Showing papers on "Sky published in 2005"
01 Dec 2005
TL;DR: The VLA Low-frequency Sky Survey (VLSS) as discussed by the authors has been used to image 95% of the 3π sr of sky north of δ = -30° at a frequency of 74 MHz (4 m wavelength).
Abstract: The VLA Low-frequency Sky Survey (VLSS) has imaged 95% of the 3π sr of sky north of δ = -30° at a frequency of 74 MHz (4 m wavelength). The resolution is 80'' (FWHM) throughout, and the typical rms noise level is σ ≈ 0.1 Jy beam-1. The typical point-source detection limit is 0.7 Jy beam-1, and so far nearly 70,000 sources have been cataloged. This survey used the 74 MHz system added to the VLA in 1998. It required new imaging algorithms to remove the large ionospheric distortions at this very low frequency throughout the entire ~11.9° field of view. This paper describes the observation and data reduction methods used for the VLSS and presents the survey images and source catalog. All of the calibrated images and the source catalog are available from the VLSS Web site for use by the astronomical community.
276 citations
TL;DR: In this paper, the authors discuss the properties of the inner puffed-up rim which forms in circumstellar disks when dust evaporates, and they show that the rim shape is controlled by a fundamental property of the disks, namely their very large vertical density gradient, through the dependence of grain evaporation temperature on gas density.
Abstract: This paper discusses the properties of the inner puffed-up rim which forms in circumstellar disks when dust evaporates. We argue that the rim shape is controlled by a fundamental property of circumstellar disks, namely their very large vertical density gradient, through the dependence of grain evaporation temperature on gas density. As a result, the bright side of the rim is "curved", rather than "vertical", as expected when a constant evaporation temperature is assumed. We have computed a number of rim models, which take into account this effect in a self-consistent way. The results show that the curved rim (as the vertical rim) emits most of its radiation in the near and mid-IR, and provides a simple explanation to the observed values of the near-IR excess (the "3 micron bump" of Herbig Ae stars). Contrary to the vertical rim, for curved rims the near-IR excess does not depend much on the inclination, being maximum for face-on objects. We have then computed synthetic images of the curved rim seen under different inclinations; face-on rims are seen as bright, centrally symmetric rings on the sky; increasing the inclination, the rim takes an elliptical shape, with one side brighter than the other.
187 citations
TL;DR: The Orion-Monoceros complex of molecular clouds made in the J = 1 → 0 line of 12 CO with the Harvard-Smithsonian 1.2 m millimetre-wave telescope was surveyed in this article.
Abstract: We report the results of a new large scale survey of the Orion-Monoceros complex of molecular clouds made in the J = 1 → 0 line of 12 CO with the Harvard-Smithsonian 1.2 m millimetre-wave telescope. The survey consists of 52 288 uniformly spaced spectra that cover an area of 432 deg 2 on the sky and represent the most sensitive large-scale survey of the region to date. Distances to the constituent molecular clouds of the complex, estimated from an analysis of foreground and background stars, have provided information on the three dimensional structure of the entire complex.
176 citations
TL;DR: In this article, an apparatus to search for optical flashes in the sky is described, which has been optimized for optical counterparts of gamma ray bursts (GRB) and consists of 2 × 16 cameras covering all the sky.
134 citations
TL;DR: In this article, the authors present results from a major program of methane filter photometry for low-mass stars and brown dwarfs, and show that these filters are effective in discriminating T dwarfs from other types of stars, and demonstrate this with the IRIS2 imager.
Abstract: We present first results from a major program of methane filter photometry for low-mass stars and brown dwarfs. The definition of a new methane filter photometric system is described. A recipe is provided for the differential calibration of methane imaging data using existing 2MASS photometry. We show that these filters are effective in discriminating T dwarfs from other types of stars, and demonstrate this with Anglo-Australian Telescope observations using the IRIS2 imager. Methane imaging data and proper motions are presented for ten T dwarfs identified as part of the 2MASS "Wide Field T Dwarf Search" -- seven of them initially identified as T dwarfs using methane imaging.
We also present near-infrared moderate resolution spectra for five T dwarfs, newly discovered by this technique. Spectral types obtained from these spectra are compared to those derived from both our methane filter observations, and spectral types derived by other observers. Finally, we suggest a range of future programs to which these filters are clearly well suited: the winnowing of T dwarf and Y dwarf candidate objects coming from the next generation of near-infrared sky surveys; the robust detection of candidate planetary-mass brown dwarfs in clusters; the detection of T dwarf companions to known L and T dwarfs via deep methane imaging; and the search for rotationally-modulated time-variable surface features on cool brown dwarfs.
133 citations
31 Jul 2005
TL;DR: In an interactive flight simulation, users would like to fly in and around realistic, volumetric clouds, and to see other aircraft convincingly pass within and behind them, and previous real-time techniques have not provided users with such experiences.
Abstract: Clouds are a ubiquitous, awe-inspiring, and ever-changing feature of the outdoors. They are an integral factor in Earth's weather systems, and a strong indicator of weather patterns and changes. Their effects and indications are important to flight and flight training. Clouds are an important component of the visual simulation of any outdoor scene, but the complexity of cloud formation, dynamics, and light interaction makes cloud simulation and rendering difficult in real time. In an interactive flight simulation, users would like to fly in and around realistic, volumetric clouds, and to see other aircraft convincingly pass within and behind them. Ideally, simulated clouds would grow and disperse as real clouds do, and move in response to wind and other forces. Simulated clouds should be realistically illuminated by direct sunlight, internal scattering, and reflections from the sky and the earth below. Previous real-time techniques have not provided users with such experiences.
111 citations
TL;DR: In this paper, the relationship between hemispherical sky cover and nadir-view cloud fraction is examined by using both model simulations and surface observations, and it is shown that 15-min averages of frequently sampled (30 s) sky cover provide a reasonable estimation of the cloud fraction for limited fields of view and that this estimation can be substantially improved if additional information about the cloud aspect ratio is incorporated into the retrieval process.
Abstract: The relationship between hemispherical sky cover and nadir-view cloud fraction is examined by using both model simulations and surface observations. Monte Carlo simulations of ground-based hemispherical measurements are based on four-dimensional cloud fields produced by a large-eddy simulation model. Surface hemispherical observations are performed during the Atmospheric Radiation Measurement Program’s Cloudiness Intercomparison Intensive Operational Period. It is shown that (i) 15-min averages of frequently sampled (30 s) sky cover provide a reasonable estimation of the cloud fraction for limited fields of view and that (ii) this estimation can be substantially improved (for cumulus clouds) if additional information about the cloud aspect ratio is incorporated into the retrieval process.
104 citations
TL;DR: In this article, the authors present a new calculation of the number of galaxies future radio telescopes will detect in surveys of the sky in neutral hydrogen (H 1), and estimate the likely statistical errors if the standard ruler method were to be applied to such surveys.
Abstract: Current surveys may be on the verge of measuring the baryonic oscillations in the galaxy power spectrum, which are clearly seen imprinted on the cosmic microwave background. It has recently been proposed that these oscillations allow a 'standard ruler' method of probing the equation of state of dark energy. In this paper we present a new calculation of the number of galaxies future radio telescopes will detect in surveys of the sky in neutral hydrogen (H 1). We estimate the likely statistical errors if the standard ruler method were to be applied to such surveys. We emphasize uncertainties in our calculations, and pinpoint the most important features of future H I surveys if they are to provide new constraints on dark energy via baryonic oscillations. Designs of future radio telescopes are required to have a large bandwidth (characterized by beta, the ratio of the instantaneous bandwidth to the bandwidth required by survey) and to have the widest instantaneous (1.4 GHz) field of view (FOV) possible. Given the expected sensitivity of a future Square Kilometre Array (SKA), given that half of its collecting area will be concentrated in a core of diameter similar to 5 km, and given a reasonable survey duration (T-0 similar to 1 yr), we show that there will be negligible shot noise on a power spectrum derived from H I galaxies out to redshift z similar or equal to 1.5. To access the largest cosmic volume possible by surveying all the sky available, we argue that beta, T-0 and FOV must obey the relation beta FOV T-0 greater than or similar to 10 deg(2) yr. A similar to 1-yr SKA survey would then contain greater than or similar to 10(9)(f(sky)/0.5) H I galaxies and provide constraints on the dark energy parameter w of order Delta w similar or equal to 0.01 (f(sky)/0.5)(-0.5), where f(sky) is the fraction of the whole sky observed.
88 citations
TL;DR: A Fourier transform infrared interferometer was deployed at Dome C during two austral summer seasons (2003 January and 2003 December/2004 January) for the purpose of acquiring satellite validation data.
Abstract: Dome C, Antarctica, (75 south, 123 east, 3250 m) is one of the coldest and driest locations on Earth, with exceptionally low winds throughout the atmosphere. It therefore has the potential to be an ideal site for astronomical observations. It is also an excellent site for the validation of satellite instruments. A Fourier transform infrared interferometer was deployed at Dome C during two austral summer seasons (2003 January and 2003 December/2004 January) for the purpose of acquiring satellite validation data. However, these data are also useful for understanding the infrared characteristics of the atmosphere for future astronomical experiments at Dome C. The Polar Atmospheric Emitted Radiance Interferometer measured the downwelling infrared radiance from the atmosphere (sky brightness) from 3 to 20 mm. Over 100 radiosondes were also launched during this time period. Typical measured values of the sky brightness in the clearest portions of the M, N, and Q bands are 0.9, 43, and 310 Jy arcsec 2 , respectively. The lowest measured values of sky brightness within these bands are 0.4, 34, and 200 Jy arcsec 2 . The spectral region of the Q band from about 18.7 to 19 mm is expected to be an excellent window for observations made from the Antarctic Plateau. The sky brightness has been measured between 10.60 and 11.30 m mi n theN band for comparisons to earlier studies at South Pole Station; the values in this band are similar to those in the 8.20-8.40 mm band. For the period of time covered by our observations, the sky brightness in the dark portions of the N band was less than about 50-60 Jy arcsec 2 for about 10% of the time, and less than about 75 Jy arcsec 2 for about 50% of the time. During a 5 day period of clear skies, the mean sky brightness was 47.7 Jy arcsec 2 , with a variation about this mean of 4.4 Jy arcsec 2 (1 j). Calculations of the summertime atmospheric transmission under clear skies over Dome C show that portions of the M, N, and Q bands have transmission greater than 95%, with some spectral regions greater than 99%.
69 citations
TL;DR: In this article, a Coarse Sun Sensor consisting of six solar cells placed on each of the six outer surfaces of the satellite is used for Sun vector determination for full 3-axes attitude determination.
57 citations
TL;DR: In this paper, the authors present an automated routine to search for H I self-absorption features within the Southern Galactic Plane Survey (SGPS) using the Australia Telescope Compact Array (ATCA) and the Parkes Radio Telescope.
Abstract: We present an automated routine to search for H I self-absorption features within the Southern Galactic Plane Survey (SGPS). The data were taken with the Australia Telescope Compact Array (ATCA) and the Parkes Radio Telescope and encompass 3°×105° of sky in the Galactic plane. We apply our routine to this entire region and derive spin temperatures and column densities for 70 of the larger HISA complexes, finding spin temperatures ranging from 6 to 41 K with H I number densities of a few cm -3. These "missing link" clouds fill in the spin temperature and density gaps between dense molecular clouds and diffuse atomic clouds. We compare the H I emission with 12CO emission and find that ∼60% of detected H I self-absorption is correlated in space and in velocity with a molecular counterpart. This is potentially due to a molecular/atomic gas transition. We also compare H I self-absorption with Galactic spiral arms and discuss the possibility of using it as a spiral arm tracer. © 2005. The American Astronomical Society. All rights reserved.
TL;DR: A photo-realistic hemispherical twilight sky is computed in less than two hours on a conventional PC, useful for high-dynamic range environment mapping, outdoor global illumination calculations, mesopic vision research and optical aerosol load probing.
Abstract: We present a physically-based approach to compute the colors of the sky during the twilight period before sunrise and after sunset. The simulation is based on the theory of light scattering by small particles. A realistic atmosphere model is assumed, consisting of air molecules, aerosols, and water. Air density, aerosols, and relative humidity vary with altitude. In addition, the aerosol component varies in composition and particle-size distribution. This allows us to realistically simulate twilight phenomena for a wide range of different climate conditions. Besides considering multiple Rayleigh and Mie scattering, we take into account wavelength-dependent refraction of direct sunlight as well as the shadow of the Earth. Incorporating several optimizations into the radiative transfer simulation, a photo-realistic hemispherical twilight sky is computed in less than two hours on a conventional PC. The resulting radiometric data is useful, for instance, for high-dynamic range environment mapping, outdoor global illumination calculations, mesopic vision research and optical aerosol load probing.
TL;DR: In this paper, the authors analyzed the properties of searches devoted to finding planetary transits by observing simple stellar systems, such as globular clusters, open clusters, and the Galactic bulge, and developed the analytic tools necessary to predict the number of planets that a survey will detect as a function of the parameters of the system.
Abstract: We analyze the properties of searches devoted to finding planetary transits by observing simple stellar systems, such as globular clusters, open clusters, and the Galactic bulge We develop the analytic tools necessary to predict the number of planets that a survey will detect as a function of the parameters of the system (age, extinction, distance, richness, mass function), the observational setup (nights observed, bandpass, exposure time, telescope diameter, detector characteristics), site properties (seeing, sky background), and the planet properties (frequency, period, and radius) We find that for typical parameters, the detection probability is maximized for I-band observations At fixed planet period and radius, the signal-to-noise ratio of a planetary transit in the I band is weakly dependent on the mass of the primary for sources with flux above the sky background and falls very sharply for sources below sky Therefore, for typical targets, the number of detectable planets is roughly proportional to the number of stars with transiting planets with fluxes above sky (and not necessarily the number of sources with photometric error less than a given threshold) Furthermore, for rising mass functions, the majority of the planets will be detected around sources with fluxes near sky In order to maximize the number of detections, experiments should therefore be tailored such that sources near sky are above the required detection threshold Once this requirement is met, the number of detected planets is relatively weakly dependent on the detection threshold, diameter of the telescope, exposure time, seeing, age of the system, and planet radius, for typical ranges of these parameters encountered in current transit searches in stellar systems The number of detected planets is a strongly decreasing functionofthe distancetothesystem,implyingthat thenearest, richestclustersmayprove tobe optimal targets Subject headingg planetary systems — surveys — techniques: photometric
TL;DR: In this article, ground-based cloud data acquired with the whole sky imager (WSI) are analyzed in relation to measurements of solar radiation performed at the Lindenberg Meteorological Observatory.
Abstract: Ground-based cloud data acquired with the whole sky imager (WSI) are analyzed in relation to measurements of solar radiation performed at the Lindenberg Meteorological Observatory. Cloud fractions derived by the cloud detection algorithm from WSI images acquired during daylight hours between 2002 and 2004 are compared with conventional cloud observations for the two sites Potsdam and Lindenberg, and also with ceilometer data of cloud-base heights at Lindenberg. The comparison statistics are discussed in the context of different principles of measurement. A few case studies illustrate the strong scattering effect of clouds on solar radiance and irradiance measured at the ground in different spectral regions. Particularly clouds close to the apparent position of the sun lead to strong enhancements of solar diffuse irradiance incident on horizontal planes and hemispheres that substantially exceed corresponding clear-sky values. Irradiances derived from WSI sky radiance fields are shown in comparison to pyranometer data of diffuse irradiance and radiative transfer model calculations performed for clear sky conditions. Examples of spectral sky radiances with moving contrails illustrate the significant enhancement the contrails have compared to clear sky, even though they may have a relatively small direct effect on global irradiance values. As contrails are observed at Lindenberg for about 18 to 19% of daylight hours, and part of them become clouds, the indirect impact of these changes on solar irradiance received at the ground may not be negligible. (orig.)
TL;DR: In this article, the authors proposed a method to measure AOD behavior at night by adjusting an AOD value into the model in order to fit measured light pollution, using spectrally calibrated stars as reference targets.
Abstract: Tracking the Aerosol Optical Depth (AOD) is of particular importance in monitoring aerosol contributions to global radiative forcing. Until now, the two standard techniques used for retrieving AOD were; (i) sun photometry, and (ii) satellite-based approaches, such as based DDV (Dense Dark Vegetation) inversion algorithms. These methods are only available for use during daylight time since they are based on direct or indirect observation of sunlight. Few attempts have been made to measure AOD behaviour at night. One such method uses spectrally-calibrated stars as reference targets but the number of available stars is limited. This is especially true for urban sites where artificial lighting hides most of these stars. In this research, we attempt to provide an alternate method, one which exploits artificial sky glow or light pollution. This methodology links a 3D light pollution model with in situ light pollution measurements. The basic idea is to adjust an AOD value into the model in order to fit measured light pollution. This method requires an accurate model that includes spatial heterogeneity in lighting angular geometry, in lighting spectral dependence, in ground spectral reflectance and in topography. This model, named ILLUMINA, computes 1 st and 2 nd order molecular and aerosol scattering, as well as aerosol absorption. These model features represent major improvements to previous light pollution models. Therefore, new possibilities for light pollution studies will arise, many of which are of particular interest to the astronomical community. In this paper we will present a first sensitive study applied to the ILLUMINA model.
TL;DR: In this paper, a 3D radiative transfer theory is used to account for arbitrary spatial variation of atmospheric parameters, and the influence of clouds on the clear sky reflectance function is quantified.
Abstract: Operational remote sensing of terrestrial atmosphere is heavily based on the 1-D radiative transfer equation. However, cloudy scenes are influenced by 3-D effects (e.g., illumination from cloud sides, etc.). This leads to biases in aerosol/cloud/land/ocean retrieval schemes for scenes with clouds. These biases can be understood and quantified only with the use of the 3-D radiative transfer theory, which allows to account for arbitrary spatial variation of atmospheric parameters. The task of this paper is twofold. First of all we introduce a novel technique for the solution of the 3-D radiative transfer equation based on the grid approximations and the straightforward iteration procedure realised on supercomputers with parallel architecture. We study the performance of our technique comparing with the solutions obtained by the Monte-Carlo code. A close correspondence is found. Secondly, we quantify the influence of neighbouring clouds on the clear sky reflection function at the nadir observation depending on the solar illumination conditions. We find that the influence of cloud on the clear sky reflectance function is not negligible (even outside the cloud geometrical shadow). Thus, the peculiar inner boundary layer arises in the sky reflectance function with shadowing and brightening effects.
TL;DR: In this article, the authors presented a new catalog of isolated galaxies obtained through an automated systematic search, in which 2980 isolated galaxies were found in ≈2099 deg2 of sky in the Sloan Digital Sky Survey Data Release 1 (SDSS DR1) photometry.
Abstract: We present a new catalog of isolated galaxies obtained through an automated systematic search. These 2980 isolated galaxies were found in ≈2099 deg2 of sky in the Sloan Digital Sky Survey Data Release 1 (SDSS DR1) photometry. The selection algorithm, implementing a variation on the criteria developed by Karachentseva in 1973, proved to be very efficient and fast. This catalog will be useful for studies of the general galaxy characteristics. Here we report on our results.
TL;DR: In this article, the authors presented an objectively defined catalog of 459 small, high-density groups of galaxies out to z ~ 0.2 in a region of ~6260 deg2 in the northern sky derived from the Digitized Second Palomar Observatory Sky Survey.
Abstract: In this paper we present an objectively defined catalog of 459 small, high-density groups of galaxies out to z ~ 0.2 in a region of ~6260 deg2 in the northern sky derived from the Digitized Second Palomar Observatory Sky Survey. Our catalog extends down to r = 19.0 and has a median redshift of zmed = 0.12, making it complementary to Hickson's catalog for the nearby universe (zmed = 0.03). The depth and angular coverage of this catalog makes it valuable for studies of the general characteristics of small groups of galaxies and how galaxies evolve in and around them. We also examine the relationship between compact groups and large-scale structure.
TL;DR: In this article, the authors analyzed the properties of searches devoted to finding planetary transits by observing simple stellar systems, such as globular clusters, open clusters, and the Galactic bulge, and developed the analytic tools necessary to predict the number of planets that a survey will detect as a function of the parameters of the system, the observational setup, site properties, and planet properties.
Abstract: We analyze the properties of searches devoted to finding planetary transits by observing simple stellar systems, such as globular clusters, open clusters, and the Galactic bulge. We develop the analytic tools necessary to predict the number of planets that a survey will detect as a function of the parameters of the system, the observational setup, site properties, and planet properties. We find that the detection probability is generally maximized for I-band observations. The signal-to-noise ratio of a planetary transit is weakly dependent on the mass of the primary for sources with flux above the sky background, and falls very sharply for sources below sky. Therefore the number of detectable planets is roughly proportional to the number of stars with fluxes above sky (and not necessarily the number of sources with photometric error less a given threshold). In order to maximize the number of detections, experiments should be tailored such that stars near sky are above the detection threshold. Once this requirement is met, the number of detected planets is relatively weakly dependent on the detection threshold, diameter of the telescope, exposure time, seeing, age of the system, and planet radius. The number of detected planets is a strongly decreasing function of the distance to the system, implying that the nearest, richest clusters may prove to be optimal targets.
TL;DR: In this paper, an objectively defined catalog of 459 small, high density groups of galaxies out to z~0.2 in a region of 6260 square degrees in the northern sky derived from the Digitized Second Palomar Observatory Sky Survey is presented.
Abstract: In this paper we present an objectively defined catalog of 459 small, high density groups of galaxies out to z~0.2 in a region of 6260 square degrees in the northern sky derived from the Digitized Second Palomar Observatory Sky Survey. Our catalog extends down to r = 19.0 and has a median redshift of z_med = 0.12, making it complementary to Hickson's catalog for the nearby universe (z_med = 0.03). The depth and angular coverage of this catalog makes it valuable for studies of the general characteristics of small groups of galaxies and how galaxies evolve in and around them. We also examine the relationship between compact groups and large scale structure.
TL;DR: In this paper, the authors studied the illuminance levels at a city in Central Europe (Bratislava) and another in the Eastern Mediterranean (Athens) and defined the prevailing sky-luminance distributions for winter and summer.
Patent•
26 Sep 2005
TL;DR: An automatic celestial navigation system for navigating both night and day by observing of K-band or H-band infrared light from multiple stars is described in this paper. But it does not specify how to determine the orientation of the platform.
Abstract: An automatic celestial navigation system for navigating both night and day by observation of K-band or H-band infrared light from multiple stars. One or more telescopes mounted on a movable platform such as a ship or airplane and directed at a substantially different portion of sky. Telescope optics focus (on to a pixel array of a sensor) H-band or K-band light from one or more stars in multiple telescopic fields of view. Each system also includes a GPS sensor and a computer processor having access to catalogued infrared star charts. The processor for each system is programmed with special algorithms to use image data from the infrared sensors, position and timing information from the GPS sensor, and the catalogued star charts information to determine orientation (attitude) of the platform.
TL;DR: In this paper, the authors examined the variability of the high-ionizaton C IV line in a sample of 105 quasars observed at multiple epochs by the Sloan Digital Sky Survey.
Abstract: We examine the variability of the high-ionizaton C IV line in a sample of 105 quasars observed at multiple epochs by the Sloan Digital Sky Survey. We find a strong correlation between the change in the C IV line flux and the change in the line width, but no correlations between the change in flux and changes in line center and skewness. The relation between line flux change and line width change is consistent with a model in which a broad line base varies with greater amplitude than the line core. The objects studied here are more luminous and at higher redshift than those normally studied for variability, ranging in redshift from 1.65 to 4.00 and in absolute r-band magnitude from roughly -24 to -28. Using moment analysis line-fitting techniques, we measure line fluxes, centers, widths and skewnesses for the C IV line at two epochs for each object. The well-known Baldwin Effect is seen for these objects, with a slope beta = -0.22. The sample has a median intrinsic Baldwin Effect slope of beta = -0.85; the C IV lines in these high-luminosity quasars appear to be less responsive to continuum variations than those in lower luminosity AGN. Additionally, we find no evidence for variability of the well known blueshift of the C IV line with respect to the low-ionization Mg II line in the highest flux objects, indicating that this blueshift might be useful as a measure of orientation.
TL;DR: In this article, the role of color vision in determining the appearance of the daytime sky is discussed, and the spectral irradiance of skylight is shown to be a metameric match to unsaturated blue light.
Abstract: The usual answer to the question “Why is the sky blue?” is based only on Rayleigh scattering from the molecules in the atmosphere and makes little mention of the contribution of color vision. We supplement this answer with a quantitative discussion of the role color vision plays in determining the appearance of the daytime sky. The anatomy of the human eye is reviewed, and its response as a function of wavelength is described via the spectral sensitivities of the cones. Color matching is examined for a mixture of monochromatic lights and for the spectrum of the daytime sky. The spectral irradiance of skylight is shown to be a metameric match to unsaturated blue light. A simple experiment is described suitable for classroom use or a student project.
TL;DR: In this article, the authors estimate sky confusion noise owing to the emission from interstellar dust clouds or cirrus, based on fluctuation analysis and detailed photometry over realistically simulated images, and find that confusion noise becomes dominant in long wavelength bands (>100 µm) with 60-90 cm aperture missions, it is expected to be two orders of magnitude lower for the next generation of space missions (with larger aperture sizes) such as Herschel and SPICA.
Abstract: Fluctuations in the brightness of the background radiation can lead to confusion with real point sources. This type of confusion with background emission is relevant when making infrared (IR) observations with relatively large beam sizes, since the amount of fluctuation tends to increase with the angular scale. To quantitively assess the effect of the background emission on the detection of point sources for current and future far-IR observations by space-borne missions such as Spitzer, ASTRO-F, Herschel and Space Infrared Telescope for Cosmology and Astrophysics (SPICA), we have extended the Galactic emission map to a higher level of angular resolution than that of the currently available data. Using this high-resolution map, we estimate the sky confusion noise owing to the emission from interstellar dust clouds or cirrus, based on fluctuation analysis and detailed photometry over realistically simulated images. We find that the confusion noise derived by simple fluctuation analysis agrees well with the results from realistic simulations. Although sky confusion noise becomes dominant in long wavelength bands (>100 µm) with 60‐90 cm aperture missions, it is expected to be two orders of magnitude lower for the next generation of space missions (with larger aperture sizes) such as Herschel and SPICA.
TL;DR: In this article, the authors analyzed auroral measurements at South Pole Station and showed that during an average winter season, the auroral contribution to the B band sky brightness is below 21.9 B mag arcsec −2 for 50% of the observing time.
Abstract: The Antarctic Plateau holds great promise for optical astronomy. One relatively unstudied feature of the polar night sky for optical astronomical observing is the potential contamination of observations by aurorae. In this study we analyse auroral measurements at South Pole Station and show that during an average winter season, the auroral contribution to the B band sky brightness is below 21.9 B mag arcsec −2 for 50% of the observing time. In V band, the median sky brightness contribution is 20.8 mag arcsec −2 during an average winter. South Pole Station is situated within the auroral zone and experiences strong and frequent auroral activity. The Antarctic locations of Dome C and Dome A are closer to the geomagnetic pole where auroral activity is greatly reduced compared with that of South Pole Station. Calculations based on satellite measurements of electron flux above the Antarctic Plateau are used to show that at Dome C, the contribution to sky background in the B and V bands is up to 3.1 mag less than that at the South Pole. The use of notch filters to reduce the contribution from the strongest auroral emission lines and bands is also discussed. The scientific potential of an extremely large telescope located at Dome C is discussed, with reference to the effect that auroral emissions would have on particular astronomical observations.
TL;DR: In this paper, the authors present simulations of the extragalactic radio sky at 151, 325, and 1400 MHz based on number density predictions from models of the evolution of the radio luminosity function.
Abstract: In this paper we present simulations of the extragalactic radio sky at 151, 325, and 1400 MHz based on number density predictions from models of the evolution of the radio luminosity function. From these simulations we predict typical source distributions, allowing us to estimate the natural confusion limit to faint flux density limits. The results are relevant to the science and design goals of future radio facilities, namely the Square Kilometre Array, the low-frequency array, and their demonstrator projects.
TL;DR: In this paper, the authors compute cloud cover in a regional climate model with a filter that removes the thinnest clouds, which is used as a proxy to identify thin clouds as they are mainly interested in the impact of clouds on radiation.
Abstract: [1] Observed monthly mean cloud cover from the SHEBA site is found to differ by a substantial amount during winter depending on cloud observing instrument. This makes it difficult for climate modelers to evaluate modeled clouds and improve parameterizations. Many instruments and human observers cannot properly detect the thinnest clouds and count them as clear sky instead, resulting in too low cloud cover. To study the impact from the difficulties in the detection of thin clouds, we compute cloud cover in our model with a filter that removes the thinnest clouds. Optical thickness is used as a proxy to identify thin clouds as we are mainly interested in the impact of clouds on radiation. With the results from a regional climate model simulation of the Arctic, we can reproduce the large variability in wintertime cloud cover between instruments when assuming different cloud detection thresholds. During winter a large fraction of all clouds are optically thin, which causes the large sensitivity to filtering by optical thickness. During summer, most clouds are far above the optical thickness threshold and filtering has no effect. A fair comparison between observed and modeled cloud cover should account for thin clouds that may be present in models but absent in the observational data set. Difficulties with the proper identification of clouds and clear sky also has an effect on cloud radiative forcing. The derived clear-sky longwave flux at the surface can vary by some W m−2 depending on the lower limit for the optical thickness of clouds. This impacts on the “observed” LW cloud radiative forcing and suggests great care is needed in using satellite-derived cloud radiative forcing for model development.
TL;DR: The Wide-Field Infrared Survey Explorer (WISE) is a NASA MIDEX mission that will survey the entire sky in four bands from 3.3 to 23 microns with a sensitivity 1000 times greater than the IRAS survey as discussed by the authors.
Abstract: The Wide-field Infrared Survey Explorer (WISE), a NASA MIDEX mission, will survey the entire sky in four bands from 3.3 to 23 microns with a sensitivity 1000 times greater than the IRAS survey. The WISE survey will extend the Two Micron All Sky Survey into the thermal infrared and will provide an important catalog for the James Webb Space Telescope. Using 10242 HgCdTe and Si:As arrays at 3.3, 4.7, 12 and 23 microns, WISE will find the most luminous galaxies in the universe, the closest stars to the Sun, and it will detect most of the main belt asteroids larger than 3 km. The single WISE instrument consists of a 40 cm diamond-turned aluminum afocal telescope, a two-stage solid hydrogen cryostat, a scan mirror mechanism, and reimaging optics giving 5" resolution (full-width-half-maximum). The use of dichroics and beamsplitters allows four color images of a 47'x47' field of view to be taken every 8.8 seconds, synchronized with the orbital motion to provide total sky coverage with overlap between revolutions. WISE will be placed into a Sun-synchronous polar orbit on a Delta 7320-10 launch vehicle. The WISE survey approach is simple and efficient. The three-axis-stabilized spacecraft rotates at a constant rate while the scan mirror freezes the telescope line of sight during each exposure. WISE is currently in its Preliminary Design Phase, with the mission Preliminary Design Review scheduled for July, 2005. WISE is scheduled to launch in mid 2009; the project web site can be found at www.wise.ssl.berkeley.edu.
TL;DR: In this paper, an all-sky cloud-monitoring system that generates relative opacity maps over many of the world's premier astronomical observatories is described, where photometric measurements of numerous background stars are combined with simultaneous sky brightness measurements to differentiate thin clouds from sky glow sources such as airglow and zodiacal light.
Abstract: An all‐sky cloud‐monitoring system that generates relative opacity maps over many of the world's premier astronomical observatories is described. Photometric measurements of numerous background stars are combined with simultaneous sky brightness measurements to differentiate thin clouds from sky glow sources such as airglow and zodiacal light. The system takes a continuous pipeline of all‐sky images and compares them to canonical images taken on other nights at the same sidereal time. Data interpolation then yields transmission maps covering almost the entire sky. An implementation of this system is currently operating through the Night Sky Live network of CONCAM3s located at Cerro Pachon (Chile), Mauna Kea (Hawaii), Haleakala (Hawaii), SALT (South Africa), and the Canary Islands (Northwestern Africa).