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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
| Near-infrared imaging of the Becklin-Neugebauer-IRc2 region in Orion with subarcsecond resolution
The Becklin-Neugebauer source has been partially resolved by speckleimagery at 3.6 micron with an angular resolution of 0.2 arcsec. Theimages, fluxes, and additional constraints are consistent with aspherical dust shell of inner diameter 0.1 arcsec, surrounding a hotstar. The surrounding region, including the vicinity of IRc2, has beenimaged with short-exposure/deconvolution methods at several wavelengths,at a resolution of 0.5 arcsec. IRc2 is resolved into four components,and the fluxes of the detected sources were determined at 2.8 and 4micron. Accurate astronomy of the infrared sources with respect to theSiO maser emission has been obtained. The centroid of the SiO maser isdefinitely not located at the center of symmetry between lobes A and B,but may correspond to IRc2 component A. Component B may arise inscattering from one lobe of a bipolar flow from source A, but otherexplanations are still possible. The multiple structure of the IRc2source, the new limits on the size of the components, and the positionalcorrelations draw into question the previous hypothesis that a single,very luminous source dominates the energetics of the BN-KL nebula.
| Image quality, tip-tilt correction, and shift-and-add infrared imaging
The image quality obtainable with shift-and-add (SAA) imaging for therecovery of diffraction-limited information is quantitativelyinvestigated using data simulating an 8-m aperture at a site withnear-IR seeing conditions as found on Mauna Kea. This is compared to theimage quality obtainable from image centroiding and wavefront tip-tiltcorrection. For good seeing conditions, image centroiding and SAA, whichtracks the image peak, show similar performance containing about 30percent of the image power in a diffraction-limited component. However,as the seeing degrades, SAA consistently yields improved resolutionmaintaining significantly greater diffraction-limited information. Thisenhances the detection threshold by about 2 magnitudes over theseeing-limited case for the seeing range studied. By comparison, thegain due to image centroiding decreases to less than 1 magnitude at thesame poor seeing limit.
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