Monthly Notices of the Royal Astronomical Society, 2015
With the use of a background Milky-Way-like potential model, we performed stellar orbital and mag... more With the use of a background Milky-Way-like potential model, we performed stellar orbital and magnetohydrodynamic (MHD) simulations. As a first experiment, we studied the gaseous response to a bisymmetric spiral arm potential: the widely employed cosine potential model and a self-gravitating tridimensional density distribution based model called PERLAS. Important differences are noticeable in these simulations, while the simplified cosine potential produces two spiral arms for all cases, the more realistic density based model produces a response of four spiral arms on the gaseous disk, except for weak arms -i.e. close to the linear regime-where a two-armed structure is formed. In order to compare the stellar and gas response to the spiral arms, we have also included a detailed periodic orbit study and explored different structural parameters within observational uncertainties. The four armed response has been explained as the result of ultra harmonic resonances, or as shocks with the massive bisymmetric spiral structure, among other. From the results of this work, and comparing the stellar and gaseous responses, we tracked down an alternative explanation to the formation of branches, based only on the orbital response to a self-gravitating spiral arms model. The presence of features such as branches, might be an indication of transiency of the arms.
Proceedings of the International Astronomical Union, 2009
We use test-particle orbit integration with a realistic Milky Way (MW) potential to study the eff... more We use test-particle orbit integration with a realistic Milky Way (MW) potential to study the effect of the resonances of the Galactic bar and spiral arms on the velocity distribution of the Solar Neighbourhood and other positions of the disk. Our results show that spiral arms create abundant kinematic substructure and crowd stars into the region of the Hercules moving group in the velocity plane. Bar resonances can contribute to the origin of low-angular momentum moving groups like Arcturus. Particles in the predicted dark disk of the MW should be affected by the same resonances as stars, triggering dark-matter moving groups in the disk. Finally, we evaluate how this study will be advanced by upcoming Gaia data.
The tidal interaction of globular clusters with the Galactic bulge is studied. We employ a Galact... more The tidal interaction of globular clusters with the Galactic bulge is studied. We employ a Galactic potential that includes a bar. In particular, clusters with orbits residing in the bar region are considered. We calculate the tidal force on the real orbit of globular clusters, rather than the usual straight-line approximation. With ideas developed by Gnedin et al. (1999), we
We present a multi-wavelength study of NGC 2992/3, an interacting system composed of two collidin... more We present a multi-wavelength study of NGC 2992/3, an interacting system composed of two colliding spiral galaxies out of which emanate long stellar tails and a bridge. Both spirals show signs of nuclear activity, in particular NGC 2992, which has a Seyfert 1.9 nucleus which is obscured by a prominent dust lane. Our Halpha map and longslit spectroscopic data indicate
Whereas it is well known that gas may be driven into the core of merging disks, fueling a central... more Whereas it is well known that gas may be driven into the core of merging disks, fueling a central AGN or a nuclear starburst, recent studies have shown that a significant fraction of the stellar/gaseous components is expelled into the intergalactic medium along tidal tails. The tidal debris might be dispersed in the intergalactic/intracluster medium where it adds to the
One of the most intriguing features in the solar neighborhood stellar velocity distribution are t... more One of the most intriguing features in the solar neighborhood stellar velocity distribution are the so called moving groups. These groups are stellar streams observed as overdensities in the velocity space, crossing the region nearby the Sun. At 140 years of their discovery, the understanding of the origin of these kinematic structures is still far from complete. Several scenarios for
In a series of papers we proposed a theory to explain the formation and properties of rings and s... more In a series of papers we proposed a theory to explain the formation and properties of rings and spirals in barred galaxies. The building blocks of these structures are orbits trapped by the invariant manifolds of the periodic orbits around the unstable Lagrangian points located near the ends of the bar. Here, we will first present a comparison of the
In this study we propose to constrain through the local stellar kinematics, the overall shape of ... more In this study we propose to constrain through the local stellar kinematics, the overall shape of the Milky Way dark matter halo. We base on the principle that the shape of the halo implies the existence of families of periodic orbits that support the triaxial shape. These groups would appear as kinematic co-mobile stars in the halo of the Galaxy.
The first mechanism invoked to explain the existence of the thick disk in the Milky Way Galaxy, w... more The first mechanism invoked to explain the existence of the thick disk in the Milky Way Galaxy, were the spiral arms. Up-to-date work summon several other possibilities that together seem to better explain this component of our Galaxy. All these processes must affect differently in distinct types of galaxies, but the contribution of each one has not been straightforward to quantify. In this work, we present a first comprehensive study of the effect of the spiral arms in the formation of thick disks, as going from early to late type disk galaxies, in an attempt to characterize and quantify this specific mechanism in galactic potentials. To this purpose, we perform numerical simulations of test particles in a three-dimensional spiral galaxy potential of normal spiral galaxies (from early to late types). By varying the parameters of the spiral arms we found that the vertical heating of the stellar disk becomes very important in some cases, and strongly depends on the galaxy morphology, pitch angle, arms mass and its pattern speed. The later the galaxy type, the larger is the effect on the disk heating. This study shows that the physical mechanism causing the vertical heating is different from simple resonant excitation. The spiral pattern induce chaotic behavior not linked necessarily to resonances but to direct scattering of disk stars, which leads to an increase of the velocity dispersion. We applied this study to the specific example of the Milky Way Galaxy, for which we have also added an experiment that includes the Galactic bar. From this study we deduce that the effect of spiral arms of a Milky-Way-like potential, on the dynamical vertical heating of the disk is negligible, unlike later galactic potentials for disks.
Monthly Notices of the Royal Astronomical Society, 2014
A general formulation to compute habitable zones for binary stars is presented. We extend the sim... more A general formulation to compute habitable zones for binary stars is presented. We extend the simple formulation of the known concept: circumstellar habitable zone for single stars, to the case of eccentric stellar binary systems, where two sources of luminosity at different orbital phases contribute to the irradiance of their planetary circumstellar and circumbinary regions. Our approach considers binaries with eccentric orbits and guarantees that orbits in the computed habitable zone remain within it at all orbital phases. We apply this formulation to calculate habitable zones for binary stars of the solar neighborhood with known orbital parameters. Regions of stable, non-intersecting orbits, supported by invariant loops have been determined using the results of , together with their habitable zones, are calculated for 51 cases, including some with discovered planets.
Proceedings of The International Astronomical Union, 2009
We present an extensive compilation of kinematic data for more than 24000 stars of the solar neig... more We present an extensive compilation of kinematic data for more than 24000 stars of the solar neighbourhood, together with ages and metallicities for an important fraction of them. Errors and biases in these data are discussed in detail in Antoja et al.(2008).
We evaluate the hypothesis that relates the formation of moving groups to the resonances of the n... more We evaluate the hypothesis that relates the formation of moving groups to the resonances of the non-axisymmetric component of the Galactic potential (spiral arms and central bar). We apply multiscale techniques to an extensive sample of more than 24000 stars of the solar neighbourhood to characterize the kinematic structures in the U-V -age-[Fe/H] space. The observational data is compared with the distribution in the kinematic plane obtained through the computation of test particle orbits under analytic models for the potential. Results from two different models for the spiral structure and/or the Galactic bar are presented here. We show that the simulations near the position of the ILR -1:4 of the spiral structure and the OLR 1:2 of the Galactic bar are able to reproduce kinematic structures similar to the observed ones. We discuss the fundamental role of the age and metallicity distributions in the confirmation of the hypothesis.
ABSTRACT We present a survey for RR Lyrae stars in an area of 50 deg 2 around the globular cluste... more ABSTRACT We present a survey for RR Lyrae stars in an area of 50 deg 2 around the globular cluster ω Centauri, aimed to detect debris material from the alleged progenitor galaxy of the cluster. We detected 48 RR Lyrae stars of which only 11 have been previously reported. Ten among the eleven previously known stars were found inside the tidal radius of the cluster. The rest were located outside the tidal radius up to distances of ∼ 6 degrees from the center of the cluster. Several of those stars are located at distances similar to that of ω Centauri. We investigated the probability that those stars may have been stripped off the cluster by studying their properties (mean periods), calculating the expected halo/thick disk population of RR Lyrae stars in this part of the sky, analyzing the radial velocity of a sub-sample of the RR Lyrae stars, and finally, studying the probable orbits of this sub-sample around the Galaxy. None of these investigations support the scenario that there is significant tidal debris around ω Centauri, confirming previous studies in the region. It is puzzling that tidal debris have been found elsewhere but not near the cluster itself.
We present three-dimensional numerical simulations of turbulence in two different regimes: a) Ful... more We present three-dimensional numerical simulations of turbulence in two different regimes: a) Full models of the ISM including the magnetic field, parameterized cooling and diffuse and stellar heating, self-gravity and rotation. b) Barotropic flows (P ~ rho (gamma ) ), with gamma smaller, equal and larger than 1. We compare the physical-space density distribution with its representation in position-position-velocity space,
Monthly Notices of the Royal Astronomical Society, 2015
With the use of a background Milky-Way-like potential model, we performed stellar orbital and mag... more With the use of a background Milky-Way-like potential model, we performed stellar orbital and magnetohydrodynamic (MHD) simulations. As a first experiment, we studied the gaseous response to a bisymmetric spiral arm potential: the widely employed cosine potential model and a self-gravitating tridimensional density distribution based model called PERLAS. Important differences are noticeable in these simulations, while the simplified cosine potential produces two spiral arms for all cases, the more realistic density based model produces a response of four spiral arms on the gaseous disk, except for weak arms -i.e. close to the linear regime-where a two-armed structure is formed. In order to compare the stellar and gas response to the spiral arms, we have also included a detailed periodic orbit study and explored different structural parameters within observational uncertainties. The four armed response has been explained as the result of ultra harmonic resonances, or as shocks with the massive bisymmetric spiral structure, among other. From the results of this work, and comparing the stellar and gaseous responses, we tracked down an alternative explanation to the formation of branches, based only on the orbital response to a self-gravitating spiral arms model. The presence of features such as branches, might be an indication of transiency of the arms.
Proceedings of the International Astronomical Union, 2009
We use test-particle orbit integration with a realistic Milky Way (MW) potential to study the eff... more We use test-particle orbit integration with a realistic Milky Way (MW) potential to study the effect of the resonances of the Galactic bar and spiral arms on the velocity distribution of the Solar Neighbourhood and other positions of the disk. Our results show that spiral arms create abundant kinematic substructure and crowd stars into the region of the Hercules moving group in the velocity plane. Bar resonances can contribute to the origin of low-angular momentum moving groups like Arcturus. Particles in the predicted dark disk of the MW should be affected by the same resonances as stars, triggering dark-matter moving groups in the disk. Finally, we evaluate how this study will be advanced by upcoming Gaia data.
The tidal interaction of globular clusters with the Galactic bulge is studied. We employ a Galact... more The tidal interaction of globular clusters with the Galactic bulge is studied. We employ a Galactic potential that includes a bar. In particular, clusters with orbits residing in the bar region are considered. We calculate the tidal force on the real orbit of globular clusters, rather than the usual straight-line approximation. With ideas developed by Gnedin et al. (1999), we
We present a multi-wavelength study of NGC 2992/3, an interacting system composed of two collidin... more We present a multi-wavelength study of NGC 2992/3, an interacting system composed of two colliding spiral galaxies out of which emanate long stellar tails and a bridge. Both spirals show signs of nuclear activity, in particular NGC 2992, which has a Seyfert 1.9 nucleus which is obscured by a prominent dust lane. Our Halpha map and longslit spectroscopic data indicate
Whereas it is well known that gas may be driven into the core of merging disks, fueling a central... more Whereas it is well known that gas may be driven into the core of merging disks, fueling a central AGN or a nuclear starburst, recent studies have shown that a significant fraction of the stellar/gaseous components is expelled into the intergalactic medium along tidal tails. The tidal debris might be dispersed in the intergalactic/intracluster medium where it adds to the
One of the most intriguing features in the solar neighborhood stellar velocity distribution are t... more One of the most intriguing features in the solar neighborhood stellar velocity distribution are the so called moving groups. These groups are stellar streams observed as overdensities in the velocity space, crossing the region nearby the Sun. At 140 years of their discovery, the understanding of the origin of these kinematic structures is still far from complete. Several scenarios for
In a series of papers we proposed a theory to explain the formation and properties of rings and s... more In a series of papers we proposed a theory to explain the formation and properties of rings and spirals in barred galaxies. The building blocks of these structures are orbits trapped by the invariant manifolds of the periodic orbits around the unstable Lagrangian points located near the ends of the bar. Here, we will first present a comparison of the
In this study we propose to constrain through the local stellar kinematics, the overall shape of ... more In this study we propose to constrain through the local stellar kinematics, the overall shape of the Milky Way dark matter halo. We base on the principle that the shape of the halo implies the existence of families of periodic orbits that support the triaxial shape. These groups would appear as kinematic co-mobile stars in the halo of the Galaxy.
The first mechanism invoked to explain the existence of the thick disk in the Milky Way Galaxy, w... more The first mechanism invoked to explain the existence of the thick disk in the Milky Way Galaxy, were the spiral arms. Up-to-date work summon several other possibilities that together seem to better explain this component of our Galaxy. All these processes must affect differently in distinct types of galaxies, but the contribution of each one has not been straightforward to quantify. In this work, we present a first comprehensive study of the effect of the spiral arms in the formation of thick disks, as going from early to late type disk galaxies, in an attempt to characterize and quantify this specific mechanism in galactic potentials. To this purpose, we perform numerical simulations of test particles in a three-dimensional spiral galaxy potential of normal spiral galaxies (from early to late types). By varying the parameters of the spiral arms we found that the vertical heating of the stellar disk becomes very important in some cases, and strongly depends on the galaxy morphology, pitch angle, arms mass and its pattern speed. The later the galaxy type, the larger is the effect on the disk heating. This study shows that the physical mechanism causing the vertical heating is different from simple resonant excitation. The spiral pattern induce chaotic behavior not linked necessarily to resonances but to direct scattering of disk stars, which leads to an increase of the velocity dispersion. We applied this study to the specific example of the Milky Way Galaxy, for which we have also added an experiment that includes the Galactic bar. From this study we deduce that the effect of spiral arms of a Milky-Way-like potential, on the dynamical vertical heating of the disk is negligible, unlike later galactic potentials for disks.
Monthly Notices of the Royal Astronomical Society, 2014
A general formulation to compute habitable zones for binary stars is presented. We extend the sim... more A general formulation to compute habitable zones for binary stars is presented. We extend the simple formulation of the known concept: circumstellar habitable zone for single stars, to the case of eccentric stellar binary systems, where two sources of luminosity at different orbital phases contribute to the irradiance of their planetary circumstellar and circumbinary regions. Our approach considers binaries with eccentric orbits and guarantees that orbits in the computed habitable zone remain within it at all orbital phases. We apply this formulation to calculate habitable zones for binary stars of the solar neighborhood with known orbital parameters. Regions of stable, non-intersecting orbits, supported by invariant loops have been determined using the results of , together with their habitable zones, are calculated for 51 cases, including some with discovered planets.
Proceedings of The International Astronomical Union, 2009
We present an extensive compilation of kinematic data for more than 24000 stars of the solar neig... more We present an extensive compilation of kinematic data for more than 24000 stars of the solar neighbourhood, together with ages and metallicities for an important fraction of them. Errors and biases in these data are discussed in detail in Antoja et al.(2008).
We evaluate the hypothesis that relates the formation of moving groups to the resonances of the n... more We evaluate the hypothesis that relates the formation of moving groups to the resonances of the non-axisymmetric component of the Galactic potential (spiral arms and central bar). We apply multiscale techniques to an extensive sample of more than 24000 stars of the solar neighbourhood to characterize the kinematic structures in the U-V -age-[Fe/H] space. The observational data is compared with the distribution in the kinematic plane obtained through the computation of test particle orbits under analytic models for the potential. Results from two different models for the spiral structure and/or the Galactic bar are presented here. We show that the simulations near the position of the ILR -1:4 of the spiral structure and the OLR 1:2 of the Galactic bar are able to reproduce kinematic structures similar to the observed ones. We discuss the fundamental role of the age and metallicity distributions in the confirmation of the hypothesis.
ABSTRACT We present a survey for RR Lyrae stars in an area of 50 deg 2 around the globular cluste... more ABSTRACT We present a survey for RR Lyrae stars in an area of 50 deg 2 around the globular cluster ω Centauri, aimed to detect debris material from the alleged progenitor galaxy of the cluster. We detected 48 RR Lyrae stars of which only 11 have been previously reported. Ten among the eleven previously known stars were found inside the tidal radius of the cluster. The rest were located outside the tidal radius up to distances of ∼ 6 degrees from the center of the cluster. Several of those stars are located at distances similar to that of ω Centauri. We investigated the probability that those stars may have been stripped off the cluster by studying their properties (mean periods), calculating the expected halo/thick disk population of RR Lyrae stars in this part of the sky, analyzing the radial velocity of a sub-sample of the RR Lyrae stars, and finally, studying the probable orbits of this sub-sample around the Galaxy. None of these investigations support the scenario that there is significant tidal debris around ω Centauri, confirming previous studies in the region. It is puzzling that tidal debris have been found elsewhere but not near the cluster itself.
We present three-dimensional numerical simulations of turbulence in two different regimes: a) Ful... more We present three-dimensional numerical simulations of turbulence in two different regimes: a) Full models of the ISM including the magnetic field, parameterized cooling and diffuse and stellar heating, self-gravity and rotation. b) Barotropic flows (P ~ rho (gamma ) ), with gamma smaller, equal and larger than 1. We compare the physical-space density distribution with its representation in position-position-velocity space,
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Papers by B. Pichardo