The TolTEC Camera, mounted on the Large Millimeter Telescope (LMT), is a 3-band continuum camera and polarimeter operating at millimeter wavelengths. This paper reviews our progress on the camera commissioning and its inaugural scientific programs, spanning the 2022/2023 commissioning phases and reviewing the winter 2024 science program. We report on mapping speed estimations, optical performance, and the first scientific imaging and polarimetry findings. Additionally, advancements in out-of-focus holography and the integration of two novel maximum likelihood mapmakers are discussed. We conclude with scientific forecasts for the first four TolTEC Legacy Surveys and an overview of the initiatives aimed at facilitating public access to the camera and the broader LMT infrastructure.
MUSCAT is a new 1.1 mm band receiver which was installed on the 50 m Large Millimeter Telescope atop Volc´an Sierra Negra in Puebla, Mexico during the final quarter of 2021 and commissioned on sky throughout 2022. MUSCAT uses a novel cooling chain consisting of a commercial pulse tube cooler, two thermal stages of passively-switched continuous sorption coolers, and a final miniature dilution refrigerator. Through this system MUSCAT achieves a continuous temperature of 120 mK at the focal plane and has shown continuous operation at this temperature for greater than 100 days during readiness testing. Through minimising the amount of helium-3 required, the design on MUSCAT’s cryogenic systems produced a reliable, cost-effective cooling platform. Here we present the cryogenic design and performance of MUSCAT on-sky and compare this to that achieved during deployment-readiness testing at Cardiff (UK). We consider both cooldown time and achieved base temperature. We look at the impact on operation of relocating a pulse-tube cooled instrument from a development lab running on a 50 Hz mains electricity supply to a site running at 60 Hz. Finally, we describe the process of preparing the MUSCAT instrument for shipping and assess the success of this process in terms of remedial work required upon arrival.
The MUSCAT camera is a second-generation continuum camera at the 50-m Large Millimetre Telescope (LMT) operating in the 1.1 mm band, installed in late 2021 and commissioned in early 2022. The instrument’s focal plane has 1458 horn-coupled lumped-element kinetic inductance detectors (LEKIDs) divided into six arrays deposited on three silicon wafers. This work presents the preliminary on-sky performance results of the focal plane obtained during the commissioning campaign. We characterise the detector’s beam size and shape, mapping the point-like source 3C 279 along the focal plane using raster scans, known as beam mapping. It also allows us to identify which resonance frequencies correspond to each detector located in the focal plane, which leads us to a more complete understanding of the behaviour of the detectors, providing us with a reasonable estimation of the array yield. Finally, we compare these results with those obtained during the characterization of the focal plane in the Cardiff laboratory, previously reported in Tapia et al. 2020.
The MUSCAT is a binational collaboration, led by the Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE) and Cardiff University, dedicated to transfer a variety of skills and experience in the development of technologies for the next generation of sub-mm instrumentation. This primary objective includes the capability to design and fabricate LEKID arrays, design and construct optical, mechanical and cryogenic refrigeration systems operating at temperatures below 150 mK, together with the integration and programming of the readout electronics for multiple detector sub-arrays. The successful development and testing of MUSCAT has provided the Large Millimeter Telescope (LMT) with a large-format millimeter-wavelength camera and a versatile cryogenic platform that can be easily modified to allow the installation of alternative continuum or on-chip spectrometer arrays using different optics, filtering, detector geometries, materials and technologies that can operate at different frequencies.
MUSCAT is a new platform for mm/sub-mm astronomy at the 50m LMT. It is currently configured for 1.1 mm continuum observations with a focal plane consisting of 1458 feedhorn-coupled LEKIDs read out over six frequency division multiplexed RF readout chains with ~250 detectors per readout. We present the performance of the detector readout and tuning system following the initial on-sky commissioning campaign in late 2021. We give details of the readout hardware, the instrument control software, the interfaces between the instrument and telescope control systems, and the automated tuning system for maintaining background-limited performance over the course of an observing night given the varying atmospheric load.
The Mexico-UK Submm Camara for Astronomy (MUSCAT) is a 1.1 mm receiver comprising 1458 Horn-Coupled Lumped Element Kinetic Inductance Detectors (LEKIDs) built through a collaborative effort led by Cardiff University in the UK and the Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE) in Mexico. MUSCAT was successfully installed on the 50 m diameter Large Millimeter Telescope (LMT) Alfonso Serrano, in December 2021
Here we provide an overview of the MUSCAT platform and present on-sky engineering tests results from scientific commissioning data.
MUSCAT is a second-generation continuum camera for the Large Millimeter Telescope (LMT) "Alfonso Serrano", to observe at the 1.1 mm atmospheric window. The camera has 1500 background-limited, horn-coupled lumped- element kinetic inductance detectors (LEKIDs) split across six arrays operating at 130-mK. The detector design for MUSCAT is based on a large-volume, double-meander geometry used as the inductive and two-polarization absorbing section of the LEKID resonator. In this paper we present the optical coupling of the meander to a choked waveguide output, the microwave design of the LEKID architecture, the device fabrication process and results demonstrating the detector sensitivity under a range of optical loads. Also presented are the performance of an aluminum absorbing layer used to minimize the optical cross-talk between detectors.
The Mexico-UK Submillimetre Camera for Astronomy (MUSCAT) is the second-generation large-format continuum camera operating in the 1.1 mm band to be installed on the 50-m diameter Large Millimeter Telescope (LMT) in Mexico. The focal plane of the instrument is made up of 1458 horn coupled lumped-element kinetic inductance detectors (LEKID) divided equally into six channels deposited on three silicon wafers. Here we present the preliminary results of the complete characterisation in the laboratory of the MUSCAT focal plane. Through the instrument's readout system, we perform frequency sweeps of the array to identify the resonance frequencies, and continuous timestream acquisitions to measure and characterise the intrinsic noise and 1/f knee of the detectors. Subsequently, with a re-imaging lens and a blackbody point source, the beams of every detector are mapped, obtaining a mean FWHM size of ~3.27 mm, close to the expected 3.1 mm. Then, by varying the intensity of a beam filling blackbody source, we measure the responsivity and noise power spectral density (PSD) for each detector under an optical load of 300 K, obtaining the noise equivalent power (NEP), with which we verify that the majority of the detectors are photon noise limited. Finally, using a Fourier Transform Spectrometer (FTS), we measure the spectral response of the instrument, which indicate a bandwidth of 1.0-1.2 mm centred on 1.1 mm, as expected.
The Mexico-UK Submillimetre Camera for AsTronomy (MUSCAT) is a 1.1 mm receiver consisting of 1,500 lumped-element kinetic inductance detectors (LEKIDs) for the Large Millimeter Telescope (LMT; Volcán Sierra Negra in Puebla, México). MUSCAT utilises the maximum field of view of the LMT's upgraded 50-metre primary mirror and is the first México-UK collaboration to deploy a millimetre/sub-mm receiver on the Large Millimeter Telescope. Using a simplistic simulator, we estimate a predicted mapping speed for MUSCAT by combining the measured performance of MUSCAT with the observed sky conditions at the LMT. We compare this to a previously calculated bolometric-model mapping speed and find that our mapping speed is in good agreement when this is scaled by a previously reported empirical factor. Through this simulation we show that signal contamination due to sky fluctuations can be effectively removed through the use of principle component analysis. We also give an overview
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