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Local interstellar medium kinematics towards the Southern Coalsack and Chamaeleon-Musca dark clouds
We present the results of a spectroscopic programme aiming toinvestigate the kinematics of the local interstellar medium componentstowards the Southern Coalsack and Chamaeleon-Musca dark clouds. Theanalysis is based upon high-resolution (R~ 60000) spectra of theinterstellar Na I D absorption lines towards 63 B-type stars (d<= 500pc) selected to cover these clouds and the connecting area defined bythe Galactic coordinates: 308°>=l>= 294° and-22°<=b<= 5°. The radial velocities, column densities,velocity dispersions, colour excess and photometric distances to thestars are used to understand the kinematics and distribution of theinterstellar cloud components. The analysis indicates that theinterstellar gas is distributed in two extended sheet-like structurespermeating the whole area, one at d<= 60 pc and another around120-150 pc from the Sun. The nearby feature is approaching the localstandard of rest with an average radial velocity of -7 kms-1, has low average column density logNNaI~ 11.2cm-2 and velocity dispersion b~ 5 km s-1. The moredistant feature has column densities between 12.3 <=logNNaI<= 13.2, average velocity dispersion b~ 2.5 kms-1 and seems associated with the dust sheet observed towardsthe Coalsack, Musca and Chamaeleon direction. Its velocity is centredaround 0 km s-1, but there is a trend for increasing from -3km s-1 near b= 1° to 3 km s-1 near b=-18°.The nearby low column density feature indicates a general outflow fromthe Sco-Cen association, in agreement with several independent lines ofdata in the general searched direction. The dust and gas feature around120-150 pc seem to be part of an extended large-scale feature of similarkinematic properties, supposedly identified with the interaction zone ofthe Local and Loop I Bubbles. Assuming that the interface and thering-like volume of dense neutral matter that would have been formedduring the collision of the two bubbles have similar properties, ourresults suggest that the interaction zone between the bubbles is twistedand folded.
| The Disk and Environment of the Herbig Be Star HD 100546
Coronagraphic imaging of the nearest Herbig Be star with the SpaceTelescope Imaging Spectrograph (STIS) on board the Hubble SpaceTelescope, Ks (2.15 μm) imaging with ADONIS at the 3.6 m telescope atLa Silla, and mid-infrared imaging with OSCIR using the 4 m BlancoTelescope at Cerro Tololo Inter-American Observatory confirm thedetection of the disk reported by Pantin et al. and map the disk out to5" (~515 AU) in the optical and at Ks. While the source is unresolved at10 and 18 μm, it can be traced to 1.5" at 11.7 μm. We confirm thechange in the radial dependence of the disk surface brightness near 2.7"seen at 1.6 μm by Augereau et al. at Ks. No such break in the powerlaw is seen in the optical. The STIS data reveal spiral dark lanestructure, making HD 100546 the third near-zero-age main-sequence HerbigAe/Be star with structure more than 100 AU from the star. We alsooptically detect a low surface brightness envelope extending 10" (1000AU) from the star, in addition to nebulosity, which is probablyassociated with DC 292.6-7.9. The survival of the envelope throughessentially the entire pre-main-sequence lifetime of the star, coupledwith the absence of physical companions within 1500 AU of the star,suggests that envelope lifetimes owe more to the star-formingenvironment than to mass-loss activity from the Herbig Ae/Be star. Basedon observations made with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555. This study is part of the STIS IDT protoplanetarydisk Key Project. This work is also based on observations collected atthe European Southern Observatory, La Silla, Chile, Proposal ID63.I-0196. This work is also based on observations made at the CerroTololo Inter-American Observatory. CTIO is operated by AURA, Inc., undercooperative agreement with the National Science Foundation.
| A homogeneous catalog of new UBV and H-beta photometry of B- and A-type stars in and around the Scorpius-Centaurus OB association
B- and A-type stars in and near the Sco-Cen OB association areinvestigated with UBV and H-beta photometry to acquire data relevant tothe luminosity function of Sco-Cen. The measurements generally consistof two 10-s integrations of U, B, V, (W, N) filters, and theobservations are corrected iteratively for atmospheric extinction andinstrumental response. The data presented give the mean V magnitude,mean B-V, mean U-B, and the estimated uncertainties for these values.The catalog provides a homogeneous catalog of data for a large fieldwith stellar objects delineating membership to the association Sco-Cenand that affect the luminosity function of the aggregate.
| An Einstein Observatory SAO-based catalog of B-type stars
About 4000 X-ray images obtained with the Einstein Observatory are usedto measure the 0.16-4.0 keV emission from 1545 B-type SAO stars fallingin the about 10 percent of the sky surveyed with the IPC. Seventy-fourdetected X-ray sources with B-type stars are identified, and it isestimated that no more than 15 can be misidentified. Upper limits to theX-ray emission of the remaining stars are presented. In addition tosummarizing the X-ray measurements and giving other relevant opticaldata, the present extensive catalog discusses the reduction process andanalyzes selection effects associated with both SAO catalog completenessand IPC target selection procedures. It is concluded that X-rayemission, at the level of Lx not less than 10 exp 30 ergs/s, is quitecommon in B stars of early spectral types (B0-B3), regardless ofluminosity class, but that emission, at the same level, becomes lesscommon, or nonexistent, in later B-type stars.
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