A. Rodríguez-González

WINDS DRIVEN BY SUPER STAR CLUSTERS: THE SELF-CONSISTENT RADIATIVE SOLUTION

Here we present a self-consistent stationary solution for spherically symmetric winds driven by massive star clusters under the impact of radiative cooling. We demonstrate that cooling may drastically modify the distribution of temperature if the rate of injected energy approaches a critical value. We also prove that the stationary wind solution does not exist when the energy radiated away at the star cluster center exceeds ~30% of the energy deposition rate. Finally, we thoroughly discuss the expected appearance of super star cluster winds in the X-ray and visible line regimes. The three solutions found, the quasi-adiabatic, the strongly radiative wind, and the inhibited stationary solution, are then compared to the winds from the Arches cluster, the NGC 4303 central cluster, and to the supernebula in NGC 5253.

MIRROR AND POINT SYMMETRIES IN A BALLISTIC JET FROM A BINARY SYSTEM

Models of accretion disks around a star in a binary system predict that the disk will have a retrograde precession with a period a factor of ~10 times the orbital period. If the star+disk system ejects a bipolar outflow, this outflow will be subject to the effects of both the orbital motion and the precession. We present an analytic, ballistic model and a three-dimensional gasdynamical simulation of a bipolar outflow from a source in a circular orbit, and with a precessing outflow axis. We find that this combination results in a jet/counterjet system with a small spatial scale, reflection-symmetric spiral (resulting from the orbital motion) and a larger-scale, point-symmetric spiral (resulting from the longer period precession). These results provide interesting possibilities for modeling specific Herbig-Haro jets and bipolar planetary nebulae.

Discrepancies between the [O iii] and [S iii] temperatures in H ii regions

Context. Analysis of published [O iii ]a nd [Siii] temperatures measurements of emission line objects consisting of Hii galaxies, giant extragalactic Hii regions, Galactic Hii regions, and Hii regions from the Magellanic Clouds reveal that the [O iii] temperatures are higher than the corresponding values from [S iii] in most objects with gas metallicities in excess of 0.2 solar. For the coolest nebulae (the highest metallicities), the [O iii] temperature excess can reach ∼3000 K. Aims. We look for an explanation for these temperature differences and explore the parameter space of models with the aim of reproducing the observed trend of TO iii > TS iii in Hii regions with temperatures below 14 000 K. Methods. Using standard photoionization models, we varied the ionization parameter, the hardness of the ionizing continuum, and the gas metallicities in order to characterize how models behave with respect to the observations. We introduced temperature inhomogeneities and varied their mean squared amplitude t 2 . We explored the possibility of inhomogeneities in abundances by combining two models of widely different metallicity. We calculated models that consider the possibility of a non-Maxwell-Boltzmann energy distribution (a κ-distribution) for the electron energies. We also considered shock heating within the photoionized nebula. Results. Simple photoionization calculations yield nearly equal [O iii ]a nd [Siii] temperatures in the domain of interest. Hence these models fail to reproduce the [O iii] temperature excess. Models that consider temperature inhomogeneities, as measured by the mean squared amplitude t 2 ,a lso fail in the regime whereTO iii TO iii.

On the Extreme Positive Feedback Star-forming Mode from Massive and Compact Super Star Clusters

The force of gravity acting within the volume occupied by young, compact, and massive super star clusters is here shown to drive in situ all the matter deposited by winds and supernovae into several generations of star formation. These events are promoted by radiative cooling, which drains the thermal energy of the ejected gas causing its accumulation to then rapidly exceed the gravitational instability criterion. A detailed account of the integrated ionizing radiation and mechanical luminosity as a function of time is here shown to lead to a new stationary solution. In this, the mass deposition rate , instead of causing a wind as in the adiabatic solution, turns into a positive feedback star-forming mode equal to the star formation rate. Some of the implications of this extreme positive feedback mode are discussed.

A MODEL OF MIRA'S COMETARY HEAD/TAIL ENTERING THE LOCAL BUBBLE

We model the cometary structure around Mira as the interaction of an asymptotic giant branch stellar wind from Mira A with a streaming environment. Our simulations introduce the following new element: we assume that after 200 kyr of evolution in a dense environment, Mira entered the Local Bubble (low-density coronal gas). As Mira enters the bubble, the head of the comet expands quite rapidly, while the tail remains well collimated for a >100 kyr timescale. The result is a broad-head/narrow-tail structure that resembles the observed morphology of Miras comet. The simulations were carried out with our new adaptive grid code WALICXE, which is described in detail.

Three-dimensional 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 successfully reproduce both the observed X-ray morphology and the total X-ray luminosity, without taking into account the thermal conduction effects.

FILAMENTS IN GALACTIC WINDS DRIVEN BY YOUNG STELLAR CLUSTERS

The starburst galaxy M82 shows a system of Hα-emitting filaments that extend to each side of the galactic disk. We model these filaments as the result of the interaction between the winds from a distribution of super stellar clusters (SSCs). We first derive the condition necessary for producing a radiative interaction between the cluster winds (a condition that is met by the SSC distribution of M82). We then compute three-dimensional (3D) simulations for SSC wind distributions that satisfy the condition for a radiative interaction, as well as for distributions that do not satisfy this condition. We find that the highly radiative models, which result from the interaction of high-metallicity cluster winds, produce a structure of Hα-emitting filaments that qualitatively agrees with the observations of M82, while the nonradiative SSC wind interaction models do not produce filamentary structures. Therefore, our criterion for radiative interactions (which depends on the mass-loss rate, the terminal velocity of the SSC winds, and the mean separation between the SSCs) can be used to predict whether or not an observed galaxy should have associated Hα-emitting filaments.

On the Extreme Stationary Outflows from Super Star Clusters: From Superwinds to Supernebulae and Further Massive Star Formation

Here we discuss the properties of star cluster winds in the supercritical, catastrophic cooling regime. We demonstrate that catastrophic cooling inhibits superwinds and that after a rapid phase of accumulation of the ejected material within the star-forming volume, a new stationary isothermal regime, supported by the ionizing radiation from the central cluster, is established. The expected appearance of this core/halo supernebula in the visible-line regime and possible late evolutionary tracks of super star cluster winds in the absence of ionizing radiation are thoroughly discussed.

Winds from clusters with non‐uniform stellar distributions

We present analytic and numerical models of the ‘cluster wind’ resulting from the multiple interactions of the winds ejected by the stars of a dense cluster of massive stars. We consider the case in which the distribution of stars (i. e., the number of stars per unit volume) within the cluster is spherically symmetric, has a power-law radial dependence, and drops discontinuously to zero at the outer radius of the cluster. We carry out comparisons between an analytic model (in which the stars are considered in terms of a spatially continuous injection of mass and energy) and 3D gasdynamic simulations (in which we include 100 stars with identical winds, located in 3D space by statistically sampling the stellar distribution function). From the analytic model, we find that for stellar distributions with steep enough radial dependencies the cluster wind flow develops a very high central density and a non-zero central velocity, and for steeper dependencies it becomes fully supersonic throughout the volume of the cluster (these properties are partially reproduced by the 3D numerical simulations). Therefore, the wind solutions obtained for stratified clusters can differ dramatically from the case of a homogeneous stellar distribution (which produces a cluster wind with zero central velocity, and a fully subsonic flow within the cluster radius). Finally, from our numerical simulations we compute predictions of X-ray emission maps and luminosities, which can be directly compared with observations of cluster wind flows.

Curved Herbig-Haro jets immersed in a stellar wind

Context. Several curved Herbig-Haro (HH) jet/counterjet systems have been observed. Some of these systems are the result of a relative motion between the outflow source and the surrounding environment. Aims. In this paper, we consider the case of an HH jet/counterjet system that is immersed in an isotropic stellar wind. This situation is somewhat different from the previously studied HH jet/plane-parallel side wind interaction, because the isotropic wind is divergent, and has a radially dependent density structure. Methods. We present an analytic model for a jet/wind interaction that is based on the balance between the ram pressure of the wind and the centrifugal pressure along the curved jet/counterjet path. We consider the case of an isothermal jet. Results. We find that, if we have a jet and a wind with similar velocities and mass loss rates, the jet/counterjet system only shows a shallow curvature, with a total deflection angle of only a few degrees. However, if we have stronger winds, quite large deflections are produced (e.g., for the interaction of an HH jet with the wind from an O star). The deflection angle depends on neither the separation between the jet and wind sources nor on the ejection direction of the jet/counterjet.