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A Map of the Ionized Component of the Intermediate-Velocity Cloud Complex K
The Wisconsin Hα Mapper (WHAM) Northern Sky Survey is revealingthat many intermediate-velocity (|vLSR|<=100 kms-1) neutral clouds and complexes have an associated ionizedcomponent. We present the first map of the Hα emission from anintermediate- or high-velocity structure: Complex K. This large,high-latitude feature stretches from l~10deg to 70°,b~+30deg to +70° and peaks in velocity overvLSR~-60 to -80 km s-1. The neutral and ionizedgas generally trace each other quite well in the complex, but thedetailed structure is not identical. In particular, the Hαemission peaks in brightness at slightly higher Galactic longitudes thancorresponding 21 cm features. The ionized gas has a peak Hαintensity of 0.5 R, corresponding to an emission measure of 1.1cm-6 pc. Structures in the complex are traced by WHAM down toabout 0.1 R (0.2 cm-6 pc). Typical line widths of theHα emission are ~30 km s-1, limiting temperatures inthe ionized gas to less than 20,000 K. If radiation is the primaryionizing mechanism, the Lyman continuum flux required to sustain themost strongly emitting ionized regions is 1.2×106photons cm-2 s-1. There appears to be no local,stellar source capable of maintaining the ionization of the gas;however, the required ionizing flux is consistent with current models ofthe escape of Lyman continuum radiation from OB stars in the disk and ofionizing radiation produced by cooling supernova remnants.
| Mapping the contours of the Local bubble: preliminary results
We present preliminary results from a long-term program of mapping theneutral absorption characteristics of the local interstellar medium,taking advantage of Hipparcos stellar distances. Equivalent widths ofthe NaI D-line doublet at 5890 Å are presented for thelines-of-sight towards some 143 new target stars lying within 300 pc ofthe Sun. Using these data which were obtained at the Observatoire deHaute Provence, together with previously published NaI absorptionmeasurements towards a further 313 nearby targets, we present absorptionmaps of the distribution of neutral gas in the local interstellar mediumas viewed from 3 different galactic projections. In particular, thesemaps reveal the Local Bubble region as a low neutral densityinterstellar cavity in the galactic plane with radii between 65-250 pcthat is surrounded by a (dense) neutral gas boundary (or ``wall''). Wehave compared our iso-column contours with the contours derived bySnowden et al. (\cite{snowden98}) using ROSAT soft X-ray emission data.Consistency in the global dimensions derived for both sets of contoursis found for the case of a million degree hot LB plasma of emissivity0.0023 cm(-6) pc with an electron density of 0.005 cm(-2) . We havedetected only one relatively dense accumulation of cold, neutral gaswithin 60 pc of the Sun that surrounds the star delta Cyg, and note thatthe nearest molecular cloud complex of MBM 12 probably resides at thevery edge of the Local Bubble at a distance of ~ 90 pc. Our observationsmay also explain the very different physical properties of the columnsof interstellar gas in the line-of-sight to the two hot stars epsilonCMa and beta CMa as being due to their locations with respect to theBubble contours. Finally, in the meridian plane the LB cavity is foundto be elongated perpendicularly to the Gould's Belt plane, possiblybeing ``squeezed'' by the expanding shells of the Sco-Cen andPerseus-Taurus OB associations. Tables 1 and 2 are also available inelectronic form at the CDS (Strasbourg) via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| The Hercules H I shell - Distances of the gas clouds and topography of the shell
The structure and distances of high-latitude (l between 35 and 75 deg)neutral gas clouds constituting the galactic H I shell GS 57 + 41(which, due to its location in the constellation of Hercules was named'Hercules shell') are investigated, using the results of an extensivesurvey of interstellar Na I D absorption lines to determine distances tothe various neutral clouds and filaments in this field of the sky. Basedon the distances, conclusions are drawn with regard to the morphologicalstructure and the physical parameters of the GS 57 + 41. The results ofoptical high-resolution absorption and 21 cm emission line measurementsof the various H I clouds were compared with the cirrus of IRAS 100micron dust emission, as well as with the diffuse X-ray backgroundemission in this area.
| Radial velocity measurements. IV - Ground-based accompaniment to the HIPPARCOS observation program
The paper presents 396 radial velocities of stars distributed in 19fields of 4 x 4 degrees. The study employs the Fehrenbach objectiveprism method and the same measuring technique used in a previous paper(Fehrenbach et al., 1987).
| UBV photometry of stars whose positions are accurately known. III
UBV photometric observations of 417 stars at BD declination 35-49 degfrom the NPZT(74) catalog of Yasuda et al. (1982) and the AGK3R catalogof Corben (1978), obtained with the 40-cm Cassegrain reflector atKvistaberg Observatory during 1984-1985, are reported. The data arepresented in tables, and the mean errors per observation are given as0.016 mag in V, 0.011 mag in B-V, 0.012 mag in U-B for U less than 10,and 0.026 mag in U-B for U greater than 10.
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