Near-infrared emission lines provide unique diagnostics of the geometry, structure, kinematics, and excitation of eta Carinae's circumstellar ejecta, and give clues to the nature of its wind. The infrared spectrum is a strong function of position in eta Car's nebula, with a mix of intrinsic and reflected emission. Molecular hydrogen traces cool gas and dust in the polar lobes, while [Fe II] blankets their inner surfaces. These lines reveal the back wall of the SE polar lobe for the first time, and give the clearest picture yet of the 3-D geometry. Additionally, collisionally-excited [Fe II] reveals the kinematic structure of a recently discovered `Little Homunculus' expanding inside the larger one. Equatorial gas in the `Fan', on the other hand, shows a spectrum indicating recombination and fluorescent pumping. Some equatorial ejecta glow in the He I 10830 line, showing evidence for material ejected in the 1890 outburst of eta Car. Closer to the star, the compact `Weigelt blobs' are marginally resolved, allowing their infrared spectrum to be separated from the star for the first time. In general, infrared spectra reveal a coherent, directional dependence of excitation in the Homunculus: polar ejecta are collisionally excited, whereas equatorial ejecta are dominated by fluorescence and normal photoexcitation. These are important clues to the geometry of the central star's UV radiation field. Reflected near-infrared emission lines also reveal interesting latitudinal dependence in the stellar wind.

Dissecting the Homunculus nebula around Eta Carinae with spatially resolved near-infrared spectroscopy

A characteristic feature that is frequently met in nearby supernova remnants (SNRs) is the existence of two antisymmetric, local protrusions that are projected as two "ears" in the morphology of the nebula. In this work, we present a novel scenario for the "ear" formation process according to which the two lobes are formed through the interaction of the SNR with a bipolar circumstellar medium (CSM) that was surrounding the explosion center. We conduct two dimensional hydrodynamic simulations and we show that the SNR shock breakout from the bipolar CSM triggers the inflation of two opposite protrusions at the equator of the remnant that retain their size and shape for several hundreds up to a few thousand years of the SNR evolution. We run a set of models by varying the supernova (SN) and CSM properties and we demonstrate that the extracted results reveal a good agreement with the observables, regarding the "ears" sizes, lifespan, morphology and kinematics. We discuss the plausibility of our model in nature and we suggest that the most likely progenitors of the "ear-carrying" SNRs are the Luminous Blue Variables or the Red/Yellow Supergiants for the SNRs resulted by core collapse SN events and the symbiotic binaries or the planetary nebulae for the remnants formed by Type Ia SNe. Finally, we compare our model with other "ear" formation models of the literature and we show that there are distinctive differences among them, concerning the "ears" orientation and the phase in which the "ear" formation process occurs.

‘Ears’ formation in supernova remnants: overhearing an interaction history with bipolar circumstellar structures

We have computed new stellar evolution models that include the effects of rotation and magnetic torques under different hypotheses. The goal is to test whether a single star can sustain the rotational velocities needed in the envelope for magnetohydrodynamical(MHD) simulations to shape bipolar planetary nebulae (PNe) when high mass-loss rates take place. Stellar evolution models with main sequence masses of 2.5 and 5 M ? and initial rotational velocities of 250?km?s?1 have been followed through the PNe formation phase. We find that stellar cores have to be spun down using magnetic torques in order to reproduce the rotation rates observed for white dwarfs. During the asymptotic giant branch phase and beyond, the magnetic braking of the core has a practically null effect on increasing the rotational velocity of the envelope since the stellar angular momentum is efficiently removed by the wind. We have also tested the best possible case scenarios in rather non-physical contexts to give enough angular momentum to the envelope. We find that we cannot get the envelope of a single star to rotate at the speeds needed for MHD simulations to form bipolar PNe. We conclude that single stellar rotators are unlikely to be the progenitors of bipolar PNe under the current MHD model paradigm.

Single Rotating Stars and the Formation of Bipolar Planetary Nebula

A very small fraction of (runaway) massive stars have masses exceeding $60$-$70\, \rm M_{\odot}$ and are predicted to evolve as Luminous-Blue-Variable and Wolf-Rayet stars before ending their lives as core-collapse supernovae. Our 2D axisymmetric hydrodynamical simulations explore how a fast wind ($2000\, \rm km\, \rm s^{-1}$) and high mass-loss rate ($10^{-5}\, \rm M_{\odot}\, \rm yr^{-1}$) can impact the morphology of the circumstellar medium. It is shaped as 100 pc-scale wind nebula which can be pierced by the driving star when it supersonically moves with velocity $20$-$40\, \rm km\, \rm s^{-1}$ through the interstellar medium (ISM) in the Galactic plane. The motion of such runaway stars displaces the position of the supernova explosion out of their bow shock nebula, imposing asymmetries to the eventual shock wave expansion and engendering Cygnus-loop-like supernova remnants. We conclude that the size (up to more than $200\, \rm pc$) of the filamentary wind cavity in which the chemically enriched supernova ejecta expand, mixing efficiently the wind and ISM materials by at least $10\%$ in number density, can be used as a tracer of the runaway nature of the very massive progenitors of such $0.1\, \rm Myr$ old remnants. Our results motivate further observational campaigns devoted to the bow shock of the very massive stars BD+43 3654 and to the close surroundings of the synchrotron-emitting Wolf-Rayet shell G2.4+1.4.

Wind nebulae and supernova remnants of very massive stars

Context. The presence of large ionised gaseous nebulae found around some ultraluminous X-ray sources (ULXs) provides the means to assess the mechanical and radiative feedback of the central source, and hence constrain the e ﬃ ciency and impact on the surroundings of the super-Eddington regime powering most of these sources. NGC 1313 X–1 is an archetypal ULX, reported to be surrounded by abnormally high [O I] λ 6300 / H α > 0.1 ratios, and for which high-resolution spectroscopy in X-rays has hinted at the presence of powerful outﬂows. Aims. We report observations taken with the integral ﬁeld unit Multi-Unit Spectroscopic Explorer (MUSE) mounted at the Very Large Telescope of NGC 1313 X–1 in order to conﬁrm the presence of a nebula inﬂated by the winds, investigate its main sources of ionisation and estimate the mechanical output of the source. Methods. We investigated the morphology, kinematics, and sources of ionisation of the bubble through the study of the main nebular lines. We compared the main line ratios with spatially resolved Baldwin–Phillips–Terlevich diagrams and with the prediction from radiative shock libraries, which allows us to di ﬀ erentiate regions excited by shocks from those excited by extreme ultraviolet and X-ray radiation. Results. We detect a bubble of 452 × 266pc in size, roughly centred around the ULX, which shows clear evidence of shock ionisation in the outer edges. We estimate shock velocities to be in the ≈ 160 − 180km / s range based on the line ratios. This suggests that an average and continuous outﬂow power of ∼ (2 − 4 . 5) × 10 40 erg / s over a timescale of (4 . 5 − 7 . 8) × 10 5 yr is required to inﬂate the bubble. In the interior of the bubble and closer to the ULX we detect an extended ( ∼ 140pc) X-ray ionised region. Additionally, we detect two supernova remnants coincidentally close to the ULX bubble of which we also report age and explosion energy estimates. Conclusions. The elongated morphology and the kinematics of the bubble strongly suggest that the bubble is being inﬂated by winds and / or jets emanating from the central source, supporting the presence of winds found through X-ray spectroscopy. The estimated mechanical power is comparable to or higher than the X-ray luminosity of the source, which provides additional evidence in support of NGC 1313 X–1 harbouring a super-Eddington accretor.

/pdf/muse-spectroscopy-of-the-ulx-ngc-1313-x-1-a-shock-ionised-dosa23c2.pdf

MUSE spectroscopy of the ULX NGC 1313 X-1: a shock-ionised bubble, an X-ray photoionised nebula, and two supernova remnants

We present the first three dimensional (3D) Morpho-Kinematic (MK) model of a supernova remnant (SNR), using as a case study the Galactic SNR VRO 42.05.01. We employed the astrophysical code SHAPE in which wide field imaging and high resolution spectroscopic data were utilized, to reconstruct its 3D morphology and kinematics. We found that the remnant consists of three basic distinctive components that we call: a "shell", a "wing" and a "hat". With respect to their kinematical behaviour, we found that the "wing" and the "shell" have similar expansion velocities (V exp = $115$$\pm 5$ km/s). The "hat" presents the lowest expansion velocity of the remnant (V exp = $90$$\pm 20$ km/s), while the upper part of the "shell" presents the highest velocity with respect to the rest of the remnant (V exp = $155$$\pm 15$ km/s). Furthermore, the whole nebula has an inclination of ~$3°- 5°$ with respect to the plane of the sky and a systemic velocity of V sys = -$17$$\pm 3$ km/s . We discuss the interpretation of our model results regarding the origin and evolution of the SNR and we suggest that VRO 42.05.01 had an interaction history with an inhomogeneous ambient medium most likely shaped by the mass outflows of its progenitor star.

First 3D morpho-kinematic model of supernova remnants. The case of VRO 42.05.01 (G166.0+4.3)

We present a systematic study of the Supernova Remnant (SNR) populations in the nearby galaxies NGC 45, NGC 55, NGC 1313, and NGC 7793 based on deep Ha and [S II] imaging. We find 42 candidate and 54 possible candidate SNRs based on the [S II] / Ha > 0.4 criterion, 84 of which are new identifications. We derive the Ha and the joint [S II]-Ha luminosity functions after accounting for incompleteness effects. We find that the Ha luminosity function of the overall sample is described with a skewed Gaussian with a mean equal to log(LHa / 10^(36) erg s^(-1)) = 0.07 and m(log(LHa / 10^(36) erg s^(-1)))) = 0.58. The joint [S II]-Ha function is parameterized by a skewed Gaussian along the log([S II] / 10^(36) erg s^(-1)) = 0.88 x log(LHa / 10^(36) erg s^(-1)) - 0.06 line and a truncated Gaussian with m(log(L[S II] / 10^(36))) = 0.024 and s(log(L[S II] / 10^(36))) = 0.14, on its vertical direction. We also define the excitation function as the number density of SNRs as a function of their [S II]/Ha ratios. This function is represented by a truncated Gaussian with a mean at -0.014. We find a sub-linear [S II]-Ha relation indicating lower excitation for the more luminous objects.

The supernova remnant populations of the galaxies NGC 45, NGC 55, NGC 1313, NGC 7793: luminosity and excitation functions

One of the key methods for determining the unknown nature of Type Ia supernovae (SNe Ia) is the search for traces of interaction between the SN ejecta and the circumstellar structures at the resulting supernova remnants (SNRs Ia). So far, the observables that we receive from well-studied SNRs Ia cannot be explained self-consistently by any model presented in the literature. In this study, we suggest that the circumstellar medium (CSM) being observed to surround several SNRs Ia was mainly shaped by planetary nebulae (PNe) that originated from one or both progenitor stars. Performing two-dimensional hydrodynamic simulations, we show that the ambient medium shaped by PNe can account for several properties of the CSM that have been found to surround SNe Ia and their remnants. Finally, we model Kepler's SNR considering that the SN explosion occurred inside a bipolar PN. Our simulations show good agreement with the observed morphological and kinematic properties of Kepler's SNR. In particular, our model reproduces the current expansion parameter of Kepler's SNR, the partial interaction of the remnant with a dense CSM at its northern region and finally the existence of two opposite protrusions (`ears') at the equatorial plane of the SNR.

The Interaction of Type Ia Supernovae with Planetary Nebulae: the Case of Kepler's Supernova Remnant

Here we explore the possible preexisting circumstellar debris of supernova type Ia systems. Classical, symbiotic and recurrent novae all accrete onto roughly solar mass white dwarfs from main sequence or Mira type companions and result in thermonuclear runaways and expulsion of the accreted material at high velocity. The expelled material forms a fast moving shell that eventually slows to planetary nebula expansion velocities within several hundred years. All such systems are recurrent and thousands of shells (each of about 0.001 Mo) snow plough into the environment. As these systems involve common envelope binaries the material is distributed in a non-spherical shell. These systems could be progenitors of some SN Ia and thus explode into environments with large amounts of accumulated gas and dust distributed in thin non-spherical shells. Such shells should be observable around 100 years after a SN Ia event in a radio flash as the SN Ia debris meets that of the ejected material of the systems previous incarnation.

The circumstellar environment of pre-SN Ia systems

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