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Nuclear Spectra of Comet 162P/Siding Spring (2004 TU12)
We present visible and near-IR spectra of the nucleus of comet162P/Siding Spring (also known as 2004 TU12) obtained in 2004 December,while it had no detectable coma. This is the third object observed tohave intermittent cometary activity even when relatively close to theSun. The spectra show no strong features in this wavelength range. Thispaucity of deep absorptions is common among low-albedo asteroids and thefew comet nuclei observed in this spectral region. Marginal spectralstructure is observed in the visible spectrum, and beyond 2 μm theflux from the nucleus is dominated by thermal emission. We compare thespectrum of 162P with published spectra of other comet nuclei, primitiveasteroids, and meteorites. Comet nuclei display a range of spectralshapes and slopes not unlike those observed among outer main-beltasteroids but closest to Trojan asteroids. No suitable spectral matchesto comet 162P were found among primitive (chondritic) meteorites. Wemodeled our visible and near-IR spectra using the scattering theorydescribed by Shkuratov et al. (1999), and our approach is similar tothat used by Emery and Brown for modeling Trojan asteroids. Our bestfits to the spectral shape and albedo include mixtures containingamorphous carbons, organics, and silicates. The absence of strongspectral features prevents the identification of specific minerals, andthe resulting model compositions are not unique. The observations beyond2 μm are interpreted in a companion publication by Fernándezand coworkers.
| Visible spectroscopy of 2003 UB313: evidence for N2 ice on the surface of the largest TNO?
Context: .The recent discovery of two large trans-Neptunian objects(TNOs) 2003 UB313 and 2005 FY9, with surface properties similar to thoseof Pluto, provides an exciting new laboratory for the study of processesconsidered for Pluto and Triton: volatile mixing and transport;atmospheric freeze-out and escape, ice chemistry, and nitrogen phasetransitions. Aims: .We studied the surface composition of TNO 2003UB313, the first known TNO larger than Pluto. Methods: .We reporta visible spectrum covering the 0.35-0.95 μm spectral range, obtainedwith the 4.2 m William Herschel Telescope at "El Roque de los Muchachos"Observatory (La Palma, Spain). Results: .The visible spectrum ofthis TNO presents very prominent absorptions bands formed in solid CH4.At wavelengths shorter than 0.6 μm the spectrum is almost featurelessand slightly red (S'=4%). The icy-CH4 bands are significantly strongerthan those of Pluto and slightly weaker than those observed in thespectrum of another giant TNO, 2005 FY9, implying that methane is moreabundant on its surface than in Pluto's and close to that of the surfaceof 2005 FY9. A shift of 15 ±3 Å relative to the position ofthe bands of the spectrum of laboratory CH4 ice is observed in the bandsat larger wavelengths (e.g. around 0.89 μm), but not at shorterwavelengths (the band around 0.73 μm is not shifted) this may beevidence for a vertical compositional gradient. Purer methane could havecondensed first while 2003 UB313 moved towards aphelion during the last200 years, and as the atmosphere gradually collapsed, the compositionbecame more nitrogen-rich as the last, most volatile componentscondensed, and CH4 diluted in N2 is present in the outer surface layers.
| Basaltic asteroids in the Near-Earth Objects population: a mineralogical analysis
Aims.We present reflectance spectra of three V-type Near-Earth Objectsobtained at the 3.6 m Telescopio Nazionale Galileo and at the 2.5 mNordic Optical Telescope covering the near-infrared and visible range,respectively. The range from 0.5 to 2.5 μm, encompassing the 1 and 2μm pyroxene features, allows a mineralogical characterization ofthese asteroids. Methods: .A preliminary analysis using theclassical methods has been applied to establish some constraints on thesurface mineralogy of these objects. Then, the Modified Gaussian Methodwas applied to gain further insight on the possible mineral componentspresent in the surface of the objects. Results: .The comparisonbetween these basaltic asteroids in near Earth orbits and the achondritebasaltic meteorites shows a quite clear mineralogical link,corroborating the long-standing hypothesis of the Near-Earth Objectspopulation as the immediate source of these meteorites.
| TNO surface ices. Observations of the TNO 55638 (2002 VE95
Aims.We investigate the surface composition of Centaurs andTrans-Neptunian objects (TNOs) to get constraints on the formation andthe evolution of this population. Methods.We report visible andnear-infrared spectroscopic observations of the Plutino 55638 (2002 VE5)obtained at VLT-ESO. The surface model has been computed using two typesof radiative transfer models considering geographical and intimatemixtures of different materials. The obtained results have been comparedwith those for objects having near-infrared spectra available in theliterature. The whole sample of 32 objects has been analyzed, inparticular the presence of ices has been investigated in relation totheir surface characteristics (taxonomic groups), their dynamicalproperties and the object sizes. Results. The main result is theclear detection of H20 and CH3OH (or a similar molecule) on the surfaceof 55638. The analysis of the whole sample shows that there are noobvious trends, but the larger objects seem to be icier. The BB groupalso seems to show more ice content on the surface, whereas RR group maycontain more organic material.
| The Inhomogeneous Surface of Centaur 32522 Thereus (2001 PT13)
Eight low-resolution near-infrared spectra (0.8-2.4 μm) of 32522Thereus were obtained on 2002 August 28 from 0:30 to 5:30 UT, coveringmore than half of its rotation period, with the 3.56 m TelescopioNazionale Galileo (TNG) at El Roque de los Muchachos Observatory (ORM,Canary Islands, Spain). All the spectra are red, probably due to amantle of organic materials resulting from long-term irradiation. Duringat least 1.5 hr, the spectra clearly present the typical water iceabsorption bands at 1.5 and 2.0 μm indicative of an inhomogeneoussurface with a major concentration of water ice in part of it. Onepossible scenario is that a collision destroyed part of the irradiationmantle and moved ice from below to the surface, part of the materialbeing vaporized over the surface by the impact.
| Search for surface variations on TNO 47171 and Centaur 32532
We present photometric and spectroscopic observations of oneTrans-Neptunian Object (TNO 47171 1999 TC{36}) and one Centaur (Thereusalso named 32532 2001 PT{13}). Near-infrared data were acquired with theISAAC instrument at one of the 8 m telecopes of the Very Large Telescope(VLT, ESO-Cerro Paranal, Chile), while visible data were obtained withthe EFOSC2 instrument on the 3.6 m telescope of La Silla (ESO, Chile).These observations were performed to search for rotational variationsfor both targets. Water ice has been confirmed on both objects. Thesurface composition models of the targets are presented and discussed,and are also compared to previous observations available in theliterature.
| Is Sedna another Triton?
90377 Sedna is, so far, the largest and most distant trans-neptunianobject. It was observed at visible and near-infrared wavelengths usingsimultaneously two 8.2 m telescopes at the Very Large Telescope of theEuropean Southern Observatory. The spectrum of Sedna suggests thepresence on its surface of different ices (total abundance >50%). Itssurface composition is different from that determined for othertrans-neptunian objects, and apparently resembles that of Triton,particularly in terms of the possible presence of nitrogen and methaneices.
| Small Main-Belt Asteroid Spectroscopic Survey in the Near-Infrared
Near-infrared spectra (~0.90 to ~1.65 μm) are presented for 181main-belt asteroids, more than half having diameters less than 20 km.These spectra were measured using a specialized grism at the NASAInfrared Telescope Facility, where the near-infrared wavelength coverageis designed to complement visible wavelength CCD measurements forenhanced mineralogic interpretation. We have focused our analysis onasteroids that appear to have surfaces dominated by olivine or pyroxenesince these objects can be best characterized with spectral coverageonly out to 1.65 μm. Olivine-dominated A-type asteroids havedistinctly redder slopes than olivine found in meteorites, possibly dueto surface alteration effects such as micro-meteoroid bombardmentsimulated by laser irradiation laboratory experiments. K-type asteroidsobserved within the Eos family tend to be well matched by laboratoryspectra of CO3 chondrites, while those independent of the Eos familyhave a variety of spectral properties. The revealed structure of the1-μm band for 3628 Božněmcová appears to refuteits previously proposed match to ordinary chondrite meteorites.Božněmcová displays a 1-μm band that is unlikethat for any currently measured meteorite; however, spectra out to 2.5μm are needed to conclusively argue thatBožněmcová has a surface mineralogy different fromthat of ordinary chondrites. Extending the spectral coverage of Vestoidsout to ~1.65 μm continues to be consistent with the ``genetic''relationship of almost all observed Vestoids with Vesta and thehowardites, eucrites, and diogenites. Eucrites/howardites provide thebest spectral matches to the observed Vestoids.
| Secondary UBVRI-CCD standard stars in the neighbourhood of Landolt standard stars
A list of 681 UBVRI secondary standard stars for CCD photometry ispresented. Visual magnitude ranges from 9.7 to 19.4, and the B-V colourindex varies from 1.15 to 1.97. The stars are grouped into 11 differentfields, each of them is generally observable in a single CCD frame. Thestars are located near Landolt UBVRI equatorial standards, accessible totelescopes in both hemispheres, and mainly within the 5 - 8 hours rangeof right ascension. Photometry, equatorial coordinates and findingcharts are provided. Based on observations made at the CentroAstronómico Hispano-Alemán and the ObservatorioAstronómico Nacional in Calar Alto, Almería, Spain. Fullversion of Table 4 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Near-Infrared Spectra of Icy Outer Solar System Surfaces: Remote Determination of H2O Ice Temperatures
We present new 1.20 to 2.35 μm spectra of satellites of Jupiter,Saturn, and Uranus, and the rings of Saturn, obtained in 1995 and 1998at Lowell Observatory. For most of the target objects, our data provideconsiderable improvement in spectral resolution and signal-to-noise overpreviously published data. Absorption bands with shapes characteristicof low-temperature, hexagonal crystalline H2O ice dominatethe spectra of most of our targets in this wavelength range. We make useof newly published temperature-dependent wavelengths and relativestrengths of H2O absorption bands to infer ice temperaturesfrom our spectra. These ice temperatures are distinct from temperaturesdetermined from thermal emission measurements or simulations ofradiative balances. Unlike those methods, which average over allterrains including ice-free regions, our temperature-sensing method isonly sensitive to the ice component. Our method offers a new constraintwhich, combined with other observations, can lead to betterunderstanding of thermal properties and textures of remote, icysurfaces. Ice temperatures are generally lower than thermal emissionbrightness temperatures, indicative of the effects of thermal inertiaand segregation between ice and warmer, darker materials. We alsopresent the results of experiments to investigate possible changes ofwater ice temperature over time, including observations of Titania attwo epochs, and of Ganymede and saturnian ring particles followingemergence from the eclipse shadows of their primary planets. Finally, wediscuss limitations of our temperature measurement method which canresult from the presence of H2O in phases other thanhexagonal ice-Ih, such as amorphous ice, hydrated mineralphases, or radiation-damaged crystalline ice. Our spectra of Europa andEnceladus exhibit peculiar spectral features which may result fromeffects such as these.
| The B jRI Photometric System
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..281G&db_key=AST
| A photometric study of the BAO-CCD BVRI system
The BAO Schmidt telescope with a Thomson CCD of 576 x 384 pixels wasutilized for BVRI photometry. Nine secondary photometric standard starsin three CCD frames were observed on 31 October 1989, to establish thecolor equations. Various problems relative to the capability of CCDphotometry are discussed.
| Transformation equations and other aids for VRI photometry
Transformations among VRI systems are commonly beset by Paschen-jumpeffects, for which fully satisfactory allowance has not previously beenmade. This paper describes two new techniques which are based on thework of Gutierrez-Moreno, and which allow fully for the effects of thePaschen jump. Values of E(V-R)/E(B-V) and E(R-I)/E(B-V) are also givenfor the Cousins system for a wide range of temperatures. These and thenew techniques contribute to a set of new transformation relations whichapply for most VRI systems; the status of the remaining systems isreviewed, and future work needed for them is described. Two majorsources of Cousins VRI data underlie the new relations; the consistencyof these sources is reviewed and found to be generally satisfactory,although more work on this question is needed. Finally, three tables oftransformed standard-star and other data are given for the Cousins andJohnson systems, and a description of ways to reproduce the latter ispresented.
| UBV Photometry of Equatorial Stars
Not Available
| Distances to eclipsing binaries. III - Masses, radii, and absolute magnitudes of 96 stars
Distances to, and absolute magnitudes of, 96 components of eclipsingbinaries with well-determined absolute dimensions have been computedusing V-R photometry. The calculations take into account interstellarreddening, which is estimated from existing UBV and uvby-betaphotometry, as well as photometric proximity effects. The resultingabsolute magnitudes, dimensions, and masses are compared with zero-agemain sequences predicted by theory. Theory is in good agreement with theobserved data for stars more massive than the sun if a composition (X,Y, Z) = (0.66 + or - 0.03, 0.303 + or - 0.03, 0.037 + or - 0.005) ischosen. The corresponding helium-to-hydrogen number ratio is 0.115 + or- 0.02, in agreement with previous estimates.
| Spectral classifications for Landolt's celestial equatorial standard stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979AJ.....84..783D&db_key=AST
| Equatorial UBVRI photoelectric sequences
From 1335 BVRI observations of 189 stars in selected areas 92-115,Landolt's (1973) network of faint UBV standards has been extended to RI. Of these stars, 173 have four or more observations. The (U-B) valuesof Landolt are adopted, and a well-observed equatorial faint-starnetwork is presented on the Johnson UBVRI photometric system.
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