اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدNight-time measurements of astronomical seeing at Dome A in Antarctica
172
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Seeing, the angular size of stellar images blurred by atmospheric turbulence, is a critical parameter used to assess the quality of astronomical sites. Median values at the best mid-latitude sites are generally in the range of 0.6--0.8,arcsec. Sites on the Antarctic plateau are characterized by comparatively-weak turbulence in the free-atmosphere above a strong but thin boundary layer. The median seeing at Dome C is estimated to be 0.23--0.36 arcsec above a boundary layer that has a typical height of 30,m. At Dome A and F, the only previous seeing measurements were made during daytime. Here we report the first direct measurements of night-time seeing at Dome A, using a Differential Image Motion Monitor. Located at a height of just 8,m, it recorded seeing as low as 0.13,arcsec, and provided seeing statistics that are comparable to those for a 20,m height at Dome C. It indicates that the boundary layer was below 8,m 31% of the time. At such times the median seeing was 0.31,arcsec, consistent with free-atmosphere seeing. The seeing and boundary layer thickness are found to be strongly correlated with the near-surface temperature gradient. The correlation confirms a median thickness of approximately 14,m for the boundary layer at Dome A, as found from a sonic radar. The thinner boundary layer makes it less challenging to locate a telescope above it, thereby giving greater access to the free-atmosphere.
قيم البحث
اقرأ أيضاً
We present an analysis of meteorological data from the second generation of the Kunlun Automated Weather Station (KLAWS-2G) at Dome A, Antarctica during 2015 and 2016. We find that a strong temperature inversion exists for all the elevations up to 14
m that KLAWS-2G can reach, and lasts for more than 10 hours for 50% or more of the time when temperature inversion occurs. The average wind speeds at 4 m elevation are 4.2 m/s and 3.8 m/s during 2015 and 2016, respectively. The strong temperature inversion and moderate wind speed lead to a shallow turbulent boundary layer height at Dome A. By analyzing the temperature and wind shear profiles, we note telescopes should be elevated by at least 8 m above the ice. We also find that the duration of temperature
The terahertz and far-infrared (FIR) band, from approximately 0.3 THz to 15 THz (1 mm to 20 micron), is important for astrophysics as the thermal radiation of much of the universe peaks at these wavelengths and many spectral lines that trace the cycl
e of interstellar matter also lie within this band. However, water vapor renders the terrestrial atmosphere opaque to this frequency band over nearly all of the Earths surface. Early radiometric measurements below 1 THz at Dome A, the highest point of the cold and dry Antarctic ice sheet, suggest that it may offer the best possible access for ground-based astronomical observations in the terahertz and FIR band. To address uncertainty in radiative transfer modelling, we carried out measurements of atmospheric radiation from Dome A spanning the entire water vapor pure rotation band from 20 micron to 350 micron wavelength by a Fourier transform spectrometer. Our measurements expose atmospheric windows having significant transmission throughout this band. Furthermore, by combining our broadband spectra with auxiliary data on the atmospheric state over Dome A, we set new constraints on the spectral absorption of water vapor at upper tropospheric temperatures important for accurately modeling the terrestrial climate. In particular, we find that current spectral models significantly underestimate the H2O continuum absorption.
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 Chajnant
or area in Chile. In this context, we report on measurements of the sky opacity at 200 um 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 environ- ment. Dome C offers exceptional conditions in terms of absolute atmospheric transmission and stability for submillimetre astron- omy. 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 um is achieved for 75% of the time. The 200-um window opens with a typical transmission of 10% to 15% for 25% of the time. 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-um 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.
Dome C in Antarctica is a promising site for photometric observations thanks to the continuous night during the Antarctic winter and favorable weather conditions. We developed instruments to assess the quality of this site for photometry in the visib
le and to detect and characterize variable objects through the Antarctic Search for Transiting ExoPlanets (ASTEP) project. We present the full analysis of four winters of data collected with ASTEP South, a 10 cm refractor pointing continuously toward the celestial south pole. We improved the instrument over the years and developed specific data reduction methods. We achieved nearly continuous observations over the winters. We measure an average sky background of 20 mag arcsec$^{-2}$ in the 579-642 nm bandpass. We built the lightcurves of 6000 stars and developed a model to infer the photometric quality of Dome C from the lightcurves themselves. The weather is photometric $67.1pm4.2$ % of the time and veiled $21.8pm2.0$ % of the time. The remaining time corresponds to poor quality data or winter storms. We analyzed the lightcurves of $sigma$ Oct and HD 184465 and find that the amplitude of their main frequency varies by a factor of 3.5 and 6.7 over the four years, respectively. We also identify 34 new variable stars and eight new eclipsing binaries with periods ranging from 0.17 to 81 days. The phase coverage that we achieved with ASTEP South is exceptional for a ground-based instrument and the data quality enables the detection and study of variable objects. These results demonstrate the high quality of Dome C for photometry in the visible and for time series observations in general.
The 0.5,m Antarctic Survey Telescopes (AST3) were designed for time-domain optical/infrared astronomy. They are located in Dome~A, Antarctica, where they can take advantage of the continuous dark time during winter. Since the site is unattended in wi
nter, everything for the operation, from observing to data reduction, had to be fully automated. Here, we present a brief overview of the AST3 project and some of its unique characteristics due to its location in Antarctica. We summarise the various components of the survey, including the customized hardware and software, that make complete automation possible.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
