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Near-IR spectral evidence for the presence of iron-poor orthopyroxenes on the surfaces of six M-type asteroids
The first verifiable near-infrared absorption features in the0.9-μm spectral region are reported for Asteroids 16 Psyche, 69Hesperia, 110 Lydia, 125 Liberatrix, 201 Penelope, and 216 Kleopatra.These weak features (1 3%) are attributed to orthopyroxenes presenton the surfaces of these asteroids. 16 Psyche and 125 Liberatrix havefull rotational coverage while 69 Hesperia, 110 Lydia, 201 Penelope, and216 Kleopatra have 75% rotational coverage. Qualitative2-μm absorption features are present, but are very weak(<1%). Absorption band positions suggest relatively low abundances ofcalcium and iron in the pyroxenes. This indicates relatively reducingredox conditions for these asteroids, their parent bodies, and thenebular regions in which they formed. Four potential interpretations forthese asteroids include: (1) they are exposed metallic cores or corefragments of differentiated parent bodies with residual orthopyroxenemantle material, (2) they are the result of a smelting-like reactionthat converts olivine to pyroxene and metallic iron in the presence ofcarbon at high temperatures, (3) they are analogs to the primitivemetal-rich Bencubbinite meteorites, or (4) they represent metallicsurfaces which have accumulated silicate debris from external sources.Of the two original interpretations for the M-asteroids, the enstatitechondrite interpretation (Chapman and Salisbury, 1973, Icarus 19, 507522; Gaffey and McCord, 1979, Mineralogical and petrologicalcharacterizations of asteroids. In: Gehrels T. (Ed.), Asteroids. Univ.of Arizona Press, Tucson, pp. 688 723) can be eliminated for theseasteroids because the pyroxene in enstatite chondrites is iron-free anddoes not exhibit such absorption features. The iron meteoriteinterpretation remains valid, but with modification. For M-Asteroids 16Psyche and 216 Kleopatra, these spectral results combined with previousdeterminations of high radar albedos indicate that these bodies are mostprobably exposed core fragments of differentiated bodies. M-Asteroids 69Hesperia, 110 Lydia, 125 Liberatrix, and 201 Penelope exhibit similarspectral features consistent with exposed core fragments, but radarobservations would be needed to confirm a high metal abundance.Observations of M-Asteroids 136 Austria and 325 Heidelberga suggest theabsence of absorption features in the 0.4- to 2.5-μm regionwithin the scatter of the data. Verification of the presence or absenceof features across the surfaces of these two asteroids requires fullrotational coverage. The interpretations for these“featureless” M-asteroids are not well-constrained, butremain consistent with the iron meteorite and enstatite chondriteinterpretations.
| The surface composition of Charon - Tentative identification of water ice
The Mar. 3, 1987, Charon occultation by Pluto was observed in theinfrared at 1.5, 1.7, 2.0, and 2.35 micrometers. Subtraction of fluxesmeasured between second and third contacts from measurements made beforeand after the event has yielded individual spectral signatures for eachbody at these wavelengths. Charon's surface appears depleted in methanerelative to Pluto. Constancy of flux at 2.0 micrometers throughout theevent shows that Charon is effectively black at this wavelength, whichis centered on a very strong water absorption band. Thus, themeasurements suggest the existence of water ice on Pluto's moon.
| The eight-color asteroid survey - Standard stars
Compositionally diagnostic information regarding the spectralreflectance of faint asteroids and planetary satellites, obtained usinga photometric system, is presented. Standard UBV and range in effectivewavelength from 0.34 to 1.04 microns are among the eight broadbandfilters relative to the study. An InGaAsP photomultiplier of highquantum efficiencies employed for longer wavelengths, allows work tomagnitude 17 and fainter when used in conjunction with a 2 m telescope.Magnitudes and color indices with mean uncertainty + or - 0.006 mag for50 standard stars are presented, and by setting the mean colors of fourof these stars to zero, the zero point of the system is established. Suncolor implications resulting from the study are U-B = 0.20 + or - 0.02,and B-V = 0.67 + or - 0.02.
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Datos observacionales y astrométricos
| Constelación: | Virgo |
| Ascensión Recta: | 13h46m57.91s |
| Declinación: | +06°01'37.7" |
| Magnitud Aparente: | 9.27 |
| Movimiento Propio en Ascensión Recta: | -41.6 |
| Movimiento Propio en Declinación: | -19.9 |
| B-T magnitude: | 10.048 |
| V-T magnitude: | 9.335 |
Catálogos y designaciones:
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