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Near-Infrared Spectra of Centaurs and Kuiper Belt Objects
We present here an extensive survey of near-infrared (NIR) spectra ofKuiper belt objects (KBOs) and Centaurs taken with the Keck I Telescope.We find that most spectra in our sample are well characterized by acombination of water ice and a featureless continuum. A comparativeanalysis reveals that the NIR spectral properties have littlecorrelation to the visible colors or albedo, with the exception of thefragment KBOs produced from the giant impact on 2003 EL61. The resultssuggest that the surface composition of KBOs is heterogeneous, thoughthe exposure of water ice may be controlled by geophysical processes.The Centaurs also display diverse spectral properties, but the source ofthe variability remains unclear. The results for both the KBOs and theCentaurs point to inherent heterogeneity in either the processes actingon these objects or materials from which they formed.
| UBV(RI)C photometric monitoring of Orion population stars in the Southern Hemisphere
UBV(RI)C photometry on a sample of southern T Tauri stars, selected fromthe Herbig and Bell (1988) catalog, is reported and four new candidates(AS 205, Wa Oph/2, Wa Oph/3, and Wa CrA/2) for rotational modulation aresingled out from the sample. The color trend for the stars showingvariability is considered. Typically, colors become redder when the staris fainter, complying with the general behavior observed in T Tauristars. This can be interpreted as due to the (variable) presence ofsurface inhomogeneities (either dark or bright) or, in some cases, itcould also be consistent with the hypothesis of variable circumstellarextinction. Estimates of gross spot properties (e.g., temperature andfilling factor) are derived for the four stars showing possibleperiodicity, from the amplitudes of the variations observed at differentwavelengths, by use of a simple blackbody model.
| UVBY observations of A, F, G and K field stars
Photoelectric data in the uvby system have been obtained for about 800southern stars of the Hipparcos Input Catalog (Grenon, 1982, 1985). Mostof the stars are F and G main sequence and fall in the magnitude range V= 8-11.
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