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This study addresses the growing concern in the astronomical community regarding the brightness and interference caused by low Earth orbit (LEO) communication satellites. Utilising data from a global network of telescopes and a custom Python pipeline, we analysed 369 observations of 159 OneWeb satellites obtained in the BVRI bandpasses with the Danish 1.54-metre telescope at ESO La Silla, Chile, revealing significant variations in brightness across different wavelengths and a substantial proportion exceeding recommended brightness limits. Our preliminary findings, incorporating diffuse sphere phase models, offer further insights into the satellite’s reflective properties and implications for future astronomical observations.

Large constellations of bright artificial satellites in low Earth orbit pose significant challenges to ground-based astronomy 1 . Current orbiting constellation satellites have brightnesses between apparent magnitudes 4 and 6, whereas in the near-infrared Ks band, they can reach magnitude 2 (ref. 2 ). Satellite operators, astronomers and other users of the night sky are working on brightness mitigation strategies 3 , 4 . Radio emissions induce further potential risk to ground-based radio telescopes that also need to be evaluated. Here we report the outcome of an international optical observation campaign of a prototype constellation satellite, AST SpaceMobile’s BlueWalker 3. BlueWalker 3 features a 64.3 m 2 phased-array antenna as well as a launch vehicle adaptor (LVA) 5 . The peak brightness of the satellite reached an apparent magnitude of 0.4. This made the new satellite one of the brightest objects in the night sky. Additionally, the LVA reached an apparent V-band magnitude of 5.5, four times brighter than the current International Astronomical Union recommendation of magnitude 7 (refs. 3 , 6 ); it jettisoned on 10 November 2022 (Universal Time), and its orbital ephemeris was not publicly released until 4 days later. The expected build-out of constellations with hundreds of thousands of new bright objects 1 will make active satellite tracking and avoidance strategies a necessity for ground-based telescopes. We report the outcome of an international optical observation campaign of a prototype constellation satellite, AST SpaceMobile’s BlueWalker 3, which features a 64.3 m 2 phased-array antenna and a launch vehicle adaptor.

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.

We have developed a new model for analysing light curves of planetary transits when there are starspots on the stellar disc. Because the parameter space contains a profusion of local minima we developed a new optimisation algorithm which combines the global minimisation power of a genetic algorithm and the Bayesian statistical analysis of the Markov chain. With these tools we modelled three transit light curves of WASP-19. Two light curves were obtained on consecutive nights and contain anomalies which we confirm as being due to the same spot. Using these data we measure the star's rotation period and velocity to be 11.76 ± 0.09 d and 3.88 ± 0.15 kms−1, respectively, at a latitude of 65°. We find that the sky-projected angle between the stellar spin axis and the planetary orbital axis is λ = 1.0° ± 1.2°, indicating axial alignment. Our results are consistent with and more precise than published spectroscopic measurements of the Rossiter-McLaughlin effect.

TESS (Transiting Exoplanet Survey Satellite) was launched in 2018 with the purpose of observing bright stars in the solar neighbourhood to search for transiting exoplanets. After the completion of the two year nominal mission, TESS has provided 2\\,minute cadence photometry of over 200\\,000 stars. This large collection of light curves opens the possibility to study the statistical and temporal properties of this ensemble of stars. Most of the currently available data pipelines are designed to work on single sector at a time. We present a new TESS data pipeline called {\\tt Taranga}, with the purpose of merging multi-sector light curves, whilst performing a period search for all the observed stars, and stores the statistical results in a database. {\\tt Taranga} pipeline has three components which 1) processes the PDCSAP fluxes of each sector and creates merged PDCSAP light curve, 2) performs a similar operation on the SAP fluxes, and 3) generates the periodograms of the merged SAP and PDCSAP light curves while performing peak identification. For all the 232\\,122 stars observed in short cadence in the nominal TESS mission, we provide the merged PDCSAP and SAP light-curves along with their periodograms. We provide a database that has the statistics of all the results produced from {\\tt Taranga} of these stars.

To begin understanding how the architecture of hot Jupiter planetary systems can be so radically different from that of our own solar system, requires the dynamical evolution of planets to be known. By measuring the sky-projected obliquity of a system it is possible to determine the dominant process in the dynamical evolution. If a transiting exoplanet that crosses the disc of its host star passes over a starspot, then the amount of received intensity from the star will change. By modelling the position of the anomaly in the lightcurve it is possible to precisely determine the position of the starspot on the stellar disc. If the position of the starspot can be found at two distinct times using two closely spaced transits, then it is possible to measure. Before now there was no definitive model capable of accurately modelling both a planetary transit and a starspot. This research focuses on the development of prism which is capable of accurately modelling a transit containing a starspot anomaly. Due to the nature of the parameter space a new optimisation algorithm was developed, gemc, which is a hybrid between a genetic algorithm and MCMC.

20573 simulations of planetary transits around spotted stars were conducted using the transit-starspot model, \\texttt{PRISM}. In total 3888 different scenarios were considered using three different host star spectral types, M4V, M1V and K5V. The mean amplitude of the starspot anomaly was measured and compared to the photometric precision of the light curve, to determine if the starspot anomaly's characteristic \"blip\" was noticeable in the light curve. The simulations show that, starspot anomalies will be observable in TESS 2\\,min cadence data. The smallest starspot detectable in TESS transit light curves has a radius of \\(\\approx1900\\)\\,km. The starspot detection limits for the three host stars are: \\(4900\\pm1700\\)\\,km (M4V), \\(13800\\pm6000\\)\\,km (M1V) and \\(15900\\pm6800\\)\\,km (K5V). The smallest change in flux of the starspot (\\(\\Delta F_\\mathrm{spot} = 0.00015\\pm0.00001\\)) can be detected when the ratio between the planetary and stellar radii, \\(k = 0.082\\pm0.004\\). The results confirm known dependencies between the amplitude of the starspot anomaly and the photometric parameters of the light curve. The results allowed the characterisation of the relationship between the change in flux of the starspot anomaly and the change in flux of the planetary transit for TESS transit light curves.

In this paper we study the joint determination of source and background flux for point sources as observed by digital array detectors. We explicitly compute the two-dimensional Cramér-Rao absolute lower bound (CRLB) as well as the performance bounds for high-dimensional implicit estimators from a generalized Taylor expansion. This later approach allows us to obtain computable prescriptions for the bias and variance of the joint estimators. We compare these prescriptions with empirical results from numerical simulations in the case of the weighted least squares estimator (introducing an improved version, denoted stochastic weighted least-squares) as well as with the maximum likelihood estimator, finding excellent agreement. We demonstrate that these estimators provide quasi-unbiased joint estimations of the flux and background, with a variance that approaches the CRLB very tightly and are, hence, optimal, unlike the case of sequential estimation used commonly in astronomical photometry which is sub-optimal. We compare our predictions with numerical simulations of realistic observations, as well as with observations of a bona-fide non-variable stellar source observed with TESS, and compare it to the results from the sequential estimation of background and flux, confirming our theoretical expectations. Our practical estimators can be used as benchmarks for general photometric pipelines, or for applications that require maximum precision and accuracy in absolute photometry.

We present photometric observations of two transits in the WASP-50 planetary system, obtained using the ESO New Technology Telescope and the defocussed-photometry technique. The rms scatters for the two datasets are 258 and 211\\,ppm with a cadence of 170 to 200\\,s, setting a new record for ground-based photometric observations of a point source. The data were modelled and fitted using the \\textsc{prism} and \\textsc{gemc} codes, and the physical properties of the system calculated. We find the mass and radius of the hot star to be \\(0.861\\pm 0.057\\Msun\\) and \\(0.855\\pm0.019\\Rsun\\), respectively. For the planet we find a mass of \\(1.437\\pm 0.068\\Mjup\\), a radius of \\(1.138\\pm0.026\\Rjup\\) and a density of \\(0.911\\pm0.033\\pjup\\). These values are consistent with but more precise than those found in the literature. We also obtain a new orbital ephemeris for the system: \\( T_0 = {\\rm BJD/TDB} \\,\\, 2\\,455\\,558.61237 (20) \\, + \\, 1.9550938 (13) \\times E \\).

We report the first unambiguous detection and mass measurement of an isolated stellar-mass black hole (BH). We used the Hubble Space Telescope (HST) to carry out precise astrometry of the source star of the long-duration (t_E~270 days), high-magnification microlensing event MOA-2011-BLG-191/OGLE-2011-BLG-0462 (hereafter designated as MOA-11-191/OGLE-11-462), in the direction of the Galactic bulge. HST imaging, conducted at eight epochs over an interval of six years, reveals a clear relativistic astrometric deflection of the background star's apparent position. Ground-based photometry of MOA-11-191/OGLE-11-462 shows a parallactic signature of the effect of the Earth's motion on the microlensing light curve. Combining the HST astrometry with the ground-based light curve and the derived parallax, we obtain a lens mass of 7.1 +/- 1.3 Msun and a distance of 1.58 +/- 0.18 kpc. We show that the lens emits no detectable light, which, along with having a mass higher than is possible for a white dwarf or neutron star, confirms its BH nature. Our analysis also provides an absolute proper motion for the BH. The proper motion is offset from the mean motion of Galactic-disk stars at similar distances by an amount corresponding to a transverse space velocity of ~45 km/s, suggesting that the BH received a 'natal kick' from its supernova explosion. Previous mass determinations for stellar-mass BHs have come from radial-velocity measurements of Galactic X-ray binaries, and from gravitational radiation emitted by merging BHs in binary systems in external galaxies. Our mass measurement is the first for an isolated stellar-mass BH using any technique.