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An Archive of IUE Low-Dispersion Spectra of the White Dwarf Stars
We have produced an archive of the ultraviolet low-dispersion spectrafor the full set of white dwarf stars observed with the InternationalUltraviolet Explorer (IUE) satellite over the course of its 18 yrmission. This archive contains the spectra of 322 individual degeneratestars which have been processed to optimize the signal-to-noise for eachstar. In particular, all spectra have been corrected for residualtemporal and thermal effects and placed on the Hubble Space TelescopeFaint Object Spectrograph absolute flux scale using procedures describedby Massa & Fitzpatrick. Wherever possible, multiple observations ofindividual stars have been co-added to further enhance signal-to-noiseand have been combined into a single spectrum including the full 1150 to3150 Å wavelength region observed by IUE. The contents of thisspectral archive are described and the details of data reductionprocedures are provided, along with the url for access to the electronicfiles of the processed spectra.
| Resolving Sirius-like binaries with the Hubble Space Telescope
We present initial results from a Hubble Space Telescope ultravioletimaging survey of stars known to have hot white dwarf companions whichare unresolved from the ground. The hot companions, discovered throughtheir EUV or UV emission, are hidden by the overwhelming brightnesses ofthe primary stars at visible wavelengths. Out of 17 targets observed, wehave resolved eight of them with the Wide Field Planetary Camera 2,using various ultraviolet filters. Most of the implied orbital periodsfor the resolved systems are hundreds to thousands of years, but in atleast three cases (56 Persei, ζ Cygni and RE J1925-566) it shouldbe possible to detect the orbital motions within the next few years, andthey may eventually yield new dynamically determined masses for thewhite dwarf components. The 56 Persei and 14 Aurigae systems are foundto be quadruple and quintuple, respectively, including the known opticalcomponents as well as the newly resolved white dwarf companions. Themild barium star ζ Cygni, known to have an 18-year spectroscopicperiod, is marginally resolved. All of these newly resolved Sirius-typebinaries will be useful in determining gravitational redshifts andmasses of the white dwarf components.
| Classification of EUV stellar sources detected by the ROSAT WFC. I. Photometric and radial velocity studies
We present the results of high-precision UBV(RI)_c photometricobservations and of spectroscopic radial velocity measurements obtainedat the European Southern Observatory for a sample of 51 cool starsdetected in the EUV by the ROSAT Wide Field Camera (WFC). Using alsorecent results from HIPPARCOS, we infer spectral types and investigatethe single or binary nature of the sample stars. Optical variability,with periods in the 0.4-13 day range, has been detected for the firsttime in 15 of these stars. based on data collected at the EuropeanSouthern Observatory, La Silla, Chile.}\fnmsep \thanks{Tables 1--5,Figs. 2-27 and the complete data set are available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.html}
| A Catalog of Spectroscopically Identified White Dwarfs
A catalog of 2249 white dwarfs which have been identifiedspectroscopically is presented complete through 1996 April. Thiscompilation is the fourth edition of the Villanova Catalog ofSpectroscopically Identified White Dwarfs. For each degenerate star, thefollowing data entries with references are provided: (1) a catalogcoordinate designation or WD number, in order of right ascension; (2)the right ascension and declination for epoch 1950.0; (3) the spectraltype based upon the new system; (4) a catalog symbol denoting binarymembership; (5) a list of most names known to exist for a given star;(6) proper motion and position angle; (7) broadband UBV photometry, V,B-V, U-B (8) multichannel spectrophotometry, v(MC), g-r (9)Strömgren narrowband photometry, y, b-y, u-b (10) an absolutevisual magnitude based upon the best available color-magnitudecalibration or trigonometric parallax; (11) the observed radial velocityuncorrected for gravitational redshift or solar motion; and (12) thetrigonometric parallax with mean error when available. Notes for unusualor peculiar stars and a coded Reference Key alphabetized by the firstauthor's last name are presented, as well as an expanded tablecross-referencing all names to the catalog WD number. An introductionand full descriptions of the entries are provided in the text.
| A search for hidden white dwarfs in theROSATEUV survey - II. Discovery of a distant DA+F6/7V binary system in a direction of low-density neutral hydrogen
The ROSAT Wide Field Camera (WFC) survey of the extreme ultraviolet(EUV) has provided us with evidence for the existence of a previouslyunidentified sample of hot white dwarfs in unresolved, detached binarysystems. These stars are invisible at optical wavelengths due to theclose proximity of their much more luminous companions (spectral type Kor earlier). However, for companions of spectral type ~A5 or later thewhite dwarfs are easily visible at far-ultraviolet wavelengths, and canbe identified in spectra taken by IUE. 16 such systems have beendiscovered in this way through ROSATEUVEIUE observations, including fouridentified by us in Paper I. In the present paper we report the resultsof our continuing search during the final year of IUE operations. Onenew system, RE J0500-364 (DA+F6/7V), has been identified. This starappears to lie at a distance of ~500-1000 pc, making it one of the mostdistant white dwarfs, if not the most distant, to be detected in the EUVsurveys. The very low line-of-sight neutral hydrogen volume density tothis object could place a lower limit on the length of the beta CMainterstellar tunnel of diffuse gas, which stretches away from the LocalBubble in a similar direction to RE J0500-364. In this paper we alsoanalyse a number of the stars observed where no white dwarf companionwas found. Some of these objects show evidence for chromospheric andcoronal activity. Finally, we present an analysis of the previouslyknown WD+active F6V binary HD 27483 (Bohm-Vitense 1993), and show that,at T~22000K, the white dwarf may be contributing significantly to theobserved EUV flux. If so, it is one of the coolest such stars to bedetected in the EUV surveys.
| A search for hidden white dwarfs in the ROSAT extreme ultraviolet survey
The ROSAT Wide Field Camera survey has provided us with evidence for theexistence of a previously unidentified sample of hot white dwarfs (WDs)in non- interacting binary systems, through the detection of extremeultraviolet (EUV) and soft X-ray emission. These stars are hidden atoptical wavelengths because of their close proximity to much moreluminous main- sequence (MS) companions (spectral type K or earlier).However, for companions of spectral type ~A5 or later, the white dwarfsare easily visible at far-UV wavelengths, and can be identified inspectra taken by the International Ultraviolet Explorer (IUE). Eleven WDbinary systems have previously been found in this way from ROSAT,Extreme Ultraviolet Explorer (EUVE) and IUE observations. In this paperwe report the discovery of three more such systems through ourprogrammes in recent episodes of IUE. The new binaries are HD 2133, REJ0357+283 (the existence of which was predicted by Jeffries, Burleigh& Robb in 1996), and BD+27 deg1888. In addition, we haveindependently identified a fourth new WD+MS binary, RE J1027+322, whichhas also been reported in the literature by Genova et al., bringing thetotal number of such systems discovered as a result of the EUV surveysto 15. We also discuss here six stars which were observed as part of theprogramme, but for which no white dwarf companion was found. Four ofthese are coronally active. Finally, we present an analysis of theWD+K0IV binary HD 18131, which includes the ROSAT PSPC X-ray data.
| A ROSAT XUV pointed phase source catalogue.
We present a catalogue of XUV sources from observations by the WideField Camera (WFC) on ROSAT during the pointed phase. The ROSAT WFC is atelescope sensitive in the extreme UV range (17-210eV) which observes inparallel with the ROSAT X-Ray Telescope (XRT). The 5916 pointedobservations processed are from the calibration and verification phasein June 1990 and from the period 9 Feb. 1991 to 15 July 1994. Thecatalogue contains 1022 independent source detections which correspondto 328 individual sources, many of which have been observed repeatedly.Each observation was done with one of four filters S_1_, S_2_, P_1_ andP_2_. Of the 328 sources 113 are new sources (they are not listed in the"2RE" catalogue) and 274 have been identified with optical counterparts.The catalogue contains coordinates, observed count rates, normalizedsource count rates and the proposed optical counterpart with itsspectral class. For observations with filters S_1_ and S_2_ an in-flightcalibration has been applied using data of White Dwarfs which wereassumed to have a constant flux and which were observed repeatedly (inpointed observations and/or during the All Sky Survey). In this way, itwas possible to correct for the time dependant degradation of thedetector efficiency and to normalize the count rates to those valid atthe beginning of the mission.
| The ROSAT Wide Field Camera all-sky survey of extreme-ultraviolet sources - II. The 2RE Source Catalogue
During 1990-1991 the Wide Field Camera (WFC) on the ROSAT satelliteperformed the first all-sky survey at EUV wavelengths. The survey wasconducted in two `colours' using broad-band filters to define wavebandscovering the ranges 60-140 A and 112-200 A. It was fully imaging, witheffective spatial resolution of about 3 arcmin FWHM, and point sourcelocation accuracy of typically better than 1 arcmin. From an initialanalysis, Pounds et al. published the WFC Bright Source Catalogue (BSC)of 383 sources. In this paper we report results from reprocessing of thecomplete survey database; the resulting list of sources is the `2RE'Catalogue. It contains 479 sources, of which 387 are detected in bothsurvey wavebands, a significant advance on the BSC (80 per cent versus60 per cent). Improvements over the original BSC include: (i) betterrejection of poor aspect periods, and smaller random errors in theaspect reconstruction; (ii) improved background screening; (iii)improved methods for source detection; (iv) inclusion of atime-variability test for each source; (v) more extensive investigationof the survey sensitivity. We define the catalogue selection criteria,and present the catalogue contents in terms of tables and sky maps. Wealso discuss the sky coverage, source number-flux relations, opticalidentifications and source variability.
| An optical Atlas of ROSAT Wide Field Camera EUV sources
The ROSAT Wide Field Camera has been detecting EUV sources since itslaunch in June 1990. A preliminary list of 384 bright sources has beensupplied by the Wide Field Camera team to the EUVE Guest ObserverCenter, and to the astronomical community. We have extracted 5.4 x 5.4arcmin images of all 384 WFC sources from the Space Telescope ScienceInstitute digitized sky archives. These images are presented asmosaicked finder charts for observers trying either to identify WFCsources or to characterize known sources.
| The ROSAT Wide Field Camera all-sky survey of extreme-ultraviolet sources. I - The Bright Source Catalogue
First comprehensive results from an initial processing of the ROSAT WideField Camera all-sky survey for cosmic sources of extreme-ultravioletradiation are presented. The reduction of the survey data has yielded acatalog of 383 relatively bright EUV sources, forming the WFC BrightSource Catalogue. Details of the EUV source positions and count ratesare given, as are optical identifications where known. It is found thatthe log N-log S distributions are unusually flat for the white dwarfstars, but almost Euclidean for the nearby main-sequence late-typestars. The sky distribution of identified white dwarfs is highlynonuniform, suggesting gross variations in the opacity of theinterstellar medium within about 100 pc.
| Etude DU Petit Nuage de Magellan par la technique DU prisme-objectif de Fehrenbach.
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