arXiv subjects

Laurane Fréour

Publications and source records attributed to Laurane Fréour.

6 recordsLinked to original sources

arXiv2026

The Wide-field Spectroscopic Telescope (WST): design trade-offs for the low-resolution multi-object spectrograph instrument

The Wide-field Spectroscopic Telescope (WST) is a planned 12-meter-class dedicated spectroscopic facility designed to address key scientific challenges through large spectroscopic surveys. This paper presents design and performance trade-offs for the Low-Resolution Multi-Object Spectrograph (MOS-LR) instrument. With a multiplex of 30,000 covering a field of view of 3.1 square degrees, this instrument will provide unprecedented survey efficiency, an order of magnitude beyond those of current facilities. Covering the 370 to 930 nm range at a resolving power of 3,000 with a sky-projected fiber diameter of 1 arcsec, this instrument faces extreme challenges in design, manufacturing, and maintenance. We present a systematic approach to trading off optical and mechanical design options, taking into account constraints such as volume and mass, but also projected availability of detectors and gratings etc.

astro-ph.IM↗

arXiv2026

WST -- Wide-field Spectroscopic Telescope: The Next Leap in Wide-field Spectroscopy

The Wide-field Spectroscopic Telescope (WST) is a concept for a dedicated 12-m spectroscopic survey facility designed to address some of the most important questions in astrophysics in the 2040s. The WST will provide unprecedented spectroscopic survey capabilities by operating simultaneously over a 2-degree diameter field of view with 54 low-resolution spectrographs fed by 30,000 fibres, 8-16 high-resolution spectrographs fed by 2,000 fibres, and a large panoramic low-resolution integral-field spectrograph. Supported by Horizon Europe, the concept study has refined the science cases, facility architecture, operations model, sustainability strategy, and technology roadmap. The resulting reference design demonstrates that the WST is both scientifically transformative and technically feasible, while identifying the developments required to mitigate the remaining risks. The WST is designed as an ESO flagship facility for the post-ELT construction era and a key spectroscopic complement to the major imaging, time-domain, and multi-messenger facilities of the coming decades.

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arXiv2026

Embedding Equity, Diversity, and Inclusion in the WST Collaboration

The proposed Wide-field Spectroscopic Telescope (WST) is a next-generation telescope facility with a 12-meter primary mirror that may be operational in the 2040s. The project has a broad range of scientific goals and engages a large Community of more than 1000 members across multiple time zones, institutions, career stages, and professional roles. As for any large-scale scientific collaboration, building WST is therefore not only a technical and scientific challenge, but also a social and organisational one. This is particularly important in Astronomy and STEM disciplines more broadly, where marginalized groups remain underrepresented, particularly in leadership positions. In this paper, we describe the creation and first year of activity of the WST Equity, Diversity, and Inclusion (EDI) working group. We discuss how the group has worked to embed EDI considerations into the early phases of the Collaboration, and we present our ongoing and future projects aimed at broadening participation, accountability, and community sustainability, while delivering groundbreaking science. We also reflect on the challenges of sustaining EDI work in a large and rapidly evolving collaboration, including recognition of EDI contribution, uneven participation, communication across heterogeneous groups, and the need to connect facility-level initiatives with broader organisational and territorial responsibilities. We present our activities as a situated example of how EDI can be approached as part of the governance, communication, and community infrastructure required to build sustainable research environments.

astro-ph.IM↗

arXiv2026

Robust ellipticity measurements of 29 Galactic globular clusters

Globular clusters (GCs) exhibit varying degrees of flattening (ellipticity), which may provide insight into their internal dynamics and evolution histories. Commonly used methods to measure ellipticity, such as ellipse fitting of density contours and principal component analysis, often produce biased results, especially for clusters that are nearly round or have few observable stars. Using a combination of ground-based and space-based photometry, we investigate the shapes of 29 Galactic GCs. To that end, we test two commonly used methods: an ellipse fit to a kernel density profile and a principal component analysis. We find that both methods suffer from bias arising when the number of stars is small or the cluster is close to round. To solve this issue, we develop a robust method to measure the ellipticity of GCs, test it extensively on mock data, and apply it to the 29 Milky Way GCs in our sample. Using the $V/σ$ diagram used in the isotropic oblate rotator framework, we examine potential causes for the flattening, including rotation and velocity anisotropy. For ten clusters: NGC~104, NGC~1261, NGC~2808, NGC 3201, NGC 5286, NGC 5904, NGC 5986, NGC 6205, NGC 6341, and NGC 7078 we identify a very good agreement between the rotation angle and semi-minor axis of the ellipse, further corroborating the findings that rotation is the main driver of the ellipticity. The $V/σ$ diagram reveals that velocity anisotropy or tides could also be important in shaping the GCs. The robust method developed provides reliable measurements of the ellipticity of GCs, emphasising the importance of taking into account the flattening in theoretical models and simulations. It also offers a promising way to investigate the shapes of multiple stellar populations within GCs, where only small samples are usually available.

astro-ph.GA↗

arXiv2025

A vision for ground-based astronomy beyond the 2030s: How to build ESO's next big telescope sustainably

Astronomy is the study of the Universe and all the objects that it comprises. Our attention is therefore usually focused beyond Earth, home to the only form of life known today. However, how can we continue to explore the secrets of the Universe, if we stand by and watch our only home burn? We know that there is no Planet B. It is therefore urgent that, as astronomers, we collectively work to protect the Earth, allowing future generations the opportunity to continue to uncover the secrets of the cosmos. As astronomical facilities account for the majority of our community's carbon footprint, we propose guidelines that we hold crucial for the European Southern Observatory (ESO) to consider in the context of the Expanding Horizons programme as it plans a next-generation, transformational facility.

astro-ph.IM↗

arXiv2024

Investigating black hole accretion disks as potential polluter sources for the formation of enriched stars in globular clusters

Accretion disks surrounding stellar mass black holes (BHs) have been suggested as potential locations for the nucleosynthesis of light elements, which are our primary observational discriminant of multiple stellar populations within globular clusters. The population of enriched stars in globular clusters are enhanced in N14, Na23, and sometimes in Al27 and/or in K39. In this study, our aim is to investigate the feasibility of initiating nucleosynthesis for these four elements in BH accretion disks, considering various internal parameters such as the temperature of the gas and timescale of the accretion. To achieve this, we employed a 132-species reaction network. We used the slim disk model, suitable for the Super-Eddington mass accretion rate and for geometrically and optically thick disks. We explored the conditions related to the mass, mass accretion rate, viscosity, and radius of the BH-accretion disk system that would allow for the creation of N14, Na23, Al27, and K39 before the gas is accreted onto the central object. Our findings reveal that there is no region in the parameter space where the formation of Na23 can occur and only a very limited region where the formation of N14, Al27, and K39 is plausible. Specifically, this occurs for BHs with masses lower than 10 solar masses, with a preference toward even lower mass values and extremely low viscosity parameters ($α<10^{-3}$). Such values are highly unlikely based on current observations of stellar mass BHs. However, such low mass BHs could actually exist in the early universe, as so-called primordial BHs. In conclusion, our study suggests that the nucleosynthesis within BH accretion disks of four elements of interest for the multiple stellar populations is improbable, but not impossible, using the slim disk model.

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