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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.
| UBV photometry of Galactic foreground and LMC member stars - III. LMC member stars - a new data base
New UBV photometry for 878 luminous member stars of the Large MagellanicCloud (LMC) and 13 stars of uncertain membership is presented. The datawill be available at Centre de Données astronomiques deStrasbourg. Including former observations now UBV data are available foraltogether 2470 luminous LMC stars and 2106 foreground stars plus 65stars of uncertain membership. The observations have been used alreadyfor several investigations dealing e.g. with interstellar reddeninglines and intrinsic colours, the dust distribution and the calibrationof charge-coupled device exposures.
| The HIPPARCOS proper motion of the Magellanic Clouds
The proper motion of the Large (LMC) and Small (SMC) Magellanic Cloudusing data acquired with the Hipparcos satellite is presented. Hipparcosmeasured 36 stars in the LMC and 11 stars in the SMC. A correctlyweighted mean of the data yields the presently available most accuratevalues, mu_alpha cos(delta) = 1.94 +/- 0.29 mas/yr, mu_delta = - 0.14+/- 0.36 mas/yr for the LMC. For the SMC, mu_alpha cos(delta) = 1.23 +/-0.84 mas/yr, mu_delta = - 1.21 +/- 0.75 mas/yr is obtained, whereby careis taken to exclude likely tidal motions induced by the LMC. Bothgalaxies are moving approximately parallel to each other on the sky,with the Magellanic Stream trailing behind. The Hipparcos proper motionsare in agreement with previous measurements using PPM catalogue data byKroupa et al. (1994), and by Jones et al. (1994) using backgroundgalaxies in a far-outlying field of the LMC. For the LMC the Hipparcosdata suggest a weak rotation signal in a clockwise direction on the sky.Comparison of the Hipparcos proper motion with the proper motion of thefield used by Jones et al. (1994), which is about 7.3 kpc distant fromthe center of the LMC, also suggests clockwise rotation. Combining thethree independent measurements of the proper motion of the LMC and thetwo independent measurements of the proper motion of the SMC improvesthe estimate of the proper motion of the LMC and SMC. The correspondinggalactocentric space motion vectors are computed. Within theuncertainties, the LMC and SMC are found to be on parallel trajectories.Recent theoretical work concerning the origin of the Magellanic Systemis briefly reviewed, but a unique model of the Magellanic Stream, forthe origin of the Magellanic Clouds, and for the mass distribution inthe Galaxy cannot yet be decided upon. Future astrometric space missionsare necessary to significantly improve our present knowledge of thespace motion of the two most conspicuous galactic neighbours of theMilky Way.
| B[e] phenomenon extending to lower luminosities in the Magellanic Clouds.
An analysis of the four recently discovered B[e] stars HenS35, S59, S93,and S137 in the Large Magellanic Cloud has been carried out usinglow-resolution IUE spectra, ESO 3.6-m CASPEC spectra, and ESO 0.5-m and1-m UBV and JHK photometry, respectively. LTE model atmospheres havebeen fitted to the observed continuum energy distributions in order toderive the stellar parameters. The results are T_eff_=22000K,R=28Rsun_, and logL/Lsun_=5.2 for HenS35,T_eff_=14000K, R=16Rsun_, and logL/Lsun_=4.0 forHenS59, and T_eff_=13000K, R=26Rsun_, andlogL/Lsun_=4.2 for HenS137. The presence of absorption linesin the optical spectrum of the B9[e]Ib star HenS93 allowed an additionalLTE line analysis for this star using Balmer, HeI, SIII, MgII, and FeIIlines to derive T_eff_=10000K, R=73Rsun_,logL/Lsun_=4.7, logg=1.75, ξ=10km/s, vsin i=65km/s, andM>14Msun_. Our investigation shows that the class of B[e]stars in the Magellanic Clouds extends to luminosities of aboutlogL/Lsun_=4, i.e. much lower than those of the previouslystudied B[e] supergiants. This result reinforces the importance of axialsymmetry in large regions of the Hertzsprung-Russell diagram.
| On the motion of the Magellanic Clouds
We have measured the proper motion of the Large and Small MagellanicClouds using Magellanic Cloud stars in the PPM Catalogue, and obtainμ = 1.7+/-0.9 mas yr^-1^ for the LMC. Systematic uncertainties arediscussed. Bound and unbound orbits of the Magellanic Clouds around theGalaxy are consistent with our result. The various models of theMagellanic Stream and their predictions for the motion of the MagellanicClouds are discussed. The predictions by several authors for the sametype of model differ by up to 0.3 mas yr^-1^. All models proposed todate that assume the Magellanic Clouds to lead the Magellanic Streampredict a proper motion for the LMC of between 1.5 and 2.0 mas yr^-1^,the smallest value being a prediction for a Galaxy with no halo. Otherindependent measurements of the proper motion of the LMC are discussed.These lie between 1 and 1.5 mas yr^-1^. Future astrometry will have toallow measurement of the proper motion of the LMC with an uncertainty nolarger than one-tenth of a milliarcsecond per year in order to help todistinguish significantly between models of the halo of the Galaxy. Theproper motion of the LMC cannot by itself distinguish between models ofthe Magellanic Stream.
| Structure of the interstellar medium in the Magellanic Clouds
Using optical and UV observations, the internal gas structure ofMagellanic Clouds (MCs) was examined for clues to the recent evolutionof the Magellanic System and further signs of this collision event.Results indicate that the intermediate velocity clouds (IVCs) havedifferent origins. Thus, the '60-km/s' IVC is clearly of Galacticorigin. The '130-km/s' IVC is probably also Galactic and is not directlyassociated with the MCs. The '170 km/s' IVC is quite clearly associatedwith the LMC and seems to be the front of the LMC. The overall gasstructure in the MCs indicates that there is a distance-velocityassociation except in two regions: one to the south-west of the SMC (andis enigmatic), and the other to the south of 30 Doradus and appears tobe smoothly linked with the H I bridge, indicating that both featureshave a common overall cause such as the recent tidal collision.
| Astrometry of SN 1987A and SK -69.202 deg
Two sets of astrometric plates (epochs 1987.2 and 1973.0) and asecondary reference system comprised of LMC members were used todetermine the position of SN 1987A relative to about 30 Perth 70 stars.The positional coincidence of the SN and Star 1 of Sanduleak -69 deg 202is confirmed to within an uncertainty of + or - 0.13 arcsec in eachcoordinate. The relative brightness of the two major components of Sk-69 deg 202 was assessed by fitting the density profiles of the blendedimages.
| Gas in and toward the Magellanic Clouds
Attention is given to the Ca II K absorption spectra of 48 early-typesupergiants in the SMC and LMC, with a view to the Clouds' possiblefragmentary nature and the distance of the gas responsible for theabsorption lines at 60 and 120 km/sec. The comparison of the spectraobtained with H I measurements toward the Clouds indicates that in bothClouds, the velocity components in the neutral hydrogen distribution lieat different distances along the line of sight. Good agreement is foundbetween the radial velocity shown in absorbing material and the radialvelocity spread predicted by Murai and Fujimoto's (1980) dynamical modelof the formation of the Magellanic Stream by tidal stripping. It isspeculated that both the SMC and LMC are extended and fragmented alongthe line of sight.
| uvby photometry of very hot stars in the Large Magellanic Cloud.
Abstract image available at:http://adsabs.harvard.edu/abs/1977A&A....58..209M
| Halpha emission-line stars in the Large Magellanic Cloud. I. A new deep survey.
Abstract image available at:http://adsabs.harvard.edu/abs/1974A&AS...18...47B
| A deep objective-prism survey for Large Magellanic Cloud members
Not Available
| Catalogues of Hα-EMISSION Stars and Nebulae in the Magellanic Clouds.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1956ApJS....2..315H&db_key=AST
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Наблюдательные данные и астрометрия
| Созвездие: | Золотая Рыба |
| Прямое восхождение: | 05h17m46.37s |
| Склонение: | -69°50'57.3" |
| Видимая звёздная величина: | 10.904 |
| Собственное движение RA: | 1.9 |
| Собственное движение Dec: | 0.5 |
| B-T magnitude: | 10.712 |
| V-T magnitude: | 10.889 |
Каталоги и обозначения:
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