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Register a new userMonitoring the atmospheric throughput at Cerro Tololo Inter-American Observatory with aTmCam
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We have built an Atmospheric Transmission Monitoring Camera (aTmCam), which consists of four telescopes and detectors each with a narrow-band filter that monitors the brightness of suitable standard stars. Each narrowband filter is selected to monitor a different wavelength region of the atmospheric transmission, including regions dominated by the precipitable water vapor and aerosol optical depth. The colors of the stars are measured by this multi narrow-band imager system simultaneously. The measured colors, a model of the observed star, and the measured throughput of the system can be used to derive the atmospheric transmission of a site on sub-minute time scales. We deployed such a system to the Cerro Tololo Inter-American Observatory (CTIO) and executed two one-month-long observing campaigns in Oct-Nov 2012 and Sept-Oct 2013. We have determined the time and angular scales of variations in the atmospheric transmission above CTIO during these observing runs. We also compared our results with those from a GPS Water Vapor Monitoring System and find general agreement. The information for the atmospheric transmission can be used to improve photometric precision of large imaging surveys such as the Dark Energy Survey and the Large Synoptic Survey Telescope.
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We present optical UBVRI sky brightness measures from 1992 through 2006. The data are based on CCD imagery obtained with the CTIO 0.9-m, 1.3-m, and 1.5-m telescopes. The B- and V-band data are in reasonable agreement with measurements previously made at Mauna Kea, though on the basis of a small number of images per year there are discrepancies for the years 1992 through 1994. Our CCD-based data are not significantly different than values obtained at Cerro Paranal. We find that the yearly averages of V-band sky brightness are best correlated with the 10.7-cm solar flux taken 5 days prior to the sky brightness measures. This implies an average speed of 350 km/sec for the solar wind. While we can measure an enhancement of the night sky levels over La Serena 10 degrees above the horizon, at elevation angles above 45 degrees we find no evidence that the night sky brightness at Cerro Tololo is affected by artificial light of nearby towns and cities.
The discovery of acceleration and dark energy arguably constitutes the most revolutionary discovery in astrophysics in recent years. Cerro Tololo Inter-American Observatory (CTIO) played a key role in this amazing discovery through three systematic supernova surveys organized by staff astronomers: the Tololo Supernova Program (1986-2000), the Calan/Tololo Project (1989-1993), and the High-Z Supernova Search Team (1994-1998). CTIOs state of the art instruments also were fundamental in the independent discovery of acceleration by the Supernova Cosmology Project (1992-1999). Here I summarize the work on supernovae carried out from CTIO that led to the discovery of acceleration and dark energy and provide a brief historical summary on the use of Type Ia supernovae in cosmology in order to provide context for the CTIO contribution.
FRAM (F/Photometric Robotic Atmospheric Monitor) is a robotic telescope operated at the Pierre Auger Observatory in Argentina for the purposes of atmospheric monitoring using stellar photometry. As a passive system which does not produce any light that could interfere with the observations of the fluorescence telescopes of the observatory, it complements the active monitoring systems that use lasers. We discuss the applications of stellar photometry for atmospheric monitoring at optical observatories in general and the particular modes of operation employed by the Auger FRAM. We describe in detail the technical aspects of FRAM, the hardware and software requirements for a successful operation of a robotic telescope for such a purpose and their implementation within the FRAM system.
The Pierre Auger Observatory is a facility built to detect air showers produced by cosmic rays above 10^17 eV. During clear nights with a low illuminated moon fraction, the UV fluorescence light produced by air showers is recorded by optical telescopes at the Observatory. To correct the observations for variations in atmospheric conditions, atmospheric monitoring is performed at regular intervals ranging from several minutes (for cloud identification) to several hours (for aerosol conditions) to several days (for vertical profiles of temperature, pressure, and humidity). In 2009, the monitoring program was upgraded to allow for additional targeted measurements of atmospheric conditions shortly after the detection of air showers of special interest, e.g., showers produced by very high-energy cosmic rays or showers with atypical longitudinal profiles. The former events are of particular importance for the determination of the energy scale of the Observatory, and the latter are characteristic of unusual air shower physics or exotic primary particle types. The purpose of targeted (or rapid) monitoring is to improve the resolution of the atmospheric measurements for such events. In this paper, we report on the implementation of the rapid monitoring program and its current status. The rapid monitoring data have been analyzed and applied to the reconstruction of air showers of high interest, and indicate that the air fluorescence measurements affected by clouds and aerosols are effectively corrected using measurements from the regular atmospheric monitoring program. We find that the rapid monitoring program has potential for supporting dedicated physics analyses beyond the standard event reconstruction.
In addition to astro-meteorological parameters, such as seeing, coherence time and isoplanatic angle, the vertical profile of the Earths atmospheric turbulence strength and velocity is important for instrument design, performance validation and monitoring, and observation scheduling and management. Here we compare these astro-meteorological parameters as well as the vertical profile itself from a forecast model based on a General Circulation Model from the European Centre for Median range Weather Forecasts and the stereo-SCIDAR, a high-sensitivity turbulence profiling instrument in regular operation at Paranal, Chile. The model is fast to process as no spatial nesting or data manipulation is performed. This speed enables the model to be reactive based on the most up to date forecasts. We find that the model is statistically consistent with measurements from stereo-SCIDAR. The correlation of the median turbulence profile from the model and the measurement is 0.98. We also find that the distributions of astro-meteorological parameters are consistent. We compare contemporaneous measurements and show that the free atmosphere seeing, isoplanatic angle and coherence time have correlation values of 0.64, 0.40 and 0.63 respectively. We show and compare the profile sequences from a large number of trial nights. We see that the model is able to forecast the evolution of dominating features. In addition to smart scheduling, ensuring that the most sensitive astronomical observations are scheduled for the optimum time, this model could enable remote site characterisation using a large archive of weather forecasts and could be used to optimise the performance of wide-field AO system.
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