arXiv subjects

Emanuel Gafton

Publications and source records attributed to Emanuel Gafton.

8 recordsLinked to original sources

arXiv2026

Visplot: A visibility plot and observation scheduling tool for astronomical observatories

We present Visplot, a free and open-source tool designed for interactive construction and refinement of nightly telescope observing schedules through a graphical user interface. The software performs hardware-aware observability analysis by explicitly incorporating telescope-specific limits alongside astronomical constraints, in order to determine feasible observation windows for both sidereal and non-sidereal targets. It also generates observing schedules that can be rapidly adapted to changing conditions. Visplot is a browser-based JavaScript application that can be used without installation, while remaining fully customizable through self-hosted deployments. The software computes target altitudes for the specified observatory coordinates on a discretized time grid spanning the entire observing night. Observability windows for individual targets are then derived by evaluating their altitude profiles against the intersection of astronomical constraints (airmass, moon distance, twilight), mechanical telescope boundaries (altitude and hour-angle limits), and custom temporal restrictions defined in coordinated universal time (UTC) or local sidereal time (LST). The scheduling engine operates within these observability windows, selecting and ordering observations using a multi-constraint heuristic optimization scheme. Mandatory targets are scheduled deterministically, while the remaining target pool is ranked using a weighted scoring function that balances user-defined priority, target urgency, altitude, and telescope slew overhead. Originally developed to address operational scheduling requirements at the Nordic Optical Telescope (NOT), Visplot has been in continuous use for a decade and has grown beyond its original development to support astronomers at multiple observatories worldwide, demonstrating its practical value in real-world observational workflows.

astro-ph.IM↗

arXiv2026

Forecast for the detectability of patchy hydrogen reionization in WEAVE-QSO measurements of the Lyman-$α$ forest power spectrum at redshift $z \geq 4$

We present the first detailed forecasts for the detectability of patchy hydrogen reionization in the one-dimensional Ly$α$ forest power spectrum to be measured by the WEAVE-QSO survey. Using the Sherwood-relics reionization simulations and a WEAVE-QSO survey configuration, we generate mock spectra in four redshift bins, $z=4.0,4.2,4.4,$ and $4.6$, in which relic ionization and temperature fluctuations from patchy hydrogen reionization enhance the Ly$α$ forest power spectrum on large scales (i.e., at wavenumber $k\sim 10^{-3},\mathrm{s\,km^{-1}}$). Our Ly$α$ forest pipeline forecasts the power spectrum covariance by considering sample size, spectral resolution, noise subtraction, continuum placement, metal contamination, and damping wings from high-column density absorbers. Applying our covariance forecast within a Bayesian parameter inference framework, we find that the signature of patchy hydrogen reionization should be detectable at a significance of $\simeq 4.5σ$. The forthcoming WEAVE-QSO 1D power spectrum measurements should therefore be able to directly detect and characterize the large-scale relic imprint of patchy hydrogen reionization in the Ly$α$ forest power spectrum at $z\geq 4$.

astro-ph.CO↗

arXiv2026

The WEAVE acquisition and guiding software: pattern recognition-based acquisition and multi-fibre guiding

We present the architecture, implementation, and on-sky validation of the fully automated acquisition and guiding system (AG) developed for the WEAVE instrument on the William Herschel Telescope. The AG operates in two distinct modes, corresponding to the observing modes of WEAVE. For the large integral field unit (LIFU), an off-axis imaging guider is used, for which we have devised an automatic acquisition method based on pattern recognition of stellar asterisms matched against Gaia predictions. For the multi-object spectrograph (MOS) and the mini-integral field units (mIFU), a multi-fibre guider uses up to eight coherent image guide fibre bundles to derive and apply continuous corrections in azimuth, altitude, and rotation. The system performs complete astrometric calculations, including atmospheric differential refraction and instrument flexure, for each guide frame, enabling accurate target placement and stable closed-loop guiding in all configurations. To support development, commissioning, and operational validation, we have also built a high-fidelity simulation mode that reproduces the behaviour of the telescope control system and of the AG cameras, and we release the standalone camera simulator as open-source software. Using two years of routine WEAVE operations spanning commissioning and early survey phases, we present a statistically robust characterization of AG performance, demonstrating that both modes meet design requirements and are ready for sustained survey operations.

astro-ph.IM↗

arXiv2025

The WEAVE-TwiLight-Survey: Expanding WEAVE's Reach to Bright and Low-Surface-Density Targets with a Novel Observing Mode

Current-day multi-object spectroscopic surveys are often limited in their ability to observe bright stars due to their low surface densities, resulting in increased observational overheads and reduced efficiency. Addressing this, we have developed a novel observing mode for WEAVE (William Herschel Telescope Enhanced Area Velocity Explorer) that enables efficient observations of low-surface-density target fields without incurring additional overheads from calibration exposures. As a pilot for the new mode, we introduce the WEAVE-TwiLight-Survey (WTLS), focusing on bright exoplanet-host stars and their immediate surroundings on the sky. High observational efficiency is achieved by superimposing multiple low-target-density fields and allocating the optical fibres in this configuration. We use a heuristic method to define fields relative to a central guide star, which serves as a reference for their superposition. Suitable guide fibres for each merged configuration are selected using a custom algorithm. Test observations have been carried out, demonstrating the feasibility of the new observing mode. We show that merged field configurations can be observed with WEAVE using the proposed method. The approach minimizes calibration times and opens twilight hours to WEAVE's operational schedule. WTLS is built upon the new observing mode and sourced from the ESA PLATO long-duration-phase fields. This survey will result in a homogeneous catalogue of approximately 6300 bright stars, including 62 known planet hosts, laying the groundwork for future elemental abundance studies tracing chemical patterns of planetary formation. This new observing mode (WEAVE-Tumble-Less) expands WEAVE's capabilities to rarely used on-sky time and low-density field configurations without sacrificing efficiency.

astro-ph.IM↗

arXiv2019

Tidal disruptions by rotating black holes: effects of spin and impact parameter

We present the results of relativistic smoothed particle hydrodynamics simulations of tidal disruptions of stars by rotating supermassive black holes, for a wide range of impact parameters and black hole spins. For deep encounters, we find that: relativistic precession creates debris geometries impossible to obtain with the Newtonian equations; part of the fluid can be launched on plunging orbits, reducing the fallback rate and the mass of the resulting accretion disc; multiple squeezings and bounces at periapsis may generate distinctive X-ray signatures resulting from the associated shock breakout; disruptions can occur inside the marginally bound radius, if the angular momentum spread launches part of the debris on non-plunging orbits. Perhaps surprisingly, we also find relativistic effects important in partial disruptions, where the balance between self-gravity and tidal forces is so precarious that otherwise minor relativistic effects can have decisive consequences on the stellar fate. In between, where the star is fully disrupted but relativistic effects are mild, the difference resides in a gentler rise of the fallback rate, a later and smaller peak, and longer return times. However, relativistic precession always causes thicker debris streams, both in the bound part (speeding up circularization) and in the unbound part (accelerating and enhancing the production of separate transients). We discuss various properties of the disruption (compression at periapsis, shape and spread of the energy distribution) and potential observables (peak fallback rate, times of rise and decay, duration of super-Eddington fallback) as a function of the impact parameter and the black hole spin.

astro-ph.HE↗

arXiv2017

Tidal disruptions by rotating black holes: relativistic hydrodynamics with Newtonian codes

We propose an approximate approach for studying the relativistic regime of stellar tidal disruptions by rotating massive black holes. It combines an exact relativistic description of the hydrodynamical evolution of a test fluid in a fixed curved spacetime with a Newtonian treatment of the fluid's self-gravity. Explicit expressions for the equations of motion are derived for Kerr spacetime using two different coordinate systems. We implement the new methodology within an existing Newtonian Smoothed Particle Hydrodynamics code and show that including the additional physics involves very little extra computational cost. We carefully explore the validity of the novel approach by first testing its ability to recover geodesic motion, and then by comparing the outcome of tidal disruption simulations against previous relativistic studies. We further compare simulations in Boyer--Lindquist and Kerr--Schild coordinates and conclude that our approach allows accurate simulation even of tidal disruption events where the star penetrates deeply inside the tidal radius of a rotating black hole. Finally, we use the new method to study the effect of the black hole spin on the morphology and fallback rate of the debris streams resulting from tidal disruptions, finding that while the spin has little effect on the fallback rate, it does imprint heavily on the stream morphology, and can even be a determining factor in the survival or disruption of the star itself. Our methodology is discussed in detail as a reference for future astrophysical applications.

astro-ph.HE↗

arXiv2015

Relativistic effects on tidal disruption kicks of solitary stars

Solitary stars that wander too close to their galactic centres can become tidally disrupted, if the tidal forces due to the supermassive black hole (SMBH) residing there overcome the self-gravity of the star. If the star is only partially disrupted, so that a fraction survives as a self-bound object, this remaining core will experience a net gain in specific orbital energy, which translates into a velocity "kick" of up to $\sim 10^3$ km/s. In this paper, we present the result of smoothed particle hydrodynamics (SPH) simulations of such partial disruptions, and analyse the velocity kick imparted on the surviving core. We compare $γ$ = 5/3 and $γ$ = 4/3 polytropes disrupted in both a Newtonian potential, and a generalized potential that reproduces most relativistic effects around a Schwarzschild black hole either exactly or to excellent precision. For the Newtonian case, we confirm the results of previous studies that the kick velocity of the surviving core is virtually independent of the ratio of the black hole to stellar mass, and is a function of the impact parameter $β$ alone, reaching at most the escape velocity of the original star. For a given $β$, relativistic effects become increasingly important for larger black hole masses. In particular, we find that the kick velocity increases with the black hole mass, making larger kicks more common than in the Newtonian case, as low-$β$ encounters are statistically more likely than high-$β$ encounters. The analysis of the tidal tensor for the generalized potential shows that our results are robust lower limits on the true relativistic kick velocities, and are generally in very good agreement with the exact results.

astro-ph.HE↗

arXiv2011

A fast recursive coordinate bisection tree for neighbour search and gravity

We introduce our new binary tree code for neighbour search and gravitational force calculations in an N-particle system. The tree is built in a "top-down" fashion by "recursive coordinate bisection" where on each tree level we split the longest side of a cell through its centre of mass. This procedure continues until the average number of particles in the lowest tree level has dropped below a prescribed value. To calculate the forces on the particles in each lowest-level cell we split the gravitational interaction into a near- and a far-field. Since our main intended applications are SPH simulations, we calculate the near-field by a direct, kernel-smoothed summation, while the far field is evaluated via a Cartesian Taylor expansion up to quadrupole order. Instead of applying the far-field approach for each particle separately, we use another Taylor expansion around the centre of mass of each lowest-level cell to determine the forces at the particle positions. Due to this "cell-cell interaction" the code performance is close to O(N) where N is the number of used particles. We describe in detail various technicalities that ensure a low memory footprint and an efficient cache use. In a set of benchmark tests we scrutinize our new tree and compare it to the "Press tree" that we have previously made ample use of. At a slightly higher force accuracy than the Press tree, our tree turns out to be substantially faster and increasingly more so for larger particle numbers. For four million particles our tree build is faster by a factor of 25 and the time for neighbour search and gravity is reduced by more than a factor of 6. In single processor tests with up to 10^8 particles we confirm experimentally that the scaling behaviour is close to O(N). The current Fortran 90 code version is OpenMP-parallel and scales excellently with the processor number (=24) of our test machine.

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