arXiv subjects

Don Pollacco

Publications and source records attributed to Don Pollacco.

At least 19 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.

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arXiv2026

DebrisWatch II: Digging deeper for geosynchronous debris

The geosynchronous (GSO) debris environment is continually evolving. Regular monitoring of the region is consequently of great importance, though the trade-off between coverage and sensitivity makes this challenging for the population of optically faint debris, where collecting area becomes a pivotal factor. Surveys conducted with large-aperture telescopes have provided crucial insights into the nature of this largely uncharacterised population. In this paper, we revisit a survey conducted with the 2.54 m Isaac Newton Telescope (INT), presenting an overhaul of the astrometric calibration and object detection stages of the original analysis pipeline. We apply a blind stacking technique to boost target recovery, unearthing 25 tracklets previously missed by single-frame extraction methods, and pushing the sensitivity limit fainter by 1 magnitude. The same algorithm is applied to a contemporaneous dataset, captured with a 36 cm astrograph, enabling performance benchmarking through the attempted recovery of INT detections from commercial-off-the-shelf observations. We achieve sub-arcsecond astrometric accuracy through a combination of improved star trail centroiding and iterative distortion fitting, allowing short arc initial orbit solutions to be obtained. High-cadence light curves extracted for trailing detections indicate that faint fragments are proportionally more variable than bright derelicts, with many exhibiting photometric signatures of rapid tumbling, often straddling the image noise floor. Lastly, we present preliminary findings from a follow-up multi-national observation campaign, utilising telescopes in Australia, Japan and La Palma. As space traffic management concerns begin to extend beyond GSO altitudes, scientifically-driven surveys of high-altitude orbits have an important role to play in characterising the faint debris environment.

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arXiv2026

An Ultra-Short Period Super-Earth and a Sub-Neptune Orbiting the K dwarf TOI-4311

We report the discovery and characterisation of the multi-planetary system around TOI-4311, a K dwarf kinematically between the Galactic thick disk and Hercules stream. TOI-4311 hosts an ultra-short-period super-Earth (P$\sim$0.99 d, $1.376\substack{+0.077\\-0.080}$ R$_\oplus$) and a longer period sub-Neptune (P$\sim$15 d, $2.47\substack{+0.12\\-0.11}$ R$_\oplus$) that was first detected in the TESS photometry. Using follow-up observations with CHEOPS and HARPS, we refine the planetary radius of both planets, derive the mass of planet b ($4.5\substack{+1.5\\-1.4}$ M$_\oplus$) and confirm the planetary nature of planet c. Intriguingly, a third periodic signal is clearly detected in our HARPS RVs that we cannot link to stellar activity. This signal could be attributed to a third planet (P$\sim$38 d, Msin(i)=$26.4\substack{+6.3\\-6.8}$ M$_\oplus$) in the system, however with the current photometric dataset we do not find a transit. Our dynamical analysis highlights that this potential outer planet would remain stable. Using the precise radius and mass for TOI-4311 b we model its interior structure and find that it is very dense given the host star's galactic kinematics and chemistry. Hence this system could challenge current formation theories and provide insights into planet formation across the galaxy.

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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.

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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.

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arXiv2026

Time-Domain Photometry and Activity Evolution of Interstellar Comet 3I/ATLAS with BHTOM

Time-domain photometric monitoring is essential for characterizing cometary evolution, particularly for rare interstellar objects with limited observing opportunities. We aimed to characterize the pre-perihelion photometric behavior and dust activity of the interstellar comet 3I/ATLAS, and to test the capability of the Black Hole Target and Observation Manager (BHTOM) platform and telescope network for coordinated high-cadence non-sidereal observations. We obtained 70 days of time-series photometry of 3I/ATLAS from 2025 July 4 - September 11 using 16 telescopes and 1554 images. The data were processed and calibrated with the BHTOM pipeline. High-cadence, multi-band imaging was used to measure the rotation period and color evolution, while the dust activity was quantified via Afp measurements. We present a pre-perihelion light curve of 3I/ATLAS from Rh = 3.18 - 2.19 au, which exhibited a steady increase of ~3 magnitudes with no evidence of anomalous behavior. We measured a rotation period of P_rot = 15.98 +/- 0.08 h. The relative dust production increased from A(0)fp ~600 - 1100 cm, and the upper limit on the dust mass-loss rate increased from \leq 217 kg/s to \leq 328 kg/s. We measured an activity index of n = -1.24 +/- 0.02, consistent with a well-developed dust coma. The colors were statistically non-changing, with only a weak, non-significant tendency for 3I/ATLAS to become bluer at 3.5 > Rh > 2.2 au.

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arXiv2025

Why the Northern Hemisphere Needs a 30-40 m Telescope and the Science at Stake: Key Targets of Opportunity on Gas and Ice Giants and their satellites

The Extremely Large Telescope (ELT) will transform our knowledge of the outer planets and their satellite systems; however the visibility of unique targets of opportunity with high scientific value will be reduced for northern objects. Uranus' declination favors observations from the Northern Hemisphere until 2055, and Neptune will be favored from the Northern Hemisphere from 2027 for the next 90 years. Jupiter and Saturn experience cycles of better observability from either hemisphere on cycles of 10 and 30 years. These planets and their satellite systems often offer unique opportunities for discovery through time-critical observations. We argue that a 30-m class size telescope in the Northern Hemisphere with complementary scientific instrumentation to that on the ELT will secure the possibility of observing high-impact unpredictable phenomena in these systems.

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arXiv2025

A search for photometric variability towards the globular cluster M3 with the TWenty Inch Survey Telescope

We present the commissioning results and first scientific observations from the newly installed TWIST observatory - a 50 cm telescope equipped with an sCMOS camera providing a $36.1\times24.1$ arcmin$^2$ field of view - housed in the former SuperWASP-North enclosure. We conducted a 67-night, 199-day baseline white-light monitoring campaign centred on the globular cluster M3 aimed at characterizing stellar variability within the cluster while also assessing the photometric performance of the newly commissioned system. We report the discovery of four new SX Phoenicis variables (V301-304), confirm their cluster membership, and identify fundamental-mode pulsation in one, allowing an independent period-luminosity-based distance estimate to M3. We revisited 231 previously known RR Lyrae stars, providing updated period measurements for 203 and white-light amplitudes for 198. We detected Blazhko-like modulation in 53 stars and characterized the modulation parameters for 28. Notably, we measure periods and amplitudes for the unclassified variables V286 and V287 for the first time. We also identify three foreground flaring M dwarfs, and assess the feasibility of detecting microlensing events in M3, concluding that expected rates are negligible. Alongside the scientific results, we introduce a new correction technique for flat-field images affected by scattered light and present a full characterization of the observatory's photometric capabilities. These results demonstrate the scientific utility of TWIST for high-cadence time-domain surveys using modest-aperture instrumentation.

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arXiv2025

Lord of the (sub-)Rings : Mapping the surface reflectance and spin-axis of Ajisai

Active debris removal techniques are posed to become an important tool in maintaining the safety of the near-Earth space environment. These techniques rely on a clear understanding of the rotational motion of the debris targets, which is challenging to constrain from unresolved imaging. The Ajisai satellite provides an ideal test case for developing and demonstrating these techniques due to its simple geometry and well constrained spin behaviour. We present four observations of the Ajisai satellite taken with SuperWASP in August of 2019, where high cadence photometry was extracted from streaked images as a part of a larger survey of Low Earth Orbit. We develop an MCMC-driven method to determine the spin-state of Ajisai by comparing the alignment between a map of modelled mirror positions and a novel derived map of surface reflectivity. We generally find good agreement within the expectation and uncertainties set by empirical models and our determined spin-state solutions align the surface reflectivity map and modelled mirror location well. Our results show that streak photometry can be used to recover the spin-axis and rotation period of fast-spinning objects such as Ajisai using modest ground-based instrumentation, making it readily scalable to a wider range of targets and observatories.

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arXiv2025

An Ultra-Short Period Super-Earth and Sub-Neptune Spanning the Radius Valley Orbiting the Kinematic Thick Disk Star TOI-2345

A crucial chemical link between stars and their orbiting exoplanets is thought to exist. If universal, this connection could affect the formation and evolution of all planets. Therefore, this potential vital link needs testing by characterising exoplanets around chemically-diverse stars. We present the discovery of two planets orbiting the metal-poor, kinematic thick-disk K-dwarf TOI-2345. TOI-2345 b is a super-Earth with a period of 1.05 days and TOI-2345 c is a sub-Neptune with a period of 21 days. In addition to the target being observed in 4 TESS sectors, we obtained 5 CHEOPS visits and 26 radial velocities from HARPS. By conducting a joint analysis of all the data, we find TOI-2345 b to have a radius of $1.504\substack{+0.047\\-0.044}$ R$_\oplus$ and a mass of $3.49\pm0.85$ M$_\oplus$; and TOI-2345 c to have a radius of $2.451\substack{+0.045\\-0.046}$ R$_\oplus$ and a mass of $7.27\substack{+2.27\\-2.45}$ M$_\oplus$. To explore chemical links between these planets and their host star, we model their interior structures newly accounting for devolatised stellar abundances. TOI-2345 adds to the limited sample of well characterised planetary systems around thick disk stars. This system challenges theories of formation and populations of planets around thick disk stars with its Ultra-Short Period super-Earth and the wide period distribution of these two planets spanning the radius valley.

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arXiv2025

High-precision light curves of geostationary objects: The PHANTOM ECHOES 2 RPO campaign

We present results from an extensive optical observation campaign that monitored the Geostationary satellites Intelsat 10-02, Mission Extension Vehicle 2, Thor 5, Thor 6, Thor 7, and Meteosat 11 over a 14 week period that covered the proximity operations and docking of Mission Extension Vehicle 2 with Intelsat 10-02. High-cadence single-color photometric observations are supplemented with targeted multi-color observations, high resolution imaging, and passive radio frequency positioning obtained using complementary facilities. The photometric signatures of the six targets are presented in the form of two-dimensional color maps. A selection of interesting features are investigated in further detail, including a rapid glinting behavior in Thor 6; a brightening event from Meteosat 11; using glints to constrain the unresolved positions of Intelsat 10-02 and MEV-2; changes in the photometric signature of Intelsat 10-02 before and after docking; and signatures of attitude changes and maneuvering in the light curves of MEV-2. A detailed description of the photometric data reduction pipeline is also presented, with a focus on details that must be considered when aiming for sub-percent photometric precision.

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arXiv2025

Classification of LEO Satellites Using Occultations of Background Stars

We present the result of a proof-of-concept simulation designed to classify LEO satellites based on their occultations of background stars. We generate satellite shapes drawn from two broad shape classes, 'boxwing' and 'square'. We then simulate the resulting occultation photometry that would be caused by these satellites orbiting in LEO and intersecting with background stars. The resulting data is then inverted to attempt to recover the input shape and classify the satellite correctly. We find that the technique is theoretically sound, but ambitious with current telescope capabilities. We construct an equation for the required success rate of the method, as a function of exposure time and density of background stars. We find that successful classification requires short exposure times and high background stellar densities. For success rates in excess of 75%, we find a required exposure time of $\sim2.0\times10^{-3}$s, and $\sim500$ stars along the satellites path. Results are presented in terms of these two key parameters, and are discussed in the context of current observational capabilities and alternative satellite characterisation methods.

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arXiv2025

A comprehensive survey of the GEO-belt using simultaneous four-colour observations with STING

Colour light curves of resident space objects (RSOs) encapsulate distinctive features that can offer insights into an object's structure and design, making them an invaluable tool for classification and characterisation. We present the results of the first large systematic colour survey of the GEO belt in which we obtain full-night multi-colour light curves for 112 active geostationary objects between April and May 2023. Colour light curve maps were created to compare and contrast the colours between different satellites and bus configurations. We find that satellites with BSS-702 and STAR-2 buses can be effectively distinguished from the colour measurements on these maps, but comparing the average colour of individual satellites within given solar equatorial phase angle ranges shows that it is difficult to distinguish between bus configurations based on colour alone. We also find tentative evidence to suggest that there is a relationship between colour and time spent on orbit for the Eurostar-3000 class satellites, which is unseen behaviour within other bus configuration classes. The satellites in our sample exhibit `redder' colours than the Sun, which is in agreement with previous findings. We found common light curve features such as symmetrical colour changes as well as unique regions of short timescale glinting which are `bluer' than other regimes within the colour light curves. If these features are indeed seasonal, this would be a powerful characterisation tool. We are able to detect and resolve features in the light curve of the LDPE-3A satellite related to manoeuvres being performed. Finally, we measured the solar panel offsets of 54 satellites in our sample and found variation in the type of colour response. The majority of which did not exhibit any colour change across the solar panel glints compared to them shifting towards 'redder' or 'bluer' colours.

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arXiv2024

In-situ observations of resident space objects with the CHEOPS space telescope

The CHaracterising ExOPlanet Satellite (CHEOPS) is a partnership between the European Space Agency and Switzerland with important contributions by 10 additional ESA member States. It is the first S-class mission in the ESA Science Programme. CHEOPS has been flying on a Sun-synchronous low Earth orbit since December 2019, collecting millions of short-exposure images in the visible domain to study exoplanet properties. A small yet increasing fraction of CHEOPS images show linear trails caused by resident space objects crossing the instrument field of view. To characterize the population of satellites and orbital debris observed by CHEOPS, all and every science images acquired over the past 3 years have been scanned with a Hough transform algorithm to identify the characteristic linear features that these objects cause on the images. Thousands of trails have been detected. This statistically significant sample shows interesting trends and features such as an increased occurrence rate over the past years as well as the fingerprint of the Starlink constellation. The cross-matching of individual trails with catalogued objects is underway as we aim to measure their distance at the time of observation and deduce the apparent magnitude of the detected objects. As space agencies and private companies are developing new space-based surveillance and tracking activities to catalogue and characterize the distribution of small debris, the CHEOPS experience is timely and relevant. With the first CHEOPS mission extension currently running until the end of 2026, and a possible second extension until the end of 2029, the longer time coverage will make our dataset even more valuable to the community, especially for characterizing objects with recurrent crossings.

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arXiv2024

Predicting RSO Populations Using a Neighbouring Orbits Technique

The determination of the full population of Resident Space Objects (RSOs) in Low Earth Orbit (LEO) is a key issue in the field of space situational awareness that will only increase in importance in the coming years. We endeavour to describe a novel method of inferring the population of RSOs as a function of orbital height and inclination for a range of magnitudes. The method described uses observations of an orbit of known height and inclination to detect RSOs on neighbouring orbits. These neighbouring orbit targets move slowly relative to our tracked orbit, and are thus detectable down to faint magnitudes. We conduct simulations to show that, by observing multiple passes of a known orbit, we can infer the population of RSOs within a defined region of orbital parameter space. Observing a range of orbits from different orbital sites will allow for the inference of a population of LEO RSOs as a function of their orbital parameters and object magnitude.

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arXiv2024

GERry: A Code to Optimise the Hunt for the Electromagnetic Counter-parts to Gravitational Wave Events

The search for the electromagnetic counterparts to gravitational wave (GW) events has been rapidly gathering pace in recent years thanks to the increasing number and capabilities of both gravitational wave detectors and wide field survey telescopes. Difficulties remain, however, in detecting these counterparts due to their inherent scarcity, faintness and rapidly evolving nature. To find these counterparts, it is important that one optimises the observing strategy for their recovery. This can be difficult due to the large number of potential variables at play. Such follow-up campaigns are also capable of detecting hundreds or potentially thousands of unrelated transients, particularly for GW events with poor localisation. Even if the observations are capable of detecting a counterpart, finding it among the numerous contaminants can prove challenging. Here we present the Gravitational wave Electromagnetic RecovRY code (GERry) to perform detailed analysis and survey-agnostic quantification of observing campaigns attempting to recover electromagnetic counterparts. GERry considers the campaign's spatial, temporal and wavelength coverage, in addition to Galactic extinction and the expected counterpart light curve evolution from the GW 3D localisation volume. It returns quantified statistics that can be used to: determine the probability of having detected the counterpart, identify the most promising sources, and assess and refine strategy. Here we demonstrate the code to look at the performance and parameter space probed by current and upcoming wide-field surveys such as GOTO & VRO.

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arXiv2024

The Gravitational-wave Optical Transient Observer (GOTO)

The Gravitational-wave Optical Transient Observer (GOTO) is a project dedicated to identifying optical counter-parts to gravitational-wave detections using a network of dedicated, wide-field telescopes. After almost a decade of design, construction, and commissioning work, the GOTO network is now fully operational with two antipodal sites: La Palma in the Canary Islands and Siding Spring in Australia. Both sites host two independent robotic mounts, each with a field-of-view of 44 square degrees formed by an array of eight 40 cm telescopes, resulting in an instantaneous 88 square degree field-of-view per site. All four telescopes operate as a single integrated network, with the ultimate aim of surveying the entire sky every 2-3 days and allowing near-24-hour response to transient events within a minute of their detection. In the modern era of transient astronomy, automated telescopes like GOTO form a vital link between multi-messenger discovery facilities and in-depth follow-up by larger telescopes. GOTO is already producing a wide range of scientific results, assisted by an efficient discovery pipeline and a successful citizen science project: Kilonova Seekers.

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arXiv2024

The PLATO Mission

PLATO (PLAnetary Transits and Oscillations of stars) is ESA's M3 mission designed to detect and characterise extrasolar planets and perform asteroseismic monitoring of a large number of stars. PLATO will detect small planets (down to <2 R_(Earth)) around bright stars (<11 mag), including terrestrial planets in the habitable zone of solar-like stars. With the complement of radial velocity observations from the ground, planets will be characterised for their radius, mass, and age with high accuracy (5 %, 10 %, 10 % for an Earth-Sun combination respectively). PLATO will provide us with a large-scale catalogue of well-characterised small planets up to intermediate orbital periods, relevant for a meaningful comparison to planet formation theories and to better understand planet evolution. It will make possible comparative exoplanetology to place our Solar System planets in a broader context. In parallel, PLATO will study (host) stars using asteroseismology, allowing us to determine the stellar properties with high accuracy, substantially enhancing our knowledge of stellar structure and evolution. The payload instrument consists of 26 cameras with 12cm aperture each. For at least four years, the mission will perform high-precision photometric measurements. Here we review the science objectives, present PLATO's target samples and fields, provide an overview of expected core science performance as well as a description of the instrument and the mission profile at the beginning of the serial production of the flight cameras. PLATO is scheduled for a launch date end 2026. This overview therefore provides a summary of the mission to the community in preparation of the upcoming operational phases.

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