Publications (34)10.8 Total impact
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Article: Comparison of the scintillation noise above different observatories measured with MASS instruments
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ABSTRACT: Scintillation noise is a major limitation of ground base photometric precision. An extensive dataset of stellar scintillation collected at 11 astronomical sites world-wide with MASS instruments was used to estimate the scintillation noise of large telescopes in the case of fast photometry and traditional long-exposure regime. Statistical distributions of the corresponding parameters are given. The scintillation noise is mostly determined by turbulence and wind in the upper atmosphere and comparable at all sites, with slightly smaller values at Mauna Kea and largest noise at Tolonchar in Chile. We show that the classical Young's formula under-estimates the scintillation noise.The temporal variations of the scintillation noise are also similar at all sites, showing short-term variability at time scales of 1 -- 2 hours and slower variations, including marked seasonal trends (stronger scintillation and less clear sky during local winter). Some correlation was found between nearby observatories.08/2012; -
Article: Using a Sodar to Measure Optical Turbulence and Wind Speed for the Thirty Meter Telescope Site Testing. Part I: Reproducibility
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ABSTRACT: In this two-part study, we investigate the usefulness of Sodars as part of a large instrument suite for the study of high mountains in the site selection process of the Thirty Meter Telescope (TMT). In this first part, we describe the reproducibility of the measurements and the comparability of results from different sites for data taken with two complementary Sodar models: the XFAS and SFAS models manufactured by Scintec Inc. To this end, a cross-calibration campaign was conducted on two of the sites comparing both the wind speeds and the optical turbulence measurements of the different units. The specific set-up conditions and the low atmospheric pressure require us to make a compromise between the amount of data available for statistics and the quality of the data. For the comparison of the wind speed, results from the same models show a systematic difference of 12 and 9% for the XFAS and SFAS, respectively. The scatter between individual measurements, which includes instrumental, set-up and statistical fluctuation contributions, was found to be 21 and 23%. For optical turbulence, the respective values are 6 and 3% for the systematic difference and 46 and 67% for the scatter. These results show that Sodars can be useful tools for astronomical site testing for projects such as the TMT. KeywordsAstronomy–Atmospheric boundary layer–Sodar–Turbulence–Wind speedBoundary-Layer Meteorology 04/2012; 141(2):273-288. · 1.74 Impact Factor -
Article: Using a Sodar to Measure Optical Turbulence and Wind Speed for the Thirty Meter Telescope Site Testing. Part II: Comparison with Independent Instruments
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ABSTRACT: In the second part of this study, we compare both the wind speed and turbulence given by the Sodars with independent sets of measurements. In the case of the wind speed we compare the lowest Sodar data bin with a sonic anemometer located on a 7-m tower. The agreement between the two instruments was convincing with a regression slope near unity. The integrated turbulence measurements of the Sodars are compared with those obtained with a combined multi-aperture scintillation sensor and differential image motion monitor (MASS/DIMM) unit. It was found that the Sodars are indeed capable of quantitatively measuring optical turbulence, and agree with the MASS/DIMM measurements with a correlation coefficient of approximately 80% and a regression slope within 10% of unity. Additional acoustic noise in the Sodar data was identified using this comparison and removed from the data. KeywordsAstronomy–Atmospheric boundary layer–Sodar–Turbulence–Wind speedBoundary-Layer Meteorology 04/2012; 141(2):289-300. · 1.74 Impact Factor -
Article: Lessons learned from the TMT site testing campaign
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ABSTRACT: After a site testing campaign spanning 5 sites over a period of 5 years, the site selection for the Thirty Meter Telescope (TMT) culminated with the choice of Mauna Kea 13N in Hawaii. During the campaign, a lot practical lessons were learned by our team and these lessons can be shared with current and future site testing campaign done for other observatories. These lessons apply to the preselection of the site, the ground work and operations of the campaign as well as the analysis of the data. We present of selection of such lessons in this paper preceded by a short summary of the TMT site testing activities.01/2011; -
Article: The First Release of the CSTAR Point Source Catalog from Dome A, Antarctica
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ABSTRACT: In 2008 January the 24th Chinese expedition team successfully deployed the Chinese Small Telescope ARray (CSTAR) to DomeA, the highest point on the Antarctic plateau. CSTAR consists of four 14.5cm optical telescopes, each with a different filter (g, r, i and open) and has a 4.5degree x 4.5degree field of view (FOV). It operates robotically as part of the Plateau Observatory, PLATO, with each telescope taking an image every 30 seconds throughout the year whenever it is dark. During 2008, CSTAR #1 performed almost flawlessly, acquiring more than 0.3 million i-band images for a total integration time of 1728 hours during 158 days of observations. For each image taken under good sky conditions, more than 10,000 sources down to 16 mag could be detected. We performed aperture photometry on all the sources in the field to create the catalog described herein. Since CSTAR has a fixed pointing centered on the South Celestial Pole (Dec =-90 degree), all the sources within the FOV of CSTAR were monitored continuously for several months. The photometric catalog can be used for studying any variability in these sources, and for the discovery of transient sources such as supernovae, gamma-ray bursts and minor planets. Comment: 1 latex file and 9 figures The paper is accepted by PASP01/2010; -
Article: The sky brightness and transparency in i-band at Dome A, Antarctica
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ABSTRACT: The i-band observing conditions at Dome A on the Antarctic plateau have been investigated using data acquired during 2008 with the Chinese Small Telescope ARray. The sky brightness, variations in atmospheric transparency, cloud cover, and the presence of aurorae are obtained from these images. The median sky brightness of moonless clear nights is 20.5 mag arcsec^{-2} in the SDSS $i$ band at the South Celestial Pole (which includes a contribution of about 0.06 mag from diffuse Galactic light). The median over all Moon phases in the Antarctic winter is about 19.8 mag arcsec^{-2}. There were no thick clouds in 2008. We model contributions of the Sun and the Moon to the sky background to obtain the relationship between the sky brightness and transparency. Aurorae are identified by comparing the observed sky brightness to the sky brightness expected from this model. About 2% of the images are affected by relatively strong aurorae.01/2010; -
Article: Four years of optical turbulence monitoring at the Cerro Tololo Inter-American Observatory (CTIO)
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ABSTRACT: The optical turbulence conditions as measured between 2004 until end of 2008 above Cerro Tololo, their seasonal as well as nocturnal behavior are presented. A comparison with the MASS-DIMM system of the Thirty Meter Telescope site testing was conducted and identifies an artificially increased seeing component in the data collected by the CTIO DIMM system under northerly winds. Evidence is shown that this increased turbulence is caused by the telescope dome. A correction for this effect is attempted and applied to the CTIO DIMM data. The MASS data of this comparison campaign allow to set constraints on the general assumption of uniform turbulent layers above a site. Comment: 30 pages, 10 figures, accepted for publication in PASP06/2009; -
Article: Thirty Meter Telescope Site Testing VI: Turbulence Profiles
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ABSTRACT: The results on the vertical distribution of optical turbulence above the five mountains which were investigated by the site testing for the Thirty Meter Telescope (TMT) are reported. On San Pedro Martir in Mexico, the 13 North site on Mauna Kea and three mountains in northern Chile Cerro Tolar, Cerro Armazones and Cerro Tolonchar, MASS-DIMM turbulence profilers have been operated over at least two years. Acoustic turbulence profilers - SODARs - were also operated at these sites. The obtained turbulence profiles indicate that at all sites the lowest 200m are the main source of the total seeing observed, with the Chilean sites showing a weaker ground layer than the other two sites. The two northern hemisphere sites have weaker turbulence at altitudes above 500m, with 13N showing the weakest 16km turbulence, being responsible for the large isoplanatic angle at this site. The influence of the jetstream and wind speeds close to the ground on the clear sky turbulence strength throughout the atmosphere are discussed, as well as seasonal and nocturnal variations. This is the sixth article in a series discussing the TMT site testing project.05/2009; -
Article: Thirty Meter Telescope Site Testing I: Overview
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ABSTRACT: As part of the conceptual and preliminary design processes of the Thirty Meter Telescope (TMT), the TMT site testing team has spent the last five years measuring the atmospheric properties of five candidate mountains in North and South America with an unprecedented array of instrumentation. The site testing period was preceded by several years of analyses selecting the five candidates, Cerros Tolar, Armazones and Tolonchar in northern Chile; San Pedro Martir in Baja California, Mexico and the 13 North (13N) site on Mauna Kea, Hawaii. Site testing was concluded by the selection of two remaining sites for further consideration, Armazones and Mauna Kea 13N. It showed that all five candidates are excellent sites for an extremely large astronomical observatory and that none of the sites stands out as the obvious and only logical choice based on its combined properties. This is the first article in a series discussing the TMT site testing project.05/2009; -
Article: Astronomical Telescopes and Instrumentation: Synergies Between Ground and Space
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ABSTRACT: Seeing stability is an important criterion of site characterization. Two sites, with the same seeing statistics, could in principle differ in their temporal stability and hence have their observatories perform differently. Temporal variability can, however, be defined in several ways, all of which may determine the performance of the observatories in different manner. In this paper, we propose three methods to measure variability each focusing on different applications: Selection (maximization of observation time), Image quality (seeing variation within a given integration time) and finally Scheduling (prediction of seeing fluctuation on a given time scale). We apply these methods to the seeing of the TMT candidate sites to determine their stability properties.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.08/2008; -
Article: Astronomical Telescopes and Instrumentation: Synergies Between Ground and Space
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ABSTRACT: One of the main tools used in the TMT site testing campaign is the turbulence profiler MASS. We describe empirical investigations and a side by side comparison of two MASS systems which were performed in order to identify the accuracy of MASS turbulence data and its dependence on the instrument calibration. The accuracy of the total seeing delivered by the TMT MASS systems is found to be better than 0"05. The combination of MASS and DIMM allows to observe the seeing within the first few hundred meters of the atmosphere and can be used to investigate possible correlations with meteorological parameters measured close to the ground. We also compare the detection of clouds and cirrus by means of MASS data (LOSSAM method) with measurements of the thermal emission of clouds using a net radiation sensor. These methods are compared with the visual cloud detection using all sky cameras.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.08/2008; -
Article: Study on the precision of the multiaperture scintillation sensor turbulence profiler (MASS) employed in the site testing campaign for the Thirty Meter Telescope.
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ABSTRACT: The multiaperture scintillation sensor (MASS) has become a device widely employed to measure the altitude distribution of atmospheric turbulence. An empirical study is reported that investigates the dependence of the MASS results on the knowledge of the instrumental parameters. Also, the results of a side-by-side comparison of two MASS instruments are presented, indicating that MASS instruments permit measurements of the integrated seeing to a precision better than 0.05 arc sec and of the individual turbulence layer strength C(n)(2)(h)dh to better than 10(-14) m(1/3).Applied Optics 06/2008; 47(14):2610-8. · 1.41 Impact Factor -
Article: Sampling the ground layer of the atmosphere at Dome C using fast sonic-anemometers
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ABSTRACT: The ground layer turbulence at Dome C is the cause for more than 90% of the total turbulence column. While the height of this layer has been currently measured to be approximately 30m, no long term statistics is available from this part of the atmosphere. In order to plan the construction of future telescope at this site temperature site, temperature, wind speed and turbulence measurements are also necessary. Using fast sonicanemometers we present, a preliminary set of data covering January to October 2007 sampling these quantities at heights of 8, 16 and 28 meters.01/2008; 7012. -
Article: Telescope and instrument robotization at Dome C
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ABSTRACT: This article reviews the situation for robotization of telescopes and instruments at the Antarctic station Concordia on Dome C. A brain-storming meeting was held in Tenerife in March 2007 from which this review emerged.We describe and summarize the challenges for night-time operations of various astronomical experiments at conditions “between Earth and Space” and conclude that robotization is likely a prerequisite for continuous astronomical data taking during the 2000-hour night at Dome C. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)Astronomische Nachrichten 06/2007; 328(6):451 - 474. · 1.01 Impact Factor -
Article: A Search for Propylene Oxide and Glycine in Sagittarius B2 (LMH) and Orion
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ABSTRACT: We have used the Mopra Telescope to search for glycine and the simple chiral molecule propylene oxide in the Sgr B2 (LMH) and Orion KL, in the 3-mm band. We have not detected either species, but have been able to put sensitive upper limits on the abundances of both molecules. The 3-sigma upper limits derived for glycine conformer I are 3.7 x 10^{14} cm^{-2} in both Orion-KL and Sgr B2 (LMH), comparable to the reported detections of conformer I by Kuan et al. However, as our values are 3-sigma upper limits rather than detections we conclude that this weighs against confirming the detection of Kuan et al. We find upper limits for the glycine II column density of 7.7 x 10^{12} cm^{-2} in both Orion-KL and Sgr B2 (LMH), in agreement with the results of Combes et al. The results presented here show that glycine conformer II is not present in the extended gas at the levels detected by Kuan et al. for conformer I. Our ATCA results (Jones et al.) have ruled out the detection of glycine (both conformers I and II) in the compact hot core of the LMH at the levels reported, so we conclude that it is unlikely that Kuan et al. have detected glycine in either Sgr B2 or Orion-KL. We find upper limits for propylene oxide abundance of 3.0 x 10^{14} cm^{-2} in Orion-KL and 6.7 x 10^{14} cm^{-2} in Sgr B2 (LMH). We have detected fourteen features in Sgr B2 and four features in Orion-KL which have not previously been reported in the ISM, but have not be able to plausibly assign these transitions to any carrier.03/2007; -
Conference Proceeding: Site testing Dome A, Antarctica
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ABSTRACT: Recent data have shown that Dome C, on the Antarctic plateau, is an exceptional site for astronomy, with atmospheric conditions superior to those at any existing mid-latitude site. Dome C, however, may not be the best site on the Antarctic plateau for every kind of astronomy. The highest point of the plateau is Dome A, some 800 m higher than Dome C. It should experience colder atmospheric temperatures, lower wind speeds, and a turbulent boundary layer that is confined closer to the ground. The Dome A site was first visited in January 2005 via an overland traverse, conducted by the Polar Research Institute of China. The PRIC plans to return to the site to establish a permanently manned station within the next decade. The University of New South Wales, in collaboration with a number of international institutions, is currently developing a remote automated site testing observatory for deployment to Dome A in the 2007/8 austral summer as part of the International Polar Year. This self-powered observatory will be equipped with a suite of site testing instruments measuring turbulence, optical and infrared sky background, and sub-millimetre transparency. We present here a discussion of the objectives of the site testing campaign and the planned configuration of the observatory.SPIE Astronomical Instrumentation, Orlando, FL; 07/2006 -
Article: Model of optical turbulence profile at Cerro Pachón
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ABSTRACT: New measurements of optical turbulence profile at the Cerro Pachón observatory in Chile are analysed jointly with previously published data to model the variations of the intensity and thickness of the ground layer and free atmosphere under a variety of observing conditions. This work is motivated by the need to predict statistically the performance of ground-layer adaptice optics. We find that the ground-layer profile can be represented by a decaying exponent with a scale height of 20–40 m, increasing to 100 m under bad conditions. The zone from 6 to 500 m contributes typically about 61 per cent to the total integral, the latter causing a median seeing of 0.77 arcsec. Turbulence integrals in the ground layer and in free atmosphere vary independently of each other, in 50 per cent of cases they deviate by less than 1.8 times from their respective median values. The existence of periods with low turbulence in the free atmosphere and their importance for adaptive optics is stressed.Monthly Notices of the Royal Astronomical Society 01/2006; 365(4):1235 - 1242. · 4.90 Impact Factor -
Article: Daytime site testing at Dome C: Results of 2003 2004 campaign
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ABSTRACT: We present results of daytime site testing at Dome C in summer 2003 2004. Daytime seeing has been monitored during 2 1/2 months using a DIMM on the bright star Canopus, giving median value of 0.54 arcsec. An every-day best seeing period has been observed around 5 pm with seeing around 0.3 arcsec. First isoplanatic angle measurements, based on stellar scintillation, were also performed during the month of January 2004, and have given median value of 6.8 arcsec.EAS Publications Series 01/2005; 14:13-18. -
Article: Aa 400, 1163--1172 (2003)
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ABSTRACT: To investigate the low-atmosphere turbulence at the South Pole, we have measured, using a SODAR, the temperature fluctuation constant (C T ) during winter, as a function of altitude up to 890 m. We found that the turbulence was on average concentrated inside a boundary layer sitting below 270 m. While at the peak of winter the turbulence was stable and clearly bounded, during other seasons there was a more complex turbulence profile which extended to higher altitudes. We found that this behaviour could be explained by the horizontal wind speed conditions whose altitude profile closely matched the turbulence profile. We also observed the presence of a vertical wind velocity change of direction at an altitude range corresponding to the turbulent region. The turbulence gives rise to an average seeing of 1.73 ## , which compares poorly with the best astronomy sites.06/2003; -
Article: Some Antarctic Site Testing Results
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ABSTRACT: Observing conditions at the South Pole have probably been better characterized than at any other site on earth. The benefits are now well established, and include greatly reduced near- and mid-infrared sky brightness, improved atmospheric transmission, and a unique atmospheric turbulence profile with almost zero turbulence above the lowest 200 meters of the atmosphere. We will review these findings, and discuss their implications for the science goals of an IR telescope. The site testing work is continuing, with a view to better understanding the residual infrared sky emission and the nature of the atmospheric turbulence. Autonomous experiments are now also currently operating at Dome C. Plans are well advanced to extend these experiments, and to study even higher altitude sites such as Vostok and Dome A.05/2002; -1:19.
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2006–2007
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California Institute of Technology
Pasadena, CA, USA
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