arXiv subjects

A. Esquivel

Publications and source records attributed to A. Esquivel.

At least 19 recordsLinked to original sources

arXiv2026

Planetary atmospheric escape and disk formation around WDJ0914+1914

The spectrum of the white dwarf WD J091405.30+191412.25 displays the absorption and double-peaked emission lines of the volatiles hydrogen, oxygen, and sulfur. This unique characteristic has been interpreted as evidence of this white dwarf accreting mass from a circumstellar disk that had formed from atmospheric material evaporating off a close-in Neptune-like or super-puff mass planet. Thus far, however, the orbital separation of the planet and its mass-loss rate have only been estimated using simple analytical approximations. We investigate this scenario using 3D radiative-hydrodynamic simulations of irradiated hydrogen atmospheres together with 1D viscous disk evolution models. We compute atmospheric escape from Neptune-like and super-puff planets exposed to extreme ultraviolet (XUV) radiation of the white dwarf at different orbital separations and follow the evolution of the escaping gas after it forms a circumstellar disk. The simulations yield planetary mass-loss rates of $(1.8-4)x10^{12}$ g/s. The injected material forms a gaseous disk that reaches a quasi-steady state in less than $10^5$ through the balance between continuous mass supply and viscous accretion onto the white dwarf. The resulting accretion rates are consistent with observational estimates. In contrast to previous interpretations, our models predict that the disk extends beyond the planetary orbit. We conclude that a gas-rich planet orbiting at 15 solar radii undergoes sustained photoevaporation and naturally produces a circumstellar disk capable of reproducing the observed accretion rates and spectral signatures of WD J0914+1914. These results provide strong support for the evaporating-planet scenario and offer new constraints on the structure and extent of the circumstellar disk.

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arXiv2025

Collisions in a system of conical jet/counterjet outflows

Stars predominantly form in compact, non-hierarchical clusters. The gas outflows ejected by protostars can intersect and interact with each other, resulting in complex interactions that affect the dynamics, morphology, and evolution of these outflows. Determining the probability of an encounter between them requires a Bayesian approach that considers the collimation, length (or age), and separation between young stellar objects in the clusters. In this study, we employ a Monte Carlo approach to estimate this probability as a function of the jet opening angle and the ratio between the jet length and the separation between stars. We propose a function that predicts the number of interactions within a cluster based on the opening angle of the gas outflows ejected by protostars.

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arXiv2025

Unveiling the collision between molecular outflows: observational evidence and hydrodynamic simulations

We present an unexplored scenario for interpreting the outflows in the EGO G338.92+0.55 (b) region (hereafter, EGO G338). Within this framework, we investigate the hypothesis that the interaction between two outflows is responsible for the observed morphology and kinematics of this astrophysical object. To explore this possibility, we reanalyse the region using observational molecular line data. We base our analysis on maps of moments 0, 1, and 2 of the CO emission associated with the molecular outflows. Additionally, we conduct three-dimensional hydrodynamic simulations to examine the presence or absence of a collision between two jets. From our numerical results, we produce synthetic CO images to facilitate a direct comparison with observations. The findings of this study provide compelling evidence that the observed morphology and kinematics in the EGO G338 region are the result of a likely collision between two molecular outflows.

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arXiv2024

Effects of Radiative Transfer on the Observed Anisotropy in MHD Turbulent Molecular Simulations

We study the anisotropy of centroid and integrated intensity maps with synthetic observations. We perform post-process radiative transfer including the optically thick regime that was not covered in Hern\'andez-Padilla et al. (2020). We consider the emission in various CO molecular lines, that range from optically thin to optically thick ($\mathrm{^{12}CO}$, $\mathrm{^{13}CO}$, $\mathrm{C^{18}O}$, and $\mathrm{C^{17}O}$). The results for the velocity centroids are similar to those in the optically thin case. For instance, the anisotropy observed can be attributed to the Alfv\'en mode, which dominates over the slow and fast modes when the line of sight is at a high inclination with respect to the mean magnetic field. A few differences arise in the models with higher opacity, where some dependence on the sonic Mach number becomes evident. In contrast to the optically thin case, maps of integrated intensity become more anisotropic in optically thick lines. In this situation the scales probed are restricted, due to absorption, to smaller scales which are known to be more anisotropic. We discuss how the sonic Mach number can affect the latter results, with highly supersonic cases exhibiting a lower degree of anisotropy.

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arXiv2023

Synthetic X-ray emission from white dwarf accreting planetary material

The emission of hard X-rays associated with white dwarfs (WD) can be generated by the presence of a stellar companion either by the companion's coronal emission or by an accretion disk formed by material stripped from the companion. Recent studies have suggested that a Jupiter-like planet can also be donor of material whose accretion onto the WD can generate hard X-rays. We use the {\sc guacho} code to reproduce the conditions of this WD-planet scenario. With the example of the hard X-ray WD KPD\,0005+5106, we explore different terminal wind velocities and mass-loss rates of a donor planet for a future network of simulations to investigate the luminosity and the spectral and temporal properties of the hard X-ray emission in WD-planet systems. Our simulations show that the material stripped from the planet forms a disk and accretes onto the WD to reach temperatures high enough to generate hard X-rays as usually seen in X-ray binaries with low-mass companions. For high terminal wind velocities, the planet material does not form a disk, but it rather accretes directly onto the WD surface. The simulations reproduce the X-ray luminosity of another X-ray accreting WD (G\,29$-$38), and only for some times reaches the hard X-ray luminosity of KPD\,0005+5106. The X-ray variability is stochastic and does not reproduce the period of KPD\,0005+5106, suggesting that additional physical processes (e.g., hot spots resulting from magnetic channelling of the accreting material) need to be explored.

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arXiv2023

Simulated non-thermal emission from SNR G1.9+0.3

Supernova remnants are the nebular leftover of defunct stellar environments, resulting from the interaction between a supernova blastwave and the circumstellar medium shaped by the progenitor throughout its life. They display a large variety of non-spherical morphologies such as ears that shine non-thermally. % We have modelled the structure and the non-thermal emission of the supernova remnant G1.9+0.3 through 3D magnetohydrodynamic numerical simulations. We propose that the peculiar ear-shaped morphology of this supernova remnant results from the interaction of the its blast wave with a magnetized circumstellar medium, which was previously asymmetrically shaped by the past stellar wind emanating from the progenitor star or its stellar companion. We created synthetic non-thermal radio and x-ray maps from our simulated remnant structure, which are in qualitative agreement with observations, forming ears on the polar directions. Our synthetic map study explains the discrepancies between the measured non-thermal radio and X-ray surface brightness distributions assuming that the Inverse Compton process produces the observed X-ray emission.

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arXiv2023

Emerging planetary nebulae within 3D spiral patterns

We present the first 3D radiation-hydrodynamic simulations of the formation of planetary nebulae (PNe) emerging from 3D spiral patterns. We use the GUACHO code to create 3D spiral structures as a consequence of the distortions on the geometry of the intrinsically isotropic wind of an asymptotic giant branch (AGB) star produced by a companion star in a circular orbit. We found that the orbital period of the binary producing the 3D spiral pattern has consequences on the formation and shaping of the PN itself. Stellar systems with longer period create less entwined 3D spirals, producing PNe with rounder inner cavities, and prevent the expansion of jet towards the polar directions. The spiral fitting procedure used in the literature to predict the binary's orbital period may be misleading in the case of proto-PNe and PNe as spiral patterns are diluted by their own thermal expansion down to the average AGB density profile within a few hundred years and are further disrupted by the action of jets. By adopting a phase of jet ejections between the AGB and post-AGB stages, we are able to recover the morphologies of proto-PNe and PNe that exhibit ring-like structures in their halos.

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arXiv2023

The sculpting of rectangular and jet-like morphologies in supernova remnants by anisotropic equatorially-confined progenitor stellar winds

Thermonuclear and core-collapse supernova remnants (SNRs) are the nebular leftovers of defunct stars. Their morphology and emission properties provide insights into the evolutionary history of the progenitor star. But while some SNRs are spherical, as expected from a point-like explosion expanding into a roughly uniform medium, many others exhibit complex non-spherical morphologies which are often not easily explained. In this work, we use three-dimensional magnetohydrodynamic simulations to show that rectangular and jet-like morphologies can be explained by supernovae (SNe), either type Ia or type II, expanding within anisotropic, bipolar stellar wind bubbles driven by the progenitor star. The stellar wind has an anisotropic density distribution, which channels the SN ejecta differently depending on the anisotropy characteristics. We compute synthetic thermal (X-ray) and non-thermal (synchrotron) emission maps from our numerical simulations to compare with observations. We find rectangular morphologies are generated when the stellar wind has a high mass loss rate and forms a dense, narrow disk at the equatorial region. Instead, a jet-like or ear-like morphology is obtained when the stellar wind develops a wide, dense disk. Stellar winds with low mass-loss rates do not strongly influence the SNR morphology. Finally, our synthetic synchrotron and X-ray maps for the high mass-loss rate case qualitatively agree with the observations of the SNRs G332.5-5.6 and G290.1-0.8.

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arXiv2022

Observational and numerical characterization of a recurrent arc-shaped front propagating along a coronal fan

Recurrent, arc-shaped intensity disturbances were detected by EUV channels in an active region. The fronts were observed to propagate along a coronal loop bundle rooted in a small area within a sunspot umbra. Previous works have linked these intensity disturbances to slow magnetoacoustic waves that propagate from the lower atmosphere to the corona along the magnetic field. The slow magnetoacoustic waves propagate at the local cusp speed. However, the measured propagation speeds from the intensity images are usually smaller as they are subject to projection effects due to the inclination of the magnetic field with respect to the line-of-sight. Here, we aim to understand the effect of projection by comparing observed speeds with those from a numerical model. Using multi-wavelength data we determine the periods present in the observations at different heights of the solar atmosphere through Fourier analysis. We calculate the plane-of-sky speeds along one of the loops from the cross-correlation time lags obtained as a function of distance along the loop. We perform a 2D ideal MHD simulation of an active region embedded in a stratified atmosphere. We drive slow waves from the photosphere with a 3 minutes periodicity. Synthetic time-distance maps are generated from the forward-modelled intensities in coronal wavelengths and the projected propagation speeds are calculated. The intensity disturbances show a dominant period between [2-3] minutes at different heights of the atmosphere. The apparent propagation speeds calculated for coronal channels exhibit an accelerated pattern with values increasing from 40 to 120 km/s as the distance along the loop rises. The propagation speeds obtained from the synthetic time-distance maps also exhibit accelerated profiles within a similar range of speeds. We conclude that the accelerated propagation in our observations is due to the projection effect.

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arXiv2022

Rectangular core-collapse supernova remnants: application to Puppis A

Core-collapse supernova remnants are the gaseous nebulae of galactic interstellar media (ISM) formed after the explosive death of massive stars. Their morphology and emission properties depend both on the surrounding circumstellar structure shaped by the stellar wind-ISM interaction of the progenitor star and on the local conditions of the ambient medium. In the warm phase of the Galactic plane (n = 1/cm3, T = 8000 K), an organised magnetic field of strength 7 microG has profound consequences on the morphology of the wind bubble of massive stars at rest. In this paper we show through 2.5D magneto-hydrodynamical simulations, in the context of a Wolf-Rayet-evolving 35 Mo star, that it affects the development of its supernova remnant. When the supernova remnant reaches its middle age (15 to 20 kyr), it adopts a tubular shape that results from the interaction between the isotropic supernova ejecta and the anisotropic, magnetised, shocked stellar progenitor bubble into which the supernova blast wave expands. Our calculations for non-thermal emission, i.e. radio synchrotron and inverse Compton radiation, reveal that such supernova remnants can, due to projection effects, appear as rectangular objects in certain cases. This mechanism for shaping a supernova remnant is similar to the bipolar and elliptical planetary nebula production by wind-wind interaction in the low-mass regime of stellar evolution. If such a rectangular core-collapse supernova remnant is created, the progenitor star must not have been a runaway star. We propose that such a mechanism is at work in the shaping of the asymmetric core-collapse supernova remnant Puppis A.

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arXiv2021

Formation and fate of the born-again planetary nebula HuBi 1

We present the first 3D radiation-hydrodynamic simulations on the formation and evolution of born-again planetary nebulae (PNe), with particular emphasis to the case of HuBi1, the inside-out PN. We use the extensively-tested GUACHO code to simulate the formation of HuBi1 adopting mass-loss and stellar wind terminal velocity estimates obtained from observations presented by our group. We found that, if the inner shell of HuBi1 was formed by an explosive very late thermal pulse (VLTP) ejecting material with velocities of $\sim$300 km s$^{-1}$, the age of this structure is consistent with that of $\simeq$200 yr derived from multi-epoch narrow-band imaging. Our simulations predict that, as a consequence of the dramatic reduction of the stellar wind velocity and photon ionizing flux during the VLTP, the velocity and pressure structure of the outer H-rich nebula are affected creating turbulent ionized structures surrounding the inner shell. These are indeed detected in Gran Telescopio Canarias MEGARA optical observations. Furthermore, we demonstrate that the current relatively low ionizing photon flux from the central star of HuBi1 is not able to completely ionize the inner shell, which favors previous suggestions that its excitation is dominated by shocks. Our simulations suggest that the kinetic energy of the H-poor ejecta of HuBi1 is at least 30 times that of the clumps and filaments in the evolved born-again PNe A30 and A78, making it a truly unique VLTP event.

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arXiv2021

Huffing, and puffing, and blowing your house in: Strong stellar winds interaction with a super massive black hole

We present analytic and numerical models of a cluster wind flow resulting from the interaction of stellar winds of massive stars, with a super massive black hole (SMBH). We consider the motion of the stars as well as the gravitational force of the SMBH. In the numerical simulations we consider two cases: the first one with the stars is in circular orbits, and the second one with the stars in eccentric orbits around the SMBH. We found that after the system reaches an equilibrium, the circular and elliptical cases are very similar. We found a very good agreement between the analytical and numerical results, not only from our numerical simulations but also from other high resolution numerical calculations. The analytical models are very interesting, since the properties of such complex systems involving strong winds and a massive compact object, can be rapidly inferred without the need of a numerical calculation.

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arXiv2021

Estimating the propagation of a uniformly accelerated jet

We study the problem of a Herbig-Haro jet with a uniformly accelerating ejection velocity, travelling into a uniform environment. For the ejection density we consider two cases: a time-independent density, and a time-independent mass loss rate. For these two cases, we obtain analytic solutions for the motion of the jet head using a ram-pressure balance and a center of mass equation of motion. We also compute axisymmetric numerical simulations of the same flow, and compare the time-dependent positions of the leading working surface shocks with the predictions of the two analytic models. We find that if the jet is over-dense and over-pressured (with respect to the environment) during its evolution, a good agreement is obtained with the analytic models, with the flow initially following the center of mass analytic solution, and (for the constant ejection density case) at later times approaching the ram-pressure balance solution.

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arXiv2020

GJ 436b and the stellar wind interaction: simulations constraints using Ly$α$ and H$α$ transits

The GJ 436 planetary system is an extraordinary system. The Neptune-size planet that orbits the M3 dwarf revealed in the Ly$α$ line an extended neutral hydrogen atmosphere. This material fills a comet-like tail that obscures the stellar disc for more than 10 hours after the planetary transit. Here, we carry out a series of 3D radiation hydrodynamic simulations to model the interaction of the stellar wind with the escaping planetary atmosphere. With these models, we seek to reproduce the $\sim56\%$ absorption found in Ly$α$ transits, simultaneously with the lack of absorption in H$α$ transit. Varying the stellar wind strength and the EUV stellar luminosity, we search for a set of parameters that best fit the observational data. Based on Ly$α$ observations, we found a stellar wind velocity at the position of the planet to be around [250-460] km s$^{-1}$ with a temperature of $[3-4]\times10^5$ K. The stellar and planetary mass loss rates are found to be $2\times 10^{-15}$ M$_\odot$ yr$^{-1}$ and $\sim[6-10]\times10^9$ g s$^{-1}$, respectively, for a stellar EUV luminosity of $[0.8-1.6]\times10^{27}$ erg s$^{-1}$. For the parameters explored in our simulations, none of our models present any significant absorption in the H$α$ line in agreement with the observations.

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arXiv2020

Velocity Centroids Anisotropy and the Signature of different MHD Modes in the Turbulent ISM

Magnetic turbulence is anisotropic as the directions of motion are constrained by the magnetic field. Such anisotropy can be observed in velocity centroids obtained from spectroscopic observations. We use magnetohydrodynamics (MHD) simulations to produce synthetic spectroscopic observations (position-position-velocity data) and study the anisotropy in the structure function of velocity centroid maps. We decomposed the velocity in the simulations into Alfvén, slow and fast-modes and studied how each of them contribute to the observed anisotropy. We found that when the angle between the line of sight and the mean magnetic field is large the Alfvén-mode dominates the observed anisotropy, while for smaller angles the anisotropy is not large enough to be used to probe the magnetization of the media, and it is dominated by the slow-mode. Our results are in fair agreement with the theoretical predictions in Kandel et al.(2016,2017).

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arXiv2020

Solar slow magneto-acoustic-gravity waves: an erratum correction and a revisited scenario

Slow waves are commonly observed on the entire solar atmosphere. Assuming a thin flux tube approximation, the cut-off periods of slow-mode magneto-acoustic-gravity waves that travel from the photosphere to the corona were obtained in Costa et al. (2018). In that paper, however, a typo in the specific heat coefficient at constant pressure $c_{\mathrm{p}}$ value led to an inconsistency in the cut-off calculation, which is only significant at the transition region. Due to the abrupt temperature change in the region, a change of the mean atomic weight (by a factor of approximately two) also occurs, but is often overlooked in analytical models for simplicity purposes. In this paper, we revisit the calculation of the cut-off periods of magneto-acoustic-gravity waves in Costa et al. (2018) by considering an atmosphere in hydrostatic equilibrium with a temperature profile, with the inclusion of the variation of the mean atomic weight and the correction of the inconsistency aforementioned. In addition, we show that the cut-off periods obtained analytically are consistent with the corresponding periods measured in observations of a particular active region.

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arXiv2019

Star-planet interaction through spectral lines

The growth of spectroscopic observations of exoplanetary systems allows the possibility of testing theoretical models and studying the interaction that exoplanetary atmospheres have with the wind and the energetic photons from the star. In this work, we present a set of numerical 3D simulations of HD 209458b for which spectral lines observations of their evaporative atmosphere are available. The different simulations aim to reproduce different scenarios for the star-planet interaction. With our models, we reconstruct the Ly$α$ line during transit and compare with observations. The results allow us to analyse the shape of the line profile under these different scenarios and the comparison with the observations suggests that HD209458b may have a magnetic field off less than 1 G. We also explore the behaviour of the magnesium lines for models with and without magnetic fields.

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arXiv2019

Hydrodynamical interaction of stellar and planetary winds: effects of charge exchange and radiation pressure on the observed Ly$α$ absorption

Lyman $α$ observations of the transiting exoplanet HD 209458b enable the study of exoplanets exospheres exposed to stellar EUV fluxes, as well as the interacting stellar wind properties. In this study we present 3D hydrodynamical models for the stellar-planetary wind interaction including radiation pressure and charge exchange, together with photoionization, recombination and collisional ionization processes. Our models explore the contribution of the radiation pressure and charge exchange on the Ly$α$ absorption profile in a hydrodynamical framework, and for a single set of stellar wind parameters appropriate for HD 209458. We find that most of the absorption is produced by the material from the planet, with a secondary contribution of neutralized stellar ions by charge exchange. At the same time, the hydrodynamic shock heats up the planetary material, resulting in a broad thermal profile. Meanwhile, the radiation pressure yielded a small velocity shift of the absorbing material. While neither charge exchange nor radiation pressure provide enough neutrals at the velocity needed to explain the observations at $-100~\mathrm{km~s^{-1}}$ individually, we find that the two effects combined with the broad thermal profile are able to explain the observations.

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