Periodic Reporting for period 1 - MATISSE (Measuring Ages Through Isochrones, Seismology, and Stellar Evolution)
Reporting period: 2022-09-01 to 2024-08-31
Over the course of the two-year MSCA funding period, the PI (Joyce) and host (Molnár) made significant advances in all three topics of the project: convection in 1D stellar models, globular cluster/isochrone analysis, and, especially, the modeling of high-mass variable stars. All of these three topics are areas of stellar physics with long-standing open questions, and the project was aimed at advancing the state of the art in each of them. And while these are all questions that concern fundamental science, they also help us create a broad understanding of how stars live and die, and how stars enrich their environments so that new stars and planets, similar to the Sun and Earth, may form from them.
This project has produced its most significant results through the advancement of our understanding of high-mass variable stars, especially two long-studied giants of different types: the asymptotic giant branch (AGB) star R Hydrae, and the nearby red supergiant and 10th brightest star in the sky, Alpha Orionis, popularly known as Betelgeuse.
As part of studying R Hya, this project produced the first ever, fully open-source grid of AGB evolutionary calculations including seismology. These models were computed with the stellar evolution code MESA and the accompanying pulsation code GYRE. Application to R Hya revealed that it is a few times heavier than the Sun, and it is likely actively enriching its environment.
Another significant result of the project was a collaborative work in which the PI participated, resulting in a Nature publication. The study found that one star out of a dozen has consumed one of its planets during their formation. The researcher contributed specialized MESA models to this end.
Important results were achieved on the ages of stars as well. The researcher found that the stars in the Galactic bulge, the center of the Milky Way, are predominantly old, exceeding 10 billion years. However, when she accounted not just for observational errors, but for modeling uncertainties properly, too, the uncertainties increased to 2-5 billion years.
In the final months of the project, the PI and host collaborated on a groundbreaking publication predicting the presence of a low-mass orbital companion to Betelgeuse: alpha Orionis B, or colloquially, “BetelBuddy.” This study has received considerable attention in popular science outlets and resulted in the PI and host winning time on both the Hubble Space Telescope and Chandra X-ray observatory to try to find the companion.
This action led to a better understanding of uncertainties in evolutionary stellar models, and especially their dependence on the mixing length parameter. The PI and the host will continue their collaboration to calibrate the parameter through the new observations they secured thanks to this action. The AGB model grid is available for modeling further AGB stars, either by the PI/Host or others. Their joint work in this action also led to successful observing proposals on the Hubble and Chandra space telescopes, which they will use to prove the existence of “Betelbuddy”.
This project has produced its most significant results through the advancement of our understanding of high-mass variable stars, especially two long-studied giants of different types: the asymptotic giant branch (AGB) star R Hydrae, and the nearby red supergiant and 10th brightest star in the sky, Alpha Orionis, popularly known as Betelgeuse.
As part of studying R Hya, this project produced the first ever, fully open-source grid of AGB evolutionary calculations including seismology. These models were computed with the stellar evolution code MESA and the accompanying pulsation code GYRE. Application to R Hya revealed that it is a few times heavier than the Sun, and it is likely actively enriching its environment.
Another significant result of the project was a collaborative work in which the PI participated, resulting in a Nature publication. The study found that one star out of a dozen has consumed one of its planets during their formation. The researcher contributed specialized MESA models to this end.
Important results were achieved on the ages of stars as well. The researcher found that the stars in the Galactic bulge, the center of the Milky Way, are predominantly old, exceeding 10 billion years. However, when she accounted not just for observational errors, but for modeling uncertainties properly, too, the uncertainties increased to 2-5 billion years.
In the final months of the project, the PI and host collaborated on a groundbreaking publication predicting the presence of a low-mass orbital companion to Betelgeuse: alpha Orionis B, or colloquially, “BetelBuddy.” This study has received considerable attention in popular science outlets and resulted in the PI and host winning time on both the Hubble Space Telescope and Chandra X-ray observatory to try to find the companion.
This action led to a better understanding of uncertainties in evolutionary stellar models, and especially their dependence on the mixing length parameter. The PI and the host will continue their collaboration to calibrate the parameter through the new observations they secured thanks to this action. The AGB model grid is available for modeling further AGB stars, either by the PI/Host or others. Their joint work in this action also led to successful observing proposals on the Hubble and Chandra space telescopes, which they will use to prove the existence of “Betelbuddy”.
During the project the researcher authored 14 publications. She wrote a well-cited review article on the use of Mixing Length Theory (MLT) in one-dimensional stellar evolution models. She then studied a sample of stars in the center of the Milky Way, called the bulge, to estimate their age distribution. For this, she calculated a grid of stellar models with varying mixing lengths. This work indicated that the bulge is made up of predominantly old stars, and earlier results suggesting a significant population of young stars were false.
She also calculated stellar models with varying levels of atomic diffusion to explain chemical differences found in stars that were born together. The results did not match the observations, confirming that this hypothesis is insufficient and the alternate (planet ingestion by stars) must be in effect.
In order to calibrate the mixing length more accurately in the models, well-characterized stars are required. The researcher and the supervisor realized that available observations are lacking in this regard. They examined the database of the Gaia space telescope to select new targets, and proposed observations of a large sample of seismic binary star targets with the TESS space telescope. This proposal was successful, and the data will be collected.
Meanwhile, she supervised the work of multiple students who learned how to use stellar models and isochrones to estimate ages with them. The researcher also organized a summer school to teach the usage of the MESA stellar evolutionary model to a large cohort of participants.
The researcher spent significant amounts of time to build up the first-ever open-source grid of asteroseismic AGB models and a data visualization app to explore them. The grid took over 5 million CPU hours of calculations to complete. Both the model grid and the visualizer have been released to the public. This grid was then used to model the seismic evolution of the star R Hya, for which nearly four centuries of observations are available.
Towards the end of the project, the researcher and the supervisor worked on the possible explanations for the light variations of the star Betelgeuse. Through a collaboration, they managed to rule out all possible explanations for its long cycle, until only binarity remained, and they proposed the existence of a companion star.
She also calculated stellar models with varying levels of atomic diffusion to explain chemical differences found in stars that were born together. The results did not match the observations, confirming that this hypothesis is insufficient and the alternate (planet ingestion by stars) must be in effect.
In order to calibrate the mixing length more accurately in the models, well-characterized stars are required. The researcher and the supervisor realized that available observations are lacking in this regard. They examined the database of the Gaia space telescope to select new targets, and proposed observations of a large sample of seismic binary star targets with the TESS space telescope. This proposal was successful, and the data will be collected.
Meanwhile, she supervised the work of multiple students who learned how to use stellar models and isochrones to estimate ages with them. The researcher also organized a summer school to teach the usage of the MESA stellar evolutionary model to a large cohort of participants.
The researcher spent significant amounts of time to build up the first-ever open-source grid of asteroseismic AGB models and a data visualization app to explore them. The grid took over 5 million CPU hours of calculations to complete. Both the model grid and the visualizer have been released to the public. This grid was then used to model the seismic evolution of the star R Hya, for which nearly four centuries of observations are available.
Towards the end of the project, the researcher and the supervisor worked on the possible explanations for the light variations of the star Betelgeuse. Through a collaboration, they managed to rule out all possible explanations for its long cycle, until only binarity remained, and they proposed the existence of a companion star.
Progress beyond the state of the art and impacts on the researcher’s career:
- The analysis of age systematics due to modeling uncertainties;
- The conclusion that most Galactic bulge stars are old;
- Planet ingestion is needed to explain chemical differences in stars instead of diffusion;
- The release of the evolutionary and seismic AGB model grid;
- The proposal that Betelgeuse may have a Sun-like companion;
- several high-impact papers and enhanced visibility in the stellar astrophysics community;
- recognition for the successful organization of the MESA@Konkoly Summer School;
- a tenure-track assistant professorship at the University of Wyoming.
Based on the high number of downloads (55) from the Zenodo page of the asteroseismic AGB grid, we anticipate that it will be used in many future projects on similar stars.
The Mixing Length review already has 33 citations, most of these in the planetary modeling community. We expect this paper will be widely consulted in the development of 1D models of sub-stellar bodies, including brown dwarfs and planets.
Astrophysics is almost exclusively a fundamental science, and its socio-economic impacts are largely indirect. Inspiration is one of the important effects, as the field generates interest in physics very efficiently through public outreach. This was showcased by the strong interest in and coverage of the discovery of Betelgeuse’s low-mass binary companion. The MESA@Konkoly Summer School also had socio-economic effects by enhancing the participants’ research skills and thus advancing their future career prospects. The PI is also the only woman on the MESA developers team and the only woman on the team responsible for discovering Betelgeuse’s companion. As a direct result of the latter, the PI has received several requests to speak at Women in Science events and participate in public outreach, including participating in a primary’s school’s initiative to put young male students in contact with female scientists.
- The analysis of age systematics due to modeling uncertainties;
- The conclusion that most Galactic bulge stars are old;
- Planet ingestion is needed to explain chemical differences in stars instead of diffusion;
- The release of the evolutionary and seismic AGB model grid;
- The proposal that Betelgeuse may have a Sun-like companion;
- several high-impact papers and enhanced visibility in the stellar astrophysics community;
- recognition for the successful organization of the MESA@Konkoly Summer School;
- a tenure-track assistant professorship at the University of Wyoming.
Based on the high number of downloads (55) from the Zenodo page of the asteroseismic AGB grid, we anticipate that it will be used in many future projects on similar stars.
The Mixing Length review already has 33 citations, most of these in the planetary modeling community. We expect this paper will be widely consulted in the development of 1D models of sub-stellar bodies, including brown dwarfs and planets.
Astrophysics is almost exclusively a fundamental science, and its socio-economic impacts are largely indirect. Inspiration is one of the important effects, as the field generates interest in physics very efficiently through public outreach. This was showcased by the strong interest in and coverage of the discovery of Betelgeuse’s low-mass binary companion. The MESA@Konkoly Summer School also had socio-economic effects by enhancing the participants’ research skills and thus advancing their future career prospects. The PI is also the only woman on the MESA developers team and the only woman on the team responsible for discovering Betelgeuse’s companion. As a direct result of the latter, the PI has received several requests to speak at Women in Science events and participate in public outreach, including participating in a primary’s school’s initiative to put young male students in contact with female scientists.