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Long term photometric monitoring with the Mercator telescope. Frequencies and mode identification of variable O-B stars
Aims. We selected a large sample of O-B stars that were considered as(candidate) slowly pulsating B, β Cep, and Maia stars after theanalysis of their hipparcos data. We analysed our new seven passbandgeneva data collected for these stars during the first three years ofscientific operations of the mercator telescope. We performed afrequency analysis for 28 targets with more than 50 high-qualitymeasurements to improve their variability classification. For thepulsating stars, we tried both to identify the modes and to search forrotationally split modes. Methods: . We searched for frequenciesin all the geneva passbands and colours by using two independentfrequency analysis methods and we applied a 3.6 S/N-level criterion tolocate the significant peaks in the periodograms. The modes wereidentified by applying the method of photometric amplitudes for which wecalculated a large, homogeneous grid of equilibrium models to perform apulsational stability analysis. When both the radius and the projectedrotational velocity of an object are known, we determined a lower limitfor the rotation frequency to estimate the expected frequency spacingsin rotationally split pulsation modes. Results: . We detected 61frequencies, among which 33 are new. We classified 21 objects aspulsating variables (7 new confirmed pulsating stars, including 2 hybridβ Cep/SPB stars), 6 as non-pulsating variables (binaries or spottedstars), and 1 as photometrically constant. All the Maia candidates werereclassified into other variability classes. We performed modeidentification for the pulsating variables for the first time. The mostprobable ℓ value is 0, 1, 2, and 4 for 1, 31, 9, and 5 modes,respectively, including only 4 unambiguous identifications. For 7 starswe cannot rule out that some of the observed frequencies belong to thesame rotationally split mode. For 4 targets we may begin to resolveclose frequency multiplets. Based on observations collected with the p7 photometer attached to theFlemish 1.2-m mercator telescope situated at the Roque de los Muchachosobservatory on La Palma (Spain). Section [see full textsee full text],including Figs. is only available in electronic form athttp://www.aanda.org, and Tables 2 and 3 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/463/243
| Composition of the Interstellar Medium
We present an analysis of the FeII, GeII, MgI, MgII, SI, SII, SiII andZnII interstellar lines for 63 stars. Column density of MgII, SII, SiIIand ZnII is well correlated with distance. However, the column density-- distance relation should be used with care for the estimation of thedistance to OB stars. For stars with large f(H_2) this relation can leadto a large overestimation of the distance. The column densities of MgII,SiII and GeII (our largest samples of data) normalized to their totalhydrogen column densities decrease with interstellar reddening E(B-V) asexpected for elements that are incorporated into dust grains. The GeIIabundance (GeII/H) is lower in dense molecular clouds. The abundances ofall analyzed elements are generally lower than their Solar Systemvalues.
| Multiperiodicity in the large-amplitude rapidly-rotating β Cephei star HD 203664
Aims.We made a seismic study of the young massive β Cephei star HD203664 with the goal of constraining its interior structure.Methods.Ourstudy is based on a time series of 328 new Geneva 7-colour photometricdata of the star spread over 496.8 days.Results.The data confirm thefrequency of the dominant mode of the star, which we refined tof_1=6.02885 c d-1. The mode has a large amplitude of 37 mmagin V and is unambiguously identified as a dipole mode (&ea;=2) from itsamplitude ratios and non-adiabatic computations. Besides f_1, wediscovered two additional new frequencies in the star with amplitudesabove 4σ: f_2=6.82902 c d-1 and f_3=4.81543 cd-1, or one of their daily aliases. The amplitudes of thesetwo modes are only between 3 and 4 mmag, which explains why they werenot detected before. Their amplitude ratios are too uncertain for modeidentification. Conclusions.We show that the observed oscillationspectrum of HD 203664 is compatible with standard stellar models butthat we have insufficient information for asteroseismic inferences.Among the large-amplitude β Cephei stars, HD 203664 stands out asthe only one rotating at a significant fraction of its critical rotationvelocity (~ 40%).
| Catalog of Galactic β Cephei Stars
We present an extensive and up-to-date catalog of Galactic β Cepheistars. This catalog is intended to give a comprehensive overview ofobservational characteristics of all known β Cephei stars, coveringinformation until 2004 June. Ninety-three stars could be confirmed to beβ Cephei stars. We use data from more than 250 papers publishedover the last nearly 100 years, and we provide over 45 notes onindividual stars. For some stars we reanalyzed published data orconducted our own analyses. Sixty-one stars were rejected from the finalβ Cephei list, and 77 stars are suspected to be β Cepheistars. A list of critically selected pulsation frequencies for confirmedβ Cephei stars is also presented.We analyze the β Cephei stars as a group, such as the distributionsof their spectral types, projected rotational velocities, radialvelocities, pulsation periods, and Galactic coordinates. We confirm thatthe majority of the β Cephei stars are multiperiodic pulsators. Weshow that, besides two exceptions, the β Cephei stars with highpulsation amplitudes are slow rotators. Those higher amplitude starshave angular rotational velocities in the same range as thehigh-amplitude δ Scuti stars (Prot>~3 days).We construct a theoretical HR diagram that suggests that almost all 93β Cephei stars are main-sequence objects. We discuss theobservational boundaries of β Cephei pulsation and the physicalparameters of the stars. We corroborate that the excited pulsation modesare near to the radial fundamental mode in frequency and we show thatthe mass distribution of the stars peaks at 12 Msolar. Wepoint out that the theoretical instability strip of the β Cepheistars is filled neither at the cool nor at the hot end and attempt toexplain this observation.
| Pulsating Stars in the ASAS-3 Database. I. beta Cephei Stars
We present results of an analysis of the ASAS-3 data for short-periodvariables from the recently published catalog of over 38000 stars. Usingthe data available in the literature we verify the results of theautomatic classification related to \beta Cep pulsators. In particular,we find that 14 stars in the catalog can be classified unambiguously asnew beta Cep stars. By means of periodogram analysis we derive thefrequencies and amplitudes of the excited modes. The main modes in thenew beta Cep stars have large semi-amplitudes, between 35 and 80 mmag.Up to four modes were found in some stars. Two (maybe three) new betaCep stars are members of southern young open clusters: ASAS164409-4719.1 belongs to NGC 6200, ASAS 164630-4701.2 is a member ofHogg 22, and ASAS 164939-4431.7 could be a member of NGC 6216.We also analyze the photometry of four known beta Cep stars in theASAS-3 catalog, namely IL Vel, NSV 24078, V1449 Aql and SY Equ. Finally,we discuss the distribution of beta Cep stars in the Galaxy.
| Metallicity of mono- and multiperiodic β Cephei stars
Analyzing IUE ultraviolet spectra of β Cep pulsating stars wenoticed that multiperiodic variables have a larger mean metal abundancein the photosphere, [ m/H] , than monoperiodic ones. We applystatistical tests to verify this dichotomy. We obtain that, with a largeprobability, the multiperiodic β Cep stars have greater values of [m/H] . This result is consistent with the linear non-adiabatic theory ofpulsation of early B-type stars.
| β Cep stars from a spectroscopic point of view
In this review we present the current status of line-profile-variationstudies of β Cep stars. Such studies have been performed for 26bright members of this class of pulsating stars in the past 25 years. Wedescribe all these currently available data and summarize theinterpretations based on them in terms of the excited pulsation modes.We emphasize that line-profile variations offer a much more detailedpicture of the pulsational behaviour of pulsating stars compared toground-based photometric data. The latter, however, remain necessary tounravel the often complex frequency pattern and to achieve unambiguousmode identification for multiperiodic β Cep stars and also toderive the pulsational properties of the faint members of the class. Wehighlight the statistical properties of the sample of 26 stars for whichaccurate spectroscopic studies are available and point out some futureprospects.
| Multiwavelength observations of the M15 intermediate-velocity cloud
We present Westerbork Synthesis Radio Telescope HI images, Lovelltelescope multibeam HI wide-field mapping, William Herschel Telescopelong-slit echelle CaII observations, Wisconsin Hα Mapper (WHAM)facility images, and IRAS ISSA 60- and 100-1μm co-added imagestowards the intermediate-velocity cloud (IVC) at +70 km s-1,located in the general direction of the M15 globular cluster. Whencombined with previously published Arecibo data, the HI gas in the IVCis found to be clumpy, with a peak HI column density of ~1.5 ×1020 cm-2, inferred volume density (assumingspherical symmetry) of ~24 cm-3/D (kpc) and a maximumbrightness temperature at a resolution of 81 × 14arcsec2 of ~14 K. The major axis of this part of the IVC liesapproximately parallel to the Galactic plane, as does the low-velocityHI gas and IRAS emission. The HI gas in the cloud is warm, with aminimum value of the full width at half-maximum velocity width of 5 kms-1 corresponding to a kinetic temperature, in the absence ofturbulence, of ~540 K. From the HI data, there are indications oftwo-component velocity structure. Similarly, the CaII spectra, ofresolution 7 km s-1, also show tentative evidence of velocitystructure, perhaps indicative of cloudlets. Assuming that there are nounresolved narrow-velocity components, the mean values oflog10[N(CaII K) cm-2]~ 12.0 and CaII/HI~2.5× 10-8 are typical of observations of high Galacticlatitude clouds. This compares with a value of CaII/HI>10-6 for IVC absorption towards HD 203664, a halo star ofdistance 3 kpc, some from the main M15 IVC condensation. The main IVCcondensation is detected by WHAM in Hα with centrallocal-standard-of-rest velocities of ~60-70 km s-1, andintensities uncorrected for Galactic extinction of up to 1.3 R,indicating that the gas is partially ionized. The FWHM values of theHα IVC component, at a resolution of 1°, exceed 30 kms-1. This is some 10 km s-1 larger than thecorresponding HI value at a similar resolution, and indicates that thetwo components may not be mixed. However, the spatial and velocitycoincidence of the Hα and HI peaks in emission towards the mainIVC component is qualitatively good. If the Hα emission is causedsolely by photoionization, the Lyman continuum flux towards the main IVCcondensation is ~2.7 × 106 photon cm-2s-1. There is not a corresponding IVC Hα detectiontowards the halo star HD 203664 at velocities exceeding ~60 kms-1. Finally, both the 60- and 100-μm IRAS images showspatial coincidence, over a 0.675 × 0.625 deg2 field,with both low- and intermediate-velocity HI gas (previously observedwith the Arecibo telescope), indicating that the IVC may contain dust.Both the Hα and tentative IRAS detections discriminate this IVCfrom high-velocity clouds, although the HI properties do not. Whencombined with the HI and optical results, these data point to a Galacticorigin for at least parts of this IVC.
| A New Measurement of the Average Far-Ultraviolet Extinction Curve
We have measured the extinction curve in the far-ultraviolet wavelengthregion of (900-1200 Å) using spectra obtained with the BerkeleyEUV/FUV spectrometer during the ORFEUS I and the ORFEUS II (Orbiting andRetrievable Far and Extreme Ultraviolet Spectrometer) missions in 1993and 1996. From the complete sample of early-type stars observed duringthese missions, we have selected pairs of stars with the same spectraltype but different reddenings to measure the differential FUVextinction. We model the effects of molecular hydrogen absorption andexclude affected regions of the spectrum to determine the extinctionfrom dust alone. We minimize errors from inaccuracies in the catalogedspectral types of the stars by making our own determinations of spectraltypes based on their IUE spectra. We find substantial scatter in thecurves of individual star pairs and present a detailed examination ofthe uncertainties and their effects on each extinction curve. We findthat, given the potentially large uncertainties inherent in using thepair method at FUV wavelengths, a careful analysis of measurementuncertainties is critical to assessing the true dust extinction. Wepresent a new measurement of the average far-ultraviolet extinctioncurve to the Lyman limit; our new measurement is consistent with anextrapolation of the standard extinction curve of Savage & Mathis.
| H I Spectra and Column Densities toward HVC and IVC Probes
We show 21 cm line profiles in the direction of stars and extragalacticobjects, lying projected on high- and intermediate-velocity clouds (HVCsand IVCs). About half of these are from new data obtained with theEffelsberg 100 m telescope, about a quarter are extracted from theLeiden-Dwingeloo Survey (LDS), and the remaining quarter were observedwith other single-dish telescopes. H I column densities were determinedfor each HVC/IVC. Paper I of this series uses these in combination withoptical and ultraviolet high-resolution measurements to deriveabundances. Here an analysis is given of the difference and ratio of N(HI) as observed with a 9' versus a 35' beam. For HVCs and IVCs the ratioN(H I-9')/N(H I-35') lies in the range 0.2-2.5. For low-velocity gasthis ratio ranges from 0.75 to 1.3 (the observed ratio is 0.85-1.4, butit appears that the correction for stray radiation is slightly off). Thesmaller range for the low-velocity gas may be caused by confusion in theline of sight, so that a low ratio in one component can be compensatedby a high ratio in another-for 11 low-velocity clouds fitted by onecomponent the distribution of ratios has a larger dispersion. Comparisonwith higher angular resolution data is possible for 16 sight lines.Eight sight lines with H I data at 1'-2' resolution show a range of0.75-1.25 for N(H I-2')/N(H I-9'), while in eight other sight lines N(HI-Lyα)/N(H I-9') ranges from 0.74 to 0.98.
| 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.
| Hi and optical spectroscopy towards the M15 intermediate-velocity cloud
We present single-dish Arecibo 21-cm Hi observations, covering a0.675°×0.625° RA-Dec. grid, of the intermediate-velocitycloud (IVC) centred upon the M15 globular cluster. The velocity andpositional structure of the IVC gas atVLSR=70kms-1 are investigated; it is found to beclumpy and has a peak surface densityNHi~8×1019cm-2. Additionally, wehave performed a long Hi integration towards HD 203664, a Galactic halostar some 3.1° from M15, in which optical IVC absorption haspreviously been detected. No Hi with a velocity exceeding60kms-1 was found to a brightness temperature limit of 0.05K.However, additional pointings did detect IVC gas approximately mid-waybetween HD 203664 and M15. Finally, we present both Arecibo Hi pointingsand low-resolution spectra in the Caii H and K lines towards 15 fieldstars in the general field towards M15, in an attempt to obtain thedistance to the IVC. Intermediate-velocity Hi is detected towards sevensightlines. Stellar spectral types are derived for 12 of the sample.Assuming that these stars lie on the main sequence, their distances areestimated to lie in the range 150<=d<=1350pc. No Caii absorptionis observed, either because the IVC is further away than ~1350pc or morelikely because the gas along these sightlines is of too low a density tobe detected by the current observations.
| Follow-up photometry of six new beta Cephei stars discovered from the HIPPARCOS mission
We present ground-based follow-up photometry in the Geneva seven-colourphotometric system of six new candidate beta Cep stars. The variabilityof these objects was originally found from the HIPPARCOS mission. Fromthe new data we are able to confirm their beta Cep-type nature, todetect the pulsational frequencies and to identify most of the degreesof the pulsation modes. All six stars turn out to have frequencies inthe expected range for beta Cep stars and the degrees of the main moderange from l =0 up to l=2, which is compatible with theoreticalexpectations. Based on observations collected with the Swiss PhotometricTelescope of the Geneva Observatory situated at La Silla, Chile.Tables~5--10 are only in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5)
| Optical observations of three Galactic halo stars: evidence for cloudlets in intermediate- and high-velocity interstellar clouds
Very high resolution (R ~ 160000) absorption line measurements of theinterstellar Ca Ii K and Na I D lines and medium resolution (R ~ 50000)measurements of the interstellar Ti Ii (3384 Ä) line towards threeGalactic halo stars are presented. The data have signal-to-noise ratiosof ~ 90-240. The sightlines studied clearly show severalintermediate-high velocity interstellar clouds with local standard ofrest velocities in the range ~ - 40 to -110 \km. Two different methodshave been used to analyze these data. Line profile fitting allows us tomodel multiple components for the different high-velocity cloudsseparated by only a few km. The close proximity of the lines in velocityspace indicates that the cloudlets are related. Conversion of theabsorption profiles to apparent optical depth profiles also allows us toexamine the column densities and their ratios as a function of velocity.Variations in N(ion {Ca}{ii})/N(ion {Na}i), N(ion {Ca}{ii})/N(ion{Ti}{ii}) and N(ion {Ti}{ii})/N(ion {Na}i) with cloud velocity arediscussed.
| A NA I Absorption Map of the Small-Scale Structure in the Interstellar Gas toward M15
Using the DensePak fiber-optic array on the KPNO WIYN telescope, we haveobtained high signal-to-noise ratio echelle spectra of the Na I Dwavelength region toward the central 27^''x43^'' of the globular clusterM15 at a spatial resolution of 4". The spectra exhibit significantinterstellar Na I absorption at LSR velocities of 3 km s^-1 (localinterstellar medium [LISM] component) and 68 km s^-1(intermediate-velocity cloud [IVC] component). Both components varyappreciably in strength on these scales. The derived Na I columndensities differ by a factor of 4 across the LISM absorption map and bya factor of 16 across the IVC map. Assuming distances of 500 and 1500 pcfor the LISM and IV clouds, respectively, these maps show evidence ofsignificant ISM structure down to the minimum scales of 2000 and 6000 AUprobed in these absorbers. The smallest scale N(Na I) variationsobserved in the M15 LISM and IVC maps are typically comparable to orhigher than the values found at similar scales in previous studies ofinterstellar Na I structure toward binary stars. The physicalimplications of the small and larger scale Na I features observed in theM15 maps are discussed in terms of variations in the H I column densityas well as in the Na ionization equilibrium.
| Low Resolution Optical Spectroscopy of The M15 High Velocity Interstellar Cloud
We present low resolution optical spectra of 16 field stars in the CaIIH and K lines towards the high velocity cloud (HVC) at V=+80 kms-1,observed in the direction of the M15 globular cluster. Stellar spectraltypes and distances are estimated for 12 of the sample. Null detectionsof HVC CaII absorption in the spectra, combined with an upper limit tothe HVC distance from observations of the Galactic halo star HD 203664,tentatively imply that the HVC lies in the distance range 400 <= d<= 3200 pc.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| High-velocity interstellar clouds towards the M 15 globular cluster. I. Low resolution optical data
We present low resolution interstellar spectra of the Ca Ii K and Na I Dlines towards 12 stars in the M 15 globular cluster. These sightlinesare used to study the small scale structure of the interstellar medium,over scales of a few arcseconds to a few arcminutes. A high-velocitycloud is detected in the Ca Ii and Na I lines at a LSR velocity ofapproximately ~ 70 km s(-1) . Tentative velocity and equivalent widthvariations are observed on scales of a few arcseconds; however, higherresolution data are necessary to quantify the magnitude of thesevariations. We discuss these observations and their importance forfuture studies of this high velocity gas at high spectral resolution.
| 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.
| The distance to Complex M and the Intermediate Velocity Arch
The Intermediate Velocity Arch is an association of Hi clouds lyingwithin the broad limits l~110 deg-210 deg,b~50 deg-80 deg. We usehigh-resolution optical, and single-dish 21-cm, observations of 10early-type halo star sightlines in this region to establish distancelimits (0.4<=z<=3.5kpc) for seven IVCs that are part of the Arch.We re-examine a previous determination of upper and lower distancelimits on the IVC Complex M using the closely aligned halo starsBD+382182 and HD93521. Our Hi spectra show no evidence of emission fromComplex M, leading us to conclude that, while an upper distance limit ofz<=3.5 kpc may be established, no useful lower distance determinationcan be made. Our new Hi observations allow new limits to be establishedon the metallicity of Complex M, and show C, O and Si variations withrespect to solar abundances in the range +/-0.3 dex.
| Radio and optical observations of intermediate velocity gas towards the M15 region
Preliminary results are presented of radio lambda 21 cm H I mapping andoptical (Ca II K, Na D, K I) observations of intermediate velocity gastowards the M15 sightline. A column density map is constructed from anextensive (2.2 deg. by 2.8 deg.) grid of radio observations made withthe Lovell radio telescope which reveals the `clumpy' nature of the gasand suggests further unresolved structure. A velocity gradient of ~30km/s is apparent across part of the field, possibly due to rotation ofthe cloud. The IVC is detected in Ca II K, Na D and K I opticalabsorption lines, these detections are unusually strong and possiblyindicate that the gas is highly shocked. Comparison with the gas of theIVC associated with the nearby star HD 203664 is made and it issuggested that the two IVCs are in fact part of the same structure.
| Interstellar Gas-Phase Abundances and Physical Conditions toward Two Distant High-Latitude Halo Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...470..893S&db_key=AST
| UHRF observations of the interstellar medium towards two stars in the Galactic Halo.
We present interstellar Na I and Ca II spectra of the halo stars HD18100 and HD 203664, obtained with the Ultra-High Resolution Facility onthe Anglo-Australian Telescope. These observations have spectralresolutions R=~210,000 and signal-to-noise ratios in the range 20-75. Wefind multiple absorbing components along both sightlines and resolve thevelocity structure within the high velocity cloud toward HD 203664. Wediscuss these spectra and their use in future Hubble Space Telescopestudies of HD 18100 and HD 203664.
| The Gas and Dust Abundances of Diffuse Halo Clouds in the Milky Way
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...457..211S&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.
| Discovery of Highly Ionized High-Velocity Clouds toward Markarian 509
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...451..616S&db_key=AST
| Properties of the +70 kilometers per second cloud toward HD 203664
I present high-resolution International Ultraviolet Explorer (IUE)spectra of the ultraviolet absorption in an intermediate-velocityinterstellar cloud (nuLSR approximately equal to +70 km/s)toward HD 203664. The combined, multiple IUE images result in spectrawith S/N = 15-40 and resolutions of approximately 20-25 km/s. Theintermediate-velocity cloud absorption is present in ultraviolet linesof C II, C II*, C IV, N I, O I, Mg I, Mg II, Al II, Al III,Si II, Si III, Si IV, S II, Cr II, Mn II, Fe II, and Zn II. The relativeabundances of low-ionization species suggest an electron density of0.15-0.34/cu cm and a temperature of 5300-6100 K in the neutral andweakly ionized gas. Given the presence of high-ionization gas tracerssuch as Si IV and C IV, ionized portions of the cloud probablycontribute to the relatively large values of ne derived frommeasurements of the lower ionization species. The high-ionizationspecies in the cloud have an abundance ratio, N(C IV)/N(Si IV)approximately equal to 4.5, similar to that inferred for collisionallyionized cloud interfaces at temperatures near 105 K alongother sight lines. When referenced to sulfur, the abundances of mostelements in the cloud are within a factor of 5 of their solar values,which suggests that the +70 km/s gas has a previous origin in theGalactic disk despite a recent determination by Little et al. that thecloud lies at a distance of 200-1500 pc below the Galactic plane. I havechecked this result against a model of the ionization for the diffuseionized gas layer of the Galaxy and find that this conclusion isessentially unchanged as long as the ionization parameter is low asimplied by the abundances of adjoining ionization states of aluminum andsilicon. The processes responsible for the production of highly ionizedgas in the +70 km/s cloud appear to be able to account for the inferreddust grain destruction as well.
| Optical and H I observations of the low-velocity and intermediate-velocity gas toward the globular cluster M13
High-resolution spectra of interstellar lines toward 11 stars in theglobular cluster M13 and toward three foreground stars which lie within3 deg from the cluster are reported. The optical spectra are comparedwith an H I profile of the gas recorded in the direction of the cluster.The principal interstellar components have LSR radial velocitiescentered near +10 km/s and -4km/s, but there is a considerable variationin the velocities and the column densities of both components across theface of the cluster. The positive velocity gas has a high Na I/H Icolumn density ratio, and it lies beyond the foreground stars at adistance approximately greater than 200 pc; this gas may be associatedwith the receding part of the Hercules shell discussed in detail byLilienthal et al. The negative velocity gas is detected toward theforeground stars, and the observed Na I/Ca II ratios suggest anassociation with gas at the approaching side of the Hercules shell. Gasat a velocity approximately equal -80 km/s has been previously reportedin H I emission in the M13 direction and in UV spectra of the post-AGBcluster star, Barnard 29. This intermediate-velocity clouds in the lowerhalo. We discuss also evidence for the detection of this gas in Na I andshow that it is most likely located at a distance.
| High-resolution optical observations of two early-type stars towards the high-velocity cloud Complex M
High-resolution optical spectra of the early-type stars HD 93521 and BD+38 deg2182, which lie only 27 arcmin apart on the sky in the directionof the high-velocity cloud (HVC) Complex M, reveal the presence of weakHVC absorption in the Ca K line towards BD +38 deg2182, with a velocityof V_LSR=-96.0+/-1.5 km s^-1 and an equivalent width W_lambda=11+/-2 mA.However, the HVC is not detected either in the Na D line for BD +38deg2182 or in the Ca K and Na D lines towards HD 93521. Theseobservations, combined with revised stellar distance estimates, implythat the HVC is at a distance from the Galactic plane of1.8<=z<=4.6 kpc. The Ca/H abundance in the HVC is found to be atleast ~=2 per cent of the solar value, consistent with the materialbeing returning condensations from a Galactic fountain flow.
| Observations of High Velocity Gas in the Galactic Halo
High resolution optical and stellar interstellar observations towardsthe halo star HD 203664 and 6 surrounding early-type stars have beencombined with a 21 cm mapping of the region to investigate a 70 km/shigh velocity cloud (HVC). The distance of the HVC from the galacticplane (z) has been constrained to lie between 200 pc and 1500 pc, upperlimits to temperature and velocity dispersion of 4600 K and 2.2 km/shave been estimated, and a column density ratio of N(Na I)/n(Ca II) =0.32 has been deduced. These parameters are consistent with the materialbeing shocked gas, possibly arising from an old supernova remnant. TheN(Na I)/N(H I) and N(Ca II)/N(H I) ratios are anomalously large byfactors of approximately 20 and 110 respectively, with respect to normaldiffuse gas.
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관측 및 측정 데이터
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