The project has achieved most of its objectives and milestones for the period, with relatively minor deviations.
Scientific objectives:
• RO1: Establish the multiplicity of the most massive stars – fully accomplished.
This objective entailed the analysis of novel spectroscopic data acquired with the Hubble Space Telescope (HST), which monitored the most massive stars known: R136 a1, a2, a3, and c in the Large Magellanic Cloud (LMC). The analysis advanced as planned, with the main result being that no companions were found for these objects, with the exception of R136 c. We concluded that the upper-mass limit still remains well above 200 solar masses. Our findings were published in a peer-reviewed journal (Shenar et al. 2023, A&A, 679, 36)
• RO2: Substantiate the evolutionary pathway of black-hole mergers – fully accomplished.
This objective included the analysis of the shortest-period Wolf-Rayet binaries in the LMC, thought to comprise of two Wolf-Rayet stars. This project was offered as a MSc thesis, which was successfully conducted by Sancho Luitjen. The student provided a full characterisation of the companions, measured their masses and physical properties. The work is published as a MSc thesis:
https://scripties.uba.uva.nl/search?id=record_49924(se abrirá en una nueva ventana) . A corresponding publication in a peer-reviewed journal is under preparation.
In addition, the project included the analysis of spectroscopic monitoring of massive stars in the LMC to uncover black holes orbiting them. The project included the discovery of the first dormant black hole in the LMC, VFTS 243. The results were published in peer-reviewed journals: Shenar et al. 2022, A&A, 665, 148; Shenar et al. 2022, Nature Astronomy, 6, 1085.
A related project led simultaneously focused on a peculiar carbon and nitrogen-rich WR binary, HD 45166, in the Galaxy, whose properties were so far at odds with our understanding of stellar winds. We discovered that the WR star in this binary has the strongest magnetic field ever detected for a massive star, and that it is the first WR star with a measured magnetic field. The results received much media coverage, and were published in the prestigious Science journal (Shenar et al. 2023, Science, 381, 761)
• RO3: Establish the multiplicity of black-hole progenitors in the Local Group – fully accomplished.
This project included the analysis of spectroscopic monitoring of the complete population of carbon-rich Wolf-Rayet stars (WC) in the LMC using novel X-SHOOTER/VLT data. The project was offered as a MSc thesis, which was led by Freek Temming. The student successfully derived the binary fraction of the sample, and the results are published as a MSc thesis:
https://scripties.uba.uva.nl/search?id=record_53809(se abrirá en una nueva ventana) . A corresponding publication in a peer-reviewed journal is under preparation.
• RO4: Boost our theories of massive-star evolution – partly accomplished.
Inputs from deliverables related to RO1-RO3 were included in studies led by theorists regarding Wolf-Rayet binaries (e.g. Sen \& Shenar, 2023, A&A, 672, 198) and black-hole formation (e.g. Rastello \& Shenar, 2023, MNRAS, 526, 740). Pending work still includes a full evolutionary modelling of the shortest Wolf-Rayet binaries in the LMC (RO2), and population synthesis that accounts for the binary fraction of LMC WC stars (RO3).
