Paranal Observatory Research Articles

Long-term changes of sodium column abundance at 24.6°S above the Atacama Desert in Chile

Aims. The utilisation of artificial laser guide star (LGS) obviates the necessity for a prominent natural guide star (NGS) within adaptive optics (AO) systems. High-power lasers are fundamental components of most AO systems today. The generation of an LGS relies on the excitation of sodium (denoted by its symbol Na) atoms situated in the upper atmosphere. Therefore, the sodium vertical column density (denoted as CNa) is a crucial parameter. Beyond ensuring the optimal and stable performance of an AO system, knowledge of the return flux from an LGS is imperative during the design phase, aiding in the accurate specification of both the LGS and the AO system. The availability of sodium in the upper atmosphere has been the focal point of diverse studies, exhibiting a pronounced dependence on the specific observatory site. Furthermore, it is well established that CNa varies across multiple timescales, including hours, nights, months, seasons, and even several years. As many of the world’s largest telescopes are located in the Atacama Desert in northern Chile, our objective is to provide CNa statistics pertinent to this specific region. Methods. We used telemetry data from the AO systems operational at the Paranal Observatory (24.6°S, 70.4°W): Ground Atmospheric Layer Adaptive Corrector for Spectroscopic Imaging (GALACSI) and Ground layer Adaptive Optics system Assisted by Lasers (GRAAL). We combined these data with measurements from two space instruments: SCanning Imaging Absorption Spectrometer for Atmospheric CHartographY (SCIAMACHY) and Optical Spectrograph and Infrared Imaging System (OSIRIS), as well as with simulated data from the Whole Atmosphere Community Climate Model (WACCM). We carefully analysed and compared these datasets to develop a statistical model for the temporal variations of CNa. Results. We validated the use of the AO telemetry data from Paranal systems to retrieve the CNa. The near-continuous measurements encompassing the period from mid-2017 to the end of 2023 facilitated the determination of monthly and yearly abundance and variability of Na in the mesopause region. Throughout the complete years of measurement, the annual and semi-annual variations exhibit consistent characteristics that align with previously documented findings in atmospheric studies. Through meticulous comparison and the fitting of various long-term datasets, we formulated a model depicting the evolution of CNa over time. The validity of our data processing and model is scrutinised, and the results obtained for the Paranal latitude exhibit noteworthy concordance with the findings of other studies.

HATS-38 b and WASP-139 b Join a Growing Group of Hot Neptunes on Polar Orbits* * Based on observations made with the ESO telescopes at the La Silla Paranal Observatory under program ID 111.24VT.001, 111.24VT.002, and 112.25W1.001.

We constrain the sky-projected obliquities of two low-density hot Neptune planets, HATS-38 b and WASP-139 b, orbiting nearby G and K stars using Rossiter–McLaughlin (RM) observations with VLT/ESPRESSO, yielding λ=−108−16+11 deg and −85.6−4.2+7.7 deg, respectively. To model the RM effect, we use a new publicly available code, ironman, which is capable of jointly fitting transit photometry, Keplerian radial velocities, and RM effects. WASP-139 b has a residual eccentricity e=0.103−0.041+0.050 while HATS-38 b has an eccentricity of e=0.112−0.070+0.072 , which is compatible with a circular orbit given our data. Using the obliquity constraints, we show that they join a growing group of hot and low-density Neptunes on polar orbits. We use long-term radial velocities to rule out companions with masses ∼0.3–50 M J within ∼10 au. We show that the orbital architectures of the two Neptunes can be explained with high-eccentricity migration from ≳2 au driven by an unseen distant companion. If HATS-38 b has no residual eccentricity, its polar and circular orbit can also be consistent with a primordial misalignment. Finally, we perform a hierarchical Bayesian modeling of the true obliquity distribution of Neptunes and find suggestive evidence for a higher preponderance of polar orbits for hot Neptunes compared to Jupiters. However, we note that the exact distribution is sensitive to the choice of priors, highlighting the need for additional obliquity measurements of Neptunes to robustly compare the hot Neptune obliquity distribution to that of Jupiters.

The VISTA Variables in the Vía Láctea eXtended (VVVX) ESO public survey: Completion of the observations and legacy

The ESO public survey VISTA Variables in the V\'ia L\'actea (VVV) surveyed the inner Galactic bulge and the adjacent southern Galactic disk from $2009-2015$. Upon its conclusion, the complementary VVV eXtended (VVVX) survey has expanded both the temporal as well as spatial coverage of the original VVV area, widening it from $562$ to $1700$ sq. deg., as well as providing additional epochs in s $ filters from $2016-2023$. With the completion of VVVX observations during the first semester of 2023, we present here the observing strategy, a description of data quality and access, and the legacy of VVVX. VVVX took sim \,$2000$ hours, covering about 4<!PCT!> of the sky in the bulge and southern disk. VVVX covered most of the gaps left between the VVV and the VISTA Hemisphere Survey (VHS) areas and extended the VVV time baseline in the obscured regions affected by high extinction and hence hidden from optical observations. VVVX provides a deep $JHK_ s $ catalogue of $ point sources, as well as a s $ band catalogue of sim \,$10^7$ variable sources. Within the existing VVV area, we produced a $5D$ map of the surveyed region by combining positions, distances, and proper motions of well-understood distance indicators such as red clump stars, RR Lyrae, and Cepheid variables. In March 2023 we successfully finished the VVVX survey observations that started in 2016, an accomplishment for ESO Paranal Observatory upon 4200 hours of observations for VVV+VVVX. The VVV+VVVX catalogues complement those from the Gaia mission at low Galactic latitudes and provide spectroscopic targets for the forthcoming ESO high-multiplex spectrographs MOONS and 4MOST.

Web Publication of Schmitt’s Map of Southern Germany (1797)—The Projection of the Map Based on Archival Documents and Geospatial Analysis

This work shows the original projection of a 1:57,600 scale map of southern Germany at the end of the 18th century, produced under the direction of Karl-Heinrich von Schmitt (1743–1805). The sections of the map were scanned and georeferenced as part of the MAPIRE project, and the results are publicly available. In the present work, we use contemporary documents, in particular the books of César-Francois Cassini de Thury and manuscript sketches of the map found in the Military Archive of Vienna, to show that the overall projection of the map is identical to that used in Cassini’s survey of France (first half of the 18th century). In the archive, we managed to find the overview sheet on which—in addition to the Paris Cassini coordinate system—the section grid of the Schmitt map was also constructed. This sketch served as the basis for the compilation and copying work, wherein the existing map works and survey sketches were inserted into 197 sections of the Schmitt map. Thus, the map coordinate system can be modeled in GIS systems using the Cassini (or Cassini-Soldner) projection, with the Paris Observatory as the projection origin. The georeferencing accuracy of using the pure Cassini projection is around 1–1.3 km (at the extremes, around 5 km), which is much more inaccurate than the one used in later topographic surveys. It is considered a combined result of the compilation of the different maps, presumably surveyed by graphic triangulation with measuring tables.

On the Pair-instability Supernova Origin of J1010+2358* * Based on observations made with the Very Large Telescope (VLT) of the ESO at the La Silla Paranal Observatory under the program ID 112.26WJ.001

The first (Population III) stars formed only out of H and He and were likely more massive than present-day stars. Massive Population III stars in the range 140–260 M ⊙ are predicted to end their lives as pair-instability supernovae (PISNe), enriching the environment with a unique abundance pattern, with high ratios of odd to even elements. Recently, the most promising candidate for a pure descendant of a zero-metallicity massive PISN (260 M ⊙) was discovered by the LAMOST survey, the star J1010+2358. However, key elements to verify the high PISN contribution, C and Al, were missing from the analysis. To rectify this, we obtained and analyzed a high-resolution Very Large Telescope/UVES spectrum, correcting for 3D and/or non-local thermodynamic equilibrium effects. Our measurements of both C and Al give much higher values (∼1 dex) than expected from a 260 M ⊙ PISN. Furthermore, we find significant discrepancies with the previous analysis and therefore a much less pronounced odd–even pattern. Our results show that J1010+2358 cannot be a pure descendant of a 260 M ⊙ PISN. Instead, we find that the best-fit model consists of a 13 M ⊙ Population II core-collapse supernova combined with a Population III supernova. Alternative, less favored solutions ( χ2/χbest2≈2.3 ) include a 50% contribution from a 260 M ⊙ PISN or a 40% contribution from a Population III Type Ia supernova. Ultimately, J1010+2358 is certainly a unique star giving insights into the earliest chemical enrichment; however, this star is not a pure PISN descendant.

Integral field spectroscopy supports atmospheric optics to reveal the finite outer scale of the turbulence

The spatial coherence wavefront outer scale ( characterizes the size of the largest turbulence eddies in Earth's atmosphere, determining low spatial frequency perturbations in the wavefront of the light captured by ground-based telescopes. Advances in adaptive optics (AO) techniques designed to compensate for atmospheric turbulence emphasize the crucial role of this parameter for the next generation of large telescopes. The motivation of this work is to introduce a novel technique for estimating \ from seeing-limited integral field spectroscopic (IFS) data. This approach is based on the impact of a finite \ on the light collected by the pupil entrance of a ground-based telescope. We take advantage of the homogeneity of IFS observations to generate band filter images spanning a wide wavelength range, enabling the assessment of image quality (IQ) at the telescope's focal plane. Comparing the measured wavelength-dependent IQ variation with predictions derived from a first-order analytical approach based on turbulence statistics simplifications using the von Kármán model provides valuable insights into the prevailing \ parameter during the observations. We applied the proposed technique to observations from the Multi-Unit Spectroscopic Explorer (MUSE) in the wide-field mode obtained at the Paranal Observatory. Our analysis successfully validates the first-order analytical expression, which combines the seeing ($ $) and the \ parameters, to predict the IQ variations with the wavelength in ground-based astronomical data. However, we observed some discrepancies between the measured and predictions of the IQ that are analyzed in terms of uncertainties in the estimated $ $ and dome-induced turbulence contributions. This work constitutes the empirical validation of the analytical expression for estimating IQ at the focal plane of ground-based telescopes under specific $ $ and finite \ conditions. Additionally, we provide a simple methodology to characterize the \ and dome-seeing ($ dome $) as by-products of IFS observations routinely conducted at major ground-based astronomical observatories.

Optimising spectroscopic observations of transiting exoplanets

Context. When observing the atmospheres of transiting exoplanets using high-resolution spectroscopy, the aim is to detect well-resolved spectral features with high signal-to-noise ratios (S/Ns), as is possible today with modern spectrographs. However, obtaining such high-quality observations comes with a trade-off: a lower cadence of fewer, longer exposures across the transit collects more photons thanks to reduced overheads, enhancing the S/N of each observation, while a higher cadence of several shorter exposures minimises spectral feature smearing due to the continuously changing radial velocity of the planet. Aims. Considering that maximising S/N and minimising smearing are both beneficial to analysis, there is a need to identify the optimal compromise between the two for a given target. In this work, we aim to establish where this compromise lies for a typical exoplanet transit observation in order to benefit future data collection and subsequent interpretation. Methods. We modelled real transit events based on targets as they would be observed with VLT/CRIRES+ at Paranal Observatory, Chile. Creating four hypothetical scenarios, we simulated each set of transmission spectra across 100 realisations of the same transit event in order to vary the time resolution only. We removed telluric and stellar lines from these data sets using the SYSREM algorithm and analysed them through cross-correlation with model templates, measuring how successfully each time resolution and case detected the planetary signal and exploring how the results vary. Results. We demonstrate that there is a continuous change in the significance of the cross-correlation detection based on the trade-off between high and low time resolutions, and that, averaged over a large number of realisations, the function of this significance has clear maxima. The strength and location of these maxima vary depending on, for example, planet system parameters, instrumentation, and the number of removal iterations. We discuss why observers should therefore take several factors into account using a strategy akin to the ‘exposure triangle’ employed in traditional photography where a balance must be struck by considering the full context of the observation. Our method is robust and may be employed by observers to estimate the best observational strategies for other targets.

A comparison of next-generation turbulence profiling instruments at Paranal

ABSTRACT A six-night optical turbulence monitoring campaign has been carried at Cerro Paranal observatory in 2023 February and March to facilitate the development and characterization of two novel atmospheric site monitoring instruments – the ring-image next-generation scintillation sensor (RINGSS) and 24-h Shack Hartmann image motion monitor (24hSHIMM) in the context of providing optical turbulence monitoring support for upcoming 20–40 m telescopes. Alongside these two instruments, the well-characterized Stereo-SCIDAR and 2016-MASS-DIMM were operated throughout the campaign to provide data for comparison. All instruments obtain estimates of optical turbulence profiles through statistical analysis of intensity and wavefront angle-of-arrival fluctuations from observations of stars. Contemporaneous measurements of the integrated turbulence parameters are compared and the ratios, bias, unbiased root mean square error, and correlation of results from each instrument assessed. Strong agreement was observed in measurements of seeing, free atmosphere seeing, and coherence time. Less correlation is seen for isoplanatic angle, although the median values agree well. Median turbulence parameters are further compared against long-term monitoring data from Paranal instruments. Profiles from the three small-telescope instruments are compared with the 100-layer profile from the stereo-SCIDAR. It is found that the RINGSS and SHIMM offer improved accuracy in characterization of the vertical optical turbulence profile over the MASS-DIMM. Finally, the first results of continuous optical turbulence monitoring at Paranal are presented which show a strong diurnal variation and predictable trend in the seeing. A value of 2.65 arcsec is found for the median daytime seeing.

The Aligned Orbit of the Eccentric Proto Hot Jupiter TOI-3362b* *Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program ID 110.23Y8.004.

High-eccentricity tidal migration predicts the existence of highly eccentric proto hot Jupiters on the “tidal circularization track,” meaning that they might eventually become hot Jupiters, but that their migratory journey remains incomplete. Having experienced moderate amounts of tidal evolution of their orbital elements, proto hot Jupiter systems can be powerful test beds for the underlying mechanisms of eccentricity growth. Notably, they may be used for discriminating between variants of high-eccentricity migration, each predicting a distinct evolution of misalignment between the star and the planet’s orbit. We constrain the spin–orbit misalignment of the proto hot Jupiter TOI-3362b with high-precision radial-velocity observations using ESPRESSO at Very Large Telescope. The observations reveal a sky-projected obliquity ° and constrain the orbital eccentricity to e = 0.720 ± 0.016, making it one of the most eccentric gas giants for which the obliquity has been measured. Although the large eccentricity and the striking orbit alignment of the planet are puzzling, we suggest that ongoing coplanar high-eccentricity migration driven by a distant companion is a possible explanation for the system's architecture. This distant companion would need to reside beyond 5 au at 95% confidence to be compatible with the available radial-velocity observations.

Popularizing precision: cultures of exactness at the Paris observatory, 1667–1742

ABSTRACT This article maps out the lexical landscape of precision from the late seventeenth to the early eighteenth century and investigate the various meanings of precision, both as a word and a concept, within the Paris Observatory and beyond. It argues that precision was first an attribute of instruments supposed to produce numerical measurements, like clocks and divided circles or sectors attached to optical devices. Less often, precision was applied to observers, the handling of instruments, and observational methods, including mathematical corrections applied to raw data. When all these aspects were combined the numerical result finally was also deemed to be precise. Moving to the debate about the shape of the Earth that shook the Academy of Sciences in the 1730s, it follows the way in which wider audiences were conveyed the various meanings of precision. Between the Cartesian resistance to the emergence of a professional science of precision and the pedagogical approach followed by the Newtonians such as Maupertuis, it argues that Cassini III embraced the professionalism of modern science, but did not feel that methodological precision was out of the reach of an educated public. While Maupertuis has seemed content with a discussion focusing on the precision of instruments and results, Cassini III set himself the hefty task of producing an accessible account of precision as a method of inquiry.

Integrated turbulence parameters' estimation from NAOMI adaptive optics telemetry data

Context.Monitoring turbulence parameters is crucial in high-angular resolution astronomy for various purposes, such as optimising adaptive optics systems or fringe trackers. The former systems are present at most modern observatories and will remain significant in the future. This makes them a valuable complementary tool for the estimation of turbulence parameters.Aims.The feasibility of estimating turbulence parameters from low-resolution sensors remains untested. We performed seeing estimates for both simulated and on-sky telemetry data sourced from the new adaptive optics module installed on the four Auxiliary Telescopes of the Very Large Telescope Interferometer.Methods.The seeing estimates were obtained from a modified and optimised algorithm that employs a chi-squared modal fitting approach to the theoretical von Kármán model variances. The algorithm was built to retrieve turbulence parameters while simultaneously estimating and accounting for the remaining and measurement error. A Monte Carlo method was proposed for the estimation of the statistical uncertainty of the algorithm.Results.The algorithm is shown to be able to achieve per-cent accuracy in the estimation of the seeing with a temporal horizon of 20 s on simulated data. A (0.76″ ± 1.2%|stat± 1.2%|sys) median seeing was estimated from on-sky data collected from 2018 to 2020. The spatial distribution of the Auxiliary Telescopes across the Paranal Observatory was found to not play a role in the value of the seeing.

Continuous daytime and nighttime forecast of atmospheric optical turbulence from numerical weather prediction models.

Future satellite-to-ground optical communication systems will benefit from accurate forecasts of atmospheric optical turbulence; namely for site selection, for the routing and the operation of optical links, and for the design of optical communication terminals. This work presents a numerical approach based on the Weather Research and Forecasting software that enables continuous forecast of the refractive index structure parameter, C n2, vertical profiles. Two different C n2 models are presented and compared. One is based on monitoring the turbulent kinetic energy, while the other is a hybrid model using the Tatarskii equation to depict the free atmosphere region, and the Monin-Obukhov similarity theory for describing the boundary layer. The validity of both models is assessed by using thermosonde measurements from the Terrain-induced Rotor Experiment campaign, and from day and night measurements of the coherence length collected during a six-day campaign at Paranal observatory by a Shack-Hartmann Image Motion Monitor. The novelty of this work is the ability of the presented approach to continuously predict optical turbulence both during daytime and nighttime, and its validation with measurements in day and night conditions.

130 years of spectroheliograms at Paris-Meudon observatories (1893–2023)

Broad-band observations of the solar photosphere began in Meudon in 1875 under the auspices of Jules Janssen. For his part, Henri Deslandres initiated imaging spectroscopy in 1892 at Paris observatory. He invented, concurrently with George Hale in Kenwood (USA), but quite independently, the spectroheliograph designed for monochromatic imagery of the solar atmosphere. Deslandres developed two kinds of spectrographs: the ‘ spectrohéliographe des formes’, that is, the narrow bandpass instrument to reveal chromospheric structures; and the ‘ spectrohéliographe des vitesses’, that is, the section spectroheliograph to record line profiles of cross sections of the Sun. This second apparatus was intended to measure the Dopplershifts of dynamic features. Deslandres moved to Meudon in 1898 to build the large quadruple spectroheliograph. The service of Hα and CaII K systematic observations was organized by Lucien d’Azambuja and continues today. The digital technology was introduced in 2002. The collection is one of the longest available: it contains sporadic images from 1893 to 1907 (during the development phase) and systematic observations along 10 solar cycles since 1908. This paper summarizes 130 years of observations, instrumental research and technical advances.

A Census of the TW Hya Association with Gaia* * Based on observations made with the Gaia mission, the Two Micron All Sky Survey, the Wide-field Infrared Survey Explorer, Gemini Observatory, and European Southern Observatory telescopes at La Silla and Paranal Observatories.

I have used high-precision photometry and astrometry from the third data release of Gaia to perform a survey for members of the TW Hya association (TWA). I have identified candidate members that appear to share similar kinematics and ages with bona fide members compiled by Gagné et al. (2017), and I have assessed their membership using radial velocities and spectroscopic diagnostics of age from various sources. My new catalog of adopted members contains 67 Gaia sources in 55 systems. The histogram of spectral types for TWA peaks near M5 (∼0.15 M ⊙), resembling the distributions measured for other nearby young associations. The UVW velocities of its members indicate that the association is expanding. The rate of expansion corresponds to an age of Myr. In a Gaia color–magnitude diagram, the members of TWA exhibit well-defined sequences of single stars and unresolved binary stars. The combined sequence of low-mass stars in TWA is indicative of an age of Myr when compared to the sequence for Upper Centaurus Lupus/Lower Centaurus Crux, for which an age of 20 Myr is assumed. Based on these expansion and isochronal ages, I have adopted an age of 10 ± 2 Myr for TWA. Finally, I have used mid-infrared photometry from the Wide-field Infrared Survey Explorer to check for excess emission from circumstellar disks among the TWA members. Fourteen members have detected disks, all of which have been reported in previous studies. The fraction of members at ≤ M6 (≳0.1 M ⊙) that have full, transitional, or evolved disks is 10/52 = . That value is similar to the fraction previously measured for the Upper Sco association, which is roughly coeval with TWA.

Cândido Baptista de Oliveira and the “Forgotten Memoir”: The First Plan of a National Astronomical Observatory After Brazilian Independence (1822-1831)

Abstract On February 1, 1828, the newspaper Diario Fluminense published in full the Plan for the establishment of an astronomical observatory in the city of Rio de Janeiro. The document was written by the Brazilian mathematician Cândido Baptista de Oliveira and substantiated the approval of the law determining the creation of the future Imperial Astronomical Observatory of Rio de Janeiro (IORJ). This paper discusses the influences embedded within Oliveira’s project, by analyzing the appropriation of different scientific traditions gained during his training as a mathematician at the Observatory of the University of Coimbra and during his studies at French scientific institutions, such as the Polytechnic School and Paris Observatory. I argue that this project had a nationalistic ideal, imbued with the notions of progress and modernity, both effects of the ongoing circulation of people and scientific knowledge during the beginning of the nineteenth century.

Sunspot positions from observations by Flaugergues in the Dalton Minimum

ABSTRACT French astronomer Honoré Flaugergues compiled astronomical observations in a series of handwritten notebooks for 1782–1830, which are preserved at Paris Observatory. We reviewed these manuscripts and encoded the records that contain sunspot measurements into a numerical table for further analysis. All measurements are timings, and we found three types of measurements, allowing the reconstruction of heliographic coordinates. In the first case, the Sun and sunspots cross vertical and horizontal wires; in the second case, one vertical and two mirror-symmetric oblique wires; and in the third case, a rhombus-shaped set of wires. Additionally, timings of two solar eclipses also provided a few sunspot coordinates. As a result, we present the time–latitude (butterfly) diagram of the reconstructed sunspot coordinates, which covers the period of the Dalton Minimum and confirms consistency with those of Derfflinger and Prantner. We identify four solar cycles in this diagram and discuss the observed peculiarities as well as the data reliability.

Uranium Abundances and Ages of r-process Enhanced Stars with Novel U ii Lines* *Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial

The ages of the oldest stars shed light on the birth, chemical enrichment, and chemical evolution of the universe. Nucleocosmochronometry provides an avenue to determining the ages of these stars independent from stellar-evolution models. The uranium abundance, which can be determined for metal-poor r-process enhanced (RPE) stars, has been known to constitute one of the most robust chronometers known. So far, U abundance determination has used a single U ii line at λ3859 Å. Consequently, U abundance has been reliably determined for only five RPE stars. Here, we present the first homogeneous U abundance analysis of four RPE stars using two novel U ii lines at λ4050 Å and λ4090 Å, in addition to the canonical λ3859 Å line. We find that the U ii lines at λ4050 Å and λ4090 Å are reliable and render U abundances in agreement with the λ3859 U abundance, for all of the stars. We, thus, determine revised U abundances for RPE stars, 2MASS J09544277+5246414, RAVE J203843.2–002333, HE 1523–0901, and CS 31082–001, using multiple U ii lines. We also provide nucleocosmochronometric ages of these stars based on the newly derived U, Th, and Eu abundances. The results of this study open up a new avenue to reliably and homogeneously determine U abundance for a significantly larger number of RPE stars. This will, in turn, enable robust constraints on the nucleocosmochronometric ages of RPE stars, which can be applied to understand the chemical enrichment and evolution in the early universe, especially of r-process elements.

The History of Wireless Telegraphy at the Eiffel Tower [Historically Speaking

Long after Gustave Eiffel’s famous tower had been built to celebrate the first century of the Republic, many Parisians were still offended by this <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">tour de fer</i> and sought its removal. Eiffel argued against this, saying that the unique advantages the tower’s elevation offered for scientific research justified its permanence; the height was particularly important for the transmission of the newly discovered Hertzian waves carrying telegraphic signals <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sans fil</i> (without wires). But it was still the age of machines. Steam power and electric lights were common. Vacuum tubes were yet to come. Here we review an array of devices used to generate and detect these invisible waves. With this new mode of communication, ships at sea were no longer bereft of news from distant ports or other ships; the French military posts on distant shores were kept in constant contact. Time signals from the Paris Observatory could be shared with anyone possessing a simple antenna and crystal receiver. Here we look back at the rapidly developing state of the art in antennas and transmitters and the people involved in this exciting era. We summarize the early stages of wireless technology from a French perspective.

Assembly and alignment of the 4-metre multi-object spectroscopic telescope wide field corrector

The 4-metre multi-object spectroscopic telescope (4MOST) is a fiber-fed multi-object spectrograph for the VISTA telescope at the European Southern Observatory (ESO) Paranal Observatory in Chile. The goal of the 4MOST project is to create a general purpose and highly efficient spectroscopic survey facility for astronomers in the 4MOST consortium and the ESO community. The instrument itself will record 2436 simultaneous spectra over a ∼4.2 square deg field of view and consists of an optical wide-field corrector (WFC), a fiber positioner system based on a tilting spine design, and three spectrographs giving both high and low spectral dispersion. The WFC comprises of six lenses grouped into four elements, two of which are cemented doublets that act as an atmospheric dispersion corrector. The first lens element is 0.9 m in diameter while the diameter of the other elements is 0.65 m. For the instrument to meet its science goals, each lens was aligned to be well within ∼100 μm—a major challenge. This was achieved using contact metrology methods supplemented by pencil beam laser probes. In particular, an off-axis laser beam system has been implemented to test the optics’ alignment before and after shipment. This work details the alignment and assembly methods and presents the latest results on the achieved lens positioning and projected performance of the WFC.

Digitization of 20 years of decametric observations of the Sun and Jupiter in Nançay between 1970 and 1990

Since 1970, decametric observations of the Sun and Jupiter have been acquired on a daily basis from the radio observatory of Nançay, France. The resulting database now forms the worldwide largest set of low frequency observations of the Solar Corona between 10 and 100 MHz and of the Jovian magnetosphere between 10 and 40 MHz. The Nançay Decameter Interferometer (NDI), a two-antenna interferometer, acquired pioneer observations from 1970 to 1978, using analog radio receivers tested on the Arecibo giant radiotelescope. The large Nançay Decameter array (NDA), a phased array of 144 helical antennas, was then constructed in the late 1970s as a ground-based support to the Voyager mission and started routine observations in January 1978 in replacement of the NDI, using similar spectrometers. The NDA is still in operation today and its observations, recorded in a digital format since 1990, are public and daily made accessible to the heliospheric and magnetospheric communities at https://www.obs-nancay.fr/reseau-decametrique/. Before 1990, though, the Nançay decametric observations were recorded on analog devices, such as 35-mm films, magnetic tapes and other paper supports, physically archived at the Observatory of Paris, on its site of the Observatory of Meudon, where they could only be accessed on demand. The NDA team recently undertook a multi-year effort to inventory all the Nançay decametric archives, to refurbish and digitize them in order to preserve and promote this historical data collection, most notably by extending the current public database over the 1970–1990 time interval. We digitized the full collection of 35-mm films, corresponding to a total film length of ∼45.5 km, with a specific high resolution scanner. Each roll was scanned by a series of pixel-to-pixel contiguous images recorded in TIF format with adequate metadata and naming convention. The final ∼40 Tb data volume was archived at Paris Astronomical Data Centre and the physical films were refurbished to be archived in a perennial way. We also digitized the associated observations sheets. Finally, we took advantage of this project to also digitize a sample of 35-mm films extracted from four other historical solar data collections hosted at the Observatory of Paris and dealing with two distinct Nançay radiotelescopes and two Lyot heliographs located at the Observatories of Meudon and Haute-Provence. The digitized, documented, Nançay decametric archives have been publicly released to the community in 2020 at http://archives-decametriques.obspm.fr. After having described the instruments, the data collections and the digitization pipeline, this articles ends with a few scientific case studies, focussing on the search for Jupiter-satellite decametric emissions. For instance, the digitized NDA archives suggest the presence of Gan-A and B emissions, while these were first reported in 2018. This work is a concrete example of how historical astronomical measurements can be preserved and archived along the IAU recommendation, to the benefit of the astronomical community.