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An Extended FUSE Survey of Diffuse O VI Emission in the Interstellar Medium
We present a survey of diffuse O VI emission in the interstellar medium(ISM) obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE).Spanning 5.5 yr of FUSE observations, from launch through 2004 December,our data set consists of 2925 exposures along 183 sight lines, includingall of those with previously published O VI detections. The data wereprocessed using an implementation of CalFUSE version 3.1 modified tooptimize the signal-to-noise ratio and velocity scale of spectra from anaperture-filling source. Of our 183 sight lines, 73 show O VIλ1032 emission, 29 at >3 σ significance. Six of the 3σ features have velocities |vLSR|>120 kms-1, while the others have |vLSR|<=50 kms-1. Measured intensities range from 1800 to 9100 LU (lineunit; 1 photon cm-2 s-1 sr-1), with amedian of 3300 LU. Combining our results with published O VI absorptiondata, we find that an O VI-bearing interface in the local ISM yields anelectron density ne=0.2-0.3 cm-3 and a path lengthof 0.1 pc, while O VI-emitting regions associated with high-velocityclouds in the Galactic halo have densities an order of magnitude lowerand path lengths 2 orders of magnitude longer. Although the O VIintensities along these sight lines are similar, the emission isproduced by gas with very different properties.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by Johns HopkinsUniversity under NASA contract NAS5-32985.
| Abundances and Depletions of Interstellar Oxygen
We report on the abundance of interstellar neutral oxygen (O I) for 26sight lines, using data from the Far Ultraviolet Spectroscopic Explorer,the International Spectroscopic Explorer, and the Hubble SpaceTelescope. O I column densities are derived by measuring the equivalentwidths of several ultraviolet absorption lines and subsequently fittingthose to a curve of growth. We consider both our general sample of 26sight lines and a more restrictive sample of 10 sight lines that utilizeHST data for a measurement of the weak 1355 Å line of oxygen andare thus better constrained owing to our sampling of all three sectionsof the curve of growth. The column densities of our HST sample showratios of O/H that agree with the current best solar value if dust isconsidered, with the possible exception of one sight line (HD 37903). Wenote some very limited evidence in the HST sample for trends ofincreasing depletion with respect to RV and f(H2),but the trends are not conclusive. Unlike a recent result from Cartledgeet al., we do not see evidence for increasing depletion with respect to, but our HST sample contains only two points moredense than the critical density determined in that paper. The columndensities of our more general sample show some scatter in O/H, but mostagree with the solar value to within errors. We discuss these results inthe context of establishing the best method for determining interstellarabundances, the unresolved question of the best value for O/H in theinterstellar medium, the O/H ratios observed in Galactic stars, and thedepletion of gas-phase oxygen onto dust grains.
| Far Ultraviolet Spectroscopic Explorer Snapshot Survey of O VI Variability in the Winds of 66 OB-Type Stars
We have used the Far Ultraviolet Spectroscopic Explorer to conduct asnapshot survey of O VI variability in the winds of 66 OB-type stars inthe Galaxy and the Magellanic Clouds. These time series consist of twoor three observations separated by intervals ranging from a few days toseveral months. Although these time series provide the bare minimum ofinformation required to detect variations, this survey demonstrates thatthe O VI doublet in the winds of OB-type stars is variable on variousscales in both time and velocity. For spectral types from O3 to B1, 64%vary in time. At spectral types later than B1, no wind variability isobserved. In view of the limitations of this survey, this fractionrepresents a lower limit on the true incidence of variability in the OVI wind lines, which is very common and probably ubiquitous. Incontrast, for S IV and P V, only a small percentage of the whole sampleshows wind variations, although this may be principally due to selectioneffects. The observed variations extend over several hundreds ofkilometers per second of the wind profile and can be strong. The widthover which the wind O VI profile varies is only weakly correlated withthe terminal velocity (v&infy;), but a significantcorrelation (close to a 1:1 relationship) is derived between the maximumvelocity of the variation and v&infy;. High-velocity O VIwind absorption features (possibly related to the discrete absorptioncomponents seen in other wind lines) are also observed in 46% of thecases for spectral types from O3 to B0.5. These features are variable,but the nature of their propagation cannot be determined from thissurvey. If X-rays can produce sufficient O VI by Auger ionization of OIV and the X-rays originate from strong shocks in the wind, this studysuggests that stronger shocks occur more frequently nearv&infy;, causing an enhancement of O VI nearv&infy;.
| Some Diffuse Interstellar Bands Related to Interstellar C2 Molecules
We have investigated the correlations between the equivalent widths of21 selected diffuse interstellar bands (DIBs) and the correspondinginterstellar column densities N(C2), N(CN), and N(CH), toward53 stars with color excesses 0.11<=E(B-V)<=1.99. The observationaldata were derived primarily from echelle spectra acquired at R=38,000 aspart of our extensive, continuing survey of the bands. All but six ofthe 53 final spectra show signal-to-noise ratios >=800 at 5780Å. The principal result presented here is that seven of the 21bands prove to be examples of ``the C2 DIBs,'' a class ofweak, narrow bands whose normalized equivalent widthsWλ(X)/Wλ (λ6196) are wellcorrelated specifically with N(C2)/E(B-V) via power laws. Incontrast, the similarly normalized equivalent widths of the 14 other,well-known DIBs analyzed here are uncorrelated, or weaklyanticorrelated, with N(C2)/E(B-V), to within theobservational uncertainties. Thus, the polyatomic molecule(s) presumedto cause these seven C2 DIBs may bear a direct chemicalrelation to C2 that is not shared by the polyatomic moleculesputatively responsible for the other 14 bands. The C2 DIBsalso show positive correlations with N(CN)/E(B-V) and N(CH)/E(B-V) inour particular sample of light paths, although generally with shallowerslopes in the case of N(CN) and with greater scatter in the case ofN(CH). Eleven additional C2 DIBs are also identified but arenot analyzed here. Among the 18 C2 DIBs identified, fourapparently have not been previously detected. The λ4963 band isgenerally the strongest of the 18 C2 DIBs, while theλ4734 band shows the most sensitive correlation withN(C2).Based on observations obtained with the Apache Point Observatory 3.5 mtelescope, which is owned and operated by the Astrophysical ResearchConsortium.
| A New Measurement of the Average Far-Ultraviolet Extinction Curve
We have measured the extinction curve in the far-ultraviolet wavelengthregion of (900-1200 Å) using spectra obtained with the BerkeleyEUV/FUV spectrometer during the ORFEUS I and the ORFEUS II (Orbiting andRetrievable Far and Extreme Ultraviolet Spectrometer) missions in 1993and 1996. From the complete sample of early-type stars observed duringthese missions, we have selected pairs of stars with the same spectraltype but different reddenings to measure the differential FUVextinction. We model the effects of molecular hydrogen absorption andexclude affected regions of the spectrum to determine the extinctionfrom dust alone. We minimize errors from inaccuracies in the catalogedspectral types of the stars by making our own determinations of spectraltypes based on their IUE spectra. We find substantial scatter in thecurves of individual star pairs and present a detailed examination ofthe uncertainties and their effects on each extinction curve. We findthat, given the potentially large uncertainties inherent in using thepair method at FUV wavelengths, a careful analysis of measurementuncertainties is critical to assessing the true dust extinction. Wepresent a new measurement of the average far-ultraviolet extinctioncurve to the Lyman limit; our new measurement is consistent with anextrapolation of the standard extinction curve of Savage & Mathis.
| Observations of Diffuse Interstellar Bands Attributed to C-7
Recent advances in laboratory gas-phase spectroscopy of large moleculesand their ions permit a direct comparison between the diffuseinterstellar bands (DIBs) and proposed carriers. On the basis ofgas-phase data, Tulej et al. recently suggested that fiveA2Πu<--X2Πgelectronic transitions of the linear carbon-chain anionC-7 match with DIBs. We have obtainedhigh-resolution visible spectra of four reddened stars (HD 46711, HD50064, HD 183143, and Cyg OB2 12) to make a detailed comparison with theC-7 laboratory data. Our data show that three ofthe C-7 bands (000 at 6270.2Å, 310 at 6064.0 Å, and120310 at 4963.0 Å)are in good agreement with DIBs in wavelength and relative intensity. Afourth band (110 at 5612.8 Å) also agrees inintensity but is apparently off by 2 Å in wavelength. All otherlaboratory bands of C-7 are not expected to bedetectable in astronomical spectra with the current level ofsensitivity. The gas-phase spectrum of C-7 agreeswith the DIBs better than that of any previously proposed molecule.However, the question of whether C-7 is a DIBcarrier cannot be definitively answered until (1) better laboratorymeasurements confirm, refute, or explain the wavelength discrepancy forthe 110 band and/or (2) better astronomicalspectra reveal the presence or absence of otherC-7 bands. Based on observations obtained with theApache Point Observatory 3.5 m telescope, which is owned and operated bythe Astrophysical Research Consortium.
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| Mesures de vitesses radiales. VIII. Accompagnement AU sol DU programme d'observation DU satellite HIPPARCOS
We publish 1879 radial velocities of stars distributed in 105 fields of4^{\circ} \times 4^{\circ}. We continue the PPO series \cite[(Fehrenbachet al. 1987;]{Feh87} \cite[Duflot et al. 1990, 1992 and 1995),]{Du90}using the Fehrenbach objective prism method. Table 1 only available inelectronic form at CDS via to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Intrinsic colour indices of O- and B- type stars in the Vilnius photometric system.
Not Available
| Photoelectric photometry of OB stars in the Vilnius system
Not Available
| An Einstein Observatory SAO-based catalog of B-type stars
About 4000 X-ray images obtained with the Einstein Observatory are usedto measure the 0.16-4.0 keV emission from 1545 B-type SAO stars fallingin the about 10 percent of the sky surveyed with the IPC. Seventy-fourdetected X-ray sources with B-type stars are identified, and it isestimated that no more than 15 can be misidentified. Upper limits to theX-ray emission of the remaining stars are presented. In addition tosummarizing the X-ray measurements and giving other relevant opticaldata, the present extensive catalog discusses the reduction process andanalyzes selection effects associated with both SAO catalog completenessand IPC target selection procedures. It is concluded that X-rayemission, at the level of Lx not less than 10 exp 30 ergs/s, is quitecommon in B stars of early spectral types (B0-B3), regardless ofluminosity class, but that emission, at the same level, becomes lesscommon, or nonexistent, in later B-type stars.
| Empirical temperature calibrations for early-type stars
Three temperature calibrations of suitable photometric quantities havebeen derived for O and B stars. A sample of 120 stars with reliableT(eff.) determinations has been used for establishing each calibration.The different calibrations have been critically discussed and compared.Temperature determinations for 1009 program stars have been obtainedwith an accuracy of the order of 10 percent.
| Observations of interstellar diffuse absorption band at 4430 A
Observations of the interstellar diffuse absorption band at 4430 A for800 O and B stars in Neckel's (1967) catalog are being carried out, and482 spectra obtained up to September 1983 have been reduced. It isconfirmed that the strength of the interstellar diffuse absorption bandat 4430 A does not simply relate to the abundance of interstellar grainson the line of sight. The relation between the color excess E(B-V) andthe equivalent width of the band to the direction of l = 130-140 deg andb = -5 to +5 deg shows that some parameter(s) other than E(B-V) is (are)needed to understand the cause of this band.
| Catalog of O-B stars observed with Tokyo Meridian Circle
A catalog of the O-B stars, selected from 'Blaauw-Parenago' list andRubin's catalog, has been compiled on the FK4 system by the observationsmade with Gautier 8-inch Meridian Circle at the Tokyo AstronomicalObservatory during the period, 1971 to 1979. It contains 1059 stars andwas compiled for the future establishment of high precision propermotions of O-B stars.
| Ultraviolet extinction and diffuse band strength correlations
Correlations between UV extinction parameters and diffuse band strengthsare south, using a data base of 50 stars with recently measuredextinction curves. A novel aspect of this study is that the basicdependence of most interstellar parameters on E(B-V) (or, nearlyequivalently, on the total hydrogen column density) has been largelycanceled out. After this cancellation, a weak correlation is foundbetween the 4430 A diffuse band and the 2175 A extinction feature. Noother correlations are found. These results support a molecular originfor the 5780 A and 6284 A bands. It is speculated that the correlationpattern found for the 4430 A band can be explained if this bandoriginates in reactions on disordered grain surfaces.
| ANS spectrophotometry - The bright X-ray binaries Hercules X-1 /HZ Herculis/ and Cygnus X-1 /HDE 226868/
Complete ultraviolet light curves for HZ Her immediately after awell-defined X-ray turn-on in 1975 are obtained. The features of thecurve are found to correspond well with features seen in the optical.The absolute level of emission at maximum light at 1550 A is in goodagreement with the calculations of the X-ray reflection effect ofMilgrom and Salpeter (1975). It is found that at 1550 A approximately20% of the light at maximum comes from the accretion disk. Similarobservations of Cyg X-1 make it possible to determine the degree ofreddening, equivalent to E(B-V) = 0.95 + or - 0.07, from the strength ofthe 2200 A interstellar absorption feature. The distance inferred fromthis amount of reddening requires that the optical star be luminous and,therefore, massive. Observations obtained during the May 1975 X-raytransition show ultraviolet excess when compared with the data obtainedsix months later.
| Copernicus observations of the N V resonance doublet in 53 early-type stars
UV spectra in the wavelength interval 1170-1270 A are presented for 53early-type stars ranging in spectral type from O6.5 V to B2.5 IV. Thesample includes four Wolf-Rayet stars, seven known Oe-Be stars, and sixgalactic halo OB stars. A qualitative analysis of the stellar N vdoublet reveals that: (1) N v is present in all stars hotter and moreluminous than type B0 for the main sequence, B1 for giants, and B2 forsupergiants; (2) shell components of N v and an unidentified absorptionfeature at 1230 A are present in about half of the stars; (3) the columndensity of N v is well correlated with bolometric luminosity over thespectral range O6 to B2; and (4) the ratio of emission to absorptionequivalent width is a factor of 2 smaller in the main sequence starsthan in supergiants, which suggests that the wind structure changes as astar evolves. For several stars, this ratio is too small to be explainedby traditional wind models.
| H-beta photometry of northern intermediate galactic latitude early-type stars and galactic structure away from the plane
Photoelectric H-beta photometry is presented for 255 early-type stars atintermediate galactic latitudes. Absolute magnitudes and distances arederived for the more luminous stars. Those with visual magnitudes lessthan or equal to 2.5 and at distances of up to 1 kpc from the galacticplane may follow the spiral structure in the plane.
| A survey of interstellar H I from L-alpha absorption measurements. II
This paper presents interstellar H I column densities, mean H I spacedensities, total neutral hydrogen column densities, and total meanhydrogen space densities toward 100 stars surveyed in the L-alpha regionwith the U2 detector of the Copernicus satellite. The data for 47 starsare compared with OAO 2 results, and ratios of gas to E(B-V) colorexcess are computed for 30 'intercloud' stars, 45 'cloud' stars, and thecombined sample of 75 stars. A definitive value of 5.8 x 10 to the 21stpower atoms/sq cm per mag is obtained for the mean ratio of totalneutral hydrogen to color excess, indicating that this ratio seems to bea constant, independent of location in the sky, except possibly towardstars with anomalous extinction. The anomalous ratio determined for RhoOph is examined, and the galactic distribution of neutral hydrogen isevaluated. The following values are estimated for matter in the galacticplane within 500 pc of the sun: a total mean hydrogen space density of1.15 atoms/cu cm, a mean H2 space density of 0.143 molecule/cu cm(possibly a lower limit), and a mean H I space density of 0.86 atom/cucm (a possible overestimate).
| Infrared colors and the diffuse interstellar bands
Broad-band infrared photometric measurements have been gathered for 105stars which exhibit diffuse interstellar bands in their spectra. Allnormal stars obey a single reddening law, and a value of R equal to 3.08+ or - 0.15 is derived. This value is consistent with other recentdeterminations of R. The diffuse band indicators, the central depth ofthe 4430-A feature and the equivalent widths of the 5780-A and 6284-Afeatures, show as large a scatter with the infrared color excesses asthey do with E(B - V). No single-valued relation between the colorexcesses and the diffuse band strengths appears to exist. This castsdoubt on whether dust grains which produce the visual and infraredextinctions are the carriers for the diffuse interstellar features.
| Intermediate-velocity gas in the local interstellar medium
Scans of interstellar ultraviolet absorption lines of N I, N II, and SiIII for 17 stars are combined with previously published data for 30stars. The extremal velocities at which detectable absorption occurs aretabulated, and it is shown that these are correlated for the threespecies. The data suggest that intermediate-velocity gas (20 to 60km/s), best known from Na I and Ca II absorption, contains both neutraland ionized hydrogen. Features characteristic of intermediate-velocityisothermal shocks (greater than 60 km/s) are conspicuously rare. Theintermediate-velocity gas may be in the form of clouds containing both HI and H II regions or of radiative shocks propagating in theinterstellar medium; in the latter case the gas should be detectable inH-alpha emission.
| Coronal gas in the Galaxy. I - A new survey of interstellar O VI
Ultraviolet spectra of 40 O- and B-type stars have been intensivelyscanned in the vicinity of the O VI transitions at 1032 and 1038 A withthe Copernicus satellite. This survey of the high-temperature (log Tabout 5.5) phase of interstellar gas is an extension of the earlierobservations of interstellar O VI by Jenkins and Meloy (1974), bringingthe total coverage up to 72 stars. Except for a few distant stars, theoverall quality of the present data surpasses that of the earlier work.Plots of absorption optical depths versus radial velocity are presentedfor both transitions in each star. Total column densities (or theirupper limits), velocity centroids, and velocity widths have beenextracted from the profiles and tabulated, with the results of Jenkinsand Meloy (1974) included. Qualitatively, the highly variable O VIdensities and velocities seem to exhibit no systematic patterns orregional trends; there is no recognizable correlation in the behavior ofcoronal gas with pronounced features of galactic structure.
| On the origin of intermediate-latitude OB stars
An attempt is made to trace the origin of early-type stars observed atappreciable distances from the galactic plane. Because uncertainties inthe proper motions make space motions and hence dynamical lifetimesrather inaccurate, a theory of oscillations normal to the plane has beenused to compute radial velocities for 138 intermediate-latitude OBstars. These theoretical values are then compared with the observedradial velocities, and it is found that the low-velocity stars wereprobably ejected from the plane some time after formation, while thehigh-velocity stars were ejected very soon after formation. Velocitiesof ejection perpendicular to the plane are computed and show a narrowdistribution with a mean absolute value of 7 km/s together with a spreadof velocities from about 40 to over 200 km/s. The data are in reasonableagreement with a 'sling' effect and 'runaway' origin for the stars inthe sample.
| UBV photometry and MK spectral classification of northern early-type stars at intermediate galactic latitudes
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977MNRAS.180..691H&db_key=AST
| A survey of interstellar molecular hydrogen. I
Data from the Copernicus satellite's ultraviolet telescope were used tosurvey column densities of atomic and molecular hydrogen from a largesample of early-type stars; these data have bearing on an eventualunderstanding of diffuse and dense interstellar clouds. Column densitiesare derived by fitting damping profiles to the observed spectra, most ofwhich exhibit strong damping lines in the lower rotational levelssurveyed. Plots of dust column density, fractional abundance ofmolecular hydrogen, and the logarithm of fractional abundance versustotal gas column density are given for many of the stars; stars withabnormally large or small hydrogen column densities, as well as somedistant stars at high galactic latitudes, are considered. Equilibriumand nonequilibrium theories accounting for the abundance of interstellarhydrogen are compared, and support is found in the data for an accountwhich balances hydrogen formation on interstellar grains withdestruction through photodissociation. Overall averages for atomic andmolecular hydrogen levels in the galactic plane are also calculated.
| UBV photometry of 180 early-type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974PASP...86..795G&db_key=AST
| Some Spectroscopic Characteristics of the OB Stars: an Investigation of the Space Distribution of Certain OB Stars and the Reference Frame of the Classification
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971ApJS...23..257W&db_key=AST
| Structure in the Interstellar-Extinction Curve
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971ApJ...166...65Y&db_key=AST
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| Csillagkép: | Hattyú |
| Rektaszcenzió: | 19h45m37.97s |
| Deklináció: | +44°57'49.5" |
| Vizuális fényesség: | 7.488 |
| Távolság: | 10000000 parszek |
| RA sajátmozgás: | -3.7 |
| Dec sajátmozgás: | -4.8 |
| B-T magnitude: | 7.32 |
| V-T magnitude: | 7.475 |
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