TY  - JOUR
A1  - Hajduk, Marcin
A1  - Todt, Helge Tobias
A1  - Hamann, Wolf-Rainer
A1  - Borek, Karolina
A1  - van Hoof, Peter A. M.
A1  - Zijlstra, Albert A.
T1  - The cooling-down central star of the planetary nebula SwSt 1
BT  - a late thermal pulse in a massive post-AGB star?
JF  - Monthly notices of the Royal Astronomical Society
N2  - SwSt 1 (PN G001.5-06.7) is a bright and compact planetary nebula containing a late [WC]-type central star. Previous studies suggested that the nebular and stellar lines are slowly changing with time. We studied new and archival optical and ultraviolet spectra of the object. The [O III] 4959 and 5007 angstrom to H beta line flux ratios decreased between about 1976 and 1997/2015. The stellar spectrum also shows changes between these epochs. We modelled the stellar and nebular spectra observed at different epochs. The analyses indicate a drop of the stellar temperature from about 42 kK to 40.5 kK between 1976 and 1993. We do not detect significant changes between 1993 and 2015. The observations show that the star performed a loop in the H-R diagram. This is possible when a shell source is activated during its post-AGB evolution. We infer that a late thermal pulse (LTP) experienced by a massive post-AGB star can explain the evolution of the central star. Such a star does not expand significantly as the result of the LTP and does not became a born-again red giant. However, the released energy can remove the tiny H envelope of the star.
KW  - stars: AGB and post-AGB
KW  - stars: atmospheres
KW  - stars: evolution
KW  - planetary
KW  - nebulae: general
KW  - planetary nebulae: individual: SwSt1
Y1  - 2020
U6  - https://doi.org/10.1093/mnras/staa2274
SN  - 0035-8711
SN  - 1365-2966
VL  - 498
IS  - 1
SP  - 1205
EP  - 1220
PB  - Oxford Univ. Press
CY  - Oxford
ER  -