Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
The Turbulent Warm Ionized Medium: Emission Measure Distribution and MHD Simulations
We present an analysis of the distribution of Hα emission measuresfor the warm ionized medium (WIM) of the Galaxy using data from theWisconsin Hα Mapper (WHAM) Northern Sky Survey. Our sample isrestricted to Galactic latitudes |b|>10deg. We removedsight lines intersecting 19 high-latitude classical H II regions,leaving only sight lines that sample the diffuse WIM. The distributionof EMsin|b| for the diffuse WIM sample is poorly characterized by asingle normal distribution, but is extraordinarily well fit by alognormal distribution, with -6)-1>=0.146+/-0.001 andstandard deviation σlogEMsin|b|=0.190+/-0.001. Thevalue of drops from 0.260+/-0.002 at Galactic latitude 10<|b|<30to 0.038+/-0.002 at Galactic latitude 60<|b|<90. The distributionmay widen slightly at low Galactic latitude. We compare the observed EMdistribution function to the predictions of three-dimensionalmagnetohydrodynamic simulations of isothermal turbulence within anonstratified interstellar medium. We find that the distribution ofEMsin|b| is well described by models of mildly supersonic turbulencewith a sonic Mach number of ~1.4-2.4. The distribution is weaklysensitive to the magnetic field strength. The model also successfullypredicts the distribution of dispersion measures of pulsars and Hαline profiles. In the best fitting model the turbulent WIM occupies avertical path length of 400-500 pc within the 1.0-1.8 kpc scale heightof the layer. The WIM gas has a lognormal distribution of densities witha most probable electron density npk~0.03 cm-3. Wealso discuss the implications of these results for interpreting thefilling factor, the power requirement, and the magnetic field of theWIM.
| Adaptive Optics Photometry and Astrometry of Binary Stars. III. a Faint Companion Search of O-Star Systems
We present the results of an adaptive optics survey for faint companionsamong Galactic O-type star systems (with V lsim 8) using the AdvancedElectro-Optical System (AEOS) 3.6 m telescope on Haleakala. We surveyedthese O-star systems in the I-band, typically being able to detect acompanion with a magnitude difference of utrimI lsim 6 in theprojected separation range 0farcs5 < ρ < 1farcs0, andutrimI lsim 9.5 in the range 1farcs0 < ρ < 5farcs0.In the course of the survey, we discovered 40 new companions among 31 ofthe 116 objects examined and made astrometric and differential magnitudemeasurements of 24 additional known pairs, several of them beingconfirmation detections. We present new astrometric orbits for twobinaries, BU 1032AB (WDS 05387–0236 σ Ori AB) and SEE 322(WDS 17158–3344 HD 155889AB). We lack magnitude differences forother filter bands, so it is difficult to determine physical fromline-of-sight companions, but we present empirical arguments for thelimiting magnitude difference where field contamination is significant.Based on observations made at the Maui Space Surveillance Systemoperated by Detachment 15 of the US Air Force Research Laboratory'sDirected Energy Directorate.
| The Far Ultraviolet Spectroscopic Explorer Survey of O VI Absorption in the Disk of the Milky Way
To probe the distribution and physical characteristics of interstellargas at temperatures T~3×105 K in the disk of the MilkyWay, we have used the Far Ultraviolet Spectroscopic Explorer (FUSE) toobserve absorption lines of O VI λ1032 toward 148 early-typestars situated at distances >1 kpc. After subtracting off a mildexcess of O VI arising from the Local Bubble, combining our new resultswith earlier surveys of O VI, and eliminating stars that showconspicuous localized X-ray emission, we find an average O VI midplanedensity n0=1.3×10-8 cm-3. Thedensity decreases away from the plane of the Galaxy in a way that isconsistent with an exponential scale height of 3.2 kpc at negativelatitudes or 4.6 kpc at positive latitudes. Average volume densities ofO VI along different sight lines exhibit a dispersion of about 0.26 dex,irrespective of the distances to the target stars. This indicates that OVI does not arise in randomly situated clouds of a fixed size anddensity, but instead is distributed in regions that have a very broadrange of column densities, with the more strongly absorbing cloudshaving a lower space density. Line widths and centroid velocities aremuch larger than those expected from differential Galactic rotation, butthey are nevertheless correlated with distance and N(O VI), whichreinforces our picture of a diverse population of hot plasma regionsthat are ubiquitous over the entire Galactic disk. The velocity extremesof the O VI profiles show a loose correlation with those of very stronglines of less ionized species, supporting a picture of a turbulent,multiphase medium churned by shock-heated gas from multiple supernovaexplosions.
| 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
| Connecting the primordial and Galactic deuterium abundances
The deuterium abundances inferred from observations of the interstellarmedium (ISM) within 1-2 kpc of the Sun range over a factor of 3 and thecorresponding oxygen abundances show an even larger dispersion. Whilethe lower D (and O) abundances likely result from depletion on to dust,the higher D abundances are consistent with the big bangnucleosynthesis-predicted primordial D abundance and chemical evolutionmodels of the Galaxy with infall of primordial or nearly primordialmaterial. The large ranges in deuterium and oxygen abundances suggestthat the effects of depletion and/or infall have not been homogenized inthe local ISM.
| The Effect of an Increased Elemental D/H Ratio on Deuterium Fractionation in the Cold Interstellar Medium
Measurements using the Far Ultraviolet Spectroscopic Explorer (FUSE)show that the gas-phase D/H ratio in the solar neighborhood is highlyvariable and suggest that the elemental abundance of deuterium in theGalactic disk may be higher than previously thought. We investigate inthis Letter the possible consequences of such an enhanced D/H ratio onthe deuterium fractionation in singly and multiply deuterated moleculesin cold, dense gas. We show that a modest increase in the elementalabundance of deuterium can lead to significant enhancements inabundances of multiply deuterated species.
| Variations in the D/H Ratio of Extended Sight Lines from Far Ultraviolet Spectroscopic Explorer Observations
We use new FUSE data to determine the column densities of interstellar DI, N I, O I, Fe II, and H2 along the HD 41161 and HD 53975sight lines. Together with N(H I) from the literature, we derive D/H,N/H, and O/H ratios. These sight lines have logN(H I)>21.00 and probegas up to ~1300 pc, allowing us to determine the gas-phase D/H ratio ina hydrogen column density range, logN(H)>20.70, where the only fivemeasurements available in the literature yield a weighted average ofD/H=(0.86+/-0.08)×10-5. We findD/H=(2.14+0.51-0.43)×10-5 alongthe HD 41161 sight line. This ratio is ~3 σ higher than theweighted mean D/H ratio quoted above, while the D/H ratio for the HD53975 line of sight,D/H=(1.02+0.23-0.20)×10-5, agreeswithin the 1 σ uncertainties. Our D/H measurement along the HD41161 sight line presents the first evidence of variations of D/H athigh N(H). Our result seems to indicate either that the long sight linesthat, according to the deuterium depletion model, are dominated by coldundisturbed gas where deuterium would be depleted onto carbonaceousgrains occur at higher N(H) than previously thought, or that theclumping of low D/H values in the literature for the long sight lineshas another explanation. Both of the O/H ratios derived here,(9.12+2.15-1.83)×10-4 and(5.37+1.35-1.14)×10-4 (for HD41161 and HD 53975, respectively), are higher than what has been foundby other authors. Finally, we derive(N/H)×105=8.32+2.09-1.76 and5.07+1.45-1.21, and(D/O)×102=2.29+0.40-0.35 and1.91+0.51-0.43, for HD 41161 and HD 53975,respectively. In addition, the relatively high signal-to-noise ratio ofthe HD 41161 data allows us to place constraints on the f-values of someneutral chlorine transitions present in the FUSE bandpass for which onlytheoretical values are available.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.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| To see or not to see a bow shock. Identifying bow shocks with Hα allsky surveys
OB-stars have the highest luminosities and strongest stellar winds ofall stars, which enables them to interact strongly with theirsurrounding ISM, thus creating bow shocks. These offer us an idealopportunity to learn more about the ISM. They were first detected andanalysed around runaway OB-stars using the IRAS allsky survey by vanBuren et al. (1995, AJ, 110, 2614). Using the geometry of such bowshocks information concerning the ISM density and its fluctuations canbe gained from such infrared observations. As to help to improve the bowshock models, additional observations at other wavelengths, e.g.Hα, are most welcome. However due to their low velocity these bowshocks have a size of 1°, and could only be observed as awhole with great difficulties. In the light of the new Hα allskysurveys (SHASSA/VTSS) this is no problem any more. We developeddifferent methods to detect bow shocks, e.g. the improved determinationof their symmetry axis with radial distance profiles. Using twoHα-allsky surveys (SHASSA/VTSS), we searched for bow shocks andcompared the different methods. From our sample we conclude, that thecorrelation between the direction of both proper motion and the symmetryaxis determined with radial distance profile is the most promisingdetection method. We found eight bow shocks around HD17505, HD 24430, HD48099, HD 57061, HD92206, HD 135240, HD149757, and HD 158186 from 37 candidatestaken from van Buren et al. (1995, AJ, 110, 2614). Additionally to thetraditional determination of ISM parameters using the standoff distanceof the bow shock, another approach was chosen, using the thickness ofthe bow-shock layer. Both methods lead to the same results, yieldingdensities ( 1 cm-3) and the maximal temperatures (104 K), that fit well to the up-to-date picture of the WarmIonised Medium.
| The origin of massive O-type field stars: II. Field O stars as runaways
In two papers we try to confirm that all Galactic high-mass stars areformed in a cluster environment, by excluding that O-type stars found inthe Galactic field actually formed there. In de Wit et al. (2004) wepresented deep K-band imaging of 5 arcmin fields centred on 43 massiveO-type field stars that revealed that the large majority of theseobjects are single objects. In this contribution we explore thepossibility that the field O stars are dynamically ejected from youngclusters, by investigating their peculiar space velocity distribution,their distance from the Galactic plane, and their spatial vicinity toknown young stellar clusters. We (re-)identify 22 field O-type stars ascandidate runaway OB-stars. The statistics show that 4 ± 2% ofall O-type stars with V<8m can be considered as formedoutside a cluster environment. Most are spectroscopically singleobjects, some are visual binaries. The derived percentage for O-typestars that form isolated in the field based on our statistical analysesis in agreement with what is expected from calculations adopting auniversal cluster richness distribution with power index of β= 1.7,assuming that the cluster richness distribution is continuous down tothe smallest clusters containing one single star.
| On the Hipparcos parallaxes of O stars
We compare the absolute visual magnitude of the majority of bright Ostars in the sky as predicted from their spectral type with the absolutemagnitude calculated from their apparent magnitude and the Hipparcosparallax. We find that many stars appear to be much fainter thanexpected, up to five magnitudes. We find no evidence for a correlationbetween magnitude differences and the stellar rotational velocity assuggested for OB stars by Lamers et al. (1997, A&A, 325, L25), whosesmall sample of stars is partly included in ours. Instead, by means of asimulation we show how these differences arise naturally from the largedistances at which O stars are located, and the level of precision ofthe parallax measurements achieved by Hipparcos. Straightforwardlyderiving a distance from the Hipparcos parallax yields reliable resultsfor one or two O stars only. We discuss several types of bias reportedin the literature in connection with parallax samples (Lutz-Kelker,Malmquist) and investigate how they affect the O star sample. Inaddition, we test three absolute magnitude calibrations from theliterature (Schmidt-Kaler et al. 1982, Landolt-Börnstein; Howarth& Prinja 1989, ApJS, 69, 527; Vacca et al. 1996, ApJ, 460, 914) andfind that they are consistent with the Hipparcos measurements. AlthoughO stars conform nicely to the simulation, we notice that some B stars inthe sample of \citeauthor{La97} have a magnitude difference larger thanexpected.
| The origin of massive O-type field stars. I. A search for clusters
We present a study aimed at clarifying the birthplace for 43 massiveO-type field stars. In this first paper we present the observationalpart: a search for stellar clusters near the target stars. We derivestellar density maps at two different resolving scales, viz. 0.25pc and 1.0 pc from NTT and TNG imaging and the 2MASS catalogue.These scales are typical for cluster sizes. The main result is that thelarge majority of the O-type field population are isolated stars: only12% (5 out of 43) of the O-type field stars is found to harbour asmall-scale stellar cluster. We review the literature and aim atcharacterizing the stellar field of each O-type field star with theemphasis on star formation and the presence of known young stellarclusters. An analysis of the result of this paper and a discussion ofthe O-type field population as products of a dynamical ejection event ispresented in an accompanying paper.Based on observations collected at the European Southern Observatory,Chile, and at the Italian Telescopio Nazionale Galileo (TNG) operated onthe island of La Palma by the Centro Galileo Galilei of the CNAA(Consorzio Nazionale per l'Astronomia e l'Astrofisica) at the SpanishObservatorio del Roque de los Muchachos of the Instituto de Astrofisicade Canarias.Table 2 and Figs. 4 to 17 are available in electronic form athttp://www.edpsciences.org
| A Galactic O Star Catalog
We have produced a catalog of 378 Galactic O stars with accuratespectral classifications that is complete for V<8 but includes manyfainter stars. The catalog provides cross-identifications with othersources; coordinates (obtained in most cases from Tycho-2 data);astrometric distances for 24 of the nearest stars; optical (Tycho-2,Johnson, and Strömgren) and NIR photometry; group membership,runaway character, and multiplicity information; and a Web-based versionwith links to on-line services.
| Optical spectroscopy of X-Mega targets - IV. CPD - 59°2636: a new O-type multiple system in the Carina Nebula
High-resolution optical spectroscopy of CPD - 59°2636, one of theO-type stars in the open cluster Trumpler 16 in the Carina Nebula,reveals this object to be a multiple system displaying triple lineswhich we label as components A, B and C of spectral types O7 V, O8 V andO9 V, respectively. From our radial velocity measurements we find thatthe components A and B form a close binary with a period of 3.6284 d,and we obtain the first circular radial velocity orbit for this systemwith semi-amplitudes of 184 and 192 km s-1, leading tominimum masses of 10.1 and 9.7 Msolar. We find that thecomponent C is a single lined binary with a period of 5.034 d andsemi-amplitude of 48 km s-1. We also analyse the X-rayradiation from CPD - 59°2636, finding neither appreciableoverluminosity nor phase-related X-ray flux variations.
| IUE Absorption-Line Observations of the Moderately and Highly Ionized Interstellar Medium toward 164 Early-Type Stars
We present measurements of Galactic interstellar Al III, Si IV, and C IVabsorption recorded in high-resolution archival ultraviolet spectra of164 hot early-type stars observed by the International UltravioletExplorer (IUE) satellite. The objects studied were drawn from the listof hot stars scheduled to be observed with the Far UltravioletSpectroscopic Explorer (FUSE) satellite as part of observing programsdesigned to investigate absorption by O VI in the Galactic disk andhalo. Multiple IUE echelle-mode integrations have been combined toproduce a single ultraviolet (1150-1900 Å) spectrum of each starwith a spectral resolution of ~25 km s-1 (FWHM). Selectedabsorption-line profiles are presented for each star along with plots ofthe apparent column density per unit velocity for each line of the AlIII, Si IV, and C IV doublets. We report absorption-line equivalentwidths, absorption velocities, and integrated column densities based onthe apparent optical depth method of examining interstellar absorptionlines. We also determine column densities and Doppler parameters fromsingle-component curve-of-growth analyses. The scientific analysis ofthese observations will be undertaken after the FUSE satellite producessimilar measurements for absorption by interstellar O IV, Fe III, S III,and other ions. Based on archival data from observations obtained withthe International Ultraviolet Explorer (IUE) satellite sponsored byNASA, SERC, and ESA.
| Mesures d'etoiles doubles effectuees a la lunette de 50 CM de l'Observatoire de Nice (2({) e. Measures of visual double stars made with the 50 CM refractor at the Nice Observatory (2^{nd
66 measures of 38 visual double stars made at the Observatoire de laCote d'Azur, at Nice, in september et december 1997, with the 50 cmequatorial refractor equipped with filar micrometer and electronicrecording device. Observation programmes of stars suspected double andnew binaries discovered by Hipparcos, and measures of double stars whichhave seldom or never been observed since the epoch of their discovery.
| ICCD speckle observations of binary stars. XIX - an astrometric/spectroscopic survey of O stars
We present the results of a speckle interferometric survey made with theCHARA speckle camera and 4 m class telescopes of Galactic O-type starswith V less than 8. We can detect with the speckle camera binaries inthe angular separation range 0.035-1.5 arcsec with delta M less than 3,and we have discovered 15 binaries among 227 O-type systems. We combinedour results on visual binaries with measurements of wider pairs from theWashington Double Star Catalog and fainter pairs from the HipparcosCatalog, and we made a literature survey of the spectroscopic binariesamong the sample. We then investigated the overall binary frequency ofthe sample and the orbital characteristics of the known binaries.Binaries are common among O stars in clusters and associations but lessso among field and especially runaway stars. There are many triplesystems among the speckle binaries, and we discuss their possible rolein the ejection of stars from clusters. The period distribution of thebinaries is bimodal in log P, but we suggest that binaries with periodsof years and decades may eventually be found to fill the gap. The massratio distribution of the visual binaries increases toward lower massratios, but low mass ratio companions are rare among close,spectroscopic binaries. We present distributions of the eccentricity andlongitude of periastron for spectroscopic binaries with ellipticalorbits, and we find strong evidence of a bias in the longitude ofperiastron distribution.
| ORFEUS-I Observations of Molecular Hydrogen in the Galactic Disk
Not Available
| Bow Shocks Around Runaway Stars.III.The High Resolution Maps
In a recent survey for bow shock structures around OB runaway starsusing the ISSA/IRAS archival data and excess maps at 60 \mum, 58candidates were found. These objects are surrounded by extended infraredemission at 60 \mum, characteristic of warm dust heated by ultravioletphotons, a signature of wind bow shocks. High resolution IRAS (HiRes)images have been produced for these 58 objects and some of thosespatially resolved are presented in this study. The images were used todistinguish between multiple confused IR sources, possible artifacts andunambiguous bow shocks, as the sources of the extended 60 \mum emission.Six new bow shocks have been identified using this method, and threehave been rejected. Twenty two of the targets, however, remain spatiallyunresolved even at the nominal HiRes resolution of ~ 1arcmin . For thelarger and better defined bow shocks some internal substructure isdiscernible. The length of these features suggest that they arise as theresult of a subtle dynamical instability. It can not be ruled out,however, that some of the bow shock morphology could be imprinted by thesurrounding medium.
| 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.
| Projected Rotational Velocities of O-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...463..737P&db_key=AST
| Absorption Line Profile Variations among the O Stars. I. The Incidence of Variability
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..103..475F&db_key=AST
| A Search for Pulsar Companions to OB Runaway Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...461..357S&db_key=AST
| 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.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| The distribution of neutral hydrogen in the interstellar medium. 1: The data
We compile, from the existing literature, the largest sample to date(842 data points) of hydrogen column density measurements, N(H I), ofthe gas in the interstellar medium. We include only results obtainedfrom absorption measurements toward individual stars (594 in our sample)in an effort to construct a three-dimensional picture of theinterstellar gas. We derive hydrogen column densities toward a fractionof the stars in the sample from published column density measurements ofmetal ions. A three-dimensional physical model derived from this dataset will be presented in a companion paper. The observed stars spandistances from a few parsecs to a few thousand parsecs, and more thanhalf of the sample serves to describe the local interstellar mediumwithin a few hundred parsecs of the Sun. Hydrogen column densities rangefrom 1017 to 1022/sq cm. We describe here thevarious observational methods used to estimate the hydrogen columndensities and present the table with the stellar and hydrogen columndensity data. The provided table is intended as a global reference work,not to introduce new results.
| 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.
| Synthetic UV Lines of Si IV, C IV, and He II from a Population of Massive Stars in Starburst Galaxies
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993ApJ...418..749R&db_key=AST
| The Diffuse Ionized Interstellar Medium: Structures Resulting from Ionization by O Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993ApJ...417..579M&db_key=AST
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Arabaci |
| Sað Açýklýk: | 06h05m52.46s |
| Yükselim: | +48°14'57.4" |
| Görünürdeki Parlaklýk: | 6.757 |
| Uzaklýk: | 4761.905 parsek |
| özdevim Sað Açýklýk: | -2.5 |
| özdevim Yükselim: | -1.8 |
| B-T magnitude: | 6.635 |
| V-T magnitude: | 6.747 |
Kataloglar ve belirtme:
|
