arXiv subjects

A. Donaldson

Publications and source records attributed to A. Donaldson.

6 recordsLinked to original sources

arXiv2026

Long-term monitoring of WASP-19 b: Signs of apsidal precession and molecular signatures

With more than 6000 exoplanets discovered so far, about 12 percent are hot Jupiters. Their large sizes and short orbital periods make them valuable targets for studying planetary formation, atmospheres, and orbital evolution. We present a homogeneous analysis of the WASP-19 b system using a 15 year dataset to investigate both its orbital dynamics and atmospheric properties. We test whether the transit times show evidence for tidal orbital decay, apsidal precession, or periodic perturbations from an additional body, and we also construct a photometric transmission spectrum. Multi-wavelength light curves are modeled with PRISM to account for starspots, and linear, quadratic, and cubic ephemeris models are fitted to the transit timing residuals. Our dataset includes 27 new transits and reveals no statistically significant periodic signal. Although none of the tested models fully reproduces the timing scatter, the transit times show systematic deviations from a constant period and are best described by the cubic ephemeris, indicating a slow long-term trend over the full baseline. This behavior is more consistent with gradual apsidal precession than with monotonic tidal decay. A precession model yields a rate of 1.00 +/- 0.12 x 10^-4 rad per orbit and a planetary Love number k2p = 0.107 +/- 0.08. The transmission spectrum shows signatures of Na, K, and H2O, with no strong evidence for TiO or VO. These results suggest that apsidal precession may dominate the long-term orbital evolution of WASP-19 b. Continued high-precision timing and spectroscopic observations are needed to further test this scenario.

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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 30-40m Telescope and the Science at Stake: from Interstellar Visitors to Planetary Defence

Small Solar system Objects (SSOs) preserve the physical, chemical, and dynamical signatures of the Sun's protoplanetary disk. Upcoming surveys will discover vast numbers of new objects, yet their scientific value will depend on follow-up observations requiring far greater sensitivity and resolution than those currently available. A 30-m class telescope like the Extremely Large Telescope (ELT) will be transformative, but its Southern location will leave significant regions of the sky poorly covered or even non accessible. A Northern 30-40m telescope is therefore essential to achieve full-sky coverage and fully exploit the small body discoveries of the 2030-2050 era, in particular for targets of opportunity or unexpected discoveries, like those of interstellar objects and potentially hazardous asteroids, as well as for distant trans-Neptunian objects and space mission targets.

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arXiv2025

Considerations on the process of target selection for the Comet Interceptor mission

Comet Interceptor is an ESA science mission with payload contributions from ESA Member States and with an international participation by JAXA. It is the first mission that is being designed, built, and potentially launched before its target is known. This approach will enable the spacecraft to perform the first mission to a Long Period Comet from the Oort Cloud, as these comets have fleeting visits to the inner Solar System lasting only months to years from first discovery, too short for the usual process of mission development to be followed. In this paper we describe a number of factors that need to be considered in selecting a target for the mission, including scientific, orbital, spacecraft and instrument constraints, and discussion of different prioritisation strategies. We find that, in the case where we have a choice of targets, our decisions will mostly be driven by orbital information, which we will have relatively early on, with information on the activity level of the comet an important but secondary consideration. As cometary activity levels are notoriously hard to predict based on early observations alone, this prioritisation / decision approach based more on orbits gives us confidence that a good comet that is compatible with the spacecraft constraints will be selectable with sufficient warning time to allow the mission to intercept it.

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arXiv2025

A search for transit timing variations in the transiting hot Jupiter systems HIP 65, NGTS-6, NGTS-10 and WASP-173

Hot Jupiters are Jupiter-mass planets with orbital periods of less than ten days. Their short orbital separations make tidal dissipation within the stellar host especially efficient, potentially leading to a measurable evolution of the orbit. One possible manifestation of this is orbital decay, which presents itself observationally through variations in the orbital period and thus times of transit. Here we select four promising exoplanetary systems for detecting this effect: HIP 65, NGTS-6, NGTS-10 and WASP-173. We present 33 new transit light curves taken with the 1.54 m Danish Telescope, and analyse these alongside photometric data from the Transiting Exoplanet Survey Satellite and transit timing data from the literature. We construct two ephemeris models for each target: a linear ephemeris and a shrinking orbital period due to tidal decay. The linear ephemeris is preferred for three of the four models - the highest significance for the quadratic ephemeris is over 3-sigma for WASP-173. We compare these results to theoretical predictions for tidal dissipation of gravity waves in radiation zones, and find that wave breaking is predicted only in WASP-173, making rapid decay plausible in this system but unclear in the other three. The sensitivity of transit timings to orbital decay depends on the square of the time interval covered by available observations, so our results establish a useful baseline against which future measurements can be compared. NGTS-6 and NGTS-10 are important objects for future study as they are in the first field to be observed by the upcoming PLATO mission.

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arXiv2024

Predictions for Sparse Photometry of Jupiter-Family Comet Nuclei in the LSST Era

The Legacy Survey of Space and Time (LSST) at Vera C. Rubin Observatory will deliver high-quality, temporally-sparse observations of millions of Solar System objects on an unprecedented scale. Such datasets will likely enable the precise estimation of small body properties on a population-wide basis. In this work, we consider the possible applications of photometric data points from the LSST to the characterisation of Jupiter-family comet (JFC) nuclei. We simulate sparse-in-time lightcurve points with an LSST-like cadence for the orbit of a JFC between 2024-2033. Convex lightcurve inversion is used to assess whether the simulation input parameters can be accurately reproduced for a sample of nucleus rotation periods, pole orientations, activity onsets, shapes and sizes. We find that the rotation period and pole direction can be reliably constrained across all nucleus variants tested, and that the convex shape models, while limited in their ability to describe complex or bilobed nuclei, are effective for correcting sparse photometry for rotational modulation to improve estimates of nucleus phase functions. Based on this analysis, we anticipate that LSST photometry will significantly enhance our present understanding of the spin-state and phase function distributions of JFC nuclei.

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