@article{GuerreroFangMillerBertolamietal.2018,
  author    = {Guerrero, Martin A. and Fang, Xuan and Miller Bertolami, Marcelo Miguel and Ramos-Larios, Gerardo and Todt, Helge Tobias and Alarie, Alexandre and Sabin, Laurence and Miranda, Luis F. and Morisset, Christophe and Kehrig, Carolina and Zavala, Saul A.},
  title     = {The inside-out planetary nebula around a born-again star},
  series = {Nature Astronomy},
  volume    = {2},
  journal   = {Nature Astronomy},
  number    = {10},
  publisher = {Nature Publ. Group},
  address   = {London},
  issn      = {2397-3366},
  doi       = {10.1038/s41550-018-0551-8},
  pages     = {784 -- 789},
  year      = {2018},
  abstract  = {Planetary nebulae are ionized clouds of gas formed by the hydrogen-rich envelopes of low- and intermediate-mass stars ejected at late evolutionary stages. The strong UV flux from their central stars causes a highly stratified ionization structure, with species of higher ionization potential closer to the star. Here, we report on the exceptional case of HuBi 1, a double-shell planetary nebula whose inner shell presents emission from low-ionization species close to the star and emission from high-ionization species farther away. Spectral analysis demonstrates that the inner shell of HuBi 1 is excited by shocks, whereas its outer shell is recombining. The anomalous excitation of these shells can be traced to its low-temperature [WC10] central star whose optical brightness has declined continuously by 10 magnitudes in a period of 46 years. Evolutionary models reveal that this star is the descendant of a low-mass star (≃1.1 M⊙) that has experienced a 'born-again' event1 whose ejecta shock-excite the inner shell. HuBi 1 represents the missing link in the formation of metal-rich central stars of planetary nebulae from low-mass progenitors, offering unique insight regarding the future evolution of the born-again Sakurai's object2. Coming from a solar-mass progenitor, HuBi 1 represents a potential end-state for our Sun.},
  language  = {en}
}
@article{RamosLariosToalaRodriguezGonzalezetal.2022,
  author    = {Ramos-Larios, Gerardo and Toala, Jes{\´u}s Alberto and Rodriguez-Gonzalez, Janis B. and Guerrero, Martin A. and Gomez-Gonzalez, V{\´i}ctor Mauricio Alfonso},
  title     = {Rings and arcs around evolved stars - III. Physical conditions of the ring-like structures in the planetary nebula IC 4406 revealed by MUSE},
  series = {Monthly notices of the Royal Astronomical Society},
  volume    = {513},
  journal   = {Monthly notices of the Royal Astronomical Society},
  number    = {2},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0035-8711},
  pages     = {2862 -- 2868},
  year      = {2022},
  abstract  = {We present the analysis of Very Large Telescope Multi Unit Spectroscopic Explorer (MUSE) observations of the planetary nebula (PN) IC 4406. MUSE images in key emission lines are used to unveil the presence of at least five ring-like structures north and south of the main nebula of IC4406. MUSE spectra are extracted from the rings to unambiguously assess for the first time in a PN their physical conditions, electron density (n(e)), and temperature (T-e). The rings are found to have similar T-e as the rim of the main nebula, but smaller n(e). Ratios between different ionic species suggest that the rings of IC4406 have a lower ionization state than the main cavity, in contrast to what was suggested for the rings in NGC 6543, the Cat's Eye Nebula.},
  language  = {en}
}
@article{ToalaOskinovaHamannetal.2018,
  author    = {Toala, Jes{\´u}s Alberto and Oskinova, Lida and Hamann, Wolf-Rainer and Ignace, Richard and Sander, Andreas Alexander Christoph and Shenar, Tomer and Todt, Helge Tobias and Chu, Y. -H. and Guerrero, Martin A. and Hainich, Rainer and Torrejon, Jose Miguel},
  title     = {On the Apparent Absence of Wolf-Rayet plus Neutron Star Systems},
  series = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters},
  volume    = {869},
  journal   = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters},
  number    = {1},
  publisher = {IOP Publ. Ltd.},
  address   = {Bristol},
  issn      = {2041-8205},
  doi       = {10.3847/2041-8213/aaf39d},
  pages     = {5},
  year      = {2018},
  abstract  = {Among the different types of massive stars in advanced evolutionary stages is the enigmatic WN8h type. There are only a few Wolf-Rayet (WR) stars with this spectral type in our Galaxy. It has long been suggested that WN8h-type stars are the products of binary evolution that may harbor neutron stars (NS). One of the most intriguing WN8h stars is the runaway WR 124 surrounded by its magnificent nebula M1-67. We test the presence of an accreting NS companion in WR 124 using similar to 100 ks long observations by the Chandra X-ray observatory. The hard X-ray emission from WR 124 with a luminosity of L-X similar to 10(31) erg s(-1) is marginally detected. We use the non-local thermodynamic equilibrium stellar atmosphere code PoWR to estimate the WR wind opacity to the X-rays. The wind of a WN8-type star is effectively opaque for X-rays, hence the low X-ray luminosity of WR 124 does not rule out the presence of an embedded compact object. We suggest that, in general, high-opacity WR winds could prevent X-ray detections of embedded NS, and be an explanation for the apparent lack of WR+NS systems.},
  language  = {en}
}
@article{ToalaRamosLariosGuerreroetal.2019,
  author    = {Toal{\´a}, Jes{\´u}s Alberto and Ramos-Larios, Gerardo and Guerrero, Martin A. and Todt, Helge Tobias},
  title     = {Hidden IR structures in NGC40},
  series = {Monthly notices of the Royal Astronomical Society},
  volume    = {485},
  journal   = {Monthly notices of the Royal Astronomical Society},
  number    = {3},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0035-8711},
  doi       = {10.1093/mnras/stz624},
  pages     = {3360 -- 3369},
  year      = {2019},
  abstract  = {We present the analysis of infrared (IR) observations of the planetary nebula NGC40 together with spectral analysis of its [WC]-type central starHD826. Spitzer IRS observations were used to produce spectral maps centred at polycyclic aromatic hydrocarbons (PAH) bands and ionic transitions to compare their spatial distribution. The ionic lines show a clumpy distribution of material around the main cavity of NGC40, with the emission from [Ar II] being the most extended, whilst the PAHs show a rather smooth spatial distribution. Analysis of ratio maps shows the presence of a toroidal structure mainly seen in PAH emission, but also detected in a Herschel PACS 70 mu m image. We argue that the toroidal structure absorbs the UV flux from HD826, preventing the nebula to exhibit lines of high-excitation levels as suggested by previous authors. We discuss the origin of this structure and the results from the spectral analysis of HD826 under the scenario of a late thermal pulse.},
  language  = {en}
}