Update on CASTOR

By / par Patrick Côté (NRC Herzberg Astronomy & Astrophysics Research Centre)
(Cassiopeia – Summer / été 2020)


The 2010 Long Range Plan for Canadian Astronomy identified Canada’s top priorities in space astronomy as “ …significant involvement in the next generation of dark energy missions — ESA`s Euclid, or the NASA WFIRST mission, or a Canadian-led mission, the Canadian Space Telescope.” Since 2011, the Canadian Space Agency (CSA) has been developing a concept for a wide-field, imaging space telescope called CASTOR: The Cosmological Advanced Survey Telescope for Optical and ultraviolet Research. Major CSA-sponsored studies undertaken since that time have included a Space Technology Development Program (STDP) study, from 2014 to 2016, and a Science Maturation Study, carried in 2018-2019. A paper summarizing results from the latter study is currently being prepared for publication, though highlights are available in the community White Paper prepared for the 2020 LRP process. Last month, LRP 2020 recommended CASTOR as Canada’s top priority among space astronomy projects for the 2020s.

Current Design

In the latest design, CASTOR uses a 1-m primary mirror and three-mirror-anastigmat design to deliver Hubble-like image quality (FWHM ~ 0.15”) over a ~0.25 sq. deg. field of view— nearly a hundred times larger than that of Hubble. CASTOR would operate at UV/blue-optical wavelengths using dichroics to image simultaneously in three passbands that span the 0.15-0.55 micron region, thus offering strong synergies with LSST (Rubin Observatory) by providing superior resolution and point-source sensitivity at blue-optical wavelengths, as well as direct access to the UV region. Likewise, CASTOR would complement the Euclid and Roman (formerly WFIRST) space telescopes by ensuring astronomers have access to high-resolution imaging capabilities over the entire UV-optical-IR region. Continued access to the UV/blue-optical region will be especially crucial when HST ceases operations, likely near the end of this decade. In the recent Science Maturation Study, a wide range of scientific opportunities for CASTOR were identified; these include the study of Dark Energy, time domain and multi-messenger astronomy, cosmic star formation, AGN and supermassive black holes, stellar populations in the local universe, the composition of exoplanet atmospheres, and small bodies in the solar system. A Primary Survey, covering more than 7000 sq. deg. to a depth of m(AB) ~ 27 mag, was identified as a potential program with outstanding legacy value, capable of addressing multiple scientific questions simultaneously. In addition, the baseline design includes dispersed imaging in the u and UV channels, and UV multi-slit spectra and high precision photometry in smaller adjacent fields of view. Through a combination of legacy surveys and Guest Observer programs, CASTOR would serve the diverse research needs of the Canadian astronomy community.

Status and Upcoming Activities

Following its strong recommendation in LRP 2020, the CASTOR project is preparing to enter the next stage of development. The CSA is planning to issue a Request for Proposals for a new STDP study that would extend the technical work carried out in 2018 and 2019, focusing on the opto-mechanical design, focal plane array and fine steering system. Negotiations continue with international collaborators, who have contributed significantly to the CASTOR design and science cases in recent years. Prospective partners include India via the Indian Space Research Organization (ISRO), the Jet Propulsion Laboratory via NASA, and a UK team via the UK Space Agency. Outreach and lobbying efforts will be important in the coming months to ensure a development path within Canada that embodies detailed international partnerships and leads to an approved and funded mission.  Members of the community who would like to participate in the next phases of CASTOR development are encouraged to contact Patrick Côté.

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