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Astronomy&Astrophysicsmanuscriptno.lwsaster (cid:13)c ESO2009 January28,2009 ⋆ Catalogue of ISO LWS observations of asteroids F.Hormuth1,2 andT.G.Mu¨ller3 1 CentroAstrono´micoHispanoAlema´n,C/Jesu´sDurba´nRemo´n2-2◦,04004Almer´ıa,Spain 2 Max-Planck-Institutfu¨rAstronomie(MPIA),Ko¨nigstuhl17,69117Heidelberg,Germany 9 e-mail:[email protected] 0 3 Max-Planck-Institutfu¨rextraterrestrischePhysik(MPE),Giessenbachstrasse,85748Garching,Germany 0 e-mail:[email protected] 2 n Received;accepted a J ABSTRACT 8 2 Context.TheLongWavelengthSpectrometer(LWS)onboardtheInfraredSpaceObservatory(ISO)observedthefourlargemain-belt asteroids(1)Ceres,(2)Pallas,(4)Vesta,and(10)Hygieamultipletimes.Thephotometricandspectroscopicdatacoverthewavelength rangebetween43and197µm,andareauniquedatasetforfutureinvestigationsanddetailedcharacterisationsofthesebodies. ] P Aims.Thestandard ISO archiveproducts, produced through the lastpost-mission LWSpipeline, werestillaffectedby instrument E artefacts.Ourgoalwastoprovidethebestpossibledataproductstoexploitthefullscientificpotentialoftheseobservations. . Methods.Forallasteroidobservationsweanalysedindetailthedarkcurrent,thecalibrationreferenceflashes,thespaceenvironment h effects(glitches), memory effects,tracking influences, and various other sources of uncertainty. Weperformed arefinedreduction p ofallmeasurements,correctedforthevariouseffects,andre-calibratedthedata.Weoutlinethedatareductionprocessandgivean - overview of theavailable dataand thequality of the observations. Weapply athermophysical model tothe fluxmeasurements to o derivefar-IRbaseddiameterandalbedovaluesoftheasteroids.Themeasuredthermalrotationallightcurveof(4)Vestaiscompared r t tomodelpredictions. s Results.ThecatalogueofLWS(LongWavelengthSpectrometer)observationsofasteroidscontains57manuallyreduceddatasets, a includingsevennon-standardobservations,whichassuchdidnothavefinalpipelineproductsavailablebefore.Intotal,thearchive [ nowcontains11spectralscansand46fixedgratingmeasurementswithasimultaneousobservationat10keywavelengthsdistributed 1 over the full LWS range. The new data products are now accessible via the ISO data archive as highly processed data products v (HPDP)⋆⋆. 7 Conclusions.Thequalityofthedataproductswascheckedagainststate-of-the-artthermophysicalmodelpredictionsandanexcellent 5 agreementwasfound.Theabsolutephotometricaccuracyisbetterthan10%.Thecalibratedspectrawillserveassourceforfuture 5 mineralogicalstudiesofdwarfplanetsanddwarfplanetcandidates. 4 Keywords.Minorplanets,asteroids–Radiationmechanisms:Thermal–Infrared:Solarsystem . 1 0 9 1. Introduction ISO Handbook, Volume III (Gryetal. 2003). In total, the ISO 0 Data Archive(IDA1) contains51 successful LWS observations : The Infrared Space Observatory (ISO; Kessleretal. 1996) v of four different asteroids covering almost 18hours of satellite i observed between 1995 and 1998 more than 40 asteroids in time.However,thescientificreturnoftheseprogrammeswasso X greatdetail,includingsomecompletespectrafrom2to200µm far verylittle. Mostof the scientific questionscouldnotbe an- r and large samplesof photometricmeasurements(Mu¨ller 2003; a sweredmainlyduetotheinstrumentalartefactswhichremained Dottoetal. 2002). The main goals of the about 100hours of inthearchiveddataproducts. asteroid observing time were the identification of surface min- The LWS data set of asteroid observations covers a wave- erals, composition, connection to meteorites and comets, sur- lengthrangewhichisnotaccessiblefromtheground.Inthenear face alteration processes, and the interpretation of taxonomic future the Herschel mission will be capable of obtaining aster- classes through the identification of mid-infrared features of oid spectra between 57 and 210µm with PACS (Photodetector well-knownminerals and meteorites. Mu¨lleretal. (2005) sum- Array Camera & Spectrometer) and between 200 and 670µm marisedthemainISOresultsfromthevarioussolarsystempro- with SPIRE (Spectral and Photometric Imaging Receiver), but grammesandfromallfourISOinstruments. asteroidsarecurrentlynotpartoftheacceptedkeyprogrammes. TheISOLongWavelengthSpectrometer(LWS;Cleggetal. Although the ISO targetlist is very limited, it includesobjects 1996) performedphotometricand spectroscopic measurements ofhighscientificinterest:(1)Ceresand(4)Vestaarethetargets inthewavelengthrange43to197µmandopened,togetherwith oftheDawn2spacecraftmission,(1)Ceresismeanwhileconsid- ISOPHOT,anewwindowforfar-infraredastronomy.Thedetails eredasadwarf-planet,and(2)Pallas,(4)Vesta,and(10)Hygiea on the instrument and the data processing can be found in the aredwarf-planetcandidates3.Ingeneral,itisbelievedthatthese Sendoffprintrequeststo:F.Hormuth ⋆ BasedonobservationswithISO,anESAprojectwithinstruments 1 http://www.iso.esac.esa.int/ida/index.html funded by ESA Member States (especially the PI countries: France, 2 http://dawn.jpl.nasa.gov/ Germany,theNetherlandsandtheUnitedKingdom)andwiththepar- 3 Dissertatio Cvm Nvncio Sidereo III, Nr. 3, August 16, 2006, ticipationofISASandNASA. http://astro.cas.cz/nuncius/ 2 F.HormuthandT.G.Mu¨ller:CatalogueofISOLWSobservationsofasteroids largestbodiesinthemain-beltareprotoplanetsremainingintact of this data still remainsdifficult, since the relative spectralre- sincetheirformation. sponsefunction(RSRF) ofthedetectorsusedinthecalibration The LWS observations comprise spectral energy distribu- processisbasedonobservationsperformedinthestandardL01 tionsoverthefullwavelengthrangebetween43and197µmwith mode.TheremainingL99datasetsdidnotincludesufficientcal- aspectralresolvingpowerof∼200andcanbeutilisedtosearch ibrationdataforreliabledarkcurrentdetermination. forspectralsignaturesrelatedtotheasteroids’mineralogiccom- AllstandardobservationsarelistedinTbl.1,whilethenon- position.Anoverviewofthespectroscopicfeaturesfromtheory standardobservationsaresummarisedinTbl.2.Contamination and lab measurementsin the infrared wavelength regime up to by158µmCIIbackgroundemissionisindicatedwhereapplica- 25µm can be foundin e.g. Salisbury (1993) and in the context ble. ofISO inDottoetal. (2002). Farinfraredlaboratoryspectraof Acomprehensiveoverviewoftheinstrumentdesign,observ- various crystalline and amorphous minerals are digitally avail- ing modes, and detector properties can be found in the LWS ablee.g.intheHeidelberg–Jena–St.Petersburg–Databaseof handbook(Gryetal.2003). OpticalConstants(HJPDOC)4 (Henningetal. 1999). Although thesemeasurementsareinprinciplesufficienttoallowtheanal- 2.2.Observationelements ysisofthedatapresentedinthispaper,theirapplicationtosolid surfaceswithnon-uniformgrainsizesandsubsurfaceradiationis Eachobservationconsistsnotonlyoffluxmeasurementsofthe notstraightforward,renderingamineralogicinterpretationdiffi- targetitself, butalsoincludescalibrationdata,typicallysplitin cult. two blocks at begin and end. By placing the Fabry-Pero´tspec- Apartfromthat,theLWSobservationscangivevaluablein- trometerintothebeamandintentionallymisaligningtheetalons, puttomodelsdescribingthethermalemissionofminorbodiesin lightfromthesourcedidnotreachthedetectors,eventuallyre- ourownorothersolarsystems,andarekeyingredientstoestab- sulting in a dark currentmeasurement. Long observations, and lishasteroidsascalibrationobjectsinthemiddleandfarinfrared especially the engineeringmode L99 data, contain intermittent (e.g.Mu¨ller&Lagerros1998,2002). additionaldarkcurrentmeasurements. Aneffortwasmadetoproduceahomogeneouslyreducedset Since the responsivity of the detectors is not constant, but oftheseobservations,eventuallyleadingtoacataloguewhichis usually drifting upwards over time due to impacts of charged availablethroughtheIDA.Wedescribethecontentsofthecata- particles,theactualresponsivityofeachdetectorhadtobedeter- logue(Section2),outlinethedatareductionprocess,andgivean minedforeachobservationseparately.Thiswas donebyflash- overview of the instrumental artefacts (Section 3) encountered ingthedetectorswithinternalilluminatorswhilelightfromthe duringcataloguecompilation.Section 4 gives a brief overview sourcewasagainblockedwiththeFabry-Pero´t.Thisallowedto of the catalogue structure. In Section 5 we discuss the quality quantifyresponsivitychangesduringthecourseofa single ob- ofthefinalproducts,presentdiameterandalbedovaluesderived servation, and to apply the so-called ’responsivity drift correc- from thermal IR data in the range 43–197µm for the observed tion’. asteroids,andanalysethethermallightcurveof(4)Vesta. Absoluteresponsivitycalibrationwasperformedbycompar- ingtheresponsivitiesmeasuredatthetimeoftheobservationto 2. Observations the ones measured during observations of Uranus, the primary LWScalibrator. 2.1.Overview Forthetargetsourcefluxmeasurements,theFabry-Pero´twas removedfromthebeam.Dependingontheobservationtemplate MostoftheLWSasteroidobservationswerecarriedoutinfixed andrequestedwavelengthcoverage,thegratingremainedeither gratingmode,usingtheastronomicalobservingtemplate(AOT) atafixedangleorwasmovedtoscanthedesiredspectralrange. L02. This produced ten photometric measurements – one in Thiscouldbedoneinunidirectionalmode,wherethegratingan- eachdetector–at46.2µm,56.2µm,66.1µm,75.7µm,84.8µm, gleconstantlyin-ordecreasedandwasresettoitsstartposition 102.4µm,141.8µm,160.6µm,and178.0µm(correspondingto beforeeachscanrepetition.Alternatively,theobservationcould detectorsSW1toSW5andLW1toLW5). be performedin bidirectional mode, with the grating angle in- OnlyfourfullgratingscansusingthetemplateL01wereper- creasingandthendecreasingwiththesamerateduringthemea- formed, covering the whole spectral range from 43 to 197µm surement.Thisis referredto asup-anddown-scan,where’up’ with typical SNRs of 20–30 for (10) Hygiea and 150–200 for and’down’doesnotcorrespondtoanincreaseordecreaseofthe (1)Ceres.Thespectrumiscomposedoftensub-spectrawiththe observedwavelength,butofthegratingpositionencodervalue. sub-spectrabeinggeneratedbythegratingscanningovertheten In fact, during an upscan the observing wavelength decreased, LWS detectorssimultaneously.Signal-to-noisewas built up by andincreasedduringdownscans. takingmorethanonescan. Additionally there exist 25 observations carried out in the non-standard engineering mode L99, most of them similar to 3. Datareduction L01 grating scans (SNR ≈150 for (1) Ceres and ≈100 for (4) Vesta).Forthecatalogue,onlyL99on-sourcegratingscanswere 3.1.Instrumentalartefacts considered,andnobackgroundmeasurementsareincluded.The The most prominentartefacts, commonto all ISO instruments, non-standardobservationsarecharacterisedbyexperimentalset- are ’glitches’, sudden increases of the measured flux due to tings of the detector parameters (bias voltages and heater cur- chargedparticleshittinga detectororpartsofthereadoutelec- rents),anunusuallyhighspectralsampling(13samplesperres- tronics.Theinitialsuddensignalincreaseissometimesfollowed olution element instead of four, as it was the standard setting bya‘glitchtail’,along-livedexponentialdecay.Thoughglitches later),andlongerintegrationtimespergratingposition. canberecognisedandfilteredoutautomaticallytosomeextent, From the available L99 observations we selected seven glitch remnants are present in all observations throughout the datasets for inclusion in this catalogue. The spectral analysis archive,regardlessofinstrumentorobservingmode.Glitchesdo 4 http://www.mpia-hd.mpg.de/HJPDOC/ notonlyoccurduringobjectfluxmeasurements,butalsoduring F.HormuthandT.G.Mu¨ller:CatalogueofISOLWSobservationsofasteroids 3 thecalibration,i.e.darkcurrentandresponsivitymeasurements, artefactsinthecalibrationdatawillaffecttheaccuracyandrelia- and adversely affect the accuracy and reliability of the actual bilityofthewholeobservation.TheLIAroutineSHORT AALwas observation.Special attention was therefore put on the manual usedtocreateISAP-compatibleoutputspectraintheLWSAuto- removalofglitchremnantsineachobservationcontainedinthe Analysisformat,andtoconverttoW/cm2/µm,thefluxunitused presentedcatalogue. for all LWS observations. This routine automatically strips all Otherfrequentlyobservedinstrumentalartefactsarefringes calibrationdataandleavesonlythebasicinformationneededfor in the spectra in the case of extended sources or off-axis ob- further scientific analysis, e.g. wavelength, flux, detector num- servations,spuriousspectralfeaturesduetouncertaintiesinthe ber,andscandirection. spectral response function used in the calibration process, and In the case of photometric L02 observations, the data was memoryeffects,i.e.changesofdetectorresponsedependingon nowaveragedperdetectortocreatethefinalFITSproduct. theilluminationhistory. In the case of grating scans a first round of manual de- Observations towards the end of the satellite mission were glitchingwasperformed,probablythemosttimeconsumingstep affectedbyso-called’warm-upeffects’,visibleasbroadspectral in the reduction process. Relative responsivity correction was featuresinsomedetectors.Thiswaspresumablycausedbyperi- achievedbycomparingthemeanfluxineachdetectorandscan odicbreaksoftheliquidheliumfilminthevicinityoftheLWS to the mean flux level of all scans together. The derived gains strap location as the satellite’s helium tank came close to ex- werethenusedto bringallscansto thesame fluxlevel–sepa- haustion.Fromtheobservationscontainedinthiscatalogue,this ratelyforeachdetectorandscandirection. affectsoneL01typeobservationof(1)CerestakeninDecember Afterfine-zappingofremainingglitches,thedatawasaver- 1997, several months before ISO’s liquid helium depletion in aged per detector with a bin width of typically 0.06µm, corre- April1998. spondingtoanoversamplingoffourwithrespecttothespectral A thorough description of caveats and unexpected effects resolution.Inthecaseofbidirectionalscansthedatawasnowav- concerning LWS data can be found in Chapter 6 of the LWS eragedoverthescandirections.Especiallyatlongerwavelengths handbook (Gryetal. 2003). All datasets included in this cata- somespectraclearlyshowedfringing,probablycausedbyback- logue were checked for the presence of the artefacts described groundemission. The affected detectorswere defringedwithin aboveand data quality was quantifiedvia a set of well-defined ISAP,usingonlytheaveragedspectrumforfringedetectionand flags. The criteria for setting these flags and the results of this defringingtogetthebestpossiblesignal-to-noiseforthefringe quality check can be found in the technical documentationac- fitting(inthecaseofbidirectionaldata). companyingthecatalogue(Hormuth&Mu¨ller2006). 4. Dataproductsandaccesstothecatalogue 3.2.Datareductionsteps Datareductionwasperformedwiththeavailablestandardreduc- TheISODataArchive(IDA)5 containsspectroscopic,imaging, tionpackagesLIA(LWSInteractiveAnalysis)Version10.2and photometric, and polarimetric measurements of more than 40 ISAP (ISO SpectralAnalysis Package)Version2.2. Additional differentasteroidsatwavelengthsbetween2and240µm.Aver- ownIDL-procedureswereusedformanualeditingofthedataat satile Java based web-interface allows to extract observational theSPD(StandardProcessedData)level,andthegenerationof datainvariousformats,rangingfromunprocessedrawdata,over thefinalFITSandASCIIfiles.TheSPDdataispreprocessedin standardpipelineprocessedmeasurementsuptomanuallyrepro- the sense that raw detector readouts have been converted into cessedhighqualitydataproducts. photocurrents, saturated readouts flagged, and strong glitches All data files associated to this catalogue can be retrieved automatically identified and removed. Housekeeping data not by searching for the specific TDT6 number of a measurement necessaryforfurtherdatareductionhasbeenremoved,butdark asgiveninTbl.1and2,bysearchingforallLWSobservations currentandresponsivitymeasurementshavebeenpreserved.In of a given asteroid, or by searching for LWS asteroid observa- thefollowingwebrieflyoutlinetheorderofreductionstepsand tionsin general.The highlyprocesseddata products,including givethenamesofthecorrespondingLIAprocedureswhereap- overviewplots, qualityflags, and cataloguedocumentationcan plicable. beobtainedviatheHPDPbuttonlefttoeachentryinthesearch In a first step, the pointing coordinatesof each observation resultwindowofthearchiveinterface. werecheckedagainsttheephemerisoftheobservedasteroidto Thecataloguedocumentation(Hormuth&Mu¨ller2006),giving detectpointingproblems.Themaximumdifferencebetweenas- athoroughdescriptionofthedatareductionsteps,isalsosepa- teroidpositionandtelescopepointingwasfoundtobe2′.′5,much ratelyavailablefromthelistofallHPDPdatasets7. smaller than the LWS beam profile (see Lloyd 2003). The re- InFig. 1andFig.2 weshowlogarithmicexampleplotsfor duction process started at SPD level with a visual inspection all observingmodes. Differentcolourshave been chosen to al- of the data in the time domain. Photometric L02 observations low distinguishmentof overlappingmeasurements by different weremanuallyde-glitchedatthisstage,capturingminorglitches detectors. The error bars in Fig. 1 include measurement and not automatically flagged during generation of the SPD data. calibration errors, incuding a 5% uncertainty attributed to the Theavailablepipelinedataofgratingscanswasadditionallyin- Uranusmodelsusedforabsolutefluxcalibration.Theslightmis- spectedwithISAPtogetaquickoverviewoftheavailablescans matchesbetweenmeasurementsfromdifferentdetectorsatsame andscandirections. wavelengthsinFig.2arecausedbymemoryeffectsofindividual Next, dark currentdetermination and subtraction were per- detectors. formed using the LIA routine IA DARK, followed by the abso- The data sets are available both as FITS tables, compati- luteresponsivitycorrectionwithIA ABSCORR.Theseinteractive ble with the ISAP software package, and as plain ASCII ta- routinesallowvisualinspectionandmanualeditingofthedark currentmeasurementsandtheinternalcalibrationsourceobser- 5 Accessibleviahttp://iso.esac.esa.int vations. Deglitching of this data and the removal of measure- 6 “TargetDedicatedTime”,auniqueidentifierforISOobservations mentsobviouslyaffectedbymemoryeffectsiscritical,sinceany 7 http://iso.esac.esa.int/ida/hpdp.php 4 F.HormuthandT.G.Mu¨ller:CatalogueofISOLWSobservationsofasteroids TDT 23000306 − 210002 PALLAS − AOT L02 TDT 76903203 − 210001 CERES − AOT L01 10−16 10−17 10−17 m m µ µ 2m/ 2m/ c c W/ W/ x / x / 10−18 Flu 10−18 Flu 10−19 40 60 80 100 120 140 160 180 50 100 150 200 Wavelength / µm Wavelength / µm TDT 84801302 − 210010 HYGIEA − AOT L02 TDT 05500201 − 210004 VESTA − AOT L01 10−17 10−17 m m µ µ 2m/ 2m/ 10−18 W/c 10−18 W/c x / x / u u Fl Fl 10−19 10−19 10−20 40 60 80 100 120 140 160 180 50 100 150 200 Wavelength / µm Wavelength / µm Fig.1. Examples for L02 observations. Left: fixed grating ob- Fig.2.Examplesforfullwavelengthrangescans.Left:standard servationof (2)Pallas. Right:shortgratingscan observationof L01observationof(1)Ceres.Right:EngineeringmodeL99ob- (10)Hygiea. servationof(4)Vesta. Table3.RatiosbetweenLWS02observationsandTPMpredic- bles.Pleaserefertothecataloguedocumentationforinformation tions,weightedmeanvaluesandstandarddeviationsperdetector aboutindividualFITSheaderkeywordsandtablecolumns. (SW1,2, 3,4,5andLW1,2, 3)andperasteroid.Thephotom- etry of the LW4 and LW5 detectorsis less reliable due to dark currentproblems. 5. Discussion 5.1.Qualityofthecatalogueproducts (1)Ceres (2)Pallas (4)Vesta (10)Hygiea In order to study the reliability of the photometric L02 data in λ 11Obs. 4Obs. 14Obs. 2Obs. thecatalogue,wecomparedthemeasuredfluxwithpredictions [µm] Obs/Mod Obs/Mod Obs/Mod Obs/Mod calculated by means of the thermophysical model (TPM; e.g. 46.4 1.04±0.05 1.00±0.02 1.02±0.04 1.21±0.05 Lagerros1998,andreferencestherein).ForTbl.3wecalculated 56.4 1.01±0.03 1.06±0.02 1.01±0.04 1.25±0.10 model fluxes for the specified targets and epochs and analysed 66.3 1.04±0.02 1.10±0.04 1.02±0.04 1.23±0.15 the observation-to-modelratios. Measurements affected by de- 75.9 1.02±0.03 1.02±0.03 1.04±0.04 1.24±0.12 tector warm-up artefacts or abnormally high dark currentwere 85.0 1.01±0.04 1.02±0.11 1.00±0.07 1.39±0.10 notincludedinthisqualitycheck. 102.9 1.09±0.04 1.13±0.04 1.24±0.06 1.40±0.26 The general agreement between the photometric observa- 122.7 0.96±0.05 0.95±0.03 1.07±0.05 1.30±0.07 tions (L02) and models (Tbl. 3) is better than 5% for Ceres, 142.2 0.89±0.04 0.84±0.07 1.10±0.11 1.33±0.04 161.0 0.99±0.05 0.99±0.04 — — Pallas, and Vesta and better than 30% for Hygiea. The higher 178.4 1.01±0.10 — — — uncertaintiesare dueto darkcurrenteffectsatthe lowfluxlev- els. The discrepancy for Hygiea is not surprising. Due to the Mean 1.01±0.05 1.03±0.08 1.05±0.08 1.27±0.14 lack of suitable good quality thermal data the thermophysical modelparametersarealso verypoor,andHygieais considered asalowqualityfar-IRcalibrator(Mu¨ller&Lagerros1998).As a rule of thumb, the absolute flux error is better than 10% for The high quality of the spectral scans can be seen in the targetsbrighterthanabout10Jy. smoothandwell-connectedcurvesofthearchivebrowseimages F.HormuthandT.G.Mu¨ller:CatalogueofISOLWSobservationsofasteroids 5 (see Fig. 2). For mineralogic studies it might still be useful to cludedthedatawhichareflaggedasbeingaffectedbyhighdark investigate the up- and down-scans separately to confirm that currents or high glitch rates. In the table we give the full stan- certainlow-level,broad-bandstructuresinthescansarereliable darddeviationof allN radiometricsolutionsto accountforthe ornot.Lowlevelfeaturesextendingovertwoormoredetectors fact that different observations see the asteroid under different as well as structures close to pronounced RSRF changes have observingandilluminationgeometries. to be analysed carefully:the detectorsare notalways behaving in exactly the same way and LWS should be considered as 10 individualspectrometers,oneperdetector. Table5.Radiometricdiameterandalbedovalues,derivedfrom theLWSL02measurements. 5.2.Diameterandalbedocalculations Object D [km] p N eff V Directsizemeasurements,evenforthelargemain-beltasteroids, (1)Ceres 959.6±16.9 0.096±0.003 55 are still difficult. Up to now, only a small sample has been re- (2)Pallas 534.4±14.7 0.142±0.009 20 solvedviaimagingtechniquesfromspace(HST,seeDottoetal. (4)Vesta 548.5±12.5 0.317±0.015 70 (2002) and references therein) and adaptive optics techniques (10)Hygiea 469.3±26.5 0.056±0.006 20 from large ground-based telescopes (e.g. Marchisetal. 2006). Occultation observations performed by well-organised groups of amateur astronomers also reveal direct sizes, expressed in These diameter and albedo values are the first ones which chord maps which represent the cross section of the asteroid are derived purely from far-IR observations. Nevertheless, the at the time of the occultation (e.g. Millis&Dunham 1989) resultsagreeverywellwiththesofarpublishedvalues. orhttp://www.psi.edu/pds/resource/occ.htmlformorerecentre- hemostaccuratevaluesforthe diameterof(1)Cerescome sults). But the largest number of asteroid sizes are originating from HST observations (Thomasetal. 2005) and adaptive op- fromthermalinfraredobservations(e.g.Tedescoetal.2002a,b) tics (AO)observationsusing theKeck IItelescope (Carryetal. viaradiometricmethodsi.e.,anindirectmethodwhichrelieson 2008). The HST observations led to an oblate spheroid with modelassumptions. axesofa=b=487.3kmandc=454.7km,resultinginaneffective We used a well-established thermophysical model (TPM; diameter of 2 × (a × b × c)1/3 =952.4km. The AO data con- Lagerros1996,1997,1998)toderiveabsoluteeffectivesizesand firmed the oblate spheroid,but with slightly differentvalues (a albedosforour4asteroidsfromthenewL02datasets. =b=479.7±2.3km,c=444.4±2.1km)andaneffectivediame- This model allows to use state-of-the-art shape models to- terof935.3km.Ourresultisderivedfromverylimitedviewing gether with corresponding spin axis solutions derived from geometries, but it is in excellent agreement with the HST re- lightcurve inversion techniques (e.g. Kaasalainenetal. 2002). sults. In this context it is interesting to note that the diameter As part of the energy equation for the asteroids the amount of derivedfrom IRAS observationsat 12, 25, 60 and 100µm was reflected sunlight is described via the H−G magnitude system 848.40±19.7km (Tedescoetal. 2002b). Also our albedo value (Bowelletal.1989).Therestofthesolarenergyisabsorbedand agreesverywell withthe 0.0936derivedviastellar occultation re-emittedasthermalemission.Knowingthesolarinsolationto- techniques(Shevchenko&Tedesco2006). getherwith thedisk-integratedthermalemissionallowsthento (2) Pallas: Tedescoetal. (2002b) obtained from IRAS solve the energy equation for the asteroid’s effective size and data values of 498.07±18.8km and a geometric albedo of albedo(e.g.Harris&Lagerros2002).Thetrueilluminationand 0.1587±0.013. A combination of speckle, occultation and observinggeometriesaretakenintoaccountin theTPM calcu- lightcurveobservationsof(2)Pallasleadtoanellipsoidalshape lations.The surfaceroughnessis describedbythe r.m.s.values with dimensions of 574 ± 10 × 526 ± 3 × 501 ± 2 km and ofthesurfaceslopes(ρ)andthefractionofthesurfacecovered a mean diameter of 533 ± 6km (Dunhametal. 1990). A re- bycraters(f).Forthesurfaceroughness,aswellasforthether- centhigh-angularresolutionadaptiveopticsstudybyCarryetal. mal properties to calculate the heat conduction into lower lay- (2007)resultedinanabsoluteeffectivesizeof519.5km(semi- ers of the surface, we used “default properties” (ρ=0.7, f=0.6, major ellipsoidal axes values of 276×256×248km, ±10km). Γ=15Jm−2s−0.5K−1) as described by Mu¨lleretal. (1999). The Drummond&Christou (2008) found 494±57km based on an- emissivity models were taken from Mu¨ller&Lagerros (1998): othersetofAOobservations.Thevariousresultsshowthatthere a standard wavelength-dependent emissivity model for Ceres, are still significant uncertainties in the overall shape and size Pallas,adHygieaandaspecialoneforVestawhereloweremis- values,butthederivedeffectivesizesagreewithinthegivener- sivitiesinthesubmm/mmrangewerefound. rorbarswithourradiometricdiameter.Therefore,webelievethat TheTPM withthe “defaultthermalproperties”hasbeentested ouralbedoof0.142isthemostreliablevaluesofarpublishedfor and validated extensively in the context of ISO for large, Pallas. regolith-coveredmain-belt-asteroids(Mu¨ller&Lagerros2002). (4)Vestahasaverycomplexsurfacewithlargealbedovari- Itisworthtonoteherethatthesurfaceroughnessandheatcon- ations on the surface (Binzeletal. 1997). Our diameter value ductionpropertiesarelessimportantforourfar-IRanalysissince is about 4% larger than the effective diameter from HST ob- they mainly influence the mid-IR radiation at the Wien-partof servations (axes 289, 280, and 229 ± 5 km; D = 529.2km; eff thespectralenergydistribution(e.g.Mu¨ller2002,Figs.2&3). Thomasetal.(1997),noteaddedinproof)andabout7%larger Asteroid-specificmodelinputparametersandthecorresponding than the mean triaxial ellipsoid solution with 563±5×534± referencesarelistedinTbl.4. 5 × 442 ± 7km (2 · (a · b · c)1/3 = 510.3± 5.6km) given by OurderiveddiameterandalbedovaluesareshowninTbl.5. Drummond&Christou (2008). This is outside the given rms- The diametersare effective diametersof a sphere of equalvol- scatterfromour70measurementswhichmightbeanindication ume.Itcanbeconsideredasa“scalingfactor”forshapemodels that the special emissivity modelfor Vesta (Mu¨ller&Lagerros which lack the absolute size information. These values are the 1998) needs a small adjustment for this wavelength range. weightedmeanvalues,basedonthe photometricallymorereli- It looks like the emissivity drop which has been seen by able shortwavelength detectors(46.4 to 85.0µm). We also ex- Redmanetal. (1992, 1998) occurs already at shorter wave- 6 F.HormuthandT.G.Mu¨ller:CatalogueofISOLWSobservationsofasteroids Table4.ObjectspecificTPMinputparameters.Theλ andβ valuesaretheeclipticcoordinatesofthespinvectordirection,with ecl ecl β countedfromtheequator. ecl Object [H,G] P [h] λ ,β sourceofshape&spinvector sid ecl ecl (1)Ceres [3.28,0.05]1 9.074184 331.51◦,+77.88◦ HSTobservations4 (2)Pallas [4.13,0.16]2 7.813225 34.80◦,-11.75◦ Lightcurveinversiontechniques5,6 (4)Vesta [3.20,0.34]3 5.342129 319.45◦,+59.23◦ HSTobservations7 (10)Hygiea [5.43,0.07]2 27.623265 117.01◦,-28.53◦ Lightcurveinversiontechniques8 1 Lagerkvistetal. (1992); 2 Lagerkvistetal. (2001); 3 Mu¨ller&Lagerros (1998); 4 Thomasetal. (2005); 5 M. Kaasalainen, priv. comm. 22/Sep/2005;6Torppaetal.(2003);7Thomasetal.(1997);8M.Kaasalainen,priv.comm.31/Jan/2006; lengths below 50µm. Almost all LWS observations of Vesta tionsareconnectedtostructures(e.g.,theOlbersfeature)which were taken on one day (revolution 805) under very similar as- arevisibleintheHSTimagesof(4)Vesta(Binzeletal.1997). pectangles.ThismightalsoinfluencetheoutcomeoftheTPM Before we combined TPM lightcurve predictions with the technique which works best when combining data from differ- observedfluxes,weexploredtheinfluenceofTPMinputparam- entwavelengths,phaseangles,rotationalphasesandaspectan- etersonthethermallightcurveamplitudeandphaseforthegiven gles (Mu¨ller&Lagerros 2002). Shevchenko&Tedesco (2006) wavelength range and aspect angles. It turned out that neither derivedanalbedoofp =0.370fromoccultationmeasurements, the thermal inertia (the range between 0 and 50Jm−2s−0.5K−1 H whileweobtainedaradiometricvalueofp =0.32±0.02,again wasconsidered)northebeamingparameter,describingvarious V thisdiscrepancymightbeexplainedbyemissivityeffectsorthe roughnessscenarios,influencedthepredictionsforourcasesig- limited aspect angle range. The albedo value in Tbl. 5 agrees nificantly. The predicted lightcurve amplitudes varied between verywellwithpreviousstudiesbyMu¨ller&Lagerros(1998)(p 5−6% (peak-to-peak) and the lightcurve phases only by a few V = 0.33)based on a set of thermalobservationsfrom mid-IRto minutes between the low and high thermal inertia predictions. mm-wavelengths. Ourdatasetswerethereforenotsufficienttoconfineanyofthese Our result for (10) Hygiea deviates significantly from parameters. previous studies: Tedescoetal. (2002b) found values of The Vesta L02 observations from revolution 805 (28-Jan- 407.12±6.8km and pV=0.0717±0.002. Mu¨ller&Lagerros 1998) were taken over a period of about 6hours, covering (1998) gave 429.9km and 0.066. But Hygiea’s shape model slightlymorethanonefullrotationperiodof5.34hours.Onthe is not that well defined due to a poor lightcurve coverage basis of the shape and spin-vectorsolution given in Tbl. 4 and (in rotational phases) and some very low quality lightcurves the diameter and albedo results from Tbl. 5 we predicted the (Kaasalainen,priv.comm.).There mightalso be a secondpole thermallightcurvesattheL02key-wavelengthsfortheLWSob- solution at around λecl = 300◦ (instead of the 117◦ used here). servations(notethatthereferencetimeframeisthatoftheISO Butneitherusingthesecondpolesolutionsnorusingaspherical satelliteandnottheasteroid-intrinsicone). shape model lower the predicted size values (or the standard Figure 3 shows the observations at 102.3µm together with deviations) significantly. One possibility for the discrepancies themodelpredictiononanabsolutefluxandtimescale.Figure4 in the diameters could be emissivity issues. If Hygiea’s far-IR showsthecombineddatabelow105µm,firstnormalisedperde- emissivityislowerthenthecorrespondingdiameterwouldalso tector over the full observing period and then averaged for a be smaller (and the albedo a bit larger). But the data quality given rotational phase angle. The quality of the data from the and the very limited aspect angle range (all LWS observations longer wavelength channels beyond 105µm was not sufficient were taken within 20days) are not sufficient to draw firm con- forthiskindofanalysis. clusions.Especiallywhenlookingatthebestqualitydirectsize Both figures show that the observations follow the model measurementbyRagazzonietal.(2000):Theygaveaneffective predictions. The errorbars in Fig. 4 correspond to the error of diameter of 444±35km (with an axis-ratio of a/b=1.11),based the mean values plus a contribution from the flux uncertainty on speckle techniques. Our radiometric results are still well in these detectors. This figure combines in total 78 indepen- withintheseerrorbars. dentmeasurements(6detectors×13measurementsatdifferent rotational phases). The model predictions match the observed lightcurve amplitude as well as the lightcurve phase (in the 5.3.Far-IRthermallightcurveof(4)Vestaintherange observer’s time frame). We also indicated the rotational phase 45−105µm wheretheOlbers-feature(Zellneretal.1997;Binzeletal.1997) The visual lightcurve of (4) Vesta is dominated by the influ- on Vesta’s surface would be visible. We cannot see any influ- ence of the albedo variations (Degewijetal. 1979). Standard enceofthissurfacefeaturewithloweralbedo.Mu¨ller&Barnes lightcurve inversion techniques failed to produce a reliable (2007)presentedamoredetaileddiscussiononhowvariousther- shape model (Kaasalainen, priv. comm.), but high resolution malpropertiesofthissurfacefeaturewouldinfluencethethermal HST imaging allowed a solution for the shape and spin vector lightcurvevariationsatdifferentwavelengths.Theyfoundstrong (Thomasetal.1997).Redmanetal.(1992)foundthatthe1mm emissivity variations which they attributed to the Olbers struc- light-curveisapparentlydominatedbythetriaxialshape,with- ture and a neighbouring region. The deviation from the model out any significant contributionsfrom the optical albedo spots. predictionsatrotationalphasesbetween240−280◦inFig.4are Mu¨ller&Barnes(2007)showedthatatevenlongerwavelengths alsoclosetotheOlbersregionandmightthereforebethefar-IR (around3.2mm)themm-lightcurvefollowsforalargefraction signature of the ejecta material which is deposited on one side of the rotational period the shape-introduced variations. They ofthe Olbersimpactstructureasdiscussedin Mu¨ller&Barnes also demonstrated that the rotational phases with clear devia- (2007). F.HormuthandT.G.Mu¨ller:CatalogueofISOLWSobservationsofasteroids 7 nicelytheshape-introducedvariations.Albedoandgraineffects areimportantinthevisualandmm-lightcurves,butseemtoplay averysmallroleatfar-IRwavelengths. The catalogue of LWS observations of asteroids contains photometricandspectroscopicmeasurementsofthemainrepre- sentativesofthemainasteroidbelt.Thedatawillremainuseful forthermophysicalandmineralogicalstudiesofthesebodies,es- peciallyinthecontextoftheDawnspacemissiontoCeresand Vesta. Acknowledgements. WewouldliketothankTimGrundyandhiscolleaguesat RALforpreprocessingthenon-standarddata,andfortheexplanationsconcern- ingthepeculiaritiesoftheseobservations. LIA is a joint development of the ISO-LWS Instrument Team at Rutherford AppletonLaboratories(RAL,UK-thePIInstitute)andtheInfraredProcessing andAnalysisCentre(IPAC/Caltech,USA). TheISOSpectralAnalysisPackage(ISAP)isajointdevelopmentbytheLWS andSWSInstrumentTeamsandDataCenters.ContributinginstitutesareCESR, IAS,IPAC,MPE,RALandSRON. References Fig.3.Theobserved(dotswitherrorbars)andthepredictedther- Binzel,R.P.,Gaffey,M.J.,Thomas,P.C.,etal.1997,Icarus,128,95 mallightcurve(continuousline)of(4)Vestaat102.3µm(detec- Bowell,E.,Hapke,B.,Domingue,D.,etal.1989,inAsteroidsII(Universityof torLW1). ArizonaPress,Tucson),524–556 Carry,B.,Dumas,C.,Fulchignoni,M.,etal.2008,A&A,478,235 Carry, B., Kaasalainen, M., Dumas, C., et al. 2007, in AAS / Division for PlanetarySciencesMeetingAbstracts,Vol.39,#30.08 Clegg,P.E.,Ade,P.A.R.,Armand,C.,etal.1996,A&A,315,L38 Degewij,J.,Tedesco,E.F.,&Zellner,B.1979,Icarus,40,364 Dotto, E.,Barucci, M. A.,Mu¨ller, T.G., Storrs, A. D.,& Tanga, P.2002, in AsteroidsIII,ed.W.F.BottkeJr.,A.Cellino, P.Paolicchi, &R.P.Binzel, 219–234 Drummond,J.&Christou,J.2008,Icarus,197,480 Dunham,D.W.,Dunham,J.B.,Binzel,R.P.,etal.1990,AJ,99,1636 Gry, C., Swinyard, B., Harwood, A., & et al. 2003, The ISO Handbook: LWS–TheLongWavelengthSpectrometer,ESASP-1262(EuropeanSpace Agency) Harris,A.W.&Lagerros,J.S.V.2002,inAsteroidsIII,ed.W.F.BottkeJr., A.Cellino,P.Paolicchi,&R.P.Binzel(UniversityofArizonaPress,Tucson), 205–218 Henning,T.,Il’In,V.B.,Krivova,N.A.,Michel, B.,&Voshchinnikov, N.V. 1999,A&AS,136,405 Hormuth,F.&Mu¨ller,T.G.2006,CatalogueofLWSobservationsofasteroids, publishedonlineat: http://ida.esac.esa.int:8080/hpdp/technical reports/technote36.pdf Kaasalainen,M.,Mottola,S.,&Fulchignoni,M.2002,inAsteroidsIII,ed.W. F.BottkeJr.,A.Cellino,P.Paolicchi,&R.P.Binzel(UniversityofArizona Press,Tucson),139–150 Kessler,M.F.,Steinz,J.A.,Anderegg,M.E.,etal.1996,A&A,315,L27 Lagerkvist,C.-I.,Magnusson,P.,Williams,I.P.,etal.1992,A&AS,94,43 Lagerkvist, C. I., Piironen, J., & Erikson, A. 2001, Asteroid Photometric Fig.4. The observed (dots with error bars, normalised and av- Catalogue,FifthUpdate,UppsalaAstron.Obs. eraged over five detectors (SW1, SW2, SW3, SW4, SW5 and Lagerros,J.S.V.1996,A&A,310,1011 LW1)andthepredictedthermallightcurve(continuousline)of Lagerros,J.S.V.1997,A&A,325,1226 Lagerros,J.S.V.1998,A&A,332,1123 (4)Vestaasafunctionoftherotationalphase. Lloyd,C.2003,inTheCalibrationLegacyoftheISOMission,ed.L.Metcalfe, A.Salama,S.B.Peschke,&M.F.Kessler,ESASP-481,399 Marchis,F.,Kaasalainen,M.,Hom,E.F.Y.,etal.2006,Icarus,185,39 Millis,R.L.&Dunham,D.W.1989,inAsteroidsII,ed.R.P.Binzel,T.Gehrels, &M.S.Matthews,148–170 6. Conclusions Mu¨ller,T.G.2002,Meteoritics&PlanetaryScience,37,1919 Mu¨ller,T.G.2003,inExploitingtheISODataArchive-InfraredAstronomy Viaradiometrictechniqueswederivedthefirstfar-IR-baseddi- intheInternetAge,ed.C.Gry,S.B.Peschke,J.Matagne,P.Garc´ıa-Lario, ameter and albedo values for the four large asteroids Ceres, R.Lorente,A.Salama,&E.Verdugo,ESASP-511,47–54 Pallas, Vesta, and Hygiea. Based on photometry in the wave- Mu¨ller,T.G.,A´braha´m,P.,&Crovisier,J.2005,SpaceScienceReviews,119, length range 46–85µm we calculated effective diameters D 141 eff Mu¨ller,T.G.&Barnes,P.J.2007,A&A,467,737 of 960±17km, 534±15km, 549±13km, and 469±27km for Mu¨ller,T.G.&Lagerros,J.S.V.1998,A&A,338,340 these four objects. The corresponding albedo values pV are Mu¨ller,T.G.&Lagerros,J.S.V.2002,A&A,381,324 0.096±0.003,0.142±0.009,0.317±0.015,and0.056±0.006,re- Mu¨ller,T.G.,Lagerros,J.S.V.,Burgdorf,M.,etal.1999,inTheUniverseas spectively.We foundexcellentagreementwith direct measure- SeenbyISO,ed.P.Cox&M.F.Kessler,Vol.ESA-SP427,141–144 ments fromHST (Ceres and Vesta) and speckle/occultationre- Ragazzoni,R.,Baruffolo,A.,Marchetti,E.,etal.2000,A&A,354,315 Redman,R.O.,Feldman,P.A.,&Matthews,H.E.1998,AJ,116,1478 sults (Pallas and Hygiea). Our data contain also the first far- Redman,R.O.,Feldman,P.A.,Matthews,H.E.,Halliday,I.,&Creutzberg,F. IRlightcurveof anasteroid:Vesta’sthermallightcurvefollows 1992,AJ,104,405 8 F.HormuthandT.G.Mu¨ller:CatalogueofISOLWSobservationsofasteroids Salisbury, J. W. 1993, in Remote Geochemical Analysis: Elemental and MineralogicalComposition,ed.C.M.Pieters&P.A.J.Englert(Cambridge UniversityPress,NewYork),79–98 Shevchenko,V.G.&Tedesco,E.F.2006,Icarus,184,211 Tedesco,E.F.,Egan,M.P.,&Price,S.D.2002a,AJ,124,583 Tedesco,E.F.,Noah,P.V.,Noah,M.,&Price,S.D.2002b,AJ,123,1056 Thomas,P.C.,Binzel,R.P.,Gaffey,M.J.,etal.1997,Icarus,128,88 Thomas,P.C.,Parker,J.W.,McFadden,L.A.,etal.2005,Nature,437,224 Torppa,J.,Kaasalainen,M.,Michalowski,T.,etal.2003,Icarus,164,346 Zellner,B.H.,Albrecht,R.,Binzel,R.P.,etal.1997,Icarus,128,83 F.HormuthandT.G.Mu¨ller:CatalogueofISOLWSobservationsofasteroids 9 Table1. OverviewofstandardLWSasteroidobservationsinourcatalogue.Fortheon-sourcepointingsthedistancetotheasteroid∆,theSun- asteroiddistancer,andthephaseangleαaregiven,basedonMPC(MinorPlanetCenter)ephemerides.TheTDTnumberisauniqueidentifer, allowingtofindtheobservationinthearchive. Object TDT Mid-observationUTC AOT ∆[AU] r[AU] α[◦] Remarks (1) Ceres 09300401 1996-02-18 04:31:18 L02 2.673 2.695 21.2 09304102 1996-02-18 15:15:23 L02 (off-sourcereferencemeasurementforTDT09300401) 10500402 1996-03-01 05:22:22 L02 2.520 2.705 21.5 11900214 1996-03-15 02:42:57 L02 2.344 2.715 21.1 11905611 1996-03-15 16:54:46 L02 (off-sourcereferencemeasurementforTDT11900214) 12600114 1996-03-22 02:03:54 L02 2.258 2.721 20.5 25800302 1996-07-31 19:30:27 L02 2.258 2.823 19.2 25805903 1996-08-01 08:55:54 L02 (off-sourcereferencemeasurementforTDT25800302) 26500301 1996-08-07 19:10:27 L02 2.351 2.828 20.0 26505602 1996-08-08 09:32:38 L02 (off-sourcereferencemeasurementforTDT26500301) 32100204 1996-10-02 15:31:35 L02 3.126 2.868 18.6 32103506 1996-10-03 03:52:44 L02 (off-sourcereferencemeasurementforTDT32100204) 53802209 1997-05-07 12:16:09 L02 3.112 2.971 18.9 57902409 1997-06-17 09:56:26 L02 2.575 2.978 19.4 59401908 1997-07-02 06:42:05 L02 2.391 2.980 17.9 72001901 1997-11-05 01:10:04 L02 2.522 2.973 18.6 74803304 1997-12-03 03:04:58 L02 2.901 2.966 19.3 74803403 1997-12-03 08:11:59 L01 2.904 2.966 19.3 containswarmupartefacts 75502902 1997-12-10 00:30:08 L01 (off-sourcereferencemeasurementforTDTs74803...) 75503003 1997-12-10 01:38:00 L02 2.994 2.964 19.0 76200502 1997-12-16 13:29:15 L02 3.081 2.962 18.6 76903102 1997-12-24 01:08:50 L02 3.177 2.960 18.0 76903203 1997-12-24 02:17:12 L01 3.178 2.960 18.0 (2) Pallas 23000306 1996-07-03 21:24:01 L02 2.497 2.823 20.9 23002907 1996-07-04 12:01:22 L02 (off-sourcereferencemeasurementforTDT23000306) 25100202 1996-07-24 19:49:12 L02 2.780 2.871 20.6 25103603 1996-07-25 09:58:26 L02 (off-sourcereferencemeasurementforTDT25100202) 26500503 1996-08-07 19:43:17 L02 2.967 2.903 19.9 26505204 1996-08-08 07:27:57 L02 (off-sourcereferencemeasurementforTDT26500503) 27200203 1996-08-14 18:19:41 L02 3.057 2.919 19.3 27202004 1996-08-15 03:27:01 L02 (off-sourcereferencemeasurementforTDT27200203) (4) Vesta 24402202 1996-07-17 23:20:20 L02 1.593 2.149 26.6 24404603 1996-07-18 06:29:49 L02 (off-sourcereferencemeasurementforTDT24402202) 80500101 1998-01-28 10:36:25 L02 2.566 2.549 22.2 80500104 1998-01-28 11:02:50 L02 2.566 2.549 22.2 80500107 1998-01-28 11:29:15 L02 2.567 2.549 22.2 80500110 1998-01-28 11:55:40 L02 2.567 2.549 22.2 80500113 1998-01-28 12:22:05 L02 2.567 2.549 22.2 80500116 1998-01-28 12:48:30 L02 2.567 2.549 22.2 80500119 1998-01-28 13:14:55 L02 2.568 2.549 22.2 80500122 1998-01-28 13:41:20 L02 2.568 2.549 22.2 80500125 1998-01-28 14:07:45 L02 2.568 2.549 22.2 80500128 1998-01-28 14:34:10 L02 2.568 2.549 22.2 80500131 1998-01-28 15:00:35 L02 2.569 2.549 22.2 80500134 1998-01-28 15:27:00 L02 2.569 2.549 22.2 80500137 1998-01-28 15:53:25 L02 2.569 2.549 22.2 (10) Hygiea 83201702 1998-02-24 22:08:03 L01 3.179 3.444 16.6 CIIbackgroundemission 83201803 1998-02-24 22:44:05 L02 3.179 3.444 16.6 84801302 1998-03-12 16:13:06 L02 3.402 3.434 16.7 85303402 1998-03-17 16:09:46 L02 3.472 3.430 16.6 10 F.HormuthandT.G.Mu¨ller:CatalogueofISOLWSobservationsofasteroids Table2. OverviewofL99asteroidobservationsinourcatalogue.AllobservationsareL01-likescanscoveringthefullwavelengthrange. Object TDT Mid-observationUTC ∆[AU] r[AU] α[◦] Remarks (1) Ceres 07500601 1996-01-31 07:52:11 2.891 2.682 19.9 CIIbackgroundemission 07500701 1996-01-31 10:10:56 2.890 2.682 19.9 CIIbackgroundemission 07501301 1996-01-31 16:08:13 2.887 2.682 19.9 CIIbackgroundemission, non-standardbiasvoltages 07501401 1996-01-31 18:32:03 2.886 2.682 20.0 CIIbackgroundemission, non-standardbiasvoltages (4) Vesta 05500201 1996-01-11 07:10:35 2.313 2.250 24.8 non-standardbiasvoltages 05500301 1996-01-11 08:54:29 2.312 2.250 24.9 non-standardbiasvoltages 05500401 1996-01-11 10:39:34 2.311 2.250 24.9 non-standardbiasvoltages

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