We here report the properties of Wolf-Rayet (W-R) stars in 14 locations in the nearby spiral galaxy M81. These locations were found serendipitously while analysing the slit spectra of a sample of ∼ 150 star-forming complexes, taken using the long-slit and Multi-Object spectroscopic modes of the OSIRIS instrument at the 10.4-m Gran Telescopio Canarias. Colours and magnitudes of the identified point sources in the Hubble Space Telescope images compare well with those of individual W-R stars in the Milky Way. Using templates of individual W-R stars, we infer that the objects responsible for the observed W-R features are single stars in 12 locations, comprising of 3 WNLs, 3 WNEs, 2 WCEs and 4 transitional WN/C types. In diagrams involving bump luminosities and the width of the bumps, the W-R stars of the same sub-class group together, with the transitional stars occupying locations intermediate between the WNE and WCE groups, as expected from the evolutionary models. However, the observed number of 4 transitional stars out of our sample of 14 is statistically high as compared to the 4% expected in stellar evolutionary models.

We present an infrared (IR) characterization of the born-again planetary nebulae (PNe) A 30 and A 78 using IR images and spectra. We demonstrate that the carbon-rich dust in A 30 and A 78 is spatially coincident with the H-poor ejecta and coexists with hot X-ray-emitting gas up to distances of 50″ from the central stars (CSPNs). Dust forms immediately after the born-again event and survives for 1000 yr in the harsh environment around the CSPN as it is destroyed and pushed away by radiation pressure and dragged by hydrodynamical effects. Spitzer IRS spectral maps showed that the broad spectral features at 6.4 and 8.0 μm, attributed to amorphous carbon formed in H-deficient environments, are associated with the disrupted disk around their CSPN, providing an optimal environment for charge exchange reactions with the stellar wind that produces the soft X-ray emission of these sources. Nebular and dust properties are modeled for A 30 with cloudy taking into account different carbonaceous dust species. Our models predict dust temperatures in the 40–230 K range, five times lower than predicted by previous works. Gas and dust masses for the born-again ejecta in A 30 are estimated to be $M_\mathrm{gas}=(4.41^{+0.55}_{-0.14})\times 10^{-3}$ M⊙ and $M_\mathrm{dust}=(3.20^{+3.21}_{-2.06})\times 10^{-3}$ M⊙, which can be used to estimate a total ejected mass and mass-loss rate for the born-again event of $(7.61^{+3.76}_{-2.20})\times 10^{-3}$ M⊙ and $\dot{M}=[5-60]\times 10^{-5}$ M⊙ yr−1, respectively. Taking into account the carbon trapped into dust grains, we estimate that the C/O mass ratio of the H-poor ejecta of A 30 is larger than 1, which favors the very late thermal pulse model over the alternate hypothesis of a nova-like event.

HuBi 1 has been proposed to be member of the rare class of born-again planetary nebulae (PNe), i.e., its central star experienced a very late thermal pulse and ejected highly processed material at high speeds inside the old hydrogen-rich PN. In this Letter we present GTC MEGARA integral field spectroscopic observations of the innermost regions of HuBi 1 at high spectral resolution ≃16 km s−1 and multi-epoch subarcsecond images obtained ≃12 yr apart. The analysis of these data indicates that the inner regions of HuBi 1 were ejected ≃200 yr ago and expand at velocities ≃300 km s−1, in excellent agreement with the born-again scenario. The unprecedented tomographic capabilities of the GTC MEGARA high-dispersion observations used here reveal that the ejecta in HuBi 1 has a shell-like structure, in contrast to the disrupted disk and jet morphology of the ejecta in other born-again PNe.

We here study the multi-band properties of a kiloparsec-size superbubble in the late-type spiral galaxy NGC 628. The superbubble is the largest of many holes seen in the early release images using JWST/MIRI filters that trace the Polycyclic Aromatic Hydrocarbon (PAH) emissions. The superbubble is located in the interarm region ∼3 kpc from the galactic center in the south-east direction. The shell surrounding the superbubble is detected in H i, CO, and Hα with an expansion velocity of 12 km s−1, and contains as much as 2× 107 M⊙ of mass in gas that is mostly in molecular form. We find a clear excess of blue, bright stars inside the bubble as compared to the surrounding disk on the HST/ACS images. These excess blue, bright stars are part of a stellar population of 105 M⊙ mass that is formed over the last 50 Myr in different star formation episodes, as determined from an analysis of color-magnitude diagrams using a Bayesian technique. The mechanical power injected by the massive stars of these populations is sufficient to provide the energy necessary for the expansion of the shell gas. Slow and steady, rather than violent, injection of energy is probably the reason for the maintenance of the shell structure over the kiloparsec scale. The expanding shell is currently the site for triggered star formation as inferred from the JWST 21-μm (F2100W filter) and the Hα images.

We present a multiwavelength study of the iconic Bubble Nebula (NGC 7635) and its ionising star BD+60 • 2522. We obtained XMM-Newton EPIC X-ray observations to search for extended X-ray emission as in other similar wind-blown bubbles around massive stars. We also obtained San Pedro Mártir spectroscopic observations with the Manchester Echelle Spectrometer to study the dynamics of the Bubble Nebula. Although our EPIC observations are deep, we do not detect extended X-ray emission from this wind-blown bubble. On the other hand, BD+60 • 2522 is a bright X-ray source similar to other O stars. We used the stellar atmosphere code PoWR to characterise BD+60 • 2522 and found that this star is a young O-type star with stellar wind capable of producing a wind-blown bubble that in principle could be filled with hot gas. We discussed our findings in line with recent numerical simulations proposing that the Bubble Nebula has been formed as the result of the fast motion of BD+60 • 2522 through the medium. Our kinematic study shows that the Bubble Nebula is composed by a series of nested shells, some showing blister-like structures, but with little signatures of hydrodynamical instabilities that would mix the material producing diffuse X-ray emission as seen in other wind-blown bubbles. Its morphology seems to be merely the result of projection effects of these different shells.