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Register a new userNear-infrared thermal emissivity from ground based atmospheric dust measurements at ORM
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We present an analysis of the atmospheric content of aerosols measured at Observatorio del Roque de los Muchachos (ORM; Canary Islands). Using a laser diode particle counter located at the Telescopio Nazionale Galileo (TNG) we have detected particles of 0.3, 0.5, 1.0, 3.0, 5.0 and 10.0 um size. The seasonal behavior of the dust content in the atmosphere is calculated. The Spring has been found to be dustier than the Summer, but dusty conditions may also occur in Winter. A method to estimate the contribution of the aerosols emissivity to the sky brightness in the near-infrared (NIR) is presented. The contribution of dust emission to the sky background in the NIR has been found to be negligible comparable to the airglow, with a maximum contribution of about 8-10% in the Ks band in the dusty days.
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Atmosphere is one of the most important noise sources for ground-based cosmic microwave background (CMB) experiments. By increasing optical loading on the detectors, it amplifies their effective noise, while its fluctuations introduce spatial and temporal correlations between detected signals. We present a physically motivated 3d-model of the atmosphere total intensity emission in the millimeter and sub-millimeter wavelengths. We derive a new analytical estimate for the correlation between detectors time-ordered data as a function of the instrument and survey design, as well as several atmospheric parameters such as wind, relative humidity, temperature and turbulence characteristics. Using an original numerical computation, we examine the effect of each physical parameter on the correlations in the time series of a given experiment. We then use a parametric-likelihood approach to validate the modeling and estimate atmosphere parameters from the POLARBEAR-I project first season data set. We derive a new 1.0% upper limit on the linear polarization fraction of atmospheric emission. We also compare our results to previous studies and weather station measurements. The proposed model can be used for realistic simulations of future ground-based CMB observations.
The ESO workshop Ground-based thermal infrared astronomy was held on-line October 12-16, 2020. Originally planned as a traditional in-person meeting at ESO in Garching in April 2020, it was rescheduled and transformed into a fully on-line event due to the COVID-19 pandemic. With 337 participants from 36 countries the workshop was a resounding success, demonstrating the wide interest of the astronomical community in the science goals and the toolkit of ground-based thermal infrared astronomy.
Jupiters banded structure undergoes strong temporal variations, changing the visible and infrared appearance of the belts and zones in a complex and turbulent way due to physical processes that are not yet understood. In this study we use ground-based 5-$mu$m infrared data captured between 1984 and 2018 by 8 different instruments mounted on the Infrared Telescope Facility in Hawaii and on the Very Large Telescope in Chile to analyze and characterize the long-term variability of Jupiters cloud-forming region at the 1-4 bar pressure level. The data show a large temporal variability mainly at the equatorial and tropical latitudes, with a smaller temporal variability at mid-latitudes. We also compare the 5-$mu$m-bright and -dark regions with the locations of the visible zones and belts and we find that these regions are not always co-located, specially in the southern hemisphere. We also present Lomb-Scargle and Wavelet Transform analyzes in order to look for possible periodicities of the brightness changes that could help us understand their origin and predict future events. We see that some of these variations occur periodically in time intervals of 4-8 years. The reasons of these time intervals are not understood and we explore potential connections to both convective processes in the deeper weather layer and dynamical processes in the upper troposphere and stratosphere. Finally we perform a Principal Component analysis to reveal a clear anticorrelation on the 5-$mu$m brightness changes between the North Equatorial Belt and the South Equatorial Belt, suggesting a possible connection between the changes in these belts.
Chopping observations with a tip-tilt secondary mirror have conventionally been used in ground-based mid-infrared observations. However, it is not practical for next generation large telescopes to have a large tip-tilt mirror that moves at a frequency larger than a few Hz. We propose an alternative observing method, a slow-scanning observation. Images are continuously captured as movie data, while the field-of-view is slowly moved. The signal from an astronomical object is extracted from the movie data by a low-rank and sparse matrix decomposition. The performance of the slow-scanning observation was tested in an experimental observation with Subaru/COMICS. The quality of a resultant image in the slow-scanning observation was as good as in a conventional chopping observation with COMICS, at least for a bright point-source object. The observational efficiency in the slow-scanning observation was better than that in the chopping observation. The results suggest that the slow-scanning observation can be a competitive method for the Subaru telescope and be of potential interest to other ground-based facilities to avoid chopping.
The Fluorescence Detector (FD) of the Pierre Auger Observatory provides a nearly calorimetric measurement of the primary particle energy, since the fluorescence light produced is proportional to the energy dissipated by an Extensive Air Shower (EAS) in the atmosphere. The atmosphere therefore acts as a giant calorimeter, whose properties need to be well known during data taking. Aerosols play a key role in this scenario, since their effect on light transmission is highly variable even on a time scale of one hour, and the corresponding correction to EAS energy can range from a few percent to more than 40%. For this reason, hourly Vertical Aerosol Optical Depth (taer(h)) profiles are provided for each of the four FD stations. Starting from 2004, up to now 9 years of taer(h) profiles have been produced using data from the Central Laser Facility (CLF) and the eXtreme Laser Facility (XLF) of the Pierre Auger Observatory. The two laser facilities, the techniques developed to measure taer(h) profiles using laser data and the results will be discussed.
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