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Hard X-ray Emission Associated with White Dwarfs. III.
Hard X-ray emission associated with white dwarfs (WDs) can be used todiagnose the presence of late-type binary companions, mass accretionfrom companions, or physical processes with unknown origins. Since ourprevious systematic searches for hard X-ray emission associated withWDs, the Galactic WD catalog has been augmented by >10,000 new WDsfrom the Sloan Digital Sky Survey and new X-ray point-source catalogsfrom XMM-Newton and ROSAT have become available. Therefore, we haveextended the search using the updated catalogs, and found 17 new casesof WDs associated with hard X-ray emission. The 32 WDs associated withhard X-ray emission, from the current and previous searches, can bedivided into five categories: (1) binary WD with a coronal companion,(2) binary WD with mass transfer from a companion, (3) single hot WDwith a hard X-ray component peaking near 1 keV in addition to a softphotospheric component, (4) two PG 1159 stars with very faint X-rayemission in the 0.9-2.0 keV band, and (5) two DA WDs whose photosphericemission component has a hard shoulder extending to 0.5-0.9 keV. Theorigin of the hard X-ray emission in the latter three categories is notyet known. Deeper X-ray observations with higher angular and spectralresolutions are needed to help us understand these WDs' hard X-rayemission.
| Comparative statistics and origin of triple and quadruple stars
The statistics of catalogued quadruple stars consisting of two binaries(hierarchy 2 + 2), is studied in comparison with triple stars, withrespective sample sizes of 81 and 724. Seven representative quadruplesystems are discussed in greater detail. The main conclusions are asfollows. (i) Quadruple systems of ? Lyr type with similar massesand inner periods are common, in 42 per cent of the sample the outermass ratio is above 0.5 and the inner periods differ by less than 10times. (ii) The distributions of the inner periods in triple andquadruple stars are similar and bimodal. The inner mass ratios do notcorrelate with the inner periods. (iii) The statistics of outer periodsand mass ratios in triples and quadruples are different. The medianouter mass ratio in triples is 0.39 independently of the outer period,which has a smooth distribution. In contrast, the outer periods of 25per cent quadruples concentrate in the narrow range from 10 to 100yr,the outer mass ratios of these tight quadruples are above 0.6 and theirtwo inner periods are similar to each other. (iv) The outer and innermass ratios in triple and quadruple stars are not mutually correlated.In 13 per cent of quadruples both inner mass ratios are above 0.85(double twins). (v) The inner and outer orbital angular momenta andperiods in triple and quadruple systems with inner periods above 30dshow some correlation, the ratio of outer-to-inner periods is mostlycomprised between 5 and 104. In the systems with small periodratios the directions of the orbital spins are correlated, while in thesystems with large ratios they are not. The properties of multiple starsdo not correspond to the products of dynamical decay of small clusters,hence the N-body dynamics is not the dominant process of theirformation. On the other hand, rotationally driven (cascade)fragmentation possibly followed by migration of inner and/or outerorbits to shorter periods is a promising scenario to explain the originof triple and quadruple stars.
| Progenitors of type Ia supernovae: Binary stars with white dwarf companions
Type Ia SNe (SNe Ia) are thought to come from carbon oxygen white dwarfsthat accrete mass from binary companions until they approach theChandrasekhar limit, ignite carbon, and undergo complete thermonucleardisruption. A survey of the observed types of binaries that containwhite dwarfs is presented. We propose that certain systems that seemmost promising as SN Ia progenitors should be more intensively observedand modeled, to determine whether the white dwarfs in these systems willbe able to reach the Chandrasekhar limit. In view of the number ofpromising single-degenerate systems and the dearth of promisingdouble-degenerate systems, we suspect that single-degenerates producemost or perhaps all SNe Ia, while double-degenerates produce some orperhaps none.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Tycho-2 stars with infrared excess in the MSX Point Source Catalogue
Stars of all evolutionary phases have been found to have excess infraredemission due to the presence of circumstellar material. To identify suchstars, we have positionally correlated the infrared Mid-Course SpaceExperiment (MSX) Point Source Catalogue and the Tycho-2 opticalcatalogue. Near-mid-infrared colour criteria have been developed toselect infrared excess stars. The search yielded 1938 excess stars; overhalf (979) have never previously been detected by IRAS. The excess starswere found to be young objects such as Herbig Ae/Be and Be stars, andevolved objects such as OH/IR (infrared) and carbon stars. A number ofB-type excess stars were also discovered whose infrared colours couldnot be readily explained by known catalogued objects.
| 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.
| Reconstructing the evolution of white dwarf binaries: further evidence for an alternative algorithm for the outcome of the common-envelope phase in close binaries
We determine the possible masses and radii of the progenitors of whitedwarfs in binaries from fits to detailed stellar evolution models anduse these to reconstruct the mass-transfer phase in which the whitedwarf was formed. We confirm the earlier finding that in the first phaseof mass transfer in the binary evolution leading to a close pair ofwhite dwarfs, the standard common-envelope formalism (theα-formalism) equating the energy balance in the system (implicitlyassuming angular momentum conservation) does not work. An algorithmequating the angular momentum balance (implicitly assuming energyconservation) can explain the observations. This conclusion is now basedon 10 observed systems rather than three. With the latter algorithm (theγ-algorithm) the separation does not change much for approximatelyequal-mass binaries. Assuming constant efficiency in the standardα-formalism and a constant value of γ, we investigate theeffect of both methods on the change in separation in general andconclude that when there is observational evidence for strong shrinkageof the orbit, the γ-algorithm also leads to this. We then extendour analysis to all close binaries with at least one white dwarfcomponent and reconstruct the mass-transfer phases that lead to thesebinaries. In this way we find all possible values of the efficiency ofthe standard α-formalism and of γ that can explain theobserved binaries for different progenitor and companion masses. We findthat all observations can be explained with a single value of γ,making the γ-algorithm a useful tool to predict the outcome ofcommon-envelope evolution. We discuss the consequences of our findingsfor different binary populations in the Galaxy, including massivebinaries, for which the reconstruction method cannot be used.
| Hard X-Ray Emission Associated with White Dwarfs. II.
We have previously conducted a search for X-ray sources coincident withwhite dwarfs using the white dwarf catalog compiled by McCook & Sionand the ROSAT sources in the WGA Catalog (Paper I). To include the whitedwarfs discovered since 1999 and to include the X-ray sources detectedin ROSAT Position Sensitive Proportional Counter (PSPC) observationsmade with a boron filter, we have carried out another search using anupdated list of white dwarfs and the final catalogs of the ROSAT PSPCobservations with and without a boron filter. Forty-seven new X-raysources convincingly coincident with white dwarfs are found and reportedin this paper. Among these, only five show hard X-ray emission: threepossess confirmed or suggested late-type companions, one is apparentlysingle, and the other is likely a misclassified BL Lac object. Theapparently single white dwarf with hard X-ray emission, KPD 0005+5106,was discussed extensively in Paper I. Photospheric origin for the hardX-ray emission from hot DO and DQZO white dwarfs remains a tantalizingpossibility, but high-quality near-IR spectroscopic observations andmonitoring of the Hα emission line are needed to rule out theexistence of a faint dMe companion.
| Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I.
We have embarked on a project, under the aegis of the Nearby Stars(NStars)/Space Interferometry Mission Preparatory Science Program, toobtain spectra, spectral types, and, where feasible, basic physicalparameters for the 3600 dwarf and giant stars earlier than M0 within 40pc of the Sun. In this paper, we report on the results of this projectfor the first 664 stars in the northern hemisphere. These resultsinclude precise, homogeneous spectral types, basic physical parameters(including the effective temperature, surface gravity, and overallmetallicity [M/H]), and measures of the chromospheric activity of ourprogram stars. Observed and derived data presented in this paper arealso available on the project's Web site.
| 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.
| Statistics of spectroscopic sub-systems in visual multiple stars
A large sample of visual multiples of spectral types F5-M has beensurveyed for the presence of spectroscopic sub-systems. Some 4200 radialvelocities of 574 components were measured in 1994-2000 with thecorrelation radial velocity meter. A total of 46 new spectroscopicorbits were computed for this sample. Physical relations are establishedfor most of the visual systems and several optical components areidentified as well. The period distribution of sub-systems has a maximumat periods from 2 to 7 days, likely explained by a combination of tidaldissipation with triple-star dynamics. The fraction of spectroscopicsub-systems among the dwarf components of close visual binaries withknown orbits is similar to that of field dwarfs, from 11% to 18% percomponent. Sub-systems are more frequent among the components of widevisual binaries and among wide tertiary components to the known visualor spectroscopic binaries - 20% and 30%, respectively. In triple systemswith both outer (visual) and inner (spectroscopic) orbits known, we findan anti-correlation between the periods of inner sub-systems and theeccentricities of outer orbits which must be related to dynamicalstability constraints. Tables 1, 2, and 6 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/382/118
| The long-period companions of multiple stars tend to have moderate eccentricities
We examined the statistics of an angle gamma between the radius vectorof a visual companion of a multiple star and the vector of its apparentrelative motion in the system. Its distribution f(gamma ) is related tothe orbital eccentricity distribution in the investigated sample. Wefound that for the wide physical subsystems of the 174 objects from theMultiple Star Catalogue f(gamma ) is bell-shaped. The Monte-Carlosimulations have shown that our f(gamma ) corresponds to the populationof the moderate-eccentricity orbits and is not compatible with thelinear distribution f(e)=2e which follows from stellar dynamics andseems to hold for wide binaries. This points to the absence of highlyelongated orbits among the outer subsystems of multiple stars. Theconstraint of dynamical stability of triple systems is not sufficient toexplain the ``rounded-off'' outer orbits; instead, we speculate that itcan result from the angular momentum exchange in multiple systems duringtheir early evolution.
| Stellar encounters with the solar system
We continue our search, based on Hipparcos data, for stars which haveencountered or will encounter the solar system(García-Sánchez et al. \cite{Garcia}). Hipparcos parallaxand proper motion data are combined with ground-based radial velocitymeasurements to obtain the trajectories of stars relative to the solarsystem. We have integrated all trajectories using three different modelsof the galactic potential: a local potential model, a global potentialmodel, and a perturbative potential model. The agreement between themodels is generally very good. The time period over which our search forclose passages is valid is about +/-10 Myr. Based on the Hipparcos data,we find a frequency of stellar encounters within one parsec of the Sunof 2.3 +/- 0.2 per Myr. However, we also find that the Hipparcos data isobservationally incomplete. By comparing the Hipparcos observations withthe stellar luminosity function for star systems within 50 pc of theSun, we estimate that only about one-fifth of the stars or star systemswere detected by Hipparcos. Correcting for this incompleteness, weobtain a value of 11.7 +/- 1.3 stellar encounters per Myr within one pcof the Sun. We examine the ability of two future missions, FAME andGAIA, to extend the search for past and future stellar encounters withthe Sun.
| 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.
| Post-Common-Envelope Binary Stars and the Precataclysmic Binary PG 1114+187
We present orbit-resolved spectroscopy and orbit-sampled photometry ofthe binary system PG 1114+187. Both photometry and radial velocitystudies reveal a period P=1.75992 days, which is taken to be the orbitalperiod of the binary. Strong modulation of emission-line strength withthe same period is also present. A preliminary mass ratio,M2/M1~0.7, is found from primary- andsecondary-star radial velocity amplitudes. No evidence is seen foreither an accretion disk or mass transfer, leading to the conclusionthat PG 1114+187 is not a cataclysmic variable (CV) but is in a pre-CVstate, before the initiation of mass transfer. The short orbital periodalso leads to the conclusion that the system passed through acommon-envelope phase at some time in the past. The current list ofknown post-common-envelope and precataclysmic binary stars is alsoreviewed and the general properties of this class of star are discussed.
| The Three-dimensional Structure of the Warm Local Interstellar Medium. I. Methodology
In this first in a series of papers, we develop a methodology forconstructing three-dimensional models of the local interstellar cloud(LIC) and adjacent warm clouds in the local interstellar medium (LISM).Our models are based on the column density of neutral hydrogen gas(NHI) inferred primarily from measurements of the deuteriumcolumn density toward nearby stars obtained from the analysis of HubbleSpace Telescope ultraviolet spectra. We also use values ofNHI inferred from spectra of hot white dwarfs and B-typestars obtained by the Extreme Ultraviolet Explorer satellite. These verydifferent methods give consistent results for the three white dwarfstars in common. We assume that along each line of sight allinterstellar gas moving with a speed consistent with the LIC velocityvector has a constant density, NHI=0.10 cm-3, andextends from the heliosphere to an edge determined by the value ofNHI moving at this speed. A number of stars have velocitiesand/or depletions that indicate absorption by other warm clouds in theirlines of sight. On this basis α Cen A and B and probably alsoɛ Ind lie inside the Galactic center (G) cloud, HZ 43 and 31 Comlie inside what we call the north Galactic pole cloud, and β Cet islocated inside what we call the south Galactic pole cloud. We show thelocations of these clouds in Galactic coordinates. The Sun is locatedvery close to the edge of the LIC toward the Galactic center and thenorth Galactic pole. The absence of Mg II absorption at the LIC velocitytoward α Cen indicates that the distance to the edge of the LIC inthis direction is <=0.05 pc and the Sun should leave the LIC and perhapsenter the G cloud in less than 3000 yr. Comparison of LIC and totalvalues of NHI toward pairs of stars with separations between0.9d and 20 deg reveals a pattern of good agreement so long as bothstars lie within 60 pc of the Sun. Thus the LIC and perhaps also othernearby warm clouds have shapes that are smooth on these angular scales.In our second paper we will therefore fit the shape of the LIC with aset of smooth basis functions (spherical harmonics).
| Extreme Ultraviolet Astronomy
Astronomical studies in the extreme ultraviolet (EUV) band of thespectrum were dismissed during the early years of space astronomy asimpossible, primarily because of the mistaken view that radiation inthis band would be absorbed by the interstellar medium. Observations inthe 1980s from sounding rockets and limited duration orbital spacecraftbegan to show the potential of this field and led to the deployment oftwo spacecraft devoted to EUV astronomy: the UK Wide Field Camera andthe Extreme Ultraviolet Explorer. The instrumentation in these missions,although quite limited in comparison with instrumentation in otherfields of space astronomy, provided unique and far-reaching results.These included new information on solar system topics, stellarchromospheres and corona, white dwarf astrophysics, cataclysmicvariables, the interstellar medium, galaxies, and clusters of galaxies.We summarize these findings herein.
| Evidence for an ionization gradient in the local interstellar medium: EUVE observations of white dwarfs
We present an enlarged and homogeneous set of interstellar hydrogen andhelium column densities obtained through continuum and ionization edgesfitting of nearby hot white dwarfs observed with the Extreme UltravioletExplorer (EUVE). We compare the HI columns towards the targets and theirlocations relative to the soft X-ray cavity contours drawn by Snowden etal. (1998). We then use the inferred ionization degrees of hydrogen andhelium (available towards 17 objects) as a database for a search ofsystematic trends in the local interstellar medium. We find that theionization degree of helium does not show any trend, with a constantvalue around 40%. At variance with helium, hydrogen ionization varieswithin the Local Bubble: there is an ionization increase along thegeneral direction of the Canis Major cavity. These results areconsistent with hydrogen being ionized by the Canis Major hot starsAdara and Mirzam. However, the co-existence of fully neutral hydrogenand strongly ionized helium along some l-o-s remains to be explained.
| 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.
| Stellar Encounters with the Oort Cloud Based on HIPPARCOS Data
We have combined Hipparcos proper-motion and parallax data for nearbystars with ground-based radial velocity measurements to find stars thatmay have passed (or will pass) close enough to the Sun to perturb theOort cloud. Close stellar encounters could deflect large numbers ofcomets into the inner solar system, which would increase the impacthazard at Earth. We find that the rate of close approaches by starsystems (single or multiple stars) within a distance D (in parsecs) fromthe Sun is given by N= 3.5D^2.12 Myr^-1, less than the number predictedby a simple stellar dynamics model. However, this value is clearly alower limit because of observational incompleteness in the Hipparcosdata set. One star, Gliese 710, is estimated to have a closest approachof less than 0.4 pc 1.4 Myr in the future, and several stars come within1 pc during a +/-10 Myr interval. We have performed dynamicalsimulations that show that none of the passing stars perturb the Oortcloud sufficiently to create a substantial increase in the long-periodcomet flux at Earth's orbit.
| A High-Dispersion Spectroscopic Survey of the Hot White Dwarfs: The IUE NEWSIPS SWP Echelle Data Set
This paper summarizes the results obtained from a comprehensive analysisof all of the SWP echelle spectra of the white dwarf stars contained inthe IUE Final Archive. A total of 209 NEWSIPS spectra of 55 degeneratestars of various types have been systematically reduced and analyzed.These include, in addition to conventional white dwarfs, severalexamples of the hot planetary nebula central stars such as NGC 246,which represent the initial stages of He-rich degenerate evolution. Arepresentative summary of the stellar, circumstellar, and interstellarfeatures found to be present in these spectra is presented. For 33 ofthe 55 stars, multiple spectra of sufficient quality exist so thatco-added spectra with improved signal-to-noise ratio can be constructed.Much previously unrecognized detail and many new features are evident inthese data. In addition, it was found necessary to apply severalcorrections to the NEWSIPS extracted spectra. These corrections,involving the wavelength scale and flux uncertainty vector, aredescribed.
| Hot White Dwarfs in the Extreme-Ultraviolet Explorer Survey. IV. DA White Dwarfs with Bright Companions
We present an analysis of optical, ultraviolet, and X-ray spectralproperties of a sample of 13 hot hydrogen-rich (DA) white dwarfs, eachpaired with a luminous unresolved companion. Using low-dispersionInternational Ultraviolet Explorer spectra, ROSAT photometry, andExtreme-Ultraviolet Explorer photometry and spectroscopy, we estimatethe effective temperature, mass, and distance of the white dwarfs.Additionally, we examine the question of their atmospheric composition.We establish orbital properties for most binaries by means ofhigh-dispersion optical spectroscopy obtained with the Hamilton echellespectrograph at Lick Observatory; the same data help uncover evidence ofactivity in some of the secondary stars that is also notable in ROSATX-ray measurements. In particular, we find high-amplitude (>20 kms-1) velocity variations in only two stars (HD 33959C and HR 8210),low-amplitude variations in four additional objects (HD 18131, HR 1608,theta Hya, and BD +27 deg1888), and no variations (<2 km s-1) in theremainder. We have observed Ca H and K in emission in four (BD +08deg102, HD 18131, HR 1608, and EUVE J0702+129) of the six objects thatwere also detected in the 0.52-2.01 keV ROSAT PSPC band, while thesource of the hard X-ray emission in HD 33959C remains unknown; otherinvestigators have noted some evidence of activity in the remaining0.52-2.01 keV detection, HD 217411. Properties of the white dwarfs arealso investigated; EUV spectroscopy shows the effect of a low heavyelement abundance in the atmosphere of the white dwarf in HD 33959C andof a high heavy element abundance in HD 223816; measurements of allother objects are apparently consistent with emission from pure-hydrogenatmospheres. However, current data do not constrain well the white dwarfparameters, and, to remedy the situation, we propose to obtainspectroscopy of the complete H Lyman line series.
| The Stellar Extreme-Ultraviolet Radiation Field
The local extreme ultraviolet (EUV) radiation field from stellar sourceshas been determined by combining the EUV spectra of 54 stars, taken withthe spectrometers aboard the Extreme Ultraviolet Explorer satellite. Theresultant spectrum over the range 70-730 A is estimated to be 95%complete above 400 A and 90% complete above 200 A. The flux contributedby two B stars and three hot white dwarfs dominate the spectrum exceptat the shortest wavelengths, where an assortment of EUV source typescontribute. The high electron densities measured toward nearby stars canbe accounted for by photoionization from this radiation field, but thespectrum is too soft to explain the overionization of helium withrespect to hydrogen recently measure in the Local Cloud.
| Catalogue of cataclysmic binaries, low-mass X-ray binaries and related objects (Sixth edition)
The catalogue lists coordinates, apparent magnitudes, orbitalparameters, stellar parameters of the components and other characteristcproperties of 318 cataclysmic binaries, 47 low-mass X-ray binaries and49 related objects with known or suspected orbital periods together witha comprehensive selection of the relevant recent literature. In additionthe catalogue contains a list of references to published finding chartsfor 394 of the 414 objects. A cross-reference list of alias objectdesignations concludes the catalogue. Literature published before 30June 1997 has, as far as possible, been taken into account. Thecatalogue is available in electronic form only via the CDS at ftp130.79.128.5 or http://cdsweb.u-strasbg.fr/Abstract.html
| The Extreme Ultraviolet Explorer Stellar Spectral Atlas
We present an atlas of extreme ultraviolet (EUV) spectra of 95 brightstellar sources observed between 1992 July and 1996 June with theExtreme Ultraviolet Explorer (EUVE) spectrometers. These data are takenin the short- (SW; 70-190 Angstroms), medium- (MW; 140-380 Angstroms),and long-wavelength bandpasses (LW; 280-760 Angstroms) at roughly 0.5,1, and 2 Angstroms resolution, respectively. We describe thespectrometers and detail the procedure used to reduce the observationaldata to spectra. The atlas is grouped by the type of source: O-A stars,F-M stars, white dwarfs, and cataclysmic variables. We present a briefoverview of the general nature and EUV spectral distribution of eachgroup and present accompanying notes and individual spectra for eachsource. We show selected F-M sources in more detail with identificationsof the brightest spectral lines illustrating the characteristics of theEUV spectra of stars of various temperatures. The current study is themost complete compilation to date of aggregate spectra of bright EUVstellar sources.
| An Optical Atlas of Extreme Ultraviolet Explorer (EUVE) Sources
The Extreme Ultraviolet Explorer (EUVE) has been detecting EUV sourcessince its launch in June 1992. Positions of 540 sources have been madeavailable to the community by the EUVE team. We have extracted 7' X 7'images centered on these 540 EUVE sources from the Space TelescopeScience Institute digitized sky archives. We present these images asmosaic finder charts to aid observers trying to identify EUVE sources,or to characterize known sources. (SECTION: Atlases)
| An All-Sky Catalog of Faint Extreme Ultraviolet Sources
We present a list of 534 objects detected jointly in the ExtremeUltraviolet Explorer (EUVE) 100 Angstroms all-sky survey and in theROSAT X-Ray Telescope 0.25 keV band. The joint selection criterionpermits use of a low count rate threshold in each survey. This lowthreshold is roughly 60% of the threshold used in the previous EUVEall-sky surveys, and 166 of the objects listed here are new EUV sources,appearing in neither the Second EUVE Source Catalog nor the ROSAT WideField Camera Second Catalog. The spatial distribution of this all-skycatalog shows three features: an enhanced concentration of objects inUrsa Major, where the Galactic integrated H I column reaches its globalminimum; an enhanced concentration in the third quadrant of the Galaxy(lII from 180 deg to 270 deg) including the Canis Major tunnel, whereparticularly low H I columns are found to distances beyond 200 pc; and aparticularly low number of faint objects in the direction of the fourthquadrant of the Galaxy, where nearby intervening H I columns areappreciable. Of particular interest is the composition of the 166detections not previously reported in any EUV catalog. We offerpreliminary identifications for 105 of these sources. By far the mostnumerous (81) of the identifications are late-type stars (F, G, K, M),while 18 are other stellar types, only five are white dwarfs (WDs), andnone are extragalactic. The paucity of WDs and extragalactic objects maybe explained by a strong horizon effect wherein interstellar absorptionstrongly limits the effective new-source search volume and, thereby,selectively favors low-luminosity nearby sources over more luminous butdistant objects.
| Orbits of new spectroscopic components in 7 multiple systems
New close sub-systems are discovered in wide physical multiple stars.Elements of spectroscopic orbits are given for the components ofquadruple systems ADS 1315C, 3608C, 3824C, 3991A and for the componentsof triple systems ADS 1849A, 6646A, 8861A. Physical parameters(magnitudes, spectral types, masses of individual components, distancesto the systems, angular separations) are estimated by combining allavailable data. The nearby M dwarf ADS 8861A = Gliese 507A is a goodcandidate for speckle resolution. The very hot white dwarf discovered by[Hodgkin et al. (1993)]{ref12} is likely to be an additional visualcomponent to ADS 3824C, so this system may be quintuple; however, asearch of 2fd 993 photometric periodicity possibly caused by the hotclose companion is highly desirable. Table 4 and Appendix are onlyavailable in electronic form at the CDS via anonymous ftp to:cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Spectroscopic Orbits for Two White Dwarf Binaries Identified in X-ray, EUV, and UV Surveys by ROSAT and IUE
We present spectroscopic orbits for two binaries with main sequenceprimaries and white dwarf companions. These systems were originallyidentified because they showed more X-ray emission than expected formain sequence stars. The presence of each white dwarf companion wassubsequently confirmed by the detection of its spectrum in theultraviolet using IUE. Velocity variations of the primary stars in bothsystems were monitored using the CfA Digital Speedometers. The orbitalperiods are 21(d) .7217 and 2(d) .9934 for HR 8210 and HD 33959C,respectively. The minimum mass for the white dwarf companion of HR 8210is 1.171 M_sun, which suggests an unusually massive progenitor. HD33959C is a candidate for a system that has undergone a common-envelopephase.
| Discovery of a White Dwarf Companion (MS0354.6-3650 = EUVE J0356-366) to a G2V Star
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112..258C&db_key=AST
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