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NaI and CaII absorption components observed towards the Orion-Eridanus Superbubble
We present medium-resolution spectra (R ~ 7.5 km s-1) of theinterstellar NaI and CaII interstellar absorption lines observed towards16 early-type stars with distances of 160-1 kpc in the line-of-sighttowards the Orion-Eridanus Superbubble (OE-S). These data have beensupplemented with measurements of NaI absorption towards a further 13stars with similar sight-lines taken from the literature. We detect twomajor absorption components with velocities of Vlsr ~ +7.0and -8.0 km s-1. The former component, seen in 70% of thesight-lines is associated with the boundary to the Local Bubble cavitylocated at a distance of 140-150 pc. The other absorption component isonly detected towards a limited region of the sky bounded by (190°< l < 215°) and (-50° < b < -30°). If gas withthis velocity is associated with an outer expansion shell of the OE-S,then we can place its distance at 163-180 pc in agreement with theestimate by Guo et al. (1995, ApJ, 453, 256). Several other negativevelocity components at Vlsr ~ -20.4, -28.5 and -33.5 kms-1 have also been detected for sight-line distances > 220pc within an area coincident with that of the 0.75 keV X-ray enhancementof the OE-S. Column density ratios, N(NaI)/N(CaII), for the mostnegative velocity components have values < 1.0, suggesting that thisgas has been disrupted by a possible shock event. Our data do notsupport a simple model for the OE-S that involves a single stellarbubble cavity that stretches from the Orion Nebula to high galacticlatitudes. Instead, our detection of multiple positive and negativevelocity components suggests the presence of several gas shells producedby supernovae and/or stellar wind-driven shocks. We also confirm thatthe prominent "hook-like" feature of H-α emission thatcharacterizes the OE-S, in in fact composed of two physically separateemission arcs, with the brighter Arc A being at a distance > 500 pc.Finally, we place a similar distance limit for any coherently structuredrear shell of neutral gas associated with expansion of the OE-S towardsthe galactic halo.
| 3D mapping of the dense interstellar gas around the Local Bubble
We present intermediate results from a long-term program of mapping theneutral absorption characteristics of the local interstellar medium,motivated by the availability of accurate and consistent parallaxes fromthe Hipparcos satellite. Equivalent widths of the interstellar NaID-line doublet at 5890 Å are presented for the lines-of-sighttowards some 311 new target stars lying within ~ 350 pc of the Sun.Using these data, together with NaI absorption measurements towards afurther ~ 240 nearby targets published in the literature (for many ofthem, in the directions of molecular clouds), and the ~ 450lines-of-sight already presented by (Sfeir et al. \cite{sfeir99}), weshow 3D absorption maps of the local distribution of neutral gas towards1005 sight-lines with Hipparcos distances as viewed from a variety ofdifferent galactic projections.The data are synthesized by means of two complementary methods, (i) bymapping of iso-equivalent width contours, and (ii) by densitydistribution calculation from the inversion of column-densities, amethod devised by Vergely et al. (\cite{vergely01}). Our present dataconfirms the view that the local cavity is deficient in cold and neutralinterstellar gas. The closest dense and cold gas ``wall'', in the firstquadrant, is at ~ 55-60 pc. There are a few isolated clouds at closerdistance, if the detected absorption is not produced by circumstellarmaterial.The maps reveal narrow or wide ``interstellar tunnels'' which connectthe Local Bubble to surrounding cavities, as predicted by the model ofCox & Smith (1974). In particular, one of these tunnels, defined bystars at 300 to 600 pc from the Sun showing negligible sodiumabsorption, connects the well known CMa void (Gry et al. \cite{gry85}),which is part of the Local Bubble, with the supershell GSH 238+00+09(Heiles \cite{heiles98}). High latitude lines-of-sight with the smallestabsorption are found in two ``chimneys'', whose directions areperpendicular to the Gould belt plane. The maps show that the LocalBubble is ``squeezed'' by surrounding shells in a complicated patternand suggest that its pressure is smaller than in those expandingregions.We discuss the locations of several HI and molecular clouds. Usingcomparisons between NaI and HI or CO velocities, in some cases we areable to improve the constraints on their distances. According to thevelocity criteria, MBM 33-37, MBM 16-18, UT 3-7, and MBM 54-55 arecloser than ~ 100 pc, and MBM 40 is closer than 80 pc. Dense HI cloudsare seen at less than 90 pc and 85 pc in the directions of the MBM 12and MBM 41-43 clouds respectively, but the molecular clouds themselvesmay be far beyond. The above closest molecular clouds are located at theneutral boundary of the Bubble. Only one translucent cloud, G192-67, isclearly embedded within the LB and well isolated.These maps of the distribution of local neutral interstellar NaI gas arealso briefly compared with the distribution of both interstellar dustand neutral HI gas within 300 pc.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp:cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/411/447
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| Photometric and spectroscopic analysis of high galactic latitude molecular clouds. II - High-resolution spectroscopic observations of NA I, CA II, CA I, CH, and CH(+1)
High-resolution spectroscopic observations in the wavelengths of thespecies Na I, Ca II, and Ca I and the molecular species CH and CH(+)have been performed toward stars behind a variety of high galacticlatitude molecular clouds (HLCs). Seventeen new detections of molecularabsorption are reported. The sizes, densities, and molecular contentfound for the HLCs are consistent with an interpretation of HLCmolecular cores as extremely compact structures of enhanced molecularcontent which may have evolved from larger H I shells.
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| קבוצת-כוכבים: | לויתן |
| התרוממות ימנית: | 03h11m42.05s |
| סירוב: | +08°07'07.6" |
| גודל גלוי: | 8.571 |
| מרחק: | 273.973 פארסק |
| תנועה נכונה: | 23.2 |
| תנועה נכונה: | 16.7 |
| B-T magnitude: | 8.633 |
| V-T magnitude: | 8.577 |
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