The WEAVE-TwiLight-Survey: expanding WEAVE’s reach to bright and low-surface-density targets with a novel observing mode

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Abstract
Current-day multi-object spectroscopic surveys are often limited in their ability to observe bright stars due to their low surface densities, resulting in increased observational overheads and reduced efficiency. Addressing this, we have developed a novel observing mode for WEAVE (William Herschel Telescope Enhanced Area Velocity Explorer) that enables efficient observations of low-surface-density target fields without incurring additional overheads from calibration exposures. As a pilot for the new mode, we introduce the WEAVE-TwiLight-Survey (WTLS), focusing on bright exoplanet-host stars and their immediate surroundings on the sky. High observational efficiency is achieved by superimposing multiple low-target-density fields and allocating the optical fibres in this configuration. We use a heuristic method to define fields relative to a central guide star, which serves as a reference for their superposition. Suitable guide fibres for each merged configuration are selected using a custom algorithm. Test observations have been carried out, demonstrating the feasibility of the new observing mode. We show that merged field configurations can be observed with WEAVE using the proposed method. The approach minimizes calibration times and opens twilight hours to WEAVE’s operational schedule. WTLS is built upon the new observing mode and sourced from the ESA PLATO long-duration-phase fields. This survey will result in a homogeneous catalogue of ∼6300 bright stars, including 62 known planet hosts, laying the groundwork for future elemental abundance studies tracing chemical patterns of planetary formation. This new observing mode (WEAVE-Tumble-Less) expands WEAVE’s capabilities to rarely used on-sky time and low-density field configurations without sacrificing efficiency.
Funding Information
  • UK Research and Innovation
  • Science and Technology Facilities Council
  • University of Oxford
  • Nurses Organization of Veterans Affairs
  • Nederlandse Organisatie voor Wetenschappelijk Onderzoek
  • Illinois Arts Council
  • Institut sur la Nutrition et les Aliments Fonctionnels
  • Institut sur la Nutrition et les Aliments Fonctionnels
  • Ministerio de Ciencia, Innovación y Universidades (PID2023-153342NB-I00)
  • European Commission (101072454)
  • H2020 European Research Council (835087)
  • H2020 European Research Council (101020057)
  • Ministerio de Ciencia e Innovación (MICINN RYC2021-032609)
  • H2020 European Research Council (81970599)

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