Showing papers on "Sky published in 2007"
TL;DR: The Sixth Data Release of the Sloan Digital Sky Survey (SDS) is now complete and includes much more extensive stellar spectroscopy than previously, and also includes detailed estimates of stellar temperatures, gravities, and metallicities as mentioned in this paper.
Abstract: With the Sixth Data Release of the Sloan Digital Sky Survey, the imaging of the Northern Galactic Cap is now complete. The survey contains images and parameters of roughly 287 million objects over 9583 deg^2, and 1.27 million spectra of stars, galaxies, quasars and blank sky (for sky subtraction) selected over 7425 deg^2. This release includes much more extensive stellar spectroscopy than previously, and also includes detailed estimates of stellar temperatures, gravities, and metallicities. The results of improved photometric calibration are now available, with uncertainties of roughly 1% in g, r, i, and z, and 2% in u, substantially better than the uncertainties in previous data releases. The spectra in this data release have improved wavelength and flux calibration, especially in the extreme blue and extreme red, leading to the qualitatively better determination of stellar types and radial velocities. The spectrophotometric fluxes are now tied to point spread function magnitudes of stars rather than fiber magnitudes, giving a 0.35 mag change in the spectrophotometric flux scale. Systematic errors in the velocity dispersions of galaxies have been fixed, and the results of two independent codes for determining spectral classifications and redshifts are made available. (Abridged)
1,483 citations
TL;DR: AKARI as discussed by the authors, the first Japanese satellite dedicated to infrared astronomy, was launched on 2006 February 21, and started observations in May of the same year, and has a 68.5 cm cooled telescope, together with two focal-plane instruments, which survey the sky in six wavelength bands from the mid- to far-infrared.
Abstract: AKARI, the first Japanese satellite dedicated to infrared astronomy, was launched on 2006 February 21, and started observations in May of the same year. AKARI has a 68.5 cm cooled telescope, together with two focal-plane instruments, which survey the sky in six wavelength bands from the mid- to far-infrared. The instruments also have the capability for imaging and spectroscopy in the wavelength range 2 - 180 micron in the pointed observation mode, occasionally inserted into the continuous survey operation. The in-orbit cryogen lifetime is expected to be one and a half years. The All-Sky Survey will cover more than 90 percent of the whole sky with higher spatial resolution and wider wavelength coverage than that of the previous IRAS all-sky survey. Point source catalogues of the All-Sky Survey will be released to the astronomical community. The pointed observations will be used for deep surveys of selected sky areas and systematic observations of important astronomical targets. These will become an additional future heritage of this mission.
704 citations
TL;DR: In this article, a locust's brain was found to be suited to code for solar azimuth by concurrent combination of signals from the spectral gradient, intensity gradient, and polarization pattern of the sky.
121 citations
TL;DR: Depending on the optical thickness of the cloud layer, the pattern of alpha of light transmitted through the ice or water clouds of totally overcast skies is qualitatively the same as the alpha pattern of the clear sky.
Abstract: The distribution of polarization in the overcast sky has been practically unknown. Earlier the polarization of light from heavily overcast skies (when the Sun's disc was invisible) has been measured only sporadically in some celestial points by point-source polarimetry. What kind of patterns of the degree p and angle α of linear polarization of light could develop after transmission through a thick layer of ice or water clouds? To answer this question, we measured the p and α patterns of numerous totally overcast skies on the Arctic Ocean and in Hungary by full-sky imaging polarimetry. We present here our finding that depending on the optical thickness of the cloud layer, the pattern of α of light transmitted through the ice or water clouds of totally overcast skies is qualitatively the same as the α pattern of the clear sky. Under overcast conditions the value of α is determined predominantly by scattering on cloud particles themselves. Nevertheless, the degrees of linear polarization of light from overcast skies were rather low (p≤16%). Our results obtained under overcast conditions complete the earlier findings that the α pattern of the clear sky also appears in partly cloudy, foggy, and smoky skies. Our results show that the celestial distribution of the direction of polarization is a very robust pattern being qualitatively always the same under all possible sky conditions. This is of great importance for the orientation of polarization-sensitive animals based on sky polarization under conditions when the Sun is not visible.
106 citations
TL;DR: The scalable theoretical model of light pollution for ground sources is presented and the parametric character of the model enables its efficient usage by illuminating engineers and/or astronomers in the study of various light-pollution situations.
Abstract: The scalable theoretical model of light pollution for ground sources is presented. The model is successfully employed for simulation of angular behavior of the spectral and integral sky radiance and/or luminance during nighttime. There is no restriction on the number of ground-based light sources or on the spatial distribution of these sources in the vicinity of the measuring point (i.e., both distances and azimuth angles of the light sources are configurable). The model is applicable for real finite-dimensional surface sources with defined spectral and angular radiating properties contrary to frequently used point-source approximations. The influence of the atmosphere on the transmitted radiation is formulated in terms of aerosol and molecular optical properties. Altitude and spectral reflectance of a cloud layer are the main factors introduced for simulation of cloudy and/or overcast conditions. The derived equations are translated into numerically fast code, and it is possible to repeat the entire set of calculations in real time. The parametric character of the model enables its efficient usage by illuminating engineers and/or astronomers in the study of various light-pollution situations. Some examples of numerical runs in the form of graphical results are presented.
100 citations
05 Sep 2007
TL;DR: The On-The-Fly (OTF) imaging technique as discussed by the authors enables single-dish radio telescopes to construct images of small areas of the sky with greater efficiency and accuracy than traditional methods.
Abstract: Aims. The On-The-Fly (OTF) imaging technique enables single-dish radio telescopes to construct images of small areas of the sky with greater efficiency and accuracy. Methods. This paper describes the practical application of the OTF imaging technique. By way of example the implementation of the OTF imaging technique at the NRAO 12 Meter Telescope is described. Results. Specific requirements for data sampling, image formation, and Doppler correction are discussed.
90 citations
TL;DR: In this article, a system for rapidly measuring the brightness of the night sky using a mosaic of CCD images obtained with a low-cost automated system is described, enabling the detailed characterization of natural sky conditions and light domes produced by cities.
Abstract: : We describe a system for rapidly measuring the brightness of the night sky using a mosaic of CCD images obtained with a low-cost automated system. The portable system produces millions of independent photometric measurements covering the entire sky, enabling the detailed characterization of natural sky conditions and light domes produced by cities. The measurements are calibrated using images of standard stars contained within the raw data, producing results closely tracking the Johnson V astronomical standard. The National Park Service has collected hundreds of data sets at numerous parks since 2001 and is using these data for the protection and monitoring of the night-sky visual resource. This system also allows comprehensive characterization of sky conditions at astronomical observatories. We explore photometric issues raised by the broadband measurement of the complex and variable night-sky spectrum, and potential indices of night-sky quality.
78 citations
TL;DR: In this paper, a catalog of astronomical sky spectra was used to study different aspects of OH spectroscopy and chemistry in the terrestrial night sky, including the vibrational population distribution.
Abstract: This study summarizes the use of a large catalog of astronomical sky spectra to study different aspects of OH spectroscopy and chemistry in the terrestrial night sky. The sky spectra are unique in that they have high spectral resolution, cover the entire visible wavelength region in one exposure, and are intensity-calibrated with respect to standard stars. The intensity calibration, in particular, allows a significant revision to the OH Meinel band intensity distribution that has been in use for 43~years and permits critical evaluation of the many available sets of OH emission coefficients. The spectra further allow the OH rovibrational population distributions to be monitored throughout many nights. The OH vibrational population distribution is found to change during the night, with the population ratio between the extreme high-v and low-v levels that we can detect, v = 9 and v = 3, varying by as much as a factor of two; the low-v levels being predominant earlier in the night. It has been common to deter...
73 citations
TL;DR: Hong Kong Representative Sky (HKRS) as mentioned in this paper was proposed to represent the sky conditions of Hong Kong by fitting the data to the CIE Standard General Sky definitions, which consist of 15 luminance distributions for modeling the sky from the heavily overcast sky to cloudless clear sky.
59 citations
TL;DR: In this article, a study for galaxy orbits in galaxy clusters using a spectroscopic sample of galaxies in SDSS and 2dF Galaxy Redshift Survey (2dFGRS) is presented.
Abstract: We present the results of a study for galaxy orbits in galaxy clusters using a spectroscopic sample of galaxies in Sloan Digital Sky Survey (SDSS) and 2dF Galaxy Redshift Survey (2dFGRS). We have determined the member galaxies of Abell clusters covered by these surveys using the galaxies' redshift and positional data. We have selected 10 clusters using three criteria: the number of member galaxies is greater than or equal to 40, the spatial coverage is complete, and X-ray mass profile is available in the literature. We derive the radial profile of the galaxy number density and velocity dispersion using all, early-type, and late-type galaxies for each cluster. We have investigated the galaxy orbits for our sample clusters with constant and variable velocity anisotropies over the clustercentric distance using Jeans equation. Using all member galaxies, the galaxy orbits are found to be isotropic within the uncertainty for most of sample clusters, although it is difficult to conclude strongly for some clusters due the large errors and the variation as a function of the clustercentric distance in the calculated velocity anisotropies. We investigated the orbital difference between early-type and late-type galaxies for four sample clusters, and found no significant difference between them.
59 citations
TL;DR: This paper introduces three methods of analysis for sky distributions, namely the relative indicatrix and gradation classification, and two other independent methods established by Kittler and Tregenza, verified for their feasibility for analysing the extreme daylight conditions in Singapore.
Abstract: A thorough analysis of sky distributions can help in the prediction of daylight patterns and thus provides a good understanding of architectural window and building envelope design. This paper intr...
TL;DR: In this article, the Harvard/Planetary Society all-sky search for pulsed optical signals from other civilizations, which saw "first light" on 11 April 2006 after 6 years of planning and construction, was reported.
01 Dec 2007
TL;DR: In this paper, the authors present a study about the way science teachers from elementary school think about astronomical elements, which is based on semi-structured interviews, which were video recorded and centered in a three-dimensional perspective of astronomical Earth, the Sun, the Moon, the planets and the stars.
Abstract: The research presented in this article is about the way science teachers from Elementary School think about astronomical elements. Its methodology is based on semi-structured interviews, which were video recorded. The research is centered in a three-dimensional perspective of astronomical Earth, the Sun, the Moon, the planets and the stars, and also the conceptions about sky and Universe. The esults indicate a Universe that contains: Sun, stars, planets and Moon; where the Solar System is a little part of the whole. Sometimes they think that the Solar System is the Universe. The objects are in the sky or in the Universe, which, for many of them, is only the space above the Earth. The flat shape of astronomical objects and the spatial structure of the Universe are striking features. Many of them think that Sun and stars are different: the Sun is a hot object and the stars are cold ones. These results worry us and they certainly indicate how urgent it is to plan Professional Development in Astronomy for teachers, after all the PCN´s emphasize that this subject is important to be taught.
TL;DR: In this article, the authors presented the results of a study on all sky modeling and daylight availability for the tropical climate found in the central region of the northeastern part of Thailand (16°14′N, 103°15′E).
TL;DR: In this article, a characterization of sky luminance and radiance under the standard sky brightness pattern proposed by Kittler using measurements from a station located north of Bangkok is presented. And the sky patterns of north Bangkok mostly fall into clear and intermediate types.
TL;DR: In this article, the stellar content of the XMM-Newton Bright Serendipitous Survey (XBSS) is analyzed to understand the recent star formation history of the Galaxy in the vicinity of the Sun.
Abstract: Context. The comparison of observed counts in a given sky direction with predictions by Galactic models yields constraints on the spatial distribution and the stellar birthrate of young stellar populations. The XMM-Newton Bright Serendipitous Survey (XBSS) is an unbiased survey that includes a total of 58 stellar sources selected in the 0.5–4.5 keV energy band, having a limiting sensitivity of 10 −2 cnt s −1 and covering an area of 28.10 sq deg. Aims. We present the results of analysing the stellar content of the XBSS so as to understand the recent star formation history of the Galaxy in the vicinity of the Sun. Methods. We compared the observations with the predictions obtained with XCOUNT, a model of the stellar X-ray content of the Galaxy. The model predicts the number and properties of the stars to be observed in terms of magnitude, colour, population and fx/fv ratio distributions of the coronal sources detected with a given instrument and sensitivity in a specific sky direction. Results. As in other shallow surveys, we observe an excess of stars not predicted by our Galaxy model. Comparing the colours of the identified infrared counterparts with the model predictions, we observe that this excess is produced by yellow (G+K) stars. The study of the X-ray spectrum of each source reveals a main population of stars with the coronal temperature stratification typical of intermediate-age stars. As no assumptions have been made for the selection of the sample, our results must be representative of the entire solar neighbourhood. Some stars show infrared excess due to circumstellar absorption, which is indicative of youth.
TL;DR: In this paper, the authors demonstrate that diffuse, translucent, and dark dust clouds at high Galactic latitudes are in many cases observed to have an excess of diffuse Hα surface brightness; i.e., they are brighter than the surrounding sky.
Abstract: Bright emission nebulae, or H II regions, around hot stars are readily seen in Hα light. However, the all-pervasive faint Hα emission has only recently been detected and mapped over the whole sky. Mostly the Hα emission observed along a line of sight is produced by ionized gas in situ. There are, however, cases where all or most of the Hα radiation is due to scattering by electrons or dust particles that are illuminated by an Hα-emitting source off the line of sight. Here we demonstrate that diffuse, translucent, and dark dust clouds at high Galactic latitudes are in many cases observed to have an excess of diffuse Hα surface brightness; i.e., they are brighter than the surrounding sky. We show that the majority of this excess surface brightness can be understood as light scattered off the interstellar dust grains. The source of incident photons is the general Galactic Hα background radiation impinging on the dust clouds from all over the sky.
TL;DR: In this paper, the authors investigate radio emission from low-to high-luminosity active galactic nuclei (AGNs) selected from the Sloan Digital Sky Survey (SDSS) and find that the radio emission in star-forming systems can dominate the emission associated with the AGN.
Abstract: We investigate faint radio emission from low- to high-luminosity active galactic nuclei (AGNs) selected from the Sloan Digital Sky Survey. Their radio properties are inferred by co-adding large ensembles of radio image cut-outs from the FIRST survey, as almost all of the sources are individually undetected. We correlate the median radio flux densities against a range of other sample properties, including median values for redshift, [O III] luminosity, emission-line ratios, and the strength of the 4000 A break. We detect a strong trend for sources that are actively undergoing star formation to have excess radio emission beyond the ~1028 ergs s-1 Hz-1 level found for sources without any discernible star formation. Furthermore, this additional radio emission correlates well with the strength of the 4000 A break in the optical spectrum, and may be used to assess the age of the star-forming component. We examine two subsamples, one containing the systems with emission-line ratios most like star-forming systems, and one with the sources that have characteristic AGN ratios. This division also separates the mechanism responsible for the radio emission (star formation vs. AGNs). For both cases we find a strong, almost identical correlation between [O III] and radio luminosity, with the AGN sample extending toward lower, and the star formation sample toward higher luminosities. A clearer separation between the two subsamples is seen as function of the central velocity dispersion σ of the host galaxy. For systems at similar redshifts and values of σ, the star formation subsample is brighter than the AGN in the radio by an order of magnitude. This underlines the notion that the radio emission in star-forming systems can dominate the emission associated with the AGN.
TL;DR: In this paper, a new algorithm was proposed to characterize sky condition in intervals of 5 min using four categories of sun exposition: apparent sun with cloud reflection effects; apparent sun without cloud effects; sun partially concealed by clouds; and sun totally concealed in clouds.
Abstract: This work describes a new algorithm to characterize sky condition in intervals of 5 min using four categories of sun exposition: apparent sun with cloud reflection effects; apparent sun without cloud effects; sun partially concealed by clouds; and sun totally concealed by clouds. The algorithm can also be applied to estimate hourly and daily sky condition in terms of the traditional three categories: clear, partially cloudy and cloudy day. It identifies sky conditions within a confidence interval of 95% by minimizing local climate and measurement effects. This is accomplished by using a logistic cumulative probability function to characterize clear sky and Weibull cumulative probability function to represent cloudy sky. Both probability functions are derived from frequency distributions of clearness index, based on 5 minutes-averaged values of global solar irradiance observed at the surface during a period of 6 years in Botucatu, Southeastern of Brazil. The relative sunshine estimated from the new algorithm is statistically comparable to the one derived from Campbell-Stocks sunshine recorder for both daily and monthly values. The new method indicates that the highest frequency of clear sky days occurs in Botucatu during winter (66%) and the lowest during the summer (38%). Partially cloudy condition is the dominant feature during all months of the year.
TL;DR: In this article, the authors describe the procedure used to fit and subtract individual stars from the SMEI full-sky maps, which is used by Buffington et al. (2007) to calibrate the SMEI instrument against the LASCO C3 coronagraph.
Abstract: The Solar Mass Ejection Imager (SMEI) instrument consists of three CCD cameras
with individual fields of view of 60° × 3° degrees that combined sweep a 160° arc of sky. SMEI covers the entire sky in one spacecraft orbit of 102 minutes. Individual 4-s exposures from each orbit are assembled into full-sky maps. The primary objective in the SMEI data reduction is to isolate the Thomson-scattering signal across the sky from free electrons in the solar wind. One of the steps needed to achieve the required photometric precision is
the individual fitting and removal of stars brighter than 6th magnitude from the full-sky maps. The point-spread function of the SMEI optics has several unusual properties. It has a full width of about one degree, is asymmetric, and varies in width depending on where in the field of view the image is formed. Moreover, the orientation of the PSF on the sidereal sky rotates over 360 degree
over the course of a year. We describe the procedure used to fit and subtract individual stars from the SMEI full-sky maps. A by-product of this procedure are time series at the orbital time resolution for stars brighter than 6th magnitude. These results are used by Buffington et al. (2007) to calibrate the SMEI instrument against the LASCO C3 coronagraph.
TL;DR: This work explores how such a representation, comprising a black skyline of objects in front of a white sky, can be obtained from dual-channel spectral contrast measures, and shows that contrasts with large differences in the wavelength of the two channels, specifically ultraviolet-infrared, blue-inf infrared, and ultraviolet-red, yield the best separation.
Abstract: Visual robot navigation in outdoor environments would benefit from an illumination-independent representation of images. We explore how such a representation, comprising a black skyline of objects in front of a white sky, can be obtained from dual-channel spectral contrast measures. Light from sky and natural objects under different conditions of illumination was analyzed by five spectral channels: ultraviolet, blue, green, red, and near infrared. Linear discriminant analysis was applied to determine the optimal linear separation between sky and object points. A statistical comparison shows that contrasts with large differences in the wavelength of the two channels, specifically ultraviolet-infrared, blue-infrared, and ultraviolet-red, yield the best separation. Within a single channel, the best separation was obtained for ultraviolet light. The gain in separation quality when all five channels were included is relatively small.
TL;DR: In this paper, a new method for the detection of meteoric dust in the upper atmosphere based on the polarimetric observations of the twilight sky is proposed, which is used to detect the mesosphere dust after the Leonids maximum in 2002, estimate its altitude range and to investigate its evolution.
TL;DR: In this paper, the sky relative radiance and luminance distributions from the analysis of sky images acquired using a monochromatic CCD wide angle lens camera were determined based on the reduction of the number of gray levels from the original image, in order to sharpen the different regions of the sky hemisphere, resulting in low level gray scale maps.
01 Jan 2007
TL;DR: In this article, a C program called LFmap is developed to generate maps of the sky from tens to hundreds of MHz, which can be used for comparison with observations made with prototype instruments and for calculating the diurnal variation of sky noise from single antennas to compare with measurements.
Abstract: A C program has been developed to generate maps of the sky from tens to hundreds of MHz. The method of calculation is described as well as instructions for running the program. Maps of the sky in the operating range of the LWA are useful and necessary for LWA development. Maps can be used for comparison with observations made with prototype instruments and for calculating the diurnal variation of sky noise from single antennas to compare with measurements. Many maps have been published below 100 MHz but most of these are not in electronic format. These maps are also at a few select frequencies while maps at any frequency in the LWA band are needed. LFmap is a program written in the C language to provide such maps. At low frequencies the brightness temperature of the sky is a power law: Tsky / The temperature spectral index is known to be large in regions of low Tsky and vice versa. This is interpreted as Tsky being a superposition of an isotropic component with a steep spectrum and an anisotropic component with a generally atter spectrum. The cosmic microwave background (CMB) is isotropic but has a at spectrum and is too cool to account for all the isotropic emission. The anisotropic component is due to synchrotron radiation from cosmic ray electrons in the Galactic magnetic eld. Thus the brightness temperature at frequency in direction , can be written:
TL;DR: In this article, the sky luminance distribution in Garston, south England, is studied using the multivariate statistical methods of Factor Analysis and Cluster Analysis, applied for 5 solar altitude intervals (6°-18°, 18°-30°,…, 54°-66°).
TL;DR: In this article, the authors presented optical UBVRI sky brightness measures from 1992 through 2006, based on CCD imagery obtained with the CTIO 0.9m, 1.3m, and 1.5m telescopes.
Abstract: We present optical UBVRI sky brightness measures from 1992 through 2006. The data are based on CCD imagery obtained with the CTIO 0.9-m, 1.3-m, and 1.5-m telescopes. The B- and V-band data are in reasonable agreement with measurements previously made at Mauna Kea, though on the basis of a small number of images per year there are discrepancies for the years 1992 through 1994. Our CCD-based data are not significantly different than values obtained at Cerro Paranal. We find that the yearly averages of V-band sky brightness are best correlated with the 10.7-cm solar flux taken 5 days prior to the sky brightness measures. This implies an average speed of 350 km/sec for the solar wind. While we can measure an enhancement of the night sky levels over La Serena 10 degrees above the horizon, at elevation angles above 45 degrees we find no evidence that the night sky brightness at Cerro Tololo is affected by artificial light of nearby towns and cities.
TL;DR: Cosmic light search by midlatitude zenith sky observations to extract diffuse light from totality of extragalactic light sources is described in this article, where the authors present a method to search for the light from the sky.
Abstract: Cosmic light search by midlatitude zenith sky observations to extract diffuse light from totality of extragalactic light sources