1996AJ 111.1748F r f r THE ASTRONOMICALJOURNAL this photometricschemeistheABsystemofOke&Gunn for theSloanDigitalSkySurvey(SDSS).Thezeropointof passband centeredat6250Âwith awidth1400Â,Visfar band centeredat4800Àwithawidthof1400Â,r'isthered bands. ThefivefiltercurvesaredisplayedinFig.1. z) thatdividetheentirerangefromatmosphericultra- be publishedinlate1997. To improvetheaccuracyoftransformations,weintro- immediate conversionfrommagnitudestophysicalfluxes. duce animprovedabsolutecalibration,whichwedesignate a fullwidthathalfmaximumof600A,gisblue-green filters havethefollowingproperties:upeaksat3500Awith CCDs at11000Âintofiveessentiallynonoverlappingpass violet cutoffat3000Âtothesensitivitylimitofsilicon in anticipationofsurveydata.Observationsthesecondary as AB.Thispaperisprimarilyintendedtofacilitatework [email protected] standard starsfortheSDSSsystembeganinspringof (1983, hereafterreferredtoasOG);thisconventionallows Yukawa Institute,KyotoUniversity, Kyoto 606,Japan;Electronicmail: 1996; alistofSDSSstandardstarsandtheirmagnitudeswill 1748 Astron.J.Ill(4),April1996 v 95 This paperdescribesthephotometricsystemtobeused The systemcomprisesfivecolorbands\r',and © American Astronomical Society • Provided by theNASA Astrophysics Data System f wide-band CCDsystemwithwavelengthcoveragefrom3000to11000Â.Thezeropointswillbebased This paperdescribestheSloanDigitalSkySurveyphotometricsystem,anewfive-color(ug'riz) is presentedinthispaper.©1996AmericanAstronomicalSociety. on anupdatedversionofthespectrophotometricAR,,system.Thiscalibration,designatedasA#, 95 1. INTRODUCTION Department ofAstronomy,PennsylvaniaStateUniversity,UniversityPark,16802 THE SLOANDIGITALSKYSURVEYPHOTOMETRICSYSTEM Electronic mail:[email protected];[email protected] Kiso Observatory,UniversityofTokyo,Kiso-gun,Nagano397-01,Japan Department ofAstronomy,UniversityTokyo,Tokyo113,Japan Princeton UniversityObservatory,Princeton,NewJersey08544 Institute forAdvancedStudy,Princeton,NewJersey08540 Received 1995September11;revisedDecember20 Electronic mail:[email protected] Electronic mail:[email protected] Electronic mail:[email protected] Electronic mail:[email protected] M. DoiANDK.Shimasaku 0004-6256/96/111 (4)/1748/9/$6.00 VOLUME 111,NUMBER4 1 D. P.Schneider M. Fukugita T. Ichikawa ABSTRACT J. E.Gunn red filtercenteredat7700Âwithawidthof1500À,andz' most salientfeatureoftheSDSSphotometricsystemis Thuan &Gunn(TG)photometricsystem(Thuan wavelengths isdeterminedbytheCCDsensitivity. is anear-infraredpassbandcenteredat9100Àwithwidth passband isdefinedbytheglass onbothsidesanditismuch bands; inthissituationcautionmustbeexercisedtheiruse. however, thatthelargewidthscanintroducesignificantflat- that ofthestandardJohnson-Morgan-Cousinssystem very widebandpassesused,evensignificantlywiderthan of 1200Â;theshapez'responsefunctionatlong cutoff long-passglassfilterontowhichiscoatedashort-pass CCDs usedin“staring”modetheredandnear-infrared cover theentireaccessibleopticalwavelengthrange.Pro- system issubstantiallydifferentfromtheTGbands.The narrower thantheothers)and the z'filter(nolongwave- with fairlysharpedges.Theexceptionsaretheu’filter(the interference film,andthusexhibitwideplateausterminated fielding problems,especiallywitholderback-illuminated exclude thestrongestnight-sky linesofOIX5577andHgI length cutoff).Thedivisionof the passbandsisdesignedto spective usersofthesystemforotherpurposesshouldnote, sure highefficiencyforfaintobjectdetectionandessentially (Johnson &Morgan1953;Cousins1978).Thesefiltersen- 1976; Wadeetal1979;Schneideral.1983),theSDSS While thenamesofthesebandsaresimilartothose The filterresponsesareingeneraldeterminedbyasharp- © 1996Am.Astron. Soc.1748 APRIL 1996 1996AJ 111.1748F r r f Fig. 1.Transmissionofthew'gVTVfilters.Redleaksshortward11000 UV-coated SITeCCD;thisisthedetectorthatusedindefinitionof  arenotshown.Thedottedcurveisthequantumefficiencyofathinned, 1749 FUKUGITAETAL.:SLOANDIGITALSKYSURVEY clearly indicatesthatthisistobepreferredawiderband the bulkofresponseisshortwardBaimerdiscon- SDSS system. Apache PointObservatory.Thedetectorisathinned,back- the SDSS“MonitorTelescope,”a60cmreflectorlocatedat with dilutionbyredderlight. lower totalthroughput.Properconsiderationofphotonnoise with g)tothemagnitudeofBalmerjumpatcost tinuity; thisproducesamuchhighersensitivity(combining AB systemisamonochromatic(jfJfirstintroduced from ScientificImagingTechnologies,Inc.(SITe).Inthesur- illuminated, UV-antireflection-coatedCCDdeviceprocured X5460, asisthecasewithTGphotometricsystem.The AB. Thissystemwaswidelyusedinthespectrophotomet- the g,r',andiwithnormalvisual-bandantireflection- vey camera,theufiltersareusedinconjunctionwith u' bandresponseissimilartoTGuandStrömgreninthat points onthespectrophotometricABmagnitudesystem.The coated thinneddevices,andthez'filterswiththick,front- by Okein1969withaprovisionalcalibration,designated illuminated CCDs. same UV-coatedchipsasisusedintheMonitorTelescope, presented byOGasthesystemAB.In ric communityinthe1970s;animprovedcalibrationwas large Balmerdiscontinuity.The moderatelyflatSEDsand these cool,metal-deficientstarsaremuchsimplerthanthose SDSS photometricsystemistheattempttoplacezero of Adwarfswiththeirverystrong, wideBalmerlinesand defining monochromaticmagnitudestandards.Thespectraof absolute fluxofthecontinuumaLyr,aretakenas subdwarfs BD+17°4708,BD+26°2606,HD19445,and spectrophotometric energydistributions(SEDs)ofthefourF tails oftheshapesystemresponse functions. weak linesoftheFsubdwarfs alsominimizetheerrorsof 84937, theabsolutefluxesofwhicharecalibratedagainst synthetic magnitudesthatarise from uncertaintiesinthede- 69 19 The SDSSsystemwillbedefinedbyobservationswith A novel(andtoourmind,longoverdue)featureofthe The greatadvantage oftheABmagnitudesystem isthat © American Astronomical Society • Provided by theNASA Astrophysics Data System 4 4 AB. the magnitudeisdirectlyrelatedtophysicalunits;OGde- fined themagnitudeby ferred toasH85;Castelli&Kurucz1994).TheSEDsofthe where fisthefluxperunitfrequencyfromobject,so Lyr fluxandthefourOGsubdwarfs;wecallnewsystem four subdwarfstandardsusingthebestmodemdataofa In thispaperweupdateAß79byrecalibratingthefluxof four A5subdwarfshavealsobeenrevisedbyOke(1990). improving theSEDofaLyr(seeHayes1985,hereafterre- Since theworkofOG,muchefforthasbeenexpendedin The filtersaremadefromoneortwoSchottcolorglassele- ments togetherwithamultilayerinterferencefilmcoatingon presses theredleakinglassfilters6700-7400 the shortside,withaninterferencefilmcoatingthatsup- cuts offthelong-wavelengthside,andBG38,which region; withoutthecoating,onewouldexpectamaximum one glass-airsurface. between 6650and8000À,sothatthenetmaximumleakage factor (^IXIO)ataround7100Â,andbya^100 transmission ofabout7%inanarrowregionaround7000Á. The coatingisdevisedtosuppresstheleakagebyalarge 95 ters, andalargeredleakappearsatwavelengthslongerthan There arenosatisfactoryredblockingglassesforthesefil- coatings whichcutoffat7000and8500Â,respectively. RG695 glasses,incombinationwithshort-passinterference but isquitetransparentinthepassband. extra BG38glasselement,whichblocksthefilterinred 5500 Â.Thiscoatingismadesimplerbytheinclusionofan ment, andashort-passinterferencecoatingthatcutsoffat ing alsoimpairsthetransmissioninpassbandslightly. and 10000Âwhencombinedwithcolorglasses.Thiscoat- does notexceed3X10~forallwavelengthsbetween6000 below. little responseatthesewavelengths thattheerrorsintroduced RG830, andthe long-wavelengthsideisopen, sothere- are verysmall.Wediscussthe performanceinmoredetail v 79 11 000Âforr'andbutordinary siliconCCDshaveso 1 1 1 -21 f f f filter glasscoating g 2mmGG400+3mmBG38short-passcoatingcutoffat5500 u' 1mmUGll+BG383mmquartzcoatingthatsuppresses6600-8200 i' 4mmRG695+1mmBK7short-passcoatingcutoffat8500 r 4mmOG550-f1mmBK7short-passcoatingcutoffat7000 z 4mmRG830+1mmBK7 /„(Jy)=3631 dex(—0.4AZU(2) AS„=-2.5 log/„(ergss~'cmHz)—48.60,(1) The ufilterismadeofacombinationUGll,which The physicalcompositionofthefiltersisgiveninTable1. The g'filterisconstructedofGG400,thelong-passele- The rand/'filtersconsistoflong-passOG550 For thezband,short-wavelength sideisdefinedby Table 1.ElementsofSDSSfilters. 2. RESPONSEFUNCTIONS 2.7 Filters 1749 1996AJ 111.1748F Fig. 2.ResponsefunctionoftheSDSSphotometricsystem,usingaUV- brought to5mmthicknessbyaddinganeutralglasselement ing atmospherictransmissionat1.2airmassesthealtitudeofApachePoint coated thinnedCCD.Dashedcurvesindicatetheresponsefunctioninclud- Observatory. peak. Forallthefilters,redleaksaresuppressedtotransmis- Extinction intheatmospheric0 andwatervaporiscalcu- tude ofApachePointObservatory(2800m),arealsoshown. mospheric extinctionat1.2airmasses,basedonthestandard tivities oftwoaluminiumsurfaces(Hass1965;seealso response curvesincludethefiltertransmission,quantum tended foruseintheMonitorTelescope)atatemperatureof À, theeffectivecutoffofCCDresponsefunction. kyo. Highpeaktransmission(over95%forr'/Vandmore Ltd., Tokyo.Themanufacturedfiltertransmissioncurvesare ing beamofaMonitorTelescopecamera.Ofcourse,this lated withasquare-rootlaw.Machine-readable versionsof Palomar monochromaticextinctiontablesscaledtothealti- efficiency forthethinned,UV-coatedCCD,andreflec- measurements at180Kfor14discretewavelengths.The constructed bymodulatingtheroom-temperaturequantum ings. Fortheu'band,weobtain78%transmissionatits than 90%forg')isattainedwithefficientantireflectioncoat- does notinduceanyeffectonthedefinedpassbands. sponse isessentiallydefinedbytheCCD.Thesefiltersare all responsecurvescanbeobtained bycontactingthefirst Shiles etal.1980;Magrath1994).Thecurvesincludingat- efficiency isflatat60%for4000-7000Â;30% efficiency curvemeasuredatSITesothatitreproducedour shown inFig.1,asmeasuredwithaShimadzuUV-3100PC same opticaldepthandcanbeincorporatedintotheconverg- airmass) andwithout atmosphericextinction,are tabulatedin author. attained intheultravioletregion. SITe CCDwithaUVantireflectioncoating(thechipin- sion levelsof^0.1%forwavelengthsshortward10500 spectrometer atNationalAstronomicalObservatoryinTo- (BK7 orquartz),sothatallfiltershaveapproximatelythe 1750 180 Kisalsodepictedinthesamefigure.Thiscurvewas 2 The quantumefficiencyofathinnedback-illuminated The interferencecoatingsareappliedbyAsahiSpectra The systemresponsefunctionsareshowninFig.2. The effectivewavelengthsfor each filter,bothwith(1.2 © American Astronomical Society • Provided by theNASA Astrophysics Data System FUKUGITA ETAL:SLOANDIGITALSKYSURVEY lists theeffectivewavelengthasdefinedbySchneideretal. frequency-weighted average(writtenascandthethird Table 2(thosefortheJohnson-Morgan-Cousinssystemare tional widthsofthefiltersor,definedas S’,, isthesystemquantumefficiency;thisincludesatmo- frequency areconsistentwitheachother.)Hereandbelow, which isinsomesensehalfwaybetweenaneffectivewave- wavelength-weighted average,thesecondcontains the effectivewavelengthsofSDSSfiltersasdefinedby effective wavelengthcannotbeuniquelydefined;wepresent length andaneffectivefrequency.(Thisdefinitionhasthe also listedforcomparison).Inanyfilteroffinitewidth,the attractive featurethat\andthesimilarlydefinedeffective (1983): several extantconventions.Thefirstrowgivesthe fective wavelengthto spectral slopechanges: The formerisusefulincalculating thesensitivityofef- and thefluxsensitivityquantityQ,definedas spheric absorption.InTable2wealsopresentthermsfrac- <5\= \ffA8n, where nisthelocalpower-law indexofthe eff Note —1)effectivewavelength.2)inverseoffrequency. cffc Table 2c.Johnson-Morgan-Cousinssystem Table 2b.Thesameas(a),butwithoutatmosphericextinction Table 2a.CharacteristicsoftheSDSSphotometricsystem(1.2airmass) \ff=exp cr= e 4 4 5 5 3) 2) 1} 5) 3) 2) 1 6) 4 5 3) 2) 15 6) fluxsensitivityquantitydefinedbyeq.(5). 5) FWHMofaneffectiveGaussianbandpassderivedfroma. 3) definedbyeq.(3).4)fractionalbandwidtheq.(4). a) (Â) FWHM (À) AA> (Â) Aff (Â) Aeff (Â) Aeff (À) Q Aff (Â) Q6) Aeff (Â) Aeff* (Á) Q <7> AA> (Â) FWHM (Â) Aeff (Â) Aff (Â) Aeff (Â) e e e 2 /d(ln v)S„[ln(\/\)] eff /d(ln v)SlnX v Mlnv)5„ /0.5]0.000[(u'/)1.3] 0r iziz 0gr gr irQk Z Qug ug 0.093 [(r'-¿')<0.5]0.399[(u'g')1.3]0.0900.013-0.032 0.091 [(r'-ï)>0.5]0.360[(u'g')1.3] K KggrKiKz © American Astronomical Society • Provided by theNASA Astrophysics Data System k kugkgr^ri T Table 3.Calculatedatmosphericextinctioncoefficients. 08 /¿(logv)S v 2.2 AtmosphericExtinction /¿(log y)/X 48.60, (7) As (b),butforBD+26°2606. Fig. 3.(a)OffsetoftheSEDaLyrbetweenAB(=H85)and racy ofbetterthanabout0.02magoverawidecolorrange. tory. Themagnitudeofthesecond-ordercolorterms tion tablesscaledtothealtitudeofApachePointObserva- ficients usingthestandardPalomarmonochromaticextinc- observed magnitude,andZistheairmass. values correctedforextinctionandthosewithoutsuffixesthe where themagnitudesandcolorindiceswithsuffix0denote indicates thattheycannotbeignoredifonedesiresanaccu- (=OG). (b)OffsetofABcalibrationagainstforBD+17°4708.(c) pose, seemideal.Theyhavereasonablyflatspectra,andthe all extinction-freemagnitudes.Weomitthesubscript0for tures. SinceabsolutecalibrationworkhascenteredonaLyr most metal-deficientoneshaveveryweakabsorptionfea- which hadalreadybeeninuseforsomeyearsthispur- faint enoughtobeusedwithlargetelescopes.Fsubdwarfs, the calibrationofoldersystembutlargelytopresentaset better fittotheKuruczmodelatmosphere, andinterpolating of well-calibratedsecondarystandardswithsimplespectra simplicity ofnotations. measured byOke &Schild(1970)(Oke Schild’s zero in thedifficultregionnear4000 Âusingdatafromveryhot the relativeSEDofaLyr,modified slightlybydemandinga absolute fluxesofaLyrinthecontinuum. absolute calibrationofthesestarsbycalibratingagainstthe (there arenobrightFsubdwarfs),itisnecessarytoobtainthe subdwarfs. Theynormalizedthe SEDat5480Áwiththeflux 957 951 The magnitudeswediscussinthefollowingsectionsare Table 3givestheexpectedvaluesforextinctioncoef- The ABsystemwasintroducedbyOGpartlytorefine OG usedthecompilationofHayes &Latham(1975)for 19 3. THEABMAGNITUDESYSTEM 95 3.1 Definition 1751 1996AJ 111.1748F -9 -21 2 2 relative fluxdistribution.Themostrecentcompilationofthe nition giveninEq.(1). point at5480Âappearstohaveanerrorintheinterpolation made oftheaLyrSED,bothforabsolutefluxand to V=0.03atthisspecificwavelength.Thisledthedefi- than wouldactuallybeobtainedfromtheOke-SchildSED). of theSED;theirvalueisclosertoHayes&Latham’s OG definedtheABmagnitudesothatthisfluxcorresponds chen region.H85alsoupdatedtheabsoluteflux;hisbest discrepancies intheBaimerabsorptionlinesandPas- on adetailedstellaratmospherecalculation,exceptforsmall agrees verywellwiththatofCastelli&Kurucz(1994)based estimate ofthefluxat5556Âis/=3.44±0.05X10 Latham’s (1975)valueand2.4%largerthanthatfoundby ergs cmsÂ,whichis1.5%largerthanHayes& 1752 FUKUGITAETAL.-.SLOANDIGITALSKYSURVEY a LyrSEDisgivenbyH85.TherelativeH85 of theH85SED,fluxat5480Áis Oke &Schild.HereweadoptthevalueofH85.Withuse broad bandcolorsasshowninTable4.WhiletheSEDitself that ofOGisshowninFig.3;thisleadstooffsetsthe the ABcalibration.TheoffsetbetweenHayesSEDand This valueis1.6%(0.018mag)largerthanthezeropointof the broadbandcolorscancelouttoaverylargeextentupon magnitude andabsorbthechangesinzeropointsfor integration overtheband,andneteffectisrathersmall. suffers fromsignificantchangesAB,thein Morgan VmagnitudeofaLyriscalculatedtobe calibrating SEDs.Withourrevision,wethenhaveAB AB system.Theyalsomeasured fluxesoftheotherthree Lyr; whileitwouldbedesirabletodefinethezeropointof x between ABandabsolutefluxes.Uncertaintiesinthere- the ABsystemsuchthatsyntheticVmagnitudehadno within 0.01magofthemeasuredVmagnitude(0.03)a Straizys (1969,hereafterreferredtoasAS69).(Notethatthe that itisbettertoretaintheoriginaldefinitionofrelation offset withrespecttotheobservationalVsystem,wefeel absorption linesinthiscolorband.)Thissyntheticvalueis SED ofaLyr,sincethestardoesnotcontainanystrong V£=0.19, usingtheresponsefunctionsofAzusienis& any attempttodoverymuchbettersuspect,andweleaveit tive toaLyr,andtabulatedthe fluxoftheformeron Here andhereafterwerefertothemagnitude calculatedbyintegratingthe as itis. sponse functionandobservationalerrorsinanycasemake V magnitudecanbecalculatedfairlyaccuratelyfromthe =0.012 foraLyrat5480Á.ThebroadbandJohnson- 19 SED withthefilter response functionassyntheticmagnitude. 19 79 A -201 -0.004 -0.000-0.0070.020-0.0090.001-0.0050.000 Table 4.OffsetofthebroadbandmagnitudeAB-ABforaLyr. 9579 /=3.59X 10ergscmHz(9) Since theworkofOG,anumberstudieshavebeen Au' Ag'Ar'Ai'Az'AUABAVARcAie We havedecidedtoretainthedefinition(1)forAB V OG havemeasuredthebrightness ofBD+17°4708rela- © American Astronomical Society • Provided by theNASA Astrophysics Data System have recalibratedthefluxesusingH85SEDforaLyr. This isessentiallythesystemproposedforABexcepta SED ofthesefoursubdwarfsandupdatedtheirfluxes.We the SEDofBD+17°4708(andotherthreesubdwarfstan- small zero-pointshift,whichwediscussinthenextsection. 84937 relativetoBD+17°4708.Oke(1990)remeasuredthe subdwarf standards,BD+26°2606,HD19445,and dards) relativetothatofaLyr,(3)errorsintheshapes response functions,and(4)theabsolutefluxnormalizationof (1) errorsinthemeasuredrelativeSEDofaLyr,(2) Note -ObservedmagnitudesaretakenfromMermilliod(1991),andtheerrorsdispersion For (2),Oke(1990)quotes0.02mag.H85estimatestheerror from acomparisonofH85withCastelli&Kurucz(1994). Morgan photometricbands:seeAS69;Buser1978),theover- of (4)tobe0.015mag.Ifanaccuracy0.02magis achieved for(3)(thisisthelevelJohnson- magnitudes withthesyntheticforfoursub- error. (except forthez'bandwhichfallsinPaschenregion) a Lyr.Theerrorarisingfrom(1)isprobablyabout0.01mag tion ofMermilliod(1991).Allfourstarshavebeenmeasured dwarfs (seeTable5).Thedataaretakenfromthecompila- all errorwillbeabout0.03magincludingthenormalization 95 band. SimilaroffsetswerealreadynotedbyOke(1990).The expected, thereseemstobeasystematicoffsetof0.04mag analysis). Whilethiserrorisroughlyconsistentwithwhat the syntheticandobservedmagnitudeisalsoseeninB servations. Theresultis(AV)_=-0.041 by 0.04magatallwavelengths(wehaveweightedtheV niques; OGwereforcedtogothroughonelevelofinterme- to thefaintstandardswithphotoelectricpulse-countingtech- origin ofthissystematicerrorisunknown,butlikelyas- to dealwiththeproblembymakingsubdwarfsallfainter diate standardstotiethetwotogether.Wehavechosenhere pendent, butweareencouraged bythegoodagreementbe- case likelytobebetween0.03and0.04).Wedonot,of sociated withthedifficultyoftyingastarasbrightLyr (synthetic magnitudeisbrighter).Asimilaroffsetbetween course, knowindetailthatthe errorisnotwavelengthde- offsets moreheavilythantheBones,butoffsetisinany 10-20 times,andMermilliodliststheaverageoftheseob- tween theBandVoffsets.We note parentheticallythatitis ±0.005 (Notethattheerrorfrom(4)doesnotcomeintothis of greatimportancetoattempt tomeasuretheratioof flux ofBD+17°4708tothat aLyrwithtrulylinear system atavariety ofwavelengthsassoon possible. syntheticobserved Table 5.Comparisonofobservedandsynthesizedmagnitudesforthe four dwarfs. The errorsinthepresentABmagnitudesystemarisefrom For verificationwehavecomparedobservedVandB BD+17°4708 9.470±0.0119.430.049.912±0.0159.880.03 HD84937 8.322±0.0228.290.038.714±0.0288.68 HD19445 8.057±0.0198.010.058.515±0.0218.480.03 BD±26°2606 9.732±0.0089.690.0410.157±0.00910.140.02 among many(11-20)measurements. 3.2 AccuracyoftheABMagnitudeZeroPoint Fobs .FAV£BAB 9ynobssyn 1752 1996AJ 111.1748F 1753 FUKUGITAETAL.:SLOANDIGITALSKYSURVEY AB isgiveninFigs.3(b)and 3(c)forBD+17°4708and Values obtainedbylinearinterpolation arelistedwhendata BD+26°2606. Thesystematicoffset discussedabovegivesa this theABcalibration.Thedifference betweenABand dominant contribution tothedifference. are notavailableatthespecified wavelength.Wedesignate shift ispresentedinTable6,togetherwiththatforaLyr. 19 95 95 The resultingcalibrationincorporatingthiszero-point Table 6.UpdatedcalibrationofthefourFsubdwarfsandaLyr. 3320 1.19410.759 3240 1.23510.853 3160 1.25110.927 3560 1.11610.572 3400 1.16310.698 3080 1.28311.015 3755 0.78310.299 3723 0.98810.412 3720 0.99410.433 3715 1.00410.428 3713 1.00910.430 3705 1.02610.438 3680 1.05010.457 3640 1.08010.511 3607 1.09910.540 3594 1.10410.541 3480 1.14910.648 4340 0.0319.906 4300 -0.1359.865 3840 0.21910.170 3782 0.59210.210 3777 0.63010.190 3759 0.75410.279 3741 0.87610.378 3736 0.90910.388 3726 0.97710.407 4380 -0.1299.753 4365 -0.0599.758 3880 0.03010.133 3866 0.07410.034 3860 0.1049.964 3822 0.33810.182 3814 0.38310.082 3800 0.46610.174 10820 0.6959.250 10260 0.6099.238 4820 -0.0419.624 4800 -0.1009.608 4760 -0.1139.620 4560 -0.1459.692 4400 -0.1969.731 4270 -0.2219.784 4020 -0.2609.851 4000 -0.1809.911 3960 -0.01110.139 3953 -0.02210.008 3947 -0.03610.028 3920 -0.07410.138 3911 -0.0289.966 3905 0.0049.994 11140 0.7369.246 4960 -0.0799.567 4900 -0.0159.587 4860 0.1249.730 4260 -0.2299.794 4240 -0.2409.786 4200 -0.2449.796 4160 -0.2469.818 4140 -0.1949.817 4120 -0.0919.826 4100 -0.0039.966 4080 -0.1049.864 4060 -0.2229.833 3993 -0.1299.880 3980 -0.02810.111 4920 -0.0729.585 5240 -0.0239.497 5120 -0.0459.526 5000 -0.0709.556 5760 0.0709.397 5560 0.0289.427 5400 -0.0039.453 6020 0.1319.373 6540 0.3679.371 6500 0.2209.330 6460 0.2049.321 6420 0.1949.325 6560 0.4239.450 6700 0.2399.299 6660 0.2339.305 6620 0.2459.330 6580 0.4199.369 8380 0.5179.226 8100 0.4639.233 7780 0.4259.254 7460 0.3719.255 7100 0.3109.270 6780 0.2509.290 6740 0.2429.294 9940 0.6349.307 9700 0.5159.225 9300 0.4959.226 8780 0.4619.226 © American Astronomical Society • Provided by theNASA Astrophysics Data System A aLyrBD+17°4708BD+26°2606HD19445HD84937 11.127 9.4469.665 11.215 9.5369.737 10.853 9.1509.417 10.901 9.2039.457 10.976 9.2739.521 11.053 9.3659.597 10.722 9.0039.293 10.750 9.0409.320 10.751 9.0419.321 10.786 9.0759.346 10.642 8.9579.197 10.657 8.9279.217 10.675 8.9509.248 10.352 8.6928.842 10.405 8.7428.948 10.460 8.7608.930 10.470 8.7808.940 10.539 8.8549.049 10.549 8.8749.074 10.628 8.8939.153 10.638 8.9039.163 10.637 8.9579.187 10.658 8.9269.212 10.656 8.9259.212 10.663 8.9529.226 10.256 8.6068.746 10.371 8.7178.888 10.274 8.6148.739 10.244 8.6198.744 10.406 8.7578.923 10.392 8.7128.872 10.095 8.4698.637 10.337 8.7098.862 10.309 8.7198.832 10.239 8.6018.696 10.010 8.3358.561 10.008 8.3388.538 10.176 8.5208.728 10.115 8.4538.613 10.137 8.4818.621 10.165 8.5218.688 10.160 8.5108.640 10.337 8.7018.861 10.243 8.6238.713 10.198 8.6088.688 10.034 8.3768.569 10.042 8.4128.581 10.033 8.4018.571 10.068 8.4238.598 10.087 8.4308.599 10.086 8.4448.611 10.209 8.5528.751 10.104 8.4548.634 10.051 8.4068.586 9.818 8.1668.395 9.852 8.1868.435 9.856 8.1888.445 9.981 8.3018.573 9.872 8.2168.448 9.874 8.2078.450 9.890 8.2278.447 9.963 8.2908.503 9.996 8.3348.537 9.751 8.0808.347 9.804 8.1548.387 9.682 8.0048.288 9.712 8.0338.309 9.776 8.1168.367 9.630 7.9438.237 9.653 7.9718.260 9.580 7.8908.203 9.553 7.8938.205 9.681 7.9928.357 9.613 7.9138.233 9.590 7.8948.218 9.539 7.8498.170 9.555 7.8658.178 9.559 7.8668.188 9.564 7.8698.191 9.570 7.8748.197 9.593 7.8938.224 9.622 7.9328.235 9.489 7.7918.143 9.496 7.7938.145 9.515 7.8198.166 9.524 7.8298.164 9.534 7.8098.227 9.509 7.7968.196 9.513 7.8058.195 9.501 7.7918.176 9.570 7.8618.239 9.489 7.7838.150 9.489 7.7878.147 9.488 7.7828.153 f an the SDSSphotometricsystem. these valueswithinstrumentalmagnitudesobtainedthe SDSS MonitorTelescopesystemwilldefinethezeropointof subdwarfs arepresentedinTable7.Aleast-squaresfitinto red leaksfortheu'filter.Forstarswithg'—+1.4 band forveryredstarsdoesnotmakemuchphysicalsense. their veryweakuvflux;ontheotherhand,errorsof0.02 leakage (mostlyfromwavelengthslongerthan10000Â)is ously discussedfilterredleaks.Figure5showstheeffectsof and r'-i'vsg'—colorsformainsequencestars. system usingthespectrophotometricatlasofGunn&Stryker Effects of(infrared)leaksarenegligiblefortheg',r',andi' changes forthesestarsanddemandinghighaccuracyinthis mag inu'correspondtotrivialtemperatureormetallicity (1983). Figure4showsthelociofu'—g’vsgr'colors filters forallordinarystars. smaller than0.02mag;alargereffectforredstarsisdueto Lyr. AlthoughtherearesmalldiscrepanciesbetweenH85and The agreementfortheBmagnitudebetweenobserved the broadbandmagnitudeofaLyrusingitscontinuousSED. the Castelli&KuruczSED,wehaveattemptedtocalculate between ABandtheconventionalmagnitudesystemin ence betweenthetwomagnitudesistakentobeoffset tionally adoptedforaLyrarealsogiven.Wenotethat In Table8wepresentABmagnitudesofaLyrforw'toz' I givenbyBessell(1990). colors andforthestandardJohnson-Morgan-Cousins and syntheticvalues(Table5)[(^-^}synthetic—observed calculation weadopttheresponse functionUgivenby which theaverageAOVcolorsaresetequaltozero.Inthis equations fromtheJohnson-Morgan-Cousins systemtothe Buser (1978),5/?(=B)d^ givenbyAS69,andR (1978) colorsintheABscheme.Thezeropointsconven- SDSS systemusing syntheticmagnitudesfrom thespectro- V—R=0 andR-I+0.006(Taylor1986).Thediffer- V=0.03, f/-5=-0.01,(Johnson&Morgan1953), =0.030±0.007] hasalsoencouragedustomakethisattempt. 95 95 c 3 2 c 95 c Table 7.SyntheticmagnitudesofthefourOGFsubdwarfsinAB scheme. 95 The synthesizedbroadbandSDSSmagnitudesofthefour We havecalculatedexpectedstellarcolorsontheSDSS Using thisatlaswehavestudiedtheeffectofprevi- 4.2 TransformationstotheJohnson-Morgan-Cousins H85 hasgiven,forthefirsttime,continuousSEDofa We havealsocalculatedapproximate colortransformation 4.1 StellarColorsintheSDSSPhotometricSystem BD+26°2606 10.789.899.619.529.50 BD+17°4708 10.569.649.359.259.23 HD84937 9.328.468.238.16 HD19445 9.088.237.927.827.79 4. STELLARCOLORSANDTRANSFORMATION TO THEJOHNSON-MORGANSYSTEM System g' r'i'z' 1753 1996AJ 111.1748F f 1754 FXJKUGITAETAL.:SLOANDIGITALSKYSURVEY photometric atlasesofGunn&Stryker(1983)andOke Fig. 4.ColorsofmainsequencestarsintheSDSSphotometricsystem,(a) versus SDSScolors.Wefind synthetically usingthespectrophotometricatlasofGunn&Stryker. u’ —gvsg'-r'colors,(b)r'-g'-r'colors.Colorsarecalculated (1990). Figure6showscolor-colorplotsforthestandard g' =V+0.56(£-V)-0.12, g’ —r'=1.05(2? —V)—0.23, r' =V-0.49(7?-V)+0.11, r' =V-0.84(V-Æ)-f-0.13, u’ —g'—1.38(77—Æ)H-1.14, c © American Astronomical Society • Provided by theNASA Astrophysics Data System g'-r' (23) Fig. 5.Effectoffilterredleaksforthew'mainsequencestars given intheGunn-Strykerspectrophotometricatlas. which arevalidforstarswith5—V^+1.5.Weapplied these relationstotheUBVRIphotometrydata(Tumshek tude calculationsusingthespectrophotometryofOke tudes withthosedirectlyobtainedfromthesyntheticmagni- et al.1989)for4OGsubdwarfsand23dwarfsgivenin Oke (1990),andcomparedthetransformedu*g'r’Vmagni- magnitudes arediscrepantbymorethan1mag;oneofthe ^syn-transformed# “0.031:0.03,g)—0.02 catalogs isobviouslyinerror). (r' —/')=0.03±0.02(excludingLT9491forwhichthetwo (1990). Thedifferencesareagainreasonablysmall: UV-antireflection coated,back-illuminated2048X2048CCD conventional two-mirrorRitchey-ChrétienCassegrainian telescope consistsof302048X2048CCDs,mosaickedon the colorsystem.Thesurveycamerainstalledon2.5m with acorrectorwhosetransmissionhasnegligibleeffecton and thefivefiltersdiscussedinthispaper.Thetelescopeisa SDSS MonitorTelescope,whichconsistsofasinglethinned — 0*05,Àsyn-transformed(#~T)0.031:0.04,^syn—transformed for thez'bandareconventionalthick,front-illuminated coated thinneddevices(forg\r\and/'),remaining6 coated thinneddevices(foru'),18arenormalantireflection- the focalplane.Among30detectors,6areUV-antireflection- C f Table 8.MagnitudesofaLyrinthe ABandtheconventional conv. 0.02 0.030.024 AB 0.981-0.0930.1660.3970.572 0.719 -0.1200.0190.2120.453 schemes. 95 95 r'-z =1.59(R—7)—0.40(R~I<+1.65) r' -/'=0.98(R/)0.23(R~I<+1.15) The photometricsystemisdefinedbythecameraat C cC = 1.40(Æ—7)—0.72(^-7^+1.15), = 2.64(R—7)2.16(R-/^+1.65), C 5. IMPLEMENTATIONOFTHESDSSSYSTEM Cc g' r'i'z'UB V RI c 1754 1996AJ 111.1748F 1755 Fig. 6.StellarcolorsintheSDSSsystemvsstandardJohnson-Morgan-Cousinssystem,(a)B-Vg'V,(b)U-Bw'-g\(c)/r'- in (b)consistsoflateMstarswhichhavesimilarultravioletcolorstoKandearlybutverydifferentdetailedspectra. and (d)R—Ivsr'-z'■TheatlasesofGunn&Stryker(1983)(solidcircles)Oke(1990)(openareused.clearlydefinedsecondsequence nificantly intheg'band,whereresponseshapesareno- devices. Thecolorresponseofthesurveycameratherefore to thatdefinedwiththeMonitorTelescopesystem,wewill instrumental magnitudesobtainedwiththe30CCDsrelative what fromCCDtoCCD.Inordercorrecttheoffsetof efficiencies ofthestate-of-the-artthinneddevicesvarysome- ticeably different(seeFig.7).Wealsofindthatthequantum differs slightlyfromthatoftheMonitorTelescope,mostsig- through theobservationofstandardstarsandappliedto introduce 30color-colorrelationsthatwillbeestablished magnitudes tobepublishedintheSDSScatalogs.Figure7 After correctionaccuraciesof 0.005 magshouldbeattain- color offsetbetweenthetwosystems amountstoasmuch compared withthoseoftheMonitor Telescope(Fig.2).The shows typicalresponsefunctions forthesurveycamera, able exceptfor very redMstarsforwhichno broadband c c ±0.02 magifitisnotcorrected withcolor-colorrelations. © American Astronomical Society • Provided by theNASA Astrophysics Data System FUKUGITA ETAL.:SLOANDIGITALSKYSURVEY U-B R-I c the u'band. the SDSSphotometricsystem.Thetwo curvesarenominallyidenticalfor compared withthatoftheMonitorTelescope (dashedcurves),whichdefines Fig. 7.ResponsefunctionoftheSDSS surveycamera(solidcurves),as 1755 1996AJ 111.1748F 2 project (primedmagnitudes)directlyrepresentABvaluesif color relationsworkwellbecauseofthecomplexitytheir relation ¿k=Xa^«asdiscussedbelowEq.(5). tometric system:thisfundamentalprogramprovidedmuchof his threedecadesofeffortindevelopingtheABspectropho- one calculatestheeffectivefrequencyofbandsvia spectra. Buser, R.1978,A&A,62,411 Bessell, M.S.1990,PASP,102,1181 Azusienis, A.,&Straizys,V.1969,AZ,13,316(AS69) Cousins, A.W.J.1978,MNASSA,37,8 Castelli, E,&Kurucz,R.L.1994,A&A,281,817 Survey Project.WewouldliketopaytributeBevOkefor Hass, G.1965,inAppliedOpticsandOpticalEngineering,Vol.Ill,edited Gunn, J.E.,&Stryker,LL.1983,ApJS,52,121 1756 FUKUGITAETAL:SLOANDIGITALSKYSURVEY Hayes, D.S.1985,CalibrationofFundamentalStellarQuantities,inIAU Johnson, H.L.,&Morgan,W.1953,ApJ,117,313 Hayes, D.S.,&Latham,W.1975,ApJ,197,593 Magrath, B.1994,CFHTInformationBull.30,15 eff by R.Kingslake(Academic,NewYork),pp.309-330 idel, Dordrecht),p.225(H85) Symposium No.Ill,StellarQuantities,editedbyD.S.Hayesetal(Re- Finally, weremarkthatthemagnitudesuseinthis This workwasdoneasapartoftheSloanDigitalSky © American Astronomical Society • Provided by theNASA Astrophysics Data System REFERENCES by aGrantNSFNo.AST91-00121(JEG).J.E.G.also thank DonYorkforhisencouragementthisworkandBev the foundationforworkpresentedinthispaper.Wealso Mermilliod, J.-C.1991,PhotoelectricPhotometryCatalogueofHomoge- M.F. wishestoacknowledgesupportfromtheFujiXerox Aid oftheMinistryEducationJapan(05101002)and manuscript. 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