Jeremy Tregloan-Reed

Context . Time-domain photometric monitoring is essential for characterizing cometary evolution, particularly for rare interstellar objects with limited observing opportunities. Aims . 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. Methods . We obtained 70 days of time-series photometry of 3I/ATLAS from 2025 July 4 to September 11 using 16 telescopes and 1554 images. The data were processed and calibrated with the BHTOM pipeline. High-cadence multiband imaging was used to measure the rotation period and color evolution, while the dust activity was quantified via Afρ measurements. Results . We present a pre-perihelion light curve of 3I/ATLAS from R _h = 3.18–2.19 au, which exhibited a steady brightening by ∼3 magnitudes with no evidence of anomalous behavior. We measured a rotation period of P _rot = 15.98 ± 0.08 h. The colors were statistically non-changing, with only a weak, non-significant tendency for 3I/ATLAS to become bluer at 3.5 > R _h > 2.2 au. The relative dust production increased from A (0°) fρ ∼600 to 1100 cm, and the upper limit on the dust mass-loss rate increased from ≤217 kg s ⁻¹ to ≤328 kg s ⁻¹ . We measured an activity index of n = −1.24 ± 0.02, which is consistent with a well-developed dust coma.

Applying astronomical techniques to characterise ground-based light pollution sources - Volume 20 Issue A31

Observations, analysis and characterisation of satellites in Low Earth Orbit megaconstellations - Volume 20 Issue A31

Optical and NIR magnitude measurements of Low Earth Orbit satellites, from a global observing network - Volume 20 Issue A31

Context . To better understand the observed brightness of low Earth orbit satellites, we must characterize their reflectivity, which in turn depends importantly on their bus designs. The reflectivity of a body can be described by Lambert’s law, in terms of its albedo, cross-sectional area, range (distance), phase angles, and the mixing coefficient between diffuse and specular reflection components. Aims . We aim to analyze the reflectivity of more than 300 ONEWEB satellites using the diffuse Lambertian sphere, diffuse and specular Lambertian sphere, and the relative reflectance brightness models. Methods . Astrometric and photometric measurements, plus two-line elements (TLE) orbital information were used to compute the apparent and range-corrected magnitude, as well as the relevant angles related to the orientation of the Sun, the satellites, and the observer. A differential evolution Monte Carlo algorithm was used to obtain each model’s parameters that best fit the data. Results . All models can fit the mean observed brightness of the satellites but cannot describe the observed phase-angle-dependent brightness modulations. The residuals in all cases have a standard deviation of ∼0.6 magnitudes, while the observational photometric errors are on average ∼0.2 magnitudes. Conclusions . The studied brightness models, which depend on the relative Sun-body-observer position but are independent of the specific orientation of the reflecting body surface(s) with respect to the observer, cannot entirely explain the observed brightness of the ONEWEB constellation satellites. Accounting for the real shape and the changing attitude of the satellite, as well as the effect of Earth’s albedo is needed to better explain satellite photometric observations.

Context . With over 6000 exoplanets discovered to date, approximately 12 % are classified as hot-Jupiters. Due to their large sizes and short orbital periods ( P < 10 day), they are easier to detect and provide crucial insights into planetary formation, atmospheric properties, and orbital dynamics. Among these, ultra-short-period exoplanets ( P ≤ 1 d) are particularly interesting, as they are expected to undergo orbital decay driven by strong tidal interactions. Despite theoretical predictions, WASP-12 b and WASP-4 b remain the confirmed hot-Jupiters experiencing measurable orbital decay. Aims . This study presents a homogeneous analysis of WASP-19 b to investigate both its orbital dynamics and atmospheric composition. Leveraging a 15-year dataset, our goal is to assess whether the system exhibits long-term deviations from a constant orbital period and to investigate whether any detected variations are consistent with tidal orbital decay, apsidal precession, or periodic signals indicative of a potential planetary perturber. Additionally, we also construct a photometric transmission spectrum to characterize its atmosphere. Methods . We analyze multi-wavelength light curves, incorporating starspot modeling with PRISM to account for stellar inhomogeneities. To assess orbital evolution, we fit linear, quadratic, and cubic ephemeris models to transit timing residuals with respect to a non-decaying orbit. Results . Our analysis, which includes 27 new transits, reveals no statistically significant periodic signal in the transit timings. Although none of the tested ephemeris models fully reproduce the observed timing scatter, the mid-transit times exhibit systematic deviations from a strictly constant orbital period and are best reproduced by the cubic ephemeris in a relative model-comparison sense, indicating a slow, non-periodic long-term trend over the ~ 15-year baseline. This behavior is more consistent with gradual orbital precession than with monotonic tidal decay, for which a dominant quadratic trend would be expected. Fitting a precession model yields a rate of ω̇ _obs = (1.00 ± 0.12) × 10 ⁻⁴ rad/orbit, corresponding to a planetary Love number k _{2 p} = 0.107 ± 0.08, in agreement with recent independent estimates. The transmission spectrum reveals signatures of Na, K, and H ₂ O, with no strong evidence of TiO/VO, likely due to the resolution limits of the photometric data. Conclusions . Our results support that apsidal precession could be the dominant process governing the long-term orbital evolution of WASP-19b, possibly sustained by weak eccentricity forcing from the wide companion WASP-19 B. These orbital dynamics can, in turn, impact the atmospheric structure by modulating the irradiation history, potentially altering molecular abundances over time. Our findings highlight the importance of combining TTV analyzes with multi-wavelength atmospheric data, while emphasizing that additional high-quality timing and spectroscopic observations are required to corroborate the fidelity of the proposed orbital model.

In this work, we present a transit timing variation analysis for 20 hot Jupiter systems, which we interpret with theoretical tidal dissipation models. For the majority of the sample, we conclude that a constant orbital period model represents the timing data best. Only WASP-12 b, TrES-1 b and WASP-121 b exhibit a changing orbital period, according to the most up-to-date results. We updated the orbital decay rate of WASP-12 b to P ̇ = − 29.4 ± 4.0 ms yr − 1 and the corresponding stellar tidal quality factor to Q ∗ ′ = 1.72 ± 0.18 × 1 0 5 . For TrES-1 b, the median quadratic model suggests a period decrease at a rate of −14.9 ± 0.6 ms yr ⁻¹ , but the corresponding Q ∗ ′ = 570 ± 60 does not agree with the theoretical estimates, which suggest Q ∗ ′ ∼ 1 0 6 due to internal gravity wave dissipation. Lastly, WASP-121 b exhibits orbital growth at a rate of 15.1 ± 0.8 ms yr ⁻¹ , and theoretical results support outward migration due to strong inertial wave dissipation.

The Astronomy Center (CITEVA) of the Universidad de Antofagasta manages the Ckoirama Observatory and the Astroengineering Laboratory of the Atacama Desert. The former is undergoing an expansion thanks to funding approved by the Chilean Science Agency (ANID) in 2022, with support from other Chilean universities, the Chilean Air Force, and the IAU CPS, so that a new satellite tracking station will begin operations in 2024, specifically designed to collect reflected sunlight from satellites. The latter, on the other hand, is developing an experimental setup designed to test space-grade materials in order to contribute data to produce bidirectional reflectance distribution function models of satellites.

WASP-4 b is a hot Jupiter exhibiting a decreasing orbital period, prompting investigations into potential mechanisms driving its evolution. We analysed 173 transit light curves, including 37 new observations, and derived mid-transit timings with exofast, forming the most extensive transit timing variation (TTV) data set for this system. Adding 58 literature timings and removing unreliable data, we constructed a TTV diagram with 216 points. Our analysis considered linear, quadratic, and apsidal motion models, with the quadratic model proving to be significantly superior in all model comparison statistics. We found no significant periodic signals in the data. The quadratic model allows us to infer a tidal quality factor of Q$^{\prime }_{\star } \sim 80\, 000$ from the orbital decay rate if this is due to stellar tides. Theoretical considerations indicate that such efficient dissipation is possible due to internal gravity waves in the radiative core of WASP-4, but only in our models with a more evolved host star, possibly near the end of its main-sequence lifetime, and with a larger radius than the observed one. Our main-sequence models produce only about a third of the required dissipation (Q$^{\prime }_{\star }\sim 2 - 5 \times 10^5$). Therefore, the observed orbital decay can only be explained by a slightly larger or more evolved host, resembling the case for WASP-12. Our findings highlight the need for further stellar modelling and improvement in our current understanding of tidal dissipation mechanisms driving orbital decay in close-in exoplanetary systems.