MolecularInterstellarAbsorptiontowardthePleiadesStarClusterAdamRitcheyDepartmentofPhysics&AstronomyUniversityofToledoJune21,2006OutlineofTalkIntroductiontothePleiadesSignificancetointerstellarstudiesMotivationforthepresentinvestigationObservingProgramDataReductionandFittingProcedureResultsandAnalysisDeterminationofcolumndensitiesImplicationsofaveragevelocitiesandb-valuesVelocitystructureofmoleculargasPhysicalconditionsfrommodelsofdiffusecloudchemistryAcknowledgementsIntroductiontothePleiadesLaboratoryforthestudyofinterstellarprocessesduetotheinteractionbetweenthestellarradiationfieldoftheclusterandsurroundingdiffuseinterstellarclouds.Spatialassociationofstarsandambientinterstellarmedium(ISM)isephemeral–resultofachanceencounterbetweentheclusterandoneormoreapproachingclouds(White2003).BlueimageofthePleiadesfromtheDigitizedSkySurveyIntroductiontothePleiadesAnomalouscharacteristics:UnusuallystrongCH+absorption(Adams1949).HighdegreeofH2rotationalexcitation(Spitzeretal.1974).PreviousInvestigations:White(1984)examinedCN,CaII,CaI,CH+,andCHtoward15Pleiadesmembers. (Dv

~3–8kms-1)Craneetal.(1995)surveyedCH+andCHatultra-highresolution. (Dv~0.6kms-1)Whiteetal.(2001)analyzedtheNaIDlinesof36starsinthePleiades.(Dv~1.1–1.5kms-1)BlueimageofthePleiadesfromtheDigitizedSkySurveyPrimarymotivation:toobtainequallyhighqualitydatafortheotherimportantopticaltracersoftheISMtowardalargenumberoftargetsinthePleiadessothatacompletepictureoftheinteractionbetweeninterstellargascloudsandthestarsoftheclustermaybeconstructed.

ObservingProgram20starsfromthelistinWhiteetal.(2001)withsecuremembershipinthecluster.Observedusingthehigh-resolutionmode(R~175,000;Dv~1.7kms-1)ofthe2dcoudespectrographontheSmith2.7mtelescopeatMcDonaldObservatory.InstrumentalsetupallowedforthedetectionofabsorptionfeaturesfromCNl3874,CaIIKl3933,CaI

l4226,CH+

l4232,andCHl4300.Smith2.7mTelescope(Ritcheyetal.2006)DataReductionandFittingProcedureStandardIRAFroutineswereusedtoextract1-DspectrathatwereDoppler-correctedandnormalizedtounity.

Signal-to-noiseratio(SNR)typically~100–200.Gaussianfitsyieldedtheequivalentwidth(Wl), radialvelocity(vLSR),andDopplerparameter (b-value)foreachcomponent.Componentstructurewasconstrainedbythe derivedb-values(0.4kms-1<b<2.5kms-1) andvelocities(comparedtoCaII).(Panetal.2005)CaIIKAbsorptionLines(Ritcheyetal.2006)MultiplecomponentsofCaIIKdetectedalongalltwentysightlines.StrongestabsorptionatvLSR

~7kms-1.CH+AbsorptionLines(Ritcheyetal.2006)CH+justaspervasiveyetonlyoneortwocomponentspersightline.(NotethestellarfeaturetowardHD23964.)CH+AbsorptionLines(Ritcheyetal.2006)CH+justaspervasiveyetonlyoneortwocomponentspersightline.(NotethestellarfeaturetowardHD23964.)StellarCHAbsorptionLines(Ritcheyetal.2006)MarginaldetectionsofCHtowardfivestars.MuchstrongercomponenttowardHD23512.(Note,again,thestellarfeaturestowardHD23964.)CHAbsorptionLines(Ritcheyetal.2006)MarginaldetectionsofCHtowardfivestars.MuchstrongercomponenttowardHD23512.(Note,again,thestellarfeaturestowardHD23964.)StellarCHAbsorptionLines(Ritcheyetal.2006)MarginaldetectionsofCHtowardfivestars.MuchstrongercomponenttowardHD23512.(Note,again,thestellarfeaturestowardHD23964.)HD23512StellarTheSightLinetowardHD23512ThissightlinepassesthroughasmallmolecularcloudfirstmappedinCOemissionbyCohen(1975,unpublished;seeFederman&Willson1984).OurvelocitiesfortheCHandCNcomponentstowardthisstar(+9.8and+9.4kms-1)agreewiththevaluedeterminedfromtheradiodata(~10kms-1).(Federman&Willson1984)CNAbsorption(Ritcheyetal.2006)COEmission:TheSightLinetowardHD23512ThissightlinepassesthroughasmallmolecularcloudfirstmappedinCOemissionbyCohen(1975,unpublished;seeFederman&Willson1984).OurvelocitiesfortheCHandCNcomponentstowardthisstar(+9.8and+9.4kms-1)agreewiththevaluedeterminedfromtheradiodata(~10kms-1).(Federman&Willson1984)CNAbsorption(Ritcheyetal.2006)HD23512HD23512COEmission:Columndensities(N)interpolatedfromcurvesofgrowthbasedonthemeasuredequivalentwidths.Adoptedaverageb-values:1.6kms-1forCaII,CH+,andCH,0.5kms-1forCN.(Sincemostlinesareweak,theuseofdifferentb-valuesdoesnotimpactthederivedcolumndensitiesinanyappreciableway.)CaIIKCNR(0)CNR(1)CNP(1)CH+CHCurvesofGrowthforVariousSpeciesDeterminationofColumnDensitiesColumndensities(N)interpolatedfromcurvesofgrowthbasedonthemeasuredequivalentwidths.Adoptedaverageb-values:1.6kms-1forCaII,CH+,andCH,0.5kms-1forCN.(Sincemostlinesareweak,theuseofdifferentb-valuesdoesnotimpactthederivedcolumndensitiesinanyappreciableway.)CaIIKCNR(0)CNR(1)CNP(1)CH+CHCurvesofGrowthforVariousSpecieslinearDeterminationofColumnDensities(Ritcheyetal.2006)AverageVelocitiesandb-values(Ritcheyetal.2006)Wefindakinematicdistinctionbetweenatomicandmoleculargas,withatomicabsorptionoccurringnear6or7kms-1andmolecularabsorptionnear9kms-1.AverageVelocitiesandb-valuesWefindakinematicdistinctionbetweenatomicandmoleculargas,withatomicabsorptionoccurringnear6or7kms-1andmolecularabsorptionnear9kms-1.Meanb-valuesforthemolecularspeciesindicatethattowardmostofthePleiades(exceptthesightlinetowardHD23512)CHisassociatedwithCH+ratherthanCN.(Ritcheyetal.2006)AverageVelocitiesandb-valuesFormolecularspecies,onecomponentwastypicallyfoundperabsorbingsightline,fallingineitheroftwocategories:WeakcomponentswithvLSR~+7kms-1StrongercomponentswithvLSR~+9.5kms-1Thetwocomponentsgenerallyoccupydifferentregionsofthecluster.(Ritcheyetal.2006)VelocityStructureofMolecularGasFormolecularspecies,onecomponentwastypicallyfoundperabsorbingsightline,fallingineitheroftwocategories:WeakcomponentswithvLSR~+7kms-1StrongercomponentswithvLSR~+9.5kms-1Thetwocomponentsgenerallyoccupydifferentregionsofthecluster.(Ritcheyetal.2006)CH:7kms-19.5kms-1VelocityStructureofMolecularGasFormolecularspecies,onecomponentwastypicallyfoundperabsorbingsightline,fallingineitheroftwocategories:WeakcomponentswithvLSR~+7kms-1StrongercomponentswithvLSR~+9.5kms-1Thetwocomponentsgenerallyoccupydifferentregionsofthecluster.(Ritcheyetal.2006)CH:CH+:7kms-17kms-19.5kms-19.5kms-1VelocityStructureofMolecularGasWederivedestimatesforthetotalgasdensity,n,andtheintensityoftheincidentUVradiationfield,Iuv,byadoptingvariousmodelsofdiffusecloudchemistry.PhysicalConditionsoftheISMnearthePleiadesWederivedestimatesforthetotalgasdensity,n,andtheintensityoftheincidentUVradiationfield,Iuv,byadoptingvariousmodelsofdiffusecloudchemistry.Steady-statemodelofCHformationfromCH+:TherateequationforCHmaybewritten:(Weltyetal.2006)PhysicalConditionsoftheISMnearthePleiadesWederivedestimatesforthetotalgasdensity,n,andtheintensityoftheincidentUVradiationfield,Iuv,byadoptingvariousmodelsofdiffusecloudchemistry.Steady-statemodelofCHformationfromCH+:TherateequationforCHmaybewritten:(Weltyetal.2006)PhysicalConditionsoftheISMnearthePleiadesWederivedestimatesforthetotalgasdensity,n,andtheintensityoftheincidentUVradiationfield,Iuv,byadoptingvariousmodelsofdiffusecloudchemistry.Steady-statemodelofCHformationfromCH+:TherateequationforCHmaybewritten:(Weltyetal.2006)PhysicalConditionsoftheISMnearthePleiadesOpticalPumpingmodelofH2rotationallevels:J=4and5levelspopulatedprimarilybyphotonpumping.Inenvironmentsoflowtomoderatedensity,theselevelswillbedepopulatedbyspontaneousemission.Therelativepopulationsofhigherandlowerrotationallevelsindicatesthedensityofthegas:(Leeetal.2002)PhysicalConditionsoftheISMnearthePleiadesOpticalPumpingmodelofH2rotationallevels:J=4and5levelspopulatedprimarilybyphotonpumping.Inenvironmentsoflowtomoderatedensity,theselevelswillbedepopulatedbyspontaneousemission.Therelativepopulationsofhigherandlowerrotationallevelsindicatesthedensityofthegas:(Leeetal.2002)PhysicalConditionsoftheISMnearthePleiadesOpticalPumpingmodelofH2rotationallevels:J=4and5levelspopulatedprimarilybyphotonpumping.Inenvironmentsoflowtomoderatedensity,theselevelswillbedepopulatedbyspontaneousemission.Therelativepopulationsofhigherandlowerrotationallevelsindicatesthedensityofthegas:(Leeetal.2002)PhysicalConditionsoftheISMnearthePleiadesSinceeqn.(2)isproportionaltofandeqn.(1)isinverselyproportionaltof,fcanbevariedasafreeparameteruntilourdensitydeterminationsagree.Wefindthatf=0.07providesthebestagreement.Therefore,wefindthedensityoftheISMnearthePleiadestoben~50cm-3.(Ritcheyetal.2006)ResultsofDensityDeterminationsSinceeqn.(2)isproportionaltofandeqn.(1)isinverselyproportionaltof,fcanbevariedasafreeparameteruntilourdensitydeterminationsagree.Wefindthatf=0.07providesthebestagreement.Therefore,wefindthedensityoftheISMnearthePleiadestoben~50cm-3.(Ritcheyetal.2006)f=0.07ResultsofDensityDeterminationsConclusion:withtheavailabilityofhighqualitydataforCN,CaII,CaI,CH+,andCHfromthisstudyandforNaIfromWhiteetal.(2001),existingmodelsofinterstellarchemistrymustnowbeimprov