arXiv subjects

Gabriele Rodeghiero

Publications and source records attributed to Gabriele Rodeghiero.

16 recordsLinked to original sources

arXiv2026

MORFEO: Advancing Towards Final Design

The Multiconjugate adaptive Optics Relay For ELT Observations (MORFEO) is a first-generation adaptive optics module for the Extremely Large Telescope (ELT), designed to deliver a diffraction-limited, highly uniform 53x53 arcsec field of view to the MICADO near-infrared camera. As the project advances toward its Final Design Review (FDR), significant consolidations have been achieved across all subsystems. This paper presents an updated overview of the MORFEO system, highlighting its dual operational modes (MCAO and SCAO) and recent developments in its opto-mechanical architecture. We dedicate specific focus to the core adaptive hardware, detailing the fifth-generation post-focal deformable mirrors, the highly complex Laser Guide Star (LGS) objective zoom system required to track sodium layer variations, and the Natural Guide Star (NGS) low-order and reference sensing strategies. Furthermore, we detail the advanced pseudo-open-loop control strategy managed by a split Hard and Soft Real-Time Computer architecture. Finally, we report the latest end-to-end performance estimations obtained via the SPECULA simulation framework, demonstrating compliance with the stringent Strehl Ratio and sky coverage requirements under median atmospheric conditions.

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arXiv2026

Laser-based metrology systems vs wavefront sensing techniques: a comparative overview between the Large Binocular Telescope and the Vera C. Rubin Observatory for the telescope alignment and collimation tracking

This work presents a comparative overview of the collimation and alignment strategies employed by two leading 8m-class facilities: the Large Binocular Telescope (LBT) and the Vera C. Rubin Observatory. While both telescopes share a challenging fast f-number of approximately f/1.2 (considering the LBT in its Prime Focus configuration), they have adopted reciprocal architectures for the initial optical alignment strategy and for maintaining collimation during the night. As an initial alignment strategy, the LBT relies on a Wavefront Sensing technique called Focal Plane Image Analysis. Conversely, the Vera C. Rubin Observatory baseline foresees the usage of a Laser Tracker system to establish the initial optical states. The strategies for preserving the optical alignment and maintaining the collimation against gravitational flexure and thermal drift during observations are instead reversed. Besides the use of open-loop corrections based on Look-Up Tables, common on both telescopes, the LBT utilizes a laser-based Telescope Metrology System to monitor the relative position of optics in real-time, applying the corrections between the exposures. In contrast, the Rubin Observatory employs a Curvature Wavefront Sensing technique, using dedicated detectors at the four corners of the focal plane. Rather than identifying a best strategy, this work aims to synthesize the strengths, limitations, and operational trade-offs of these complementary approaches, from the perspective of the next generation of Extremely Large Telescopes and their instruments.

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arXiv2026

Modeling of the diffuse background produced by the Vera C. Rubin Observatory M2 baffle scattered light

The Vera C. Rubin Observatory, with its unprecedented field of view and fast focal ratio, will survey the entire sky every 3.5 nights. This unique capacity requires dealing with off axis light that can produce stray light artefacts on the images. The secondary mirror (M2) baffle restricts the light that reaches the LSSTCam detector and it contributes to shaping the inner edge of the telescope optical pupil. This work studies the contribution to the background from the light scattered by the M2 baffle itself. The evanescence of this feature, together with the challenge of isolating it from the sky background, led to the necessity of performing in dome tests using a Collimated Beam Projector (CBP), normally used for calibration purposes. To complete the analysis, in addition to the in dome tests, an on sky observational campaign was conducted. This campaign employed both stellar targets and the Moon as illumination sources in order to determine the actual energy associated with the feature. The test data have been retro fitted thanks to the combination of ray tracing simulation, CBP and on sky data to infer the intensity and spatial distribution of the background scattered light within the different LSSTCam filters. We quantified the on sky impact of scattered light from the M2 baffle, both for light coming from bright and red stars and from the Moon. We also developed an approximate relation to transform the in dome measurements into predictions of on sky behavior. This transformation was achieved by comparing the illumination footprint produced by an off axis star with that generated by the CBP and by mapping the stellar Spectral Energy Distribution (SED) onto the CBP's set of discrete wavelengths. Finally, we extrapolated the scattered light behavior of the Moon to stellar sources, in order to build a compplete description of the M2 baffle contribution over the full range of magnitudes.

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arXiv2026

Mechanical Studies of an Additional Light Baffle for the LSST Camera

Commissioning the NSF-DOE Vera C. Rubin Observatory consisted of engineering operation and on-sky data-taking, initially with the Commissioning Camera followed by the commissioning run of the LSST Camera (LSSTCam). As with other wide-field astronomical projects, the Rubin team anticipated a significant amount of stray light effects which would necessitate investigation and systematic mitigation. This led the Rubin stray light working group to develop tools, including a robust model of the entire observatory in Zemax, to trace the light paths of stray light artifacts back to their sources. This model along with the other efforts of the working group enabled significant improvements in stray light mitigation leading up to the commencement of the Legacy Survey of Space and Time (LSST). One such potential source was identified as a small chamfer on the L3 lens, for which it was hypothesized that a simple baffle added inside of the LSSTCam near the L3 should prove beneficial to the quality of data being collected in the LSST. Initial Zemax models proved this hypothesis to be correct, but it is important to weigh the improvements made versus the effort, risk, and cost especially when considering any hardware modifications to an instrument that is already running and collecting immense amounts of data each night. This paper investigates the impacts of installing an L3 baffle via a collection of mechanically focused studies, where the principal areas of focus are installation feasibility, baffle geometry, materials & coating selection, and potential impacts to the purge system.

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arXiv2026

Investigation and Mitigation of a Prominent Off-Axis Stray Light Path in Rubin Observatory Commissioning

The "scratched tape" stray light feature is the most prominent and prevalent stray light artifact identified during the commissioning of the Vera C. Rubin Observatory. The scratched tape feature originates when light from large off-axis angles (~20 deg) passes between the mid-level and center-section light baffles, reflects off the primary mirror, and illuminates the LSST Camera focal plane. This scenario represented an unobstructed stray light path to the sky during Rubin commissioning due to delays in the integration of the dome slit light-wind screen. This document describes the identification, modeling, characterization, and mitigation of the scratched tape stray light artifact.

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arXiv2026

An overview of stray light findings and interpretation during on-sky commissioning of LSSTCam

Wide-field telescopes are intrinsically difficult to shield from unwanted stray and scattered light, while the search to identify sources of contaminating light is frequently a challenging task. The Vera C.~Rubin Observatory, which achieved its first photon with the LSST Camera (LSSTCam) on April 15, 2025, will initiate a revolutionary era for the study of dark matter, dark energy, the transient sky, the Solar System, and the Milky Way. LSSTCam will provide near seeing-limited images of the sky in six bands ($u,g,r,i,z,y$) over a $3.^\circ 5$-diameter field of view, and over the course of a decade, it will execute the Legacy Survey of Space and Time (LSST). This work provides an overview of the dedicated stray and scattered light test campaign that has been undertaken since the start of Rubin commissioning. In particular, we highlight the processes used to characterize, model, and mitigate stray light present in LSSTCam images. The Rubin commissioning team created a series of testing and analysis tools to track stray light artifacts from their initial discovery through reproduction with timely observations, simulation using ray tracing to identify opto-mechanical origins, and finally devising corrective actions. The complex stray light features encountered by Rubin provide a wealth of experience for the future wide-field and extremely wide-field observatories. This work covers the many stages of a long journey that started with conceiving an innovative and challenging optical design, followed by the engineering and system engineering efforts to build it, to finally delivering an optimized and revolutionary cutting-edge facility.

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arXiv2025

SHINS, the SHARK-NIR Instrument Control Software

SHARK-NIR is a new compact instrument for coronagraphic imaging, direct imaging, and coronagraphic spectroscopy in the near-infrared wavelengths mounted at LBT. Taking advantage of the telescope's adaptive optics system, it provides high contrast imaging with coronagraphic and spectroscopic capabilities and is focused on the direct imaging of exoplanets and circumstellar discs. We present SHINS, the SHARK-NIR instrument control software, mainly realized with the TwiceAsNice framework from MPIA - Heidelberg and the ICE framework using the C++ programming language. We describe how we implemented the software components controlling several instrument subsystems, through the adaptation of already tested libraries from other instruments at LBT, such as LINC-NIRVANA. The scientific detector comes with its own readout electronic and control software interfaced with our software through INDI. We describe the C++ core software Observation Control Software, responsible for dispatching commands to the subsystems, also implementing a software solution to avoid a potential collision between motorized components, fully transparent to final users. It exposes an ICE interface and can be controlled by clients developed in different languages. Observation, calibration, and maintenance procedures are implemented by means of template scripts, written in python language, controlling Observation Control Software through its ICE interface. These templates and their parameters are configured using "ESO-style", XML Observation Blocks prepared by observers, or in general SHARK-NIR users. The high-level control is carried out by REST HTTP APIs implemented in a python back-end, also acting as a web server for the several browser-based front-end GUIs. Finally, we present the first scientific results obtained by SHARK-NIR using coronagraphic mode.

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arXiv2023

MORFEO enters final design phase

MORFEO (Multi-conjugate adaptive Optics Relay For ELT Observations, formerly MAORY), the MCAO system for the ELT, will provide diffraction-limited optical quality to the large field camera MICADO. MORFEO has officially passed the Preliminary Design Review and it is entering the final design phase. We present the current status of the project, with a focus on the adaptive optics system aspects and expected milestones during the next project phase.

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arXiv2021

MAORY: A Multi-conjugate Adaptive Optics RelaY for ELT

MAORY is the adaptive optics module for ELT providing two gravity invariant ports with the same optical quality for two different client instruments. It enable high angular resolution observations in the near infrared over a large field of view (~1 arcmin2 ) by real time compensation of the wavefront distortions due to atmospheric turbulence. Wavefront sensing is performed by laser and natural guide stars while the wavefront sensor compensation is performed by an adaptive deformable mirror in MAORY which works together with the telescope's adaptive and tip tilt mirrors M4 and M5 respectively.

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arXiv2019

Towards an overall astrometric error budget with MICADO-MCAO

MICADO is the Multi-AO Imaging Camera for Deep Observations, and it will be one of the first light instruments of the Extremely Large Telescope (ELT). Doing high precision multi-object differential astrometry behind ELT is particularly effective given the increased flux and small diffraction limit. Thanks to its robust design with fixed mirrors and a cryogenic environment, MICADO aims to provide 50 $μ$as absolute differential astrometry (measure star-to-star distances in absolute $μ$as units) over a 53" FoV in the range 1.2-2.5 $μ$m. Tackling high precision astrometry over large FoV requires Multi Conjugate Adaptive Optics (MCAO) and an accurate distortion calibration. The MICADO control scheme relies on the separate calibration of the ELT, MAORY and MICADO systematics and distortions, to ensure the best disentanglement and correction of all the contributions. From a system perspective, we are developing an astrometric error budget supported by optical simulations to assess the impact of the main astrometric errors induced by the telescope and its optical tolerances, the MCAO distortions and the opto-mechanical errors between internal optics of ELT, MAORY and MICADO. The development of an overall astrometric error budget will pave the road to an efficient calibration strategy complementing the design of the MICADO calibration unit. At the focus of this work are a number of opto-mechanical error terms which have particular relevance for MICADO astrometry applications, and interface to the MCAO design.

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arXiv2019

Development of the Warm Astrometric Mask for MICADO astrometry calibration

The achievement of $μ$arcsec relative astrometry with ground-based, near infrared, extremely large telescopes requires a significant endeavour of calibration strategies. In this paper we address the removal of instrument optical distortions coming from the ELT first light instrument MICADO and its adaptive optics system MAORY by means of an astrometric calibration mask. The results of the test campaign on a prototype mask (scale 1:2) has probed the manufacturing precision down to $\sim$ 50nm/1mm scale, leading to a relative precision $δσ\sim 5e-5$. The assessed manufacturing precision indicates that an astrometric relative precision of $δσ\sim 5e-5 = \frac{50μas}{1 arcsec}$ is in principle achievable, disclosing $μ$arcsec near infrared astrometry behind an extremely large telescope. The impact of $\sim$ 10-100 nm error residuals on the mask pinholes position is tolerable at a calibration level as confirmed by ray tracing simulations of realistic MICADO distortion patterns affected by mid spatial frequencies residuals. We demonstrated that the MICADO astrometric precision of 50 $μ$as is achievable also in presence of a mid spatial frequencies pattern and manufacturing errors of the WAM by fitting the distorted WAM pattern seen through the instrument with a 10$^{th}$ order Legendre polynomial.

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arXiv2018

The MICADO first light imager for the ELT: overview, operation, simulation

MICADO will enable the ELT to perform diffraction limited near-infrared observations at first light. The instrument's capabilities focus on imaging (including astrometric and high contrast) as well as single object spectroscopy. This contribution looks at how requirements from the observing modes have driven the instrument design and functionality. Using examples from specific science cases, and making use of the data simulation tool, an outline is presented of what we can expect the instrument to achieve.

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arXiv2018

The impact of ELT distortions and instabilities on future astrometric observations

The paper discusses an assessment study about the impact of the distortions on the astrometric observations with the Extremely Large Telescope originated from the optics positioning errors and telescope instabilities. Optical simulations combined with Monte Carlo approach reproducing typical inferred opto-mechanical and dynamical instabilities, show RMS distortions between $\sim$ 0.1-5 mas over 1 arcmin field of view. Over minutes timescales the plate scale variations from ELT-M2 caused by wind disturbances and gravity flexures and the field rotation from ELT-M4-M5 induce distortions and PSF jitter at the edge of 1 arcmin FoV (radius 35 arcsec) up to $\sim$ 5 mas comparable to the diffraction-limited PSF size $FWHM_H = 8.5$ mas. The RMS distortions inherent to the ELT design are confined to the 1$^{st}$-3$^{rd}$ order and reduce to an astrometric RMS residual post fit of $\sim$ 10-20 $μas$ for higher order terms. In this paper, we study which calibration effort has to be undertaken to reach an astrometric stability close to this level of higher order residuals. The amplitude and timescales of the assumed telescope tolerances indicate the need for frequent on-sky calibrations and MCAO stabilization of the plate scale to enable astrometric observations with ELT at the level of $\leq 50 μas$, which is one of the core science missions for the ELT / MICADO instrument.

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arXiv2018

Spectropolarimetry of Galactic stars with anomalous extinction sightlines

Highly reddened type Ia Supernovae (SNe Ia) with low total-to-selective visual extinction ratio values, $R_V$, also show peculiar linear polarization wavelength dependencies with peak polarizations at short wavelengths ($λ_{max} \lesssim 0.4 μm$). It is not clear why sightlines to SNe Ia display such different continuum polarization profiles from interstellar sightlines in the Milky Way with similar $R_V$ values. We investigate polarization profiles of a sample of Galactic stars with low $R_V$ values, along anomalous extinction sightlines, with the aim to find similarities to the polarization profiles that we observe in SN Ia sightlines. We undertook spectropolarimetry of 14 stars, and used archival data for three additional stars, and run dust extinction and polarization simulations to infer a simple dust model that can reproduce the observed extinction and polarization curves. Our sample of Galactic stars with low $R_V$ values and anomalous extinction sightlines displays normal polarization profiles with an average $λ_{max} \sim 0.53 {μm}$, and is consistent within 3$σ$ to a larger coherent sample of Galactic stars from literature. Despite the low $R_V$ values of dust towards the stars in our sample, the polarization curves do not show any similarity to the continuum polarization curves observed towards SNe Ia with low $R_V$ values. There is a correlation between the best-fit Serkowski parameters $K$ and $λ_{max}$, but we did not find any significant correlation between $R_V$ and $λ_{max}$. Our simulations show that the $K-λ_{max}$ relationship is an intrinsic property of polarization. Furthermore, we have shown that in order to reproduce polarization curves with normal $λ_{max}$ and low $R_V$ values, a population of large (a $\geq 0.1 μm$) interstellar silicate grains must be contained in the dust's composition.

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arXiv2016

High-precision astrometry towards ELTs

With the aim of paving the road for future accurate astrometry with MICADO at the European-ELT, we performed an astrometric study using two different but complementary approaches to investigate two critical components that contribute to the total astrometric accuracy. First, we tested the predicted improvement in the astrometric measurements with the use of an atmospheric dispersion corrector (ADC) by simulating realistic images of a crowded Galactic globular cluster. We found that the positional measurement accuracy should be improved by up to ~2 mas with the ADC, making this component fundamental for high-precision astrometry. Second, we analysed observations of a globular cluster taken with the only currently available Multi-Conjugate Adaptive Optics assisted camera, GeMS/GSAOI at Gemini South. Making use of previously measured proper motions of stars in the field of view, we were able to model the distortions affecting the stellar positions. We found that they can be as large as ~200 mas, and that our best model corrects them to an accuracy of ~1 mas. We conclude that future astrometric studies with MICADO requires both an ADC and an accurate modelling of distortions to the field of view, either through an a-priori calibration or an a-posteriori correction.

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arXiv2016

A facility to evaluate the focusing performance of mirrors for Cherenkov Telescopes

Cherenkov Telescopes are equipped with optical dishes of large diameter -- in general based on segmented mirrors -- with typical angular resolution of a few arc-minutes. To evaluate the mirror's quality specific metrological systems are required that possibly take into account the environmental conditions in which typically these telescopes operate (in open air without dome protection). For this purpose a new facility for the characterization of mirrors has been developed at the labs of the Osservatorio Astronomico di Brera of the Italian National Institute of Astrophysics. The facility allows the precise measurement of the radius of curvature and the distribution of the concentred light in terms of focused and scattered components and it works in open air. In this paper we describe the facility and report some examples of its measuring capabilities.

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