The Deaths of Stars and the Lives of Galaxies
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Astronomical News Report on the ESO Workshop The Deaths of Stars and the Lives of Galaxies held at ESO Vitacura, Santiago, Chile, 8–12 April 2013 Henri M. J. Boffin1 amount of chemical elements produced along these lines, including the discovery Dave Jones1 (and expelled into the interstellar medium), of PNe in which there was a clear proof Roger Wesson1 knowing how many happen before the of mass transfer between the two compo AGB star evolves to become a white nents of the system, as well as showing dwarf (WD) is crucial, but also extremely that the jets observed in the PNe always 1 ESO dependent on the assumed mass-loss precede the formation of the PN itself. rate, whose exact mechanism is still far from being understood. This fiveday meeting was attended Novae by about 100 astronomers and con- The situation is yet more complicated, sisted of 16 invited and 26 contributed as shown by Falk Herwig in his review on Close binaries containing a white dwarf talks and more than 40 posters, still the role that hydrodynamic mixing pro were the topic of the next session, and leaving ample time for discussions and cesses, which are closely related to the Claus Tappert reviewed our current social activities. A brief overview of convection and nuclear reaction rate knowledge of novae. A nova eruption is the topics is presented, from mass loss uncertainties, play in predictions of the a thermonuclear runaway on the surface in low- and high-mass stars and the evolution and nucleosynthetic yields of of the white dwarf component in a close ubiquitous importance of binaries, to AGB stars. He also talked about the role binary system known as a cataclysmic the influence of this ejected material on of rotation in AGB stars, and how it may variable (CV). During this event a certain galaxy evolution. be best investigated in interacting bina fraction of the previously accreted matter ries, such as the post-merger evolution is ejected as a shell, thus enriching the of coalescing He+CO WDs and other interstellar medium (ISM) with nuclear AGB and planetary nebulae sources similar to Sakurai’s object. Bina processed material. Due to the consider ries are also useful to explain the for- able increase in brightness during the The workshop started with a review of mation of planetary nebulae (PNe), as eruption, novae are observable in other the life of solar-like stars by Amanda Orsola de Marco explained. The problem galaxies, which makes them attractive as Karakas, with an emphasis on the asymp is to understand how the spherical mass- distance indicators. The class of novae totic giant branch (AGB) phase, when loss on the AGB can produce the colli may not be very homogeneous, however. stars lose most of their envelope mass in mated outflows seen in many PNe (Figure Nova eruptions are the primary mecha a series of episodic thermal pulses. 2). Magnetic fields alone cannot do the nism for mass loss in CVs, and as such These thermal pulses (TPs), which each trick — an additional source of angular they may well prevent the formation last only a couple of hundred years and momentum is needed — so that the of Type Ia supernovae (SNe) via the sin are separated by some hundred thou most natural explanation is that PNe con gle-degenerate mechanism since they sand years, increase the carbon content tain a close or wide binary system. This prevent the white dwarf from reaching of the envelope, and only a few TPs are has now been verified in many cases. the Chandra sekhar mass limit. Olivier required to make a solar-like star appear The remaining problem is how to go from Chesneau showed how adaptive optics as C-rich (C/O > 1). This enrichment in the known ~ 30% binary fraction of solar- and optical interferometry can be used to carbon alters the stellar opacity, but this like stars to the apparent ~ 80% binary study interacting binaries in detail, while was only very recently taken into account fraction in PNe. This, perhaps, implying Ken Shen and Ashley Ruiter presented in stellar evolution models, leading to that single stars do not form PNe at all! models of the formation of Type Ia SNe, a decrease in the time spent on the AGB A series of talks by the PN group in ESO and of the possible number of TPs. As Chile (Henri Boffin, Dave Jones, Amy Figure 1. The participants at the workshop in the the TPs are responsible for the final grounds of ESO Vitacura. Tyndall) presented further developments R. Wesson 38 The Messenger 152 – June 2013 it was an ~ 8 MA star. The case of SN 2009ip is even stranger as this object underwent several outbursts in a few H. Boffin et al. years, before actually exploding in 2012. The progenitor in this case is thought to be a luminous blue variable (i.e. not unlike η Carinae) with a mass of about 50–90 MA. Nathan Smith made the link between massive stars and planetary nebulae, presenting the similarities and dissimi- larities in the morphology of these two kinds of objects (Figure 3). Cool hyper giants with large circumstellar envelopes, Figure 2. The amazing bipolar planetary nebula that show evidence of mixed chemistry such as the “Rotten Egg Nebula”, are the Fleming 1 was shown by several speakers at the with emission from both silicate dust and massive analogues of OH/IR stars (i.e. workshop. polycyclic aromatic hydrocarbons. The embedded AGB stars), while rings are mixedchemistry phenomenon is appar seen in both PNe (e.g., the Necklace either via double detonations or white ently best explained through hydrocarbon Nebula) and massive stars (SN 1987A is a dwarf mergers. chemistry in an ultraviolet-irradiated, fine example), and there are also clear dense torus. This highlights the need to resemblances between some PNe such consider carefully the shape of the PNe as Hubble 5 or the Ant Nebula (Mz 3) and Nebular abundances when determining nebular abundances. some of the most massive stars such as η Carinae. These bipolar outflows may Returning to the topic of PNe, Denise in fact represent evidence of explosive Gonçalves provided an overview of the From massive stars … to PNe again events also taking place in PNe. On the determination of nebular abundances, other hand, while PNe often present jets, and in particular, on the improvements The second day of the meeting dealt these are missing from massive stars. that have been achieved recently. Abun with more massive objects, starting with All circumstellar shells, around PNe or dances in PNe are particularly relevant a review of the evolution of massive massive stars, suffer the effects of ionisa to provide information about low-to- stars by Georges Meynet. Massive stars tion, photoevaporation, shocks, winds intermediate mass stellar nucleosynthe form only a very small fraction of all stars and explosions. As such, the wind inter sis, while at the same time, PNe archive produced in a given stellar generation, action mechanism for explaining PNe progenitor abundances of a elements. but nevertheless are of great importance: might be too naïve in many cases. To derive nebular abundances, two meth if only 0.3% of all stars have masses ods are widely used: the empirical ioni- above 8 MA, they contain 14% of all the sation correction factor (ICF) method and mass, and almost half of that is returned Making stars explode photoionisation model fitting. The former to the host galaxy in the form of pro is often the only one used, and despite cessed material with huge amounts of Going further in the evolution of massive severe shortcomings, can provide rea kinetic energy and on very short time stars, Hans-Thomas Janka presented sonable results, even though it is advisa scales. Nor can binarity be ignored, as the state of the art in explosion models, ble to extend the wavelength range used the most recent censuses show that the highlighting the importance of neutrino as much as possible. The second binary fraction of massive stars is more heating as the trigger for core-collapse method uses empirical abundances as than 50%, or even 70% in some cases. supernovae and the need to use 3D the input for photoionisation model fitting, Apart from mass transfer and drastic simulations — not only in explosion simu that is, the abundances are varied until evolution, binarity can imply tidal effects lations, but also for the proper initial the predicted line ratios (and emission that lead to extra mixing inside the stars. conditions inside the progenitor. 3D sim line maps if available) match the observa It is also likely that binaries produce ulations are very time-consuming, how tions. Unfortunately, abundances are not 50% of all existing Wolf–Rayet (WR) stars. ever, and require CPU power that is necessarily better determined from the hardly available yet. Nevertheless the few model-fitting method, but it can provide Massive stars will explode as super- 3D simulations that do exist clearly show more accurate ICFs than using the simple novae and/or gamma-ray bursts, and the different results than in 2D — models formulae in the literature. To apply one of study of these explosions can reveal exploding in 2D don’t necessarily do so in these methods, a wide range of software much about stellar evolution. Jose Groh 3D, but at the current state of the art, it exists, such as nebular, ELSA, 2D_Neb, stressed the fact that in some very rare is not clear if this is just a resolution NEAT, PyNeb, CLOUDY and MOCASSIN. cases, such as SN 2008bk, we are lucky issue.