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MERLIN Astrometry of 11 Radio Stars
We report accurate positions in the International Celestial ReferenceFrame (ICRF) for 11 radio stars. Observations were made using theMulti-Element Radio Linked Interferometer Network at a radio frequencyof 5 GHz. The positions are estimated to be accurate at the 5 mas level.Positions were obtained directly in the ICRF by phase referencing theradio stars to ICRF quasars whose positions are estimated to be accurateat the 0.25 mas level. We use our results together with results ofprevious observations to obtain proper-motion estimates for these stars.The average proper-motion uncertainties are 1.1 mas yr-1 inμαcosδ and 1.2 mas yr-1 inμδ, comparable to the Hipparcos values.
| Observed Orbital Eccentricities
For 391 spectroscopic and visual binaries with known orbital elementsand having B0-F0 IV or V primaries, we collected the derivedeccentricities. As has been found by others, those binaries with periodsof a few days have been circularized. However, those with periods up toabout 1000 or more days show reduced eccentricities that asymptoticallyapproach a mean value of 0.5 for the longest periods. For those binarieswith periods greater than 1000 days their distribution of eccentricitiesis flat from 0 to nearly 1, indicating that in the formation of binariesthere is no preferential eccentricity. The binaries with intermediateperiods (10-100 days) lack highly eccentric orbits.
| Evidence for Superhumps in the Radio Light Curve of Algol and a New Model for Magnetic Activity in Algol Systems
Extensive radio data of two Algol systems and two RS CVn binaries werereanalyzed. We found evidence for a new periodicity that we interpret asa superhump in β Per (Algol), for which it may have been expectedaccording to its semidetached nature and low binary mass ratio. Theconcluded presence of an accretion disk (or an annulus) is consistentwith previous studies of optical data and numerical simulations ofβ Per. In our model, the 50 day period, previously found in theradio data of β Per, is explained as the apsidal precession of theelliptical accretion disk or annulus. If our interpretation is correct,this is the first detection of the superhump phenomenon in the radio andthe first observation of superhumps in Algol systems. According to ourresult, the accretion disk or annulus in β Per precesses in spiteof its non-Keplerian nature, and therefore, this phenomenon is notrestricted to the classical Keplerian accretion disks in compactbinaries. We propose that in Algol systems with short orbital periods,which have accretion disks or annuli, the disk is magnetically active inaddition to the cool secondary star. The magnetic field in the diskoriginates from amplification of the seed field in the magnetizedmaterial transferred from the secondary. The disk and stellar fieldsinteract with each other, with reconnection of the field lines causingflares and particle acceleration. Relativistic particles are trapped inthe field and directed toward the polar regions of the secondary starbecause of the dipole structure of its magnetic field. These systemsare, therefore, somewhat analogous to the RS CVn systems, which have twomagnetically interacting stars. Our proposed model for the magneticactivity in Algol systems provides a simple explanation for the observedproperties of β Per in the radio wavelengths, and in particular,for the presence of quiescent gyrosynchrotron emission near the polarregion of the secondary star, where electrons are difficult to confineif the field lines are open as in normal, single, magnetic stars. Itfurther explains the recent discovery that the Doppler shifts of theemission lines in the X-ray data of β Per are somewhat lower thanwhat is expected from the orbital motion of the secondary star. Wepropose that the superhump variation in the radio is generated byenhanced reconnection when the elongated side of the elliptic accretiondisk is the closest to the cool star. This leads to flares andenhancement in particle acceleration and is manifested as strongergyrosynchrotron radiation. The observed superhump period, at3.037+/-0.013 days (~6% longer than the orbital period), was used todeduce a binary mass ratio of ~0.23 in β Per, which is consistentwith previous studies. Our finding opens the possibility to extend thesuperhump phenomenon to Algol systems and to test the theories ofprecessing accretion disks in various types of interacting binaries. Itprovides a new method to estimate the mass ratios in these binaries. Italso offers new insights and improves our understanding of thecomplicated magnetic interaction and feedback between mass transferdynamics, time-dependent disk accretion, and induced magnetic activityin the Algol and related systems.
| Cyclic Period Changes in the Algol WW Cygni
Year to decade-long cyclic period changes have been observed in manyclasses of close binaries. The Algol binary WW Cygni shows a cyclicchange in its orbital period with an amplitude of slightly more than0.02 days and a period of 56 years. A hypothetical third or fourth bodydoes not satisfactorily explain the observed variation in the orbitalperiod. The change in luminosity and color of the system at primaryeclipse minimum are in agreement with the model proposed by Applegatefor a magnetic cycle induced period change in WW Cygni. We havecommenced monitoring 9 close binaries for evidence of the luminosity andcolor changes consistent with the magnetic cycle hypothesis. δLibrae is suggested as a case suitable for observation with an opticalinterferometer to test the third body proposed for this Algol system.
| From the Solar Corona to Clusters of Galaxies: The Radio Astronomy of Bruce Slee
Owen Bruce Slee is one of the pioneers of Australian radio astronomy.During World War II he independently discovered solar radio emission,and, after joining the CSIRO Division of Radiophysics, used a successionof increasingly more sophisticated radio telescopes to examine anamazing variety of celestial objects and phenomena. These ranged fromthe solar corona and other targets in our solar system, to differenttypes of stars and the ISM in our Galaxy, and beyond to distant galaxiesand clusters of galaxies. Although long retired, Slee continues to carryout research, with emphasis on active stars and clusters of galaxies. Aquiet and unassuming man, Slee has spent more than half a century makingan important, wide-ranging contribution to astronomy, and his workdeserves to be more widely known.
| 163. List of Minima Timings of Eclipsing Binaries by BBSAG Observers
Not Available
| Tidal Effects in Binaries of Various Periods
We found in the published literature the rotational velocities for 162B0-B9.5, 152 A0-A5, and 86 A6-F0 stars, all of luminosity classes V orIV, that are in spectroscopic or visual binaries with known orbitalelements. The data show that stars in binaries with periods of less thanabout 4 days have synchronized rotational and orbital motions. Stars inbinaries with periods of more than about 500 days have the samerotational velocities as single stars. However, the primaries inbinaries with periods of between 4 and 500 days have substantiallysmaller rotational velocities than single stars, implying that they havelost one-third to two-thirds of their angular momentum, presumablybecause of tidal interactions. The angular momentum losses increase withdecreasing binary separations or periods and increase with increasingage or decreasing mass.
| Doppler tomography of Algols
The technique of Doppler tomography has been influential in the study ofmass transfer in Algol-type interacting binaries. The Algols contain ahot blue dwarf star with a magnetically-active late-type companion. Inthe close Algols, the gas stream flows directly into the photosphere ofthe blue mass-gaining star because it does not have enough room to avoidimpact with that star. Doppler tomograms of the Algols have beenproduced from over 2500 time-resolved spectra at wavelengthscorresponding to Hα, Hβ, He I (6678 Å), Si II (6371Å) and Si IV (1394 Å). These tomograms display images ofaccretion structures that include a gas stream, accretion annulus,accretion disk, stream-star impact region, and occasionally a source ofchromospheric emission associated with the cool, mass-losing companion.Some Algol systems alternate between stream-like and disk-like states,and provide direct evidence of active mass transfer within the Algols.This work produced the very first images of the gas stream for theentire class of interacting binaries, and demonstrated that the Algolsare far more active than formerly believed, with variability on timescales of weeks to months.
| Catalogue of Algol type binary stars
A catalogue of (411) Algol-type (semi-detached) binary stars ispresented in the form of five separate tables of information. Thecatalogue has developed from an earlier version by including more recentinformation and an improved layout. A sixth table lists (1872) candidateAlgols, about which fewer details are known at present. Some issuesrelating to the classification and interpretation of Algol-like binariesare also discussed.Catalogue is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/417/263
| The eclipsing binary star RZ Cas. I. First spectroscopic detection of rapid pulsations in an Algol system
In a first report on the results of a multi-site campaign in 2001 ofphotometric and spectroscopic observations of the active semi-detachedAlgol-type system RZ Cas, we concentrate on the radial velocity (RV)variations. Using weak absorption lines we obtain an improved orbitalsolution for both components. In the orbital RV curve we observe astrong, asymmetric rotation effect. For the first time we detect rapidspectroscopic multi-mode pulsations in an Algol system. Whereas thephotometrically observed oscillations were dominated by monoperiodicpulsations at frequency 64.19 c d-1 until the year 2000, wefind in 2001 a multiperiodic behaviour with two dominant frequencies off1=56.600 c d-1 and f2=64.189 cd-1.Both modes show amplitude variations over the orbital phase with a aminimum at orbital phases φ= 0.6-0.8 and a maximum just after theprimary minimum (f2) and at φ ≈ 0.25 (f1).The different shape of amplitude modulation of the f1 andf2 modes points to different (l,m) mode structures. Themodulation itself can be explained by assuming a variable extinction dueto gas streams and an inhomogeneous accretion annulus that weakens thelight from different regions of the primary depending on its orbitalposition. This assumption is well supported by the gas densitydistribution obtained in preliminary hydrodynamic simulations.We found strong variations and cycle-to-cycle variable shapes of theorbital RV-curves of Balmer lines that have maximum magnitude in theHα line indicating a strong variability of mass-transfer rates anda non-stationary circumbinary envelope.The research is based on spectroscopic observations made with the 2-mtelescope at the Thüringer Landessternwarte Tautenburg, Germany.Table 3 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/413/293
| Statistical Analysis of 5 Year Continuous Radio Flare Data from β Persei, V711 Tauri, δ Librae, and UX Arietis
We report on the longest-running continuous radio flare survey of twoAlgol-type systems (β Per and δ Lib) and two RS CVn systems(V711 Tau and UX Ari). All four systems have late-type components, andall were known to display radio flaring activity. The primary aim of thecampaign was to determine the timescales for flaring activity in thesesystems. The radio continuum flux at 2.3 and 8.3 GHz was monitored withthe NRAO-Green Bank Interferometer from 1995 January to 2000 October.The survey spanned 2096 days with interruptions during maintenance runsand temporary closings of the interferometer. Many strong flares weredetected with continuum fluxes at 8.3 GHz as high as 1.17 Jy in βPer, 1.44 Jy in V711 Tau, and 0.82 Jy in UX Ari. Only two flares weredetected from δ Lib during 1123 days of monitoring, and thecontinuum flux reached a maximum of only 0.034 Jy at 8.3 GHz. Theindependent techniques of Power Spectrum Analysis and Phase DispersionMinimization were used to determine the periodicity of flaring activityin each binary. The strongest periodicities found were 48.9+/-1.7 daysfor β Per, 120.7+/-3.4 days for V711 Tau, and 141.4+/-4.5 days forUX Ari, with other significant periodicities of 80.8+/-2.5 days for V711Tau and 52.6+/-0.7 days for UX Ari. In the case of δ Lib, thestrongest periodicities were related to the duration of the twomonitoring cycles within the data set and are not real. The continuoussurvey has demonstrated that there are active and quiescent flaringcycles in V711 Tau and β Per. During both of these cycles, βPer had more flares than V711 Tau, but its strongest flares weretypically weaker than those of V711 Tau.
| Astrometric Positions and Proper Motions of 19 Radio Stars
We have used the Very Large Array, linked with the Pie Town Very LongBaseline Array antenna, to determine the astrometric positions of 19radio stars in the International Celestial Reference Frame (ICRF). Thepositions of these stars were directly linked to the positions ofdistant quasars through phase-referencing observations. The positions ofthe ICRF quasars are known to 0.25 mas, thus providing an absolutereference at the angular resolution of our radio observations. Averagevalues for the errors in our derived positions for all sources were 13and 16 mas in αcosδ and δ, respectively, withaccuracies approaching 1-2 mas for some of the stars observed.Differences between the ICRF positions of the 38 quasars and thosemeasured from our observations showed no systematic offsets, with meanvalues of -0.3 mas in αcosδ and -1.0 mas in δ.Standard deviations of the quasar position differences of 17 and 11 masin αcosδ and δ, respectively, are consistent with themean position errors determined for the stars. Our measured positionswere combined with previous Very Large Array measurements taken from1978 to 1995 to determine the proper motions of 15 of the stars in ourlist. With mean errors of ~1.6 mas yr-1, the accuracies ofour proper motions approach those derived from Hipparcos and, for a fewof the stars in our program, are better than the Hipparcos values.Comparing the positions of our radio stars with the Hipparcos Catalogue,we find that at the epoch of our observations, the two frames arealigned to within formal errors of approximately 3 mas. This resultconfirms that the Hipparcos frame is inertial at the expected level.
| Infrared light curves and absolute stellar parameters of the Algol system δ Librae: is δ Librae really an overmassive Algol binary?
We present the first infrared (IR) light curves in the J, H and K bandsof δ Lib obtained at different observing runs from 1994 to 1998.These IR light curves, showing a secondary minimum much deeper than invisual bands, have been analysed in order to determine a new set ofphysical parameters. A new program using the Roche geometry, and stellarsurface brightness from ATLAS model atmospheres, has been used in theanalysis and allows us to determine the physical parameters and thedistance of the binary. We compare these results with the Hipparcosparallax, with the spectroscopic masses of the components derived fromthe radial velocity curves, and with evolutionary stellar modelpredictions. The adoption of a mass M1~= 2.85Msolar for the primary star would remove the discrepanciesbetween our results and the Hipparcos distance, and the unusual locationof the δ Lib components in the Teff- log g diagram. Ourphotometric analysis suggests that the stellar masses in δ Libcould be overestimated, casting doubt on the claim that the primarycomponent of the system is overmassive and oversized compared withsingle main-sequence stars of similar masses.
| A study of the behaviour of the NaI/KI column density ratio in the interstellar medium using the Na ultraviolet doublet
Here we make a new study of the behaviour of the NaI/KI column densityratio in the interstellar medium, using a sample of new observations of28 stars obtained at the Nordic Optical Telescope (NOT) in 1996 and1997, and previously published observations (obtained by some of theauthors) of 21 stars. The sightlines cover a range of distances anddirections, including into the Galactic halo. We make use of newobservations of the NaI ultraviolet (UV) doublet for some 18 stars. Thisdoublet is much weaker than the NaI D doublet and so is less susceptibleto saturation effects, and it is well known that it can be used toobtain more accurate NaI column densities with a smaller error range. Wefind an average N(NaI)/N(KI) ratio from the NaI UV data of about 90,which is rather higher than that found previously by Hobbs and Lequeux.The Na UV-KI ratio shows a small increase in value with increasingcolumn density, while we also find a sample of low N(NaI)/N(KI) ratioclouds generally seen towards distant objects on high-latitudesightlines that reach into the halo, so that the ratio decreases moresharply at lower column densities. As the values of the ratio for thesehalo clouds (10-20) bracket the cosmic Na/K abundance ratio, we suggestthat these ratios result from a harder radiation field in the lowerhalo, such that the ionized fractions of NaI and KI become similar.Clearly caution needs to be applied in using any kind of `standardvalue' for the NaI/KI column density ratio.
| TOPS Telescope Projects on Variable Stars and Other Objects
Teachers and high school students who attended the University ofHawaii's "Toward Other Planetary Systems" workshop in June 2002 gavepresentations on introductory telescope projects on lunar photography,variable stars, and Messier Objects at the AAVSO 91st Spring meeting inJuly 2002. Other participants discussed advanced projects on photometry,CCDs, and spectroscopy. Former student participants presented thediscovery of a new variable star and an on-going remote observingproject utilizing the Lowell Observatory 31-inch telescope. Thesevarious projects are described and/or summarized.
| Zwei helle Algosterne fur den Sommer.
Not Available
| Das Brunner Punktesystem.
Not Available
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| The Origin of Cyclic Period Changes in Close Binaries: The Case of the Algol Binary WW Cygni
Year- to decade-long cyclic orbital period changes have been observed inseveral classes of close binary systems, including Algol, W UrsaeMajoris, and RS Canum Venaticorum systems and the cataclysmic variables.The origin of these changes is unknown, but mass loss, apsidal motion,magnetic activity, and the presence of a third body have all beenproposed. In this paper, we use new CCD observations and thecentury-long historical record of the times of primary eclipse for WWCygni to explore the cause of these period changes. WW Cyg is an Algolbinary whose orbital period undergoes a 56 yr cyclic variation with anamplitude of ~0.02 days. We consider and reject the hypotheses of masstransfer, mass loss, apsidal motion, and the gravitational influence ofan unseen companion as the cause for these changes. A model proposed byApplegate, which invokes changes in the gravitational quadrupole momentof the convective and rotating secondary star, is the most likelyexplanation of this star's orbital period changes. This finding is basedon an examination of WW Cyg's residual O-C curve and an analysis of theperiod changes seen in 66 other Algols. Variations in the gravitationalquadrupole moment are also considered to be the most likely explanationfor the cyclic period changes observed in several different types ofbinary systems.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| Evidence of a Third Star Orbiting the Eclipsing Binary δ Librae
Radial velocity observations obtained at the Kitt Peak NationalObservatory in 1981, 1983, 1984, and 1991 confirm the suggestion made byMcLaughlin six decades ago that the bright Algol-type binary δLibrae has a long-period companion. An analysis of this eclipsingsystem's barycentric velocity for these four epochs and four earlierones where published observations were available yield thesespectroscopic elements for its center of mass: P=2.762+/-0.001 yr,K=5.46+/-0.15 km s-1, e=0.28+/-0.05,ω=198deg+/-7deg, and T=1983.24+/-0.04. Fromthese results, it can be inferred that the third star's mass andspectral type are 0.95+/-0.04 Msolar and G9 and that theentire δ Lib system is even more similar to the archetypaleclipsing binary β Persei (Algol) than was previously recognized.The spectroscopic orbital elements for the B9.5 V primary star in theeclipsing system are also updated.
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| Survey of Hα Mass Transfer Structures in Classical Algol-Type Binaries
Five years of Hα survey data for 37 ``classical'' Algol-typebinaries are presented. All these systems have primaries with a spectraltype of A or B, have a period of less than 5 days, and are visible inthe Northern Hemisphere. Data were collected with the 1.02 m reflectorat the US Naval Observatory, Flagstaff Station. The survey consists ofover 460 system spectra. Each system was observed at least once duringthe 5 years, with many systems observed several times over severalepochs. Difference profiles are calculated for most spectra by modelingand subtracting the spectrum of the photospheres of the stellarcomponents. We examined each spectrum for the presence of mass transfer,stream-star and stream-disk interaction, a disk or circumstellar bulge,and chromospheric emission. We present information on the prevalence ofmass transfer activity, disk presence, and system states associated withparticular mass transfer structures. We show that no currently publishedstudy, including this one, has enough data for a rigorous statisticalidentification of system states.
| Eclipsing Binaries and the Lutz-Kelker Bias
Using examples from the literature, we demonstrate that ignoring theLutz- Kelker bias may degrade agreement between results derived fromeclipsing binaries and those based on trigonometric parallaxes. Inaddition, we show that eclipsing binaries are excellent standardcandles.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| On the Variability of Late B III-V Stars
We investigate the Hipparcos Satellite photometry of luminosity classIII-V B6-B9 stars. Most are relatively non-variable. Candidates forwhich further study is desirable are identified.
| RBSC-NVSS Sample. I. Radio and Optical Identifications of a Complete Sample of 1556 Bright X-Ray Sources
We cross-identified the ROSAT Bright Source Catalog (RBSC) and the NRAOVLA Sky Survey (NVSS) to construct the RBSC-NVSS sample of the brightestX-ray sources (>=0.1 counts s-1~10-12 ergscm-2 s-1 in the 0.1-2.4 keV band) that are alsoradio sources (S>=2.5 mJy at 1.4 GHz) in the 7.8 sr of extragalacticsky with |b|>15deg and δ>-40deg. Thesky density of NVSS sources is low enough that they can be reliablyidentified with RBSC sources having rms positional uncertainties>=10". We used the more accurate radio positions to make reliableX-ray/radio/optical identifications down to the POSS plate limits. Weobtained optical spectra for many of the bright identifications lackingpublished redshifts. The resulting X-ray/radio sample is unique in itssize (1557 objects), composition (a mixture of nearly normal galaxies,Seyfert galaxies, quasars, and clusters), and low average redshift[~0.1].
| The ROSAT Bright Survey: II. Catalogue of all high-galactic latitude RASS sources with PSPC countrate CR > 0.2 s-1
We present a summary of an identification program of the more than 2000X-ray sources detected during the ROSAT All-Sky Survey (Voges et al.1999) at high galactic latitude, |b| > 30degr , with countrate above0.2 s-1. This program, termed the ROSAT Bright Survey RBS, isto more than 99.5% complete. A sub-sample of 931 sources with countrateabove 0.2 s-1 in the hard spectral band between 0.5 and 2.0keV is to 100% identified. The total survey area comprises 20391deg2 at a flux limit of 2.4 x 10-12 ergcm-2 s-1 in the 0.5 - 2.0 keV band. About 1500sources of the complete sample could be identified by correlating theRBS with SIMBAD and the NED. The remaining ~ 500 sources were identifiedby low-resolution optical spectroscopy and CCD imaging utilizingtelescopes at La Silla, Calar Alto, Zelenchukskaya and Mauna Kea. Apartfrom completely untouched sources, catalogued clusters and galaxieswithout published redshift as well as catalogued galaxies with unusualhigh X-ray luminosity were included in the spectroscopic identificationprogram. Details of the observations with an on-line presentation of thefinding charts and the optical spectra will be published separately.Here we summarize our identifications in a table which contains opticaland X-ray information for each source. As a result we present the mostmassive complete sample of X-ray selected AGNs with a total of 669members and a well populated X-ray selected sample of 302 clusters ofgalaxies with redshifts up to 0.70. Three fields studied by us remainwithout optical counterpart (RBS0378, RBS1223, RBS1556). While the firstis a possible X-ray transient, the two latter are isolated neutron starcandidates (Motch et al. 1999, Schwope et al. 1999).
| Comparison of Parallaxes from Eclipsing Binaries Method with Hipparcos Parallaxes
The parallaxes determined by Lacy (1979) by means of eclipsing binariesmethod are compared with the Hipparcos parallaxes for 19 systems. Theresidual scatter of the distance moduli inferred from eclipsing binariesmethod - after allowing for known errors as given by Lacy and Hipparcos- is equal to 0.18 mag. It decreases to 0.08 mag when obviously notfitting semi-detached systems and systems with chromospheric activity ofcomponents are removed from the sample.
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