Project Coordinator: Neil Webster
There’s so much more to these objects than two stars orbiting a common centre of mass. In fact, there are rarely just two… Spectroscopic analysis often reveals very close stars orbiting the main visual stars. And again and again a third member is found, so we really are talking multiple star systems. And just how/why do these systems form from the original collapsing gas cloud and initial open star cluster. Studies of open cluster members usually reveal double star systems within.
Historically, they are important as they were the first method of ascertaining stellar masses (using good old Kepler’s 3 laws), but they seem to have fallen out of favour with astronomers, although they can be observed in bad light-polluted areas (as I know!!), and there are so many within range of small telescopes (comfortable separations and comparable magnitudes/colours between components). And, forgetting the science, they can be very beautiful!!
The Washington Double Star catalogue, Webb Deep Sky society, The American Astronomical League and The BAA all have lists of neglected doubles requiring measurements from amateurs. More measurements mean possible future orbit calculations. The downside is that they are neglected for a reason (very tight separations with large magnitude differences between the components!!)…………………….but it could be a challenge.
Please contact Neil if you need any advice.
Definition and types of double/binary stars
Two stars in close proximity as seen through a telescope
- OPTICAL DOUBLES: chance alignments and not physically related
- VISUAL BINARIES: physically related orbiting around a “Common Centre of Mass” (barycentre) and can be separated with a telescope.
- NON-VISUAL BINARIES: usually not possible to separate with a visual telescope
- COMMON PROPER MOTION PAIRS (CPMs)
These 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
- VISUAL BINARIES
These are seen to orbit over shorter time periods of a few years to 100s of years
Types of NON-VISUAL BINARIES:
- INTERFEROMETRIC BINARIES
Ultra close. Less than 0.15 seconds of arc. Measurements down to 0.01 arc seconds!
- ASTROMETRIC BINARIES
Detected using CCD astrometry through anomalies in proper motions. Hipparcos (1989 – 1993)
- SPECTROSCOPIC BINARIES
Revealed through spectroscopy
4. ECLIPSING BINARIES
(extrinsic) revealed through occultation and associated light curves e.g. Algol (John Goodricke 1782)
5. CONTACT/CATACLYSMIC BINARIES
involved in mass exchange, Novae, Dwarf Novae, Supernovae (Type 1a)
General double star observing lists (binocular and telescopic) can be found at the American Astronomical League:
A useful list can be found at the Sky and Telescope site:
An interesting collection of sketches and info on selected doubles in Auriga, Orion and Gemini:
There are many, many more on the web!
The Cambridge Double Star Atlas James Mullany/Wil Tirion
Following on from the above is a fascinating paper on “training the binary eye”
Information on selected “classic” double stars focussing on history and measurements:
An introduction to Double Stars from the Astronomy Society of New South Wales:
A couple of papers written by amateurs on measurement techniques:
Astrometric Measurements of the Visual Double Star Epsilon Lyrae (Estrada, Magana, Salam……..2011)
Double Star Measurements with a Three Inch Tasco Telescope (Grisham, Johnson, Genet, Arnold 2008)
Double Star Posts
By Neil Webster CASTOR: a six-star system αGEM Σ 1110 RA 07 35 Dec 31 53 Castor was discovered in 1678 by G.D. Cassini and formally classified as a true “binary” in 1803 by William Herschel. The system lies at a distance of about 52 light years and is a six star...
A double star primer covering types of double star, how to observe them and their history, essential reading for anyone interested in observing double stars. Double Stars History etc (PowerPoint...
Neil Webster, REDACTED e-mail: REDACTED Introduction The following measurements were made throughout 2017 using a Meade 12mm astrometric illuminated reticle eyepiece plus 2.5x powermate attached to a Altair Astro 115mm refractor (focal length...
Neil Webster, REDACTED E-mail : REDACTED Introduction The following measurements were made with a Meade 12-mm astrometric illuminated reticule eyepiece attached to a recently purchased Altair Astro 115-mm refractor (focal length 805mm, f7). The optical train also...