Patrick Moore’s Practical Astronomy Series Forothertitlespublishedinthisseries,goto http://www.springer.com/series/3192 Astronomical Spectroscopy for Amateurs Ken M. Harrison 123 KenM.Harrison Cobham,UK Additionalmaterialtothisbookcanbedownloadedfromhttp://extras.springer.com ISSN1431-9756 ISBN978-1-4419-7238-5 e-ISBN978-1-4419-7239-2 DOI10.1007/978-1-4419-7239-2 SpringerNewYorkDordrechtHeidelbergLondon ©SpringerScience+BusinessMedia,LLC2011 Allrightsreserved.Thisworkmaynotbetranslatedorcopiedinwholeorinpartwithoutthewritten permissionofthepublisher(SpringerScience+BusinessMedia,LLC,233SpringStreet,NewYork,NY 10013,USA),exceptforbriefexcerptsinconnectionwithreviewsorscholarlyanalysis.Useinconnection with any form of information storage and retrieval, electronic adaptation, computer software, or by similarordissimilarmethodologynowknownorhereafterdevelopedisforbidden. Theuseinthispublicationoftradenames,trademarks,servicemarks,andsimilarterms,eveniftheyare notidentifiedassuch,isnottobetakenasanexpressionofopinionastowhetherornottheyaresubject toproprietaryrights. Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) Preface Therehavebeenthreesignificantmilestonesinthehistoryofobservationalastron- omy:theinventionofthetelescope,photography,andthespectroscope.Thedevel- opmentofthespectroscopehascontributedmoretothesciencethananyothertele- scopeaccessory.Ithasbeensaidthat85%ofallastronomicaldiscoverieshavebeen madewiththespectroscope. Probably due to the perception that lots of mathematics and calculations are involved, plus the fact that it doesn’t have the “Ohh” or “Ahh” impact of some of thespectacularastronomicalimagesnowbeingregularlydistributedontheforums andwebsites,spectroscopyisanareathathasbeenlongoverlookedandneglectedby theamateur.Byusingamateurtelescopes,mountings,andCCDcamerascurrently available, this book will show how, with the addition of a simple spectroscope we can observe and record spectra that reveal the temperature, composition, and age ofstars,thenatureoftheglowinggasesinnebulae,andeventheexistenceofother exoplanetscirclingarounddistantstars. The basic challenge facing the novice is where to start. What equipment will I need?WherecanIfindaspectroscope?HowdoIprocesstheCCDimage?Howdo Ianalyzemyfirstspectrum?Thesequestionsandmoreareaddressedinthisbook. Uptodateinformationonequipment,spectroscopes,andmethodsavailabletothe amateur,andmoreimportantly“Howto...”.areallincludedinthisbook. Therearethreebasicsectionsinthisbook: 1. IntroductiontoSpectroscopy.Thispartprovidesabriefoverviewofthehistoryof spectroscopy,thetheorybehindthespectrumlines,andtypesofspectroscopes. 2. ObtainingandAnalyzingSpectra.Tellshowtosetupanduseyourspectroscope; describes different commercially available spectroscopes, cameras, and CCD’s; explains how to analyze your spectra; and presents some interesting amateur projects. v vi Preface 3. Spectroscope Design and Construction. Here you will find basic spectroscope designideasandhowtoconstructyourownspectroscope. Each section is independent of the other, so if you want to jump straight into takingyourfirstspectrum,gotothesecondsectionandgetstarted! “Spectroscope”isthegenerictermforvisualspectroscopes,spectrographs(imag- ing),andspectrometers(linearCCDmeasuringdevices).(Telescopesarenotgiven different names when used with eyepieces, cameras, or filters, so why should spectroscopes?!) Unitsofmeasurearealwaysanissueofdebate.BoththeSIunitnanometer(nm) andAngstromunits(Å)arewidelyusedinspectroscopyasameasureofwavelength, asaremeasurementsandsizesinmillimetersratherthaninches. As you gain practice and experience you may want to increase the resolution of your spectroscope, contribute to the ever-growing list of amateur and pro-am projects,orevenconstructyourownspectroscope.Thevarioussectionsinthisbook will guide you through the issues and hopefully answer your questions on all the differentaspectsofspectroscopy.It’sanewandchallengingfieldforamateurs,and witheventhemostbasicofequipmentitcanbeinteresting,thoughtprovoking,and mostofallfun! Cobham,UK KenM.Harrison February2010 Contents PARTONE IntroductiontoSpectroscopy 1 EarlyExperimentsinSpectroscopy .............................. 3 ForFurtherReading ............................................ 8 WebPages..................................................... 8 2 AHistoryofAstronomicalSpectroscopy.......................... 9 FurtherReading................................................ 14 WebPages..................................................... 14 3 TheoryofSpectra.............................................. 15 Kirchhoff’sLaws ............................................... 15 BlackBodyRadiation ........................................... 16 QuantumTheory .............................................. 17 ForbiddenLines................................................ 18 DopplerandRedShifts.......................................... 20 SolarSpectrum ................................................ 21 StellarSpectra ................................................. 22 TheH-RDiagram.............................................. 22 HDClassifications.............................................. 23 StandardSpectralLinesandReferenceSpectra...................... 25 FlouroSpectrum............................................... 26 OtherUsefulSpectralReferenceLines ............................. 26 AiryDisk,RayleighLimits,andFWHM,PSF ....................... 28 vii viii Contents FocusandExitPupil............................................ 31 ExitPupilandEyeRelief ...................................... 33 FurtherReading................................................ 33 WebPages..................................................... 34 4 Prisms,GratingsandSpectroscopes.............................. 35 Dispersion,PlateScale,andResolution ............................ 35 EfficiencyofYourSpectroscope .................................. 36 Prisms........................................................ 37 Resolution.................................................. 38 EfficiencyofaPrismSpectroscope.............................. 38 AmiciPrismSystems ......................................... 39 Gratings ...................................................... 39 GratingTheory.............................................. 40 FurtherReading................................................ 44 WebPages..................................................... 44 5 TypesofSpectroscopes ......................................... 45 ObjectivePrismorGrating ...................................... 45 PrismwithCollimator/Camera-CCD ............................. 46 TraditionalPrismLittrow ..................................... 46 TransmissionGratinginConvergingBeam ...................... 47 TransmissionGratinginCollimatedBeam(withorwithoutSlit).... 48 Grisms ..................................................... 48 ReflectionGrating(withorwithoutSlit)........................... 49 FurtherReading................................................ 53 Webpages..................................................... 53 PARTTWO ObtainingandAnalyzingSpectra 6 SettingUptheSpectroscope..................................... 57 ObjectivePrisms/Gratings ....................................... 57 CameraLenses .............................................. 57 Telescopes .................................................. 57 MountingtheObjectivePrism/Grating ............................ 58 ObjectivePrisms............................................. 58 ObjectiveGratings ........................................... 58 AdjustmentsandFocus ......................................... 60 Prisms ..................................................... 60 Gratings.................................................... 61 FlatsandDarks ................................................ 63 WebPages..................................................... 63 7 UsingSpectroscopesintheConvergingBeam ..................... 65 ObtainingYourFirstSpectrum................................... 67 PointstoNote ................................................. 67 Contents ix CameraResponsevs.RecordedSpectra ............................ 68 UsingOtherTransmissionGratings ............................... 69 UsingGratingsinaCollimatedBeam ............................. 70 WebPages..................................................... 72 8 ReflectionGratingSpectroscopes ................................ 73 MountingtheSpectroscope...................................... 74 GettingaStarFocusedontheSlit................................. 76 BeamsplittersandNon-reflectiveSlits ............................. 77 SBIGSoftwareControlledSpectroscopes........................... 77 BaaderDadosSpectrograph...................................... 79 Shelyak’sLhiresIII .............................................. 80 QuestarQMaxSolarSpectrometer................................ 81 OtherSpectroscopes............................................ 82 TheeShelSpectrographfromShelyak........................... 82 TheBaaderBachesEchelleSpectroscope ........................ 83 TheOptomechanics10C ..................................... 84 RemoteControlofSpectroscopes................................. 84 WebPages..................................................... 85 9 CamerasandCCD’s............................................ 87 CCDChipSize................................................. 87 PixelSize...................................................... 87 QuantumEfficiency ............................................ 89 BayerMatrix .................................................. 89 Bias,Darks,andFlats ........................................... 92 SpectroscopeFlats.............................................. 93 FurtherReading................................................ 95 WebPages..................................................... 95 10 ProcessingSpectra............................................. 97 PreparingtheRawImageforProcessing ........................... 98 GratingSpectra:LinearDispersion................................ 98 SmileandTilt.................................................. 99 VisualSpec(VSpec) ............................................ 100 StandardStellarSpectra....................................... 100 StandardElementLines....................................... 101 ObtainingaSpectralPixelProfile............................... 101 WavelengthCalibration....................................... 102 CameraResponse............................................ 104 CorrectingSpectraUsingtheCameraResponseCurve............. 107 UsingtheCCDQECurves–ResponseCurve .................... 107 CalibratingUsingaReferenceLamp ............................ 108 Resolution.................................................. 108 NormalizedSpectrum ........................................ 108 SignaltoNoiseRatio(SNR) ................................... 108