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Mid-Infrared Images of the Debris Disk around HD 141569
We have imaged the circumstellar debris disk around the A0 Ve/B9.5 Vestar HD 141569 (D=99 pc), at λ=12.5, 17.9, and 20.8 μm usingthe Keck II telescope, and confirm the general morphology from otherrecently published mid-infrared observations. Model fits to an assumedflat radially symmetric dust disk yield an inclinationi=53deg+/-5deg and a position angle of-6deg+/-4deg for the tilt axis and indicate thepresence of a depression in optical depth by a factor of about 4 withina radial distance of 30 AU (0.3") from the star. Such a depression issuggestive of a density depletion and is consistent with publishedspectral energy distributions that indicate the absence of anear-infrared excess even though a mid-infrared excess is present. Ourmid-infrared results, in conjunction with previously publishednear-infrared scattering images, suggest that the two wavelength regimesare viewing, respectively, the inner and outer parts of a common diskstructure, which is dominated by small (probably submicron) grainsthroughout.
| UvbyH-beta photoelectric and CCD photometry of IC 4651
An analysis of uvbyH-beta photoelectric and CCD photometry of IC4651shows a Fe/H abundance ratio of 0.23 + or - 0.02, an E(b-y) value of0.064 + or - 0.006, and an age on the system of VandenBerg (1985) of 2.4+ or - 0.2 x 10 to the 9th yr. Scatter noted in the clustercolor-magnitude diagram can be explained by binaries, nonmembers, and ablueward hook due to the hydrogen-exhaustion phase. The cluster turnoffindicates some evidence for the presence of bimodality which issuggested to be the result of nonstandard evolution near theBohm-Vitense gap.
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