TY  - JOUR
A1  - Reindl, Nicole
A1  - Rauch, Thomas
A1  - Miller Bertolami, Marcelo Miguel
A1  - Todt, Helge Tobias
A1  - Werner, K.
T1  - Breaking news from the HST
BT  - the central star of the Stingray Nebula is now returning towards the AGB
JF  - Monthly notices of the Royal Astronomical Society
N2  - SAO 244567 is a rare example of a star that allows us to witness stellar evolution in real time. Between 1971 and 1990, it changed from a B-type star into the hot central star of the Stingray Nebula. This observed rapid heating has been a mystery for decades, since it is in strong contradiction with the low mass of the star and canonical post-asymptotic giant branch (AGB) evolution. We speculated that SAO 244567 might have suffered from a late thermal pulse (LTP) and obtained new observations with Hubble Space Telescope (HST)/COS to follow the evolution of the surface properties of SAO 244567 and to verify the LTP hypothesis. Our non-LTE spectral analysis reveals that the star cooled significantly since 2002 and that its envelope is now expanding. Therefore, we conclude that SAO 244567 is currently on its way back towards the AGB, which strongly supports the LTP hypothesis. A comparison with state-of-the-art LTP evolutionary calculations shows that these models cannot fully reproduce the evolution of all surface parameters simultaneously, pointing out possible shortcomings of stellar evolution models. Thereby, SAO 244567 keeps on challenging stellar evolution theory and we highly encourage further investigations.
KW  - stars: AGB and post-AGB
KW  - stars: atmospheres
KW  - stars: evolution
Y1  - 2016
U6  - https://doi.org/10.1093/mnrasl/slw175
SN  - 0035-8711
SN  - 1365-2966
VL  - 464
SP  - L51
EP  - L55
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Toalá, Jesús Alberto
A1  - Bowman, Dominic
A1  - Van Reeth, Timothy
A1  - Todt, Helge Tobias
A1  - Dsilva, Karan
A1  - Shenar, Tomer
A1  - Koenigsberger, Gloria Suzanne
A1  - Estrada-Dorado, Sandino
A1  - Oskinova, Lida
A1  - Hamann, Wolf-Rainer
T1  - Multiple variability time-scales of the early nitrogen-rich Wolf-Rayet star WR 7
JF  - Monthly notices of the Royal Astronomical Society
N2  - We present the analysis of the optical variability of the early, nitrogen-rich Wolf-Rayet (WR) star WR 7. The analysis of multisector Transiting Exoplanet Survey Satellite (TESS) light curves and high-resolution spectroscopic observations confirm multiperiodic variability that is modulated on time-scales of years. We detect a dominant period of 2.6433 +/- 0.0005 d in the TESS sectors 33 and 34 light curves in addition to the previously reported high-frequency features from sector 7. We discuss the plausible mechanisms that may be responsible for such variability in WR 7, including pulsations, binarity, co-rotating interaction regions (CIRs), and clumpy winds. Given the lack of strong evidence for the presence of a stellar or compact companion, we suggest that WR 7 may pulsate in quasi-coherent modes in addition to wind variability likely caused by CIRs on top of stochastic low-frequency variability. WR 7 is certainly a worthy target for future monitoring in both spectroscopy and photometry to sample both the short (less than or similar to 1 d) and long (greater than or similar to 1000 d) variability time-scales.
KW  - stars: atmospheres
KW  - stars: evolution
KW  - stars: individual: WR 7
KW  - stars: winds
KW  - outflows
KW  - stars: Wolft-Rayet
Y1  - 2022
U6  - https://doi.org/10.1093/mnras/stac1455
SN  - 0035-8711
SN  - 1365-2966
VL  - 514
IS  - 2
SP  - 2269
EP  - 2277
PB  - Oxford University Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Meyer, Dominique M.-A.
A1  - Velazquez, Pablo F.
A1  - Petruk, Oleh
A1  - Chiotellis, Alexandros
A1  - Pohl, Martin
A1  - Camps-Farina, Artemi
A1  - Petrov, Miroslav
A1  - Reynoso, Estela M.
A1  - Toledo-Roy, Juan C.
A1  - Schneiter, E. Matias
A1  - Castellanos-Ramirez, Antonio
A1  - Esquivel, Alejandro
T1  - Rectangular core-collapse supernova remnants
BT  - application to Puppis A
JF  - Monthly notices of the Royal Astronomical Society
N2  - Core-collapse supernova remnants are the gaseous nebulae of galactic interstellar media (ISM) formed after the explosive death of massive stars. Their morphology and emission properties depend both on the surrounding circumstellar structure shaped by the stellar wind-ISM interaction of the progenitor star and on the local conditions of the ambient medium. In the warm phase of the Galactic plane (n approximate to 1 cm(-3), T approximate to 8000 K), an organized magnetic field of strength 7 mu G has profound consequences on the morphology of the wind bubble of massive stars at rest. In this paper, we show through 2.5D magnetohydrodynamical simulations, in the context of a Wolf-Rayet-evolving 35 M 0 star, that it affects the development of its supernova remnant. When the supernova remnant reaches its middle age (15-20 kyr), it adopts a tubular shape that results from the interaction between the isotropic supernova ejecta and the anisotropic, magnetized, shocked stellar progenitor bubble into which the supernova blast wave expands. Our calculations for non-thermal emission, i.e. radio synchrotron and inverse-Compton radiation, reveal that such supernova remnants can, due to projection effects, appear as rectangular objects in certain cases. This mechanism for shaping a supernova remnant is similar to the bipolar and elliptical planetary nebula production by wind-wind interaction in the low-mass regime of stellar evolution. If such a rectangular core-collapse supernova remnant is created, the progenitor star must not have been a runaway star. We propose that such a mechanism is at work in the shaping of the asymmetric core-collapse supernova remnant Puppis A.
KW  - stars: evolution
KW  - stars: massive
KW  - ISM: supernova remnants
KW  - methods: MHD
Y1  - 2022
U6  - https://doi.org/10.1093/mnras/stac1832
SN  - 0035-8711
SN  - 1365-2966
VL  - 515
IS  - 1
SP  - 594
EP  - 605
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
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  - 
TY  - JOUR
A1  - Shenar, Tomer
A1  - Sablowski, D. P.
A1  - Hainich, Rainer
A1  - Todt, Helge Tobias
A1  - Moffat, Anthony F. J.
A1  - Oskinova, Lida
A1  - Ramachandran, Varsha
A1  - Sana, Hugues
A1  - Sander, Andreas Alexander Christoph
A1  - Schnurr, O.
A1  - St-Louis, N.
A1  - Vanbeveren, D.
A1  - Gotberg, Y.
A1  - Hamann, Wolf-Rainer
T1  - The Wolf-Rayet binaries of the nitrogen sequence in the Large Magellanic Cloud Spectroscopy, orbital analysis, formation, and evolution
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. Massive Wolf-Rayet (WR) stars dominate the radiative and mechanical energy budget of galaxies and probe a critical phase in the evolution of massive stars prior to core collapse. It is not known whether core He-burning WR stars (classical WR; cWR) form predominantly through wind stripping (w-WR) or binary stripping (b-WR). Whereas spectroscopy of WR binaries has so-far largely been avoided because of its complexity, our study focuses on the 44 WR binaries and binary candidates of the Large Magellanic Cloud (LMC; metallicity Z approximate to 0.5 Z(circle dot)), which were identified on the basis of radial velocity variations, composite spectra, or high X-ray luminosities. Aims. Relying on a diverse spectroscopic database, we aim to derive the physical and orbital parameters of our targets, confronting evolution models of evolved massive stars at subsolar metallicity and constraining the impact of binary interaction in forming these stars. Methods. Spectroscopy was performed using the Potsdam Wolf-Rayet (PoWR) code and cross-correlation techniques. Disentanglement was performed using the code Spectangular or the shift-and-add algorithm. Evolutionary status was interpreted using the Binary Population and Spectral Synthesis (BPASS) code, exploring binary interaction and chemically homogeneous evolution. Results. Among our sample, 28/44 objects show composite spectra and are analyzed as such. An additional five targets show periodically moving WR primaries but no detected companions (SB1); two (BAT99 99 and 112) are potential WR + compact-object candidates owing to their high X-ray luminosities. We cannot confirm the binary nature of the remaining 11 candidates. About two-thirds of the WN components in binaries are identified as cWR, and one-third as hydrogen-burning WR stars. We establish metallicity-dependent mass-loss recipes, which broadly agree with those recently derived for single WN stars, and in which so-called WN3/O3 stars are clear outliers. We estimate that 45 +/- 30% of the cWR stars in our sample have interacted with a companion via mass transfer. However, only approximate to 12 +/- 7% of the cWR stars in our sample naively appear to have formed purely owing to stripping via a companion (12% b-WR). Assuming that apparently single WR stars truly formed as single stars, this comprises approximate to 4% of the whole LMC WN population, which is about ten times less than expected. No obvious differences in the properties of single and binary WN stars, whose luminosities extend down to log L approximate to 5.2 [L-circle dot], are apparent. With the exception of a few systems (BAT99 19, 49, and 103), the equatorial rotational velocities of the OB-type companions are moderate (v(eq) less than or similar to 250 km s(-1)) and challenge standard formalisms of angular-momentum accretion. For most objects, chemically homogeneous evolution can be rejected for the secondary, but not for the WR progenitor. Conclusions. No obvious dichotomy in the locations of apparently single and binary WN stars on the Hertzsprung-Russell diagram is apparent. According to commonly used stellar evolution models (BPASS, Geneva), most apparently single WN stars could not have formed as single stars, implying that they were stripped by an undetected companion. Otherwise, it must follow that pre-WR mass-loss/mixing (e.g., during the red supergiant phase) are strongly underestimated in standard stellar evolution models.
KW  - stars: massive
KW  - stars: Wolf-Rayet
KW  - Magellanic Clouds
KW  - binaries: close
KW  - binaries: spectroscopic
KW  - stars: evolution
Y1  - 2019
U6  - https://doi.org/10.1051/0004-6361/201935684
SN  - 0004-6361
SN  - 1432-0746
VL  - 627
PB  - EDP Sciences
CY  - Les Ulis
ER  -