WST instrument Exposure Time Calculator: full simulation of multi-mode spectrograph performance from source to detector

Matteo Ferro; Matteo Genoni; Henri M. J. Boffin; Jose Schiappacasse-Ulloa; Sofia Randich; Roland Bacon; Vincenzo Mainieri; Alessio Mucciarelli; Carmela Lardo; Michele Moresco; Cristian Vignali; Margherita Talia; Andrea Scaudo; Marco Landoni; Roelof S. de Jong; Olga Bellido-Tirado

arXiv · 2608.00193

WST instrument Exposure Time Calculator: full simulation of multi-mode spectrograph performance from source to detector

Matteo Ferro·Matteo Genoni·Henri M. J. Boffin·Jose Schiappacasse-Ulloa·Sofia Randich·Roland Bacon·Vincenzo Mainieri·Alessio Mucciarelli·Carmela Lardo·Michele Moresco·Cristian Vignali·Margherita Talia·Andrea Scaudo·Marco Landoni·Roelof S. de Jong·Olga Bellido-Tirado

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Abstract

We present a comprehensive Exposure Time Calculator (ETC) developed for the Wide-field Spectroscopic Telescope (WST) concept. The WST, currently in its conceptual phase, is designed as a next-generation large spectroscopic survey facility featuring three complementary observing modes: an Integral Field Spectrograph (IFS) covering 370-930 nm at R of about 4800; a high-resolution Multi-Object Spectrograph (MOS-HR) with four bands at R of about 40000; and a low-resolution Multi-Object Spectrograph (MOS-LR) with four channels at R of about 3800-4900. The ETC simulates the complete photon-propagation path from astronomical source to detector, incorporating wavelength-dependent system throughput (telescope transmission, instrumental optics, detector quantum efficiency), accurate sky background via ESO SkyCalc integration, and a comprehensive noise treatment (photon noise, sky background, read-out noise, dark current). The computational core is implemented as the "pyetc_wst" Python library built on the MPDAF framework, supporting multiple target spectral energy distributions (stellar templates, blackbody, power-law, emission lines, and user-uploaded spectra with arbitrary redshift) and spatial morphologies (point sources and Sersic extended profiles). Four operational modes enable flexible exposure-time optimization. Full spectral outputs include wavelength-dependent signal-to-noise ratio (SNR), source and sky photon counts, noise decomposition by component, and simulated extracted spectra. An interactive web interface, together with a REST API and a command-line tool, complete the user experience and enable batch survey-design workflows.

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Matteo Ferro, Matteo Genoni, Henri M. J. Boffin, Jose Schiappacasse-Ulloa, Sofia Randich, Roland Bacon, Vincenzo Mainieri, Alessio Mucciarelli, Carmela Lardo, Michele Moresco, Cristian Vignali, Margherita Talia, Andrea Scaudo, Marco Landoni, Roelof S. de Jong, Olga Bellido-Tirado. 2026-07-31. WST instrument Exposure Time Calculator: full simulation of multi-mode spectrograph performance from source to detector. https://arxiv.org/abs/2608.00193

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