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StarlightWinds Report Summary

Project ID: 656725
Funded under: H2020-EU.1.3.2.

Periodic Reporting for period 1 - StarlightWinds (Mass loss in the lives and deaths of massive stars)

Reporting period: 2015-07-01 to 2017-06-30

Summary of the context and overall objectives of the project

Across our Universe, the dynamics and chemical evolution of spiral galaxies like the Milky Way are primarily controlled by the lives and deaths of stars with masses many times that of the Sun. But the evolution of these massive stars is, in turn, highly regulated by the huge amounts of mass lost from their surfaces, by means of powerful starlight-driven winds. These stellar winds critically determine how such massive stars evolve through their lives, how they finally die in giant supernova explosions, and how they leave behind them exotic remnants such as neutron stars and black holes. However, due to the very large quantitative uncertainties associated with this mass loss, present-day predictions for such massive-star evolution are seriously flawed. As just one recent example of this, mass loss is currently being highlighted as a main uncertainty in massive-star progenitor models of gravitational wave sources like the ones recently observed by the advanced LIGO-detectors.

The overarching goal of this ambitious project has been to fundamentally improve this situation by using novel methods to develop new models of radiation-driven winds from hot, massive stars. Using state-of-the art numerical techniques, as well as innovative analytic theory development, for the effects of light-transfer on the wind-dynamics, we have developed a new generation of drastically improved wind models from massive stars in their hydrogen core burning phase. Including critical physics ingredients lacking in earlier generations of such simulations, our new models show systematically lower mass-loss rates when compared to these earlier models, which are the current standard predictions included in calculations of the star's evolution. First results from a few observationally driven studies seem further to empirically support our lower predicted mass-loss rates, and tentative studies reducing the mass-loss rates in evolution calculations indicate significant effects on e.g. the evolution of the star's surface rotation. Spurred by this, the former fellow and his old and new collaborators are now planning several exciting spin-off scientific projects, which will build directly on the results obtained during the Marie-Curie action.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

"The project ""StarlightWinds"" was executed at Centro de Astrobiologia, Madrid, Spain, and witnessed progress in general accordance with the original plan. However, on Sep. 30 2016 the project was terminated early (original project running until June 2017), since the fellow (Prof. Dr. Jon O. Sundqvist) had been offered, and accepted, a position as Asst. Professor (""tenure track"" professor/docent) at KU Leuven, Belgium. The former fellow is thus working at KU Leuven at the present, where his current position as Asst. Prof. after 5 years is intended to transform into tenure and a permanent professorship (following standard procedures for evaluation of such academic tenure tracks). As such, the action has fulfilled and highlighted principal aims of the Marie Sklodowska-Curie individual fellowship: creating strong and invaluable collaborations between scientific institutes within the European Union (CAB and KU Leuven) and -- perhaps even more important -- advanced significantly the professional career of the fellow (now Prof. Sundqvist).

Prof. Sundqvist and his former group at CAB are still working closely together, though, and several peer-reviewed research articles with the former fellow as co-author have also already been published (6 such papers in which the current Marie-Curie project 656725 has been acknowledged have already appeared in the literature, and several more are underway, see further below). Moreover, several beneficial synergy effects and collaborations have been initiated, as the fellow has actively participated in the various activities in the research-group led by previous project supervisor Dr. F. Najarro at CAB in Madrid. For example, at the present Dr. Najarro's PhD student M. Rubio is conducting the final parts of her thesis (expected to be finished summer 2017), and Prof. Sundqvist has since his first arrival to Madrid been highly involved in Ms. Rubio's work; as such, he gained plenty of invaluable experience as mentor and co-supervisor during his time in Madrid, preparing him very well for his current teaching and supervising duties as professor at KU Leuven.

More specifically, during our time at CAB we have delivered a new, significantly improved generation of radiation-hydrodynamic, steady-state wind simulations of hot star wind. These models now include two critical physics components neglected in earlier generations, and first results of them indeed show systematically lower mass-loss rates compared to the current standard predictions included in stellar evolution calculations. First observational results carried out by M. Rubio at CAB, together with former fellow Sundqvist and supervisor Najarro, seem to support such general reduction of mass-loss rates. A cornerstone-paper about these findings is currently being written (led by Sundqvist, in close collaboration with former project-supervisor F. Najarro at CAB), and will be submitted to a peer-review journal shortly. Simultaneously, PhD candidate Rubio leads the writing-up of the corresponding empirical results. What is already clear though, is that these mass-loss rate reductions potentially will have quite dramatic consequences for both massive-star evolution models and the many other astronomical applications that rely on a firm understanding of the lives and deaths of such massive stars."

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

As outlined above, our new improved predictions of mass-loss rates could have quite drastic implications for various fields of astronomical research, ranging from direct effects of stellar evolution and feedback, and potentially all the way to prediction-rates of the number of expected gravitational wave sources. In addition, as outlined in the technical report,the project has already led to the initiation of direct spin-off projects in stellar astrophysics by the former fellow and his collaborators.

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