42 research outputs found
3D hydrodynamic numerical models for nebulae around runaway Wolf-Rayet stars
We present 3D hydrodynamical simulations of the circumstellar bubble from a Wolf-Rayet runaway star. In the models two properties were taken into account: (a) the proper motion of the central star through the interstellar medium (ISM) and (b) the evolution of the stellar wind from the red supergiant (RSG) stage to the Wolf-Rayet (WR) stage. From the hydrodynamic results synthetic X-ray maps in the [0.3 − 1.2] keV energy range were computed. These maps show that the bubble morphology is affected by the stellar motion, producing a bow shock in the RSG stage that can explain the limb-brightened morphology observed. Additionally, these synthetic maps show filamentary and clumpy appearance produced by instabilities triggered from the interaction between the WR wind and the RSG shell. It was found that these types of collisions can explain the origin of the X-ray emission observed in the nebulae of Wolf- Rayet stars.Fil: Reyes Iturbide, J.. Universidad Nacional Autónoma de México. Instituto de Ciencias Nucleares; México. Tecnológico de Estudios Superiores de Tianguistenco; MéxicoFil: Velázquez, Pablo F.. Universidad Nacional Autónoma de México. Instituto de Ciencias Nucleares; MéxicoFil: Rosado, M.. Universidad Nacional Autónoma de México. Instituto de Astronomía; MéxicoFil: Schneiter, Ernesto Matías. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Ramírez Ballinas, I.. Universidad Nacional Autónoma de México. Instituto de Astronomía; Méxic
3D numerical model of the Omega Nebula (M17): simulated thermal X-ray emission
We present 3D hydrodynamical simulations of the superbubble M17, also known
as the Omega nebula, carried out with the adaptive grid code yguazu'-a, which
includes radiative cooling. The superbubble is modelled considering the winds
of 11 individual stars from the open cluster inside the nebula (NGC 6618), for
which there are estimates of the mass loss rates and terminal velocities based
on their spectral types. These stars are located inside a dense interstellar
medium, and they are bounded by two dense molecular clouds.
We carried out three numerical models of this scenario, considering different
line of sight positions of the stars (the position in the plane of the sky is
known, thus fixed). Synthetic thermal X-ray emission maps are calculated from
the numerical models and compared with ROSAT observations of this astrophysical
object. Our models reproduce successfully both the observed X-ray morphology
and the total X-ray luminosity, without taking into account thermal conduction
effects.Comment: 8 pages, 6 figures, accepted for publication in MNRA
X-ray emission and dynamics from large diameter superbubbles: The case of N 70 superbubble
The morphology, dynamics and thermal X-ray emission of the superbubble N70 is
studied by means of 3D hydrodynamical simulations, carried out with the
{\sc{yguaz\'u-a}} code. We have considered different scenarios: the superbubble
being the product of a single supernova remnant, of the stellar winds from an
OB association, or the result of the joint action of stellar winds and a
supernova event. Our results show that, in spite that all scenarios produce
bubbles with the observed physical size, only those where the bubble is driven
by stellar winds and a SN event are successful to explain the general
morphology, dynamics and the X-ray luminosity of N70. Our models predict
temperatures in excess of at the interior of the superbubble,
however the density is too low and the emission in thermal X-ray above is too faint to be detected.Comment: 9 pages, 11 figures, ApJ accepte
An extensive study of dynamical friction in dwarf galaxies: the role of stars, dark matter, halo profiles and MOND
We investigate the in-spiraling timescales of globular clusters in dwarf
spheroidal (dSph) and dwarf elliptical (dE) galaxies, due to dynamical
friction. We address the problem of these timescales having been variously
estimated in the literature as much shorter than a Hubble time. Using
self-consistent two-component (dark matter and stars) models, we explore
mechanisms which may yield extended dynamical friction timescales in such
systems in order to explain why dwarf galaxies often show globular cluster
systems. As a general rule, dark matter and stars both give a comparable
contribution to the dynamical drag. By exploring various possibilities for
their gravitational make-up, it is shown that these studies help constrain the
parameters of the dark matter haloes in these galaxies, as well as to test
alternatives to dark matter. Under the assumption of a dark haloes having a
constant density core, dynamical friction timescales are naturally extended
upwards of a Hubble time. Cuspy dark haloes yield timescales 4.5
Gyr, for any dark halo parameters in accordance with observations of stellar
line-of-sight velocity dispersion in dwarf spheroidal galaxies. We find that
under the hypothesis of MOND dynamics, due to the enhanced dynamical drag of
the stars, the dynamical friction timescales would be extremely short. Taking
the well-measured structural parameters of the Fornax dSph and its globular
cluster system as a case study, we conclude that requiring dynamical friction
timescales comparable to the Hubble time strongly favours dark haloes with a
central core.Comment: 18 pages, four figures, final version, accepted in MNRA