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The Hamburg/RASS Catalogue of optical identifications. Northern high-galactic latitude ROSAT Bright Source Catalogue X-ray sources
We present the Hamburg/RASS Catalogue (HRC) of optical identificationsof X-ray sources at high-galactic latitude. The HRC includes all X-raysources from the ROSAT Bright Source Catalogue (RASS-BSC) with galacticlatitude |b| >=30degr and declination delta >=0degr . In thispart of the sky covering ~ 10 000 deg2 the RASS-BSC contains5341 X-ray sources. For the optical identification we used blue Schmidtprism and direct plates taken for the northern hemisphere Hamburg QuasarSurvey (HQS) which are now available in digitized form. The limitingmagnitudes are 18.5 and 20, respectively. For 82% of the selectedRASS-BSC an identification could be given. For the rest either nocounterpart was visible in the error circle or a plausibleidentification was not possible. With ~ 42% AGN represent the largestgroup of X-ray emitters, ~ 31% have a stellar counterpart, whereasgalaxies and cluster of galaxies comprise only ~ 4% and ~ 5%,respectively. In ~ 3% of the RASS-BSC sources no object was visible onour blue direct plates within 40\arcsec around the X-ray sourceposition. The catalogue is used as a source for the selection of(nearly) complete samples of the various classes of X-ray emitters.
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| 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.
| A ROSAT Survey of Hot DA White Dwarfs in Non-Interacting Binary Systems
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.270..499B&db_key=AST
| The hot white-dwarf companions of HR 1608, HR 8210, and HD 15638
We have obtained low-dispersion IUE spectra of the late-type stars HD15638 (F3 V), HR 1608 (=63 Eridani, KO IV), and HR 8210 (A8m). Each ofthese stars had been detected as a strong EUV source with the Wide FieldCamera aboard the ROSAT satellite. The short-wavelength IUE spectrum ofeach star reveals the presence of a hot white-dwarf companion. We havefit the Lyman-alpha profile and UV continuum of each white dwarf usingpure hydrogen models. The excellent fit of the data to the modelsprovides confirmation of the Finley and Koester absolute calibration ofthe SWP camera of IUE. The UV data alone are insufficient to constrainthe model gravity, but an additional constraint is provided by thephotometric distance to the late-type primary. The most interesting ofthe three white dwarfs is the companion to HR 8210 for which our resultsimply a mass of 1.15 +0.05/-0.15 solar mass. This result is in goodagreement with the lower limit on the mass derived from thespectroscopic orbit (greater than 1.1 solar mass), provided that theinclination is close to 90 deg.
| ROSAT/IUE discovery of a white dwarf companion to HD 33959C (F4V)
We report the discovery, from the ROSAT EUV and X-ray all-sky surveys,and from IUE spectra, of a white dwarf (WD) companion to HD 33959C. RE0515 + 324 is among the 10 brightest EUV sources in the sky in the100-200 A band. It is also a strong soft X-ray source. IUE observationsof candidate objects have revealed a previously uncataloged hot DA WD,visually unresolved from HD 33959C, making the pair one of three or foursuggested Sirius-like systems. The estimated EUV luminosity is of theorder of 400 times greater than that of Sirius B, implying that the WDis much hotter and probably hydrogen-rich. This is confirmed bymodelling of the WD atmosphere, which shows that T(eff) over 46,000 K.We discuss these results in the context of WDs in general andSirius-like systems in particular.
| 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.
| Atmospheric parameters of the white-dwarf companion to HD 74389
An optical slit spectrum of the recently discovered DA white-dwarfcompanion to the A2 V star HD 74389 is presented. Fits of theoreticalspectra to six observed Balmer lines lead to estimates of Tc = 41,000(+4000, -1000) K and log g = 7.85 (+0.20, -0.06). The latter impliesthat the white dwarf does not have a substantially higher mass than themean for field DA white dwarfs. These parameters lead to an estimatedM(v) = +9.4, a value not inconsistent with the assumption that the twostars lie at a similar distance from the sun.
| On a possible white-dwarf companion to HD 74389
The discovery of a new white dwarf about 20 arcsec east of the A-typestar HD 74389 is reported. A physical association is not highlyprobable. Because of the importance of binaries with degeneratecomponents, attention is drawn to this star in the hope of stimulatingfurther observations.
| UBV photometry of stars whose positions are accurately known. III
UBV photometric observations of 417 stars at BD declination 35-49 degfrom the NPZT(74) catalog of Yasuda et al. (1982) and the AGK3R catalogof Corben (1978), obtained with the 40-cm Cassegrain reflector atKvistaberg Observatory during 1984-1985, are reported. The data arepresented in tables, and the mean errors per observation are given as0.016 mag in V, 0.011 mag in B-V, 0.012 mag in U-B for U less than 10,and 0.026 mag in U-B for U greater than 10.
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