arXiv subjects

A. C. Raga

Publications and source records attributed to A. C. Raga.

At least 19 recordsLinked to original sources

arXiv2026

A Study of HH 270 with the James Webb Space Telescope

We present a study of the Herbig-Haro object HH 270 based on observations from the James Webb Space Telescope (JWST), Subaru Telescope, and Atacama Large Millimeter/submillimeter Array (ALMA). High-resolution infrared images of H$_2$ and CO were obtained with the NIRCam instrument (JWST) using the F212N (2.12 $μ$m) and F460M (4.60 $μ$m) filters, revealing a previously unseen collimated protostellar jet closer to the source, in addition to the very well defined bipolar cavities carved by the outflow. Newly identified knots associated with the jet were also detected. Ground-based optical images in the H$α$ (660 nm) emission line, alongside millimeter spectral observations of the (2-1) transition of $^{12}$CO, $^{13}$CO, and C$^{18}$O, further enrich the analysis. The Subaru images show a connection between the optical outflow in H$α$ and the protostellar jet observed in the infrared. ALMA CO observations trace the kinematics of the entrained molecular gas in the protostellar outflow and reveal the dense, slow-moving material distributed around the driving source, HH270VLA1. These multi-wavelength observations show evidence of the interaction between the shock-excited jet emission and the molecular outflow seen at optical, infrared and radio wavelengths, which provides a detailed view of the complex structure and dynamics of HH 270.

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arXiv2025

Bowshocks driven by the pole-on molecular jet of outbursting protostar SVS 13

Outflows play a key role in the star and planet formation processes. Some outflows show discrete clumps of cold molecular gas moving at extremely high velocities (EHVs) of $\sim$100 km s$^{-1}$, known as ''molecular bullets'', that are likely closely associated with their primary driving agent. Here we present ALMA CO(J=3-2) observations of a bright EHV molecular bullet that reveal its morphology in detail down to scales of 30 au and its kinematic structure across the entire intermediate velocity range ($\sim$30-100 km s$^{-1}$). These provide important new insights into how outflows transfer mass and momentum to the surrounding medium. The observed channel maps display several sequences of ring-like features whose velocity increases and size decreases with projected distance from the driving source, each sequence tracing a thin, bow-shaped shell culminating on-axis in a bright EHV head. The shape, kinematics, and mass of each shell all agree remarkably well with the simplest textbook models of momentum-conserving bowshocks produced by a time-variable EHV jet. The dynamical timescale between consecutive shells is of a few decades, with the latest ejection event coinciding with the protostar optical/IR outburst observed in $\sim$1990. The very strong evidence for bowshock-driven entrainment induced by jet variability revealed by this work suggests that accretion bursts, and therefore variations in the disk snowlines, should occur on decade timescales, which could substantially impact grain growth and planet formation.

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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

Thackeray's globules in IC 2944: the rocket effect revisited by ALMA

The prominent Thackeray's globules are a collection of cloudlets seen in silhouette against the bright emission of the IC 2944 HII region, ionized by the Collinder 249 cluster of early-type stars (placed at 2331$\pm$30 pc, derived from a Gaia DR3 analysis of the parallaxes of 11 massive stars). Here we present the analysis of Band 3 ALMA data that reveals the cold emission (continuum and molecular) associated with the neutral gas and its kinematic behavior. Many of the globules follow a linear velocity gradient that can be explained as the result of an acceleration process due to the rocket effect, where freshly ionized material streams away from the globule, compressing and accelerating it. We identified 46 globules (12 of which are new detections), measured their kinematics, and estimated their densities and masses. At least 5 of them are associated with emission of dense molecular tracers and/or millimeter continuum sources and have indications of possible gravitational collapse. We applied a simple model for the acceleration of the globules which accounts for the observed kinematics. In this scenario only the most massive of the globules will be able to gravitationally collapse before being completely destroyed, in the process reaching speeds of tens km/s, and potentially becoming low-mass walkaway/runaway protostars.

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arXiv2025

HH 270/110 as a jet/shear layer interaction

New observations obtained with JWST of the proto-stellar HH~270 jet and the "deflected" HH 110 system, show that HH 110 has a morphology of a series of distorted working surfaces. These working surfaces appear to be "deflected versions" of the heads of the incident, HH 270 jet. We compute a series of 3D numerical simulations, in which we explore the possible parameters of a shearing environment that could give origin to the deflection of HH 270 into the HH 110 flow. We find that we need a quite high sideways velocity for the streaming environment (of ~30km/s) in order to produce the complex structure observed in HH 110. This high velocity would be possible in an environment which has been strongly perturbed by the passage of other outflows.

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arXiv2024

Dark matter free dwarf galaxy formation at the the tips of the tentacles of jellyfish galaxies

When falling into a galaxy cluster, galaxies experience a loss of gas due to ram pressure stripping. In particular, disk galaxies lose gas from their disks and very large tentacles of gas can be formed. Because of the morphology of these stripped galaxies they have been referred to as Jellyfish galaxies. It has been found that star formation is triggered not only in the disk, but also in the tentacles of such Jellyfish galaxies. The observed star forming regions located in the tentacles of those galaxies have been found to be as massive as $3\times10^7$ M$_{\odot}$ and with sizes $> 100$ pc. Interestingly, these parameters in mass and size agree with those of dwarf galaxies. In this work we make use of the state of the art magneto-hydrodynamical cosmological simulation Illustris TNG-50, to study massive jellyfish galaxies with long tentacles. We find that, in the tentacles of TNG-50 Jellyfish galaxies, the star formation regions (gas+stars) formed could be as massive as $\sim2\times10^8$ M$_{\odot}$. A particular star forming region was analyzed. This region has a star formation rate of $0.04$ M$_{\odot}$/yr, it is metal rich, has an average age of $0.46$ Gyr, and has a half mass radius of $\sim1$ kpc, typical of standard dwarf galaxies. Most importantly, this region is gravitationally self-bound. All and all, we identify a new type of dwarf galaxy being born from the gas tentacles of jellyfish galaxies, that by construction lacks a dark matter (hereafter DM) halo.

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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

The HH 24 Complex: Jets, Multiple Star Formation, and Orphaned Protostars

The HH 24 complex harbors five collimated jets emanating from a small protostellar multiple system. We have carried out a multi-wavelength study of the jets, their driving sources, and the cloud core hosting the embedded stellar system, based on data from the HST, Gemini, Subaru, APO 3.5m, VLA, and ALMA telescopes. The data show that the multiple system, SSV 63, contains at least 7 sources, ranging in mass from the hydrogen-burning limit to proto-Herbig Ae stars. The stars are in an unstable non-hierarchical configuration, and one member, a borderline brown dwarf, is moving away from the protostellar system with 25 km/s, after being ejected about 5,800 yr ago as an orphaned protostar. Five of the embedded sources are surrounded by small, possibly truncated, disks resolved at 1.3 mm with ALMA. Proper motions and radial velocities imply jet speeds of 200-300 km/s. The two main HH 24 jets, E and C, form a bipolar jet system which traces the innermost portions of parsec-scale chains of Herbig-Haro and H2 shocks with a total extent of at least 3 parsec. H2CO and C18O observations show that the core has been churned and continuously fed by an infalling streamer. 13CO and 12CO trace compact, low-velocity, cavity walls carved by the jets and an ultra-compact molecular outflow from the most embedded object. Chaotic N-body dynamics likely will eject several more of these objects. The ejection of stars from their feeding zones sets their masses. Dynamical decay of non-hierarchical systems can thus be a major contributor to establishing the initial mass function.

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arXiv2021

Numerical simulations of the 1840s great eruption of $η$ Carinae: I. Revisiting the explosion scenario

In this work, we present new two-dimensional hydrodynamical simulations of the major eruption of $η$ Car in the 1840s, which resulted in the formation of a bipolar nebula that is commonly known as the large Homunculus. In our numerical models, we have included the high-speed component of 10000 km s$^{-1}$, detected in recent observations, that provides direct evidence of an explosive event. Here, we investigate whether such a violent explosion is able to explain both the shape and the dynamical evolution of $η$ Car's nebula. As in our previous work, we have assumed a two-stage scenario for $η$ Car's eruption: a slow outflow phase during a few decades before the eruption followed by the explosive event. From the collision of these outflow phases, the large Homunculus is produced. Our numerical simulations show that such scenario does not resemble some of the observed physical features and the expansion of the nebula. Notwithstanding, we also explore other injection parameters (mass-loss rate and ejection velocity) for these outflow phases. In particular, we find that an explosion with an intermediate-speed of 1000 km s$^{-1}$ is able to reproduce the morphology and the kinematical age of the large Homunculus.

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arXiv2021

Two-wind interactions in binaries with two orbiting giant stars

Some red giant envelopes present spiral structures (seen either in dust scattered stellar continuum or in molecular line emission), the most striking example probably being AFGL 3068. This object has been modeled (both analytically and numerically) in terms of a wind ejected from a star in orbit around a binary companion. We revisit both analytical models and 3D simulations of a wind from an orbiting red giant star, and extend the numerical simulations to the case of a binary with two red giants with strong winds. We find that most two-wind models on the orbital plane show a "double spiral" structure close to the binary source, and that these two arms merge into a single spiral structure at larger distances. However, for the case of a binary with two identical winds the two spiral arms are still present at large distances from the binary source. We also find that for models of two (not identical) dynamically important winds, a region close to the orbital plane has material from both winds. Also, an approximately conical region centered on the orbital axis is filled exclusively by the wind with larger momentum rate. These two structures lead to morphologies reminiscent of the so-called "hour glass" planetary nebulae. Finally, we find that increasing wind velocity disparities lead to the formation of clumpy structures along the spiral amrs. Observations of "clumpy spirals" are therefore likely to indicate the presence of two strong winds from the stars in the central binary system.

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arXiv2021

An orbital release model for the Orion BN/KL fingers

We present a simple model in which the bullets that produce the "Orion fingers" (ejected by the BN/KL object) are interpreted as protoplanets or low mass protostars in orbit around a high mass star that has a supernova explosion. As the remnant of the SN explosion has only a small fraction of the mass of the pre-supernova star, the orbiting objects then move away in free trajectories, preserving their orbital velocity at the time of release. We show that a system of objects arranged in approximately co-planar orbits results in trajectories with morphological and kinematical characteristics resembling the Orion fingers. We show that, under the assumption of constant velocity motions, the positions of the observed heads of the fingers can be used to reconstruct the properties of the orbital structure from which they originated, resulting in a compact disk with an outer radius of $\sim 2.4$~AU.

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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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arXiv2021

Velocity segregation in a clump-like outflow with a non-top hat velocity cross-section

High velocity clumps joined to the outflow source by emission with a "Hubble law" ramp of linearly increasing radial velocity vs. distance are observed in some planetary nebulae and in some outflows in star formation regions. We propose a simple model in which a "clump" is ejected from a source over a period $τ_0$, with a strong axis to edge velocity stratification. This non-top hat cross section results in the production of a highly curved working surface (initially being pushed by the ejected material, and later coasting along due to its inertia). From both analytic models and numerical simulations we find that this working surface has a linear velocity vs. position ramp, and therefore reproduces in a qualitative way the "Hubble law clumps" in planetary nebulae and outflows from young stars.

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arXiv2020

A "head/tail" plasmon model with a Hubble law velocity profile

We present a model of a hypersonic, collimated, "single pulse" outflow, produced by an event with an ejection velocity that first grows, reaches a peak, and then decreases again to zero velocity in a finite time (simultaneously, the ejection density can have an arbitrary time-variability). We obtain a flow with a leading "head" and a trailing "tail" that for times greater than the width of the pulse develops a linear, "Hubble law" velocity vs. position. We present an analytic model for a simple pulse with a parabolic ejection velocity vs. time and time-independent mass-loss rate, and compare it to an axisymmetric gasdynamic simulation with parameters appropriate for fast knots in planetary nebulae. This "head/tail plasmon" flow might be applicable to other high-velocity clumps with "Hubble law" tails.

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arXiv2019

The jet/counter-jet symmetry of the HH 212 outflow

We present Spitzer (IRAC) images observations and a VLT 2.1micron image of the HH 212 outflow. We find that this outflow has a strong symmetry, with jet/counterjet knot pairs with Delta x less than 1 arcsec position offsets. We deduce that the jet/counterjet knots are ejected with time differences Delta tau_0 approx. 6 yr and velocity differences Delta v_0~ 2 km/s. We also analyze the deviations of the knot positions perpendicular to the outflow axis, and interpret them in terms of a binary orbital motion of the outflow source. Through this model, we deduce a ~0.7M_solar mass for the outflow source, and a separation of ~80 AU between the components of the binary (assuming equal masses for the two components). Finally, using the IRAC data and the VLT 2.1micron image we have measured the proper motion velocities, obtaining values from 50 to 170km/s.

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arXiv2019

The Giant Herbig-Haro Flow HH 212 and Associated Star Formation

The bipolar jet HH 212, among the finest collimated jets known, has so far been detected only in near-infrared H$_2$ emission. Here we present deep optical images that show two of the major bow shocks weakly detected in optical [SII] emission, as expected for a bona fide Herbig-Haro jet. We present widefield H$_2$ images which reveal two more bow shocks located symmetrically around the source and along the main jet axis. Additionally, examination of Spitzer 4.5 $μ$m images reveals yet another bright bow shock further to the north along the jet axis; no corresponding bow shock is seen to the south. In total, the HH 212 flow has an extent of 1050 arcsec, corresponding to a projected dimension of 2.0 pc. HH 212 thus joins the growing group of parsec-scale Herbig-Haro jets. Proper motion measurements indicate a velocity of about 170 km/sec, highly symmetric around the source, with an uncertainty of $\sim$30 km/sec, suggesting a probable age of the giant HH 212 flow of about 7000 yr. The jet is driven by a deeply embedded source, known as IRAS 05413-0104. We draw attention to a Spitzer near- and mid-infrared source, which we call IRS-B, located only 7 arcsec from the driving source, towards the outskirts of the dense cloud core. Infrared photometry and spectroscopy suggests that IRS-B is a K-type star with a substantial infrared excess, except that for an extinction of A$_V$ = 44 the star would have only a weakinfrared excess, and so in principle it could be a K-giant at a distance of about 2 kpc.

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arXiv2017

A comparison of the radio and optical time-evolution of HH~1 and 2

We present a comparison between the time-evolution over the past $\sim 20$ years of the radio continuum and H$α$ emission of HH~1 and 2. We find that the radio continuum and the H$α$ emission of both objects show very similar trends, with HH~1 becoming fainter and HH~2 brightening quite considerably (about a factor of 2). We also find that the $F_{\rm Hα}/F_{ff}$ (H$α$ to free-free continuum) ratio of HH~1 and 2 has higher values than the ones typically found in planetary nebulae (PNe) which we interpret as an indication that the H$α$ and free-free emission of HH~1/2 is produced in emitting regions with lower temperatures ($\sim 2000$~K) than the emission of PNe (with $\sim 10^4$~K).

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arXiv2017

Proper motions of the HH1 jet

We describe a new method for determining proper motions of extended objects, and a pipeline developed for the application of this method. We then apply this method to an analysis of four epochs of [S~II] HST images of the HH~1 jet (covering a period of $\sim 20$~yr). We determine the proper motions of the knots along the jet, and make a reconstruction of the past ejection velocity time-variability (assuming ballistic knot motions). This reconstruction shows an "acceleration" of the ejection velocities of the jet knots, with higher velocities at more recent times. This acceleration will result in an eventual merging of the knots in $\sim 450$~yr and at a distance of $\sim 80"$ from the outflow source, close to the present-day position of HH~1.

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