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Session 45 - Interstellar Medium I.
Display session, Tuesday, January 16
North Banquet Hall, Convention Center
We present HI 21-cm maps of the neutral atomic gas distribution in the Pleiades Reflection Nebula at both parsec and subparsec scales. These include a 2^o \times 2^o mosaic of 64 pointings taken with the Very Large Array in D-configuration, and a much larger map (171 square degrees in a 19^o \times 11^o region) composed of single-dish scans made with the Green Bank 43-m telescope. The maps have resolutions of 1' and 21' respectively, or 0.04 and 0.8 pc at the cluster distance of 130 pc.
We find numerous correlations of features between 21-cm images of the gas and Burrell Schmidt B_J-band (3600-5200 Åand IRAS 100 \mu m images of the dust in the reflection nebula around the cluster. The VLA data in particular show HI structure on scales finer\/ than the filaments seen in IRAS. Such agreement permits 21-cm velocity-mapping of the IRAS and Schmidt nebular features. The majority of these fall around +7-10 km/s LSR, the same velocity range occupied by prominent NaI-D interstellar absorption lines we have observed toward many stars in the cluster with the 0.9m KPNO Coudé Feed Telescope. A large amount of the associated material must therefore lie in front\/ of the Pleiades, a picture consistent with a mostly forward-scattering geometry for the nebula.
Together with ultraviolet imaging polarimetry (1640 amp; 2180 Åtaken during the recent flight of WISP (the Wide-field Imaging Survey Polarimeter, a sounding rocket payload telescope), these data are being used in a multiwavelength investigation of extended reflection nebulosity in the Pleiades. Goals of the study include constraint of both the 3-D nebular scattering geometry and the optical properties of the dust grains, including the ultraviolet intensity phase function. The HI data may additionally be used to examine filamentary structure and local dynamics in the general context of the diffuse neutral interstellar medium. This work is supported by the WISP project under NASA grant NAG5-647.
Program listing for Tuesday