arXiv subjects

Nicholas Jannsen

Publications and source records attributed to Nicholas Jannsen.

8 recordsLinked to original sources

arXiv2026

Following up the Kepler field with PLATO: Transit Timing Performance

The European Space Agency is set to launch PLATO, the third medium-class mission of its Cosmic Vision programme, in early 2027. Using the transit method, PLATO is expected to detect thousands of exoplanets orbiting bright, nearby stars of spectral types F5-K7. Although the mission is primarily designed to enable mass measurements via radial velocities, its precise photometry and long observational baselines may also permit the detection of transit timing variations (TTVs), which can provide complementary dynamical constraints in multi-planet systems. One possible PLATO observing scenario involves a two-year-long observation of a Northern field that may partially or fully overlap with the original Kepler field, creating an opportunity to revisit known multi-planet systems with a photometric baseline exceeding 20 years. We simulate PLATO observations of 152 Kepler host stars containing at least one planet with previously detected TTVs, yielding a sample of 361 transiting planets. Our CCD-level simulations incorporate realistic stellar variability and employ both aperture and point spread function (PSF)-fitting photometry, accounting for each target's real photometric contaminants. While the extended temporal baseline offers the potential for improved dynamical constraints in favourable cases, our simulations show that this potential is strongest for carefully selected systems, as PLATO's smaller collecting area and larger pixel scale limit the achievable per-transit precision relative to Kepler. We identify a subset of systems most likely to benefit from complementary dynamical constraints through PLATO observations.

astro-ph.EP↗

arXiv2026

Plato's view on supermassive black hole binaries: Exploring the faint limit of ESA's Plato space mission

The search for supermassive black hole binaries (SMBHBs) has, in recent years, seen the dawn of exploration with several hundred candidates claimed from photometric and spectroscopic surveys monitoring AGNs. While only a handful persist to date, the advent of upcoming high-precision wide-field photometric missions motivates continuing the pursuit of confirming SMBHBs in the optical. We explore the possibility of using the ESA Plato space mission to detect photometric signatures of SMBHBs. Motivated by the Kepler observation of Spikey, the best known self-lensing flare (SLF) candidate to date, this work aims to benchmark the scientific outcome if Plato were to observe Spikey-like objects via its Guest Observer programme. Starting from the Gaia database, we assemble a catalogue of 12,226 bright ($G < 19$) high-probability Quasars for the two pointing fields of Plato's nominal mission. This Plato Quasar catalogue will be pivotal for future follow-up observations of larger photometric searches such as the Vera Rubin LSST survey. We use the Plato camera simulator, PlatoSim, to realistically explore the noise budget in Plato's faint limit, while generating mock light curves to benchmark Plato's ability to recover signatures of SMBHBs. We show that, although not at all designed for the purpose, Plato is capable of detecting Spikey-like SMBHB candidates through their relativistic photometric signatures using Bayesian inference and evidence. Plato will in particular be able to confirm or rule out Spikey and Spikey-like objects with a limiting magnitude of $G\leq18$. With a minimum 2-yr baseline per pointing field, we show that Plato not only could play an essential role in future SMBHB research, but may be an integrated part of the observational fleet of continuous high-precision facilities monitoring SMBHB candidates in the near future.

astro-ph.GA↗

arXiv2026

Variability classification of TESS targets in LOPS2, the first long-term pointing field of PLATO. Version 1 of the public variability catalogue

The PLAnetary Transits and Oscillations of stars (PLATO) mission is expected to launch in January 2027. A total of 8\% of its data rate will be dedicated to complementary science targets selected from approved Guest Observer proposals. We seek to provide an open-source catalogue of variable stars in PLATO's first long-term observing field, LOPS2. We want to use existing observations from the Transiting Exoplanet Survey Satellite (TESS), which has observed many stars in LOPS2. We classified 38 million calibrated aperture light curves from the TESS-Gaia Light Curve pipeline (TGLC, $G\lesssim17$) for 6 million unique sources in LOPS2 with two machine learning frameworks -- a deep neural network and a feature-based gradient-boosted decision-tree ensemble. We combined their predictions to create this first version of the LOPS2 variability catalogue, performed manual vetting of a sub-sample classified light curves, and a statistical analysis of the results to validate our methodology and to assess the variability properties and parameters of the stars in the catalogue. Our classification resulted in the identification of approximately 72% of the light curves having dominant instrument- or pipeline-induced signal, with the remaining 28% representing 3.6 million individual candidate variable stars, including pulsating, rotating, and eclipsing stars. Candidate pulsators exhibit varied behaviour in terms of their frequencies, amplitudes, rotation, and fundamental parameters. To ensure purity of the samples, filtering on colour, luminosity, the dominant frequency and its amplitude, and presence of close neighbours is helpful. We provide the first version of our PLATO LOPS2 variability catalogue to the community for further study and scrutiny. It is to date one of the largest catalogues of variable stars from an automated classification pipeline.

astro-ph.SR↗

arXiv2026

Assessment of PLATO Science Performance

The PLATO mission is scheduled for launch early 2027. In this paper we present an overview of the performance drivers for the mission at the time where all flight models of the cameras have been tested and integrated on the optical bench. The PLATO consortium needs an estimate of the planet detection yield to dimension the ground-based radial velocity follow-up resources. We provide updated estimates on the yield of planet detections that can be expected from the mission under certain assumptions. As of today, large uncertainties remain on the planet occurrence rates, especially for small planets in long-period orbits, and on our ability to detect these planets in the presence of stellar variability and instrumental noise. To partially overcome these limitations, we compare results using different planet occurrence rates, detectability rates, and we include an estimate on the expected contribution of stellar variability to the noise budget. The final detection yield of PLATO will provide constraints to planet occurrence rates which in turn will help constraining planet formation models.

astro-ph.EP↗

arXiv2026

The PLATO Science Calibration and Validation Plan: Targets for the First Long-pointing Field

In order to meet the science goals of the PLATO space mission, an extensive science calibration and validation plan has been designed. This paper describes this plan, as well as the methodology adopted to select the science calibration and validation stars that have entered its input catalogue. This is the so-called {\tt scvPIC}, which is part of the general PLATO Input Catalogue (PIC) for the first selected long pointing field in the Southern Hemisphere known as LOPS2. While many of PLATO's science requirements needed dedicated stars as calibrators as discussed here, its most stringent requirement is the delivery of the age of the host stars of exoplanetary systems with an accuracy better than 10\% for a G0V star of {\it V} = 10 mag, i.e. a nearby Sun-like star. This is presently not within reach for large populations of dwarfs and subgiants in the Milky Way as it requires the models of their stellar interiors to be improved. We discuss how this ambitious age requirement led to the selection of tens of thousands of red giants, and of thousands of main-sequence early F-type gravity-mode pulsators in order to deduce their internal rotation profile across stellar evolution. This asteroseismic observable will then be imported as key information into improved models of dwarfs and subgiants in the Milky Way as optimal modelling tools for ever better age-dating of the exoplanet hosts as the PLATO mission moves along. Additional calibrators and validators included in the {\tt scvPIC} are a few thousands of binaries, a few hundreds of legacy and benchmark stars, a few hundred photometrically stable stars, and six transiting brown dwarfs.

astro-ph.SR↗

arXiv2026

Imaging magnetically driven astrospheres: a forward modelling approach

An astrosphere is a vast, tailed bubble-like volume around a star, formed through the interaction between the stellar magnetic field, the stellar wind, and the interstellar medium (ISM). Detecting and characterizing astrospheres are essential for constraining stellar wind properties, understanding stellar evolution, and assessing the habitability of surrounding exoplanetary systems. Charge exchanges between ionized stellar wind particles and cold ISM hydrogen atoms populate the astrosphere with neutral hydrogen, which can leave observable signatures in the Lyman-$\alpha$ (Ly$\alpha$) line absorption profile. Previous studies have inferred stellar mass-loss rates by measuring Ly$\alpha$ absorption in stellar spectra caused by astrospheric neutral hydrogen. However, our knowledge of the global morphology of astrospheres remains limited and largely dependent on sometimes contradictory simulations. Here we investigate the feasibility of detecting Ly$\alpha$ emission generated by resonant scattering from \NH{} surrounding the star, enabling the construction of a two-dimensional map of the astrosphere. With a three-dimensional magnetohydrodynamic astrosphere model, we perform forward modelling of the Ly$\alpha$ emission and assess the observation feasibility according to the observational limits of the {\it Hubble Space Telescope} (HST). We further discuss the influence of varied line-of-sight orientations and averaged ISM velocity along the line-of-sight. The spatially resolved circumstellar Ly$\alpha$ emission could provide important constraints on the astrospheric configuration and stellar wind properties, such as the bow shock standing distance, the stellar wind symmetry, and the shape of the astro-tail. Our results highlight Ly$\alpha$ astrosphere detections as a promising science case for {\it HST} and future missions such as the \textit{Habitable Worlds Observatory}.}

astro-ph.SR↗

arXiv2025

Observing bright pulsating white dwarfs with PLATO: A new window into the late stages of stellar evolution

We present the scientific case for exploiting the capabilities of the PLATO mission to study bright pulsating white dwarfs across a wide spectral range, including hydrogen-deficient types (GW Vir and DBV stars) and hydrogen-rich classes (classical DAVs, pulsating extremely low-mass DA white dwarfs, and ultra-massive DA white dwarfs). PLATOs exceptional photometric precision, long-duration continuous monitoring, and extensive sky coverage promise transformative advances in white dwarf asteroseismology. Our key objectives include probing the internal structure and chemical stratification of white dwarfs, detecting secular changes in pulsation modes over extended timescales, and discovering rare or previously unknown classes of pulsators. To assess feasibility, we constructed a sample of 650 white dwarf candidates identified within PLATOs Southern LOPS2 field using the PLATO complementary science catalogue combined with Gaia DR3, and derived atmospheric parameters through photometric modeling. This sample comprises 118 DA white dwarfs (including 23 ZZ Ceti candidates), and 41 non-DAs (including 35 DBV candidates). Simulated observations using PlatoSim demonstrate that PLATO will be capable of detecting white dwarf pulsation modes with amplitudes as low as 0.1 mma depending on stellar magnitude, observation duration, pixel location, and the number of contributing cameras. We provide detailed detection limits and visibility forecasts for known pulsators across a representative range of these parameters. Furthermore, we emphasize strong synergies with Gaia astrometry, TESS photometry, and targeted spectroscopic campaigns, which together will enable robust mode identification and detailed stellar modeling. Collectively, these efforts will unlock unprecedented insights into white dwarf origins, evolution and internal physics, and the fate of their planetary systems.

astro-ph.SR↗

arXiv2025

A search for periodic AGN variability in $\textit{Gaia}$ Data Release 3

Supermassive black hole binaries (SMBHB) are expected to produce periodic modulations in active galactic nuclei (AGN) light curves, but distinguishing such signals from stochastic red-noise variability remains a major challenge. We present the first systematic search for statistically significant AGN periodicities using the optical photometry from the Gaia space mission Data Release 3 (DR3), with the goal of identifying SMBHB candidates and establishing a methodological data analysis framework that can be scaled to the forthcoming Data Release 4 (DR4). We analyse Gaia G band light curves of 377,128 sources from the Gaia celestial reference frame (CRF3). Stochastic variability is modelled as a damped random walk Gaussian process, and empirical false alarm probabilities are derived by comparing observed Lomb-Scargle periodogram peaks against 100,000 synthetic red-noise realisations. Candidates from this first stage are then re-evaluated using full Markov chain Monte Carlo inference under both exponential and powered-exponential kernels. We find 13 sources surviving our statistical criterion ($p < \alpha = 10^{-5}$) after both stages of filtering, which is consistent with the expected false-positive rate. All candidates cover fewer than 2.5 cycles of the candidate period and are systematically concentrated in a region of the parameter space indicative of model misspecification. No reliable periodic SMBHB candidates are retained. The ${\sim}950$-day baseline of Gaia DR3 confines all detections to the few-cycle regime where red noise most convincingly mimics periodicity, a limitation that photometric precision alone cannot overcome. The longer baseline of Gaia DR4 will be essential to push beyond this regime. We offer our data analysis software pipeline in open access to the community.

astro-ph.HE↗