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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.
| Four-colour and H-beta photometry of blue stars selected from a balloon-ultraviolet survey and other sources
New uvby and/or H-beta photometry is obtained at the Chiranhigh-altitude outstation for 105 stars. Certain of the program stars areselected from a comparison of the SCAP 2000 balloon-ultraviolet skysurvey of the Laboratoire d'Astronomie Spatiale with the correspondingblue and red prints of the Palomar Observatory sky survey. Only a smallportion of these stars turn out to be B stars, whereas, the rest of thestars, which are selected from a variety of other sources, are mostly Bstars and if of normal luminosity are in many cases many Population Iscale heights from the galactic plane. It is shown that theidentification of B stars is practicable only at a good observing siteand that if H-beta photometry is also obtained, sdOB, sdB, and hothorizontal branch B stars can be distinguished from normal stars bytheir position in the beta/c(0) diagram.
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