Table Of ContentPatrick 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
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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
