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Tirela: an unusual asteroid family in the outer main belt
Context: Earlier visible spectroscopic classification of (1400) Tirelasuggests that this object is a D-type. As the Tirela family has higheccentricities and inclinations, its parent-body could have beenimplanted in the main belt during the late heavy bombardment, a scenariorecently proposed for some D-type asteroids. Spectra of other members ofthe family have not been available until now, except for colors from theSloan Digital Sky Survey (filters u, g, r, i, and z) for some of them.These colors also suggest that the family has slopes similar to D-types.Aims: Thus, we wanted to spectroscopically characterize the Tirelafamily. Due to the faintness of the objects, we used some relatively bigtelescopes in some observing runs. Methods: We obtained visiblespectra of 10 faint Tirela family members at telescopes TNG and GEMINIand the NIR spectrum of two members of the family at the IRTF telescope.These spectra were classified and comparisons were made with meteoritesand minerals in an attempt to infer the mineralogical surfacecomposition of the members. Results: The Tirela family was foundto be composed of Ld-type asteroids. Comparisons with minerals suggestthat the combined visible+near-infrared spectrum of (1400) Tirela showsome similarities to the spectrum of the pure mineral pigeonite. Conclusions: We conclude that the family is not a D-type, butcomparisons with minerals suggest similarities between the absorptionsfound in Tirela with those found in the mineral pigeonite.
| Visible spectroscopy of the new ESO large program on trans-Neptunian objects and Centaurs. Part 1
Aims. A second large observational program was started to improve ourknowledge of the physical properties of Centaurs and trans-Neptunianobjects, TNOs. The program is being executed in the facilities at theCerro Paranal of the European Southern Observatory, ESO, in Chile. Methods: Visible spectroscopy was carried out using FORS1 at the UT2 ofthe VLT telescope. We computed the spectral slope, S, for each object,and we searched for the possible existence of weak absorption features.We compared our data with those from the literature. Results: Wepresent spectra for 21 objects, 7 of them with no previously reportedspectra. Our sample includes 5 Centaurs, 5 resonant objects, 8 classicalTNOs, 2 detached objects, and 1 scattered disk object. There aresignificant differences between the distribution of spectral slopes forCentaurs and classical TNOs. The data presented here generally agreewith previous published data. One exception is 60 558 Echeclus, whosespectral slope is considerably smaller than previous measurements.Another interesting object is 47 932 (2000 GN{171}), which does not showevidence of a proposed feature at 0.7 μm. Most of the spectra arelinear and featureless; however, the well-known bands of solid methaneare detected in 136 199 Eris spectra and some weak features are detectedfor a few other objects. The most interesting case is that of 2003AZ{84}, which has a feature at about 0.65 μm, maybe due to aqueousalteration.Based on observations at the VLT Observatory Cerro Paranal of EuropeanSouthern Observatory, ESO, Chile, in the framework of program178.C-0036.
| An Atlas of Spectrophotometric Landolt Standard Stars
We present CCD observations of 102 Landolt standard stars obtained withthe Ritchey-Chrétien spectrograph on the Cerro TololoInter-American Observatory 1.5 m telescope. Using stellar atmospheremodels, we have extended the flux points to our six spectrophotometricsecondary standards, in both the blue and the red, allowing us toproduce flux-calibrated spectra that span a wavelength range from 3050Å to 1.1 μm. Mean differences between UBVRI spectrophotometrycomputed using Bessell's standard passbands and Landolt's publishedphotometry were determined to be 1% or less. Observers in bothhemispheres will find these spectra useful for flux-calibrating spectra,and through the use of accurately constructed instrumental passbands,will be able to compute accurate corrections to bring instrumentalmagnitudes to any desired standard photometric system (S-corrections).In addition, by combining empirical and modeled spectra of the Sun,Sirius, and Vega, we calculate and compare synthetic photometry toobserved photometry taken from the literature for these three stars.
| Analysis of near-IR spectra of 1 Ceres and 4 Vesta, targets of the Dawn mission
We obtained high signal to noise spectra of the two targets of the Dawnmission, 4 Vesta and 1 Ceres from observations carried out in remotecontrol between the Observatoire de Paris-Meudon and the NASA InfraredTelescope Facility on Mauna Kea. 4 Vesta was observed in the 0.7-2.5μm spectral region at three different rotational phases in order toi) determine the mineral composition; ii) understand the spectralvariations across the surface. Vesta was also observed in the 2.0-3.8μm range. The 3 μm absorption feature was not detected, implyingthe absence of OH and/or H2O-bearing minerals on the asteroid surface atthe latitude of our observations. The spectrum of 1 Ceres was obtainedin the 2.0-4.1 μm range and the presence of the 3.06 μm absorptionfeature confirmed. Laboratory measurement of ion-irradiated organics andices suggest that the 3.06 μm feature can be reproduced with a linearmixture of crystalyne ice and residues of ion-irradiated asphaltite.
| Near-IR spectroscopy of asteroids 21 Lutetia, 89 Julia, 140 Siwa, 2181 Fogelin and 5480 (1989YK8), potential targets for the Rosetta mission; remote observations campaign on IRTF
In the frame of the international campaign to observe potential targetasteroids for the Rosetta mission, remote observations have been carriedout between Observatoire de Paris, in Meudon-France and the NASAInfrared Telescope Facility on Mauna Kea. The SpeX instrument was usedin the 0.8-2.5 μm spectral region, for two observing runs in Marchand June 2003.This paper presents near-IR spectra of the asteroids 21 Lutetia, 89Julia, 140 Siwa, 2181 Fogelin and 5480 (1989YK8).Near-IR spectra of the asteroids 21 Lutetia and 140 Siwa are flat andfeatureless. The spectrum of 89 Julia reveals absorption bands around 1and 2 μm, which may indicate the presence of olivine andolivine-pyroxene mixtures and confirm the S-type designation.The small main-belt asteroids 2181 Fogelin and 5480 (1989YK8) areinvestigated spectroscopically for the first time. Near-IR spectra ofthese asteroids also show an absorption feature around 1 μm, whichcould be and indicator of igneous/metamorphic surface of the objects;new observations in visible as well as thermal albedo data are necessaryto draw a reliable conclusion on the surface mineralogy of bothasteroids.
| 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.
| UBV(RI)c photometry of equatorial standard stars - A direct comparison between the northern and southern systems
UBV(RI)c photometry of 212 stars from Landolt's list of equatorialstandards is presented. The observations are tied to the system definedby Cousin's E-region standards. A comparison of the present results withLandolt's reveals reasonably good agreement for (V-R)c and (V-I)c, butmarked systematic differences for (B-V) and (U-B). The UBV systems ofCousins and Landolt are evidently not the same and both probably differfrom Johnson's original system.
| Walraven VBLUW photometry in Basel halo fields. I - Photometric data for selected areas SA141 (South Galactic Pole), SA94 and SA107
In 1981 a joint Swiss-Dutch program was initated to obtain photoelectricphotometry in the Walraven VBLUW system for F-G stars in fields of theBasel halo survey. The aim of this project is to determine temperature,surface gravity, and metal abundance for these stars in order to studythe distribution of the average stellar metallicity as a function ofdistance from the galactic place up to z-distances of about 1 kpc. Thispaper presents the VBLUW data for 112 program stars in Selected AreaSA141 at the South Galactic Pole, 93 stars in SA94 (l = 175 deg, b = -49deg), and 46 stars in SA107 (l = 6 deg, b = +41 deg).
| Photoelectric observations of classical cepheids.
Not Available
| UBVRI photometric standard stars around the celestial equator
It is pointed out that accurate, internally consistent, and readilyaccessible standard star photometric sequences are necessary for thecalibration of the intensity and color data which astronomers obtain atthe telescope. The photometric results provided in connection with thepresent study represent the first part of an effort which is concernedwith the presentation of UBVRI photoelectric photometric standard starsin the magnitude range from 7 to 17 over as broad a range in color aspossible. All of the photometric observations were made with a 31034type photomultiplier used in a pulse counting mode. Some 15 to 25standard stars chosen from Cousins' lists (1973, 1976) in the E-regionswere observed with an 0.4-m telescope each night along with the programstars. UBVRI standard stars were observed periodically throughout thenight. Observations with a 0.9-m telescope were also conducted. TheUBVRI photoelectric observations take into account 223 stars.
| 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.
| UBV sequences in selected star fields
Not Available
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Besorolás csoportokba:
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Pozíciós és asztrometriai adatok
| Csillagkép: | Kígyó |
| Rektaszcenzió: | 15h37m18.15s |
| Deklináció: | -00°09'49.7" |
| Vizuális fényesség: | 8.446 |
| Távolság: | 83.264 parszek |
| RA sajátmozgás: | 61.5 |
| Dec sajátmozgás: | -34.5 |
| B-T magnitude: | 9.189 |
| V-T magnitude: | 8.508 |
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