This is a good article. Click here for more information.

61 Cygni

From Wikipedia, the free encyclopedia
Jump to: navigation, search
61 Cygni
Diagram showing star positions and boundaries of the Cygnus constellation and its surroundings
Cercle rouge 100%.svg

Location of 61 Cygni (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cygnus
61 Cygni A
Right ascension 21h 06m 53.9434s[1]
Declination +38° 44′ 57.898″[1]
Apparent magnitude (V) 5.20[1]
61 Cygni B
Right ascension 21h 06m 55.31s[2]
Declination +38° 44′ 31.4″[1]
Apparent magnitude (V) 6.05[2]
Characteristics
Spectral type K5V[1] / K7V[3]
U−B color index +1.155 / +1.242[4]
B−V color index +1.139 / +1.320[4]
Variable type A: BY Draconis[1]
B: Flare star[3]
Astrometry
Radial velocity (Rv) -64.3[1]/-63.5[3] km/s
Proper motion (μ) RA: 4156.93[1]/
 4109.17[3] mas/yr
Dec.: 3259.39[1]/
 3144.17[3] mas/yr
Parallax (π) 285.88 ± 0.54[5] mas
Distance 11.41 ± 0.02 ly
(3.498 ± 0.007 pc)
Absolute magnitude (MV) 7.506/8.228[6]
Details
61 Cygni A
Mass 0.70[7] M
Radius 0.665 ± 0.005[8] R
Luminosity 0.153 ± 0.01[8] L
Surface gravity (log g) 4.40[9] cgs
Temperature 4,526 ± 66[10] K
Metallicity [Fe/H] –0.20[9] dex
Rotation 35.37 d[11]
Age 6.1 ± 1[8] Gyr
61 Cygni B
Mass 0.63[7] M
Radius 0.595 ± 0.008[8] R
Luminosity 0.085 ± 0.007[8] L
Surface gravity (log g) 4.20[9] cgs
Temperature 4,077 ± 59[10] K
Metallicity [Fe/H] –0.27[9] dex
Rotation 37.84 d[11]
Age 6.1 ± 1[8] Gyr
Orbit[12]
Companion 61 Cygni B
Period (P) 678 ± 34 yr
Semi-major axis (a) 24.272 ± 0.592"
Eccentricity (e) 0.49 ± 0.03
Inclination (i) 51 ± 2°
Longitude of the node (Ω) 178 ± 2°
Periastron epoch (T) 1709 ± 16
Argument of periastron (ω)
(secondary)
149 ± 6°
Other designations
61 Cyg A/B

GJ 820 A/B, Struve 2758 A/B, ADS 14636 A/B, V1803 Cyg A/B, GCTP 5077.00 A/B [13]

61 Cyg A

V* V1803 Cyg, HD 201091, HIP 104214, HR 8085, BD+38°4343, LHS 62, SAO 70919 [1]

61 Cyg B

HD 201092, HIP 104217, HR 8086, BD+38°4344, LHS 63

[3]

61 Cygni /ˈsɪɡnɪ/ [note 1] is a visual binary system in the constellation Cygnus. Also known sometimes as "Bessel's Star" or "Piazzi's Flying Star", it consists of a pair of K-type dwarf stars that orbit each other in a period of about 659 years, forming a visual binary. At fifth and sixth apparent magnitudes, they can be seen with the naked eye only in rural areas without light pollution, requiring binoculars to be seen in city skies.

61 Cygni first attracted the attention of astronomers when its large proper motion was first demonstrated by Giuseppe Piazzi in 1804. In 1838, Friedrich Wilhelm Bessel measured its distance from Earth at about 10.3 light years, very close to the actual value of about 11.4 light years; this was the first distance estimate for any star other than the Sun, and first star to have its stellar parallax measured.

Over the course of the twentieth century, several different astronomers reported evidence of a massive planet orbiting one of the two stars, but recent high-precision radial velocity observations have shown that all such claims were erroneous.[14] However, no habitable planets have been confirmed in this stellar system to date.[15]

Name[edit]

61 Cygni is relatively dim and does not appear on ancient star maps and hence has not been associated with a traditional name in western[16] or Chinese systems.[17] Nonetheless, a full accounting of the over 3000 stars in the Chinese system has not yet been completed.

The name "61 Cygni" is part of the Flamsteed designation assigned to stars. According to this designation scheme, devised by John Flamsteed to catalog his observations, stars of a particular constellation are numbered in the order of their Right ascension, not in Greek letters as the Bayer designation does.[18][19] The star does not appear under that name in Flamsteed's Historia Coelestis Britannica,[20] although it has been stated by him that 61 Cygni actually corresponds to what he referred to as 85 Cygni in the 1712 edition, which was published against his wishes due to some known errors.[21]

Observation history[edit]

Early observations[edit]

The first well recorded observation of the star system using optical instruments was made by James Bradley on 25 September 1753, when he noticed it was a double star. William Herschel began systematic observations of 61 Cygni as part of a wider study on binary stars. His observations led to the conclusion that binary stars were separated enough that they would show different movements in parallax over the year, and hoped to use this as a way to measure the distance to the stars.[22]

61 Cygni showing proper motion at one year intervals.

In 1792, Giuseppe Piazzi was comparing his own observations of 61 Cygni with those of Bradley made 40 years earlier and noticed the high proper motion. This led to considerable interest in 61 Cygni by contemporary astronomers, and its continual observation since that date.[22] Piazzi's repeated measurements, which led to a definitive value of its motion, whose results he published in 1804.[23][24] It was in this record he christened the system as the "Flying Star".[25]

Piazzi noted that this motion likely corresponded to it being close to the Sun, and suggested it would be a prime candidate for an attempt to determine its distance though parallax measurements, along with two other possibilities, D Eridani and µ Cassiopeiae.[24]

Parallax measurement[edit]

A number of astronomers soon took up the task. Attempts include François Arago and Claude-Louis Mathieu in 1812 who recorded the distance at 500 mas and Christian Heinrich Friedrich Peters used Arago's data to calculate a value of 550 mas. Peters further calculated and made another better value based on observations made by Bernhard von Lindenau at Seeburg between 1812 and 1814 and calculated it to be 470 ±510 mas. Von Lindenau had already noted that he had seen no parallax, and as Friedrich Georg Wilhelm von Struve pointed out after his own test series between 1818 and 1821, all of these numbers are more accurate than the range of the instrument used.[22]

Friedrich Wilhelm Bessel made a notable contribution in 1812 when he used a different method to measure distance. Assuming the orbital period of the two stars in the binary to be 400 years, he estimated the distance between the two this would require, and then measured the angular distance between the stars. This led to a value of 460 mas. He then followed this up with direct parallax measurements in a series of observations between 1815 and 1816, comparing it with six other stars. The two sets of measurements produced values of 760 and 1320 mas. All of these estimates, like earlier attempts by others, retained inaccuracies greater than the measurements.[22]

When Joseph von Fraunhofer invented a new type of heliometer, Bessel carried out another set of measurements using this device in 1837 and 1838 at Königsberg. He published his findings in 1838 with a value of 369.0±19.1 mas to A and 260.5±18.8 to B, and estimated the center point to be at 313.6±13.6. This corresponds to a distance of about 600,000 astronomical units, or about 10.4 light years. This was the first direct and reliable measurement of the distance to a star other than the sun.[22][26] His measurement was published only shortly before similar parallax measurements of Vega by Friedrich Georg Wilhelm von Struve and Alpha Centauri by Thomas Henderson that same year.[27] Bessel continued to make additional measurements at Königsberg, publishing a total of four complete observational runs, the last in 1868. The best of these placed the center point at 360.2 ±12.1 mas, made during observations in 1849.[22] This is close to the currently accepted value of 287.18 mas (yielding 11.36 light years).[28]

Only a few years after Bessel's measurement, in 1842 Friedrich Wilhelm Argelander noted that Groombridge 1830 had an even larger proper motion, and 61 Cygni became the second highest known. It was later moved further down the list by Kapteyn's Star and Barnard's Star. 61 Cygni currently has the seventh highest proper motion of all stellar systems listed in the modern Hipparcos Catalogue, but retains the title of highest proper motion among visible stars.[29]

By 1911, further observations had improved on Bessel's parallax measurement of 313.6 mas to 310.0 mas. This corresponds to a motion transverse to our line of sight of 79 km/s. Observations at Yerkes Observatory had measured its radial velocity as 62 km/s.[30] Using the two measurements together yielded a space velocity of about 100 km/s, moving towards a point about 12 degrees west of Orion's belt.[note 2][note 3]

Binary observations[edit]

Due to the wide angular separation between A and B, and the correspondingly slow orbital motion, it was initially unclear whether the two stars in the 61 Cygni system were a gravitationaly bound system or simply a juxtaposition of stars.[31] von Struve first argued for its status as a binary in 1830, but the matter remained open.[31]

However, by 1917 refined measured parallax differences demonstrated that the separation was significantly less.[32] The binary nature of this system was clear by 1934, and orbital elements were published.[33]

In 1911, Benjamin Boss published data indicating that the 61 Cygni system was a member of a comoving group of stars.[30] This group containing 61 Cygni was later expanded to include 26 potential members. Possible members include Beta Columbae, Pi Mensae, 14 Tauri and 68 Virginis. The typical space velocities of this group of stars is 105–114 km/s relative to the Sun.[34][35]

Amateur observation[edit]

An observer using 7×50 binoculars can find 61 Cygni two binocular fields south-east of the bright star Deneb. The angular separation of the two stars is slightly greater than the angular size of Saturn (16–20″).[36] So, under ideal viewing conditions, the binary system can be resolved by a telescope with a 7 mm aperture.[note 4] This is well within the capability for aperture of typical binoculars, though to resolve the binary these need a steady mount and some 10x magnification. With a separation of 28 arc-seconds between the component stars, 10x magnification would give an apparent separation of 280 arc-seconds, above the generally-regarded eye resolution limit of 4 arc-minutes or 240 arc-seconds.[37]

Properties[edit]

Although it appears to be a single star to the naked eye, 61 Cygni is in fact a widely separated binary star system, composed of two K class (orange) main sequence stars, 61 Cygni A and 61 Cygni B. The brighter star 61 Cygni A is of apparent magnitude 5.2, the fainter 61 Cygni B is 6.1. Both appear to be old-disk stars,[38][39] with an estimated age that is older than the Sun. The system has a net space velocity of 108 km/s[40] relative to the Sun, which results in the high proper motion across the sky.[41] At a distance of just over 11 light years, it is the 15th nearest known star system to the Earth (not including the Sun). 61 Cygni A is the fourth nearest star that is visible to the naked eye for mid-latitude northern observers, after Sirius, Epsilon Eridani, and Procyon A.[7] This system will make its closest approach at about 20,000 CE, when the separation from the Sun will be about 9 light years.[40]

61 Cygni A's long term stability led to it being selected as an "anchor star" in the Morgan–Keenan (MK) classification system in 1943, serving as the K5 V "anchor point" since that time.[42] Starting in 1953, 61 Cygni B has been considered a K7 V standard star (Johnson & Morgan 1953,[43] Keenan & McNeil 1989[44]).

A size comparison between the Sun (left), 61 Cygni A (bottom) and 61 Cygni B (upper right).

61 Cygni A is a typical BY Draconis variable star designated as V1803 Cyg while 61 Cygni B is a flare type variable star named HD 201092 with their magnitudes varying 5.21 V and 6.03 respectively.[45] The two stars orbit their common barycenter in a period of 659 years, with a mean separation of about 84 AU—84 times the separation between the Earth and the Sun. The relatively large orbital eccentricity of 0.48 means that the two stars are separated by about 44 A.U. at periapsis and 124 A.U. at apoapsis.[note 5] The leisurely orbit of the pair has made it difficult to pin down their respective masses, and the accuracy of these values remain somewhat controversial. In the future this issue may be resolved through the use of asteroseismology.[8] Cygnus A has about 11% more mass than Cygnus B.[7]

It has an activity cycle that is much more pronounced than the solar sunspot cycle. This is a complex activity cycle that varies with a period of about 7.5±1.7 years.[46] (An earlier estimate gave a period of 7.3 years.)[47] The combination of starspot activity combined with rotation and chromospheric activity is characteristic of a BY Draconis variable. Because of differential rotation, this star's surface rotation period varies by latitude from 27 to 45 days, with an average period of 35 days.[11]

The orbital motion of component B relative to component A as seem from Earth as well as the true appearance from face-on view. The time steps are approximately 10 years.

The outflow of the stellar wind from component A produces a bubble within the local interstellar cloud. Along the direction of the star's motion within the Milky Way, this extends out to a distance of only 30 AU, or roughly the orbital distance of Neptune from the Sun. This is lower than the separation between the two components of 61 Cygni, and so the two most likely do not share a common atmosphere. The compactness of the astrosphere is likely due to the low mass outflow and the relatively high velocity through the local medium.[48]

Cygnus B displays a more chaotic pattern of variability than A, with significant short-term flares. There is an 11.7-year periodicity to the overall activity cycle of B.[47] Both stars exhibit stellar flare activity, but the chromosphere of B is 25% more active than for Cygnus A.[49] As a result of differential rotation, the period of rotation varies by latitude from 32 to 47 days, with an average period of 38 days.[11]

There is some disagreement over the evolutionary age of this system. Kinematic data gives an age estimate of about 10 Gyr.[41] Gyrochronology, or the age determination of a star based on its rotation and color, results in an average age of 2.0 ± 0.2 Gyr. The ages based on chromospheric activity for A and B are 2.36 Gyr and 3.75 Gyr, respectively. Finally the age estimates using the isochrone method, which involve fitting the stars to evolutionary models, yield upper limits of 0.44 Gyr and 0.68 Gyr.[50] However, a 2008 evolutionary model using the CESAM2k code from the Côte d'Azur Observatory gives an age estimate of 6.0 ± 1.0 Gyr for the pair.[8]

Claims of a planetary system[edit]

On several occasions, it has been claimed that 61 Cygni might have unseen low-mass companions, planets or a brown dwarf. Kaj Strand of the Sproul Observatory, under the direction of Peter van de Kamp, made the first such claim in 1942 using observations to detect tiny but systematic variations in the orbital motions of 61 Cygni A and B. These perturbations suggested that a third body of about 16 Jupiter masses must be orbiting 61 Cygni A.[51] Reports of this third body served as inspiration for Hal Clement's 1953 science fiction novel Mission of Gravity.[52] In 1957, van de Kamp narrowed his uncertainties, claiming that the object had a mass of eight times that of Jupiter, a calculated orbital period of 4.8 years, and a semi-major axis of 2.4 AU.[53] In 1977, Soviet astronomers at the Pulkovo Observatory near Saint Petersburg suggested that the system included three planets: two giant planets with six and twelve Jupiter masses around 61 Cyg A,[54] and one giant planet with seven Jupiter masses around 61 Cygni B.[55]

In 1978, Wulff-Dieter Heintz of the Sproul Observatory proved that these claims, as well as the claims for unseen companions around many other stars, were spurious, having failed to detect any evidence of such motion down to six percent of the Sun's mass—equivalent to about 60 times the mass of Jupiter.[56][57]

The habitable zone for 61 Cygni A, defined as the locations where liquid water could be present on an Earth-like planet, is 0.26–0.58 AU, where 1 AU is the average distance from the Earth to the Sun. For 61 Cygni B, the habitable zone is 0.24–0.50.[58]

Refining planetary boundaries[edit]

Since no certain planetary object has been detected around either star so far, McDonald Observatory team has set limits to the presence of one or more planets around 61 Cygni A and 61 Cygni B with masses between 0.07 and 2.1 Jupiter masses and average separations spanning between 0.05 and 5.2 AU.[59]

Because of the proximity of this system to the Sun, it is a frequent target of interest for astronomers. Both stars were selected by NASA as "Tier 1" targets for the proposed optical Space Interferometry Mission.[60] This mission is potentially capable of detecting planets with as little as 3 times the mass of the Earth at an orbital distance of 2 AU from the star.

Measurements of this system appeared to have detected an excess of far infrared radiation, beyond what is emitted by the stars. Such an excess is sometimes associated with a disk of dust, but in this case it lies sufficiently close to one or both of the stars that it has not been resolved with a telescope.[61] A 2011 study using the Keck Interferometer Nuller failed to detect any exozodiacal dust around 61 Cygni A.[62]

See also[edit]

Distance estimates[edit]

61 Cygni distance estimates

Source Parallax, mas Distance, pc Distance, ly Distance, Pm Ref.
Bessel (1839) ~ 313.6 ~ 3.2 ~ 10.4 ~ 98.4 [28]
Woolley et al. (1970) 296±4 3.38±0.05 11.02±0.15 104.2±1.4 [63]
Gliese & Jahreiß (1991) 288.7±1.9 3.464±0.023 11.3±0.07 106.9±0.7 [64]
van Altena et al. (1995) 286.9±1.1 3.486±0.013 11.37±0.04 107.6±0.4 [65]
Perryman et al. (1997) (A)
(Hipparcos)
287.13±1.51 3.483±0.018 11.36±0.06 107.5±0.6 [66]
Perryman et al. (1997) (B)
(Hipparcos)
285.42±0.72 3.504±0.009 11.427±0.029 108.11±0.27 [67]
Perryman et al. (1997) (A)
(Tycho)
(absents) [68]
Perryman et al. (1997) (B)
(Tycho)
282.20±5.7 3.54±0.07 11.56+0.24
−0.23
109.3+2.3
−2.2
[69]
van Leeuwen (2007) (A) 286.82±6.78 3.49±0.08 11.37+0.28
−0.26
107.6+2.6
−2.5
[70]
van Leeuwen (2007) (B) 285.88±0.54 3.498±0.007 11.409±0.022 107.94±0.2 [71]
RECONS TOP100 (2012) 286.08±0.48[note 6] 3.496±0.006 11.401±0.019 107.86±0.18 [72]

Non-trigonometric distance estimates are marked in italic. The most precise estimate is marked in bold.

Notes[edit]

  1. ^ Not to be confused with 16 Cygni, a more distant system containing two G-type stars harboring the gas giant planet 16 Cygni Bb.
  2. ^ The space velocity calculated from 1911 data: parallax 310 mas yields 10.5 light years; total proper motion= 5.205 arcsec/year (average by mass) or 79.4 km/s; and radial velocity = -62 km/s.
  3. ^ This yields a 1911 space velocity of \begin{smallmatrix}\sqrt{79.4^2\ +\ 62^2}\ =\ 100\end{smallmatrix} km/s. Compare with more accurate 1953, 1997 data: parallax 287.18 yields 11.36 ly and so an increased proper motion velocity of 87 km/s; radial velocity -64 km/s yields a net space velocity of \begin{smallmatrix}\sqrt{87^2\ +\ 64^2}\ =\ 106\end{smallmatrix} km/s.
  4. ^ Per the Rayleigh criterion: \begin{smallmatrix}\alpha_R\ =\ \frac{138}{D}\end{smallmatrix} mm.
  5. ^ At periapsis: \begin{smallmatrix}r_{per}\ =\ (1\ -\ e)\cdot a\ \approx\ 44\end{smallmatrix} A.U.
    At apoapsis: \begin{smallmatrix}r_{ap}\ =\ (1\ +\ e)\cdot a\ \approx\ 124\end{smallmatrix} A.U.
  6. ^ Weighted parallax based on parallaxes from van Altena et al. (1995) and van Leeuwen (2007) for A and B components.

References[edit]

  1. ^ a b c d e f g h i j "SIMBAD Query Result: V* V1803 Cyg -- Variable of BY Dra type". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2007-07-15.  (61 Cygni A)
  2. ^ a b "stellar-database.com". Retrieved March 19, 2015. 
  3. ^ a b c d e f "SIMBAD Query Result: NSV 13546 -- Flare Star". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2007-07-15.  (61 Cygni B)
  4. ^ a b Blanco, C.; Marilli, E.; Catalano, S. (1979). "Photoelectric observations of stars with variable H and K emission components. III". Astronomy and Astrophysics Supplement Series 36: 297–306. Bibcode:1979A&AS...36..297B. 
  5. ^ van Leeuwen, F. (November 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 
  6. ^ Kovtyukh, V. V.; Soubiran, C., Belik, S. I.; Gorlova, N. I.; Gorlova, N. I. (December 2003), "High precision effective temperatures for 181 F-K dwarfs from line-depth", Astronomy and Astrophysics 411 (3): 559–564, arXiv:astro-ph/0308429, Bibcode:2003A&A...411..559K, doi:10.1051/0004-6361:20031378  See Mv values in Table 1, p. 9.
  7. ^ a b c d Staff (June 8, 2007), List of the Nearest 100 Stellar Systems, Research Consortium on Nearby Stars, Georgia State University, archived from the original on 1 July 2007, retrieved 2007-07-15 
  8. ^ a b c d e f g h Kervella, P. et al. (September 2008), "The radii of the nearby K5V and K7V stars 61 Cygni A & B. CHARA/FLUOR interferometry and CESAM2k modeling", Astronomy and Astrophysics 488 (2): 667–674, arXiv:0806.4049, Bibcode:2008A&A...488..667K, doi:10.1051/0004-6361:200810080 
  9. ^ a b c d Luck, R. Earle; Heiter, Ulrike (2005), "Stars within 15 Parsecs: Abundances for a Northern Sample", The Astronomical Journal 129 (2): 1063–1083, Bibcode:2005AJ....129.1063L, doi:10.1086/427250 
  10. ^ a b van Belle, Gerard T.; von Braun, Kaspar (2009), "Directly Determined Linear Radii and Effective Temperatures of Exoplanet Host Stars", The Astrophysical Journal 694 (2): 1085–109, arXiv:0901.1206, Bibcode:2009ApJ...694.1085V, doi:10.1088/0004-637X/694/2/1085 
  11. ^ a b c d Böhm-Vitense, Erika (March 2007), "Chromospheric Activity in G and K Main-Sequence Stars, and What It Tells Us about Stellar Dynamos", The Astrophysical Journal 657 (1): 486–493, Bibcode:2007ApJ...657..486B, doi:10.1086/510482 
  12. ^ Hartkopf, W. I.; Mason, Brian D. "Sixth Catalog of Orbits of Visual Binary Stars". U.S. Naval Observatory. Retrieved 2008-07-12. 
  13. ^ "SIMBAD Query Result: ADS 14636 AB -- Double or multiple star". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2009-04-01.  (61 Cygni)
  14. ^ Wittenmyer, R. A.; Endl, M.; Cochran, W.D.; Hatzes , A.; Walker, G. A. H.; Yang, S. L. S.; Paulson, D. B. (2006). "Detection limits from the McDonald Observatory planet search program". Astronomical Journal 132 (1): 177–188. arXiv:astro-ph/0604171. Bibcode:2006AJ....132..177W. doi:10.1086/504942. 
  15. ^ "61 Cygni B". Retrieved March 17, 2015. 
  16. ^ Allen, Richard Hinckley (2003). Star Names and Their Meanings. Kessinger. p. 219. ISBN 9780766140288. 
  17. ^ Sun, Xiaochun; Kistemaker, Jacob (1997). The Chinese Sky During the Han: Constellating Stars and Society. Brill. ISBN 9789004107373. 
  18. ^ "Naming Objects Outside the Solar System-Stars". IAU. Retrieved March 19, 2015. 
  19. ^ "Stars-astro-illinois". Retrieved March 19, 2015. 
  20. ^ Flamsteed, John (1725). Historia Coelestis Britannica. Meere. p. 5. 
  21. ^ Dibon-Smith, Richard (1998). The Flamsteed Collection. Clear Skies. p. xi. 
  22. ^ a b c d e f Hopkins, Mary Murray (November 1916). "The Parallax of 61 Cygni". Journal of the Royal Astronomical Society of Canada: 498–504. 
  23. ^ Piazzi, Giuseppe (1803). Praecipuarum stellarum inerrantium positiones mediae ineunte seculo XIX: ex observationibus habitis in specula Panormitana ab anno 1792 ad annum 1802. Typis regiis. p. 111. 
  24. ^ a b Fodera-Serio, G. (1990). "Giuseppe Piazzi and the Discovery of the Proper Motion of 61-Cygni". Journal of the History of Astronomy 21 (3): 275. Bibcode:1990JHA....21..275F. 
  25. ^ Hirshfeld, Alan (2001). Parallax: The Race to Measure the Cosmos. Macmillan. ISBN 0-7167-3711-6. 
  26. ^ Frommert, Hartmut; Kronberg, Christine. "Friedrich Wilhelm Bessel". Students for the Exploration and Development of Space. Retrieved 2009-04-03. 
  27. ^ Hughes, Stefan (2012). Catchers of the Light. ArtDeCiel Publishing. p. 702. ISBN 9781620509616. 
  28. ^ a b Bessel, F. W. (1839). "Bestimmung der Entfernung des 61sten Sterns des Schwans. Von Herrn Geheimen – Rath und Ritter Bessel". Astronomische Nachrichten (in German) 16 (5-6): 65. Bibcode:1839AN.....16...65B. doi:10.1002/asna.18390160502. (page 92) Ich bin daher der Meinung, daß nur die jährliche Parallaxe = 0"3136 als das Resultat der bisherigen Beobachtungen zu betrachten ist 
  29. ^ Staff (May 4, 2007). date "High Proper Motion Stars: Interesting Areas to View". ESA. Retrieved 2007-07-16. 
  30. ^ a b Boss, Benjamin (1911). "Community of motion among several stars of large proper-motion". Astronomical Journal 27 (629): 33–37. Bibcode:1911AJ.....27...33B. doi:10.1086/103931. 
  31. ^ a b Davis, Merhan S. (1898). "Remarks regarding the parallaxes of 61 Cygni and the probable physical connection of these two stars". Astrophysical Journal 8: 246–247. Bibcode:1898ApJ.....8..246D. doi:10.1086/140527. 
  32. ^ Adams, W. S.; Joy, A. H. (1917). "The luminosities and parallaxes of five hundred stars". Astrophysical Journal 46: 313–39. Bibcode:1917ApJ....46..313A. doi:10.1086/142369. —See Table I, page 326
  33. ^ Baize, P. (1950). "Second catalogue d'orbites d'Etoiles Doubles visuelles". Journal des Observateurs (in French) 33: 1–31. Bibcode:1950JO.....33....1B. —on page 19, the authority is listed as Zagar (1934).
  34. ^ Eggen, O. J. (1959). "White dwarf members of the 61 Cygni group". The Observatory 79: 135–39. Bibcode:1959Obs....79..135E.  – Gives space velocity components of U=+94, V=–53 and W=–7 for HD 201091/2.
  35. ^ Sol Company. "System Summary Pi Mensae". Sol Company. Retrieved May 1, 2015. 
  36. ^ Espenak, Fred (July 25, 1996). "Twelve Year Planetary Ephemeris: 1995–2006". NASA. Retrieved 2007-07-25. 
  37. ^ "SAT.com". SAT.com. Retrieved March 19, 2015. 
  38. ^ Gudel, M. (1992). "Radio and X-ray emission from main-sequence K stars". Astronomy and Astrophysics 264 (2): L31–L34. Bibcode:1992A&A...264L..31G. 
  39. ^ Eggen, Olin J. (October 1969), "Stellar Groups in the Old Disk Population", Publications of the Astronomical Society of the Pacific 81 (482): 553, Bibcode:1969PASP...81..553E, doi:10.1086/128823 
  40. ^ a b Anonymous (March 18, 2006). "Long-Term Stellar Motions, part 2: Shortcuts". The Astronomy Nexus. Archived from the original on 9 November 2007. Retrieved 2007-10-21. 
  41. ^ a b Affer, L.; Micela, G.; Morel, T.; Sanz-Forcada, J.; Favata, F. (2005). "Spectroscopic determination of photospheric parameters and chemical abundances of 6 K-type stars". Astronomy and Astrophysics 433 (2): 647–658. Bibcode:2005A&A...433..647A. doi:10.1051/0004-6361:20041308. 
  42. ^ Garrison, R. F. (December 1993), "Anchor Points for the MK System of Spectral Classification", Bulletin of the American Astronomical Society 25: 1319, Bibcode:1993AAS...183.1710G, retrieved 2012-02-04 
  43. ^ Johnson, H. L.; Morgan, W. W. (1953). "Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas". Astrophysical Journal 117: 313. Bibcode:1953ApJ...117..313J. doi:10.1086/145697. 
  44. ^ Keenan, P. C.; McNeil, R. C. (October 1989). "The Perkins Catalog of Revised MK Types for the Cooler Stars". Astrophysical Journal Supplement Series 71: 245–266. Bibcode:1989ApJS...71..245K. doi:10.1086/191373. 
  45. ^ "Simbad". Retrieved March 20, 2015. 
  46. ^ Frick, P.; Baliunas, S. L.; Galyagin, D.; Sokoloff, D.; Soon, W. (1997). "Wavelet Analysis of Chromospheric Activity". Astrophysical Journal 483 (1): 426–434. Bibcode:1997ApJ...483..426F. doi:10.1086/304206. 
  47. ^ a b Hempelmann, A.; Schmitt, J. H. M. M.; Baliunas, S. L.; Donahue, R. A. (2003). "Evidence for coronal activity cycles on 61 Cygni A and B". Astronomy and Astrophysics 406 (2): L39–L42. Bibcode:2003A&A...406L..39H. doi:10.1051/0004-6361:20030882. 
  48. ^ Wood, Brian E.; Müller, Hans-Reinhard; Zank, Gary P.; Linsky, Jeffrey L. (July 2002). "Measured Mass-Loss Rates of Solar-like Stars as a Function of Age and Activity". The Astrophysical Journal 574 (1): 412–425. arXiv:astro-ph/0203437. Bibcode:2002ApJ...574..412W. doi:10.1086/340797. 
  49. ^ Hempelmann, A.; Robrade, J.; Schmitt, J. H. M. M.; Favata, F.; Baliunas, S. L.; Hall, J. C. (2006). "Coronal activity cycles in 61 Cygni". Astronomy and Astrophysics 460 (1): 261–267. Bibcode:2006A&A...460..261H. doi:10.1051/0004-6361:20065459. 
  50. ^ Barnes, Sydney A. (November 2007). "Ages for Illustrative Field Stars Using Gyrochronology: Viability, Limitations, and Errors". The Astrophysical Journal 669 (2): 1167–1189. arXiv:0704.3068. Bibcode:2007ApJ...669.1167B. doi:10.1086/519295. 
  51. ^ Strand, K. Aa. (1943). "61 Cygni as a Triple System". Publications of the Astronomical Society of the Pacific 55 (322): 29–32. Bibcode:1943PASP...55...29S. doi:10.1086/125484. 
  52. ^ Darrell Schweitzer, Theodore Sturgeon, Alfred Bester (2009). "Science Fiction Voices #1". Wildside Press LLC. pp. 64 pages. Retrieved May 1, 2015. 
  53. ^ Strand, K. Aa. (1957). "The orbital motion of 61 Cygni". The Astronomical Journal 62: 35. Bibcode:1957AJ.....62Q..35S. doi:10.1086/107588. 
  54. ^ Cumming, A.; Marcy, G. W.; Butler, R. P. (1999). "The Lick planet search: detectability and mass thresholds". Astrophysical Journal 526 (2): 890–915. arXiv:astro-ph/9906466. Bibcode:1999ApJ...526..890C. doi:10.1086/308020. 
  55. ^ Deich, A. N. (1977). "Invisible companions of the binary star 61 Cygni". [Soviet Astronomy] 21: 182–188. Bibcode:1977SvA....21..182D. 
  56. ^ Heintz, W. D. (1978). "Reexamination of suspected unresolved binaries". The Astrophysical Journal 220: 931–934. Bibcode:1978ApJ...220..931H. doi:10.1086/155982. 
  57. ^ Walker, G. A. H.; Walker, A. R.; Irwin, A. W.; Larson, A. M.; Yang, S. L. S.; Richardson, D. C (1995). "A search for Jupiter-mass companions to nearby stars". Icarus 116 (2): 359–375. Bibcode:1995Icar..116..359W. doi:10.1006/icar.1995.1130. 
  58. ^ Cantrell, Justin R. et al. (October 2013), "The Solar Neighborhood XXIX: The Habitable Real Estate of Our Nearest Stellar Neighbors", The Astronomical Journal 146 (4): 99, arXiv:1307.7038, Bibcode:2013AJ....146...99C, doi:10.1088/0004-6256/146/4/99 
  59. ^ Wittenmyer, R. A. et al. (May 2006). "Detection Limits from the McDonald Observatory Planet Search Program". The Astronomical Journal 132 (1): 177–188. arXiv:astro-ph/0604171. Bibcode:2006AJ....132..177W. doi:10.1086/504942. 
  60. ^ "SIM Planet Search Tier 1 Target Stars". San Francisco State University. Archived from the original on 4 August 2007. Retrieved 2007-07-23. 
  61. ^ Kuchner, Marc J.; Brown, Michael E.; Koresko, Chris D. (1998). "An 11.6 Micron Keck Search for Exo-Zodiacal Dust". The Publications of the Astronomical Society of the Pacific 110 (753): 1336–41. arXiv:astro-ph/0002040. Bibcode:1998PASP..110.1336K. doi:10.1086/316267. 
  62. ^ Millan-Gabet, R.; Serabyn, E.; Mennesson, B.; Traub, W. A.; Barry, R. K.; Danchi, W. C.; Kuchner, M.; Stark, C. C.; Ragland, S.; Hrynevych, M.; Woillez, J.; Stapelfeldt, K.; Bryden, G.; Colavita, M. M.; Booth, A. J. (June 2011), "Exozodiacal Dust Levels for Nearby Main-sequence Stars: A Survey with the Keck Interferometer", The Astrophysical Journal 734 (1): 67, arXiv:1104.1382, Bibcode:2011ApJ...734...67M, doi:10.1088/0004-637X/734/1/67.  See Table 5, p. 58.
  63. ^ Woolley R.; Epps E. A.; Penston M. J.; Pocock S. B. (1970). "Woolley 820". Catalogue of stars within 25 parsecs of the Sun. Retrieved 2015-03-18. 
  64. ^ Gliese, W. and Jahreiß, H. (1991). "Gl 820". Preliminary Version of the Third Catalogue of Nearby Stars. Retrieved 2015-03-18. 
  65. ^ Van Altena W. F., Lee J. T., Hoffleit E. D. (1995). "GCTP 5077". The General Catalogue of Trigonometric Stellar Parallaxes (Fourth ed.). Retrieved 2015-03-18. 
  66. ^ Perryman et al. (1997). "HIP 104214". The Hipparcos and Tycho Catalogues. Retrieved 2015-03-18. 
  67. ^ Perryman et al. (1997). "HIP 104217". The Hipparcos and Tycho Catalogues. Retrieved 2015-03-18. 
  68. ^ Perryman et al. (1997). "HIP 104214". The Hipparcos and Tycho Catalogues. Retrieved 2015-03-18. 
  69. ^ Perryman et al. (1997). "HIP 104217". The Hipparcos and Tycho Catalogues. Retrieved 2015-03-18. 
  70. ^ van Leeuwen F. (2007). "HIP 104214". Validation of the new Hipparcos reduction. Retrieved 2015-03-18. 
  71. ^ van Leeuwen F. (2007). "HIP 104217". Validation of the new Hipparcos reduction. Retrieved 2015-03-18. 
  72. ^ "RECONS TOP100". THE ONE HUNDRED NEAREST STAR SYSTEMS brought to you by RECONS (Research Consortium On Nearby Stars). 2012. Retrieved 2015-03-18. 

External links[edit]

Coordinates: Sky map 21h 06m 53.9434s, +38° 44′ 57.898″