Showing papers on "Sky published in 2003"

A Full-Sky Hα Template for Microwave Foreground Prediction

Abstract: A full-sky Hα map with 6' (FWHM) resolution is presented. This map is a composite of the Virginia Tech Spectral line Survey (VTSS) in the north and the Southern H-Alpha Sky Survey Atlas (SHASSA) in the south. The Wisconsin H-Alpha Mapper (WHAM) survey provides a stable zero point over 3/4 of the sky on a 1° scale. This composite map can be used to provide limits on thermal bremsstrahlung (free-free emission) from ionized gas known to contaminate microwave-background data. The map is available on the World Wide Web for public use.

The Wisconsin Hα Mapper Northern Sky Survey

Abstract: The Wisconsin Hα Mapper (WHAM) has surveyed the distribution and kinematics of ionized gas in the Galaxy above declination -30°. The WHAM Northern Sky Survey (WHAM-NSS) has an angular resolution of 1° and provides the first absolutely calibrated, kinematically resolved map of the Hα emission from the warm ionized medium (WIM) within ~±100 km s-1 of the local standard of rest. Leveraging WHAM's 12 km s-1 spectral resolution, we have modeled and removed atmospheric emission and zodiacal absorption features from each of the 37,565 spectra. The resulting Hα profiles reveal ionized gas detected in nearly every direction on the sky with a sensitivity of 0.15 R (3 σ). Complex distributions of ionized gas are revealed in the nearby spiral arms up to 1-2 kpc away from the Galactic plane. Toward the inner Galaxy, the WHAM-NSS provides information about the WIM out to the tangent point down to a few degrees from the plane. Ionized gas is also detected toward many intermediate velocity clouds at high latitudes. Several new H II regions are revealed around early B stars and evolved stellar cores (sdB/O). This work presents the details of the instrument, the survey, and the data reduction techniques. The WHAM-NSS is also presented and analyzed for its gross properties. Finally, some general conclusions are presented about the nature of the WIM as revealed by the WHAM-NSS.

Cosmic microwave background lensing reconstruction on the full sky

Abstract: Gravitational lensing of the microwave background by the intervening dark matter mainly arises from large-angle fluctuations in the projected gravitational potential and hence offers a unique opportunity to study the physics of the dark sector at large scales. Studies with surveys that cover greater than a percent of the sky will require techniques that incorporate the curvature of the sky. We lay the groundwork for these studies by deriving the full sky minimum variance quadratic estimators of the lensing potential from the CMB temperature and polarization fields. We also present a general technique for constructing these estimators, with harmonic space convolutions replaced by real space products, that is appropriate for both the full sky limit and the flat sky approximation. This also extends previous treatments to include estimators involving the temperature-polarization cross-correlation and should be useful for next generation experiments in which most of the additional information from polarization comes from this channel due to sensitivity limitations.

The Solar Mass Ejection Imager (SMEI)

Abstract: We describe an instrument (SMEI) which has been specifically designed to detect and forecast the arrival of solar mass ejections and other heliospheric structures which are moving towards the Earth. Such events may cause geomagnetic storms, with resulting radiation hazards and disruption to military and commercial communications; damage to Earth-orbiting spacecraft; and also terrestrial effects such as surges in transcontinental power transmission lines. The detectors are sensitive over the optical wave-band, which is measured using CCD cameras. SMEI was launched on 6 January 2003 on the Coriolis spacecraft into a Sun-synchronous polar orbit as part of the US DoD Space Test Programme. The instrument contains three cameras, each with a field of view of 60°×3°, which are mounted onto the spacecraft such that they scan most of the sky every 102-min orbit. The sensitivity is such that changes in sky brightness equivalent to a tenth magnitude star in one square degree of sky may be detected. Each camera takes an image every 4 s. The normal telemetry rate is 128 kbits s−1. In order to extract the emission from a typical large coronal mass ejection, stellar images and the signal from the zodiacal dust cloud must be subtracted. This requires accurate relative photometry to 0.1%. One consequence is that images of stars and the zodiacal cloud will be measured to this photometric accuracy once per orbit. This will enable studies of transient zodiacal cloud phenomena, flare stars, supernovae, comets, and other varying point-like objects.

A flux-calibrated, high-resolution atlas of optical sky emission from UVES

Abstract: This paper presents a flux-calibrated, high-resolution, high-SNR atlas of optical and near-IR sky emission. It provides a complete template of the high-resolution night-sky emission spectrum with the deepest exposures ever obtained from the ground. The data have been acquired by UVES, ESO's echelle spectrograph at the 8.2-m UT2 telescope of the Very Large Telescope (VLT). Raw data stacks with up to 16 hours of integration time have been combined. The spectrum covers the range 3140-10 430 A at a resolving power of about 45 000. A total of 2810 sky emission lines have been measured. This high-resolution spectrum is intended to be used for the identification of previously unknown faint sky lines, for simulations of ground based observations where the sky background is important, as a template for checks on the accuracy and stability of the wavelength scale, and as a reference for the reduction of spectra of faint objects.

Redshifted 21 cm Emission From the Pre-Reionization Era I. Mean Signal and Linear Fluctuations

Abstract: We use cosmological simulations of reionization to predict the possible signal from the redshifted 21 cm line of neutral hydrogen in the pre-reionization era and to investigate the observability of this signal. We show that the separation of the mean (global) signal over the whole sky from the known foreground contamination may be feasible, but very challenging. In agreement with previous studies, we demonstrate that measuring angular fluctuations in the HI signal is likely to be extremely difficult if not impossible because of the overwhelming contamination from the galactic and extragalactic foregrounds. However,we show that the sharp HI fluctuations in the frequency domain should be easily separable from the relatively smooth spectra of the foregrounds, and that these fluctuations should be detectable even at moderate angular resolution (10-20 arcmin).

The Richness-Dependent Cluster Correlation Function: Early SDSS Data

Abstract: The cluster correlation function and its richness dependence are determined from 1108 clusters of galaxies -- the largest sample of clusters studied so far -- found in 379 deg^2 of Sloan Digital Sky Survey early data. The results are compared with previous samples of optically and X-ray selected clusters. The richness-dependent correlation function increases monotonically from an average correlation scale of ~ 12 h^{-1} Mpc for poor clusters to ~ 25 h^{-1} Mpc for the richer, more massive clusters with a mean separation of ~ 90 h^{-1} Mpc. X-ray selected clusters suggest slightly stronger correlations than optically selected clusters (~ 2-\sigma). The results are compared with large-scale cosmological simulations. The observed richness-dependent cluster correlation function is well represented by the standard flat LCDM model (\Omega_m ~= 0.3, h ~= 0.7), and is inconsistent with the considerably weaker correlations predicted by \Omega_m = 1 models. An analytic relation for the correlation scale versus cluster mean separation, r_0 - d, that best describes the observations and the LCDM prediction is r_0 ~= 2.6 \sqrt{d} (for d ~= 20 - 90 h^{-1} Mpc). Data from the complete Sloan Digital Sky Survey, when available, will greatly enhance the accuracy of the results and allow a more precise determination of cosmological parameters.

The Galaxy Evolution Explorer

Abstract: The Galaxy Evolution Explorer (GALEX), a NASA Small Explorer Mission planned for launch in Fall 2002, will perform the first Space Ultraviolet sky survey. Five imaging surveys in each of two bands (1350-1750a and 1750-2800a) will range from an all-sky survey (limit mAB~20-21) to an ultra-deep survey of 4 square degrees (limit mAB~26). Three spectroscopic grism surveys (R=100-300) will be performed with various depths (mAB~20-25) and sky coverage (100 to 2 square degrees) over the 1350-2800a band. The instrument includes a 50 cm modified Ritchey-Chretien telescope, a dichroic beam splitter and astigmatism corrector, two large sealed tube microchannel plate detectors to simultaneously cover the two bands and the 1.2 degree field of view. A rotating wheel provides either imaging or grism spectroscopy with transmitting optics. We will use the measured UV properties of local galaxies, along with corollary observations, to calibrate the UV-global star formation rate relationship in galaxies. We will apply this calibration to distant galaxies discovered in the deep imaging and spectroscopic surveys to map the history of star formation in the universe over the red shift range zero to two. The GALEX mission will include an Associate Investigator program for additional observations and supporting data analysis. This will support a wide variety of investigations made possible by the first UV sky survey.

A Study of 15 Sky Luminance Patterns against Hong Kong Data

Abstract: A good knowledge of the sky luminance distribution is essential for efficient day lighting designs and developments. This paper studies a set of 15 standard skies established by Kittler, Perez and Darula using the measured sky luminance data from subtropical Hong Kong. A statistical analysis of the results has shown that the standard sky set is adequate to cover the various sky conditions. A reduction of the standard set to five skies is sufficient to model the luminance distributions. The ratio of zenith luminance to horizontal diffuse illuminance (L/zD) which can be used to define homogeneous sky standards was analysed based on these five selected skies. It has been shown that the trend of L/zDv ratios under different sky types followed the ranges described by Kittler et al.

New High Proper Motion Stars from the Digitized Sky Survey. II. Northern Stars with 0.5<mu<2.0 arcsec/yr at High Galactic Latitudes

Abstract: In a continuation of our systematic search for high proper motion stars in the Digitized Sky Survey, we have completed the analysis of northern sky fields at galactic latitudes above 25 degrees. With the help of our SUPERBLINK software, a powerful automated blink comparator developed by us, we have identified 1146 stars in the magnitude range 8

The trispectrum of the Cosmic Microwave Background on sub-degree angular scales: an analysis of the BOOMERanG data

Abstract: The trispectrum of the cosmic microwave background can be used to assess the level of non-Gaussianity on cosmological scales. It probes the fourth order moment, as a function of angular scale, of the probability distribution function of fluctuations and has been shown to be sensitive to primordial non-gaussianity, secondary anisotropies (such as the Ostriker-Vishniac effect) and systematic effects (such as astrophysical foregrounds). In this paper we develop a formalism for estimating the trispectrum from high resolution sky maps which incorporates the impact of finite sky coverage. This leads to a series of operations applied to the data set to minimize the effects of contamination due to the Gaussian component and correlations between estimates at different scales. To illustrate the effect of the estimation process, we apply our procedure to the BOOMERanG data set and show that it is consistent with Gaussianity. This work presents the first estimation of the CMB trispectrum on sub-degree scales.

Scientific optimization of a ground-based CMB polarization experiment

Abstract: We investigate the science goals achievable with the upcoming generation of ground-based Cosmic Microwave Background polarization experiments and calculate the optimal sky coverage for such an experiment including the effects of foregrounds. We find that with current technology an E-mode measurement will be sample-limited, while a B-mode measurement will be detector-noise-limited. We conclude that a 300 sq deg survey is an optimal compromise for a two-year experiment to measure both E and B-modes, and that ground-based polarization experiments can make an important contribution to B-mode surveys. Focusing on one particular experiment, QUaD, a proposed bolometric polarimeter operating from the South Pole, we find that a ground-based experiment can make a high significance measurement of the acoustic peaks in the E-mode spectrum, and will be able to detect the gravitational lensing signal in the B-mode spectrum. Such an experiment could also directly detect the gravitational wave component of the B-mode spectrum if the amplitude of the signal is close to current upper limits. We also investigate how a ground-based experiment can improve constraints on the cosmological parameters. We estimate that by combining two years of QUaD data with the four-year WMAP data, an optimized ground-based polarization experiment can improve constraints on cosmological parameters by a factor of two. If the foreground contamination can be reduced, the measurement of the tensor-to-scalar ratio can be improved by up to a factor of six over that obtainable from WMAP alone.

Daylight visible/NIR whole-sky imagers for cloud and radiance monitoring in support of UV research programs

Abstract: Measurements of UV radiation at the earth’s surface may be highly impacted by the presence of clouds. In order to provide support for UV research, a Daylight Visible/NIR Whole Sky Imager was developed to provide cloud fraction assessment over the whole sky, as well as measurements of the radiance distribution over the full sky in several spectral bands. Radiances are determined in approximately 700,000 directions simultaneously with a given optical filter. Data may be acquired in seven spectral bands that may be selected for the application. The current instrument uses filters near 450 and 650 nm, open-hole, filters in the blue-green broadband and NIR long-pass, and two polarizers. Opaque and thin cloud fraction is determined from images acquired in the blue and red wavelengths. A more sophisticated version of the algorithm to detect thinner clouds and enable aerosol assessment is in development, and will be based on use of the NIR data in conjunction with the blue and red data. This paper will provide an overview of the instrument design and calibration, and sample sky radiance results. The cloud algorithms for determination of cloud fraction will be discussed, and the cloud imager results will also be presented.

The Faint Sky Variability Survey - I. Goals and data reduction process

Abstract: The Faint Sky Variability Survey is aimed at finding photometric and/or astrometric variable objects in the brightness range between ∼16th and ∼24th mag on time-scales between tens of minutes and years with photometric precisions ranging from 3 millimag for the brightest to 0.2 mag for the faintest objects. An area of ∼23 deg 2 , located at mid and high Galactic latitudes, has been covered using the Wide Field Camera on the 2.5-m Isaac Newton Telescope on La Palma. Here we describe the main goals of the Faint Sky Variability Survey and the data reduction process.

Serendipity and the Sloan Digital Sky Survey: Discovery of the Largest Known Planetary Nebula on the Sky

Abstract: Investigation of spectra from the Sloan Digital Sky Survey reveals the presence of a region of ionized gas of greater than 2° diameter centered approximately at α = 10h37m, δ = -00°18' (J2000.0) (Galactic coordinates l = 248°, b = +48°). [O III] λλ4959, 5007 emission is particularly strong, and emission from Hα and [N II] λλ6548, 6583 is also detectable over a substantial area on the sky. The combination of emission-line ratios, the close to zero heliocentric radial velocity, and the morphology of the structure is consistent with an identification as a very nearby planetary nebula. The proximity of the hot, DO white dwarf PG 1034+001 further strengthens this interpretation. The object is (1) the largest planetary nebula on the sky, (2) certainly closer than any planetary nebula other than Sh 2-216, and (3) the first to be unambiguously associated with a DO white dwarf. A parallax distance for PG 1034+001 would establish whether the structure is in fact the closest, and one of the physically largest, planetary nebulae known.

Astronomical Observing Conditions at the Xinglong Station in 1995–2001

Abstract: This paper summarizes the measurements of astronomical observing conditions with a fixed pointing to the North Pole over 6 years at the Xinglong Station, where the BATC Multicolor Sky Survey has been conducted since 1995. Three major effects that influence the sky quality the most have been studied: the atmospheric transparency, the sky brightness, and the seeing. No obvious annual variation of the transparency was detected, but seasonal changes on a regular basis have been observed. The transparency is better and more stable in the winter than in the summer, which points to the fact that winter is the season for precise photometric work in Xinglong. The relations of sky brightness versus lunar phase and versus lunar altitude are derived and discussed. We find, on average, that the value of sky brightness in moonlight-corrected V magnitude of the North Pole field is about 21.0 mag arcsec 2 . The sky is darker in the fall and winter than in the spring and summer, and the transparency is better. It is conjectured that there are fewer particles in the air in the winter, thus both absorption and scattering are minimal. The seeing in the winter is worse than in the summer. This is probably due to the gusty wind from the northwest in the winter. The results of the North Pole monitoring presented in this paper show that the Xinglong Station is an astronomically good observing site. The North Pole observations will continue as a part of the BATC sky survey.

All-sky upper limit for gravitational radiation from spinning neutron stars

Abstract: We present results of the all-sky search for gravitational-wave signals from spinning neutron stars in the data of the EXPLORER resonant bar detector. Our data analysis technique was based on the maximum likelihood detection method. We briefly describe the theoretical methods that we used in our search. The main result of our analysis is an upper limit of 2 × 10−23 for the dimensionless amplitude of the continuous gravitational-wave signals coming from any direction in the sky and in the narrow frequency band from 921.00 Hz to 921.76 Hz.

Color and luminance asymmetries in the clear sky

Abstract: A long-standing assumption about the clear sky is that its colors and luminances are distributed symmetrically about the principal plane. As useful as this approximation is, our digital-image analyses show that clear-sky color and luminance routinely depart perceptibly from exact symmetry. These analyses reconfirm our earlier measurements with narrow field-of-view spectroradiometers [J. Opt. Soc. Am. A 18, 1325 (2001)], and they do so with much higher temporal and angular resolution across the entire sky dome.

All sky imager

Abstract: Disclosed is an All Sky Imager which uses a camera capable of capturing color images of cloud cover that is housed in an environmentally protected enclosure to protect it from weather elements. To obtain a good hemispherical view of the sky, the fish-eye lens is attached to the camera to provide a 360-degree, horizon-to-horizon view. The All Sky Imager is mounted on a solar tracker so that the image of the sun is blocked by one of the solar tracker's obscuration balls. This in effect places a shadow over the lens of the camera allowing the color capture of sky images, particularly cloud cover, without the danger of damaging the camera. As the earth rotates, the obscuration ball of the solar tracker keeps the camera obscured from the sun. This provides continuous images of sky cloud cover from sunrise to sunset. The invention also includes an embodiment using an infrared camera that allows for nighttime cloud imaging.

X‐Ray Flashes and X‐Ray Counterparts of Gamm‐Ray Bursts

Abstract: The brightest transients in the sky, Supernovae and Gamma‐Ray Bursts, are associated with the collapse of cores of massive stars. They shine in the optical and in the gamma‐ray sky. On theoretical grounds one would expect to see similar events in the x‐ray and ultra‐violet sky. Here we summarize recent observational evidence demonstrating the existence of X‐ray bursts, termed X‐ray Flashes (XRFs). We argue that they are most likely very large explosions on a cosmological distant scale, similar to Gamma‐Ray Bursts (GRBs). They may either be highly redshifted GRBs, GRBs viewed at a large angle or another geometrical effect. Or they may be a new type of cosmic explosion expanding mildly relativistically, much larger than the initial expansion of supernova remnants, but less than the extreme relativistic cosmic fireballs of Gamma‐Ray Bursts. The ratio of the energy contained in the X‐ray part (2–10 keV) of Gamma‐Ray Bursts to the γ‐range (50–350 keV) varies widely. GRBs for which this fraction is typically mo...

Using routine meteorological data to derive sky conditions

Abstract: . Sky condition is a matter of interest for public and weather predictors as part of weather analyses. In this study, we apply a method that uses total solar radiation and other meteorological data recorded by an automatic station for deriving an estimation of the sky condition. The impetus of this work is the intention of the Catalan Meteorological Service (SMC) to provide the public with real-time information about the sky condition. The methodology for deriving sky conditions from meteorological records is based on a supervised classification technique called maximum likelihood method. In this technique we first need to define features which are derived from measured variables. Second, we must decide which sky conditions are intended to be distinguished. Some analyses have led us to use four sky conditions: (a) cloudless or almost cloudless sky, (b) scattered clouds, (c) mostly cloudy – high clouds, (d) overcast – low clouds. An additional case, which may be treated separately, corresponds to precipitation (rain or snow). The main features for estimating sky conditions are, as expected, solar radiation and its temporal variability. The accuracy of this method of guessing sky conditions compared with human observations is around 70% when applied to four sites in Catalonia (NE Iberian Peninsula). The agreement increases if we take into account the uncertainty both in the automatic classifier and in visual observations. Key words. Meteorological and atmospheric dynamics (instruments and techniques; radiative processes) – Atmospheric composition and structure (cloud physics and chemistry)

The XMM-Newton Serendipitous Sky Survey

Abstract: The main properties of the XMM-Newton serendipitous sky survey are outlined. The XMM-Newton Survey Science Centre’s role in the survey is described with emphasis on its follow-up and identification programme and the production of the XMM-Newton catalogue.

Simulating and calculating sky luminance distribution with CIE standard DS 011.2

Abstract: For over half a century, the experts have been trying to describe the daylight and sky luminance distribution with different models. Different approaches were used to describe the luminance of sky in different weather and climactic conditions. But until recently, only two types of sky had been standardized: The CIE Standard Clear Sky and Overcast Sky. As the use of daylight is gaining on importance in the lighting design, the TC 3 at CIE also started drafting a standard description of other types of sky between clear and overcast sky. The new standard will be used in calculations of lighting conditions in interiors lit by natural daylight. In the paper, the new CIE standard is described together with two computer programs developed in our laboratory. The first program is used for calculation of the position of the Sun according to the point of observation on the Earth and time (date). The position of the Sun is then used in the second program for calculation of the sky luminance distribution according to the proposed standard. The program calculates the luminance of 77 patches representing the sky vault. The luminance of this sky model will then be used for calculating lighting conditions in interiors lit by daylight.

Sky luminance and radiance distributions: a comparison based on data from Bahrain, Israel, Japan and Europe:

Abstract: Predictive models of building performance are increasingly being based on sky luminance and radiance distributions. These, though, tend to exist as separate records and the word-wide coverage is not complete: sky luminance, in particular, has been recorded at relatively few locations. It is important in practice to ensure that luminance and radiation values are consistent with each other and that radiation measurements are used to supplement the illumination records. The paper compares data from the authors’ research in several climatic regions and shows that an anisotropic model of the sky distribution can be significantly more accurate than an isotropic function. This is discussed with particular reference to shadow band correction.