Epsilon Lyrae

Epsilon Lyrae (ε Lyr, ε Lyrae), also known as the Double Double,[7] is a multiple star system of at least five stars approximately 162 light-years away in the constellation of Lyra.

"The Double Double" redirects here. For other uses, see double-double (disambiguation).

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 20.34589^s[1]
Declination	+39° 40′ 12.4533″[1]
Apparent magnitude (V)	4.66[2]
Epsilon^2 Lyrae
Right ascension	18^h 44^m 22.78056^s[1]
Declination	+39° 36′ 45.7851″[1]
Apparent magnitude (V)	4.59[2]
Characteristics
ε^1 Lyr
Spectral type	A3V + F0V[3]
U−B color index	+0.065[2]
B−V color index	+0.16[2]
ε^2 Lyr
Spectral type	A6Vn + A7Vn[3]
U−B color index	+0.075[2]
B−V color index	+0.18[2]
Astrometry
ε^1 Lyr
Radial velocity (Rv)	−31.20 ± 1.7[4] km/s
Proper motion (μ)	RA: 11.09[1] mas/yr Dec.: 61.39[1] mas/yr
Parallax (π)	20.10 ± 0.76[1] mas
Distance	162 ± 6 ly (50 ± 2 pc)
ε^2 Lyr
Radial velocity (Rv)	−24.40 ± 1.7[5] km/s
Proper motion (μ)	RA: 6.18[1] mas/yr Dec.: 50.42[1] mas/yr
Parallax (π)	20.97 ± 0.50[1] mas
Distance	156 ± 4 ly (48 ± 1 pc)
Details
ε^1 Lyr A
Mass	2.03[6] M☉
Luminosity	24[6] L☉
Temperature	7,943[6] K
Rotational velocity (v sin i)	165[6] km/s
ε^1 Lyr B
Mass	1.61[6] M☉
Luminosity	8.4[6] L☉
Temperature	7,047[6] K
Rotational velocity (v sin i)	159[6] km/s
ε^2 Lyr A
Mass	2.11[6] M☉
Luminosity	29[6] L☉
Temperature	7,816[6] K
Rotational velocity (v sin i)	212[6] km/s
ε^2 Lyr B
Mass	2.15[6] M☉
Luminosity	32[6] L☉
Temperature	7,852[6] K
Rotational velocity (v sin i)	233[6] km/s
Other designations
ADS 11635, WDS 18443+3940
ε^1 Lyr: 4 Lyrae, HIP 91919, BD+39°3509
ε^1 Lyr A: HD 173582, HR 7051, SAO 67310
ε^1 Lyr B: HD 173583, HR 7052, SAO 67309
Other designations
ε^2 Lyr: 5 Lyrae, HIP 91926, BD+39°3510
ε^2 Lyr A: HD 173607, HR 7053, SAO 67315
ε^2 Lyr B: HD 173608, HR 7054
Database references
	ε^1 Lyr
	ε^1 Lyr A
	ε^1 Lyr B
	ε^2 Lyr
	ε^2 Lyr A
	ε^2 Lyr B

Star System

Epsilon Lyrae, the Double Double

The widest two components of the system are easily separated when viewed through binoculars, or even with the naked eye under excellent conditions.[8]

The northern component is called ε¹ (ADS 11635 AB in multiple star notation) and the southern ε² (ADS 11635 CD); they lie around 160 light years from Earth and orbit each other over hundreds of thousands of years. Their separation of 208″ is about one hundred times that of the subcomponents. When viewed at higher magnifications, each intuitively likely "star" proves to be a set of shorter-term, close-orbiting binary stars. Ability to view these sub-components is a common benchmark for the resolving power of telescopes, since they 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. Main components of ε² have magnitudes 5.1 and 5.5 separated by 2.3", and orbit in perhaps half that period. ε¹ and ε² are more than 0.16 light years apart. An observer at one pair would see the other as strongly as a quarter (also known as half) Moon (which is about mv = −5.0), less than a degree away from each other.[9][10]

The fifth component of this system, orbiting one of the ε² pair, was detected by speckle interferometry in 1985 and confirmed in two later 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 further five nearby dimmer stars are also listed in multiple star catalogues:[11]

Multiple star components

	Magnitude	Spectral Type
A	5.15	A2
B	6.10	A4
C	5.25	A3
D	5.38	A5
E	11.71
F	11.2
G	13.83
H	13.22
I	10.43
Cb	?

Orbit pairs[8][11][12]

	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-Cb	0.1	5	225			recently discovered interferometric companion

References

1. van Leeuwen, F.; et al. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
2. Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Bibcode:1986EgUBV........0M. Cite journal requires |journal= (help)
3. Abt, Helmut A.; Morrell, Nidia I. (1995). "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars". Astrophysical Journal Supplement. 95: 135. Bibcode:1995ApJS...99..135A. doi:10.1086/192182.
4. Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065.
5. Kharchenko, N. V.; et al. (2007). "Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ~55000 stars and mean radial velocities of 516 Galactic open clusters and associations". Astronomische Nachrichten. 328 (9): 889. arXiv:0705.0878. Bibcode:2007AN....328..889K. doi:10.1002/asna.200710776.
6. Zorec, J.; Royer, F. (2012). "Rotational velocities of A-type stars. IV. Evolution of rotational velocities". Astronomy and Astrophysics. 537: A120. arXiv:1201.2052. Bibcode:2012A&A...537A.120Z. doi:10.1051/0004-6361/201117691.
7. Dawes, W R (1867). Catalogue of Micrometrical Measurements of Double Stars. Royal Astronomical Society. p. 409.
8. Burnham, Robert (1966). Burnham's Celestial Handbook. Dover Publications Inc. pp. 1151–1153. ISBN 0-486-24064-9.
9. Jim Kaler. "Epsilon Lyrae". Kaler's Stars. Retrieved 18 November 2013.
10. http://observing.skyhound.com/archives/jul/HR_7051.html
11. "Washington Double Star Catalog". Archived from the original on 17 May 2011. Retrieved 19 December 2010.
12. "Sixth Orbit Catalog". Archived from the original on 12 April 2009. Retrieved 19 December 2010.

External links

• Epsilon Lyrae -- The Double Double
• Epsilon Lyrae