Epsilon Lyrae
Encyclopedia
Epsilon Lyrae (ε Lyr, ε Lyrae), also known as the Double Double, is a multiple star system
approximately 162 light-year
s away in the constellation
of Lyra
.
under excellent conditions. The northern star is called ε1 and the southern one is called ε2; they both lie around 162 light years from Earth and orbit each other. When viewed at higher magnifications, both stars of the binary can be further split into binaries; that is, the system contains two binary stars orbiting each other. Being able to view the components of each is a common benchmark for the resolving power of telescopes, since the individual doubles are so close together: the stars of ε1 were 2.35 arc-seconds apart in 2006, those of ε2 were separated by about the same amount in that year. Since the first high-precision measurements of their orbit in the 1980s, both binaries have moved only a few degrees in position angle
.
The component stars of ε1 have magnitudes of 4.7 and 6.2 separated by 2.6" and have an orbital period that can only be crudely estimated at 1200 years, which places them at roughly 140 AU apart. The component stars of ε2 have magnitudes 5.1 and 5.5 separated by 2.3", and orbit in perhaps half that period. ε1 and ε2 themselves are not closer than 0.16 light years apart, and would take hundreds of thousands of years to complete an orbit. An observer at one pair would see the other pair shining with the light of a quarter Moon (which is about mv = -5.0), less than a degree away from each other.
A fifth component of this system, orbiting one of the ε2 pair, was detected by speckle interferometry
in 1985 and confirmed in two subsequent observations. No orbit can be prepared from such limited data, but its rapid motion suggests a period of a few tens of years. Its maximum observed separation of 0.2 arc-seconds precludes direct visual observation.
A number of other nearby stars may also be part of the system, bringing the system to a total of ten stars. The arrangement of the system is summarised in the tables below.
Multiple star
A multiple star consists of three or more stars which appear from the Earth to be close to one another in the sky. This may result from the stars being physically close and gravitationally bound to each other, in which case it is physical, or this closeness may be merely apparent, in which case...
approximately 162 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s away in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
of Lyra
Lyra
Lyra is a small constellation. It is one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations recognized by the International Astronomical Union. Its principal star, Vega — a corner of the Summer Triangle — is one of the brightest...
.
Star System
The widest two components of the system are easily separated when viewed through binoculars, or even with the naked eyeNaked eye
The naked eye is a figure of speech referring to human visual perception unaided by a magnifying or light-collecting optical device, such as a telescope or microscope. Vision corrected to normal acuity using corrective lenses is considered "naked"...
under excellent conditions. The northern star is called ε1 and the southern one is called ε2; they both lie around 162 light years from Earth and orbit each other. When viewed at higher magnifications, both stars of the binary can be further split into binaries; that is, the system contains two binary stars orbiting each other. Being able to view the components of each is a common benchmark for the resolving power of telescopes, since the individual doubles are so close together: the stars of ε1 were 2.35 arc-seconds apart in 2006, those of ε2 were separated by about the same amount in that year. Since the first high-precision measurements of their orbit in the 1980s, both binaries have moved only a few degrees in position angle
Position angle
Position angle, usually abbreviated PA, is a measurement derived from observing visual binary stars. It is defined as the angular offset in degrees of the secondary star to the primary, relative to the north celestial pole....
.
The component stars of ε1 have magnitudes of 4.7 and 6.2 separated by 2.6" and have an orbital period that can only be crudely estimated at 1200 years, which places them at roughly 140 AU apart. The component stars of ε2 have magnitudes 5.1 and 5.5 separated by 2.3", and orbit in perhaps half that period. ε1 and ε2 themselves are not closer than 0.16 light years apart, and would take hundreds of thousands of years to complete an orbit. An observer at one pair would see the other pair shining with the light of a quarter Moon (which is about mv = -5.0), less than a degree away from each other.
A fifth component of this system, orbiting one of the ε2 pair, was detected by speckle interferometry
Speckle imaging
Speckle imaging describes a range of high-resolution astronomical imaging techniques based either on the shift-and-add method or on speckle interferometry methods...
in 1985 and confirmed in two subsequent observations. No orbit can be prepared from such limited data, but its rapid motion suggests a period of a few tens of years. Its maximum observed separation of 0.2 arc-seconds precludes direct visual observation.
A number of other nearby stars may also be part of the system, bringing the system to a total of ten stars. The arrangement of the system is summarised in the tables below.
| Magnitude | Spectral Type | |
|---|---|---|
| A | 5.02 | A2 |
| B | 6.02 | A4 |
| C | 5.14 | A3 |
| D | 5.37 | A5 |
| E | 11.71 | |
| F | 11.2 | |
| G | 13.83 | |
| H | 13.22 | |
| I | 10.43 | |
| a | 10.43 |
| Separation (arcsec) | Separation (au) | Most Recent Position Angle | Period (years) | Semi-major axis (arcseconds) | Notes | |
|---|---|---|---|---|---|---|
| AB-CD | 208.2 | 10,500 | 238 | ε1-ε2 | ||
| AB | 2.3 | 116 | 347 | 1804.41 | 4.742 | components of ε1 |
| CD | 2.4 | 121 | 79 | 724.307 | 2.92 | components of ε2 |
| Ca | 0.1 | 5 | 225 | recently discovered interferometric companion | ||
| AI | 149.6 | 7500 | 138 | |||
| CE | 63.7 | 3200 | 333 | |||
| EF | 46 | 2300 | 37 | |||
| EG | 50 | 2500 | 238 | |||
| GH | 35 | 1800 | 358 |