| 1. |
- Tremblin, P., et al.
(författare)
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Site testing for submillimetre astronomy at Dome C, Antarctica
- 2011
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 535:A112
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Tidskriftsartikel (refereegranskat)abstract
- Aims. Over the past few years a major effort has been put into the exploration of potential sites for the deployment of submillimetre astronomical facilities. Amongst the most important sites are Dome C and Dome A on the Antarctic Plateau, and the Chajnantor area in Chile. In this context, we report on measurements of the sky opacity at 200 mu m over a period of three years at the French-Italian station, Concordia, at Dome C, Antarctica. We also present some solutions to the challenges of operating in the harsh polar environment.Methods. The 200-mu m atmospheric opacity was measured with a tipper. The forward atmospheric model MOLIERE (Microwave Observation LIne Estimation and REtrieval) was used to calculate the atmospheric transmission and to evaluate the precipitable water vapour content (PWV) from the observed sky opacity. These results have been compared with satellite measurements from the Infrared Atmospheric Sounding Interferometer (IASI) on Metop-A, with balloon humidity sondes and with results obtained by a ground-based microwave radiometer (HAMSTRAD). In addition, a series of experiments has been designed to study frost formation on surfaces, and the temporal and spatial evolution of thermal gradients in the low atmosphere.Results. Dome C offers exceptional conditions in terms of absolute atmospheric transmission and stability for submillimetre astronomy. Over the austral winter the PWV exhibits long periods during which it is stable and at a very low level (0.1 to 0.3 mm). Higher values (0.2 to 0.8 mm) of PWV are observed during the short summer period. Based on observations over three years, a transmission of around 50% at 350 mu m is achieved for 75% of the time. The 200-mu m window opens with a typical transmission of 10% to 15% for 25% of the time.Conclusions. Dome C is one of the best accessible sites on Earth for submillimetre astronomy. Observations at 350 or 450 mu m are possible all year round, and the 200-mu m window opens long enough and with a sufficient transparency to be useful. Although the polar environment severely constrains hardware design, a permanent observatory with appropriate technical capabilities is feasible. Because of the very good astronomical conditions, high angular resolution and time series (multi-year) observations at Dome C with a medium size single dish telescope would enable unique studies to be conducted, some of which are not otherwise feasible even from space.
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| 2. |
- Schneider, N., et al.
(författare)
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Atmospheric transmission at Dome C between 0 and 10 THz
- 2010
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Ingår i: EAS Publications Series. - : EDP Sciences. - 1633-4760 .- 1638-1963. ; 40, s. 327-332
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Tidskriftsartikel (refereegranskat)abstract
- We present model calculations of the atmospheric transmission for DOME C in Antarctica for frequencies up to 10THz (30 μm) using the forward model MOLIERE-5. Measurements of precipitable water vapor (pwv), obtained by the SUMMIT radiometer installed at the Concordia station during 2008 and working at a wavelength of 200μm, are translated into atmospheric transmission using MOLIERE. Quartiles of transmission, calculated from 200μm data are extrapolated to 350 μm and compared to the CCAT (Cornell-Caltech Atacama Telescope) site in Chile. It turns out that for 25% of the time at DOME C (CCAT), the transmission is around 20% (5%) at 200μm. This corresponds to a pwv of 0.18mm for DOME C. At 350μm, for 50% of time at DOME C (CCAT) the transmission is around 55% (25%). This corresponds to a pwv of 0.22mm for DOME C. These results show that DOME C is one of the best observing sites on Earth for submm-astronomy with respect to high atmospheric transmission over long time periods
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| 3. |
- Tremblin, P., et al.
(författare)
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Dome C: The best accessible site on Earth for submillimetre astronomy
- 2010
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Ingår i: EAS Publications Series. - : EDP Sciences. - 1633-4760 .- 1638-1963. ; 40, s. 333-336
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Tidskriftsartikel (refereegranskat)abstract
- We present preliminary results of the measurements of sky transparency conducted at Dome C during the winter 2008. Using MOLIERE modeling, we estimate a low precipitable water vapour content above Concordia station, which is very promising for future submillimetre wave observations on the Antarctic Plateau.
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| 4. |
- Tremblin, P., et al.
(författare)
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A worldwide comparison of the best sites for submillimetre astronomy
- 2012
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Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. - 9781107033771 ; 8:S288, s. 29-33
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Konferensbidrag (refereegranskat)abstract
- Over the past few years a major effort has been put into the exploration of potential sites for the deployment of submillimetre (submm) astronomical facilities. Amongst the most important sites are Dome C and Dome A on the Antarctic Plateau, and the Chajnantor area in Chile. In this context, we report on measurements of the sky opacity at 200 μm over a period of three years at the French-Italian station, Concordia, at Dome C, Antarctica. Based on satellite data, we present a comparison of the atmospheric transmission at 200, 350 μm between the best potential/known sites for submillimetre astronomy all around the world. The precipitable water vapour (PWV) was extracted from satellite measurements of the Infrared Atmospheric Sounding Interferometer (IASI) on the METOP-A satellite, between 2008 and 2010. We computed the atmospheric transmission at 200 μm and 350 μm using the forward atmospheric model MOLIERE (Microwave Observation LIne Estimation and REtrieval). This method allows us to compare known sites all around the world without the calibration biases of multiple in-situ instruments, and to explore the potential of new sites.
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| 5. |
- Tremblin, Pascal, et al.
(författare)
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Age, size, and position of H II regions in the Galaxy : Expansion of ionized gas in turbulent molecular clouds
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 568, s. A4-
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Tidskriftsartikel (refereegranskat)abstract
- Aims. This work aims to improve the current understanding of the interaction between H II regions and turbulent molecular clouds. We propose a new method to determine the age of a large sample of OB associations by investigating the development of their associated H II regions in the surrounding turbulent medium. Methods. Using analytical solutions, one-dimensional (ID), and three-dimensional (3D) simulations, we constrained the expansion of the ionized bubble depending on the turbulence level of the parent molecular cloud. A grid of 1D simulations was then computed in order to build isochrone curves for Hit regions in a pressure size diagram. This grid of models allowed us to date a large sample of OB associations that we obtained from the Hit Region Discovery Survey (HRDS). Results. Analytical solutions and numerical simulations showed that the expansion of H II regions is slowed down by the turbulence up to the point where the pressure of the ionized gas is in a quasi-equilibrium with the turbulent ram pressure. Based on this result, we built a grid of ID models of the expansion of Hit regions in a profile based on Larson's laws. We take the 3D turbulence into account with an effective ID temperature profile. The ages estimated by the isochrones of this grid agree well with literature values of well known regions such as Rosette, RCW 36, RCW 79, and M 16. We thus propose that this method can be used to find ages of young OB associations through the Galaxy and also in nearby extra-galactic sources.
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| 6. |
- Tremblin, P., et al.
(författare)
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Worldwide site comparison for submillimetre astronomy
- 2012
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 548, s. A65-
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Tidskriftsartikel (refereegranskat)abstract
- Aims. The most important limitation for ground-based submillimetre (submm) astronomy is the broad-band absorption of the total water vapour in the atmosphere above an observation site, often expressed as the precipitable water vapour (PWV). A long-term statistic on the PWV is thus mandatory to characterize the quality of an existing or potential site for observational submm-astronomy. In this study we present a three-year statistic (2008–2010) of the PWV for ground-based telescope sites all around the world and for stratospheric altitudes relevant for SOFIA (Stratospheric Observatory for Far-Infrared Astronomy). The submm-transmission is calculated for typical PWVs using an atmospheric model.Methods. We used data from IASI (Infrared Atmospheric Sounding Interferometer) on the Metop-A satellite to retrieve water vapour profiles for each site (11 in total, comprising Antarctica, Chile, Mauna Kea, Greenland, Tibet). The use of a single instrument to make the comparison provides unbiased data with a common calibration method. The profiles are integrated above the mountain/stratospheric altitude to get an estimation of the PWV. We then applied the atmospheric model MOLIERE (Microwave Observation and LIne Estimation and REtrieval) to compute the corresponding atmospheric absorption for wavelengths between 150 μm and 3 mm.Results. We present the absolute PWV values for each site sorted by year and time percentage. The PWV corresponding to the first decile (10%) and the quartiles (25%, 50%, 75%) are calculated and transmission curves between 150 μm and 3 mm for these values are shown. The Antarctic and South-American sites present very good conditions for submillimetre astronomy. The 350 μm and 450 μm atmospheric windows are open all year long, whereas the 200 μm atmospheric window opens reasonably for 25% of the time in Antarctica and the extremely high-altitude sites in Chile. Potential interesting new facilities are Macon in Argentina and Summit in Greenland, which show similar conditions to for example, Mauna Kea (Hawaii). For SOFIA, we present transmission curves for different altitudes (11 to 14 km), PWV values, and higher frequencies (up to 5 THz) in more detail. Though the atmosphere at these altitude is generally very transparent, the absorption at very high frequencies becomes more important, partly caused by minor species. The method presented in this paper could identify sites on Earth, with great potential for submillimetre astronomy, and guide future site testing campaigns in situ.
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