Periodic Reporting for period 1 - LSP-MIST (A MISTery of Long Secondary Periods in Pulsating Red Giants - Traces of Exoplanets?)
Periodo di rendicontazione: 2022-10-01 al 2025-03-31
Planets, particularly extrasolar ones, have always captivated human curiosity. We wonder whether life exists on other planets and if we might one day encounter the inhabitants of distant worlds. For astronomers, discovering a large number of extrasolar planets is crucial for deepening our understanding of how and where planetary systems can form.
Exoplanetary science is among the most dynamic and challenging fields in modern astrophysics. Over the past few decades, various planet detection techniques have enabled astronomers to identify thousands of extrasolar planets in our Galaxy, particularly in the vicinity of the Sun. These discoveries provide valuable, though limited, insights for testing planet formation theories. However, current methods remain insufficient for detecting planets in the distant regions of the Milky Way or in other galaxies. As a result, fundamental questions in exoplanetary science remain unanswered: How are planets distributed throughout our and other galaxies? And how does the frequency of planets vary with the chemical composition of their environments?
Therefore, it is essential to develop a new detection method capable of identifying distant planets and expanding the horizons of exoplanetary studies.
The goal of my project LSP-MIST is to create such a method. I will use bright giant stars that exhibit long secondary periods (LSPs) as traces of extrasolar planets. These stars are thought to be binary systems where the primary is a red giant at the end of its evolutionary stage, and the secondary is a substellar object enshrouded in a dusty cloud. The hypothesis is that the companion is a former planet that has accreted enough material from the host star to become a brown dwarf.
I will use the high quality photometric and spectroscopic data of LSPs from large-scale surveys and combine it with modern hydrodynamical simulations to verify this hypothesis. If successful, this method could revolutionize the field of exoplanet detection by enabling the discovery of planets beyond our immediate galactic neighborhood, and especially in other galaxies, which is impossible with the current techniques.
In the next phase of my research, I will apply this novel method to hundreds of thousands of LSP variables from the OGLE catalogs of the Milky Way and the Magellanic Clouds. This will allow me to study the distribution and properties of planets in diverse chemical environments, providing completely new constraints on planet formation theories.
Exoplanetary science is among the most dynamic and challenging fields in modern astrophysics. Over the past few decades, various planet detection techniques have enabled astronomers to identify thousands of extrasolar planets in our Galaxy, particularly in the vicinity of the Sun. These discoveries provide valuable, though limited, insights for testing planet formation theories. However, current methods remain insufficient for detecting planets in the distant regions of the Milky Way or in other galaxies. As a result, fundamental questions in exoplanetary science remain unanswered: How are planets distributed throughout our and other galaxies? And how does the frequency of planets vary with the chemical composition of their environments?
Therefore, it is essential to develop a new detection method capable of identifying distant planets and expanding the horizons of exoplanetary studies.
The goal of my project LSP-MIST is to create such a method. I will use bright giant stars that exhibit long secondary periods (LSPs) as traces of extrasolar planets. These stars are thought to be binary systems where the primary is a red giant at the end of its evolutionary stage, and the secondary is a substellar object enshrouded in a dusty cloud. The hypothesis is that the companion is a former planet that has accreted enough material from the host star to become a brown dwarf.
I will use the high quality photometric and spectroscopic data of LSPs from large-scale surveys and combine it with modern hydrodynamical simulations to verify this hypothesis. If successful, this method could revolutionize the field of exoplanet detection by enabling the discovery of planets beyond our immediate galactic neighborhood, and especially in other galaxies, which is impossible with the current techniques.
In the next phase of my research, I will apply this novel method to hundreds of thousands of LSP variables from the OGLE catalogs of the Milky Way and the Magellanic Clouds. This will allow me to study the distribution and properties of planets in diverse chemical environments, providing completely new constraints on planet formation theories.
We have analysed observational data from the fourth phase of the Optical Gravitational Lensing Experiment (OGLE-IV), covering the Magellanic Clouds, the Galactic Bulge and Disk, in order to identify all long period variables (LPVs), including LSP stars. This required processing 2.4 billion light curves. To achieve this, we adapted software designed for detecting periodicities in time-resolved observations using Fourier transforms, to efficiently process large datasets. We are currently working on developing efficient methods to classify variable stars with machine learning techniques.
Additionally, we identified bright LSP variables stars in the All Sky Automated Survey (ASAS) data as candidates for interferometric follow-up. Such observations could provide valuable insights for testing the hypothesis proposed in the grant, that is, that there is a spiral dusty structure following the companion on its orbit around the red giant host star.
During our analysis of the radial velocity data of 9,614 LPV stars published as a Focused Product Release by the Gaia Collaboration, we found unexpected phase shifts between the light and radial velocity curves. These shifts differ from predictions made by existing LSP system models, and this investigation is ongoing. In the course of this analysis we also discovered a classical Cepheid with a pulsation period of 78 days, which makes it the first ultra-long period Cepheid discovered in the Milky Way. Previously, such stars had only been observed in neighbouring galaxies, raising questions about their apparent absence in our own Galaxy.
In parallel, we have been working on hydrodynamic simulations of the LSP systems using the Smoothed Particle Hydrodynamics code Phantom, focusing on cooling processes which are crucial for dust formation around the red giant. We have identified and resolved problems in the existing implementation of the cooling processes and are working on further improvement to the numerical integration methods.
Additionally, we identified bright LSP variables stars in the All Sky Automated Survey (ASAS) data as candidates for interferometric follow-up. Such observations could provide valuable insights for testing the hypothesis proposed in the grant, that is, that there is a spiral dusty structure following the companion on its orbit around the red giant host star.
During our analysis of the radial velocity data of 9,614 LPV stars published as a Focused Product Release by the Gaia Collaboration, we found unexpected phase shifts between the light and radial velocity curves. These shifts differ from predictions made by existing LSP system models, and this investigation is ongoing. In the course of this analysis we also discovered a classical Cepheid with a pulsation period of 78 days, which makes it the first ultra-long period Cepheid discovered in the Milky Way. Previously, such stars had only been observed in neighbouring galaxies, raising questions about their apparent absence in our own Galaxy.
In parallel, we have been working on hydrodynamic simulations of the LSP systems using the Smoothed Particle Hydrodynamics code Phantom, focusing on cooling processes which are crucial for dust formation around the red giant. We have identified and resolved problems in the existing implementation of the cooling processes and are working on further improvement to the numerical integration methods.
The project's main goal is to prove the hypothesis, that the LSP stars are binary systems in which the companion is a former planet. If true, this will give us a new planet detection method, which will revolutionize the field of exoplanet detection by enabling the discovery of planets beyond our immediate galactic neighbourhood, and especially in other galaxies, which is impossible with the current techniques. This is necessary for investigating the planet prevalence and distribution in environments of different density and chemical composition, to provide a new set of constraints for planet formation theories.
The high risk of the project is that the hypothesis is wrong and LSP variables cannot be used as traces of exoplanetary systems, but this risk does not affect the ambitious intermediate goals of this proposal which will go beyond the state of the art in observational and theoretical studies of variable red giants.
The high risk of the project is that the hypothesis is wrong and LSP variables cannot be used as traces of exoplanetary systems, but this risk does not affect the ambitious intermediate goals of this proposal which will go beyond the state of the art in observational and theoretical studies of variable red giants.