61 Cygni

:"Not be confused with 16 Cygni, a more distant system containing two G-type stars harboring the gas giant planet 16 Cygni Bb."Starbox begin
name=61 CygniStarbox image


caption=Expanded view of the star field around 61 Cygni. This system is located at the end of the arrow above.Starbox observe 2s
epoch = J2000.0
equinox = J2000.0
constell = Cygnus
component1 = 61 Cygni A
ra1 = RA|21|06|53.9434cite web |url=http://simbad.u-strasbg.fr/sim-id.pl?protocol=html&Ident=HD+201091 |title=SIMBAD Query Result: V* V1803 Cyg -- Variable of BY Dra type |work=SIMBAD |publisher=Centre de Données astronomiques de Strasbourg |accessdate=2007-07-15 (61 Cygni A)]
dec1 = DEC|+38|44|57.898
appmag_v1 = 5.21
component2 = 61 Cygni B
ra2 = RA|21|06|55.2648cite web |url=http://simbad.u-strasbg.fr/sim-id.pl?protocol=html&Ident=HD+201092 |title=SIMBAD Query Result: NSV 13546 -- Flare Star| work=SIMBAD |publisher=Centre de Données astronomiques de Strasbourg |accessdate=2007-07-15 (61 Cygni B)]
dec2 = DEC|+38|44|31.400
appmag_v2 = 6.03Starbox character
class=K5V / K7V
b-v=+1.139 / +1.320cite journal
author=Blanco, C.; Marilli, E.; Catalano, S.
title=Photoelectric observations of stars with variable H and K emission components. III
journal=Astronomy and Astrophysics Supplement Series
year=1979 | volume=36 | pages=297–306
url=http://adsabs.harvard.edu/abs/1979A%26AS...36..297B
accessdate=2007-02-04 ]
u-b=+1.155 / +1.242
variable=A: BY Draconis
B: Flare star Starbox astrometry
radial_v=-64.3/-63.5
prop_mo_ra=4156.93/
4109.17
prop_mo_dec=3259.39/
3144.17
parallax=287.18
p_error=1.51
parallax_footnote=
absmag_v=7.48/8.33Starbox detail
source =
component1 = 61 Cygni A
mass = 0.70cite web | author=Staff
date=June 8, 2007 | url=http://joy.chara.gsu.edu/RECONS/ | title=List of the Nearest 100 Stellar Systems | publisher=Research Consortium on Nearby Stars, Georgia State University | accessdate=2007-07-15 ]
radius = 0.72cite journal | author=Johnson, H. M.; Wright, C. D.
title=Predicted infrared brightness of stars within 25 parsecs of the sun | journal=Astrophysical Journal Supplement Series | year=1983 | volume=53 | pages=643–711
url=http://adsabs.harvard.edu/abs/1983ApJS...53..643J | accessdate=2007-09-05 | doi = 10.1086/190905 ]
gravity = 4.40
luminosity = 0.085
luminosity_bolometric =
luminosity_visual =
temperature = 4,640
metal = [Fe/H] = -0.20cite journal | author=Luck, R. Earle; Heiter, Ulrike | title=Stars within 15 Parsecs: Abundances for a Northern Sample | journal=The Astronomical Journal | year=2005 | volume=129 | issue=2 | pages=1063–1083 | url=http://adsabs.harvard.edu/abs/2005AJ....129.1063L | accessdate=2007-07-17 | doi = 10.1086/427250 ]
rotation = 37 [cite journal | author=Dorren, J. D.; Guinan, E. F. | title=Evidence for starspots on single solar-like stars | journal=Astrophysical Journal | year=1982 | volume=87 | pages=1546–1557 | url=http://adsabs.harvard.edu/abs/1982AJ.....87.1546D | accessdate=2007-07-15 | doi=10.1086/113245 ]
age = ~10¹⁰cite journal |author=Affer, L.; Micela, G.; Morel, T.; Sanz-Forcada, J.; Favata, F.|title=Spectroscopic determination of photospheric parameters and chemical abundances of 6 K-type stars|journal=Astronomy and Astrophysics|year=2005|volume=433|issue=2|pages=647–658 |url=http://adsabs.harvard.edu/abs/2005A&A...433..647A|accessdate=2007-07-25|doi = 10.1051/0004-6361:20041308 ]
component2 = 61 Cygni B
mass2 = 0.63
radius2 = 0.67
gravity2 = 4.20
luminosity2 = 0.039
luminosity_bolometric2 =
luminosity_visual2 =
temperature2 = 4,640/4,440
metal2 = [Fe/H] = -0.27
rotation2 =
age2 = Starbox visbin
reference=cite web
author=Hartkopf, W. I.; Brian D. Mason, B. D.
url=http://ad.usno.navy.mil/wds/orb6.html
title=Sixth Catalog of Orbits of Visual Binary Stars
publisher=U.S. Naval Observatory
accessdate=2008-07-12]
name=61 Cygni B
period=678 ± 34
axis=24.272 ± 0.592
eccentricity=0.49 ± 0.03
inclination=51 ± 2
node=178 ± 2
periastron=1709 ± 16
periarg=149 ± 6 Starbox catalog
names=61 Cyg A/B, HD 201091 & 201092, HR 8085 & 8086, BD+38°4343 & 4344, GCTP 5077.00 A/B, GJ 820 A/B, LHS 62/63, Struve 2758 A/B, ADS 14636 A/B, and HIP 104214/104217.

61 Cygni, sometimes called Bessel's Star [cite book
first=Anton | last=Pannekoek | year=1989
title=A History of Astronomy
publisher=Courier Dover Publications | pages=p. 343
id=ISBN 0486659941 ] or Piazzi's Flying Star,cite book
first=Alan | last=Hirshfeld | year=2001
title=Parallax: The Race to Measure the Cosmos
publisher=Macmillan | isbn=0716737116 ] is a binary star system in the constellation Cygnus. 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 are among the least conspicuous stars visible in the night sky to an observer without an optical instrument.

61 Cygni first attracted the attention of astronomers because of its large proper motion. In 1838, Friedrich Wilhelm Bessel measured its distance from Earth at about 10.4 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.Friedrich Wilhelm Bessel, at http://www.seds.org/MESSIER/xtra/Bios/bessel.html.] Over the course of the twentieth century, several different astronomers reported detections 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.Walker GAH, Walker AR, Irwin AW, Larson AM, Yang SLS, Richardson DC. (1995) A search for Jupiter-mass companions to nearby stars. Icarus, 116 (2) 359-375. Abstract at http://adsabs.harvard.edu/abs/1995Icar..116..359W.] Cumming A, Marcy GW, Butler RP. (1999) The Lick planet search: detectability and mass thresholds. Astrophysical Journal, 526: 890-915. Abstract at http://adsabs.harvard.edu/abs/1999ApJ...526..890C.] Wittenmyer RA, Endl M, Cochran WD, Hatzes A, Walker GAH, Yang SLS, Paulson DB.(2006) Detection limits from the McDonald Observatory planet search program. Astronomical Journal, 132: 177–188. Abstract at http://adsabs.harvard.edu/abs/2006AJ....132..177W.] To date, no planets have been confirmed in this system.

Observation history

The large proper motion of 61 Cygni was first demonstrated by Giuseppe Piazzi in 1804, who christened it the "Flying Star". Piazzi's result, however, received little attention at the time due to the relatively short time span of his observations—a mere 10 years. It would take a publication by Friedrich Wilhelm Bessel in 1812 to bring this star to the widespread attention of astronomers. [cite journal
last=Fodera-Serio | first=G.
title=Giuseppe Piazzi and the Discovery of the Proper Motion of 61-Cygni
journal=Journal of the History of Astronomy
year=1990 | volume=21 | issue=3 | pages=275
url=http://adsabs.harvard.edu/abs/1990JHA....21..275F
accessdate=2007-07-14 ]

Friedrich Georg Wilhelm von Struve first argued for its status as a binary in 1830. For many years thereafter, however, some uncertainty remained as to whether this pair was a mere juxtaposition of stars or a gravitationally bound system. [cite journal
last = Davis | first = Merhan S.
title=Remarks regarding the parallaxes of 61 Cygni and the probable physical connection of these two stars.
journal=Astrophysical Journal
year=1898 | volume=8 | pages=246–247
url=http://adsabs.harvard.edu/abs/1898ApJ.....8..246D
accessdate=2007-07-15
doi=10.1086/140527 ]

The system's large proper motion, the largest known for any star at the time, made 61 Cygni a candidate for the determination of its distance by the method of parallax when the quality of astronomical observations first made this possible. The system therefore has the distinction of being the first star (excluding the Sun) to have its distance from Earth measured. This was accomplished in 1838 by Bessel, who arrived at a parallax of 313.6 mas, close to the currently accepted value of 287.18 mas (yielding 11.36 light years). [cite journal
last=Bessel | first=F. W.
title=Bestimmung der Entfernung des 61sten Sterns des Schwans. Von Herrn Geheimen - Rath und Ritter Bessel
journal=Astronomische Nachrichten
year=1839 | volume=16 | pages=65
url=http://adsabs.harvard.edu/abs/1839AN.....16...65B
language=German
quote=(page 92) Ich bin daher der Meinung, daß nur die jährliche Parallaxe = 0"3136 als das Resultat der bisherigen Beobachtungen zu betrachten ist
accessdate=2007-07-17 A parallax of 313.6 mas yields a distance of 10.4 light years]

Only a few years later, however, Groombridge 1830 was discovered to have a larger proper motion. 61 Cygni retains the distinction of having the largest proper motion of any star visible to the unaided eye (although Groombridge 1830 at magnitude 6.4 can be seen with the naked eye under exceptionally dark skies). It has the seventh highest proper motion of all stellar systems listed in the Hipparcos Catalogue. [cite web
author=Staff | date=May 4, 2007
url=http://www.rssd.esa.int/index.php?project=HIPPARCOS&page=areas
title=High Proper Motion Stars: Interesting Areas to View
publisher=ESA | accessdate=2007-07-16 ]

By 1911 Bessel's parallax of 0.3136 had only slightly improved to 0.310, and observations at Yerkes Observatory had measured its radial velocity as 62 km/s which together with its proper motion—transverse to our line of sight—of around 79 km/s yielded a space velocity of about 100 km/s towards a point about 12 degrees west of Orion's belt. [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.] [This yields a 1911 space velocity of $sqrt\{79.4^2\; +\; 62^2\}\; =\; 100$ km/s. Compare with more accurate 1953, 1997 data: parallax 287.18 yields 11.36 ly and so an increased proper motion velocity of 87km/s; radial velocity -64km/s yields a net space velocity of $sqrt\{87^2\; +\; 64^2\}\; =\; 106$ km/s.]

In 1911, Benjamin Boss published data indicating that the 61 Cygni system was a member of a comoving group of stars.cite journal
last=Boss | first=Benjamin
title=Community of motion among several stars of large proper-motion
journal=Astronomical Journal
year=1911 | volume=27 | issue=629 | pages=33–37
url=http://adsabs.harvard.edu/abs/1911AJ.....27...33B
accessdate=2007-07-17
doi=10.1086/103931 ] This was group later expanded to include 26 potential members. Possible members include Beta Columbae, Pi Mensae, 14 Taurus and 68 Virginis. The typical space velocities of this group of stars is 105–114 km/s relative to the Sun. [cite journal
last = Eggen | first = O. J.
title=White dwarf members of the 61 Cygni group
journal=The Observatory
year=1959 | volume=79 | pages=135–139
url=http://adsabs.harvard.edu/abs/1959Obs....79..135E
accessdate=2007-07-17 – Gives space velocity components of U=+94, V=-53 and W=-7 for HD 201091/2.]

Because of their wide angular separation (and correspondingly slow orbital motion), it was initially unclear whether the two stars in this system were physically connected. The respective parallax measurements of 0.360″ and 0.288″ gave a separation of more than two light years. [cite journal
last=Davis | first=H. S.
title=Remarks regarding the parallaxes of 61 Cygni and the probable physical connection of these two stars
journal=Astrophysical Journal
year=1898 | volume=61 | issue=2 | pages=246–247
url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?1898ApJ.....8..246D
accessdate=2007-09-11
doi=10.1086/140527] However, by 1917 refined measured parallax differences demonstrated that the separation was significantly less. [cite journal
author=Adams, W. S.; Joy, A. H.
title=The luminosities and parallaxes of five hundred stars
journal=Astrophysical Journal
year=1917 | volume=46 | pages=313–339
url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?1917ApJ....46..313A&db_key=AST&nosetcookie=1
accessdate=2007-09-11
doi = 10.1086/142369 —See Table I, page 326] . The binary nature of this system was clear by 1934, and orbital elements were published. [cite journal
last=Baize | first=P.
title=Second catalogue d'orbites d'Etoiles Doubles visuelles
journal=Journal des Observateurs
year=1950 | volume=33 | pages=1–31 | language=French
url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?1917ApJ....46..313A&db_key=AST&nosetcookie=1
accessdate=2007-09-11—on page 19, the authority is listed as Zagar (1934).]

Properties

Although it appears to be a single star to the naked eye, 61 Cygni is in fact a widely separated binary 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, [cite journal
last =Gudel | first = M.
title=Radio and X-ray emission from main-sequence K stars
journal=Astronomy and Astrophysics
year=1992 | volume=264 | issue=2 | pages=L31–L34
url=http://adsabs.harvard.edu/abs/1992A&A...264L..31G
accessdate=2007-07-16 ] with an estimated age that is older than the Sun. The system has a net space velocity of 108 km/scite web
author=Anonymous | date=March 18, 2006
url=http://www.astronexus.com/node/41
title=Long-Term Stellar Motions, part 2: Shortcuts
publisher=The Astronomy Nexus
accessdate=2007-10-21 ] relative to the Sun, which results in the high proper motion across the sky. At a distance of just over 11 light years, it is one of the nearest star systems to the Earth. This system will make its closest approach at about 20,000 CE, when the separation from the Sun will be about 9 light years.

The two orbit their common barycenter in a period of 659 years, with a mean separation of about 84 A.U.—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. [At periapsis: $r\_\{per\}\; =\; (1\; -\; e)a\; approx\; 44$ A.U.
At apoasis: $r\_\{ap\}\; =\; (1\; +\; e)a\; approx\; 124$ A.U.]

Component A is the slightly more massive of the pair. 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. [cite journal
author=Frick, P.; Baliunas, S. L.; Galyagin, D.; Sokoloff, D.; Soon, W.
title=Wavelet Analysis of Chromospheric Activity
journal=Astrophysical Journal
year=1997 | volume=483 | pages=426–434
url=http://adsabs.harvard.edu/abs/1997ApJ...483..426F
accessdate=2007-07-15 | doi = 10.1086/304206 ] (An earlier estimate gave a period of 7.3 years.)cite journal
author=Hempelmann, A.; Schmitt, J. H. M. M.; Baliunas, S. L.; Donahue, R. A.
title=Evidence for coronal activity cycles on 61 Cygni A and B
journal=Astronomy and Astrophysics
year=2003 | volume=406 | pages=L39–L42
url=http://adsabs.harvard.edu/abs/2003A&A...406L..39H
accessdate=2007-07-15 | doi = 10.1051/0004-6361:20030882 ] The combination of starspot activity combined with rotation and chromospheric activity is characteristic of a BY Draconis variable.

Component 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. Both stars exhibit stellar flare activity, but the chromosphere of component B is 25% more active than for component A. [cite journal
author=Hempelmann, A.; Robrade, J.; Schmitt, J. H. M. M.; Favata, F.; Baliunas, S. L.; Hall, J. C.
title=Coronal activity cycles in 61 Cygni
journal=Astronomy and Astrophysics
year=2006 | volume=460 | issue=1 | pages=261–267
url=http://adsabs.harvard.edu/abs/2006A&A...460..261H
accessdate=2007-07-16 | doi = 10.1051/0004-6361:20065459 ]

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″). [cite web
last=Espenak | first=Fred | date=July 25, 1996
url=http://sunearth.gsfc.nasa.gov/eclipse/TYPE/preface.html
title=Twelve Year Planetary Ephemeris: 1995 - 2006
publisher=NASA | accessdate=2007-07-25 ] So, under ideal seeing conditions, the binary system can be resolved by a telescope with a 6 mm aperture. [Per the Rayleigh criterion:$alpha\_R\; =\; frac\{138\}\{D\}$ mm.] This iswell within the capability of a typical pair of binoculars.

Possible low-mass companions

On several occasions it has been claimed that 61 Cygni has unseen low-mass companions, planets or a brown dwarf. Kaj Strand 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 was orbiting 61 Cygni A. [cite journal
last=Strand | first=K. Aa.
title=61 Cygni as a Triple System
journal=Publications of the Astronomical Society of the Pacific
year=1943 | volume=55 | issue=322 | pages=29–32
url=http://adsabs.harvard.edu/abs/1943PASP...55...29S
accessdate=2007-07-15
doi=10.1086/125484 ] In 1957 additional data allowed him to narrow his uncertainties, claiming that the object appeared to have about eight times the mass of Jupiter. With a calculated orbital period of 4.8 years, the estimated semi-major axis of 2.4 A.U. [cite journal
last=Strand | first=K. Aa.
title=The orbital motion of 61 Cygni.
journal=Astronomical Journal
year=1957 | volume=62 | pages=35
url=http://adsabs.harvard.edu/abs/1957AJ.....62Q..35S
accessdate=2007-07-15
doi=10.1086/107588 ] 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, and one giant planet with seven Jupiter masses around 61 cygni B. [cite book
last=Asimov | first=Isaac
title=Extraterrestrial Civilizations
authorlink = Isaac Asimov
publisher = Pan Books Ltd
date = 1981
location = London
isbn =0330262491] In 1978 Wulff Dieter Heintz suggested these claims 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. [cite journal
last=Heintz | first=W. D.
title=Reexamination of suspected unresolved binaries
journal=Astrophysical Journal
year=1978 | volume=220 | pages=931–934
url=http://adsabs.harvard.edu/abs/1978ApJ...220..931H
accessdate=2007-07-15
doi=10.1086/155982 ]

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. [cite web
url =http://tauceti.sfsu.edu/~chris/SIM/t1.html
title =SIM Planet Search Tier 1 Target Stars
publisher = San Francisco State University
accessdate = 2007-07-23 ] 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 A.U. from the star. Measurements of this system 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 yet been resolved with a telescope. [cite journal
author=Kuchner, Marc J.; Brown, Michael E.; Koresko, Chris D.
title=An 11.6 Micron Keck Search for Exo-Zodiacal Dust
journal=The Publications of the Astronomical Society of the Pacific
year=1998 | volume=110 | issue=753 | pages=1336–1341
url=http://adsabs.harvard.edu/cgi-bin/bib_query?1998PASP..110.1336K
accessdate=2007-07-25
doi=10.1086/316267 ]

ee also

*List of nearest stars
*61 Cygni in fiction — Stars and planetary systems in fiction

Notes

External links

* cite web
title=61 Cygni 2
url = http://www.solstation.com/stars/61cygni2.htm
publisher = SolStation
accessdate = 2007-07-16
* cite web
last = Kaler | first = James B. | title=61 Cygni
url = http://www.astro.uiuc.edu/~kaler/sow/61cyg.html
publisher =University of Illinois at Urbana-Champaign
accessdate = 2007-07-16