Full Sky Coverage Research Articles

The First US Naval Observatory CCD Astrograph Catalog

The USNO CCD Astrograph (UCA) started an astrometric survey in 1998 February at Cerro Tololo, Chile. This first, preliminary catalog (UCAC1) includes data taken up to 1999 November with about 80% of the Southern Hemisphere covered. Observing continues, and full sky coverage is expected by mid-2003 after moving the instrument to a Northern Hemisphere site in early 2001. The survey is performed in a single bandpass (579–642 nm), a twofold overlap pattern of fields, and with a long and a short exposure on each field. Stars in the magnitude range 10–14 have positional precisions of ≤20 mas. At the limiting magnitude of R ≈ 16 mag, the positional precision is 70 mas. The UCAC aims at a density (stars per square degree) larger than that of the Guide Star Catalog (GSC) with a positional accuracy similar to Tycho. The UCAC program is a major step toward a high-precision densification of the optical reference frame in the post–Hipparcos era, and the first stage, the UCAC1 contains over 27 million stars. Preliminary proper motions are included, which were derived from Tycho-2, Hipparcos, and ground-based transit circle and photographic surveys for the bright stars (V ≤ 12.5 mag) and the USNO A2.0 for the fainter stars. The accuracy of the proper motions varies widely, from 1 to over 15 mas yr-1. The UCAC1 is available on CD-ROM from the US Naval Observatory.

The Pierre Auger observatory

We present the scientific motivation, conceptual design and status of the P. Auger Observatory, a hybrid detector designed to measure both the longitudinal and the lateral profile of giant air-showers produced by cosmic-rays of energy above 10 19 eV. Two ground arrays of water Čerenkov tanks overlooked by fluorescence detectors will cover an area of 3000 km 2 each. They will be build in the Southern and Northern hemisphere to provide full sky coverage. The total aperture of 14000 km 2 sr will allow to study all observable aspects of cosmic rays from below 10 EeV up to arbitrarily high energies with an unprecedented accuracy.

The UCAC as Input Catalog for FAME

AbstractA new, highly accurate, astrometric star catalog is available from the U.S. Naval Observatory, covering ≈ 80% of the Southern Hemisphere to R ≈ 16m. The observing program is ongoing and full-sky coverage is expected by 2003. The final catalog will be used as the input catalog for the FAME space mission.

Absolute Tilt from a Laser Guide Star: A First Experiment

Absolute tip–tilt recovery using a tilt signal measured on a Laser Guide Star is a central problem in the framework of the development of Adaptive Optics Systems reaching full sky coverage down to visible wavelengths. In the past few years, various techniques aimed at solving this problemhave been proposed. However only a couple of these has been recentlytested in practice.We report about an experiment aimed at evaluating the performance of one of these techniques called the ‘Elongation Perspective’ technique. Our experiment has been performed using the ALFA system inCalar-Alto (Spain) and involves the simultaneous operation of the 3.6 m and the 2.2 m telescopes at the Observatory.This article describes the telescope configuration used, as well as the datareduction process carried out in order to estimate the scientific objecttilt. The technique performances are discussed in terms of the residualtilt error variance and related correlation coefficient. The analysisshows that, despite the low SNR of our measurements, the atmospheric tiltvariance is reduced to 80% of its initial value corresponding to acorrelation coefficient of about 0.6. To get a betterestimate of the performance achievable using this technique,the tilt error variance due to photon noise in the laser measurementis estimated and removed from the obtained tilt error variance.When this correction is done, thisvariance is reduced to about 50% of its initial value, showingthat the use of this technique can give rise to a significant reduction of the scientific object image motion.

The Planck-LFI instrument: Analysis of the $1/f$ noise and implications for the scanning strategy

We study the impact of the 1/f noise on the PLANCK Low Frequency Instrument (LFI) osbervations (Mandolesi et al 1998) and describe a simple method for removing striping effects from the maps for a number of different scanning stategies. A configuration with an angle between telescope optical axis and spin-axis just less than 90 degrees (namely 85 degress) shows good destriping efficiency for all receivers in the focal plane, with residual noise degradation < 1-2 %. In this configuration, the full sky coverage can be achieved for each channel separately with a 5 degrees spin-axis precession to maintain a constant solar aspect angle.

X-ray luminosities for a magnitude-limited sample of early-type galaxies from the ROSAT All-Sky Survey

For a magnitude-limited optical sample (BT≤ 13.5 mag) of early-type galaxies, we have derived X-ray luminosities from the ROSAT All-Sky Survey. The results are 101 detections and 192 useful upper limits in the range from 1036 to 1044 erg s-1. For most of the galaxies no X-ray data have been available until now. On the basis of this sample with its full sky coverage, we find no galaxy with an unusually low flux from discrete emitters. Below log (LB)≈ 9.2 L⊗ the X-ray emission is compatible with being entirely due to discrete sources. Above log (LB)≈ 11.2 Lo˙ no galaxy with only discrete emission is found. We further confirm earlier findings that Lx is strongly correlated with LB. Over the entire data range the slope is found to be 2.23 (± 0.12). We also find a luminosity dependence of this correlation. Below log Lx = 40.5 erg s-1 it is consistent with a slope of 1, as expected from discrete emission. Above this value the slope is close to 2, as expected from gaseous emission. Comparing the distribution of X-ray luminosities with the models of Ciotti et al. leads to the conclusion that the vast majority of early-type galaxies are in the wind or outflow phase. Some of the galaxies may have already experienced the transition to the inflow phase. They show X-ray luminosities in excess of the value predicted by cooling flow models with the largest plausible standard supernova rates. A possible explanation for these super X-ray-luminous galaxies is suggested by the smooth transition in the Lx--LB plane from galaxies to clusters of galaxies. Gas connected to the group environment might cause the X-ray overluminosity.

Sky coverage with the auxiliary telescopes Laser Guide Star tilt recovery technique

Auxiliary telescopes in the neighbourhoods of a main telescope equipped with an LGS can provide, in principle, full sky coverage. The auxiliary telescopes, however, should be able to move around in order to acquire a useful natural guide star (NGS), and to track the LGS, comoving with the scientific target. Detailed expressions and results of numerical simulations are given.

Project Argus and the Challenge of Real-Time All-Sky Seti

AbstractProject Argus, a global effort of the non-profit SETI League, Inc., seeks to achieve continuous microwave monitoring of all four pi steradians of space, in real time. This most ambitious SETI project ever undertaken without benefit of Government support will ultimately involve 5,000 small radiotelescopes worldwide, built, maintained and operated by private individuals (primarily radio amateurs and microwave experimenters), coordinated so as to miss no likely candidate signals, and providing independent verification of any interesting signals detected. Prototype stations went into operation in 1996; full sky coverage is planned for 2001. Sensitivity and range are assessed by comparison of current capabilities to those in place at the Ohio State Radio Observatory nineteen years ago, when the so-called «Wow!» signal was detected. The «Wow!» signal serves as a convenient benchmark, even though its exact nature remains unknown. Should a similar candidate signal appear during the fully deployed phase of Project Argus, it will not evade detection. Though utilizing just a small satellite TV dish as its antenna, each station achieves range and sensitivity on a par with the Ohio State Big Ear radio telescope, circa 1977. This paper explores the technological breakthroughs which have made this level of performance possible.

Propagation Delay of a Laser Beacon as a Tool to Retrieve Absolute Tilt Measurements

The knowledge of the temporal evolution of a star wandering for a limited time interval (e.g., a fraction of a second) can be used to increase dramatically the sky coverage of a laser-beacon adaptive optics system. A technique to achieve such short-term tracking is described. The full sky coverage is easily achieved by using the whole telescope as a laser projector.

COBE/DIRBE Studies of Scattering By Interplanetary Dust

AbstractThe high photometric quality and full-sky coverage in the COBE DIRBE datasets make possible detailed studies of the interplanetary medium. This paper presents a preliminary derivation of the infrared scattering phase function of interplanetary dust. The ultimate purpose of these investigations is to use the DIRBE observations to constrain the composition, size and structure of interplanetary dust grains.

On determining the spectrum of primordial inhomogeneity from the COBE DMR sky maps: Method

The natural approach to a spectral analysis of data distributed on the sky employs spherical harmonic decomposition. A common problem encountered in practical astronomy is the lack of full sky coverage in the available data. For example, the removal of the Galactic plane data from the Cosmic Background Explorer (COBE) Differential Microwave Radiometer (DMR) sky maps compromises Fourier analysis of the cosmic microwave background (CMB) temperature distribution due to the loss of orthogonality of the spherical harmonics. An explicit method for constructing orthonormal functions on an incomplete (e.g., Galaxy-cut) sphere is presented. These functions should be used in the proper Fourier analysis of the COBE DMR sky maps to provide the correct input for the determination of the spectrum of primordial inhomogeneity. The results of such an analysis are presented in an accompanying Letter. A similar algebraic construction of appropriate functions can be devised for other astronomical applications.

The Cosmic Background Explorer

Late last year the National Aeronautics and Space Administration launched its first satellite dedicated to the study of phenomena related to the origins of the universe. The satellite, called the Cosmic Background Explorer (COBE), carries three complementary detectors that will make fundamental measurements of the celestial radiation. Part of that radiation is believed to have originated in processes that occurred at the very dawn of the universe. By measuring the remnant radiation at wavelengths from one micrometer to one centimeter across the entire sky, scientists hope to be able to solve many mysteries regarding the origin and evolution of the early universe. Unfortunately, these radiative relics of the early universe are weak and veiled by local astrophysical and terrestrial sources of radiation. The wavelengths of the various cosmic components may also overlap, thereby making the understanding of the diffuse celestial radiation a challenge. Nevertheless, the COBE instruments, with their full-sky coverage, high sensitivity to a wide range of wavelengths and freedom from interference from the earth's atmosphere, will constitute for astrophysicists an observatory of unprecedented sensitivity and scope. The interesting cosmic signals will then be separated from one another and from noncosmic radiation sources by a comprehensive analysis of themore » data.« less

All-sky monitors for X-ray astronomy

We discuss the rationale for a semi-permanent all-sky X-ray monitor, and investigate a variety of options for its implementation. We conclude that the Space Station offers an excellent opportunity for hosting such a monitor, and that a set of pinhole cameras can be configured to provide an effective and economical monitor system. A baseline of six independent pinhole modules, each of which requires approximately one cubic foot, 30 pounds, 2 watts, and 100 bits per second, can provide full sky coverage with scientifically interesting sensitivities. No other resources or special accommodation (such as detailed alignment registration, time-tagging or on-orbit servicing) would be required. The baseline system can locate bright sources to a few arc min, and can simultaneously measure each of the several hundred sources in the sky brighter than a few thousandths the intensity of the Crab nebula every day for decades.

A sparse-sampling strategy for the estimation of large-scale clustering from redshift surveys

The form of the power spectrum of galaxy clustering at large wavelengths provides a powerful test of theories for galaxy formation. We show that estimating the two-point correlation function from a complete, magnitude limited redshift survey provides a rather inefficient way to apply this test. By sampling only a randomly chosen fraction of the galaxies, but to a fainter magnitude limit, one can significantly reduce the uncertainty in the two-point function, ξ, for a given investment of telescope time. In order to extend our knowledge of ξ beyond the point at which the currently available estimates fall to a level consistent with vanishing correlations, which we estimate to be around |$r\simeq15\enspace h^{-1}\enspace \text {Mpc}$|⁠, one should sample at a rate of about one in 20 bright galaxies. The signal-to-noise ratio for such a sparse sample is roughly twice that provided by a complete survey of the same cost, and this performance is the same as for a larger complete survey of about seven times the cost. The same increase in performance can be obtained if the redshifts are collected multiply on a wide-field telescope, provided that the survey is sufficiently large that close to full sky coverage can be maintained. For smaller, multiply collected surveys one should ideally sample at the somewhat denser rate of about one in 10 bright galaxies, though the improvement in performance in this case is relatively small. The optimum-sampling fraction for Abell's rich clusters is close to unity and, in this case, no significant improvement in performance is provided by sparsely sampling.

The Southern Cluster Survey

We are searching for clusters of galaxies on photographs taken for the Southern Sky Survey with the U.K. Schmidt telescope at Siding Spring, and we are preparing a comprehensive catalogue of the southern clusters. The purpose is to extend the early cluster survey made from the Palomar Sky Survey (Abell 1958) to full-sky coverage. We are taking special pains to delineate those clusters in the new southern survey that as nearly as possible match those criteria set for the northern survey clusters to be included in a homogeneous statistical sample. It is our expectation, therefore, that there will be a homogeneous all-sky sample of clusters for studying the large-scale distribution of matter in the universe.

The COBE Project

As described in the paper by John Mather and Tom Kelsall, theCOBE (Cosmic Background Explorer) project is designed tomake a substantial improvement in our knowledge of the condition in the universe at large red shifts. The focus of themission is to study attributes of the primeval cosmic background radiation and to set limits on the universal radiationenergy density at shorter wavelengths - radiation emanatingfrom distant sources but at later times than the primevalfireball. In introducing the accompanying paper, I thoughtit might be worthwhile to describe the scientific strategy drivingthe COBE mission.The COBE mission has been under study since 1974 by ateam of scientists consisting of S. Gulkis (Jet Propulsion Laboratory), M. Hauser (NASA Goddard Space Flight Center), J.Mather (NASA), G. Smoot (University of California, Berkeley),R. Weiss (MIT), and D. Wilkinson (Princeton). The teammembers have been involved in ground based, balloon borneand airborne experiments to measure the background radiationand are keenly aware of limitations of these platforms and thearguments in favor of a space borne experiment. It is worthrepeating these arguments:(1) Freedom from atmospheric emission and fluctuationsin the emission.(2) Full sky coverage with a single instrument.(3) A benign and controlled thermal environment to reducesystematic errors.(4) The ability to perform absolute primary calibration inflight without the necessity of windows to avoid condensationof the atmosphere on calibrators and instruments.(5) Sufficient time both to perform tests for systematicerrors and to gain the increase in sensitivity permitted byextended observation time.In planning the COBE mission, the team came to know thepeculiar difficulties of carrying out a space mission. Aside fromthe ever present problem of maintaining the project within anassigned budget, the mission had to be designed so that it wouldstill be the "right thing to do" in the field after the 5 to 10years it takes between initial planning and execution. One hadto anticipate the progress that could still be made by usingother platforms and blend this with the fact that in the spacemission one would be dealing with technology that was 3 to5 years behind the state of the art (to allow time for spacequahfication).In an interim report to NASA in 1977, the conclusion of theteam was that the technology was sufficiently advanced and theinstrument systematic noise sources were well enoughunderstood or controllable so that the major limitation in aspace mission to perform precision measurements of the background would be the "noise" produced by the local astrophysical environment. The complement of instruments chosenfor the mission, as well as the need for full sky coverage andextended observation time, are based primarily on the hopethat the local astrophysical "noise" can be discriminated fromthe cosmic background by its peculiar set of spectra and anisotropic angular distribution. In the COBE mission, the datafrom one instrument truly serves to enhance the value of thatfrom another. Examples of this are discussed in theaccompanying paper.

A survey of the X-ray sky with HEAO A-1

The primary mission of the A-1 instrument aboard the first N. A. S. A. High Energy Astronomical Observatory (HEAO) is to enlarge the catalogue of X-ray sources to about 1000. Seven modules of X-ray proportional counters, having an average effective aperture of about 1700 cm 2 apiece, cover an energy range from 0.25 keV to about 25 keV. Full sky coverage is obtained by spinning the spacecraft at 2 rev. h -1 about the direction to the Sun. The detectors view the sky at right angles to the spin axis, so that 48 great circle sweeps normal to the ecliptic plane are completed each day. As the Earth carries the spacecraft around the Sun, the scan plane rotates 1° in ecliptic latitude each day. The basic scan is obtained with four modules having 1° x 4° collimation, giving 10000 resolution elements on the full sky. Assuming one source detection for every ten resolution elements, the survey should detect about 1000 sources.