61 Cygni
Observation data Epoch J2000.0 Equinox J2000.0 | ||
---|---|---|
Constellation | Cygnus | |
61 Cygni A | ||
Right ascension | 21h 06m 53.9396s[1] | |
Declination | +38° 44′ 57.902″[1] | |
Apparent magnitude (V) | 5.21[2] | |
61 Cygni B | ||
Right ascension | 21h 06m 55.2638s[3] | |
Declination | +38° 44′ 31.359″[3] | |
Apparent magnitude (V) | 6.05[4] | |
Characteristics | ||
61 Cyg A | ||
Spectral type | K5V[2] | |
U−B color index | +1.155[5] | |
B−V color index | +1.139[5] | |
Variable type | BY Dra[6] | |
61 Cyg B | ||
Spectral type | K7V | |
U−B color index | +1.242[5] | |
B−V color index | +1.320[5] | |
Variable type | Flare star[7] | |
Absolute magnitude (MV) | 8.228[8] | |
Argument of periastron (ω)(secondary) | 149 ±6° | |
Details | ||
61 Cygni A | ||
Gyr | ||
HIP 104214,
LHS 63[7] | ||
Database references | ||
SIMBAD | The system | |
A | ||
B |
61 Cygni /ˈsɪɡni/ is a binary star system in the constellation Cygnus, consisting of a pair of K-type dwarf stars that orbit each other in a period of about 659 years. Of apparent magnitude 5.20 and 6.05, respectively, they can be seen with binoculars in city skies or with the naked eye in rural areas without light pollution.
61 Cygni first attracted the attention of astronomers when its large
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 unfounded.[18] No planets have been confirmed in this stellar system to date.
Name
61 Cygni is relatively dim, so it does not appear on ancient star maps, nor is it given a name in
The name "61 Cygni" is part of the
Observation history
Early observations
The first well recorded observation of the star system using optical instruments was made by James Bradley on 25 September 1753, when he noticed that it was a double star. William Herschel began systematic observations of 61 Cygni as part of a wider study of 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.[27]
In 1792, Giuseppe Piazzi noticed the high proper motion when he compared his own observations of 61 Cygni with those of Bradley, made 40 years earlier. This led to considerable interest in 61 Cygni by contemporary astronomers, and its continual observation since that date.[27] Piazzi's repeated measurements led to a definitive value of its motion, which he published in 1804.[28][29] It was in this record he christened the system as the "Flying Star".[30]
Piazzi noted that this motion meant that it was probably one of the closest stars, and suggested it would be a prime candidate for an attempt to determine its distance through parallax measurements, along with two other possibilities, Delta Eridani and Mu Cassiopeiae.[29]
Parallax measurement
A number of astronomers soon took up the task, including attempts by
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.[citation needed] 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.[27]
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[31][32] 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.[27][33] 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.[34] 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.[27] This is close to the currently accepted value of 287.18 mas (yielding 11.36 light-years).[35]
Only a few years after Bessel's measurement, in 1842
Binary observations
Due to the wide angular separation between 61 Cygni A and B, and the correspondingly slow orbital motion, it was initially unclear whether the two stars in the 61 Cygni system were a
However, by 1917 refined measured parallax differences demonstrated that the separation was significantly less.[37] The binary nature of this system was clear by 1934, and orbital elements were published.[38]
In 1911,
Observations taken by planet search programs show that both components have strong linear trends in the radial velocity measurements.[42]
Amateur observation
An observer using 7×50
Properties
Although it appears to be a single star to the naked eye, 61 Cygni is a widely-separated binary star system, composed of two
61 Cygni A is a typical
The system 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.[52][53] The starspot activity combined with rotation and chromospheric activity is a 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.[54]
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 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 interstellar medium.[55]
61 Cygni 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.[53] Both stars exhibit stellar flare activity, but the chromosphere of B is 25% more active than for 61 Cygni A.[56] 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.[54]
There is some disagreement over the evolutionary age of this system.
Claims of a planetary system
On different occasions, it has been claimed that 61 Cygni might have unseen low-mass companions, planets or a
In 1978, Wulff-Dieter Heintz of the Sproul Observatory proved that these claims were spurious, as they were unable 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.[63][64]
In 2018, analysis of the DR2 data gathered by the Gaia space telescope revealed significant proper motion anomalies in the orbits of the binary stars around each other; the stars were not quite orbiting around their centre of mass with 61 Cygni B also orbiting too slowly for its assumed mass. These anomalies taken together are indicative of the possible presence of a perturbing third object in orbit around 61 Cygni B.[65]
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. For 61 Cygni B, the habitable zone is 0.24–0.50 AU.[66]
Refining planetary boundaries
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.[67]
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.[68] 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.[69] A 2011 study using the Keck Interferometer Nuller failed to detect any exozodiacal dust around 61 Cygni A.[70]
Object for biosignature research
The two stars are among five (all nearby star) paradigms listed among those K-type stars of a type in a 'sweet spot' between Sun-analog stars and M stars for the likelihood of evolved life, per analysis of Giada Arney from NASA's Goddard Space Flight Center.[71]
See also
- List of nearest stars and brown dwarfs
- Barnard's Star
Notes
- ^ By convention, limiting visual magnitude of 6.0
- ^ Per the Rayleigh criterion: mm.
- ^ At periapsis: AU
At apoapsis: AU
References
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- ^ S2CID 244398875. Gaia DR3 record for this source at VizieR.
- ^ "61 Cygni". The Internet Stellar Database. 4 April 2011. Archived from the original on 1 February 2020. Retrieved 3 February 2019.
- ^ Bibcode:1979A&AS...36..297B.
- ^ a b "SIMBAD Query Result: V* V1803 Cyg -- Variable of BY Dra type". SIMBAD. Centre de Données astronomiques de Strasbourg. Archived from the original on 20 January 2021. Retrieved 3 February 2019. (61 Cygni A)
- ^ a b "SIMBAD Query Result: NSV 13546 -- Flare Star". SIMBAD. Centre de Données astronomiques de Strasbourg. Archived from the original on 21 January 2021. Retrieved 3 February 2019. (61 Cygni B)
- ^ S2CID 18478960See Mv values in Table 1, p. 9.
- ^ Hartkopf, W. I.; Mason, Brian D. "Sixth Catalog of Orbits of Visual Binary Stars". U.S. Naval Observatory. Archived from the original on 12 April 2009. Retrieved 12 July 2008.
- ^ a b c d Staff (7 August 2007), RECONS Mission Statement, Research Consortium on Nearby Stars, Georgia State University, archived from the original on 1 July 2007, retrieved 11 February 2019
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- ^ a b Staff (6 July 2007). "High Proper Motion Stars: Interesting Areas to View". ESA. Archived from the original on 20 January 2021. Retrieved 14 June 2015.
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- ^ "61 Cyg (Piazzi's Flying Star)". Science&Space News. Archived from the original on 4 February 2019. Retrieved 20 February 2019.
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- ^ Piazzi, Giuseppe (1803). Præcipuarum stellarum inerrantium positiones mediae ineunte seculo XIX: ex observationibus habitis in specula Panormitana ab anno 1792 ad annum 1802. Typis regiis. p. 111.
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(page 92) Ich bin daher der Meinung, daß nur die jährliche Parallaxe = 0"3136 als das Resultat der bisherigen Beobachtungen zu betrachten ist
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- ^ Espenak, Fred (25 July 1996). "Twelve Year Planetary Ephemeris: 1995–2006". NASA. Archived from the original on 5 December 2012. Retrieved 3 February 2019.
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This PMa offset between 61 Cyg A and B points at the possible presence of a third body in the system, likely orbiting around 61 Cyg B.
- S2CID 44208180
- S2CID 16755455.
- ^ McCarthy, Christopher (2005). "SIM Planet Search Tier 1 Target Stars". San Francisco State University. Archived from the original on 4 August 2007. Retrieved 23 July 2007.
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- ^ Bill Steigerwald (7 March 2019). ""Goldilocks" Stars May Be "Just Right" for Finding Habitable Worlds". NASA. Archived from the original on 17 June 2019. Retrieved 12 May 2020.
'I find that certain nearby K stars like 61 Cyg A/B, Epsilon Indi, Groombridge 1618, and HD 156026 may be particularly good targets for future biosignature searches,' said Arney.
External links
- "61 Cygni 2". SolStation. Archived from the original on 15 July 2007. Retrieved 16 July 2007.
- Kaler, James B. "61 Cygni". University of Illinois at Urbana–Champaign. Archived from the originalon 7 July 2007. Retrieved 16 July 2007.