TY  - JOUR
A1  - Guerrero, Martin A.
A1  - Fang, Xuan
A1  - Miller Bertolami, Marcelo Miguel
A1  - Ramos-Larios, Gerardo
A1  - Todt, Helge Tobias
A1  - Alarie, Alexandre
A1  - Sabin, Laurence
A1  - Miranda, Luis F.
A1  - Morisset, Christophe
A1  - Kehrig, Carolina
A1  - Zavala, Saul A.
T1  - The inside-out planetary nebula around a born-again star
JF  - Nature Astronomy
N2  - 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.
KW  - Astronomy and astrophysics
KW  - Astronomy and planetary science
KW  - Interstellar medium
KW  - Stars
KW  - Stellar evolution
Y1  - 2018
U6  - https://doi.org/10.1038/s41550-018-0551-8
SN  - 2397-3366
VL  - 2
IS  - 10
SP  - 784
EP  - 789
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Rubio, Gabriel
A1  - Toalá, Jesús Alberto
A1  - Todt, Helge Tobias
A1  - Sabin, Laurence
A1  - Santamaría, Edgar
A1  - Ramos-Larios, Gerardo
A1  - Martín Guerrero, José David
T1  - Planetary nebulae with Wolf-Rayet-type central stars - IV. NGC 1501 and its mixing layer
JF  - Monthly notices of the Royal Astronomical Society
N2  - 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.
KW  - stars: evolution
KW  - stars: individual: WD0402+607
KW  - stars: winds
KW  - outflows;
KW  - stars: Wolf-Rayet
KW  - planetary nebulae: general
KW  - planetary nebulae
KW  - individual: NGC1501
Y1  - 2022
U6  - https://doi.org/10.1093/mnras/stac3011
SN  - 0035-8711
SN  - 1365-2966
VL  - 517
IS  - 4
SP  - 5166
EP  - 5179
PB  - Oxford Univ. Press
CY  - Oxford
ER  -