The SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars) project aims to detect temperate terrestrial planets transiting nearby ultracool dwarfs, including late M-dwarf stars and brown dwarfs, which are well-suited for atmospheric characterization using the James Webb Space Telescope (JWST) and upcoming giant telescopes like the European Extremely Large Telescope (ELT). Led by the University of Liège, SPECULOOS is conducted in partnership with the University of Cambridge, the University of Birmingham, the Massachusetts Institute of Technology, the University of Bern, and ETH Zurich. The project operates a network of robotic telescopes at two main observatories: SPECULOOS-South in Chile, with four telescopes, and SPECULOOS-North in Tenerife, currently with one telescope (soon to be two). This network is complemented by the SAINT-EX telescope located in San Pedro Mártir, Mexico. In this paper, we review the status of our facilities after five years of operations, the current challenges and development plans, and our latest scientific results.
We present the photometric performance of SPIRIT, a ground-based near-infrared InGaAs CMOS-based instrument (1280 by 1024 pixels, 12 μm pitch), using on-sky results from the SPECULOOS-Southern Observatory during 2022 – 2023. SPIRIT was specifically designed to optimise time-series photometric precision for observing late M and L type stars. To achieve this, a custom wide-pass filter (0.81 – 1.33 μm, zYJ ) was used, which was also designed to minimise the effects of atmospheric precipitable water vapour (PWV) variability on differential photometry. Additionally, SPIRIT was designed to be maintenance-free by eliminating the need for liquid nitrogen for cooling. We compared SPIRIT’s performance with a deeply-depleted (2048 by 2048 pixels, 13.5 μm pitch) CCD-based instrument (using an I+z’ filter, 0.7 – 1.1 μm) through simultaneous observations. For L type stars and cooler, SPIRIT exhibited better photometric noise performance compared to the CCD-based instrument. The custom filter also significantly minimised red noise in the observed light curves typically introduced by atmospheric PWV variability. In SPIRIT observations, the detector’s read noise was the dominant limitation, although in some cases, we were limited by the lack of comparison stars.
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