Gabriel Prieto | Pontificia Universidad Catolica de Chile (original) (raw)

Papers by Gabriel Prieto

Research paper thumbnail of O uso do ultra-som na movimentação dentária induzida

Revista Dental Press De Ortodontia E Ortopedia Facial, 2005

Este trabalho teve por objetivo avaliar histologicamente o mecanismo de remodelação do periodonto... more Este trabalho teve por objetivo avaliar histologicamente o mecanismo de remodelação do periodonto de sustentação dos dentes caninos de cães adultos jovens, sob aplicação de forças ortodônticas com e sem a utilização do ultra-som. Oito cães sem raça definida, de ambos os gêneros, com 1 a 2 anos de idade, pesando de 10 a 15 Kg, receberam uma força de 150g estabelecida por uma mola superelástica, colocada por mesial do primeiro molar superior direito e tracionada até a face distal do canino superior direito. O grupo controle foi constituído por 4 animais e os demais representaram o grupo experimental. Estimulações de ultra-som foram aplicadas nos animais do grupo experimental, durante 20 minutos diários, sobre a região de movimentação dentária, com 200 microssegundos de largura de pulso e 1.000Hz de freqüência de repetição de pulso. Um animal de cada grupo foi sacrificado nos períodos de 7, 14, 21 e 28 dias. Os hemiarcos dentários foram removidos, fixados em solução de Bouin e foram obtidos cortes histológicos com coloração de Hematoxilina e Eosina e Tricrômico de Masson para análise de microscopia óptica. Os aspectos histológicos mostraram-se diferentes entre os dois grupos, sendo que os animais estimulados pelo ultra-som responderam com intensa neoformação vascular e celular no LP e osso alveolar, apresentando maior organização nas fibras colágenas e regularização dos tecidos mineralizados. Estes resultados sugerem que o ultra-som pode ser indicado na estabilização dos dentes de ancoragem, estimulando a neoformação óssea mais rápida em pacientes submetidos à cirurgia ortognática.

Research paper thumbnail of Involvement of Breast Cancer Resistance Protein (BCRP1/ABCG2) in the Bioavailability and Tissue Distribution of trans- Resveratrol in Knockout Mice

Journal of Agricultural and Food Chemistry, 2010

To determine whether multidrugresistance efflux transporters are expressed on immune effector cel... more To determine whether multidrugresistance efflux transporters are expressed on immune effector cells in synovial tissue from patients with rheumatoid arthritis (RA) and compromise the efficacy of methotrexate (MTX) and leflunomide (LEF).

Research paper thumbnail of Completing the Census of (Bright) Variable Stars in Galactic Globular Clusters

We present a long-term project aimed at completing the census of (bright) variable stars in Galac... more We present a long-term project aimed at completing the census of (bright) variable stars in Galactic globular clusters. While our main aim is to obtain a reliable assessment of the populations of RR Lyrae and type II Cepheid stars in the Galactic globular cluster system, due attention is also being paid to other types of variables, including SX Phoenicis stars, long-period variables, and eclipsing binaries.

Research paper thumbnail of Completing the census of (bright) variable stars in galactic globular clusters

We present a long-term project aimed at completing the census of (bright) variable stars in Galac... more We present a long-term project aimed at completing the census of (bright) variable stars in Galactic globular clusters. While our main aim is to obtain a reliable assessment of the populations of RR Lyrae and type II Cepheid stars in the Galactic globular cluster system, due attention is also being paid to other types of variables, including SX Phoenicis stars, long-period variables, and eclipsing binaries.

Research paper thumbnail of A deep near-infrared view of the Galactic globular cluster 2 MASS GC 02

Astronomy & Astrophysics, 2007

Context: We have obtained deep infrared images and K-band spectra of the Galactic globular cluste... more Context: We have obtained deep infrared images and K-band spectra of the Galactic globular cluster 2 MASS GC 02. A variable star search has also been carried out. Aims: Some basic physical properties of the cluster, such as metallicity, reddening, distance modulus and radial velocity, are derived. Methods: These measurements are based on an analysis of the J-Ks versus Ks

Research paper thumbnail of Completing the Census of (Bright) Variable Stars in Galactic Globular Clusters

We present a long-term project aimed at completing the census of (bright) variable stars in Galac... more We present a long-term project aimed at completing the census of (bright) variable stars in Galactic globular clusters. While our main aim is to obtain a reliable assessment of the populations of RR Lyrae and type II Cepheid stars in the Galactic globular cluster system, due attention is also being paid to other types of variables, including SX Phoenicis stars, long-period variables, and eclipsing binaries.

Research paper thumbnail of Completing the census of (bright) variable stars in galactic globular clusters

We present a long-term project aimed at completing the census of (bright) variable stars in Galac... more We present a long-term project aimed at completing the census of (bright) variable stars in Galactic globular clusters. While our main aim is to obtain a reliable assessment of the populations of RR Lyrae and type II Cepheid stars in the Galactic globular cluster system, due attention is also being paid to other types of variables, including SX Phoenicis stars, long-period variables, and eclipsing binaries.

Research paper thumbnail of A deep near-infrared view of the Galactic globular cluster 2 MASS GC 02

Astronomy & Astrophysics, 2007

Context: We have obtained deep infrared images and K-band spectra of the Galactic globular cluste... more Context: We have obtained deep infrared images and K-band spectra of the Galactic globular cluster 2 MASS GC 02. A variable star search has also been carried out. Aims: Some basic physical properties of the cluster, such as metallicity, reddening, distance modulus and radial velocity, are derived. Methods: These measurements are based on an analysis of the J-Ks versus Ks

Research paper thumbnail of Seeing, Wind, and Outer Scale Effects on Image Quality at the Magellan Telescopes

Publications of The Astronomical Society of The Pacific, 2010

We present an analysis of the science image quality obtained on the twin 6.5 metre Magellan teles... more We present an analysis of the science image quality obtained on the twin 6.5 metre Magellan telescopes over a 1.5 year period, using images of ~10^5 stars. We find that the telescopes generally obtain significantly better image quality than the DIMM-measured seeing. This is qualitatively consistent with expectations for large telescopes, where the wavefront outer scale of the turbulence spectrum plays a significant role. However, the dominant effect is found to be wind speed with Magellan outperforming the DIMMs most markedly when the wind is strongest. Excluding data taken during strong wind conditions (>10 m/s), we find that the Magellan telescopes still significantly outperform the DIMM seeing, and we estimate the site to have L_0 ~ 25 m on average. We also report on the first detection of a negative bias in DIMM data. This is found to occur, as predicted, when the DIMM is affected by certain optical aberrations and the turbulence profile is dominated by the upper layers of the atmosphere.

Research paper thumbnail of Comparison of precipitable water vapour measurements made with an optical echelle spectrograph and an infrared radiometer at Las Campanas Observatory

We present simultaneous precipitable water vapour (PWV) measurements made at the Las Campanas Obs... more We present simultaneous precipitable water vapour (PWV) measurements made at the Las Campanas Observatory in late 2007 using an Infrared Radiometer for Millimetre Astronomy (IRMA) and the Magellan Inamori Kyocera Echelle (MIKE) optical spectrograph. Opacity due to water vapour is the primary concern for ground based infrared astronomy. IRMA has been developed to measure the emission of rotational transitions of water vapour across a narrow spectral region centred around 20 μm, using a 0.1 m off-axis parabolic mirror and a sophisticated atmospheric model to retrieve PWV. In contrast, the MIKE instrument is used in conjunction with the 6.5 m Magellan Clay telescope, and determines the PWV through absorption measurements of water vapour lines in the spectra of telluric standard stars. With its high spectral resolution, MIKE is able to measure absorption from optically thin water vapour lines and can derive PWV values using a simple, single layer atmospheric model. In an attempt to improve the MIKE derived PWV measurements, we explore the potential of fitting a series of MIKE water vapour line measurements, having different opacities.

Research paper thumbnail of Support for site testing of the European Extremely Large Telescope: precipitable water vapor over La Silla

The European Southern Observatory (ESO), the Institute for Space Imaging Science (ISIS) and the A... more The European Southern Observatory (ESO), the Institute for Space Imaging Science (ISIS) and the AstroMeteorology group at the Universidad de Valparaiso collaborated on a project to understand the precipitable water vapour (PWV) over the La Silla Paranal Observatory. Both La Silla and Paranal were studied with the goal of using them as reference sites to evaluate potential E-ELT sites. As ground-based infrared astronomy matures, our understanding of the atmospheric conditions over the observatories becomes paramount, specifically water vapour since it is the principle source of atmospheric opacity at infrared wavelengths. Several years of archival optical spectra (FEROS) have been analysed to reconstruct the PWV history above La Silla using an atmospheric radiative transfer model (BTRAM) developed by ISIS. In order to better understand the systematics involved, a dedicated atmospheric water vapour measurement campaign was conducted in May 2009 in close collaboration with Las Campanas observatory and the GMT site testing team. Several methods of determining the water column were employed, including radiosonde launches, continuous measurements by infrared radiometers (IRMA), a compact echelle spectrograph (BACHES) and several high-resolution optical echelle spectrographs (FEROS, HARPS and MIKE). All available observations were compared to concurrent satellite estimates of water vapour in an attempt to ground-truth the satellite data. We present a comparison of the methods used, and results from the archival study and measurement campaign. A mean PWV of 3.4 ± 2.4 mm is found for La Silla using FEROS data covering the period 2005-2009. Important lessons on the strengths and limitations of satellite data are presented. The value of a stand-alone high time resolution PWV monitor has been demonstrated in the context of parallel observations from Las Campanas and La Silla.

Research paper thumbnail of Giant Magellan Telescope site testing: PWV statistics and calibration

Cerro Las Campanas located at Las Campanas Observatory (LCO) in Chile has been selected as the si... more Cerro Las Campanas located at Las Campanas Observatory (LCO) in Chile has been selected as the site for the Giant Magellan Telescope. We report results obtained since the commencement, in 2005, of a systematic site testing survey of potential GMT sites at LCO. Atmospheric precipitable water vapor (PWV) adversely impacts mid-IR astronomy through reduced transparency and increased background. Prior to the GMT site testing effort, little was known regarding the PWV characteristics at LCO and therefore, a multi-pronged approach was used to ensure the determination of the fraction of the time suitable for mid-IR observations. High time resolution monitoring was achieved with an Infrared Radiometer for Millimeter Astronomy (IRMA) from the University of Lethbridge deployed at LCO since September of 2007. Absolute calibrations via the robust Brault method (described in Thomas-Osip et al.1) are provided by the Magellan Inamori Kyocera Echelle (MIKE), mounted on the Clay 6.5-m telescope on a timescale of several per month. We find that conditions suitable for mid-IR astronomy (PWV < 1.5 mm) are concentrated in the southern winter and spring months. Nearly 40% of clear time during these seasons have PWV < 1.5mm. Approximately 10% of these nights meet our PWV requirement for the entire night.

Research paper thumbnail of Giant Magellan Telescope site testing seeing and turbulence statistics

Cerro Las Campanas located at Las Campanas Observatory in Chile has been selected as the site for... more Cerro Las Campanas located at Las Campanas Observatory in Chile has been selected as the site for the Giant Magellan Telescope. We report results obtained since the commencement, in 2005, of a systematic site testing survey of potential GMT sites at LCO. Seeing data have been obtained at three potential sites, and are compared with identical data taken at the site of the twin Magellan 6.5m telescopes. In addition, measurements of the turbulence profile of the free-atmosphere have been collected. Co. Las Camapanas and the Magellan site are nearly identical in their seeing statistics, and apparently their average ground-layer characteristics.

Research paper thumbnail of Giant Magellan Telescope site testing: summary

Cerro Las Campanas located at Las Campanas Observatory (LCO) in Chile has been selected as the si... more Cerro Las Campanas located at Las Campanas Observatory (LCO) in Chile has been selected as the site for the Giant Magellan Telescope. We report results obtained since the commencement, in 2005, of a systematic site testing survey of potential GMT sites at LCO. Meteorological (cloud cover, temperature, pressure, wind, and humidity) and DIMM seeing data have been obtained at three potential sites, and are compared with identical data taken at the site of the twin Magellan 6.5m telescopes. In addition, measurements of the turbulence profile of the free-atmosphere above LCO have been collected with a MASS/DIMM. Furthermore, we consider photometric quality, light pollution, and precipitable water vapor (PWV). LCO, and Co. Las Campanas in particular, have dark skies, little or no risk of future light pollution, excellent seeing, moderate winds, PWV adequate for mid-IR astronomy during a reasonable fraction of the nights, and a high fraction of clear nights overall. Finally, Co. Las Campanas meets or exceeds all the defined science requirements.

Research paper thumbnail of Two campaigns to compare three turbulence profiling techniques at Las Campanas Observatory

In preparation to characterize the Giant Magellan Telescope site and guide the development of its... more In preparation to characterize the Giant Magellan Telescope site and guide the development of its adaptive optics system, two campaigns to systematically compare the turbulence profiles obtained independently with three different instruments were conducted at Las Campanas Observatory in September, 2007 and January 2008. Slope detection and ranging (SLODAR) was used on the 2.5-m duPont telescope. SLODAR measures the C2n profile as a function of altitude through observations of double stars. The separation of the observed double star sets the maximum altitude and height resolution. Ground layer (altitudes < 1 km) and free atmosphere turbulence profiles are compared with those obtained with a lunar scintillometer (LuSci) and a multi-aperture scintillation sensor (MASS), respectively. In addition, the total atmospheric seeing was measured by both SLODAR and a differential image motion monitor (DIMM).

Research paper thumbnail of Giant Magellan Telescope Site Testing Summary

Cerro Las Campanas located at Las Campanas Observatory (LCO) in Chile has been selected as the si... more Cerro Las Campanas located at Las Campanas Observatory (LCO) in Chile has been selected as the site for the Giant Magellan Telescope. We report results obtained since the commencement, in 2005, of a systematic site testing survey of potential GMT sites at LCO. Meteorological (cloud cover, temperature, pressure, wind, and humidity) and DIMM seeing data have been obtained at three potential sites, and are compared with identical data taken at the site of the twin Magellan 6.5m telescopes. In addition, measurements of the turbulence profile of the free-atmosphere above LCO have been collected with a MASS/DIMM. Furthermore, we consider photometric quality, light pollution, and precipitable water vapor (PWV). LCO, and Co. Las Campanas in particular, have dark skies, little or no risk of future light pollution, excellent seeing, moderate winds, PWV adequate for mid-IR astronomy during a reasonable fraction of the nights, and a high fraction of clear nights overall. Finally, Co. Las Campanas meets or exceeds all the defined science requirements.

Research paper thumbnail of Giant Magellan Telescope site evaluation and characterization at Las Campanas Observatory

Las Campanas Observatory has been designated as the location for the Giant Magellan Telescope (GM... more Las Campanas Observatory has been designated as the location for the Giant Magellan Telescope (GMT). We report results obtained since the commencement, in 2005, of a systematic site testing campaign at LCO. Meteorological (cloud cover, temperature, pressure, wind, and ...

Research paper thumbnail of Seeing, Wind, and Outer Scale Effects on Image Quality at the Magellan Telescopes

Publications of The Astronomical Society of The Pacific, 2010

We present an analysis of the science image quality obtained on the twin 6.5 metre Magellan teles... more We present an analysis of the science image quality obtained on the twin 6.5 metre Magellan telescopes over a 1.5 year period, using images of ~10^5 stars. We find that the telescopes generally obtain significantly better image quality than the DIMM-measured seeing. This is qualitatively consistent with expectations for large telescopes, where the wavefront outer scale of the turbulence spectrum plays a significant role. However, the dominant effect is found to be wind speed with Magellan outperforming the DIMMs most markedly when the wind is strongest. Excluding data taken during strong wind conditions (>10 m/s), we find that the Magellan telescopes still significantly outperform the DIMM seeing, and we estimate the site to have L_0 ~ 25 m on average. We also report on the first detection of a negative bias in DIMM data. This is found to occur, as predicted, when the DIMM is affected by certain optical aberrations and the turbulence profile is dominated by the upper layers of the atmosphere.

Research paper thumbnail of Comparison of precipitable water vapour measurements made with an optical echelle spectrograph and an infrared radiometer at Las Campanas Observatory

We present simultaneous precipitable water vapour (PWV) measurements made at the Las Campanas Obs... more We present simultaneous precipitable water vapour (PWV) measurements made at the Las Campanas Observatory in late 2007 using an Infrared Radiometer for Millimetre Astronomy (IRMA) and the Magellan Inamori Kyocera Echelle (MIKE) optical spectrograph. Opacity due to water vapour is the primary concern for ground based infrared astronomy. IRMA has been developed to measure the emission of rotational transitions of water vapour across a narrow spectral region centred around 20 μm, using a 0.1 m off-axis parabolic mirror and a sophisticated atmospheric model to retrieve PWV. In contrast, the MIKE instrument is used in conjunction with the 6.5 m Magellan Clay telescope, and determines the PWV through absorption measurements of water vapour lines in the spectra of telluric standard stars. With its high spectral resolution, MIKE is able to measure absorption from optically thin water vapour lines and can derive PWV values using a simple, single layer atmospheric model. In an attempt to improve the MIKE derived PWV measurements, we explore the potential of fitting a series of MIKE water vapour line measurements, having different opacities.

Research paper thumbnail of Support for site testing of the European Extremely Large Telescope: precipitable water vapor over La Silla

The European Southern Observatory (ESO), the Institute for Space Imaging Science (ISIS) and the A... more The European Southern Observatory (ESO), the Institute for Space Imaging Science (ISIS) and the AstroMeteorology group at the Universidad de Valparaiso collaborated on a project to understand the precipitable water vapour (PWV) over the La Silla Paranal Observatory. Both La Silla and Paranal were studied with the goal of using them as reference sites to evaluate potential E-ELT sites. As ground-based infrared astronomy matures, our understanding of the atmospheric conditions over the observatories becomes paramount, specifically water vapour since it is the principle source of atmospheric opacity at infrared wavelengths. Several years of archival optical spectra (FEROS) have been analysed to reconstruct the PWV history above La Silla using an atmospheric radiative transfer model (BTRAM) developed by ISIS. In order to better understand the systematics involved, a dedicated atmospheric water vapour measurement campaign was conducted in May 2009 in close collaboration with Las Campanas observatory and the GMT site testing team. Several methods of determining the water column were employed, including radiosonde launches, continuous measurements by infrared radiometers (IRMA), a compact echelle spectrograph (BACHES) and several high-resolution optical echelle spectrographs (FEROS, HARPS and MIKE). All available observations were compared to concurrent satellite estimates of water vapour in an attempt to ground-truth the satellite data. We present a comparison of the methods used, and results from the archival study and measurement campaign. A mean PWV of 3.4 ± 2.4 mm is found for La Silla using FEROS data covering the period 2005-2009. Important lessons on the strengths and limitations of satellite data are presented. The value of a stand-alone high time resolution PWV monitor has been demonstrated in the context of parallel observations from Las Campanas and La Silla.

Research paper thumbnail of O uso do ultra-som na movimentação dentária induzida

Revista Dental Press De Ortodontia E Ortopedia Facial, 2005

Este trabalho teve por objetivo avaliar histologicamente o mecanismo de remodelação do periodonto... more Este trabalho teve por objetivo avaliar histologicamente o mecanismo de remodelação do periodonto de sustentação dos dentes caninos de cães adultos jovens, sob aplicação de forças ortodônticas com e sem a utilização do ultra-som. Oito cães sem raça definida, de ambos os gêneros, com 1 a 2 anos de idade, pesando de 10 a 15 Kg, receberam uma força de 150g estabelecida por uma mola superelástica, colocada por mesial do primeiro molar superior direito e tracionada até a face distal do canino superior direito. O grupo controle foi constituído por 4 animais e os demais representaram o grupo experimental. Estimulações de ultra-som foram aplicadas nos animais do grupo experimental, durante 20 minutos diários, sobre a região de movimentação dentária, com 200 microssegundos de largura de pulso e 1.000Hz de freqüência de repetição de pulso. Um animal de cada grupo foi sacrificado nos períodos de 7, 14, 21 e 28 dias. Os hemiarcos dentários foram removidos, fixados em solução de Bouin e foram obtidos cortes histológicos com coloração de Hematoxilina e Eosina e Tricrômico de Masson para análise de microscopia óptica. Os aspectos histológicos mostraram-se diferentes entre os dois grupos, sendo que os animais estimulados pelo ultra-som responderam com intensa neoformação vascular e celular no LP e osso alveolar, apresentando maior organização nas fibras colágenas e regularização dos tecidos mineralizados. Estes resultados sugerem que o ultra-som pode ser indicado na estabilização dos dentes de ancoragem, estimulando a neoformação óssea mais rápida em pacientes submetidos à cirurgia ortognática.

Research paper thumbnail of Involvement of Breast Cancer Resistance Protein (BCRP1/ABCG2) in the Bioavailability and Tissue Distribution of trans- Resveratrol in Knockout Mice

Journal of Agricultural and Food Chemistry, 2010

To determine whether multidrugresistance efflux transporters are expressed on immune effector cel... more To determine whether multidrugresistance efflux transporters are expressed on immune effector cells in synovial tissue from patients with rheumatoid arthritis (RA) and compromise the efficacy of methotrexate (MTX) and leflunomide (LEF).

Research paper thumbnail of Completing the Census of (Bright) Variable Stars in Galactic Globular Clusters

We present a long-term project aimed at completing the census of (bright) variable stars in Galac... more We present a long-term project aimed at completing the census of (bright) variable stars in Galactic globular clusters. While our main aim is to obtain a reliable assessment of the populations of RR Lyrae and type II Cepheid stars in the Galactic globular cluster system, due attention is also being paid to other types of variables, including SX Phoenicis stars, long-period variables, and eclipsing binaries.

Research paper thumbnail of Completing the census of (bright) variable stars in galactic globular clusters

We present a long-term project aimed at completing the census of (bright) variable stars in Galac... more We present a long-term project aimed at completing the census of (bright) variable stars in Galactic globular clusters. While our main aim is to obtain a reliable assessment of the populations of RR Lyrae and type II Cepheid stars in the Galactic globular cluster system, due attention is also being paid to other types of variables, including SX Phoenicis stars, long-period variables, and eclipsing binaries.

Research paper thumbnail of A deep near-infrared view of the Galactic globular cluster 2 MASS GC 02

Astronomy & Astrophysics, 2007

Context: We have obtained deep infrared images and K-band spectra of the Galactic globular cluste... more Context: We have obtained deep infrared images and K-band spectra of the Galactic globular cluster 2 MASS GC 02. A variable star search has also been carried out. Aims: Some basic physical properties of the cluster, such as metallicity, reddening, distance modulus and radial velocity, are derived. Methods: These measurements are based on an analysis of the J-Ks versus Ks

Research paper thumbnail of Completing the Census of (Bright) Variable Stars in Galactic Globular Clusters

We present a long-term project aimed at completing the census of (bright) variable stars in Galac... more We present a long-term project aimed at completing the census of (bright) variable stars in Galactic globular clusters. While our main aim is to obtain a reliable assessment of the populations of RR Lyrae and type II Cepheid stars in the Galactic globular cluster system, due attention is also being paid to other types of variables, including SX Phoenicis stars, long-period variables, and eclipsing binaries.

Research paper thumbnail of Completing the census of (bright) variable stars in galactic globular clusters

We present a long-term project aimed at completing the census of (bright) variable stars in Galac... more We present a long-term project aimed at completing the census of (bright) variable stars in Galactic globular clusters. While our main aim is to obtain a reliable assessment of the populations of RR Lyrae and type II Cepheid stars in the Galactic globular cluster system, due attention is also being paid to other types of variables, including SX Phoenicis stars, long-period variables, and eclipsing binaries.

Research paper thumbnail of A deep near-infrared view of the Galactic globular cluster 2 MASS GC 02

Astronomy & Astrophysics, 2007

Context: We have obtained deep infrared images and K-band spectra of the Galactic globular cluste... more Context: We have obtained deep infrared images and K-band spectra of the Galactic globular cluster 2 MASS GC 02. A variable star search has also been carried out. Aims: Some basic physical properties of the cluster, such as metallicity, reddening, distance modulus and radial velocity, are derived. Methods: These measurements are based on an analysis of the J-Ks versus Ks

Research paper thumbnail of Seeing, Wind, and Outer Scale Effects on Image Quality at the Magellan Telescopes

Publications of The Astronomical Society of The Pacific, 2010

We present an analysis of the science image quality obtained on the twin 6.5 metre Magellan teles... more We present an analysis of the science image quality obtained on the twin 6.5 metre Magellan telescopes over a 1.5 year period, using images of ~10^5 stars. We find that the telescopes generally obtain significantly better image quality than the DIMM-measured seeing. This is qualitatively consistent with expectations for large telescopes, where the wavefront outer scale of the turbulence spectrum plays a significant role. However, the dominant effect is found to be wind speed with Magellan outperforming the DIMMs most markedly when the wind is strongest. Excluding data taken during strong wind conditions (>10 m/s), we find that the Magellan telescopes still significantly outperform the DIMM seeing, and we estimate the site to have L_0 ~ 25 m on average. We also report on the first detection of a negative bias in DIMM data. This is found to occur, as predicted, when the DIMM is affected by certain optical aberrations and the turbulence profile is dominated by the upper layers of the atmosphere.

Research paper thumbnail of Comparison of precipitable water vapour measurements made with an optical echelle spectrograph and an infrared radiometer at Las Campanas Observatory

We present simultaneous precipitable water vapour (PWV) measurements made at the Las Campanas Obs... more We present simultaneous precipitable water vapour (PWV) measurements made at the Las Campanas Observatory in late 2007 using an Infrared Radiometer for Millimetre Astronomy (IRMA) and the Magellan Inamori Kyocera Echelle (MIKE) optical spectrograph. Opacity due to water vapour is the primary concern for ground based infrared astronomy. IRMA has been developed to measure the emission of rotational transitions of water vapour across a narrow spectral region centred around 20 μm, using a 0.1 m off-axis parabolic mirror and a sophisticated atmospheric model to retrieve PWV. In contrast, the MIKE instrument is used in conjunction with the 6.5 m Magellan Clay telescope, and determines the PWV through absorption measurements of water vapour lines in the spectra of telluric standard stars. With its high spectral resolution, MIKE is able to measure absorption from optically thin water vapour lines and can derive PWV values using a simple, single layer atmospheric model. In an attempt to improve the MIKE derived PWV measurements, we explore the potential of fitting a series of MIKE water vapour line measurements, having different opacities.

Research paper thumbnail of Support for site testing of the European Extremely Large Telescope: precipitable water vapor over La Silla

The European Southern Observatory (ESO), the Institute for Space Imaging Science (ISIS) and the A... more The European Southern Observatory (ESO), the Institute for Space Imaging Science (ISIS) and the AstroMeteorology group at the Universidad de Valparaiso collaborated on a project to understand the precipitable water vapour (PWV) over the La Silla Paranal Observatory. Both La Silla and Paranal were studied with the goal of using them as reference sites to evaluate potential E-ELT sites. As ground-based infrared astronomy matures, our understanding of the atmospheric conditions over the observatories becomes paramount, specifically water vapour since it is the principle source of atmospheric opacity at infrared wavelengths. Several years of archival optical spectra (FEROS) have been analysed to reconstruct the PWV history above La Silla using an atmospheric radiative transfer model (BTRAM) developed by ISIS. In order to better understand the systematics involved, a dedicated atmospheric water vapour measurement campaign was conducted in May 2009 in close collaboration with Las Campanas observatory and the GMT site testing team. Several methods of determining the water column were employed, including radiosonde launches, continuous measurements by infrared radiometers (IRMA), a compact echelle spectrograph (BACHES) and several high-resolution optical echelle spectrographs (FEROS, HARPS and MIKE). All available observations were compared to concurrent satellite estimates of water vapour in an attempt to ground-truth the satellite data. We present a comparison of the methods used, and results from the archival study and measurement campaign. A mean PWV of 3.4 ± 2.4 mm is found for La Silla using FEROS data covering the period 2005-2009. Important lessons on the strengths and limitations of satellite data are presented. The value of a stand-alone high time resolution PWV monitor has been demonstrated in the context of parallel observations from Las Campanas and La Silla.

Research paper thumbnail of Giant Magellan Telescope site testing: PWV statistics and calibration

Cerro Las Campanas located at Las Campanas Observatory (LCO) in Chile has been selected as the si... more Cerro Las Campanas located at Las Campanas Observatory (LCO) in Chile has been selected as the site for the Giant Magellan Telescope. We report results obtained since the commencement, in 2005, of a systematic site testing survey of potential GMT sites at LCO. Atmospheric precipitable water vapor (PWV) adversely impacts mid-IR astronomy through reduced transparency and increased background. Prior to the GMT site testing effort, little was known regarding the PWV characteristics at LCO and therefore, a multi-pronged approach was used to ensure the determination of the fraction of the time suitable for mid-IR observations. High time resolution monitoring was achieved with an Infrared Radiometer for Millimeter Astronomy (IRMA) from the University of Lethbridge deployed at LCO since September of 2007. Absolute calibrations via the robust Brault method (described in Thomas-Osip et al.1) are provided by the Magellan Inamori Kyocera Echelle (MIKE), mounted on the Clay 6.5-m telescope on a timescale of several per month. We find that conditions suitable for mid-IR astronomy (PWV < 1.5 mm) are concentrated in the southern winter and spring months. Nearly 40% of clear time during these seasons have PWV < 1.5mm. Approximately 10% of these nights meet our PWV requirement for the entire night.

Research paper thumbnail of Giant Magellan Telescope site testing seeing and turbulence statistics

Cerro Las Campanas located at Las Campanas Observatory in Chile has been selected as the site for... more Cerro Las Campanas located at Las Campanas Observatory in Chile has been selected as the site for the Giant Magellan Telescope. We report results obtained since the commencement, in 2005, of a systematic site testing survey of potential GMT sites at LCO. Seeing data have been obtained at three potential sites, and are compared with identical data taken at the site of the twin Magellan 6.5m telescopes. In addition, measurements of the turbulence profile of the free-atmosphere have been collected. Co. Las Camapanas and the Magellan site are nearly identical in their seeing statistics, and apparently their average ground-layer characteristics.

Research paper thumbnail of Giant Magellan Telescope site testing: summary

Cerro Las Campanas located at Las Campanas Observatory (LCO) in Chile has been selected as the si... more Cerro Las Campanas located at Las Campanas Observatory (LCO) in Chile has been selected as the site for the Giant Magellan Telescope. We report results obtained since the commencement, in 2005, of a systematic site testing survey of potential GMT sites at LCO. Meteorological (cloud cover, temperature, pressure, wind, and humidity) and DIMM seeing data have been obtained at three potential sites, and are compared with identical data taken at the site of the twin Magellan 6.5m telescopes. In addition, measurements of the turbulence profile of the free-atmosphere above LCO have been collected with a MASS/DIMM. Furthermore, we consider photometric quality, light pollution, and precipitable water vapor (PWV). LCO, and Co. Las Campanas in particular, have dark skies, little or no risk of future light pollution, excellent seeing, moderate winds, PWV adequate for mid-IR astronomy during a reasonable fraction of the nights, and a high fraction of clear nights overall. Finally, Co. Las Campanas meets or exceeds all the defined science requirements.

Research paper thumbnail of Two campaigns to compare three turbulence profiling techniques at Las Campanas Observatory

In preparation to characterize the Giant Magellan Telescope site and guide the development of its... more In preparation to characterize the Giant Magellan Telescope site and guide the development of its adaptive optics system, two campaigns to systematically compare the turbulence profiles obtained independently with three different instruments were conducted at Las Campanas Observatory in September, 2007 and January 2008. Slope detection and ranging (SLODAR) was used on the 2.5-m duPont telescope. SLODAR measures the C2n profile as a function of altitude through observations of double stars. The separation of the observed double star sets the maximum altitude and height resolution. Ground layer (altitudes < 1 km) and free atmosphere turbulence profiles are compared with those obtained with a lunar scintillometer (LuSci) and a multi-aperture scintillation sensor (MASS), respectively. In addition, the total atmospheric seeing was measured by both SLODAR and a differential image motion monitor (DIMM).

Research paper thumbnail of Giant Magellan Telescope Site Testing Summary

Cerro Las Campanas located at Las Campanas Observatory (LCO) in Chile has been selected as the si... more Cerro Las Campanas located at Las Campanas Observatory (LCO) in Chile has been selected as the site for the Giant Magellan Telescope. We report results obtained since the commencement, in 2005, of a systematic site testing survey of potential GMT sites at LCO. Meteorological (cloud cover, temperature, pressure, wind, and humidity) and DIMM seeing data have been obtained at three potential sites, and are compared with identical data taken at the site of the twin Magellan 6.5m telescopes. In addition, measurements of the turbulence profile of the free-atmosphere above LCO have been collected with a MASS/DIMM. Furthermore, we consider photometric quality, light pollution, and precipitable water vapor (PWV). LCO, and Co. Las Campanas in particular, have dark skies, little or no risk of future light pollution, excellent seeing, moderate winds, PWV adequate for mid-IR astronomy during a reasonable fraction of the nights, and a high fraction of clear nights overall. Finally, Co. Las Campanas meets or exceeds all the defined science requirements.

Research paper thumbnail of Giant Magellan Telescope site evaluation and characterization at Las Campanas Observatory

Las Campanas Observatory has been designated as the location for the Giant Magellan Telescope (GM... more Las Campanas Observatory has been designated as the location for the Giant Magellan Telescope (GMT). We report results obtained since the commencement, in 2005, of a systematic site testing campaign at LCO. Meteorological (cloud cover, temperature, pressure, wind, and ...

Research paper thumbnail of Seeing, Wind, and Outer Scale Effects on Image Quality at the Magellan Telescopes

Publications of The Astronomical Society of The Pacific, 2010

We present an analysis of the science image quality obtained on the twin 6.5 metre Magellan teles... more We present an analysis of the science image quality obtained on the twin 6.5 metre Magellan telescopes over a 1.5 year period, using images of ~10^5 stars. We find that the telescopes generally obtain significantly better image quality than the DIMM-measured seeing. This is qualitatively consistent with expectations for large telescopes, where the wavefront outer scale of the turbulence spectrum plays a significant role. However, the dominant effect is found to be wind speed with Magellan outperforming the DIMMs most markedly when the wind is strongest. Excluding data taken during strong wind conditions (>10 m/s), we find that the Magellan telescopes still significantly outperform the DIMM seeing, and we estimate the site to have L_0 ~ 25 m on average. We also report on the first detection of a negative bias in DIMM data. This is found to occur, as predicted, when the DIMM is affected by certain optical aberrations and the turbulence profile is dominated by the upper layers of the atmosphere.

Research paper thumbnail of Comparison of precipitable water vapour measurements made with an optical echelle spectrograph and an infrared radiometer at Las Campanas Observatory

We present simultaneous precipitable water vapour (PWV) measurements made at the Las Campanas Obs... more We present simultaneous precipitable water vapour (PWV) measurements made at the Las Campanas Observatory in late 2007 using an Infrared Radiometer for Millimetre Astronomy (IRMA) and the Magellan Inamori Kyocera Echelle (MIKE) optical spectrograph. Opacity due to water vapour is the primary concern for ground based infrared astronomy. IRMA has been developed to measure the emission of rotational transitions of water vapour across a narrow spectral region centred around 20 μm, using a 0.1 m off-axis parabolic mirror and a sophisticated atmospheric model to retrieve PWV. In contrast, the MIKE instrument is used in conjunction with the 6.5 m Magellan Clay telescope, and determines the PWV through absorption measurements of water vapour lines in the spectra of telluric standard stars. With its high spectral resolution, MIKE is able to measure absorption from optically thin water vapour lines and can derive PWV values using a simple, single layer atmospheric model. In an attempt to improve the MIKE derived PWV measurements, we explore the potential of fitting a series of MIKE water vapour line measurements, having different opacities.

Research paper thumbnail of Support for site testing of the European Extremely Large Telescope: precipitable water vapor over La Silla

The European Southern Observatory (ESO), the Institute for Space Imaging Science (ISIS) and the A... more The European Southern Observatory (ESO), the Institute for Space Imaging Science (ISIS) and the AstroMeteorology group at the Universidad de Valparaiso collaborated on a project to understand the precipitable water vapour (PWV) over the La Silla Paranal Observatory. Both La Silla and Paranal were studied with the goal of using them as reference sites to evaluate potential E-ELT sites. As ground-based infrared astronomy matures, our understanding of the atmospheric conditions over the observatories becomes paramount, specifically water vapour since it is the principle source of atmospheric opacity at infrared wavelengths. Several years of archival optical spectra (FEROS) have been analysed to reconstruct the PWV history above La Silla using an atmospheric radiative transfer model (BTRAM) developed by ISIS. In order to better understand the systematics involved, a dedicated atmospheric water vapour measurement campaign was conducted in May 2009 in close collaboration with Las Campanas observatory and the GMT site testing team. Several methods of determining the water column were employed, including radiosonde launches, continuous measurements by infrared radiometers (IRMA), a compact echelle spectrograph (BACHES) and several high-resolution optical echelle spectrographs (FEROS, HARPS and MIKE). All available observations were compared to concurrent satellite estimates of water vapour in an attempt to ground-truth the satellite data. We present a comparison of the methods used, and results from the archival study and measurement campaign. A mean PWV of 3.4 ± 2.4 mm is found for La Silla using FEROS data covering the period 2005-2009. Important lessons on the strengths and limitations of satellite data are presented. The value of a stand-alone high time resolution PWV monitor has been demonstrated in the context of parallel observations from Las Campanas and La Silla.