Epsilon Lyrae

Epsilon Lyrae

ε (circled) in the constellation Lyra.
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Lyra
Epsilon^1 Lyrae
Right ascension	18^h 44^m 20.3453^s
Declination	+39° 40′ 12.444″
Apparent magnitude (V)	4.7
Epsilon^2 Lyrae
Right ascension	18^h 44^m 22.7803^s
Declination	+39° 36′ 45.798″
Apparent magnitude (V)	5.1
Characteristics
Spectral type	F1V + A8V
Astrometry
Parallax (π)	20.10 ± 0.76 mas
Distance	162 ± 6 ly (50 ± 2 pc)
Other designations
4 Lyr,
Other designations
4 Lyr, ADS 11635, BD +39 03509, HIP 91919, WDS 18443+3940.
ε^1 Lyr: HD 173582, HR 7051, SAO 67310.
ε^2 Lyr: HD 173583, HR 7052, SAO 67309.
Database references
SIMBAD	data
Database references
SIMBAD	data

Epsilon Lyrae (ε Lyr, ε Lyrae), also known as the Double Double, is a multiple star system approximately 162 light-years away in the constellation of Lyra.

Star System

The widest two components of the system are easily separated when viewed through binoculars, or even with the naked eye under excellent conditions.^[1] The northern component 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 sets of 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.^[2][3]

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.

Stars in the system

	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

^[1][4]

Orbit pairs

	Separation (arcsec)	Separation (au)	Most Recent Position Angle	Period (years)	Semi-major axis (arcseconds)	Notes
AB-CD	208.2	10,500	172			ε^1-ε^2
AB	2.3	116	347	1804.41	4.742	components of ε^1
CD	2.4	121	79	724.307	2.92	components of ε^2
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

^[1][4][5]

See also

• HD 98800

References

1. Burnham, Robert (1966). Burnham's Celestial Handbook. Dover Publications Inc. pp. 1151–1153. ISBN 0-486-24064-9.
2. Jim Kaler. "Epsilon Lyrae". Kaler's Stars. Retrieved 18 November 2013.
3. http://observing.skyhound.com/archives/jul/HR_7051.html
4. "Washington Double Star Catalog". Retrieved 19 December 2010.
5. "Sixth Orbit Catalog". Retrieved 19 December 2010.

External links

• Epsilon Lyrae -- The Double Double
• Epsilon Lyrae