1. DOUBLE STARS Neil Webster William James Observatory www.itslifejim.btinternet.co.uk NEIL WEBSTER 03/2015

2. William James Observatorywww.itslifejim.btinternet.co.uk 1)Definition and types of double/binary stars 2)History and early catalogues 3)Present day sources 4)Important Results from Double Star/Binary System observations 5)Recommended reading 6)Measurement techniques 7)Observing tips

3. William James Observatorywww.itslifejim.btinternet.co.uk Definition and types of double/binary stars Two stars in close proximity as seen through a telescope Either: 1)OPTICAL DOUBLES: chance alignments and not physically related 2)VISUAL BINARIES: physically related orbiting around a “Common Centre of Mass” (barycentre) Can be separated with a telescope 3)NON-VISUAL BINARIES: usually not possible with a visual telescope

4. William James Observatorywww.itslifejim.btinternet.co.uk VISUAL BINARIES divide into: 1)COMMON PROPER MOTION PAIRS (CPMs)…………that are drifting through space like a single body They are physically in orbit around a common centre of mass (barycentre) but over long orbital periods of 1000+ years 1)VISUAL BINARIES that are seen to orbit over shorter time periods of a few years to 100s of years

5. William James Observatorywww.itslifejim.btinternet.co.uk Types of NON-VISUAL BINARIES: 1)INTERFEROMETRIC BINARIES ………ultra close. Less than 0.15 seconds of arc. Measurements down to 0.01 arc seconds!! 2)ASTROMETRIC BINARIES……..detected using CCD astrometry through anomalies in proper motions. Hipparcos (1989 – 1993) 3)SPECTROSCOPIC BINARIES…revealed through spectroscopy Mizar: all three stars are spectroscopic binaries (6-star system) Castor: visual triple but six star system Third star is eclipsing binary as well

6. William James Observatorywww.itslifejim.btinternet.co.uk 4)ECLIPSING BINARIES (extrinsic) revealed through occultation and associated light curves Algol (John Goodricke 1782) 5)CONTACT/CATACLYSMIC BINARIES….mass exchange…..Novae, Dwarf Novae, Supernovae (Type 1a)

7. William James Observatorywww.itslifejim.btinternet.co.uk History and early catalogues Early telescopic observations/discoveries: Nu SGRObserved as a double over 2000 years ago by Ptolemy MIZARGiovanni Battista Riccioli (1650) Earlier by Benedetto Castelli and Galileo (1564 – 1642)? GAMMA ARIETISRobert Hooke (1664) ACRUX (Southern Cross)Fontenay (1685)

8. William James Observatorywww.itslifejim.btinternet.co.uk All stars in close proximity were thought to be mere line of sight chance alignments But JOHN MICHELL (who also predicted black holes) in 1776 argued that close stars were connected “under the influence of some general law” First observed by WILLIAM HERSCHEL (1780s+) who used powerful reflectors to measure small stellar parallaxes of alpha Geminorum (Castor) gamma Leonis (Algieba) epsilon Bootis (Izar) zeta Herculis delta Serpentis gamma Virginis (Porrima)

9. William James Observatorywww.itslifejim.btinternet.co.uk but by 1802 concluded that they must be gravitationally connected and in mutual orbits due to similar: Proper motions, parallaxes, radial velocities Herschel first used the term “ Binary Stars ”

10. William James Observatorywww.itslifejim.btinternet.co.uk CATALOGUESrepeated observations allow orbit calculations and classification of systems as “optical” or “binary” EARLY CATALOGUES 1779 Christian Mayer80 entries (led by Herschel, Struve) 1782 William Herschel269 entries 1784 484 entries 1821 145 entries 1824 John Herschel / James South380 1822 Wilhelm Struve795 1827 3112 1878 Otto W. Struve 547 1874 John Herschel 10,300 (post.)

11. William James Observatorywww.itslifejim.btinternet.co.uk 1906Sherburne Wesley BurnhamA General Catalogue of Double Stars (BDS)within 121 degrees of the North Pole 13, 665 systems 1932Robert Grant Aitken (ADS)New General Catalogue of Double Stars within 120 degrees of the North pole 17, 180 entries 26, 650 (by time of death) Further work by Hamilton Jeffers (1893 – 1976), Willem van den Bos, Albert Edward Whitford (1905 – 2002), Kaj Aage Strand (1907 – 2000), Charles Edmund Worley (1935 – 1997) and Brian D. Mason (1961 - ) lead eventually to the WASHINGTON DOUBLE STAR CATALOGUE

12. William James Observatorywww.itslifejim.btinternet.co.uk Read in detail KEEPERS OF THE DOUBLE STARS Joseph S. Tenn (2013) http://arxiv.org/ftp/arxiv/papers/1304/1304.5494.pdf An excellent paper outlining the history of double star catalogues, containing brief biographies of the main astronomers from Castelli to the present day contributors of the Washington Double Star Catalogue Also of interest: THE WILLIAM HERSCHEL DOUBLE STAR CATALOGS RESTORED Bruce MacEvoy http://www.handprint.com/ASTRO/Herschel.html

13. William James Observatorywww.itslifejim.btinternet.co.uk Present day catalogues: The WASHINGTON VISUAL DOUBLE STAR CATALOGUE http://ad.usno.navy.mil/wds/wdstext.html#intro The definitive catalogue covering the whole sky compiled from many earlier lists (see website) and containing 132,120 entries (2000) 20437 physical doubles, 4584 optical doubles and 107099 unknown (!!!!!!) Has lists of “neglected doubles” and welcomes amateur measurements!!!

14. William James Observatorywww.itslifejim.btinternet.co.uk www.webbdeepsky.com/double-stars/ WEBB DEEP SKY SOCIETY has info on many double star systems (“double star of the month” - Rob Argyle ( Also Astronomy Now)) 46150 measured systems https://www.astroleague.org/ AMERICAN ASTRONOMICAL LEAGUE Contains both binocular and telescopic observing program listings…..which can lead to a reward/badge!! www.britastro.org BRITISH ASTRONOMICAL SOCIETY buried in the Deep Sky section with seemingly little activity??

15. William James Observatorywww.itslifejim.btinternet.co.uk

16. William James Observatorywww.itslifejim.btinternet.co.uk 2) Mass - luminosity relationship (Eddington) / H-R diagram Both follow from previous mass determinations 3) Type 1a supernovae Form from binary system (White Dwarf +……). Accretion/mass transfer onto WD up to maximum Chandrasekhar mass of 1.4 solar masses…..supernovae!! Consistent peak luminosity and therefore “Standard Candles” Vital for refined distance measurements, re-evaluation of Hubble constant and………………… accelerating expansion of the universe (1998: Supernova Cosmology Project/High Z supernovae search team)

17. William James Observatorywww.itslifejim.btinternet.co.uk 4) Evidence for gravitational waves?? Studies of the binary pulsar PSR 1913+16 using the Arecibo 305-m radio telescope in 1974 by Alan Russell Hulse (1950 - ) and Joseph Taylor (1941 - ) showed: A decaying orbit due to energy loss by gravitational waves (as predicted by Einstein’s GR) However, gravitational waves have, as yet, to be directly detected!! 5) Astrophysical phenomena Dwarf Novae, Novae, X-Ray Binaries, Type 1a Supernovae, Contact Binary/Accretion Disk systems All at the forefront of current research Binary systems are important

18. William James Observatorywww.itslifejim.btinternet.co.uk Recommended reading: Double and Multiple Stars…..and how to observe them James Mullaney (Springer) A good first book…but expensive!! Cambridge Double Star Atlas James Mullany/Wil Tirion Contains about half of Mullany’s book and is an excellent general atlas. Over 100+ “showcase doubles” at the front and over 3000+ doubles at the end. Highly recommended!! Observing and Measuring Visual Double Stars (The Patrick Moore Practical Astronomy Series) R. W. Argyle An in depth survey of the field and measurement techniques (both professional and amateur). Very detailed and theoretical in places

19. William James Observatorywww.itslifejim.btinternet.co.uk Double Star Measurements Separation: distance in arc seconds between the primary (brighter) and the secondary stellar surfaces Position Angle: of the secondary with respect to the primary Observations of these quantities by many astronomers (professional and amateur) over many years can lead to future orbital trajectory calculations

20. William James Observatorywww.itslifejim.btinternet.co.uk Measurement Techniques 1) John McCue (BAA journal: June 2014) Uses crosshair/reticle eyepiece and stopwatch 2) Meade Astrometric Eyepiece (manual) Meade eyepiece plus stopwatch 3) Rob Argyle (described in Observing and Measuring Visual Double Stars (The Patrick Moore Practical Astronomy Series) Meade eyepiece plus stopwatch (drift method) 4) Ronald Charles Tanguay Observing Double Stars for Fun and Science http://www.skyandtelescope.com/observing/observing-double-stars-for-fun-and- science/ 5) Others: chronometer, filar micrometer, mask diffraction, CCD. Occultation………

21. William James Observatorywww.itslifejim.btinternet.co.uk Observing tips: Dawes limitR = 4.56/D ( D equals telescope aperture in inches) R = 116/D ( aperture in millimetres) Defines the minimum separation achievable with a given aperture Separation: a slither of black between the stars. A double with the stellar surfaces touching is not split!! For example An 80mm refractor can theoretically split double stars down to 1.45 arc seconds But, in practise, this implies perfect seeing and little light pollution I can usually split down to 2 arc seconds but anything less is a challenge!

22. William James Observatorywww.itslifejim.btinternet.co.uk Navigation: SW Synscan systems To date (2015) the object catalogues contain very few double stars To find most doubles navigation using R.A./ Dec coordinates is required This is easy but not obvious!

23. William James Observatorywww.itslifejim.btinternet.co.uk 1)Select all doubles to be observed and have the coordinates to hand. I make a list to save time Plan them so they are in the same part of the sky 2) Start by slewing the scope to the nearest named object (star, M.., NGC…) 3) From this position you can slew using the directional arrows but the coordinates will not change on the handset So precise slewing to set coordinates can not be achieved with any accuracy 4) But: hit EXIT (more than once maybe) 5) Go to UTILITIES…………….and then SHOW POSITION

24. William James Observatorywww.itslifejim.btinternet.co.uk 6)Now you can slew and watch the coordinates change. Set the rate fairly low (4,5) 7)Use the directional arrows to slew. If your polar alignment is good when you are moving in R.A. the DEC coordinates will hardly change and vice versa 8)When you approach the coordinates of the target object take the RATE down and carefully slew in precisely to the target coordinates I then use a low power eyepiece (20x) to look for the star…….and then centre precisely in the eyepiece. Spotting the candidate double star becomes easier with practise!! Then zoom in and enjoy (Zoom lenses are ideal for this purpose as the best magnification can then be selected to view)

25. William James Observatorywww.itslifejim.btinternet.co.uk An observation plan (NW: using the Cambridge Double Star Atlas) Decide on a constellation that will be easily accessible all night Pick an easy double (a “showcase” double) from the front list in the Cambridge atlas to begin the tour From the back list select a series of doubles in order of increasing RA from this star (Try to keep to small changes in DEC between doubles if possible. The aim is to spend the session looking at doubles and not performing long slews between the targets) Select doubles that will be possible……not too great a magnitude difference and not too close Start with easy doubles for the first few sessions…………challenges come later!! (note: it may be tempting to choose very wide separations but these can often prove difficult to identify in a general field of stars: which two stars are actually the double?)

26. William James Observatorywww.itslifejim.btinternet.co.uk Make a list of the target doubles with their RA and DEC coordinates, magnitudes and separations on a single piece of paper (this will save time outside!!) OBSERVE After a few sessions: The eye becomes practised at seeing separation distances and estimating magnitudes at each session Gradually closer doubles can be targeted Doubles with larger magnitude differences can be attempted Planning becomes more efficient with less time wasted……………and more doubles are seen and logged!!

27. William James Observatorywww.itslifejim.btinternet.co.uk Observing Take time to let the eye adjust to the double star and everything else in the eyepiece. I let my eye wander around the field of vision for about a minute allowing any faint stars to “pop out”. Play with the focuser control knob to bring out the details Using the focuser controls focus on the primary star (the brightest). When the best focus is achieved let the eye settle Repeat for the secondary star (usually at a different focus especially if there is a noticeable colour contrast) Now find the best focus point to view both stars as a double…………and split them if they’re very close Very soon an eye to focus control knob coordination is achieved and more detail will be seen (subtle colourations for example) Sketch, make notes, measure??.............and log the double star!!