arXiv subjects

Giorgio Savini

Publications and source records attributed to Giorgio Savini.

At least 19 recordsLinked to original sources

arXiv2026

Illuminating the Physics of Cosmic Origin and Evolution: A UK Space Frontiers 2035 White Paper

Understanding the Universe's origins and evolution remains one of the most fundamental challenges in modern cosmology. This white paper explores three key science priorities in this field: unravelling the physics of cosmic inflation, investigating the accelerating expansion of the Universe, and precisely measuring the sum of the neutrino masses. Achieving these goals requires a dedicated survey to map the large-scale structure at high redshift in unprecedented detail. We describe how this can be achieved through a mission concept called SIRMOS, providing a high-throughput, highly multiplexed spectroscopic capability to obtain accurate redshifts for over 100 million galaxies over a wide sky area. Such a survey would leverage the deepest existing wide-area photometric catalogues for targeting, with spectra offering continuous 1.25-2.5~$μ$m wavelength coverage at moderate resolution, allowing precise redshift measurements in the $1<z<4$ range with minimal bias. We outline the scientific opportunities this presents. Recent years have seen significant advances in instrumentation, including digital micromirror devices, complex telescope mirrors, large detector arrays, and data processing pipelines. While these technologies have been demonstrated in terrestrial applications, such a survey is a unique opportunity to apply these proven capabilities in space to address fundamental questions in cosmology. Participation in such a mission will simultaneously deliver a compelling science case, help align UK Space Agency and STFC strategies, demonstrate the UK's growing capability in end-to-end space missions, and strengthen the national space economy through high-value industrial participation.

astro-ph.IM↗

arXiv2026

The SPace-based InterFerometer Feasibility (SPIFF) Project: Enabling Future High-Resolution Astronomy Across the EM Spectrum

A plethora of astronomical science cases can only be achieved with high angular resolution observations, and we can expect the number of these to grow as astronomers are constrained by the size limitations of single-aperture space telescopes, making space-based interferometry inevitable. However, the enabling technologies do not have flight heritage at the system level, and the concept remains immature to much of the community, meaning no direct-detection synthetic-aperture space-based interferometer has yet flown and an opportunity exists for the UK to take a world leading role. Here we propose the SPace-based InterFerometry Feasibility (SPIFF) Project as a program to address both issues simultaneously by: 1) completing a thorough survey of the science cases across the EM spectrum that would directly benefit from, or be impossible without, space-based interferometry; 2) down selecting key requirements via a Science Traceability Matrix mapping exercise; 3) host a workshop for the UK astronomical community to consolidate these findings; 4) build a technology demonstration mission to raise TRL and achieve flight heritage of critical technologies. Such a program positions the UK as the partner of choice for any future NASA or ESA space-based interferometry mission, allowing the UK to lead groundbreaking scientific discoveries, while also directly benefiting the UK industrial base by advancing domestic exportable technologies and building direct synergy with other UK space priorities. Indeed, the UK is uniquely positioned to lead in space-based interferometry, possessing a rare trifecta of domestic strengths: world-class expertise in ground-based interferometry and space-based instrumentation; commercial entities developing mission-critical technologies; and scientists whose research spans the full range of science cases that would benefit directly from space-based interferometry.

astro-ph.IM↗

arXiv2025

Transformational astrophysics and exoplanet science with Habitable Worlds Observatory's High Resolution Imager

Habitable Worlds Observatory (HWO) will be NASA's flagship space telescope of the 2040s, designed to search for life on other planets and to transform broad areas of astrophysics. NASA are seeking international partners, and the UK is well-placed to lead the design and construction of its imaging camera - which is likely to produce the mission's most visible public impact. Early participation in the mission would return investment to UK industry, and bring generational leadership for the UK in space science, space technology, and astrophysics.

astro-ph.IM↗

arXiv2025

DISCO: A Browser-Based Privacy-Preserving Framework for Distributed Collaborative Learning

Data is often impractical to share for a range of well considered reasons, such as concerns over privacy, intellectual property, and legal constraints. This not only fragments the statistical power of predictive models, but creates an accessibility bias, where accuracy becomes inequitably distributed to those who have the resources to overcome these concerns. We present DISCO: an open-source DIStributed COllaborative learning platform accessible to non-technical users, offering a means to collaboratively build machine learning models without sharing any original data or requiring any programming knowledge. DISCO's web application trains models locally directly in the browser, making our tool cross-platform out-of-the-box, including smartphones. The modular design of \disco offers choices between federated and decentralized paradigms, various levels of privacy guarantees and several approaches to weight aggregation strategies that allow for model personalization and bias resilience in the collaborative training. Code repository is available at https://github.com/epfml/disco and a showcase web interface at https://discolab.ai

cs.LG↗

arXiv2025

MauveSim: the instrument simulator software for the Blue Skies Space Mauve satellite

We present MauveSim, the instrument simulator software for Mauve, the latest mission from Blue Skies Space dedicated to time-domain stellar astronomy. MauveSim functions as an end-to-end simulator, employing the most up-to-date knowledge of the instrument's performance and characteristics that will be reviewed and updated after commissioning. The software accepts a stellar spectrum - either observed or synthetic - as input and produces a simulated observation. The tool thus enables the assessment of various scientific objectives, as well as determining limiting magnitudes and conducting signal-to-noise (S/N) analyses. The results of MauveSim have been validated against instrument performance data from extensive ground testing campaigns, ensuring that the software reflects the most up-to-date understanding of the payload performance. Accessible to all scientists involved in the mission, MauveSim serves as a crucial tool for target selection and observation planning.

astro-ph.IM↗

arXiv2025

JCMT POL-2 observations of magnetic fields potentially shaped by outflows in the pre-planetary nebulae CRL 618 and OH231.8+4.2

We present the first observations of magnetic fields in pre-planetary nebulae (PPNe) made with the POL-2 polarimeter on the James Clerk Maxwell Telescope (JCMT). We observed the PPNe CRL 618 and OH231.8+4.2 in 850 $μ$m polarized light. In both cases, we observe ordered magnetic fields that appear to arise from dusty circumstellar material that has been swept up by the passage of outflows driven by the central post-Asymptotic Giant Branch (post-AGB) star. CRL 618 shows a magnetic field aligned with one of the most extreme position angles of the outflowing bullets ejected from the central source. We hypothesize that polarized emission in CRL 618 may preferentially arise from material in the walls of the dust cavity opened by the ejected bullets. Conversely, OH231.8+4.2 shows a magnetic field that is aligned approximately perpendicular to the outflow direction, which may preferentially arise from an infrared-bright dense clump embedded near the base of the outflow. Despite CRL 618 being carbon-rich and OH231.8+4.2 being oxygen-rich, there is no significant difference in the polarization fractions of the two sources. This suggests that at linear resolutions $\sim 10^{4}$ au, the complexity of the magnetic field geometry on scales smaller than the beam, rather than grain composition, sets the measured polarization fraction of these sources.

astro-ph.GA↗

arXiv2025

De-jittering Ariel: an optimized algorithm

The European Space Agency's Ariel mission, scheduled for launch in 2029, aims to conduct the first large-scale survey of atmospheric spectra of transiting exoplanets. Ariel achieves the high photometric stability on transit timescales required to detect the spectroscopic signatures of chemical elements with a payload design optimized for transit photometry that either eliminates known systematics or allows for their removal during data processing without significantly degrading or biasing the detection. Jitter in the spacecraft's line of sight is a source of disturbance when measuring the spectra of exoplanet atmospheres. We describe an improved algorithm for de-jittering Ariel observations simulated in the time domain. We opt for an approach based on the spatial information on the Point Spread Function (PSF) distortion from jitter to detrend the optical signals. The jitter model is based on representative simulations from Airbus Defence and Space, the prime contractor for the Ariel service module. We investigate the precision and biases of the retrieved atmospheric spectra from the jitter-detrended observations. At long wavelengths, the photometric stability of the Ariel spectrometer is already dominated by photon noise. Our algorithm effectively de-jitters both photometric and spectroscopic data, ensuring that the performance remains photon noise-limited across the entire Ariel spectrum, fully compliant with mission requirements. This work contributes to the development of the data reduction pipeline for Ariel, aligning with its scientific goals, and may also benefit other astronomical telescopes and instrumentation.

astro-ph.EP↗

arXiv2025

A metamaterial telescope at millimetre wavelengths

In this paper we present a novel telescope composed exclusively of thin, flat optical elements, each being a hot-pressed multi-layered structure combining the properties of a lens, its anti-reflection coating and frequency selection or filtering. We discuss the design process, from fundamental physical metamaterial properties of the single periodic cell structure to the lens concept, which constitutes the building block of the telescope design, and the iterative process that is part of the lens optimization. We provide the results of a laboratory test campaign for different telescope designs based on three-lens arrangements. Beam cuts and focus measurements both on- and off-axis are compared with models showing good agreement. We conclude that a broad-band mm-wave complete telescope system consisting entirely of metamaterial flat lenses has been built and tested, showing comparable performance with conventional state-of-the-art refractive telescopes in the same wavelength region. This new broadband design, highly efficient at frequencies between 90 and 190 GHz, offers multiple advantages. These include a $> 80\%$ weight reduction, reduced issues tied to coating-survivability at cryogenic temperatures caused by differential contraction exacerbated by non-flat surfaces, as well as a reduction in the overall number of components and mechanical mounts.

astro-ph.IM↗

arXiv2024

The JCMT BISTRO Survey: The magnetised evolution of star-forming cores in the Ophiuchus Molecular Cloud interpreted using Histograms of Relative Orientation

The relationship between B-field orientation and density structure in molecular clouds is often assessed using the Histogram of Relative Orientations (HRO). We perform a plane-of-the-sky geometrical analysis of projected B-fields, by interpreting HROs in dense, spheroidal, prestellar and protostellar cores. We use James Clerk Maxwell Telescope (JCMT) POL-2 850 $μ$m polarisation maps and Herschel column density maps to study dense cores in the Ophiuchus molecular cloud complex. We construct two-dimensional core models, assuming Plummer column density profiles and modelling both linear and hourglass B-fields. We find high-aspect-ratio ellipsoidal cores produce strong HRO signals, as measured using the shape parameter $ξ$. Cores with linear fields oriented $< 45^{\circ}$ from their minor axis produce constant HROs with $-1 < ξ< 0$, indicating fields are preferentially parallel to column density gradients. Fields parallel to the core minor axis produce the most negative value of $ξ$. For low-aspect-ratio cores, $ξ\approx 0$ for linear fields. Hourglass fields produce a minimum in $ξ$ at intermediate densities in all cases, converging to the minor-axis-parallel linear field value at high and low column densities. We create HROs for six dense cores in Ophiuchus. $ρ$ Oph A and IRAS 16293 have high aspect ratios and preferentially negative HROs, consistent with moderately strong-field behaviour. $ρ$ Oph C, L1689A and L1689B have low aspect ratios, and $ξ\approx 0$. $ρ$ Oph B is too complex to be modelled using a simple spheroidal field geometry. We see no signature of hourglass fields, agreeing with previous findings that dense cores generally exhibit linear fields on these size scales.

astro-ph.GA↗

arXiv2023

The science case for a far-infrared interferometer in the era of JWST and ALMA

A space-based far-infrared interferometer could work synergistically with the James Webb Space Telescope (JWST) and the Atacama Large Millimeter Array (ALMA) to revolutionize our understanding of the astrophysical processes leading to the formation of habitable planets and the co-evolution of galaxies and their central supermassive black holes. Key to these advances are measurements of water in its frozen and gaseous states, observations of astronomical objects in the spectral range where most of their light is emitted, and access to critical diagnostic spectral lines, all of which point to the need for a far-infrared observatory in space. The objects of interest - circumstellar disks and distant galaxies - typically appear in the sky at sub-arcsecond scales, which rendered all but a few of them unresolvable with the successful and now-defunct 3.5-m Herschel Space Observatory, the largest far-infrared telescope flown to date. A far-infrared interferometer with maximum baseline length in the tens of meters would match the angular resolution of JWST at 10x longer wavelengths and observe water ice and water-vapor emission, which ALMA can barely do through the Earth's atmosphere. Such a facility was conceived and studied two decades ago. Here we revisit the science case for a space-based far-infrared interferometer in the era of JWST and ALMA and summarize the measurement capabilities that will enable the interferometer to achieve a set of compelling scientific objectives. Common to all the science themes we consider is a need for sub-arcsecond image resolution.

astro-ph.IM↗

arXiv2022

Twinkle -- a small satellite spectroscopy mission for the next phase of exoplanet science

With a focus on off-the-shelf components, Twinkle is the first in a series of cost competitive small satellites managed and financed by Blue Skies Space Ltd. The satellite is based on a high-heritage Airbus platform that will carry a 0.45 m telescope and a spectrometer which will provide simultaneous wavelength coverage from 0.5-4.5 $\rm{μm}$. The spacecraft prime is Airbus Stevenage while the telescope is being developed by Airbus Toulouse and the spectrometer by ABB Canada. Scheduled to begin scientific operations in 2025, Twinkle will sit in a thermally-stable, sun-synchronous, low-Earth orbit. The mission has a designed operation lifetime of at least seven years and, during the first three years of operation, will conduct two large-scale survey programmes: one focused on Solar System objects and the other dedicated to extrasolar targets. Here we present an overview of the architecture of the mission, refinements in the design approach, and some of the key science themes of the extrasolar survey.

astro-ph.IM↗

arXiv2021

Ariel: Enabling planetary science across light-years

Ariel, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey, was adopted as the fourth medium-class mission in ESA's Cosmic Vision programme to be launched in 2029. During its 4-year mission, Ariel will study what exoplanets are made of, how they formed and how they evolve, by surveying a diverse sample of about 1000 extrasolar planets, simultaneously in visible and infrared wavelengths. It is the first mission dedicated to measuring the chemical composition and thermal structures of hundreds of transiting exoplanets, enabling planetary science far beyond the boundaries of the Solar System. The payload consists of an off-axis Cassegrain telescope (primary mirror 1100 mm x 730 mm ellipse) and two separate instruments (FGS and AIRS) covering simultaneously 0.5-7.8 micron spectral range. The satellite is best placed into an L2 orbit to maximise the thermal stability and the field of regard. The payload module is passively cooled via a series of V-Groove radiators; the detectors for the AIRS are the only items that require active cooling via an active Ne JT cooler. The Ariel payload is developed by a consortium of more than 50 institutes from 16 ESA countries, which include the UK, France, Italy, Belgium, Poland, Spain, Austria, Denmark, Ireland, Portugal, Czech Republic, Hungary, the Netherlands, Sweden, Norway, Estonia, and a NASA contribution.

astro-ph.IM↗

arXiv2020

Observations of magnetic fields surrounding LkH$α$ 101 taken by the BISTRO survey with JCMT-POL-2

We report the first high spatial resolution measurement of magnetic fields surrounding LkH$α$ 101, a part of the Auriga-California molecular cloud. The observations were taken with the POL-2 polarimeter on the James Clerk Maxwell Telescope within the framework of the B-fields In Star-forming Region Observations (BISTRO) survey. Observed polarization of thermal dust emission at 850 $μ$m is found to be mostly associated with the red-shifted gas component of the cloud. The magnetic field displays a relatively complex morphology. Two variants of the Davis-Chandrasekhar-Fermi method, unsharp masking and structure function, are used to calculate the strength of magnetic fields in the plane of the sky, yielding a similar result of $B_{\rm POS}\sim 115$ $\mathrmμ$G. The mass-to-magnetic-flux ratio in critical value units, $λ\sim0.3$, is the smallest among the values obtained for other regions surveyed by POL-2. This implies that the LkH$α$ 101 region is sub-critical and the magnetic field is strong enough to prevent gravitational collapse. The inferred $δB/B_0\sim 0.3$ implies that the large scale component of the magnetic field dominates the turbulent one. The variation of the polarization fraction with total emission intensity can be fitted by a power-law with an index of $α=0.82\pm0.03$, which lies in the range previously reported for molecular clouds. We find that the polarization fraction decreases rapidly with proximity to the only early B star (LkH$α$ 101) in the region. The magnetic field tangling and the joint effect of grain alignment and rotational disruption by radiative torques are potential of explaining such a decreasing trend.

astro-ph.GA↗

arXiv2020

Non-gray, Month-long Brightening of KIC 8462852 in the Immediate Aftermath of a Deep Dip

We present an analysis of the results of long-term multi-band photometric monitoring of the enigmatic star, KIC 8462852. Observations in the $B$, $g'$, $V$, $r'$ and $I_C$ passbands have been acquired at University College London Observatory (UCLO) between May 2017 and September 2018. We interrogate the wavelength dependence of the $\sim$month-long dimming and brightening exhibited by the target star over an 85-day interval, immediately following a days-long $\sim5$ per cent drop in brightness on Julian Date (JD) 2458203. Between JD 2458215--300 we measure brightness variations which correspond to relative extinctions of $A_B/A_V = 1.39\pm0.27$, $A_{g'}/A_V = 1.16\pm0.11$, $A_{r'}/A_V = 0.80\pm0.25$ and $A_{Ic}/A_V = 0.49\pm0.19$, from which we infer an Angström absorption coefficient of $1.33\pm0.43$ ($R_V \simeq 3.2^{+2.6}_{-1.0}$). As with the days-long `dips', the wavelength dependence of the longer-term brightness variations must also be associated with extinction arising from a dust distribution containing a substantial fraction of sub-micron-sized grains. This implies some common mechanism is responsible for the star's variability over both these short and longer timescales.

astro-ph.SR↗

arXiv2020

Original Research By Young Twinkle Students (ORBYTS): Ephemeris Refinement of Transiting Exoplanets

We report follow-up observations of transiting exoplanets that have either large uncertainties (>10 minutes) in their transit times or have not been observed for over three years. A fully robotic ground-based telescope network, observations from citizen astronomers and data from TESS have been used to study eight planets, refining their ephemeris and orbital data. Such follow-up observations are key for ensuring accurate transit times for upcoming ground and space-based telescopes which may seek to characterise the atmospheres of these planets. We find deviations from the expected transit time for all planets, with transits occurring outside the 1 sigma uncertainties for seven planets. Using the newly acquired observations, we subsequently refine their periods and reduce the current predicted ephemeris uncertainties to 0.28 - 4.01 minutes. A significant portion of this work has been completed by students at two high schools in London as part of the Original Research By Young Twinkle Students (ORBYTS) programme.

astro-ph.EP↗

arXiv2019

Small Bodies Science with Twinkle

Twinkle is an upcoming 0.45m space-based telescope equipped with a visible and two near-infrared spectrometers covering the spectral range 0.4 to 4.5μm with a resolving power R~250 (λ<2.42μm) and R~60 (λ>2.42μm). We explore Twinkle's capabilities for small bodies science and find that, given Twinkle's sensitivity, pointing stability, and spectral range, the mission can observe a large number of small bodies. The sensitivity of Twinkle is calculated and compared to the flux from an object of a given visible magnitude. The number, and brightness, of asteroids and comets that enter Twinkle's field of regard is studied over three time periods of up to a decade. We find that, over a decade, several thousand asteroids enter Twinkle's field of regard with a brightness and non-sidereal rate that will allow Twinkle to characterise them at the instrumentation's native resolution with SNR > 100. Hundreds of comets can also be observed. Therefore, Twinkle offers researchers the opportunity to contribute significantly to the field of Solar System small bodies research.

astro-ph.EP↗

arXiv2019

Relative Alignment Between the Magnetic Field and Molecular Gas Structure in the Vela C Giant Molecular Cloud using Low and High Density Tracers

We compare the magnetic field orientation for the young giant molecular cloud Vela C inferred from 500-$μ$m polarization maps made with the BLASTPol balloon-borne polarimeter to the orientation of structures in the integrated line emission maps from Mopra observations. Averaging over the entire cloud we find that elongated structures in integrated line-intensity, or zeroth-moment maps, for low density tracers such as $^{12}$CO and $^{13}$CO $J$ $\rightarrow$ 1 - 0 are statistically more likely to align parallel to the magnetic field, while intermediate or high density tracers show (on average) a tendency for alignment perpendicular to the magnetic field. This observation agrees with previous studies of the change in relative orientation with column density in Vela C, and supports a model where the magnetic field is strong enough to have influenced the formation of dense gas structures within Vela C. The transition from parallel to no preferred/perpendicular orientation appears to happen between the densities traced by $^{13}$CO and by C$^{18}$O $J$ $\rightarrow$ 1 - 0. Using RADEX radiative transfer models to estimate the characteristic number density traced by each molecular line we find that the transition occurs at a molecular hydrogen number density of approximately $10^3$ cm$^{-3}$. We also see that the Centre-Ridge (the highest column density and most active star-forming region within Vela C) appears to have a transition at a lower number density, suggesting that this may depend on the evolutionary state of the cloud.

astro-ph.GA↗

arXiv2019

Remote-sensing Characterisation of Major Solar System Bodies with the Twinkle Space Telescope

Remote-sensing observations of Solar System objects with a space telescope offer a key method of understanding celestial bodies and contributing to planetary formation and evolution theories. The capabilities of Twinkle, a space telescope in a low Earth orbit with a 0.45m mirror, to acquire spectroscopic data of Solar System targets in the visible and infrared are assessed. Twinkle is a general observatory that provides on demand observations of a wide variety of targets within wavelength ranges that are currently not accessible using other space telescopes or that are accessible only to oversubscribed observatories in the short-term future. We determine the periods for which numerous Solar System objects could be observed and find that Solar System objects are regularly observable. The photon flux of major bodies is determined for comparison to the sensitivity and saturation limits of Twinkle's instrumentation and we find that the satellite's capability varies across the three spectral bands (0.4-1, 1.3-2.42, and 2.42-4.5μm). We find that for a number of targets, including the outer planets, their large moons, and bright asteroids, the model created predicts that with short exposure times, high-resolution spectra (R~250, λ < 2.42μm; R~60, λ > 2.42μm) could be obtained with signal-to-noise ratio (SNR) of >100 with exposure times of <300s.

astro-ph.EP↗