Periodic Reporting for period 2 - MULTIPLES (The MULTIPLicity of supErnova progenitorS)
Periodo di rendicontazione: 2020-04-01 al 2021-09-30
With stellar masses in the range of eight to several hundreds of solar masses (Msun), massive stars are among the most important cosmic engines, each individual object strongly impacting its local environment and populations of massive stars driving the evolution of galaxies throughout the history of the Universe. Recently, we have shown that stars more massive than 15Msun rarely, if at all, form and live in isolation but rather as part of a binary or higher-order multiple system. Understanding the life cycle of massive multiple systems, from their birth to their death as supernovae and long-duration gamma ray bursts, is one of the most pressing scientific questions in modern astrophysics.
To obtain the key observational breakthroughs needed to revolutionize our understanding of high-mass stars, the MULTIPLES research program is developed along three themes:
- Investigate the physical processes that set the multiplicity properties of massive stars.
- Establish the multiplicity properties of unevolved massive stars across the entire mass range.
- Identify and uniquely characterize post-interaction products.
The implementation of the MULTIPLES program involves ambitious time-resolved observational campaigns targeting large populations of massive stars at key stages of their pre-supernova evolution and in different metallicity environments. These campaigns will combine state-of-the-art spectroscopy and high-angular resolution techniques with novel multiplicity and atmosphere analysis methods appropriate for multiple systems. Upon completion, the observational constraints that will be obtained in this project will have implications that extend well beyond the sole domain of stellar astrophysics.
To obtain the key observational breakthroughs needed to revolutionize our understanding of high-mass stars, the MULTIPLES research program is developed along three themes:
- Investigate the physical processes that set the multiplicity properties of massive stars.
- Establish the multiplicity properties of unevolved massive stars across the entire mass range.
- Identify and uniquely characterize post-interaction products.
The implementation of the MULTIPLES program involves ambitious time-resolved observational campaigns targeting large populations of massive stars at key stages of their pre-supernova evolution and in different metallicity environments. These campaigns will combine state-of-the-art spectroscopy and high-angular resolution techniques with novel multiplicity and atmosphere analysis methods appropriate for multiple systems. Upon completion, the observational constraints that will be obtained in this project will have implications that extend well beyond the sole domain of stellar astrophysics.
Since the beginning of the project, the MULTIPLES team has focused on three scientific questions: (1) what the origin of massive star multiplicity is and of the pairing mechanism; (2) what are the multiplicity properties of massive star populations for which it has been less well established (with a focus on B and Wolf-Rayet stars) and (3) what is the role of binary evolution in the formation of evolved objects such as Wolf-Rayet or Be stars. To help answering these questions, the MULTIPLES team has collected and analysed new high-angular-resolution and spectroscopic observations and developed and implemented novel analysis methods and bias correction techniques. It further has established strong synergies with other projects and researchers at KU Leuven and beyond.
Among the main published results, we have shown that most Carbon-rich Wolf-Rayet stars are binaries in long period orbits and that binary evolution is not necessarily required to explain Wolf-Rayet stars in the Large Magellanic Clouds. We have unveiled two prototypical objects of a rare class of post-interaction binaries, formed by a stripped star and a bloated OB-type companion that is out of thermal equilibrium as a result of their recent accretion of material. We also have obtained some of the most precise mass measurements of stars more massive than 50 solar masses, providing new high-quality data to confront evolutionary models. We have also brought the multiplicity properties of B-type stars on firmer ground, showing that about half of them have companions on a less than 10-year orbit and that their period distribution is compatible with that derive at higher masses and at LMC metallicities, pointing towards a joint pairing mechanism across the massive star regime. Preliminary result at high angular resolution however point to the fact that early B-type stars might have more interferometric companion than the more massive O-type stars, a preliminary finding that might help constraining the origin of the pairing mechanism but that requires further investigations.
Among the main published results, we have shown that most Carbon-rich Wolf-Rayet stars are binaries in long period orbits and that binary evolution is not necessarily required to explain Wolf-Rayet stars in the Large Magellanic Clouds. We have unveiled two prototypical objects of a rare class of post-interaction binaries, formed by a stripped star and a bloated OB-type companion that is out of thermal equilibrium as a result of their recent accretion of material. We also have obtained some of the most precise mass measurements of stars more massive than 50 solar masses, providing new high-quality data to confront evolutionary models. We have also brought the multiplicity properties of B-type stars on firmer ground, showing that about half of them have companions on a less than 10-year orbit and that their period distribution is compatible with that derive at higher masses and at LMC metallicities, pointing towards a joint pairing mechanism across the massive star regime. Preliminary result at high angular resolution however point to the fact that early B-type stars might have more interferometric companion than the more massive O-type stars, a preliminary finding that might help constraining the origin of the pairing mechanism but that requires further investigations.
Technical progress involves the development and implementation of novel methods and analysis tools:
Spectral disentangling: the MULTIPLES team has developed a novel spectral disentangling approach optimised to be more stable and robust than previous approaches at the cost of restraining the number of degrees of freedom in the fit. This can be safely done by relying on complementary data or prior knowledge of some of the orbital parameters. The method has proven to be more reliable for long period systems where the Doppler separation between the spectral lines of the two components remains similar to or smaller than the full width at half maximum of the spectral lines as well as for system with extreme luminosity ratios.
SB2 binary detection probability: the MULTIPLES team has developed and implemented a novel approach to compute the detection probability of double-lined spectroscopic binaries. It relies on rapid-diagnostic recipes developed using a repeat of the measurement process on artificial data and its implementation in existing Monte Carlo simulations codes. This allowing us to obtain more realistic estimate of the observational biases that previously possible, and to obtain more precise measurements of the intrinsic binary fraction of the stellar populations that we are scrutinising.
Orbital solution: the MULTIPLES team has developed and implemented an open-source tool providing state-of-the-art user-friendly environment to adjust the orbit of spectroscopic and interferometric binaries, including appropriate graphical user interface, data visualisation and error estimates.
The results expected at the end of the project remain along the line of its initial goals: (i) constraining the multiplicity properties of massive stars across the entire mass-range relevant for CCSN and GW progenitors and in different metallicity environments, (ii) shedding new light on the origin of close massive binaries and (iii) characterising the nature and frequency of post-interaction products in populations of massive stars. No deviation from this framework is currently expected.
Spectral disentangling: the MULTIPLES team has developed a novel spectral disentangling approach optimised to be more stable and robust than previous approaches at the cost of restraining the number of degrees of freedom in the fit. This can be safely done by relying on complementary data or prior knowledge of some of the orbital parameters. The method has proven to be more reliable for long period systems where the Doppler separation between the spectral lines of the two components remains similar to or smaller than the full width at half maximum of the spectral lines as well as for system with extreme luminosity ratios.
SB2 binary detection probability: the MULTIPLES team has developed and implemented a novel approach to compute the detection probability of double-lined spectroscopic binaries. It relies on rapid-diagnostic recipes developed using a repeat of the measurement process on artificial data and its implementation in existing Monte Carlo simulations codes. This allowing us to obtain more realistic estimate of the observational biases that previously possible, and to obtain more precise measurements of the intrinsic binary fraction of the stellar populations that we are scrutinising.
Orbital solution: the MULTIPLES team has developed and implemented an open-source tool providing state-of-the-art user-friendly environment to adjust the orbit of spectroscopic and interferometric binaries, including appropriate graphical user interface, data visualisation and error estimates.
The results expected at the end of the project remain along the line of its initial goals: (i) constraining the multiplicity properties of massive stars across the entire mass-range relevant for CCSN and GW progenitors and in different metallicity environments, (ii) shedding new light on the origin of close massive binaries and (iii) characterising the nature and frequency of post-interaction products in populations of massive stars. No deviation from this framework is currently expected.