AO-1 Programmes - Abstracts of Waitlisted Programmes

Multimode pulsations, resonances, and binarity in a homogeneous Galactic RR Lyrae sample - Proposal 1, Benko (HU)

RR Lyrae stars are not only crucial for measuring cosmic distances but also serve as key probes of stellar structure and evolution. However, several aspects of their variability remain poorly understood. In particular, the temporal behaviour of low-amplitude non-radial pulsations, the incidence and stability of the Blazhko effect, the properties of multiple modulations and their possible resonant relationships, and the binary properties of these stars remain open questions. Previous space missions have either provided high-precision data for small samples or studied large samples with limited temporal coverage. PLATO will, for the first time, combine high photometric precision with multi-year, uninterrupted observations for a large and homogeneous sample of RR Lyrae stars. We propose to exploit this unique dataset to carry out a systematic investigation of multimode pulsation, modulation phenomena, and binarity. Our analysis will be based on dedicated time-series methods optimised for high-amplitude variables. The expected results will provide new constraints on non-linear pulsation, the physical origin of the Blazhko effect, and the binary fraction of RR Lyrae stars, thereby significantly advancing our understanding of these evolved low-mass stars.

Tracing the modulation phenomenon in High-Amplitude delta Scuti stars - Proposal 15, Plachy (HU)

High-amplitude delta Scuti (HADS) stars are a subclass of delta Scuti variables characterized by large photometric amplitudes and pulsation dominated by one or a small number of radial modes. Recent observations have revealed amplitude and phase modulation in a small number of HADS, in some cases showing intriguing similarities to the Blazhko effect known in RR Lyrae stars, while in other cases beating between closely spaced frequencies or mode coupling may offer alternative explanations. The limited time coverage of existing observations has so far prevented a clear distinction between these scenarios. We propose to exploit PLATO’s unique long-term, high-precision photometry to investigate this behavior in a carefully selected sample of 253 HADS stars in the LOPS2 field. Nearly half of the sample already shows visible or suspected amplitude variability in TESS data, indicating that this phenomenon may be common in this class. Using long-cadence on-board light-curve products, we will characterize amplitude and phase variability, and search for Blazhko-like signatures including multiplet structures, loop-diagram patterns, irregular modulation, and period doubling. We will distinguish intrinsic modulation from beating through time-dependent frequency analysis and comparisons with synthetic amplitude-equation models. These observations will provide new constraints on mode interaction, nonlinear pulsation, and the origin of modulation across radial pulsators.

Constraining interior rotation and mixing of massive pulsating stars: ensemble asteroseismology of β Cephei and SPB stars - Proposal 35, Scott (UK)

Massive stars are critical drivers of galactic evolution through interactions with their environments, via supernovae, winds and radiation. The understanding of massive stars hinges on the physics of their interiors, particularly rotation and chemical mixing, which affect the end products of stellar evolution such as black holes. Asteroseismology, the use of pulsations to understand stellar structure, is uniquely suited to using PLATO data to refine the understanding of massive star interior physics. In particular, the slowly-pulsating B-type (SPB) stars and the β Cephei stars, two classes of pulsating, hydrogen-burning stars above around 8 solar masses, are important targets for investigating mixing and rotation. This is due to the properties of pulsation modes in these classes of variable stars, which are sensitive to the structure near the convective core. Massive star evolution depends on the extent of the convective core, which can be recovered by comparing pulsation models to data. Each pulsation mode also probes the rotation at different depths within the star, allowing direct measurement of interior rotation. This project will observe 102 β Cephei stars and 314 SPBs across a range of masses and ages, and will provide the highest-quality large asteroseismic sample to-date. Since mixing and rotation is known to vary between individual stars, these data will allow measurement of the variation of mixing and rotation with mass and age, thus calibrating stellar models.

Multiplying the eclipsing binary sample for circumbinary planet detection - Proposal 36, Deeg (ES)

Circumbinary planets (CBPs) are one of the most dynamically complex and scientifically valuable populations in exoplanetary science. The current sample of 14 transiting CBPs around 12 eclipsing binaries (EBs) is very small and strongly affected by detection biases, consisting mainly of Uranus- to Jupiter-sized planets in nearly coplanar orbits, with a concentration near the inner dynamical stability limit around the central EBs. We seek to exploit the unique capabilities of PLATO to determine the true demographic distribution of CBPs with corresponding implications to formation and migration scenarios, by a significant expansion of the current CBP sample. With the requested 2-year long observations, the program also aims to detect long-period and potentially habitable CBPs, identify mutually inclined systems exhibiting sparse or episodic transit sequences, and improve sensitivity toward smaller planetary radii, down to terrestrial sizes. From a compilation of all known detached EBs with periods greater than 4 days within LOPS2, the project adds 717 targets to the 161 similar EBs that are already in the PIC; thereby increasing the number of targets suitable for a CBP search by a factor of ~ 4.5. These 717 targets are essential for initiating a substantial CBP search with PLATO, which should result in the first major amplification of the sample of known CBPs since the end of the Kepler mission some 15 years before.

Understanding outbursts and the formation of a decretion disk around Be stars via angular momentum transport - Proposal 37, Neiner (FR)

Be stars are rapidly rotating, pulsating, late-O to early-A stars surrounded by a hot gaseous decretion disk fed by discrete mass-loss events. How these outbursts occur has remained a mystery since the discovery of Be stars ∼160 years ago. Only one Be outburst has been ob served with precise, long-term photometry so far: it is in the Be star HD 49330 observed with CoRoT. Analysis of these CoRoT data found that its outburst was directly correlated to the pulsation frequencies visible at the stellar surface. Models showed that the outburst was due to the transport of angular momentum from the stellar core to the surface by pulsations stochastically excited in the core. Such pulsations can be excited and have a high amplitude thanks to the rapid rotation of the star. In this proposal, we wish to test this explanation on more outbursting Be stars and provide a general explanation to the long-standing questions surrounding Be stars, their ejections of matter, and the formation of their disks. We therefore propose to observe for 2 years 57 hot Be stars visible in the LOPS2 PLATO field that are likely to undergo an outburst during that time.

High-Precision Asteroseismology of Main-Sequence Hybrid Pulsators with PLATO: Empirical Instability Strips and Differential Rotation - Proposal 43, Kliapets (BE)

Hybrid pulsators, stars with both gravity (g) and pressure (p) modes, are perfect laboratories for stellar astrophysics. Thanks to both types of pulsation modes, one can probe their stellar interior almost entirely. Despite that, to date there have been no dedicated asteroseismology population studies of hybrid pulsators. Instead, they are typically treated as pure g- or pure p-mode pulsators. Thanks to its long-baseline, fine sampling, and low noise budget, PLATO offers a unique opportunity to remedy this gap by performing the first high-precision asteroseismology study of hybrid pulsators. Our goal is two-fold. First, we will measure differential rotation by obtaining near-core rotation from g modes and envelope rotation from rotational splittings of p modes. This will allow us to infer radial rotation profiles on an unprecedented scale, looking at slow to fast rotators across a wide mass regime. Second, we will empirically map the instability strips of hybrid pulsators, which has so far only been done for g- and p-mode pulsators separately. We will investigate the continuum between intermediate- and high-mass main-sequence pulsators and the effect rotation has on the position of hybrids on the Hertzsprung-Russell Diagram. The results of this project will help us constrain the angular momentum transport mechanisms and calibrate rotating stellar models, helping the stellar astrophysics field well outside the domain of hybrid asteroseismology.

The impact of metallicity on stochastic low-frequency variability revealed by PLATO light curves of massive stars in the LMC - Proposal 52, Bowman (UK)

Massive stars are important cosmic engines in the Universe with their ionizing radiation, strong winds, and explosive end-of-life events providing kinematic, radiative, and chemical feedback to the interstellar medium. However, the physical processes of rotation and mixing, which largely dictate the evolution and final fates of massive stars, are not yet fully understood. The efficiencies of various mixing processes and angular momentum transport mechanisms are also expected to differ for low-metallicity stars, but remain uncalibrated in stellar evolution models. A recent important piece of the puzzle for mixing and angular momentum transport inside massive stars came from the discovery of ubiquitous stochastic low-frequency (SLF) variability in space photometry that is consistent with hydrodynamical simulations of gravity waves excited by convection. We request 2-yr imagettes of 121 massive stars in the LMC to investigate SLF variability in a large sample of low-metallicity massive stars for the first time. We will compare the observations of SLF variability to hydrodynamical simulations of stellar interiors to constrain interior rotation, mixing, and angular momentum transport. PLATO imagettes are necessary for two reasons: (i) a 25-sec cadence is needed to prevent high-frequency signal suppression, and (ii) imagettes will allow on-ground PSF fitting to extract light curves, which was crucial to mitigate contamination in analyses of SLF variability using TESS image data.

A PLATO view of the final evolutionary phases of massive stars - Proposal 56, Mahy (BE)

This project exploits long-duration, high-precision photometry from PLATO to probe the most extreme phases of massive-star evolution: Wolf–Rayet (WR) stars and Luminous Blue Variables (LBVs). These objects govern the final stages before core collapse, yet their mass-loss rates, internal mixing, and instability mechanisms remain poorly constrained. We will use two years of continuous PLATO monitoring to dissect both coherent pulsations and stochastic variability linked to winds, subsurface convection, and internal gravity waves. By combining Galactic targets with Large Magellanic Cloud (LMC) counterparts, we will directly test the role of metallicity in shaping mass loss, rotation, and envelope stripping, crucial for black-hole and supernova progenitors. For crowded LMC fields, PSF-based photometry on PLATO imagettes (LEMONS pipeline) will ensure precise light curves. Fourier and time-resolved analyses will track evolving variability regimes inaccessible to previous missions. This programme will deliver new constraints on the pre-supernova physics of the most massive stars, bridging stellar structure, binary interaction, and the origin of compact remnants.

Survey of pulsation in the most rapidly rotating B stars - Proposal 63, Labadie-Bartz (DK)

The aim of this proposal is to acquire 2 year PLATO photometry for 101 rapidly-rotating intermediate- and high-mass B star pulsators to enable the first asteroseismic analysis of this population. Four years of Kepler photometry has enabled a proof of concept, but is only available for a few rapidly rotating B stars. TESS photometry, even in the 1-year Continuous Viewing Zones, is too short in duration and provides insufficient frequency resolution. Currently, asteroseismology for rapidly rotating B stars is impeded by a lack of data -- PLATO is the only mission capable of remedying this by providing both sufficient frequency resolution and photometric precision for a large number of targets.

Eclipse timing variations in short-period binaries: a PLATO search for circumbinary planets and low-mass companions - Proposal 68, Korth (ES)

No circumbinary planets (CBPs), planets orbiting both stars of a binary system, have been detected around main-sequence eclipsing binaries (EBs) with binary periods below 7 days. Dynamical suppression and tidal shrinkage are predicted to push companions to wide separations where transit probability vanishes, yet this population remains entirely unprobed. Eclipse timing variation (ETVs) detect companions at all orbital inclinations and separations, uniquely accessing these wide-separation orbits around tight binaries. We propose the first systematic ETV survey targeting 1968 short-period EBs (P_bin = 0.1 to 4 d) in the PLATO LOPS2 field. Using the light travel time effect and dynamical ETVs, we search for companions in the mass range 1 to 10 M_Jup, independent of orbital inclination. Even a null result provides the first meaningful upper limits on CBP occurrence around short-period binaries, constraining formation and migration models. This programme is entirely complementary to transit-based CBP searches, addressing a region of parameter space inaccessible to any current or planned survey.

Asteroseismology of Mass-Accreting Pulsators: PLATO Survey of Oscillating Eclipsing Algol Systems - Proposal 85, Derekas (HU)

Oscillating eclipsing Algol-type (oEA) stars are mass-accreting δ Scuti pulsators in semi-detached binary systems. They offer a unique laboratory where binary dynamics and asteroseismology converge. By combining precise dynamical stellar parameters with pulsation frequency spectra, oEA stars allow direct probing of internal physics including core overshooting, differential rotation, and accretion-driven chemical gradients. We propose PLATO observations of 10 oEA systems (G ~ 8–15 mag) in the LOPS2 continuous viewing zone, all requiring 50-second cadence to resolve high-frequency p-modes without aliasing. PLATO's multi-year baseline delivers a 25-fold improvement in frequency resolution over TESS, enabling unambiguous identification of rotational multiplets and detection of year-timescale amplitude/phase modulations driven by mass transfer. Key science objectives include: quantifying mode detuning triggered by stochastic accretion bursts; unambiguous mode identification via eclipse mapping; characterization of tidally trapped and tidally excited pulsations; breaking stellar evolution model degeneracies using model-independent dynamical masses; and mapping accretion-driven differential rotation. Ground-based radial-velocity follow-up will provide masses and radii to 1–2% precision, serving as direct inputs to asteroseismic modeling. The proposed program offers high scientific return.

Long-period eclipsing binaries - Proposal 88, Helminiak (PL)

Long-period detached eclipsing binaries provide fundamental tests of stellar evolution because their components evolve similarly to single stars while still allowing precise measurements of masses and radii. In wide systems, tidal interactions are weak, making them ideal laboratories for investigating the transition between genuinely single-star evolution and subtle binary-induced effects. However, such systems remain poorly sampled, particularly among binaries containing two main-sequence stars, because long orbital periods reduce eclipse probability and complicate observations. PLATO’s continuous two-year observations will greatly improve the characterization of these binaries compared to the typical 28-day TESS sectors. Many long-period systems currently have incomplete or poorly sampled eclipses, leading to uncertain orbital periods and eclipse timings. PLATO will provide dense phase coverage over multiple orbital cycles, enabling precise determination of orbital and stellar parameters as well as improved eclipse ephemerides and timing studies. The program will include systems containing evolved stars, including double giants, which provide stringent constraints on post-main-sequence evolution. Many giant components are also expected to exhibit solar-like oscillations, allowing combined eclipsing-binary and asteroseismic analyses. Dedicated spectroscopic follow-up will deliver radial velocities and, for brighter targets, disentangled spectra and atmospheric parameters.

Testing Binary Interaction, Rapid Rotation, and Disk Feeding in Be Stars with PLATO - Proposal 101, Emilio (BR)

Classical Be stars are rapidly rotating, non-supergiant B-type stars surrounded by gaseous decretion disks, yet the origin of their rapid rotation and episodic disk feeding remains unresolved. This proposal uses PLATO high-precision photometry of Be and Be-related binary systems to test how binary interaction contributes to rapid rotation, angular-momentum evolution, and disk formation or modulation. The selected targets are not intended to represent all Be stars, but to serve as diagnostic laboratories in which orbital motion, radial velocities, dynamical mass constraints where feasible, pulsations, rotation, and disk variability can be studied within a single framework. The programme will test three scenarios: primordial rapid rotation, spin-up through past binary mass transfer, and present-day orbital modulation of the decretion disk. PLATO light curves will separate pulsational, rotational, orbital, and disk-related variability over timescales inaccessible to most existing space photometry. These data will be combined with spectroscopic follow-up, archival radial velocities, Hα monitoring, Gaia constraints, and literature data. The project will provide new constraints on the angular-momentum budget, evolutionary status, and disk-feeding mechanisms of Be stars, helping clarify the role of binarity in the Be phenomenon.

Benchmark Be Stars with PLATO and Long-Term Spectroscopic Monitoring - Proposal 107, Andrade (BR)

This proposal requests PLATO observations of a benchmark sample of bright classical Be stars in the LOPS2 field, supported by long-term spectroscopic monitoring. Classical Be stars are rapidly rotating B-type stars surrounded by viscous Keplerian decretion disks, but the connection between rapid rotation, pulsations, mass ejection, and disk feeding remains poorly understood. PLATO’s long, high-precision photometric baseline will resolve dense low-frequency pulsation spectra, amplitude variability, transient events, and possible mode-coupling signatures, including low-frequency daughter or difference signals. Contemporaneous spectroscopy will provide complementary diagnostics through Halpha disk monitoring and photospheric line-profile variations, helping determine whether photometric changes arise from stellar pulsations, disk evolution, or temporary occultation by circumstellar material. By combining PLATO photometry with spectroscopic disk-state classifications, this project will establish a benchmark dataset for connecting pulsations, mass ejection, and circumstellar disk evolution in rapidly rotating Be stars.

Dead Stars, Living Worlds: Discovering Planets and Debris Around White Dwarfs - Proposal 118, Korth (ES)

Nearly half of all white dwarfs (WDs) exhibit metals in their atmospheres, thought to originate from accreted planetary or asteroidal material. These systems provide a unique insight into the bulk abundances of extrasolar planetary bodies. Interpreting these abundances correctly requires to understand the full process from the original scattering of the body on a distant orbit, through its tidal disruption, formation of a close-in disc around the WD, and accretion into the atmosphere. Transit photometry plays a key role in tracing this process. A growing number of WDs show transits, usually with comet-like morphology arising from a dust cloud rather than a solid body. These occur on periods of hours to >100 days and often exhibit long-term variability, and help us understand the intermediate stages between the scattering of asteroids and their accretion. We will monitor 583 bright WDs to discover those with transiting debris and/or planets. Our goals are to constrain the occurrence rates of planets and transiting debris close to the WDs, search for planets within WD's habitable zones, and characterise the long-term behaviour of the transiting objects and their duty cycles. Compared to previous surveys, PLATO offers improved cadence, essential to better characterise brief transits across the small WD surface, and an uninterrupted long-time baseline, necessary to fully understand the long-term evolution of the transiting material as dust production rises and falls.

PLATO observations of open cluster stars - Proposal 124, Nardiello (IT)

For many Galactic field stars, fundamental properties cannot be determined with high accuracy and precision. In contrast, the well-constrained properties of stellar clusters and their members, including radii, masses, metallicities, and ages, make them powerful reference systems for tracing the formation and evolution of stars and their companions. The analysis of high-precision, long-baseline light curves of cluster members provides a unique opportunity to investigate a broad range of astrophysical phenomena, from stellar variability, including rotation-, pulsation-, and granulation-driven signals, to eclipsing binaries and transiting exoplanets. We propose to observe with PLATO, in imagette mode and with at least 12 NCAMs, 565 members of 73 open clusters located in the LOPS2 field that are not included in the PIC. The selected cluster members span ages from 10 Myr to 2.5 Gyr, have approximately solar metallicity, and include stars with masses down to 0.7 Msun. By applying state-of-the-art photometric-extraction tools, these observations will provide high-precision light curves to identify and characterize variable stars, binaries, and exoplanets. The inferred properties of stars and companions will be investigated as a function of cluster age, chemical composition, density, and location in the Galaxy. This will clarify how environment shapes the formation and evolution of stars, binaries, and planets, while providing key benchmarks for Galactic field stars.

Stormy Youth: A PLATO survey for planet-induced flaring in young systems - Proposal 130, Ilin (NL)

At ages below 300 Myr, young star-planet systems undergo a phase of intense stellar activity that permanently shapes planetary atmospheres. A recent discovery of star-planet interaction (SPI) in the 17 Myr system HIP 67522, where a close-in planet triggers giant stellar flares that may strip its own atmosphere, opens a new window on this violent phase. SPI manifests as periodic clustering of flares with the planetary orbital period, and is in principle detectable without prior knowledge of the orbit. We propose 50-s cadence observations of 429 flare-active young cluster members in the PLATO LOPS2 field over a full 2-year baseline. An estimated 145k flares will be identified; then each star will be tested for phase clustering. Depending on the true SPI occurrence rate, we expect 0–10 detections; a null result rules out interaction at >10% occurrence with high confidence. Each detection probes the stellar Alfvén zone, constraining wind speed and density, quantities otherwise inaccessible beyond 50 pc and critical inputs for atmospheric mass loss models. PLATO is uniquely suited for this search: its nearly uninterrupted observations maximize the ratio of time on target to observing baseline, avoiding the sparse cadence that limits TESS-based clustering searches, while its bluer bandpass and superior photometric precision deliver a factor of at least 3 more flares per star, enabling the large, well-characterized sample of young flaring stars this program requires.

M&Ms in PLATO: Benchmarking M-dwarf Eclipsing Binaries to Test Stellar Models - Proposal 132, Lantzi (ES)

Eclipsing binary stars (EBs), particularly double-lined EBs, provide the most accurate measurements of stellar masses and radii, making them fundamental benchmarks for testing stellar evolution models. The few well-studied M-dwarf EBs revealed discrepancies between their component stars and theoretical models, showing radii 5–10% larger and cooler effective temperatures than predicted. The origin of this “radius inflation” problem remains unclear, partly due to the small number of well-characterized systems, especially at long orbital periods where magnetic activity is expected to be weaker. This project aims to exploit the high-precision photometry of the PLATO mission to identify and characterize a large sample of M-dwarf EBs. We have identified 71 systems in the PLATO LOPS2 field that have not been well characterised, including 8 systems with orbital periods longer than 10 days. Combined analysis of PLATO light curves and ground-based high-resolution spectroscopy will provide accurate stellar masses, radii, and temperatures with precisions better than 3%, increasing the sample of M-dwarf EBs by a factor of 4. The resulting sample will significantly improve empirical constraints on the low-mass mass–radius relationship, test the role of magnetic activity in radius inflation, and provide benchmark systems to test stellar models. PLATO observations will also enable apsidal motion studies in eccentric binaries, offering insights into the interior of stars in EBs.

Tracing Supermassive Black Hole Accretion Disc Variability at the Eddington Limit with PLATO from Kiloseconds to Years - Proposal 141, Jiang (UK)

The discovery of massive supermassive black holes at high redshifts poses a fundamental challenge to cosmological models. Some suggest that early black holes may have undergone phases of super-Eddington accretion. Narrow-Line Seyfert 1 galaxies in the local universe serve as vital laboratories for super-Eddington accretion physics. We propose the first dedicated PLATO active galactic nucleus (AGN) study targeting the nearby, near/super-Eddington AGN PKS 0558-504. While previous space-based monitoring with Kepler successfully detected characteristic power spectral density (PSD) breaks in three standard Seyfert 1 AGN, these objects were strictly limited to low-rate, sub-Eddington accretion. By expanding this sample into the near- and super-Eddington domain, this program will definitively test if the physical mechanisms driving accretion disc variability scale universally or change fundamentally at extreme, radiation-pressure-dominated rates. Using PLATO’s exceptional continuous monitoring, we will map disc dynamics seamlessly across timescales from minutes to months, bridging a vital gap that numerical simulations of accretion discs cannot convincingly model. This pathfinder variability study will unlock sub-microarcsecond physical scales inaccessible to direct optical imaging, establishing a foundational baseline for a larger PLATO AGN demographic catalog as the mission observes subsequent fields of view.

Tracing second-generation circumbinary disc geometry and disc-binary interaction through optical variability in Galactic post-AGB binaries - Proposal 146, Andrych (AU)

Post-Asymptotic Giant Branch binary systems with dusty circumbinary discs are key laboratories for studying binary interaction, disc evolution, and the possible conditions for second-generation planet formation. Many of these systems show optical variability that combines stellar pulsations with longer-term disc-related modulation, but existing ground-based light curves are often too sparse and heterogeneous to disentangle these components robustly. We propose to use PLATO data for four Galactic post-AGB binaries in the LOPS2 field to obtain homogeneous, high-precision optical time series. These data will allow us to separate pulsational variability from disc-induced brightness changes, refine pulsation periods, and support independent luminosity constraints through period–luminosity–colour relations. They will also enable us to test whether long-term variability occurs on the binary orbital period and whether it can be explained by variable obscuration, scattering, or illumination of the disc inner rim. Combined with existing multi-technique constraints, the PLATO light curves will provide the time-domain inputs needed for radiative-transfer and hydrodynamic modelling of disc–binary interaction.

Probing unexplained oscillation spectra in intermediate-mass stars with PLATO - Proposal 149, Swiech (DK)

Wildly Oscillating Stars (WOS) are a recently identified subgroup of intermediate-mass pulsators exhibiting unusually dense and structured frequency spectra that are not reproduced by standard pulsation theory. Their oscillation spectra contain agglomerated frequency regions, ridge-like structures, and clusters of closely spaced peaks concentrated within narrow parts of the frequency spectrum. The currently known WOS population occupies a narrow region of the Hertzsprung–Russell diagram, suggesting that the phenomenon is linked to specific stellar properties and internal structure. Several physical explanations have been proposed, including rotational effects, binary evolution, chemical peculiarity, nonlinear mode interactions, and weak magnetic activity; however, none currently explains the observed morphology. The short duration of typical TESS observations additionally limits the achievable frequency resolution and prevents detailed characterization of the dense agglomerated frequency regions. The proposed PLATO observations will provide the long uninterrupted photometric baselines required to resolve the structure of the WOS frequency agglomerations. Combined with Gaia information and future spectroscopic follow-up observations, the data will enable detailed seismic investigations of the physical origin of the WOS phenomenon and determine whether these stars represent a previously unrecognized pulsational regime in intermediate-mass stars.

MainCandsProp - Proposal 152, Bryant (UK)

Our knowledge of transiting giant planet demographics with existing facilities, such as TESS, is limited primarily to short period planets and occurrence rates. With this proposal we aim to leverage the high-precision continuous photometric monitoring of PLATO to push our knowledge of planet populations to longer periods, and begin to bridge the gap between known transiting planets and the planets in our own Solar System. We will observe an unbiased statistical sample of 30 intermediate period (20 - 100 days) transiting giant planets. Using the PLATO observations we will: (1) detect small planet companions on close orbits to the intermediate period giant and constrain the occurrence rate of these systems; (2) detect transiting outer companions; (3) detect non-transiting companions through the monitoring of transit timing variations; (4) constrain the eccentricity distribution of our statistical giant planet sample. These are all observable tracers of how giant planets form and evolve, and in particular how they migrate from their formation location to the orbits on which we observe them. Therefore, through these PLATO observations we will be able to unlock the migration histories of the population of observed giant exoplanets.

Exoplanets around mid-to-late M dwarfs - Proposal 157, Bouchy (CH)

The statistical characterization and occurrence rates of planetary systems as a function of stellar host properties is one of the central challenges of exoplanet science. In this context, low-mass dwarfs offer a compelling environment to test theories of planet formation and evolution. TESS statistics for mid-to-late M dwarfs (< 0.35Msun) remain limited to periods below 30 days and radii larger than Earth, leaving the cold planet regime and sub-Earth regime largely unexplored. Late M dwarfs are the best opportunity to explore sub-Earth-radius planets. We selected a sample of 1970 mid-to-late M dwarfs (MTL) within the LOPS2 field to extend the P4 sample towards later spectral types. This sample will extend by a factor 5 the TESS sample of mid-to-late M dwarfs observed during at least 100 days. It will offer the unique opportunity to 1) detect a significant number of small transiting planets around mid-to-late M dwarfs for which the occurrence rate is poorly known, 2) to characterize the brightest and most interesting ones with radial velocity follow-up for internal structure studies, and 3) identify the best targets for atmospheric characterization with JWST and ANDES. The MTL sample will triple the planet detections around stars cooler than 3300 K, while delivering the first PLATO discoveries around the lowest-mass stars. By extending the sample to mid-to-late M-dwarfs, this GO program will enable a truly global view of the exoplanet population.

Testing the Spite plateau with PLATO-GO and 4MOST - Proposal 159, Bergemann (DE)

Big-bang nucleosynthesis (BBN) describes the birth of hydrogen, helium, and lithium isotopes in the first minutes of cosmic time. Measuring the abundances of these light elements probes the early Universe and test particle physics. But while precision deuterium and helium observations agree spectacularly with theory, lithium observations in metal-poor halo stars disagree with predictions at the ~5s level. This “lithium problem” is a major open question in cosmology. In this project, we aim to open a qualitatively new window onto the lithium problem. We will exploit the recent detection of extremely-metal-poor (EMP) stars in the Galactic disc to measure lithium and metal abundances versus time. We will do this using a large ensemble of EMP main-sequence stars from the 4MOST Disc & Bulge high-resolution survey 4MIDABLE-HR. The PLATO-GO asteroseismic data offer a new opportunity to determine ages of these stars and, therefore, to add - for the first time - a timeline to the evolution of Li in the early disc, a unique and novel approach compared to all previous work. This will allow us to address fundamental questions: (1) What is the evolution vs time of lithium and metallicity in the first disc stars? (2) Do early disc stars show the same primordial Li feature (Spite plateau) as halo stars?

Constraining the internal structure of blue straggler stars with asteroseismology - Proposal 167, Briganti (IT)

The study of binary-interaction products is crucial to improving our knowledge of stellar structure and evolution. These products include blue straggler stars (BSSs), which are core-hydrogen-burning stars that acquired mass through mass transfer, mergers, or collisions. These stars lie, in the colour-magnitude diagram of their host clusters, in a bluer and brighter extension of the main sequence. While they have been extensively studied from astrometric, photometric, and spectroscopic points of view, there is still a need to improve our knowledge of their internal structure, to better constrain their formation pathways and distinguish them from single-stellar-evolution objects. Recently, asteroseismology showed that both mass-transfer and collisional products present peculiar gravity-mode period spacing patterns, which are hints of previous dynamical events. With this proposal, taking advantage of the unprecedented combination of precision and stellar clusters in the field of view provided by the PLATO mission, we aim to study a large sample of confirmed BSSs in open clusters, to characterize these products and take a step further in our understanding of binary interactions.

The SPECULATO survey: searching for planets and characterising the activity of the coolest stars - Proposal 170, Hooton (UK)

The SPECULOOS mission targets late M dwarfs to search for terrestrial transiting planets in habitable zones, where TESS's yields are very poor. While its network's optical and near infrared observations are well designed for this purpose, its strategy naturally limits its sensitivity to planets with periods of less than 8 days. The PLATO mission already has its own M dwarf programme (P4), but its target list is dominated by early type M dwarfs, with no plans to observe our sample of 115 late M and L dwarfs with PLATOmag<17. For these targets, the SPECULATO survey proposes to downlink all the available NCAM short cadence light curves for the full 2 year duration of LOPS2 observations. Our yield estimates suggest that we are likely to detect at least one new exoplanet amongst these targets, which would likely constitute the coolest host star for any PLATO discovery in LOPS2. In the event of no exoplanet detections, the data will still provide useful limits on planetary occurrence rates around late M dwarfs, particularly at longer periods. Finally, a global analysis of the PLATO data alongside existing and future SPECULOOS observations of these targets will yield unrivalled insight into late M dwarf properties. This includes rotation periods, starspot coverage and temperatures, and flare amplitudes and occurrence rates. As stellar activity is widely acknowledged to be the limiting factor in interpreting JWST transmission spectra, such a study will be particularly timely.

Asteroseismology of early-type stars in OB associations - Proposal 171, Pedersen (AU)

The stellar structure and evolution theory of intermediate- and high-mass stars born with convective cores on the main-sequence is dominated by uncertainties in their interior mixing and angular momentum transport processes. The study of pulsating stars in clusters and OB associations provide exciting opportunities for constraining these interior physical processes, by utilizing the synergies between the interior probing power of stellar oscillations and the coeval nature of stellar groups born from the same molecular clouds. However, asteroseismic studies of early-type stars in OB associations have so far been limited. Here we propose to use the high-frequency precision enabled through 2-years of continuous PLATO observations of 392 early-type stars in nine OB associations to determine both the fundamental stellar parameters of the stars (masses, radii, ages) and constrain their interior mixing and rotation properties through ensemble asteroseismology. Additionally, our proposed work will enable the first asteroseismic age map of OB associations.

Primordial disc survey with PLATO GO and 4MOST - Proposal 179, Dimoff (DE)

The main science goal of our PLATO GO proposal is to confirm and characterize the primordial Galactic disc population. This goal is achievable only with high-quality time-domain data, uniquely accessible with PLATO, and precision age analysis of metal-poor stars in the LOPS2 field. These stars exhibit disc-like kinematics and their metallicities, [Fe/H] ≲ -2, indicating they formed in extremely-metal-poor (EMP) environments. The PLATO GO data will enable determination of accurate ages of these VMP and EMP stars and thus constrain the epoch of the formation of the oldest rotationally-supported component of the Milky Way - the ‘first’ disc.