Vincent Picouet The California Institute of Technology, 1200 E. California Blvd., Pasadena, CA, 91125, USA
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Abstract:
This paper introduces a basic tool at the frontier between an exposure time calculator (ETC) and an instrument model, aiming for broader applicability, with a high level of genericity. Its goal goes slightly beyond the nominal use of traditional ETCs which predict the signal-to-noise ratio (SNR) of a source given some instrument parameter. As others ETC, it estimates the expected SNR and predicts observations to improve the reduction pipeline or adapt detection strategy, but more importantly, it enables analysis of the evolution of the SNR with all the instrument/observation parameters, allowing to examine the instrument efficiency, explore the SNR evolution under different scenarios and run different trade studies. The ETC is linked to an online database to allow any scientist to add their own spectrograph instrument. The current version already encompasses more than 20 instruments, some with several channels or configurations. This tool can be valuable for instrument comparisons and trade-off analysis to either optimize the instrument design or the observation strategy. Despite being a personal initiative with modest resources, it serves as an illustrative example of development simplicity with collaborative database utilization. Observations predictions have been cross-checked with ETC-42 based on several spectrograph designs. This article briefly outlines its development philosophy and role in facilitating trade-off analyses for future instrument developments.
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Keywords: Spectrographs, Astronomical Instruments, Astronomical Observations, Exposure Time Calculator, Simulation, Spectroscopy
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Links: GitHub, Database, Online-ETC
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Exposure Time Calculators (ETCs) are critical tools for optimizing observational strategies in astronomy. Traditionally, these calculators have been tailored to specific instruments, however, there has been some development of universal ETCs capable of accommodating a variety of imagers or spectrographs \citep{ETC42}.
These ETCs are mostly released after the commissioning phase and addressed to observers. In the development phase, instrument builders and scientist usually rely on more or less complex instrument models to optimize their designs or some of their subsystems. Even though this development brings a lot of interesting considerations, it requires significant resources. Creating an initial model during the exploration phase, evolving it into a more complex tool during the instrument development, and finally building an ETC post-commissioning can be resource-intensive, especially for experimental spectrographs or low-budget projects like suborbital missions.
To address these challenges, we present a simple generic tool that can allow to address several of these specific needs bridging some of the gaps between an ETC and an instrument model. This straightforward ETC enables instrument builders to both explore how spectrograph designs influence observations and analyze how some more specific changes in instrument parameters impact the SNR , but also allows observers to optimize their observations strategies when the instrument is finalized.
The ETC offers insights into the evolution of signal and noise contributions, as well as SNR, with respect to various instrument parameters. This not only provides a quick overview of what drives SNR but also highlights potential trade-offs and optimization opportunities. The ETC is designed to accommodate any spectro-imager, and scientists can easily contribute new instruments or configurations via an online database for direct integration with the tool.
In this paper, we describe the ETC's goals, input and output in Section 2 and its deployment philosophy in Section 3. In Section 4 we describe the ETC’s design and architecture. Section 5 describes the FIREBall case, performed to analyze different SNR tradeoffs and optimize the instrument design and observations strategy accordingly. Finally, we discuss our conclusions and potential future developments in Section 6.
Currently, there are two main visualization options: the SNR evolution visualization and an image or cube (integral field units: slicers, fiber IFU, etc) simulation, both capable of accommodating any instruments stored in the database.
These visualizations are dynamic, adjusting to any parameter changes made via the intuitive interface widgets.