TY  - JOUR
A1  - Fang, X.
A1  - Guerrero, Martín A.
A1  - Marquez-Lugo, R. A.
A1  - Toala, Jesús Alberto
A1  - Arthur, S. J.
A1  - Chu, Y.-H.
A1  - Blair, William P.
A1  - Gruendl, R. A.
A1  - Hamann, Wolf-Rainer
A1  - Oskinova, Lida
A1  - Todt, Helge Tobias
T1  - Expansion of hydrogen-poor knots in the born-again planetary nebulae A30 and A78
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We analyze the expansion of hydrogen-poor knots and filaments in the born-again planetary nebulae A30 and A78 based on Hubble Space Telescope ( HST) images obtained almost 20 yr apart. The proper motion of these features generally increases with distance to the central star, but the fractional expansion decreases, i.e., the expansion is not homologous. As a result, there is not a unique expansion age, which is estimated to be 610-950 yr for A30 and 600-1140 yr for A78. The knots and filaments have experienced complex dynamical processes: the current fast stellar wind is mass loaded by the material ablated from the inner knots; the ablated material is then swept up until it shocks the inner edges of the outer, hydrogen-rich nebula. The angular expansion of the outer filaments shows a clear dependence on position angle, indicating that the interaction of the stellar wind with the innermost knots channels the wind along preferred directions. The apparent angular expansion of the innermost knots seems to be dominated by the rocket effect of evaporating gas and by the propagation of the ionization front inside them. Radiation-hydrodynamical simulations show that a single ejection of material followed by a rapid onset of the stellar wind and ionizing flux can reproduce the variety of clumps and filaments at different distances from the central star found in A30 and A78.
KW  - ISM: kinematics and dynamics
KW  - planetary nebulae: individual (A30 and A78)
Y1  - 2014
U6  - https://doi.org/10.1088/0004-637X/797/2/100
SN  - 0004-637X
SN  - 1538-4357
VL  - 797
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Toala, Jesús Alberto
A1  - Guerrero, Martín A.
A1  - Todt, Helge Tobias
A1  - Hamann, Wolf-Rainer
A1  - Chu, Y.-H.
A1  - Gruendl, R. A.
A1  - Schönberner, Detlef
A1  - Oskinova, Lida
A1  - Marquez-Lugo, R. A.
A1  - Fang, X.
A1  - Ramos-Larios, Gerardo
T1  - The born-again Planetary nebula A78: an X-RAY twin of A30
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We present the XMM-Newton discovery of X-ray emission from the planetary nebula (PN) A78, the second born-again PN detected in X-rays apart from A30. These two PNe share similar spectral and morphological characteristics: they harbor diffuse soft X-ray emission associated with the interaction between the H-poor ejecta and the current fast stellar wind and a point-like source at the position of the central star (CSPN). We present the spectral analysis of the CSPN, using for the first time an NLTE code for expanding atmospheres that takes line blanketing into account for the UV and optical spectra. The wind abundances are used for the X-ray spectral analysis of the CSPN and the diffuse emission. The X-ray emission from the CSPN in A78 can be modeled by a single C VI emission line, while the X-ray emission from its diffuse component is better described by an optically thin plasma emission model with a temperature of kT = 0.088 keV (T approximate to 1.0 x 10(6) K). We estimate X-ray luminosities in the 0.2-2.0 keV energy band of L-X,L-CSPN =(1.2 +/- 0.3) x 10(31) erg s(-1) and L-X,L-DIFF =(9.2 +/- 2.3) x 10(30) erg s(-1) for the CSPN and diffuse components, respectively.
KW  - planetary nebulae: general
KW  - planetary nebulae: individual (A78)
KW  - stars: winds, outflows
KW  - X-rays: ISM
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/799/1/67
SN  - 0004-637X
SN  - 1538-4357
VL  - 799
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  -