Observing and Measuring Visual Double Stars PDF
Preview Observing and Measuring Visual Double Stars
Patrick Moore’s Practical Astronomy Series Forfurthervolumes: http://www.springer.com/series/3192 Observing and Measuring Visual Double Stars Second Edition R.W. Argyle (Editor) 123 Editor R.W.Argyle Lyndhurst CB259NWWaterbeach UK ISSN1431-9756 ISBN978-1-4614-3944-8 ISBN978-1-4614-3945-5(eBook) DOI10.1007/978-1-4614-3945-5 SpringerNewYorkHeidelbergDordrechtLondon LibraryofCongressControlNumber:2012939486 ©SpringerScience+BusinessMediaNewYork2012 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpartof thematerialisconcerned,specificallytherightsoftranslation,reprinting,reuseofillustrations,recitation, broadcasting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionorinformation storageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilarmethodology nowknownorhereafterdeveloped.Exemptedfromthislegalreservationarebriefexcerptsinconnection with reviews or scholarly analysis or material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. 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Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) Foreword The first edition of this volume appeared in 2004. Since then, interest in visual double-starobservationhasincreasedconsiderably,andtherearenowseveralvery active groupsaroundthe world. I have taken the opportunityto thoroughlyrevise thefirsteditionandalsotoaddsixnewchapterswhichIhopeandbelievereflectthe increasedinterestandactivityinthissubject. Although there is no CD with this edition, the programmes in Chap.25 will be downloadable from the Springer website (www.extras.springer.com). Faster download times now mean that it is better to access the double-star catalogues at theUSNOdirectly. v Preface Double stars are the rule, rather than the exception, in the solar neighbourhood and probablybeyond.Current theoriesof star formationpointto multiple stars or stars and planets as the preferential outcome of gravitating protostellar material. Stellar pairs can be detected at many wavelengths from X-rays, where modern satellitescanresolvethetwobrightestcomponentsofCastor(separation3.8arcsec) to the radio where the precision of long baseline interferometry can also see the 4milli-arcsecond(mas)“wobble”inthe2.87-dayeclipsingsystemofAlgolandcan distinguish which of the two stars is emitting the radio waves. Optical techniques have also constantly improved—array observations now regularly give positional accuraciesofbetterthan1masforbrightbinariessuchasbetaLyrae. Binarystarscomeinawiderangeoforbitalsizes,periods,andmasses–fromthe multiplesystemalpha+KULibwherethestarsareseparatedbyalmost1parsecand whosemotionisbarelyperceptible,throughthespectroscopicbinarieswithperiods ofweeks,downtoexoticpairslikedoublewhitedwarfcontactsystemswithperiods of 5min. FromyoungO-star binarieslike NGC 3603A1 in the LargeMagellanic Cloud containingtwo extremelybrightand hot stars, of 116 and 89 solar masses, downtothewidesystemknownasSource11intheOphiuchusstar-formingregion 16222-2405.In this case the two M9 dwarfs both have masses thoughtto be less than0.02solarmassesalthoughtheuncertaintyisaround50%ineachcase. Inthisvolumeweareconcentratingononlyoneaspect,thevisualdoublestars, whichwe candefineas thosepairswhichcanbe seen orimagedina telescopeof moderateaperture.InFig.1thiscorrespondstotherangeofseparationsfromabout (cid:2)(cid:2) (cid:2)(cid:2) 0 .2 upwards. Modern, large telescopes can reach 0 .02 whilst the ground-based (cid:2)(cid:2) interferometerarrayscanreach0 .002.Thissortofresolutioncanalsobereached with the ordinarytelescope, if lunar occultationsare considered. It also offersthe observerachancetomakeanewdiscovery,anddetailscanbefoundinthechapter byGrahamAppleby(Chap.21). vii viii Preface Fig.1 Thecategoriesofdoubleandmultiplestars The classic image of the double-starobserveras a professionalscientist with a largerefractorand a brassfilar micrometeris no longervalid. Researcherscannot affordto spenda lifetime measuringa large numberof pairsin orderto get a few dozenorbits.Thehigh-precisionastrometricsatellites,ground-basedinterferometer arrays,andinfraredspeckleinterferometryhaveallhelped,respectively,todiscover large numbers of new pairs, push direct detection into the spectroscopic regime withmeasurementofbinarieswithperiodsofafewdays,andtoprobethenearand mid-infraredwherefaintredandbrowndwarfcompanionsand,ultimately,planets appear.Thishasleftalargenumberofwide,faintpairswhichareunderobserved. There has been a common perception that double star observing either is not veryinterestingordoesnotaffordanyopportunitiesforusefulwork.Theaimofthis bookistodispeltheseviewsandindicatewhereobserversmightusefullydirecttheir efforts.Atthebasiclevel,wegiveadviceabouthowtoobservethemwithbinoculars and small telescopes. At a more serious level, chapters about micrometers, CCD cameras,DSLRcameras,andothertechniqueshavebeenincluded.Forthosewho donotwish tospendseveralhundredpoundsona filarmicrometer,assumingthat you can find one, the graticule eyepieces such as the Celestron Micro Guide, as describedbyE.T.H.TeagueinChap.12,areavailableforcatadioptrictelescopesand canbeusedeffectivelyforrelativepositionmeasurementofwiderpairs.Forthose whofindobservingtootaxing,astrometryoffaintpairscanbedonebyexamination ofsomeofthehugecataloguesproducedfromthevariousSchmidtsurveys,andin Chap. 19RafaelCaballerotakesusthroughthemeansandfacilities. Clearly for the observer,the role of the telescope is very important.For casual viewinganyopticalaidcangivereasonableviewsofwideandbrightdoublestars. Preface ix I spent several years accumulating visual estimates of colour, magnitudes, and relative positions of more than 1,000 pairs using a 21-cm reflector using Webb’s CelestialObjectsforCommonTelescopes(VolumeII)andNorton’sStarAtlas(15th edition,1964).EveninthiscopyofNortonmanyofthemeasuresgivenweremore than30yearsoldanditwasthisthatsparkedaninterestinobtainingamicrometer tobringthemuptodate. For thosewho wish to enjoythe gloryandcoloursof doublestars, thisversion retainstheadvicefromMichaelRopelewskiondoublestarsaccessibletoordinary binoculars(Chap.3),andwiththiseditionwehaveawelcomeadditionalchapterby JeremyPerezonhowtosketchthem(Chap.4). On the whole, equatorially mounted telescopes are almost a necessity and althoughDobsoniantelescopescangivefineviewsofdoublestars,usingthemfor measurementisnotstraightforward.PotentialusersshouldlookatChap.25where MichaelGreaneyshowshowtocalculatepositionangleinsituationswherethefield rotates.Whilstthegratingmicrometer(describedbyAndreasMaurerinChap.14) is relatively insensitive to the lack of an RA drive the field rotation is an added problem. Resolutionisultimatelydependentonaperture,andalthoughmanyofthemost interesting binaries are significantly closer than 1arcsec, the aperture available to today’sobserversisnolongerlimitedtothesmallsizesthatwerecommonabout30 or 40 yearsagowhen the 12.5-in.reflector was the exceptionrather thanthe rule. Thesedaysnooneissurprisedtoseeamateurobserverssporting30-,40-oreven50- in.telescopesandforthosewhothoughtthatrefractorsweretherequiredtelescope fordouble-starobservingthenChristopherTaylorhasotherideas(Chap.11). In the last 20 years the CCD camera has become a dominant force in obser- vationalastronomy.As botha positionaland photometricdetector it hasexcellent applicationsintheobservationofdoublestarsandthesewillbediscussedlaterby BobBuchheim(Chap.15). Whilst filar micrometers were available commercially at the time of the first edition, they are now more difficult to obtain. See the references to Chap.13 for possiblecommercialcontacts.Themainadvantageisthattheyareeffectiveuptothe resolvinglimitofthetelescopeanddonotrequiresoftwaretoproduceresults.Bob ArgyledescribeshowtouseamoderninstrumentinChap.13.Thosewiththelarger apertures,however,shouldconsiderthe speckleinterferometeras an alternativeto themicrometer.Withatmosphericeffectsbecomingmoresignificantwithtelescope size,thespecklecameracanpunchthroughtheturbulenceandproducediffraction limitimaging.InChap.18NilsTurnershowshowthiscanbeachievedatrelatively low cost. An alternative technique, lucky imaging, takes advantages of moments of quietair to capturegoodqualityimagesin shortexposuresandis describedby RainerAntoninChap.16. Theavailabilityofinexpensiveandyetpowerfulpersonalcomputershasbrought severalotheraspectsofdouble-starastronomywithinreach.Thelateststaticversion oftheUnitedStatesNavalObservatorydouble-starcatalogue,WDS2006.5,isnow available on CD-ROM (the regularly updated WDS catalogue is available online only and incremental files can be downloaded to update the static version of the
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