Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
Variations in D/H and D/O from New Far Ultraviolet Spectroscopic Explorer Observations
We use data obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) to determine the interstellar abundances of D I, N I, O I, Fe II,and H2 along the sight lines to WD 1034+001, BD +39 3226, andTD1 32709. Our main focus is on determining the D/H, N/H, O/H, and D/Oratios along these sight lines, with logN(H)>20.0, that probe gaswell outside of the Local Bubble. Hubble Space Telescope (HST) andInternational Ultraviolet Explorer (IUE) archival data are used todetermine the H I column densities along the WD 1034+001 and TD1 32709sight lines, respectively. For BD +39 3226, a previously published N(HI) is used. We find(D/H)×105=2.14+0.53-0.45,1.17+0.31-0.25, and1.86+0.53-0.43 and(D/O)×102=6.31+1.79-1.38,5.62+1.61-1.31, and7.59+2.17-1.76 for the WD 1034+001, BD +39 3226,and TD1 32709 sight lines, respectively (all 1 σ). The scatter inthese three D/H ratios exemplifies the scatter that has been found byother authors for sight lines with column densities in the range19.2
| Measuring interstellar gas-phase D/H ratios in the presence of H_2
Aims.To clarify the circumstances under which it is acceptable toapproximate the interstellar gas-phase D/H ratio by D I/H I.Methods: .Observed column densities of H I, D I, H2 and HD are comparedfor six lines of sight having appreciable fractions of H2.Results: .The overall fraction of deuterium in HD varies by a factor 3-4but is found to be much smaller than the fraction of H in H2 in allcases, implying that deuterium appears as D I and N(D I)/N(H I) exceedsthe gas-phase D/H ratio in H2-bearing gas. Conclusions: .Deuteriumin H2-bearing gas contributes to the observed D I absorption and the D/Hratio should be inferred from N(D)/N(H) where N(D) = (N(D I) + N(HD)),N(H) = N(H I) + 2N(H2): failure to do so biases the resulting D/H ratioupward, typically by 5%-15% in present data. Along sightlines withmultiple kinematic components having different molecular fractions,fractionation can cause velocity differences between D I and H Iprofiles. Shifts between H2 and HD velocity centroids may arise when themolecule-bearing gas has kinematic substructure reflecting regions ofdifferent ionization balance and HD/H2 ratios.
| FUSE Determination of a Low Deuterium Abundance along an Extended Sight Line in the Galactic Disk
We present a study of the deuterium abundance along the extended sightline toward HD 90087 with the Far Ultraviolet Spectroscopic Explorer(FUSE). HD 90087 is a O9.5 III star located in the Galactic disk at adistance of ~2.7 kpc away from the Sun. Both in terms of distance andcolumn densities, HD 90087 has the longest and densest sight lineobserved in the Galactic disk for which a deuterium abundance has beenmeasured from ultraviolet absorption lines so far. Because manyinterstellar clouds are probed along this sight line, possiblevariations in the properties of individual clouds should be averagedout. This would yield a deuterium abundance that is characteristic ofthe interstellar medium on scales larger than the Local Bubble. The FUSEspectra of HD 90087 show numerous blended interstellar and stellarfeatures. We have measured interstellar column densities of neutralatoms, ions, and molecules by simultaneously fitting the interstellarabsorption lines detected in the different FUSE channels. As far aspossible, saturated lines were excluded from the fits in order tominimize possible systematic errors. IUE (International UltravioletExplorer) archival data are also used to measure neutral hydrogen. Wereport D/O=(1.7+/-0.7)×10-2 andD/H=(9.8+/-3.8)×10-6 (2 σ). Our new resultsconfirm that the gas-phase deuterium abundance in the distantinterstellar medium is significantly lower than the one measured withinthe Local Bubble. We supplement our study with a revision of the oxygenabundance toward Feige 110, a moderately distant (~200 pc) sdOB star,located ~150 pc below the Galactic plane. Excluding saturated lines fromthe fits of the FUSE spectra is critical; this led us to derive an O Icolumn density about 2 times larger than the one previously reported forFeige 110. The corresponding updated D/O ratio on this sight line isD/O=(2.6+/-1.0)×10-2 (2 σ), which is lower thanthe one measured within the Local Bubble. The data set available nowoutside the Local Bubble, which is based primarily on FUSE measurements,shows a contrast between the constancy of D/O and the variability ofD/H. As oxygen is considered to be a good proxy for hydrogen within theinterstellar medium, this discrepancy is puzzling.
| The D/H Ratio toward PG 0038+199
We determine the D/H ratio in the interstellar medium toward the DOwhite dwarf PG 0038+199 using spectra from the Far UltravioletSpectroscopic Explorer (FUSE), with ground-based support from KeckHIRES. We employ curve-of-growth, apparent optical depth, andprofile-fitting techniques to measure the column densities and limits ofmany other species (H2, Na I, C I, C II, C III, N I, N II, OI, Si II, P II, S III, Ar I, and Fe II), which allows us to determinerelated ratios such as D/O, D/N, and the H2 fraction. Ourefforts are concentrated on measuring gas-phase D/H, which is key tounderstanding Galactic chemical evolution, and comparing it topredictions from big bang nucleosynthesis. We find column densitieslogN(HI)=20.41+/-0.08, logN(DI)=15.75+/-0.08, andlogN(H2)=19.33+/-0.04, yielding a molecular hydrogen fractionof 0.14+/-0.02 (2 σ errors), with an excitation temperature of143+/-5 K. The high H I column density implies that PG 0038+199 liesoutside of the Local Bubble; we estimate its distance to be297+164-104 pc (1 σ).[DI+HD]/[HI+2H2] toward PG 0038+199 is1.91+0.52-0.42×10-5 (2 σ).There is no evidence of component structure on the scale ofΔv>8 km s-1, based on Na I, but there is marginalevidence for structure on smaller scales. The D/H value is high comparedto the majority of recent D/H measurements but consistent with thevalues for two other measurements at similar distances. D/O is inagreement with other distant measurements. The scatter in D/H valuesbeyond ~100 pc remains a challenge for Galactic chemical evolution.This paper is dedicated in memory of Ervin J. Williger, father of thefirst author, who passed away on 2003 September 13. His enthusiasticsupport and encouragement were essential to its successful completion.Based on data from the Far Ultraviolet Spectroscopic Explorer and the W.M. Keck Observatory.
| Evidence of Correlated Titanium and Deuterium Depletion in the Galactic Interstellar Medium
Current measurements indicate that the deuterium abundance in diffuseinterstellar gas varies spatially by a factor of ~4 among sight linesextending beyond the Local Bubble. One plausible explanation for thescatter is the variable depletion of D onto dust grains. To test thisscenario, we have obtained high signal-to-noise, high- resolutionprofiles of the refractory ion Ti II along seven Galactic sight lineswith D/H ranging from 0.65 to 2.1×10-5. Thesemeasurements, acquired with the recently upgraded Keck/HIRESspectrometer, indicate a correlation between Ti/H and D/H at the betterthan 95% confidence level Therefore, our observations support theinterpretation that D/H scatter is associated with differentialdepletion. We note, however, that Ti/H values taken from the literaturedo not uniformly show the correlation. Finally, we identify significantcomponent-to-component variations in the depletion levels amongindividual sight lines and discuss complications arising from thisbehavior.
| The Deuterium-to-Hydrogen Ratio in a Low-Metallicity Cloud Falling onto the Milky Way
Using Far Ultraviolet Spectroscopic Explorer (FUSE) and Hubble SpaceTelescope observations of the QSO PG 1259+593, we detect D I Lymanseries absorption in high-velocity cloud Complex C, a low-metallicitygas cloud falling onto the Milky Way. This is the first detection ofatomic deuterium in the local universe in a location other than thenearby regions of the Galactic disk. We construct a velocity model forthe sight line based on the numerous O I absorption lines detected inthe ultraviolet spectra. We identify eight absorption-line components,two of which are associated with the high-velocity gas in Complex C at~-128 and ~-112 km s-1. A new Westerbork Synthesis RadioTelescope (WSRT) interferometer map of the H I 21 cm emission toward PG1259+593 indicates that the sight line passes through a compactconcentration of neutral gas in Complex C. We use the WSRT data togetherwith single-dish data from the Effelsberg 100 m radio telescope toestimate the H I column density of the high-velocity gas and toconstrain the velocity extents of the H I Lyman series absorptioncomponents observed by FUSE. We find N(HI)=(9.0+/-1.0)×1019 cm-2, N(DI)=(2.0+/-0.6)×1015 cm-2, and N(OI)=(7.2+/-2.1)×1015 cm-2 for the Complex Cgas (68% confidence intervals). The corresponding light-elementabundance ratios are D/H=(2.2+/-0.7)×10-5,O/H=(8.0+/-2.5)×10-5, and D/O=0.28+/-0.12. Themetallicity of Complex C gas toward PG 1259+593 is approximately 1/6solar, as inferred from the oxygen abundance[O/H]=-0.79+/-0.120.16. While we cannot rule out avalue of D/H similar to that found for the local ISM (i.e.,D/H~1.5×10-5), we can confidently exclude values as lowas those determined recently for extended sight lines in the Galacticdisk (D/H<1×10-5). Combined with the sub-solarmetallicity estimate and the low nitrogen abundance, this conclusionlends support to the hypothesis that Complex C is located outside theMilky Way, rather than inside in material recirculated between theGalactic disk and halo. The value of D/H for Complex C is consistentwith the primordial abundance of deuterium inferred from recentWilkinson Microwave Anisotropy Probe observations of the cosmicmicrowave background and simple chemical evolution models that predictthe amount of deuterium astration as a function of metallicity.
| Two New Low Galactic D/H Measurements from the Far Ultraviolet Spectroscopic Explorer
We analyze interstellar absorption observed toward two subdwarf O stars,JL 9 and LS 1274, using spectra taken by the Far UltravioletSpectroscopic Explorer (FUSE). Column densities are measured for manyatomic and molecular species (H I, D I, C I, N I, O I, P II, Ar I, FeII, and H2), but our main focus is on measuring the D/Hratios for these extended lines of sight, as D/H is an importantdiagnostic for both cosmology and Galactic chemical evolution. We findD/H=(1.00+/-0.37)×10-5 toward JL 9 andD/H=(0.76+/-0.36)×10-5 toward LS 1274 (2 σuncertainties). With distances of 590+/-160 and 580+/-100 pc,respectively, these two lines of sight are currently among the longestGalactic lines of sight with measured D/H. With the addition of thesemeasurements, we see a significant tendency for longer Galactic lines ofsight to yield low D/H values, consistent with previous inferences aboutthe deuterium abundance from D/O and D/N measurements. Short lines ofsight with H I column densities of logN(HI)<19.2 suggest that thegas-phase D/H value within the Local Bubble is(D/H)LBg=(1.56+/-0.04)×10-5. However, thefour longest Galactic lines of sight with measured D/H, which haved>500 pc and logN(HI)>20.5, suggest a significantly lower valuefor the true local disk gas-phase D/H value,(D/H)LDg=(0.85+/-0.09)×10-5. Oneinterpretation of these results is that D is preferentially depletedonto dust grains relative to H and that longer lines of sight thatextend beyond the Local Bubble sample more depleted material. In thisscenario, the higher Local Bubble D/H ratio is actually a betterestimate than (D/H)LDg for the true local disk D/H,(D/H)LD. However, if (D/H)LDg is different from(D/H)LBg simply because of variable astration and incompleteinterstellar medium mixing, then (D/H)LD=(D/H)LDg.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer (FUSE), which is operated for NASA by JohnsHopkins University under NASA contract NAS5-32985.
| The Deuterium-to-Oxygen Ratio in the Interstellar Medium
Because the ionization balances for H I, O I, and D I are lockedtogether by charge exchange, the deuterium-to-oxygen ratio, D/O, is animportant tracer for the value of the D/H ratio and for potentialspatial variations in the ratio. As the D I and O I column densities areof similar orders of magnitude for a given sight line, comparisons ofthe two values will generally be less subject to systematic errors thancomparisons of D I and H I, which differ by about 5 orders of magnitude.Moreover, D/O is additionally sensitive to astration, because as starsdestroy deuterium, they should produce oxygen. We report here theresults of a survey of D/O in the interstellar medium performed with theFar Ultraviolet Spectroscopic Explorer. We also compare these resultswith those for D/N. Together with a few results from previous missions,the sample totals 24 lines of sight. The distances range from a few to~2000 pc and logN(D I) from ~13 to ~16 cm-2. The D/O ratio isconstant in the local interstellar medium out to distances of ~150 pcand N(DI)~=1×1015 cm-2, i.e., within theLocal Bubble. In this region of the interstellar space, we findD/O=(3.84+/-0.16)×10-2 (1 σ in the mean). Thehomogeneity of the local D/O measurements shows that the spatialvariations in the local D/H and O/H must be extremely few, if any. Acomparison of the Local Bubble mean value with the few D/O measurementsavailable for low-metallicity quasar sight lines shows that the D/Oratio decreases with cosmic evolution, as expected. Beyond the LocalBubble, we detected significant spatial variations in the value of D/O.This likely implies a variation in D/H, as O/H is known to not varysignificantly over the distances covered in this study. Our data setsuggests a present-epoch deuterium abundance below1×10-5, i.e., lower than the value usually assumed,around 1.5×10-5.
| Potential Variations in the Interstellar N I Abundance
We present Far Ultraviolet Spectroscopic Explorer (FUSE) and SpaceTelescope Imaging Spectrograph observations of the weak interstellar N Iλ1160 doublet toward 17 high-density sight lines[N(Htot)>=1021 cm-2]. When combinedwith published data, our results reveal variations in the fractional N Iabundance showing a systematic deficiency at large N(Htot).At the FUSE resolution (~20 km s-1), the effects ofunresolved saturation cannot be conclusively ruled out, although O Iλ1356 shows little evidence of saturation. We investigated thepossibility that the N I variability is due to the formation ofN2 in our mostly dense regions. The 0-0 band of thec'41Σ+u-X1Σ+gtransition of N2 at 958 Å should be easily detected inour FUSE data; for 10 of the denser sight lines, N2 is notobserved at a sensitivity level of a few times 1014cm-2. The observed N I variations are suggestive of anincomplete understanding of nitrogen chemistry.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer, which is operated for NASA by the Johns HopkinsUniversity under NASA contract NAS 5-32985, and the NASA/ESA HubbleSpace Telescope, obtained from the Multimission Archive at the SpaceTelescope Science Institute, which is operated by the Association ofUniversities for Research in Astronomy, Inc., under the NASA contractNAS 5-26555.
| 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;.
| Deuterium toward Two Milky Way Disk Stars: Probing Extended Sight Lines with the Far Ultraviolet Spectroscopic Explorer
We have carried out an investigation of the abundance of deuterium alongtwo extended sight lines through the interstellar medium (ISM) of theGalactic disk. The data include Far Ultraviolet Spectroscopic Explorer(FUSE) observations of HD 195965 (B1 Ib) and HD 191877 (B0 V), as wellas Space Telescope Imaging Spectrograph (STIS) observations of HD195965. The distances to HD 195965 and HD 191877, derived fromspectroscopic parallax, are 794+/-200 and 2200+/-550 pc, respectively,making these the longest Galactic disk sight lines in which deuteriumhas been investigated with FUSE. The FUSE spectra contain all of the H ILyman series transitions (and the corresponding D transitions) exceptLyα. The higher Lyman lines clearly show the presence ofdeuterium. We use a combination of curve-of-growth analyses and lineprofile fitting to determine the D I abundance toward each object. Wealso present column densities for O I and N I toward both stars, as wellas H I measured from Lyα absorption in the STIS spectrum of HD195965. Toward HD 195965 we findD/H=(0.85+0.34-0.24)×10-5 (2σ),O/H=(6.61+1.03-1.11)×10-4, andN/H=(7.94+1.69-1.34)×10-5. TowardHD 191877 we findD/H=(0.78+0.52-0.25)×10-5 (2σ) andN/H=(6.76+2.22-1.97)×10-5. The OI column density toward HD 191877 is very uncertain. Our preferred valuegives O/H=(3.09+1.98-0.98)×10-4,but we cannot rule out O/H values as low asO/H=1.86×10-4, so the O/H value for this sight lineshould be taken with caution. The D/H ratios along these sight lines arelower than the average value of (1.52+/-0.15)×10-5 (2σ in the mean) found with FUSE for the local interstellar medium(~37-179 pc from the Sun). These observations lend support to earlierdetections of variation in D/H over distances greater than a few hundredparsecs. The O/H ratio toward HD 195965 is supersolar. This star is partof an OB association, so there may be local enrichment by nearby massivestars. The D/H and O/H values measured along these sight lines supportthe expectation that the ISM is not well mixed on distances of ~1000 pc.These observations demonstrate that although D/H studies through Lymanabsorption may become impractical at d>2500 pc and logN(HI)>21,D/H studies in the distance range from 500 to 2500 pc may be very usefulfor investigating mixing and chemical evolution in the ISM.
| A search for O VI in the winds of B-type stars
We have conducted a survey of FUSE spectra of 235 Galactic B-type starsin order to determine the boundaries in the H-R diagram for theproduction of the superion {O Vi} in their winds. By comparing thelocations and morphology of otherwise unidentified absorption featuresin the vicinity of the {O Vi} resonance doublet with the bona fide windprofiles seen in archival IUE spectra of the resonance lines of {N V},{Si Iv} and {C Iv}, we were able to detect blueshifted {O Vi} lines inthe spectra of giant and supergiant stars with temperature classes aslate as B1. No features attributable to {O Vi} were detected in dwarfslater than B0, or in stars of any luminosity class later than B1,although our ability to recognize weak absorption features in thesestars is severely restricted by blending with photospheric andinterstellar features. We discuss evidence that the ratio of the ionfractions of {O Vi} and {N V} is substantially different in the winds ofearly B-type stars than O-type stars.
| 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.
| 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.
| Cross-correlation characteristics of OB stars from IUE spectroscopy
We present a catalogue of homogeneous measures of the linewidthparameter, v_esin i, for 373 O-type stars and early B supergiants(including the separate components of 25 binary and three triplesystems), produced by cross-correlating high-resolution,short-wavelength IUE spectra against a `template' spectrum of tauSco. Wealso tabulate terminal velocities. There are no O supergiants in oursample with v_esin i<65 km s^-1, and only one supergiant earlier thanB5 has v_esin i<50 km s^-1, confirming that an important linebroadening mechanism in addition to rotation must be present in theseobjects. A calibration of the area under the cross-correlation peakagainst spectral type is used to obtain estimates of continuum intensityratios of the components in 28 spectroscopically binary or multiplesystems. At least seven SB2 systems show evidence for the `Struve-Sahadeeffect', a systematic variation in relative line strength as a functionof orbital phase. The stellar wind profiles of the most rapid rotator inour sample, the O9III:n* star HD 191423 (v_esin i=436km s^-1), show itto have a `wind-compressed disc' similar to that of HD 93521; this starand other rapid rotators are good candidates for studies of non-radialpulsation.
| The ROSAT all-sky survey catalogue of optically bright OB-type stars.
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
| 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
| An IUE survey of interstellar H I LY alpha absorption. 1: Column densities
We measure Galactic interstellar neutral hydrogen column densities byanalyzing archival interstellar Ly alpha absorption line data toward 554B2 and hotter stars observed at high resolution with the IUE satellite.This study more than doubles the number of lines of sight with measuresof N(H I) based on Ly alpha. We have included the scattered lightbackground correction algorithm of Bianchi and Bohlin in our datareduction. We use the correlation between the Balmer discontinuity(c1) index and the stellar Ly alpha absorption in order toassess the effects of stellar Ly alpha contamination. Approximately 40%of the B stars with measured (c1) index, exhibit seriousstellar Ly alpha contamination. One table contains the derived values ofthe interstellar N(H I) for 393 stars with at most small amounts ofstellar contamination. Another lists the observed values of total N(H I)for 161 stars with suspected stellar Ly alpha contamination and/oruncertain stellar parameters.
| The distribution of interstellar dust in the solar neighborhood
We surveyed the IRAS data base at the positions of the 1808 O6-B9.5stars in The Bright Star Catalog for extended objects with excessemission at 60 microns, indicating the presence of interstellar dust atthe location of the star. Within 400 pc the filling factor of theinterstellar medium, for dust clouds with a density greater than 0.5/cucm is 14.6 + or - 2.4%. Above a density of 1.0/cu cm, the densitydistribution function appears to follow a power law index - 1.25. Whenthe dust clouds are mapped onto the galactic plane, the sun appears tobe located in a low-density region of the interstellar medium of widthabout 60 pc extending at least 500 pc in the direction of longitudes 80deg - 260 deg, a feature we call the 'local trough'.
| Photospheric Absorption Lines in the Ultraviolet Spectra of O-Stars and B-Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990MNRAS.246..392P&db_key=AST
| Terminal velocities for a large sample of O stars, B supergiants, and Wolf-Rayet stars
It is argued that easily measured, reliable estimates of terminalvelocities for early-type stars are provided by the central velocityasymptotically approached by narrow absorption features and by theviolet limit of zero residual intensity in saturated P Cygni profiles.These estimators are used to determine terminal velocities, v(infinity),for 181 O stars, 70 early B supergiants, and 35 Wolf-Rayet stars. For OBstars, the values are typically 15-20 percent smaller than the extremeviolet edge velocities, v(edge), while for WR stars v(infinity) = 0.76v(edge) on average. New mass-loss rates for WR stars which are thermalradio emitters are given, taking into account the new terminalvelocities and recent revisions to estimates of distances and to themean nuclear mass per electron. The relationships between v(infinity),the surface escape velocities, and effective temperatures are examined.
| 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.
| A different analysis of UV photospheric lines of OBN and OBC stars
The paper presents measurements of the equivalent widths of severalphotospheric C, N, O, He, Si and Fe lines in the ultra-violet spectra of55 OBN, OBC and normal supergiants and main-sequence stars. Seventy-twoshort-wavelength, high-resolution spectrograms obtained with IUE wereused. The differences in equivalent widths of OBN and OBC stars relativeto normal stars are interpreted as abundance differences and yield upperand lower limits to respectively under- and overabundances of theelements C, N and O. The effects of anomalous strength of CNO linesappear to be less pronounced in the UV than in the visual. The mainreason for this is the saturation of the lines investigated. Differentscenarios to bring products of the CNO-cycle to the stellar surface arediscussed. The OBN stars can be explained in terms of abundancedifferences due to evolutionary effects as well as initial differences.The OBC stars may be explained by differences in atmospheric structureor initial abundances.
| 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.
| A catalog of ultraviolet interstellar extinction excesses for 1415 stars
Ultraviolet interstellar extinction excesses are presented for 1415stars with spectral types B7 and earlier. The excesses with respect to Vare derived from Astronomical Netherlands Satellite (ANS) 5-channel UVphotometry at central wavelengths of approximately 1550, 1800, 2500, and3300 A. A measure of the excess extinction in the 2200-A extinction bumpis also given. The data are valuable for investigating the systematicsof peculiar interstellar extinction and for studying the character of UVinterstellar extinction in the general direction of stars for which theextinction-curve shape is unknown.
| New UBVRI photometry for 900 supergiants
A description is presented of the results obtained in connection with asystematic program of supergiant photometry on the Johnson UBVRI system.During the eight years after the start of the program, almost 1000 starshave been observed, about 400 three or more times each. The originalselection of stars used the spectral type catalog of Jaschek et al.(1964) to choose supergiants. Since observations were possible from bothChile and Canada, no declination limits were imposed, and no particularselection criteria were imposed other than to eliminate carbon stars.These are so red as to require enormous extrapolations of thetransformation equations.
| A study of B-type supergiants with the uvby,beta photometric system
The applicability of the uvby,beta photometric system to theclassification and study of B-type supergiants (BTS) is investigatedusing published data on 157 BTS and observations of 17 BTS made with the36-in. reflector at McDonald Observatory. The results are presented intabular form and analyzed to produce preliminary calibrations ofluminosity class vs. beta index and of absolute magnitude (Mv) vs. beta(or delta Mv vs. delta beta) for four associations of stars. Theeffectiveness of various color indices as temperature indicators isdiscussed. It is shown that there is good correspondence between MK anduvby,beta classifications of B-type main-sequence stars, giants, andBTS, confirming the usefulness of the uvby,beta system in furtherresearch on BTS.
| On some extreme metal-deficient giants
Attention is given to the temperatures, metallicities, and colorexcesses of five giants with extreme metal deficiency. Observations withthe Vilnius photometric system, after correction for interstellarreddening, yield the following Fe/H abundance ratios: -3.0 for BD -18deg 5550 and HD 4306; -2.8 for CD -25 deg 13871 and HD 115444; and -2.6for HD 126587. Their effective temperatures are found to be within4800-4950 K.
| H I absorption measurements of seven low-latitude pulsars
The neutral hydrogen absorption spectra of seven low-latitude pulsarsare measured and used to estimate their distances and mean electrondensities along the lines of sight. Calculations made in terms of theSchmidt (1965) galactic rotation model on the basis of the spectralobservations made using the Arecibo 305-m telescope indicate thatpulsars 1919+21 and 1929+10 are within 1.5 kpc of the earth and pulsars2016+28 and 2020+28 are further than 1.3 kpc. Considerations ofabsorption spectra, dispersion and rotation measurements and Stromgrenspheres along the line of sight indicate that PSR 0525+21 isapproximately as distant as the Crab Nebula pulsar (2 kpc), while PSR0540+23 is more distant. Absorption in PSR 0611+22 is found to besimilar to that of the nearby supernova remnant IC 443, but theresemblance may be due to the small change of velocity with distance inthe direction of the anticenter. The dispersion measured and distancesof 32 known pulsars indicates extended regions of enhanced electrondensity in the inner part of the Galaxy and the Gum Nebula, withelectron density elsewhere generally between 0.02 and 0.03/cu cm.Possible sources of the ionization include stellar UV radiation.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Kis Róka |
| Rektaszcenzió: | 20h11m21.10s |
| Deklináció: | +21°52'32.0" |
| Vizuális fényesség: | 6.26 |
| Távolság: | 9090.909 parszek |
| RA sajátmozgás: | -1.8 |
| Dec sajátmozgás: | -12.1 |
| B-T magnitude: | 6.206 |
| V-T magnitude: | 6.26 |
Katalógusok és elnevezések:
|
