The quest for the cosmological parameters that describe our universe continues to motivate the scientific community to undertake very large survey initiatives across the electromagnetic spectrum. Over the past two decades, the Chandra and XMM-Newton observatories have sup- ported numerous studies of X-ray-selected clusters of galaxies, active galactic nuclei (AGNs), and the X-ray background. The present paper is the first in a series reporting results of the XXL-XMM survey; it comes at a time when the Planck mission results are being finalised. We present the XXL Survey, the largest XMM programme totaling some 6.9Ms to date and involving an international consortium of roughly 100 members. The XXL Survey covers two extragalactic areas of 25deg^2^ each at a point-source sensitivity of ~5x10^-15^erg/s/cm^2^ in the [0.5-2]keV band (completeness limit). The survey's main goals are to provide constraints on the dark energy equation of state from the space-time distribution of clusters of galaxies and to serve as a pathfinder for future, wide-area X-ray missions. We review science objectives, including cluster studies, AGN evolution, and large-scale structure, that are being conducted with the support of approximately 30 follow-up programmes. List of XXL papers: I. Scientific motivations - XMM-Newton observing plan - Follow-up observations and simulation programme. II. The bright cluster sample: catalogue and luminosity function. III. Luminosity-temperature relation of the bright cluster sample. IV. Mass-temperature relation of the bright cluster sample. VI. The 1000 brightest X-ray point sources. VII. A supercluster of galaxies at z = 0.43. VIII. MUSE characterisation of intracluster light in a z~0.53 cluster of galaxies. IX. Optical overdensity and radio continuum analysis of a supercluster at z=0.43. X. K-band luminosity - weak-lensing mass relation for groups and clusters of galaxies. XI. ATCA 2.1 GHz continuum observations. XII. Optical spectroscopy of X-ray-selected clusters and the frequency of AGN in superclusters. XIII. Baryon content of the bright cluster sample. XIV. AAOmega redshifts for the southern XXL field.
We present a thorough analysis of multicolour CCD observations of two modulated RRab-type variables, XY And and UZ Vir. These Blazhko stars show relatively simple light-curve modulation with the usual multiplet structures in their Fourier spectra. One additional, independent frequency with linear-combination terms of the pulsation frequency is also detected in the residual spectrum of each of the two stars. The amplitude and phase relations of the triplet components are studied in detail. Most of the epoch-independent phase differences show a slight, systematic colour dependence. However, these trends have opposite signs in the two stars. The mean values of the global physical parameters and their changes with the Blazhko phase are determined, utilizing the inverse photometric method (IPM). The modulation properties and the IPM results are compared for the two variables. The pulsation period of XY And is the shortest when its pulsation amplitude is the highest, while UZ Vir has the longest pulsation period at this phase of the modulation. Despite this contrasting behaviour, the phase relations of the variations in their mean physical parameters are similar. These results do not agree with the predictions of the Blazhko model of Stothers.
New CCD photometric observations of the chromospherically active binary XY Ursae Majoris (XY UMa) were obtained every year since 2006. The light curves obtained in the late Spring of 2006 show obvious variations on a short timescale, while the light curves obtained in 2008 December do not. But both sets of light curves are markedly asymmetric, and were analyzed using the 2003 version of the Wilson-Devinney code with spot model. New absolute physical parameters are obtained.
The XZ catalog was created at the U.S. Naval Observatory in 1977 by Richard Schmidt and Tom Van Flandern, primarily for the purpose of generating predictions of lunar occultations, and for analyzing timings of these events. It was designed to include all stars from Robertson's Zodiacal Catalog (ZC), the SAO catalog, and the AGK3 catalog that are within 6d 40' of the ecliptic (a region hereafter called "the Zodiac"), which is as far as the Moon's limb can ever get as seen from anywhere on the Earth's surface, leaving some margin for stellar proper motions and change in the obliquity of the ecliptic over the course of three centuries. The original version contained 32,221 entries. Since that time, a number of changes have been made in succeeding versions, including better positions and proper motions, and the elimination and addition of stars. The catalog contains visual magnitudes and radial velocities as well as astrometric data. Two years after the catalog was created, and observations were already reported using its numbers, it was found that about 200 stars near the equator from the AGK3 catalog were outside the Zodiac, and a similar number that should have been included were not. Since the numbering system had already been established, the catalog was not changed to correct this deficiency. Over the years, some errors in the catalog, due mainly to errors in the SAO and AGK3, were corrected. A few stars with very bad data were "eliminated" by changing their declination to -89d and adding 40 to their magnitudes. In 1986, most of the stellar positional data were replaced with improved data from Harrington's and Douglass' Zodical Zone (ZZ) catalog, which used for its observing list SAO stars in the Zodiac (actually broader than the XZ Zodiac because ecliptic latitudes to +/-15d were used) north of declination approximately -25d. The positional data for many of the stars south of declination -25d with right ascensions greater than 18h were improved with data from the Lick Voyager Uranus catalog. In 1991, the photographic magnitudes of the AGK3 stars not in the SAO were converted to photovisual magnitudes by applying corrections based on each star's spectral type, when available. Stellar magnitudes and double-star codes have been updated periodically based on reports from observers. Each time a series of updates was made, the XZ version was changed. The current version is XZ80N, created during the summer of 1992. Late in the summer of 1992, Mitsuru Soma in Japan created a J2000 version of the XZ, which we call XZ80NJ2. The next update is planned for 1994, when the positional data may also be replaced with PPM data; probably only the J2000 version will be updated. The XZ catalog is no longer maintained at the U.S. Naval Observatory (USNO); it is now maintained by the International Occultation Timing Association (IOTA). The changes made to the different versions of the XZ catalog during the past several years have been documented in Occultation Newsletter, IOTA's quarterly publication.
The XZ catalog was created at the U.S. Naval Observatory in 1977 by Richard Schmidt and Tom Van Flandern, primarily for the purpose of generating predictions of lunar occultations, and for analyzing timings of these events. It was designed to include all stars within 6d 40' of the ecliptic (the "Zodiac"), which is as far as the Moon's limb can ever get as seen from anywhere on the Earth's surface, leaving some margin for stellar proper motions and change in the obliquity of the ecliptic over the course of three centuries. The original version contained 32,221 entries; since that time, many changes have been made in succeeding versions, including better positions and proper motions, and the elimination and addition of stars. Details about the history of XZ catalog can be found in the "doc.txt" file. The XZ80Q revision has been developed from XZ80P, which was created by Mitsuru Soma. It is now complete over the Zodiac for stars down to visual magnitude 12.0. The "xz80q.dat" file contains the list of stars making the catalog; additional files provide details about double and variable stars included in the XZ80Q. The catalog includes also lists of the various existing names of the stars.
This is a completely revised and enlarged edition of the General Catalogue of Trigonometric Stellar Parallaxes containing 15,994 parallaxes for 8,112 stars published before the end of 1995. In this Fourth Edition, 1,722 (27%) new stars have been added to those contained in the previous edition by Jenkins (1963). The mode of the parallax accuracy for the newly added stars (0.004" s.e.) is considerably better than in the previous editions (about 0.016"). Approximately 2300 stars are not in the Hipparcos Catalog. The catalog contains equatorial coordinates in the system of the FK4 for 1900, the total proper motion and its position angle, the weighted average absolute parallax and its standard error, the number of parallax observations, quality of interagreement of the different values, the visual magnitude and various cross identifications with other catalogs. Auxiliary information is listed, including UBV photometry, MK spectral types, data on the variability and binary nature of the stars, and miscellaneous information to aid in determining the reliability of the data.
The various volumes of the Yale Zone Catalogues have been combined into a single, homogeneous, machine-readable volume, sorted by position, containing the information common to most of the volumes. Additional data are provided in separate files. The notes have been transcribed into a machine-readable form. Errors detected in the course of the preparation of the catalogue, as well as previously known errors, have been corrected, and supplementary data have been added.
The Yarkovsky effect is a thermal process acting upon the orbits of small celestial bodies, which can cause these orbits to slowly expand or contract with time. The effect is subtle (<da/dt>~10^-4^au/My for a 1km diameter object) and is thus generally difficult to measure. We analyzed both optical and radar astrometry for 600 Near-Earth Asteroids (NEAs) for the purpose of detecting and quantifying the Yarkovsky effect. We present 247 NEAs with measured drift rates, which is the largest published set of Yarkovsky detections. This large sample size provides an opportunity to examine the Yarkovsky effect in a statistical manner. In particular, we describe two independent population-based tests that verify the measurement of Yarkovsky orbital drift. First, we provide observational confirmation for the Yarkovsky effect's theoretical size dependence of 1/D, where D is diameter. Second, we find that the observed ratio of negative to positive drift rates in our sample is 2.34, which, accounting for bias and sampling uncertainty, implies an actual ratio of 2.7_-0.7_^+0.3^. This ratio has a vanishingly small probability of occurring due to chance or statistical noise. The observed ratio of retrograde to prograde rotators is two times lower than the ratio expected from numerical predictions from NEA population studies and traditional assumptions about the sense of rotation of NEAs originating from various main belt escape routes. We also examine the efficiency with which solar energy is converted into orbital energy and find a median efficiency in our sample of 12%. We interpret this efficiency in terms of NEA spin and thermal properties.
Rapid advancements in light-curve and radial-velocity curve modelling, as well as improvements in the accuracy of observations, allow more stringent tests of the theory of stellar evolution. Binaries with rapid apsidal advance are particularly useful in this respect since the internal structure of the stars can also be tested. Thanks to its long and rich observational history and rapid apsidal motion, the massive eclipsing binary Y Cyg represents one of the cornerstones of critical tests of stellar evolutionary theory for massive stars. Nevertheless, the determination of the basic physical properties is less accurate than it could be given the existing number of spectral and photometric observations. Our goal is to analyse all these data simultaneously with the new dedicated series of our own spectral and photometric observations from observatories widely separated in longitude.
The Crab pulsar is a bright gamma-ray source, which has been detected at photon energies up to ~1TeV. Its phase-averaged and phase-resolved gamma-ray spectra below 10GeV exhibit exponential cutoffs, while those above 10GeV apparently follow simple power laws. We re-visit the gamma-ray properties of the Crab pulsar with ten-year Fermi Large Area Telescope (LAT) data in the range of 60MeV-500GeV. With the phase-resolved spectra, we investigate the origins and mechanisms responsible for the emissions. The phaseograms were reconstructed for different energy bands and further analysed using a wavelet decomposition. The phase-resolved energy spectra were combined with the observations of ground-based instruments, such as MAGIC and VERITAS, to achieve a larger energy converage. We fitted power-law models to the overlapping energy spectra from 10GeV to ~1TeV. In the fit, we included a relative cross-calibration of energy scales between air-shower-based gamma-ray telescopes with the orbital pair-production telescope from the Fermi mission. We confirm the energy-dependence of the gamma-ray pulse shape and, equivalently, the phase-dependence of the spectral shape for the Crab pulsar. A relatively sharp cutoff at a relatively high energy of ~8GeV is observed for the bridge-phase emission. The E>10 GeV spectrum observed for the second pulse peak is harder than those for other phases. In view of the diversity of phase-resolved spectral shapes of the Crab pulsar, we tentatively propose a multi-origin scenario where the polar-cap, outer-gap, and relativistic-wind regions are involved.
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