12 spiral galaxies was used to analyze the spiral structure in their disks. Amplitude and shape of the main two-armed spiral arms were determined. Further, synthetic rotation curves were derived using the radial distribution of the K surface photometry and kinematic data available for the galaxies. The radial extent of the main spiral patterns was compared to the locations of major resonances (e.g., ILR, 4:1, CR, OLR) suggested by the rotation curves. This was used to estimate possible values for the angular speed of the spiral patterns.

Although interarm features in the Population I disk frequently give an impression of a three-fold... more Although interarm features in the Population I disk frequently give an impression of a three-fold symmetry, three-armed spiral structures in the old stellar disk are seldom seen. Such case, like NGC 7137, are of special interest since they can be used to study unique conditions which favor the growth of m=3 modes in stellar disks. The current paper presents the structure of the main family of periodic orbits in a model of the three-armed galaxy NGC 7137 and compares it with near-infrared maps of the galaxy. Finally we examine the relation of the orbital dynamics with 3-armed patterns we find in self-gravitating N-body models.

Monthly Notices of the Royal Astronomical Society, 2010

Astronomy & Astrophysics

Aims. Periodic orbits (POs) have been exhaustively studied. On the contrary, to our knowledge, no... more Aims. Periodic orbits (POs) have been exhaustively studied. On the contrary, to our knowledge, no complete and systematic study of higher-multiplicity (ℳ) POs, that is, orbits that close after more than one revolution in phase space, exists. Here, we fill this gap and also extend the standard tools used for studies of the x1 POs to studies of higher multiplicity POs. Methods. We adopted a multi-aspect approach, using surfaces of section, stability diagrams, characteristic diagrams, studies of the shapes of individual orbits, and other properties of the POs. We modified and extended the standard tools used for ℳ = 1, to ℳ > 1 cases, allowing them to use the snapshot information more fully. Our potential is more realistic than those of most previous studies, as it is obtained directly from a snapshot of a fully self-consistent, high-resolution numerical simulation. Results. We find five main pairs of PO families with ℳ = 2. Two of these bifurcate from the x1 family and are direct r...

Monthly Notices of the Royal Astronomical Society, 2018

Astrophysics and Space Science Proceedings, 2008

1 Research Center for Astronomy, Academy of Athens, Soranou Efessiou 4, GR-11527, Athens, Greece ... more 1 Research Center for Astronomy, Academy of Athens, Soranou Efessiou 4, GR-11527, Athens, Greece mkatsan@yahoo.gr, patsis@academyofathens.gr 2 Department of Economic Studies, University of Thessaly, Volos, Greece zachilas@uth.gr ... Summary. In order to ...

… Astronomy with the …, 2008

Communicating Astronomy with the Public 2007: Proceedings from the IAU/National Observatory of At... more Communicating Astronomy with the Public 2007: Proceedings from the IAU/National Observatory of Athens/ESA/ESO Conference, Athens, Greece, 8-11 October 2007, Christensen LL, Zoulias M. & Robson, I. (eds.). Published by Eugenides Foundation. ... The Society for Space and ...

The flow in the arms of spiral galaxies is qualitatively different among different morphological ... more The flow in the arms of spiral galaxies is qualitatively different among different morphological types. The stars that reinforce the spiral arms can be either participating in an ordered or in a chaotic flow. Ordered flows are typically described by precessing ellipses corresponding to stable periodic orbits at successive energies (Jacobi constants). Contrarily, there are spiral arms in barred-spiral systems which may be supported by stars in chaotic motion "along" the arms. The trajectories of these stars are associated with the invariant manifolds of unstable periodic orbits at corotations region. We find that the spirals and the outer parts of the bars share the same orbital content. However, there also barredspiral systems with spirals inside corotation, consisting mainly by chaotic orbits, or by ordered flows. The talk will present models where various dynamical mehanisms coexits and will compare them with structures that are possible the result of the concerted actio...

It has proven very difficult to estimate the amplitudes of spiralperturbations in disk galaxies f... more It has proven very difficult to estimate the amplitudes of spiralperturbations in disk galaxies from observations due to the variation ofmass-to-light ratio and extinction across spiral arms. Deep, near-infraredimages of grand-design spiral galaxies obtained with HAWK-I/VLT were used toanalyze the azimuthal amplitude and shape of arms, which, even in the K-bandmay,be significantly biased by the presence of young stellar populations. Severaltechniques were applied to evaluate the relative importance of young starsacross the arms, such as surface brightness of the disk with light fromclusters subtracted, number density of clusters detected, and texture of thedisk. The modulation of the texture measurement,which correlates with the numberdensity of faint clusters, yields amplitudes of the spiral perturbation in therange 0.1-0.2. This estimate gives a better estimate of the mass perturbationin the spiral arms, since it is dominated by old clusters.

International Journal of Bifurcation and Chaos, 1994

The problems encountered in the study of three-dimensional Hamiltonian systems by means of the Po... more The problems encountered in the study of three-dimensional Hamiltonian systems by means of the Poincare cross-sections are reviewed. A new method to overcome these problems is proposed. In order to visualize the four-dimensional “space” of section we introduce the use of color and rotation. We apply this method to the case of a family of simple periodic orbits in a three-dimensional potential and we describe the differences in the orbital behavior between regions close to stable and unstable periodic orbits. We outline the differences between the transition from stability to simple instability and the transition from stability to complex instability. We study the changes in the structure of the 4D “spaces” of section, which occur when the family becomes complex unstable after a DU →Δ or a S →Δ transition. We conclude that the orbital behavior after the transition depends on the orbital behavior before it.

Monthly Notices of the Royal Astronomical Society, 2005

Using N-body simulations we study the structures induced on a galactic disc by repeated flybys of... more Using N-body simulations we study the structures induced on a galactic disc by repeated flybys of a companion in decaying eccentric orbit around the disc. Our system is composed by a stellar disc, bulge and live dark matter halo, and we study the system's dynamical response to a sequence of a companion's flybys, when we vary i) the disc's temperature (parameterized by Toomre's Q-parameter) and ii) the companion's mass and initial orbit. We use a new 3D Cartesian grid code: MAIN (Mesh-adaptive Approximate Inverse N-body solver). The main features of MAIN are reviewed, with emphasis on the use of a new Symmetric Factored Approximate Sparse Inverse (SFASI) matrix in conjunction with the multigrid method that allows the efficient solution of Poisson's equation in three space variables. We find that: i) companions need to be assigned initial masses in a rather narrow window of values in order to produce significant and more long-standing non-axisymmetric structure...

The Opacity of Spiral Disks, 1995

Monthly Notices of the Royal Astronomical Society, 2010

International Journal of Bifurcation and Chaos, 2011

We study the orbital behavior at the neighborhood of complex unstable periodic orbits in a 3D aut... more We study the orbital behavior at the neighborhood of complex unstable periodic orbits in a 3D autonomous Hamiltonian system of galactic type. At a transition of a family of periodic orbits from stability to complex instability (also known as Hamiltonian Hopf Bifurcation) the four eigenvalues of the stable periodic orbits move out of the unit circle. Then the periodic orbits

Monthly Notices of the Royal Astronomical Society, 2016

I will review the dynamical mechanisms that have been found to shape the observed structures of d... more I will review the dynamical mechanisms that have been found to shape the observed structures of disk galaxies, such as the spirals and the bars. The morphological properties of the spiral arms will be described in association with different dynamical mechanisms that have been proposed to build them. Differences are expected due to the fact that the spirals can be reinforced by stars in regular or in chaotic motion. Also in bars chaos may contribute to the observed morphologies in percentages that vary from case to case. I will also discuss the vertical structure of disk galaxies and the possible contribution of chaotic orbits to their density profiles away from the equatorial plane.

The spiral structure of five ordinary spiral galaxies was studied using deep BVIK' surface ph... more The spiral structure of five ordinary spiral galaxies was studied using deep BVIK' surface photometry maps obtained at the 2.2m ESO/MPI telescope. The detailed shape of the arms was analyzed in terms of the spiral density wave theory. Grand design spirals were found on the K' maps in all five galaxies although at least two would be classified as flocculent

Deep K-band surface photometry of 12 spiral galaxies was used to analyze the spiral structure in ... more Deep K-band surface photometry of 12 spiral galaxies was used to analyze the spiral structure in their disks. Amplitude and shape of the main two-armed spiral arms were determined. Further, synthetic rotation curves were derived using the radial distribution of the K surface photometry and kinematic data available for the galaxies. The radial extent of the main spiral patterns was compared to the locations of major resonances (e.g., ILR, 4:1, CR, OLR) suggested by the rotation curves. This was used to estimate possible values for the angular speed of the spiral patterns.

Although interarm features in the Population I disk frequently give an impression of a three-fold... more Although interarm features in the Population I disk frequently give an impression of a three-fold symmetry, three-armed spiral structures in the old stellar disk are seldom seen. Such case, like NGC 7137, are of special interest since they can be used to study unique conditions which favor the growth of m=3 modes in stellar disks. The current paper presents the structure of the main family of periodic orbits in a model of the three-armed galaxy NGC 7137 and compares it with near-infrared maps of the galaxy. Finally we examine the relation of the orbital dynamics with 3-armed patterns we find in self-gravitating N-body models.

Monthly Notices of the Royal Astronomical Society, 2010