The Origins and Evolutionary Status of B Stars Found Far from the Galactic Plane. II. Kinematics and Full Sample Analysis
This paper continues the analysis of faint high-latitude B stars fromMartin. Here we analyze the kinematics of the stars and combine themwith the abundance information from the first paper to classify eachone. The sample contains 31 Population I runaways, 15 old evolved stars(including 5 blue horizontal-branch [BHB] stars, 3 post-HB stars, 1pulsating helium dwarf, and 6 stars of ambiguous classification), 1 Fdwarf, and 2 stars that do not easily fit in one of the othercategories. No star in the sample unambiguously shows thecharacteristics of a young massive star formed in situ in the halo. Thetwo unclassified stars are probably extreme Population I runaways. Thelow binary frequency and rotational velocity distribution of thePopulation I runaways imply that most were ejected from dense starclusters by the dynamic ejection scenario. However, we remain puzzled bythe lack of runaway Be stars. We also confirm that PB 166 and HIP 41979are both nearby solar-metallicity BHB stars.Based on observations made at the 2.1 m Otto Struve Telescope ofMcDonald Observatory, operated by the University of Texas at Austin.
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The Origins and Evolutionary Status of B Stars Found Far from the Galactic Plane. I. Composition and Spectral Features
The existence of faint blue stars far above the Galactic plane that havespectra that are similar to nearby Population I B stars presents severalinteresting questions. Among them are the following: Can a Population IB star travel from the disk to a position many kiloparsecs above theplane in a relatively short main-sequence lifetime? Is it possible thatsingle massive star formation is occurring far from the Galactic plane?Are these objects something else masquerading as main-sequence B stars?This paper (the first of two) analyzes the abundances of a sample ofthese stars and reveals several that are chemically similar to nearbyPopulation I B stars, whereas others clearly have abundance patternsmore like those expected in blue horizontal-branch (BHB) orpost-asymptotic giant branch stars. Several of those with old evolvedstar abundances also have interesting features of note in their spectra.We also consider why this sample does not have any classical Be starsand identify at least two nearby solar-metallicity BHB stars.Based on observations made at the 2.1 m Otto Struve Telescope ofMcDonald Observatory operated by the University of Texas at Austin.
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Radio HI and optical absorption-line spectra of an intermediate-velocity cloud in the general direction of the M15 globular cluster
Using HI spectra obtained with the Lovell telescope (FWHM ~ 12 arcmin)we present maps showing the HI distribution and velocity structure of anintermediate-velocity cloud (IVC; v_LSR~70 km s^-1) which is observed inthe general direction of the globular cluster M15. The gas is shown tobe clumpy in nature and we examine its position and velocity structure.The IVC is detected in absorption in the CaII K line towards fivecluster stars in intermediate resolution spectra obtained with ISIS/WHTand in high resolution UES/WHT NaI D line spectra of two cluster stars(II-75; IV-38). The clumpy nature of the gas is indicated by the NaI andKI spectra obtained in the II-75 and IV-38 sightlines, which haveangular separation ~ 3.5 arcmin. The IVC is detected in KI in the highercolumn density II-75 sightline; this appears to be the first detectionof IVC or HVC gas in KI. The IVC gas towards M15 has a similar velocityto that observed towards HD 203664, some 3.1 deg away from the cluster.Similarities in the IVC gas velocity suggest a gas structure thatextends across both sightlines, although gas column densities areconsiderably higher towards M15. For a common feature, this would placethe M15 IVC at a height above the Galactic plane (z-distance) of<~1.5 kpc based on the Little et al. estimate of the HD 203664distance. From the fine-scale structure and column density observations,estimates are made of the space density of the small-scaleconcentrations. However, these remain uncertain and the presentobservations emphasize the need for higher spatial and spectralresolution studies to provide firmer estimates of cloud properties. Wereport also on a radio HI and CaII line survey towards a sample of 24stars over a wider field. This was carried out in an attempt to detectany wider distribution of the IVC gas and to place better limits on itsdistance. Although these observations are of sufficient spectralquality, no new optical detections are reported.
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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.
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Interstellar titanium in the galactic halo
We present observations of Ti II lambda 3384 absorption toward 15distant stars in the Galactic halo and the Magellanic Clouds. These newdata extend existing surveys of the distribution of Ti(+) to largerdistances from the plane of the Galaxy than sampled previously, allowingthe scale height of titaniumn to be determined for the first time. Wefind hTi(+ = 1.5 +/- 0.2 kpc, a value which although greaterthan those of other tracers of neutral gas, is not as large as had beensuspected. We interpret the extended distribution of Ti(+) as anindication that its severe depletion in interstellar clouds in the diskis reduced at the lower densities prevailing in the halo. The data areconsistent with a simple power-law dependence of the Ti abundance on theambient density, with exponent k approximately = -1. If the model iscorrect, it implies that refractory elements like Ti are fully returnedto the gas phase at distances beyond approximately 1 kpc from the planeof the Galaxy.
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The Spacelab-1 Very Wide Field Survey of UV-excess objects. IV. The performance of the instrument in combination with optical photometry as a means of identifying stars with peculiar properties.
UV (195 nm) and Stroemgren uvby photometry of a 110 square degree fieldat high southern galactic latitudes are analyzed through a comparison ofi) UV magnitudes for 57 stars of various types common to the publishedTD1 catalogue and the Very Wide Field Camera (VWFC); and ii) observedand theoretical two-colour diagrams. The higher sensitivity of the VWFC(=~0.5magnitude) and its more complete survey are exemplified by thedetection and UV measurement of a series of objects with moderateUV-excess in addition to detection of some very blue objects of variousnature down to fainter than 12th magnitude in the optical domain. Adeeper survey with a VWFC-type instrument could provide a completesample for studies of the group properties of faint blue stars. Duringthe uvby reductions it was found that the usual procedure of plottingresiduals as functions of declination, hour angle and airmass can be apowerful and diagnostic test of photometer rigidity.
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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.
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Broad-band photometry of selected southern ultraviolet-bright stars.
Not Available
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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.
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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.
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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
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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.
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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.
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Four-colour and H beta photometry of southern B stars at high galactic latitudes
Four-color and H beta photometry has been obtained for 105 early-type HDstars with galactic latitudes less than -45 deg. They are mostly late Bstars of luminosity class V to III. Two new Am stars and several Ap orBp stars are detected photometrically. Absolute magnitudes aredetermined from the photometry and from MK types where available. Theinterstellar reddening of many of the more distant stars is very small,suggesting either the existence of undetected peculiar stars in thesample or that there are areas of effectively zero reddening at highsouthern galactic latitudes.
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INHABITED SKY
