@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{RubioToalaTodtetal.2022,
  author    = {Rubio, Gabriel and Toal{\´a}, Jes{\´u}s Alberto and Todt, Helge Tobias and Sabin, Laurence and Santamar{\´i}a, Edgar and Ramos-Larios, Gerardo and Mart{\´i}n Guerrero, Jos{\´e} David},
  title     = {Planetary nebulae with Wolf-Rayet-type central stars - IV. NGC 1501 and its mixing layer},
  series = {Monthly notices of the Royal Astronomical Society},
  volume    = {517},
  journal   = {Monthly notices of the Royal Astronomical Society},
  number    = {4},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0035-8711},
  doi       = {10.1093/mnras/stac3011},
  pages     = {5166 -- 5179},
  year      = {2022},
  abstract  = {Theory predicts that the temperature of the X-ray-emitting gas (similar to 10(6) K) detected from planetary nebulae (PNe) is a consequence of mixing or thermal conduction when in contact with the ionized outer rim (similar to 10(4) K). Gas at intermediate temperatures (similar to 10(5) K) can be used to study the physics of the production of X-ray-emitting gas, via C iv, N v, and O vi ions. Here, we model the stellar atmosphere of the CSPN of NGC 1501 to demonstrate that even this hot H-deficient [WO4]-type star cannot produce these emission lines by photoionization. We use the detection of the C iv lines to assess the physical properties of the mixing region in this PNe in comparison with its X-ray-emitting gas, rendering NGC 1501 only the second PNe with such characterization. We extend our predictions to the hottest [WO1] and cooler [WC5] spectral types and demonstrate that most energetic photons are absorbed in the dense winds of [WR] CSPN and highly ionized species can be used to study the physics behind the production of hot bubbles in PNe. We found that the UV observations of NGC 2452, NGC 6751, and NGC 6905 are consistent with the presence mixing layers and hot bubbles, providing excellent candidates for future X-ray observations.},
  language  = {en}
}