Narrow Results

We have constructed a five station 12 GHz atmospheric phase interferometer (API) for the Submillimeter Array (SMA) located near the summit of Mauna Kea, Hawaii. Operating at the base of unoccupied SMA antenna pads, each station employs a commercial low noise mixing block coupled to a 0.7 m off-axis satellite dish which receives a broadband, white noise-like signal from a geostationary satellite. The signals are processed by an analog correlator to produce the phase delays between all pairs of stations with projected baselines ranging from 33–261 m. Each baseline's amplitude and phase is measured continuously at a rate of 8 kHz, processed, averaged and output at 10 Hz. Further signal processing and data reduction is accomplished with a Linux computer, including the removal of the diurnal motion of the target satellite. The placement of the stations below ground level with an environmental shield combined with the use of low temperature coefficient, buried fiber optic cables provides excellent system stability. The sensitivity in terms of rms path length is 1.3 microns which corresponds to phase deviations of about 1° of phase at the highest operating frequency of the SMA. The two primary data products are: (1) standard deviations of observed phase over various time scales, and (2) phase structure functions. These real-time statistical data measured by the API in the direction of the satellite provide an estimate of the phase front distortion experienced by the concurrent SMA astronomical observations. The API data also play an important role, along with the local opacity measurements and weather predictions, in helping to plan the scheduling of science observations on the telescope.

Photon counting detector systems on sounding rocket payloads often require interfacing asynchronous outputs with a synchronously clocked telemetry (TM) stream. Though this can be handled with an on-board computer, there are several low cost alternatives including custom hardware, microcontrollers and field-programmable gate arrays (FPGAs). This paper outlines how a TM interface (TMIF) for detectors on a sounding rocket with asynchronous parallel digital output can be implemented using low cost FPGAs and minimal custom hardware. Low power consumption and high speed FPGAs are available as commercial off-the-shelf (COTS) products and can be used to develop the main component of the TMIF. Then, only a small amount of additional hardware is required for signal buffering and level translating. This paper also discusses how this system can be tested with a simulated TM chain in the small laboratory setting using FPGAs and COTS specialized data acquisition products.

Modern radio astronomical facilities are able to detect extremely weak electromagnetic signals not only from the universe but also from man-made radio frequency interference of various origins. These range from wanted signals to unwanted out-of-band emission of radio services and applications to electromagnetic interference produced by all kinds of electronic and electric devices. Energy harvesting wind turbines are not only equipped with electric power conversion hardware but also copious amounts of electronics to control and monitor the turbines. A wind turbine in the vicinity of a radio telescope could therefore lead to harmful interference, corrupting the measured astronomical data. Many observatories seek to coordinate placement of new wind farms with wind turbine manufacturers and operators, as well as with the local planning authorities, to avoid such a situation. In our study, we provide examples as well as guidelines for the determination of the separation distances between wind turbines and radio observatories, to enable a benign co-existence for both.

The proposed calculations entail three basic steps. At first, the anticipated maximum emitted power level based on the European EN 550011 (CISPR, 2015) standard, which applies to industrial devices, is determined. Then secondly, the propagation loss along the path to the radio receiver is computed via a model provided by the international telecommunication union. Finally, the received power is compared to the permitted power limit that pertains in the protected radio astronomical observing band under consideration. This procedure may be carried out for each location around a telescope site, in order to obtain a map of potentially problematic wind turbine positions.

The frequencies of interest for redshifted 21cm observations are heavily affected by terrestrial radio-frequency interference (RFI). We identify the McGill Arctic Research Station (MARS) as a new RFI-quiet site and report its RFI occupancy using 122h of data taken with a prototype antenna station developed for the Array of Long-Baseline Antennas for Taking Radio Observations from the Sub-Antarctic. Using an RFI flagging process tailored to the MARS data, we find an overall RFI occupancy of 1.8% averaged over 20–125MHz. In particular, the FM broadcast band (88–108MHz) is found to have an RFI occupancy of at most 1.6%. The data were taken during the Arctic summer, when degraded ionospheric conditions and an active research base contributed to increased RFI. The results quoted here therefore represent the maximum-level RFI environment at MARS.

Since a few years measurements of the optical turbulence vertical distribution have been done at Mt. Graham with a Generalized Scidar (GS) located at the focus of the 1.75 m Vatican Advance Technological Telescope (VATT). Such a telescope is placed on the summit of Mt. Graham (Arizona) at around 250 m far away from the Large Binocular Telescope (LBT). Thanks to a new technique¹ that we recently proposed based on the GS observations of wide-binaries (30-35 arcsec), measurements of profiles characterized by a vertical resolution as high as 20-30 m in the first 600 m have been also collected. The statistic sample of measurements consists, at present, of 43 nights distributed in different periods of the year. In this contribution we present the main scientific motivations as well as the analysis of this extended survey and new insights into the turbulence characterization achieved so far by this on-going activity.

The Thirty Meter Telescope (TMT) project has undertaken a large program to select the final site for the telescope. Five candidate sites were selected in Chile, Mexico and Hawaii for testing, and a site testing station was erected on each mountain. The site testing station consists of an extensive suite of instruments that operate robotically on each of the candidate sites. The systems are all monitored and the data archived to a central server system. Testing began in April, 2003, and each site testing station was installed for at least three years. The project is now nearing completion, with the final site selection decision scheduled for mid-2009.

The Thirty Meter Telescope Project has been testing several mountains in Chile, Mexico and Hawaii to determine the eventual placement of the telescope. The site testing project has operated for several years, and employed a variety of methods to measure the suitability of each of the sites. Here, we discuss the calibration of instruments and methods and some top level results from the candidate sites.

The characterization of the optical turbulence (OT) done with meso-scale models for astronomical applications is an alternative approach to this science that intrinsically presents some interesting and complementary features/advantages with respect to the characterization done with measurements.

The most important advantages are namely: (1) the possibility to describe a 3D map of the in a region around a telescope, (2) the possibility to forecast the optical turbulence i.e. to know with some hours in advance the state of the turbulence conditions above an astronomical site and (3) the possibility to perform a climatology of the optical turbulence extended over decades. No other tool of investigation with comparable potentialities can be figured out at present to achieve these 3 scientific goals.

The forecast of the optical turbulence is a fundamental requirement for the optimization of the management of the scientific programs to be carried out at ground-based telescopes foci. Ground-based astronomy will remain an appealing option for astronomers with respect to the spaced-based one only if the telescopes management will be performed taking advantage of the best turbulence conditions. The future of new ground-based telescopes generation relies therefore upon the success of these studies.

ForOT is a scientific project but even more, it identifies a philosophic approach to studies related to the characterization of the optical turbulence in an astronomical context. In this contribution we will deal about the main success obtained so far in this discipline in the past, the new goals predetermined by ForOT and the main results we obtained so far. To conclude, we will trace a perspective at long time scale indicating where our research is addressed to and how the scientific community and the managers who lead the ground-based astronomical facilities can support our researchers to progress in these studies.

Mesoscale model such as Meso-NH have proven to be highly reliable in reproducing 3D maps of optical turbulence (OT).^1–3 These last years ground-based astronomy has been looking towards Antarctica, especially its summits and the continental plateau where the OT appears to be confined in a shallow layer close to the surface. However some uncertainties remain. That's why our group is focusing on a detailed study of the atmospheric flow and turbulence in the internal Antarctic Plateau. Our intention in this study is to use the Meso-NH model to do predictions of the atmospheric flow in the internal plateau. The use of this model permits us to have access to informations inside an entire 3D volume, which is not the case with observations only. Two different configurations of the model have been used: one with a low horizontal resolution (ΔX = 100 km) and another one with higher horizontal resolution with the help of the grid-nesting interactive technique (ΔX = 1 km in the innermost domain). The impact of the configuration on the meteorological parameters has already been studied.⁴ We present here the results obtained with Meso-Nh of forecasted profiles, surface layer thickness (SLT) and seeing values at Dome C for the 16 winter nights, whose profiles have been measured by Ref.5.

In this contribution we briefly summarize the results recently published in Ref.1.

The atmosphere above three sites on the Internal Antarctic Plateau (Dome A, Dome C and the South Pole) is investigated for astronomical applications using the analysis-data from the ECMWF (European Centre for Medium-Range Weather Forecasts) for an entire year (2005). The monthly median of several meteorological parameters, such as wind speed and potential temperature, are calculated. Radiosoundings from Dome C and the South Pole are used to verify the reliability of the analyses and to study the wind speed in the first 100 m as the analysis-data are not optimized for this altitude-range. The wind speed in the free atmosphere is obtained from the ECMWF-analyses for all three sites. In this context a fourth site, Dome F, is also discussed. In the free atmosphere the stability is studied using the Richardson number, which is an indicator of the probability to trigger thermodynamical instabilities. We find that the free atmosphere over the Internal Antarctic Plateau is more stable than at mid-latitude sites. Dome C shows worse thermodynamic instability conditions than those predicted above the South Pole and Dome A in the same vertical slab. Finally we provide a ranking of the three sites with respect to wind speed, in the free atmosphere (ECMWF analyses) as well as in the surface layer (radiosoundings)

Seismicity induces ground vertical and horizontal displacements that could affect the image quality obtained by telescopes in a similar fashion than atmospheric turbulence. In this work, we study the effect of local seismicity relative to atmospheric turbulence upon the image quality of astronomical observations at El Teide observatory and Roque de los Muchachos observatory, both in the Canary Islands, Spain. Three different aspects of seismicity are studied, namely regional volcanism and seismicity (that is compared with other astronomical sites), seismic noise and possible resonances between seismic noise and the structure of telescopes.

The requirements for excellent image quality of current large and future very large telescopes demand a proper knowledge of atmospheric turbulence. Thus several projects are already pursuing this aim. The precise characterization of the turbulence above a particular site requires long-term monitoring. In this sense, due to the lack of long-term information on turbulence, high-altitude winds (in particular winds at the 200-mbar pressure level, V₂₀₀) have been proposed (Sarazin & Tokovinin 2002,¹ S&T02 hereafter) as a parameter for estimating the total turbulence at a particular site, because records of this parameter exist from several sources. This choice is based on the idea that the greatest source for turbulence generation is related to the highest peak in the vertical wind profile, which is located at the 200-mbar pressure level globally. Moreover, S&T02 found a good correlation between the average velocity of the turbulence, V₀, and V₂₀₀ of the form: V₀= 0.4*V₂₀₀ at the Cerro Pachón and Paranal Observatories in Chile. A linear relationship between V₀ and V₂₀₀ was also found in San Pedro Mártir (Mexico) (Masciadri & Egner 2006,² M&E06 hereafter). We study here the possible connection between V₀ and V₂₀₀ at the Teide Observatory (Spain).

The QiTai radio Telescope (QTT) is a fully steerable Gregorian-type telescope with the main reflector aperture 110 m in diameter. QTT adopts an umbrella support, homology-symmetric lightweight design, and the main reflector is active adjustable through actuators. QTT will operate from 150 MHz to 115 GHz frequency and ultra-wideband receivers and large field-of-view multi-beam receivers will be equipped. A multi-function signal processing system based on RFSoC and GPU processor will be developed. QTT will allow high sensitivity observations on pulsars, spectral line, continuum and Very Long Baseline Interferometer (VLBI) observing modes, and form a world-class observational platform in these areas. This chapter briefly introduces the engineering design and the science goals of QTT.