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Young Stars far from the Galactic Plane: Runaways from Clusters
Quite recently, a significant number of OB stars far from the galacticplane have been found, situated at z-distances ranging from severalhundreds of pc to several kpc. The short lifetimes of these stars poseproblems for their interpretation in terms of the standard picture ofstar formation. Different mechanisms have been put forward to explainthe existence of these stars, either within the conventional view, orpostulating star formation in the galactic halo itself. These mechanismsrange from arguing that they are misidentified evolved or abnormalstars, to postulating powerful ejection mechanisms for young disk stars;in situ formation also admits several variants. We have collected fromthe literature a list of young stars far from the plane, for which theevidence of youth seems convincing. We discuss two possible formationmechanisms for these stars: ejection from the plane as the result ofdynamical evolution of small clusters (Poveda et al. 1967) and in situformation, via induced shocks created by spiral density waves (Martos etal. 1999). We compute galactic orbits for these stars, and identify thestars that could be explained by one or the other mechanism. We findthat about 90 percent of the stars can be accounted for by the clusterejection mechanism, that is, they can be regarded as runaway stars inthe galactic halo.
| Distances and Metallicities of High- and Intermediate-Velocity Clouds
A table is presented that summarizes published absorption linemeasurements for the high- and intermediate-velocity clouds (HVCs andIVCs). New values are derived for N(H I) in the direction of observedprobes, in order to arrive at reliable abundances and abundance limits(the H I data are described in Paper II). Distances to stellar probesare revisited and calculated consistently, in order to derive distancebrackets or limits for many of the clouds, taking care to properlyinterpret nondetections. The main conclusions are the following. (1)Absolute abundances have been measured using lines of S II, N I, and OI, with the following resulting values: ~0.1 solar for one HVC (complexC), ~0.3 solar for the Magellanic Stream, ~0.5 solar for a southern IVC,and ~solar for two northern IVCs (the IV Arch and LLIV Arch). Finally,approximate values in the range 0.5-2 solar are found for three moreIVCs. (2) Depletion patterns in IVCs are like those in warm disk or halogas. (3) Most distance limits are based on strong UV lines of C II, SiII, and Mg II, a few on Ca II. Distance limits for major HVCs aregreater than 5 kpc, while distance brackets for several IVCs are in therange 0.5-2 kpc. (4) Mass limits for major IVCs are0.5-8×105 Msolar, but for major HVCs theyare more than 106 Msolar. (5) The Ca II/H I ratiovaries by up to a factor 2-5 within a single cloud, somewhat morebetween clouds. (6) The Na I/H I ratio varies by a factor of more than10 within a cloud, and even more between clouds. Thus, Ca II can beuseful for determining both lower and upper distance limits, but Na Ionly yields upper limits.
| Five-colour photometry of OB-stars in the Southern Hemisphere
Observations of OB-stars, made in 1959 and 1960 at the Leiden SouthernStation near Hartebeespoortdam, South Africa, with the VBLUW photometerattached to the 90 cm light-collector, are given in this paper. They arecompared with photometry obtained by \cite[Graham (1968),]{gra68}\cite[Walraven & Walraven (1977),]{wal77} \cite[Lub & Pel(1977)]{lub77} and \cite[Van Genderen et al. (1984).]{gen84} Formulaefor the transformation of the present observations to those of\cite[Walraven & Walraven (1977)]{wal77} and \cite[Lub & Pel(1977)]{lub77} are given. Table 4 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| The interstellar clouds of ADAMS and Blaauw revisited: an HI absorption study - II.
Not Available
| The interstellar clouds of ADAMS and Blaauw revisited: an HI absorption study - I.
Not Available
| Supplementary southern standards for UBV(RI)c photometry
We present UBV(RI)c photometry for 80 southern red and blue stars foruse as additional standards. The data are tied to the Johnson UBV andCousins (RI)c systems and extend the range of the available stars forcolor equation determination, especially in (U-B) for blue stars and(V-R) and (V-I) for red stars. Comparisons with published data are madeand particularly good agreement is found with Bessell for the red(Gliese) stars.
| Classification of Population II Stars in the Vilnius Photometric System. II. Results
The results of photometric classification of 848 true and suspectedPopulation II stars, some of which were found to belong to Population I,are presented. The stars were classified using a new calibrationdescribed in Paper I (Bartkevicius & Lazauskaite 1996). We combinethese results with our results from Paper I and discuss in greaterdetail the following groups of stars: UU Herculis-type stars and otherhigh-galactic-latitude supergiants, field red horizontal-branch stars,metal-deficient visual binaries, metal-deficient subgiants, stars fromthe Catalogue of Metal-deficient F--M Stars Classified Photometrically(MDPH; Bartkevicius 1993) and stars from one of the HIPPARCOS programs(Bartkevicius 1994a). It is confirmed that high galactic latitudesupergiants from the Bartaya (1979) catalog are giants or even dwarfs.Some stars, identified by Rose (1985) and Tautvaisiene (1996a) as fieldRHB stars, appear to be ordinary giants according to our classification.Some of the visual binaries studied can be considered as physical pairs.Quite a large fraction of stars from the MDPH catalog are found to havesolar metallicity. A number of new possible UU Herculis-type stars, RHBstars and metal-deficient subgiants are identified.
| High-Velocity Rain: The Terminal Velocity Model of Galactic Infall
A model is proposed for determining the distances to fallinginterstellar clouds in the galactic halo by measuring the cloud velocityand column density and assuming a model for the vertical densitydistribution of the Galactic interstellar medium. It is shown thatfalling clouds with N(H I) <~ 1019 cm-2 may be decelerated to aterminal velocity which increases with increasing height above theGalactic plane. This terminal velocity model correctly predicts thedistance to high-velocity cloud Complex M and several other interstellarstructures of previously determined distance. It is demonstrated howinterstellar absorption spectra alone may be used to predict thedistances of the clouds producing the absorption. If the distance,velocities, and column densities of enough interstellar clouds are knownindependently, the procedure can be reversed, and the terminal velocitymodel can be used to estimate the vertical density structure (both themean density and the porosity) of the interstellar medium. Using thedata of Danly and assuming a drag coefficient of CD ≅ 1, thederived density distribution is consistent with the expected densitydistribution of the warm ionized medium, characterized by Reynolds.There is also evidence that for z >~ 0.4 kpc one or more of thefollowing occurs: (1) the neutral fraction of the cloud decreases to ~31+/- 14%, (2) the density drops off faster than characterized byReynolds, or (3) there is a systematic decrease in CD with increasing z.Current data do not place strong constraints on the porosity of theinterstellar medium.
| DO OB Runaway Stars Have Pulsar Companions?
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.1220P&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.
| 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.
| A high-resolution optical and radio study of Milky Way halo gas
Optical interstellar absorption lines of Ti II and Ca II and the 21 cmemission line of H I were observed at high-resolution (6 and 1 km/s,respectively) and high detection sensitivity along 25 lines of sight inthe Galactic halo. The sample includes 16 distant halo stars matchedwith one or more nearly aligned foreground stars as well as local starsalong five extragalactic sight lines. The data show substantialinterstellar material, at both low and intermediate velocities, between250 and 1000 pc beyond the Galactic plane. As much as one-third of thetotal gas observed in Ca II absorption may be beyond 1 kpc, and thegaseous Ti II may lie in an even thicker layer. The directly determinedgaseous Ti abundance above the Galactic plane exceeds that in the disk,on the average, by a factor of 4 to 6 and, for individual cloudcomponents, is further enhanced at higher LSR velocity. Thirty threediscrete high-latitude clouds are detected in Ca II absorption, and 17discrete clouds, including three high-velocity clouds, are identified inH I emission. The kinematics of the high-latitude gas observed in Ti IIand Ca II absorption is characterized by significant peculiar velocitieswith respect to a model corotating halo.
| Ultraviolet and radio observations of Milky Way halo gas
Interstellar-absorption-line and 21-cm emission-line data for sightlines to 56 stars are combined in order to study the kinematics andspatial distribution of the gas that is at great distances from theGalactic plane. Measurements of the interstellar velocities and H Icolumn densities from the 21-cm emission and Ly-alpha absorption areincluded. The problem of contamination of the interstellar Ly-alphaabsorption line by stellar Ly-alpha absorption is analyzed, and thisinformation is used to reevaluate the vertical distribution of H I. Anew method for determining lower limits on the vertical distribution ofgas by including information on the velocity structure in the gas ispresented. The data for individual sight lines are discussed.
| The runaway nature of distant early-type stars in the galactic halo
The kinematics of a sample of 32 distant halo B-stars with masses in therange 3-21 solar masses are investigated using the current 'runawaystar' hypotheses to establish if they belong to this group of stars.Whether postmass transfer secondaries in evolved massive close binariescan be normal low mass B-stars is discussed, but support for this ideais not found. Thus it appears that the lower mass stars could not havebeen ejected out of the disk as a result of supernova explosions inmassive close binaries, while the higher mass objects do not in generalreveal a binary nature as expected from this theory. The results ofrecent N-body simulations of the purely dynamical ejection of runawaystars from young galactic star clusters are in excellent agreement withthe observations. Thus it appears that these halo stars are the mostdistant subgroup of OB runaways produced by cluster ejection yetobserved.
| Runaway stars from young star clusters containing initial binaries. II - A mass spectrum and a binary energy spectrum
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990AJ.....99..608L&db_key=AST
| Estimation of the equivalent width of the interstellar CA II K absorption line
Literature values for the equivalent width of the interstellarabsorption line of Ca II K (3933 A) are used to constrain a simpleempirical model for the strength of this line as a function of distancefrom the galactic plane. The best-fit model has an integrated Ca II Kequivalent width in the direction perpendicular to the galactic plane ofapproximately 200 mA and a 'scale height' of approximately 1100 pc. Sucha model is useful for estimating (and correcting for) the contributionof the interstellar Ca II K feature to the total observed Ca II K linestrength in the spectra of metal-deficient stars in the galactic halo.
| Broad-band photometry of selected southern ultraviolet-bright stars.
Not Available
| The kinematics of Milky Way halo gas. I - Observations of low-ionization species
Ultraviolet interstellar line day observed with the IUE toward 70 halostars and four extragalactic sight lines are analyzed in a study of thelarge-scale kinematic properties of the Milky Way halo gas. The motionsof the low-ionization gas is focused on. Large systematic velocities arefound, and a pronounced asymmetry in the absorption characteristics ofhalo gas toward the Galactic poles is indicated. In the north,substantial amounts of material are falling toward the disk atvelocities up to about 120 km/s in the most extreme case. Toward thesouth, low-ionization material shows no extreme or systematic motions.
| The density distribution of refractory elements away from the Galactic plane
The density distributions of the three refractory elements Ti II, Ca II,and Fe II away from the Galactic plane are compared with thedistribution of hydrogen and dust by examining plots of N s in b versusz. It is found that Ti II and Ca II are considerably more extended in zthan the H I and dust and that Fe II has an intermediate extension.Although the results are strongly influenced by sample bias, theindicated exponential scale heights for the data sample are h(Ti II) notless than 2 kpc, h(Ca II) = 1 kpc, h(Fe II) = 0.5 kpc, H(H I) = 0.3 kpc,and h(E/B-V) = 0.1 kpc. Furthermore, it is demonstrated that Ti II andCa II are much more smoothly distributed in space than the hydrogen ordust. The large scale heights for Ti II and Ca II and their smoothdistributions are most easily understood as the effect of a mixturealong the line of sight of two H I phases namely, a diffuse cloud phase,in which nearly all of the Ti and Ca are tied up in dust, and anintercloud medium, where refractory elements are less depleted. It isfound that Ti II and Ca II mostly trace the smoothly distributedintercloud medium. The smoothness of the distributions of Ti II and CaII makes them candidates for use as distance indicators.
| Radial velocities and spectral types for a sample of faint blue stars.
Not Available
| IUE-IRAS studies of the infrared cirrus
The 60 and 100 micron cirrus emission around 256 lines of sight in theIRAS all-sky survey was measured, and the flux averages were used tostudy the distribution, variations, and correlations of the IRASinfrared cirrus fluxes with various interstellar parameters. It wasfound that the 60 and 100 micron fluxes correlate with the depletion ofSi and show a trend with the depletion of Fe for 51 lines of sighttoward the Galactic halo. No correlation was found with the abundancesof Si, Mn, Fe, S, or Zn or with abundance ratios for the full sample of256 stars. An abundance ratio of about 3 x 10 to the 7th by numberrelative to H was derived from 60 and 100 micron flux ratios and the Hcolumn along the line of sight; this ratio appears to decrease by afactor of 10 into the halo.
| Galactic interstellar abundance surveys with IUE. III - Silicon, manganese, iron, sulfur, and zinc
This paper continues a survey of intestellar densities, abundances, andcloud structure in the Galaxy using the IUE satellite. A statisticaldata set of 223 O3-B2.5 stars is constructed, including 53 stars in theGalactic halo. It is found that S II lines in B stars, of luminosityclasses IV and V, have possible contamination from stellar S II,particular for stars with v sin i less than 200 km/s. The meanlogarithmic depletions are -1.00, -1.19. -0.63, and -0.23 (Si, Mn,Fe,S,Zn). Depletions of Si, Mn, and Fe correlate with the mean hydrogendensity n-bar along the line of sight, with a turnover for n-bar greaterthan 1/cm. Sulfur depletions correlate with n-bar along the line ofsight. The slight Zn depletion correlation also appears to bestatistically insignificant. No correlation of depletion is found withthe physical density derived from H2 rotational states in 21 lines ofsight. Depletion variations in the disk are consistent with a Galacticabundance gradient or with enhanced mean depletions in the anticenterregion.
| Galactic interstellar abundance surveys with IUE. II - The equivalent widths and column densities
This paper continues a survey of interstellar densities, abundances, andcloud structure in the Galaxy, using the International UltravioletExplorer (IUE) satellite. Equivalent widths of 18 ultraviolet resonancetransitions are presented and column densities for Si II, Mn II, Fe II,S II, and Zn II toward 261 early-type stars are derived. Theseequivalent widths and column densities agree within the stated errors ofearlier Copernicus, BUSS, or IUE surveys of Mn II, Fe II, S II, and ZnII for 45 stars in common. The column densities are derived fromsingle-component curves of growth with a common b-value based on that ofFe II and Si II.
| Interstellar CA II absorption toward early-type stars at high Galactic latitudes
New high resolution AAT and INT observations of the Ca II 3933 Åinterstellar line towards nine early-type stars at high galacticlatitudes are presented. These are combined with the authors' earlierAAT data to investigate the distribution of Ca II in the galactic halo.A comparison of these results with Ca II equivalent widths forextragalactic sightlines implies that there is a significant amount ofthis ion out to z ≅ 1 kpc, but not much beyond z ≅ 2 kpc. Nocoincident high velocity Ca II absorption is detected in the spectra ofstars near known high velocity clouds (HVC). Although this may indicatethat the HVCs are either at greater distances than the stars or haveangular extents smaller than the separations of the stellar and HVCsightlines, it is also possible that they are nearby but contain toolittle Ca II to produce an observable absorption line.
| The galactic corona
The IUE observations and theories involving the gaseous galactic coronaof the Milky Way are reviewed. Observational topics emphasized includeresults relevant to the z distribution, kinematics, and ionic andelemental abundances of the gas. The theories for the support,ionization, and kinematics of the galactic halo appear to require amerging of the ideas associated with the galactic fountain models andthe photoionized halo models. The Si IV found in the galactic halo islikely mostly produced by photoionization while the N V is probablymostly produced by collisional ionization in cooling fountain gas; C IVmay represent an intermediate case with important contributions fromphotoionization and from collisional ionization.
| The extent of the local H I halo
Forty-five high-latitude, OB stars have been observed in the Ly alphaand 21 cm lines of HI in an effort to map out the vertical distributionand extent of the local HI halo. The 25 stars for which a reliable HIcolumn density can be obtained from Ly alpha lie between 60 and 3100 pcfrom the plane. The principal result is that the total column density ofHI at an absolute value of z greater than 1 kpc is, on the average, 5 +or - 3 x 10 to the 19th power/sq cm, or 15 percent of thetotalHI. At relatively low z the data toward some starssuggest a low effective scale height and fairly high average foregrounddensity, while toward others the effective scale height is large and theaverage density is low. This can be understood as the result ofirregularities in the interstellar medium. A model with half of the HImass in clouds having radii of a few pc and a Gaussian verticaldistribution with sigma2 = 135 pc, and half of the mass in anexponential component with a scale height of 500 pc, gives asatisfactory fit to the data. The technique of comparing Ly alpha and 21cm column densities is also used to discuss the problem of estimatingthe distance to several possibly subluminous stars.
| 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.
| Galactic interstellar abundance surveys with IUE. I - Neutral hydrogen
A survey is initiated of interstellar densities, abundances, and cloudstructure in the Galaxy, using the International Ultraviolet Explorer.From high-resolution (0.1-A) spectra, interstellar column densities arederived toward 244 early-type stars by fitting the damping wings of theLy-alpha absorption line. Published B-V photometry is used to deriveE(B-V) color excesses, stellar distances r, and the mean hydrogendensities, n-bar = N(H I)/r. The data set includes stars out to r = 8.5kpc and E(B-V) = 0.86, with 68 stars in the galactic halo (absolute bgreater than 20 deg). The statistical sample consists of 205 stars oftype O3-B2.5 within 5 kpc (53 stars in the halo). The column densities,log N(H I), range from less than 19.44 per square centimeter for alphaVir to 21.81 for HD 37061. A statistical analysis of the E(B-V)distribution suggests variations in the line-of-sight cloud density andthe mean reddening per cloud.
| The galactic reddening law - The evidence from uvby-beta photometry of B stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1985A&A...142..189T&db_key=AST
| Photometry of faint blue stars. IV - Some 'very definitely blue' PHL stars
Photometry on the uvby system is presented for 56 faint blue stars,mostly from the Palomar-Haro-Luyten 'very definitely blue' list. Themajority of these stars are hot subdwarfs.
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| קבוצת-כוכבים: | דלי |
| התרוממות ימנית: | 23h21m50.86s |
| סירוב: | -09°45'41.0" |
| גודל גלוי: | 7.643 |
| מרחק: | 4545.455 פארסק |
| תנועה נכונה: | -6.2 |
| תנועה נכונה: | -6 |
| B-T magnitude: | 7.409 |
| V-T magnitude: | 7.624 |
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