Thermal Noise Measurements in a Reverberation Chamber

The letter describes the properties of thermal noise measured in an electromagnetic reverberation chamber. The consequences for the detection of weak signals in the presence of the noise are outlined.

Thermal Noise Measurements in a Reverberation Chamber

The letter describes the properties of thermal noise measured in an electromagnetic reverberation chamber. The consequences for the detection of weak signals in the presence of the noise are outlined.

WASP-127b: a misaligned planet with a partly cloudy atmosphere and tenuous sodium signature seen by ESPRESSO

Context. The study of exoplanet atmospheres is essential for understanding the formation, evolution, and composition of exoplanets. The transmission spectroscopy technique is playing a significant role in this domain. In particular, the combination of state-of-the-art spectrographs at low- and high-spectral resolution is key to our understanding of atmospheric structure and composition. Aims. We observed two transits of the close-in sub-Saturn-mass planet, WASP-127b, with ESPRESSO in the frame of the Guaranteed Time Observations Consortium. We aim to use these transit observations to study the system architecture and the exoplanet atmosphere simultaneously. Methods. We used the Reloaded Rossiter-McLaughlin technique to measure the projected obliquity λ and the projected rotational velocity veq ⋅sin(i*). We extracted the high-resolution transmission spectrum of the planet to study atomic lines. We also proposed a new cross-correlation framework to search for molecular species and we applied it to water vapor. Results. The planet is orbiting its slowly rotating host star (veq ⋅sin(i*) = 0.53−0.05+0.07 km s−1) on a retrograde misaligned orbit (λ = −128.41−5.46+5.60 °). We detected the sodium line core at the 9-σ confidence level with an excess absorption of 0.34 ± 0.04%, a blueshift of 2.74 ± 0.79 km s−1, and a full width at half maximum of 15.18 ± 1.75 km s−1. However, we did not detect the presence of other atomic species but set upper limits of only a few scale heights. Finally, we put a 3-σ upper limit on the average depth of the 1600 strongest water lines at equilibrium temperature in the visible band of 38 ppm. This constrains the cloud-deck pressure between 0.3 and 0.5 mbar by combining our data with low-resolution data in the near-infrared and models computed for this planet. Conclusions. WASP-127b, with an age of about 10 Gyr, is an unexpected exoplanet by its orbital architecture but also by the small extension of its sodium atmosphere (~7 scale heights). ESPRESSO allows us to take a step forward in the detection of weak signals, thus bringing strong constraints on the presence of clouds in exoplanet atmospheres. The framework proposed in this work can be applied to search for molecular species and study cloud-decks in other exoplanets.

Detection Algorithm for Weak Signals of Multiple Input and Output Radars

In order to detect weak signals generated by multiple-input and output radars, algorithms used for detecting weak signal are to be studied. The target echo model of multiple input and output radars is constructed by the transmit signal model, the target response model and the clutter fluctuation. Then, sparse decomposition is utilized to remove the noise present in the signal. A generalized likelihood ratio algorithm based on the spatial scattering density is used to weight-accumulate the amplitude of the observed echo, resulting in smaller echo amplitude. The influence of the distance resolution unit of SNR and distance resolution unit with clutters on the detection performance of the detector is reduced to complete the detection of weak signals of multiple input and output radars. The experimental results show that the proposed method has strong anti-interference and the accuracy of the detection is extraordinary.