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The Influence of Deuteration and Turbulent Diffusion on the Observed D/H Ratio
The influence of turbulent mixing on the chemistry of the interstellarmedium (ISM) has so far received little attention. Previous studies ofthis effect have suggested that it might play an important role inmixing the various phases of the ISM. In this paper, we examine thepotential effects of turbulent diffusion on the deuterium chemistrywithin molecular clouds. We find that such mixing acts to reduce theefficiency of deuteration in these clouds by increasing the ionizationfraction and reducing freeze-out of heavy molecules. This leads to lowerabundances for many deuterated species. We also examine the influence ofturbulent mixing on the transition from atomic hydrogen to H2and from atomic deuterium to HD near the cloud edge. We find thatincluding turbulent diffusion in our models serves to push thesetransitions deeper into the cloud and helps maintain a higher atomicfraction throughout the cloud envelope. Based on these findings, wepropose a new process to account for the significant scatter in theobserved atomic D/H ratio for galactic sightlines extending beyond theLocal Bubble. Although several mechanisms have been put forward toexplain this scatter, they are unable to fully account for the range inD/H values. We suggest a scenario in which turbulent mixing of atomicand molecular gas at the edges of molecular clouds causes the observedatomic D/H ratio to vary by a factor of ~2.
| A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun
Traditionally, runaway stars are O- and B-type stars with large peculiarvelocities. We would like to extend this definition to young stars (upto ?50 Myr) of any spectral type and to identify those present in theHipparcos catalogue by applying different selection criteria, such aspeculiar space velocities or peculiar one-dimensional velocities.Runaway stars are important for studying the evolution of multiple starsystems or star clusters, as well as for identifying the origins ofneutron stars. We compile the distances, proper motions, spectral types,luminosity classes, V magnitudes and B-V colours, and we utilizeevolutionary models from different authors to obtain star ages. We studya sample of 7663 young Hipparcos stars within 3 kpc from the Sun. Theradial velocities are obtained from the literature. We investigate thedistributions of the peculiar spatial velocity and the peculiar radialvelocity as well as the peculiar tangential velocity and itsone-dimensional components and we obtain runaway star probabilities foreach star in the sample. In addition, we look for stars that aresituated outside any OB association or OB cluster and the Galactic planeas well as stars for which the velocity vector points away from themedian velocity vector of neighbouring stars or the surrounding local OBassociation/cluster (although the absolute velocity might be small). Wefind a total of 2547 runaway star candidates (with a contamination ofnormal Population I stars of 20 per cent at most). Thus, aftersubtracting these 20 per cent, the runaway frequency among young starsis about 27 per cent. We compile a catalogue of runaway stars, which isavailable via VizieR.
| Interstellar TiII in the Milky Way and Magellanic Clouds
We discuss several sets of TiII absorption-line data, which probe avariety of interstellar environments in our Galaxy and in the MagellanicClouds. Comparisons of high-resolution [full width at half-maximum(FWHM) ~ 1.3-1.5kms-1] TiII spectra of Galactic targets withcorresponding high-resolution spectra of NaI, KI and CaII reveal bothsimilarities and differences in the detailed structure of theabsorption-line profiles - reflecting component-to-component differencesin the ionization and depletion behaviour of those species.Moderate-resolution (FWHM ~ 3.4-4.5kms-1) spectra of moreheavily reddened Galactic stars provide more extensive information onthe titanium depletion in colder, denser clouds - where more than 99.9per cent of the Ti may be in the dust phase. Moderate-resolution (FWHM ~4.5-8.7kms-1) spectra of stars in the Magellanic Cloudssuggest that the titanium depletion is generally much less severe in theLarge and Small Magellanic Clouds than in our Galaxy [for a givenN(Htot), E(B - V), or molecular fraction f(H2)] -providing additional evidence for differences in depletion patterns inthose two lower-metallicity galaxies. We briefly discuss possibleimplications of these results for the interpretation of gas-phaseabundances in quasi-stellar object absorption-line systems and ofvariations in the D/H ratio in the local Galactic interstellar medium.This paper is based in part on observations collected at the EuropeanSouthern Observatory, Chile, under programmes 65.I-0526, 67.C-0281,67.D-0238, 70.D-0164, 72.C-0682 and 74.D-0109. Based in part onobservations made with the NASA/ESA Hubble Space Telescope, obtainedfrom the data archive at the Space Telescope Science Institute. STScI isoperated by the Association of Universities for Research in Astronomy,Inc. under NASA contract NAS5-26555.Visiting observer, European Southern Observatory and Kitt Peak NationalObservatory. ‡E-mail: dwelty@astro.illinois.edu (DEW); Paul.crowther@sheffield.ac.uk(PAC)
| Exploring interstellar titanium and deuterium abundances and other correlations
Aims. The origin of the observed variability of the gas-phase D/H ratioin the local interstellar medium is still debated, and in particular therole of deuterium depletion onto dust grains. Here we extend the studyof the relationship between deuterium and titanium, a refractory speciesand tracer of elemental depletion, and explore other relationships. Methods: We have acquired high resolution spectra for nine early-typestars using the VLT/UVES spectrograph, and detected the absorption linesof interstellar TiII. Using a weighted orthogonal distance regression(ODR) code and a special method to treat non symmetric errors, wecompare the TiII columns with the corresponding HI, DI and also OIcolumns. In parallel we perform the same comparisons for available FeIIdata. Results: We find a significant correlation between TiII/HI andD/H in our data set, and, when combined with published results, weconfirm and better constrain the previously established trends andextend the trends to low HI columns. We exclude uncertainties in HI andOI columns as the main contributor to the derived metals-deuteriumcorrelations by showing that the TiII/HI ratio is positively correlatedwith DI/OI. We find a similar correlation between FeII/HI and DI/OI. TheTiII gradients are similar or slightly smaller than for FeII, while onewould expect larger variations on the basis of the higher condensationtemperature of titanium. However we argue that ionisation effectsintroduce biases that affect iron and not titanium and may explain thegradient similarity. We find a less significant negative correlationbetween the TiII/DI ratio and the hydrogen column, possibly a sign ofdifferent evaporation of D and metals according to the cloud properties.More TiII absorption data along very low H column lines-of-sight wouldbe useful to improve the correlation statistics.Based on observations taken with the Ultraviolet and Visual EchelleSpectrograph (UVES) on the Very Large Telescope (VLT) Unit 2 (Kueyen) atParanal, Chile, operated by ESO.
| The Galactic deuterium abundance and dust depletion: insights from an expanded Ti/H sample
The primordial abundance of deuterium (D/H) yields a measure of thedensity of baryons in the Universe and is an important complement todeterminations from cosmic microwave background (CMB) experiments.Indeed, the current small samples of high-redshift D/H measurements fromquasar absorption line studies are in excellent agreement withCMB-derived values. Conversely, absorption line measurements of theGalactic D/H ratio in almost 50 stellar sightlines show a puzzlinglylarge scatter outside the local bubble which is difficult to explainsimply by astration from the primordial value. The currently favouredexplanation for these large variations is that D is differentiallydepleted relative to H in some parts of the local interstellar medium(ISM). Here, we test this scenario by studying the correlation betweenD/H and the abundance of titanium, one of the most refractory elementsreadily observed in the ISM. Previous work by Prochaska, Tripp &Howk found tentative evidence for a correlation between Ti/H and D/Hbased on seven sightlines. Here we almost triple the number of previousTi measurements and include several sightlines with very high or low D/Hthat are critical for quantifying any correlations with D/H. With ourlarger sample, we confirm a correlation between Ti/H and D/H at the 97per cent confidence level. However, the magnitude of this dependence isdifficult to reconcile with a simple model of dust depletion for tworeasons. First, contrary to what is expected from local depletion rates,the gradient of the highly refractory Ti is much shallower than thatobserved for Fe and Si. Secondly, we do not observe the establishedtight, steep correlation between [Ti/H] and the mean volume density ofhydrogen. Therefore, whilst dust remains a plausible explanation for thelocal D/H variations, the abundances of at least some of the refractoryelements do not provide unanimous support for this scenario. We alsoargue that the correlations of [Si/H], [Fe/H] and [Ti/H] with D/H areinconsistent with a simple infall model of low-metallicity gas withapproximately solar abundances as the dominant cause for D variations.Based on observations made with ESO Telescopes at the ParanalObservatories under programme ID 076.C-0503(A).E-mail: sarae@uvic.ca
| What Is the Total Deuterium Abundance in the Local Galactic Disk?
Analyses of spectra obtained with the Far Ultraviolet SpectroscopicExplorer (FUSE) satellite, together with spectra from the Copernicus andinterstellar medium absorption profile spectrograph (IMAPS) instruments,reveal an unexplained, very wide range in the observeddeuterium/hydrogen (D/H) ratios for interstellar gas in the Galacticdisk beyond the Local Bubble. We argue that spatial variations in thedepletion of deuterium onto dust grains can explain these localvariations in the observed gas-phase D/H ratios. We present a variabledeuterium depletion model that naturally explains the constant measuredvalues of D/H inside the Local Bubble, the wide range of gas-phase D/Hratios observed in the intermediate regime [logN(HI)=19.2-20.7], and thelow gas-phase D/H ratios observed at larger hydrogen column densities.We consider empirical tests of the deuterium depletion hypothesis: (1)correlations of gas-phase D/H ratios with depletions of the refractorymetals iron and silicon, and (2) correlation with the H2rotational temperature. Both of these tests are consistent withdeuterium depletion from the gas phase in cold, not recently shockedregions of the ISM, and high gas-phase D/H ratios in gas that has beenshocked or otherwise heated recently. We argue that the mostrepresentative value for the total (gas plus dust) D/H ratio within 1kpc of the Sun is >=23.1+/-2.4(1σ) parts per million (ppm).This ratio constrains Galactic chemical evolution models to have a verysmall deuterium astration factor, the ratio of primordial to total (D/H)ratio in the local region of the Galactic disk, which we estimate to befd<=1.19+0.16-0.15(1σ) or<=1.12+/-0.14(1σ) depending on the adopted light-elementnuclear reaction rates.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by the Johns HopkinsUniversity under NASA contract NAS5-32985.
| 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
| The Subdwarf Database: Released
The work on the Subdwarf Database, presented at the previous meeting,has been completed, and the tool is now publicly available. The firstrelease contains data from close to 240 different literature sources,but more still awaits entry. The database interface includes advancedsearch capabilities in coordinate, magnitude and color space. Outputtables can be generated in HTML with hyperlinks to automaticallygenerated finding charts, the Aladin viewer and a detailed data sheetthat displays all registered data for each target, including physicaldata such as temperature, gravity and helium abundance, together with afinding chart. Search results can be visualized automatically asinteractive position, magnitude or color diagrams.
| Deuterium measurements toward WD1034+001, BD+393226, and TD1 32709
Observations of the D/H ratio in the interstellar medium provideimportant constraints on Galactic chemical evolution models as well ason the Big Bang nucleosynthesis theory. The behavior of the D/H ratio inthe interstellar medium is far from being well understood. D/H seems tohave a single value inside the Local Bubble (logN(DI) < 14.5).However, beyond 100 pc there is a wide range of D/H values which areinconsistent with the Local Bubble value.In order to increase the number of measurements that will allow us tounderstand this behavior, we present a preliminary analysis of threesightlines located outside the Local Bubble. All three sightlines havelog N(DI) > 15. We use data obtained with FUSE, IUE, and HST/GHRS todetermine the column densities of many species, including H I, D I, N I,O I, and H2. We derive D/H, N/H, O/H, and D/O ratios which are thencompared to values published in the literature.This work is based on data obtained for the Guaranteed Time Team by theNASA-CNES-CSA FUSE mission operated by The Johns Hopkins University.Financial support to U. S. participants has been provided in part byNASA contract NAS5-32985 to Johns Hopkins University.
| Spatial Variability in the Ratio of Interstellar Atomic Deuterium to Hydrogen. II. Observations toward γ2 Velorum and ζ Puppis by the Interstellar Medium Absorption Profile Spectrograph
High-resolution far-ultraviolet spectra of the early-type starsγ2 Vel and ζ Pup were obtained to measure theinterstellar deuterium abundances in these directions. The observationswere made with the Interstellar Medium Absorption Profile Spectrograph(IMAPS) during the ORFEUS-SPAS II mission in 1996. IMAPS spectra coverthe wavelength range 930-1150 Å withλ/Δλ~80,000. The interstellar D I features areresolved and cleanly separated from interstellar H I in the Lyδand Lyɛ profiles of both sight lines and also in the Lyγprofile of ζ Pup. The D I profiles were modeled using a velocitytemplate derived from several N I lines in the IMAPS spectra recorded athigher signal-to-noise ratio. To find the best D I column density, weminimized χ2 for model D I profiles that included notonly the N(D I) as a free parameter, but also the effects of severalpotential sources of systematic error, which were allowed to vary asfree parameters. H I column densities were measured by analyzingLyα absorption profiles in a large number of IUE high-dispersionspectra for each of these stars and applying this sameχ2-minimization technique. Ultimately we found thatD/H=2.18+0.36-0.31×10-5 forγ2 Vel and1.42+0.25-0.23×10-5 for ζPup, values that contrast markedly with D/H derived in Paper I forδ Ori A (the stated errors are 90% confidence limits). Evidently,the atomic D/H ratio in the ISM, averaged over path lengths of 250-500pc, exhibits significant spatial variability. Furthermore, the observedspatial variations in D/H do not appear to be anticorrelated with N/H,one measure of heavy-element abundances. We briefly discuss somehypotheses to explain the D/H spatial variability. Within the frameworkof standard big bang nucleosynthesis, the large value of D/H foundtoward γ2 Vel is equivalent to a cosmic baryon densityof ΩBh2=0.023+/-0.002, which we regard as anupper limit since there is no correction for the destruction ofdeuterium in stars. This paper is dedicated in memory of Judith L.Tokel, wife of the first author, who passed away on 2000 June 10. Herenthusiastic support and encouragement were essential to its successfulcompletion.
| Hubble Space Telescope Imaging Spectrograph Observations of the Hot White Dwarf in the Close Binary Feige 24
We obtained and analyzed two Hubble Space Telescope Imaging Spectrographspectra of the white dwarf in the DA plus dMe binary Feige 24. Thespectra, obtained at orbital quadratures, provide new estimates of thewhite dwarf motion and gravitational redshift resulting in revised whitedwarf parameters. An analysis of interstellar absorption lines revealsthe presence of two clouds (+3.1 km s-1, +17.6 kms-1) in the line of sight toward Feige 24; one of theseclouds (+17.6 km s-1) is identified with the ``local cloud.''A study of the Ly? H I and D I interstellar medium lines showsthat the deuterium-to-hydrogen abundance ratio(D/H=1.3×10-5) is consistent with other measurementssupporting a relative constancy of this ratio throughout the localinterstellar medium. The total hydrogen column density measured withLy? (lognH=2.95×1018 cm-2)is in agreement with EUV Lyman continuum flux measurements. Finally, wepresent a complete abundance pattern for the white dwarf, demonstratingthe predominance of iron and nickel over lighter elements. Residualionization imbalance in the case of several elements, most notably inthe case of O IV/O V, which cannot be explained by temperature orsurface gravity variations, may indicate the presence of otheratmospheric constituents, inhomogeneous stratification of oxygen in thephotosphere, and/or remaining inaccuracies in the treatment of modelatoms. The abundance patterns in Feige 24 and in the hot DA white dwarfG191-B2B are remarkably similar, indicating that the same processes areoperating equally in both stars.
| ORFEUS II echelle spectra: deuterium and molecular hydrogen in the ISM towards BD +39 3226
In ORFEUS II spectra of the sdO star BD +39 3226interstellar hydrogen and deuterium is detected. >From Ly alphaprofile fitting and a curve of growth analysis of the Lyman series of HI and D I we derive the column densities N_H =1.20+0.28}-0.22}{*10{20 cm-2and N_D = 1.45+0.50}-0.38}{*10{15cm-2. >From the analysis of metal absorption lines inORFEUS and IUE spectra we obtain column densities for 11 elements. Inaddition, we examine absorption lines of H_2 for rotational excitationstates up to J=7. We find an H_2 ortho-to-para ratio of 2.5, thefractional abundance of molecular hydrogen has a low value of logf=-4.08 for a total amount ofN(H_2)=4.8+2.0}-1.6}{*10{15cm-2. The column densities of the excitation states reveal a moderateBoltzmann excitation temperature of 130 K and an equivalent excitationtemperature for the excited upper states due to UV pumping of <1800K. Based on data obtained under the DARA ORFEUS guest observer programme
| ORFEUS II Echelle Spectra: Interstellar Deuterium and Molecular Hydrogen towards BD +39 3226
The FUV echelle spectrum obtained during the ORFEUS II mission inNov./Dec 1996 is used to derive H i, D i, H_2, and metal columndensities on the line of sight towards BD +39 3226. This sdO star islocated at l=65.00, b=+28.77 in a distance of about 270 pc. It has apure helium line spectrum in the optical and some additional lines ofhighly ionized metals in the UV, which are well separated from theinterstellar lines because of the stellar radial velocity of ={-273} kms^{-1}. A theoretical fit to the Ly alpha line taking into account thestellar He ii line approx1.57 Å bluewards gives a H i columndensity of 1.12^{+0.29}_{-0.23}?{1020} cm^{-2}. Thisvalue is consistent with a curve-of-growth analysis of the D and H Lymanseries, including Ly delta, epsilon, zeta, and kappa, which leads to N(Hi)=1.6^{+0.9}_{-0.6}?{1020} cm^{-2} and N(Di)=1.45^{+0.50}_{-0.38}?{1015} cm^{-2}. Averaging theN(H i) results we derive D/H=1.2^{+0.5}_{-0.4}?10^{-5}. We alsoinvestigated metal lines in ORFEUS and IUE spectra. Their columndensities indicate only moderate depletion (<=1.7 dex), in agreementwith the small E(B-V)=0.05 and the low abundance of H_2(N(H_2)=4.8^{+2.0}_{-1.6}?1015 cm^{-2}). H_2 is examinedfor absorption by rotational exitation states up to J=7. The columndensities of these exitation states reveal a H_2 ortho-to-para ratio of2.5, a Boltzmann excitation temperature of 130 K and UV-pumping with anequivalent temperature of <1800 K.
| Infrared flux excesses from hot subdwarfs. II. 72 more objects
In our search, started in February, 1994, for JHK excess fluxes amongthe hot subdwarf population as an indicator for the presence of binarycompanions, results for 72 more hot objects (=63 hot subdwarfs + 1Horizontal Branch B star + 7 white dwarfs + 1 non-subdwarf object)observed with the Carlos Sanchez CVF IR photometer (in June and October,1994), are presented. The exact number of binary hot subdwarfs hasgained renewed importance after the recent discovery of pulsators withG-F companions. The total number of candidates we propose may help toset some constraints; for example, out of 41 objects with excesses, 13may have G-type binary companions. From our new sample, 14 discoveriesof binary candidates have been found: BD+25 4655, Feige 108, HD 4539, HD149382, HD 216135, KPD 2109+440, LSI+63 198, LSIV+10 9, LSV+22 38, PG0011+221, PG 0116+242, PG 0314+103, PG 2151+100 and TON 139. Besides, 2more from reanalysis of February, 1994, data - BD+37 1977 and BD+481777, may now be found to be IR excess candidates. Two suspectedbinaries, PB 8555 and SB 7, are also confirmed. By fitting \cite[Kurucz(1993)]{kur93} model spectra and assuming zero-age main sequencecompanions, we find upper limits on the subdwarf gravities. Thedistributions of upper limits on log(g), mostly between about 5.25 and6.5, are nearly identical for both sdBs and sdOs. Figure~1 is onlyavailable in the electronic version of the paper(http://www.edpsciences.com)
| A catalogue of spectroscopically identified hot subdwarf stars.
Not Available
| A survey of ultraviolet objects
An all-sky survey of ultraviolet objects is presented together with astatistical analysis that leads to the conclusion that there is asignificantly higher population of hot subdwarfs lying below themain-sequence than hitherto thought. The distribution of all ultravioletobjects, main sequence ultraviolet objects, and MK unclassifiedultraviolet objects are shown in galactic coordinates, and the absolutemagnitudes and color-color diagrams for these groups are presented.Scale heights are derived, giving values similar to planetary nebulaefor the hottest groups.
| Optical observations of ultraviolet objects. II - Classification and photometry /l = 0 to 145 deg/
UBV photometry and MK spectral classification are presented for a sampleof stars originally selected as UV objects from satellite photometrywith the S2/68 experiment. Although most stars of the sample arespectroscopically normal, a number of hot, subluminous stars were alsofound. Radial velocities are given for some of the stars observed. It isproposed that the majority of the apparently normal early B stars athigh galactic latitudes which are not runaway stars are subluminousdisc-population analogues of horizontal branch B stars of Population II.
| SB 21, an extremely helium-rich subdwarf O-star
Spectral observations of the subdwarf O star SB 21 are reported. Theobservations were made at a dispersion of 29 A/mm in the spectral range4250-4800 A using a 3.6-m telescope and an image dissector scanner. TheH gamma line is found to be absent in SB 21, while the He I lines at4388, 4471 and 4713 A and the He II lines at 4686 and possibly 4542 aredetected. A detailed nonlocal thermodynamic equilibrium model analysisof the data indicates an effective temperature of 35,000 K, log g of 5.5and a He/H density ratio greater than 10. Differences between theextremely helium rich objects SB 21, CPD-31 1701 and BD + 48 177 andother extremely helium-rich objects such as BD +37 1877 and BD +37 442are pointed out.
| Photometric calibration of the International Ultraviolet Explorer /IUE/ - Low dispersion
Absolute sensitivity curves for IUE low-resolution spectra are obtainedby comparing IUE measurements of hot stars with the absolute energydistributions established for these objects by previous satellite androcket experiments. The differences between these earlier experimentsare discussed quantitatively, and a common absolute flux scale isproposed as the basis for the absolute calibration of IUE.
| Spectral classification of ultraviolet objects.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&A....66L...9B&db_key=AST
| Three new hot subdwarfs: AGK2 +81 266, BD +39 3226, BD +34 1543.
Abstract image available at:http://adsabs.harvard.edu/abs/1978A&A....64L...9B
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| קבוצת-כוכבים: | הרקולס |
| התרוממות ימנית: | 17h46m31.91s |
| סירוב: | +39°19'09.0" |
| גודל גלוי: | 10.217 |
| תנועה נכונה: | 21.7 |
| תנועה נכונה: | -5 |
| B-T magnitude: | 9.778 |
| V-T magnitude: | 10.181 |
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