GroundBIRD is a ground-based cosmic microwave background (CMB) experiment for observing the polarization pattern imprinted on large angular scales (ℓ > 6 ) from the Teide Observatory in Tenerife, Spain. Our primary scientific objective is a precise measurement of the optical depth τ (σ(τ ) ∼ 0.01) to the reionization epoch of the Universe to cross-check systematic effects in the measurements made by previous experiments. GroundBIRD observes a wide sky area in the Northern Hemisphere (∼ 40% of the full sky) while continuously rotating the telescope at a high speed of up to 20 rotations per minute (rpm) to overcome the fluctuations of atmospheric radiation. We have adopted the NbTiN/Al hybrid microwave kinetic inductance detectors (MKIDs) as focal plane detectors. We observe two frequency bands centered at 145 GHz and 220 GHz. The 145 GHz band picks up the peak frequency of the CMB spectrum. The 220 GHz band helps accurate removal of the contamination of thermal emission from the Galactic interstellar dust. The MKID arrays (138 MKIDs for 145GHz and 23 MKIDs for 220GHz) were designed and optimized so as to minimize the contamination of the two-level-system noise and maximize the sensitivity. The MKID arrays were successfully installed in May 2023 after the performance verification tests were performed at a laboratory. GroundBIRD has been upgraded to use the full MKID arrays, and scientific observations are now underway. The telescope is automated, so that all observations are performed remotely. Initial validations, including polarization response tests and observations of Jupiter and the moon, have been completed successfully. We are now running scientific observations.
The QUIJOTE (Q-U-I joint Tenerife) experiment combines the operation of two radio-telescopes and three instruments working in the microwave bands 10–20 GHz, 26–36 GHz and 35–47 GHz at the Teide Observatory, Tenerife, and has already been presented in previous SPIE meetings (Hoyland, R. J. et al, 2012; Rubi˜no-Mart´ın et al., 2012). The Cosmology group at the IAC have designed a new upgrade to the MFI instrument in the band 10–20 GHz. The aim of the QUIJOTE telescopes is to characterise the polarised emission of the cosmic microwave background (CMB), as well as galactic and extra-galactic sources, at medium and large angular scales. This MFI2 will continue the survey at even higher sensitivity levels. The MFI2 project led by the Instituto de Astrof´ısica de Canarias (IAC) consists of five polarimeters, three of them operating in the sub-band 10–15 GHz, and two in the sub-band 15–20 GHz. The MFI2 instrument is expected to be a full two–three times more sensitive than the former MFI. The microwave complex correlator design has been replaced by a simple correlator design with a digital back-end based on the latest Xilinx FPGAs (ZCU111). During the first half of 2019 the manufacture of the new cryostat was completed and since then the opto-mechanical components have been designed and manufactured. It is expected that the cryogenic front-end will be completed by the end of 2022 along with the FPGA acquisition and observing system. This digital system has been employed to be more robust against stray ground-based and satellite interference, having a frequency resolution of 1 MHz
The Tenerife Microwave Spectrometer (TMS) is part of a renewed effort to study and characterize the CMB frequency distribution. The spectrometer is based on a pseudo-correlation architecture with two 10–20 GHz radiometer chains making use of both orthogonal linear polarizations, and will observe in this band with an angular and frequency resolutions of 3° and 1 MHz. The optical arrangement includes two corrugated feedhorns, one facing an internal calibrator to provide a cold reference signal, and the other pointing to the sky through the cryostat window by means of an offset-fed reflector. The optical system provides optimal cross-polarization properties (≤-30 dB) and symmetric beams, with minimum frequency dependence. The readout system is based on a SoC FPGA, providing fast data acquisition, high spectral resolution and stability. We present the current status of the TMS instrument, having described the scientific case of this instrument in the accompanying publication.
The Tenerife Microwave Spectrometer (TMS) is a new 10-20 GHz experiment that will be installed at the Teide Observatory (Tenerife, Spain), next to the QUIJOTE CMB experiment. The main TMS scientific driver is to accurately measure absolute distortions of the sky spectrum in the 10-20 GHz frequency range, with special emphasis on the characterization of the absolute synchrotron monopole from our Galaxy, and the possible deviations of the CMB spectrum from a pure blackbody law. TMS will provide an absolute calibration for the QUIJOTE experiment, and it will also serve as a prototype for future instruments of its type, both ground-based and satellites. Among its new instrumental design is an octave bandwidth high quality cryogenic front-end, a thermally stabilized cold black body and a new design of wide-band Fourier transform spectrometer. The spectrometer will have a resolution of 250 MHz, giving 40 spectrally stable sub-bands.
GroundBIRD is a millimeter-wave telescope to observe the polarization patterns of the cosmic microwave background (CMB). The target science topics are primordial gravitational waves from cosmic inflation and reionization optical depth. Therefore, this telescope is designed to achieve the highest sensitivity at large angular scales, ℓ = 6 - 300. For wide sky observations (~40% full-sky), scanning at a high rotation speed (120°/s) is important to remove atmospheric fluctuations. Microwave kinetic inductance detector (MKID) is utilized with the fast GroundBIRD rotation since its good time response. We have started the commissioning run at the Teide Observatory in the Canary Islands. We report the performance of the telescope, receiver, and data acquisition system, including cooling achievements, observations of astronomical objects, and observations taken during several days ahead of our main survey observations.
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