TY  - JOUR
A1  - Toala, Jesús Alberto
A1  - Oskinova, Lida
A1  - Hamann, Wolf-Rainer
A1  - Ignace, Richard
A1  - Sander, Andreas Alexander Christoph
A1  - Shenar, Tomer
A1  - Todt, Helge Tobias
A1  - Chu, Y. -H.
A1  - Guerrero, Martin A.
A1  - Hainich, Rainer
A1  - Torrejon, Jose Miguel
T1  - On the Apparent Absence of Wolf-Rayet plus Neutron Star Systems
BT  - the Curious Case of WR124
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters
N2  - 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.
KW  - circumstellar matter
KW  - ISM: jets and outflows
KW  - stars: massive
KW  - stars: evolution
KW  - stars: neutron
KW  - stars: Wolf-Rayet
Y1  - 2018
U6  - https://doi.org/10.3847/2041-8213/aaf39d
SN  - 2041-8205
SN  - 2041-8213
VL  - 869
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
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  -