55 Cancri

55 Cancri
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cancer
55 Cancri A
Right ascension 08h 52m 35.81s [1]
Declination +28° 19′ 51.0″ [1]
Apparent magnitude (V) 5.95
55 Cancri B
Right ascension 08h 52m 40.9s
Declination +28° 19′ 59″
Apparent magnitude (V) 13.15
Characteristics
Spectral type G8V / M3.5-4V
U−B color index 0.65 / 1.66
B−V color index 0.86 / 1.21
Astrometry
Radial velocity (Rv) 27.3 km/s
Proper motion (μ) RA: -485.80 ± 0.97 [1] mas/yr
Dec.: -234.05 ± 0.68 [1] mas/yr
Parallax (π) 81.03 ± 0.75[1] mas
Distance 40.3 ± 0.4 ly
(12.3 ± 0.1 pc)
Absolute magnitude (MV) 5.46 / 12.66
Details
Mass 0.95 ± 0.1 / 0.13 M☉
Radius 1.152 ± 0.035 [2] / 0.30 R☉
Luminosity (bolometric) 0.63 / 0.0076 L☉
Temperature 5373 ± 9.7 [3] K
Rotation 42.2 d
Age (7.4–8.7) × 109[4] years
Other designations
BD+28°1660, Gliese 324, HD 75732, HIP 43587, HR 3522, Rho1 Cancri
Database references
SIMBAD data
NStED data
ARICNS data
Extrasolar Planets
Encyclopaedia		 data

55 Cancri (pronounced /ˈkæŋkraɪ/ or /ˈkæŋkriː/), also cataloged Rho1 Cancri or abbreviated 55 Cnc, is a binary star approximately 41 light-years away from Earth in the constellation of Cancer. The system consists of a yellow dwarf star and a smaller red dwarf star, separated by over 1,000 AUs (one thousand times the distance from the Earth to the Sun).

As of 2010, five extrasolar planets have been confirmed to be orbiting the primary, 55 Cancri A (the yellow dwarf). The innermost planet is thought to be a terrestrial "super-Earth" planet, with a mass similar to Neptune, while the outermost planets are thought to be Jovian planets with masses similar to Jupiter. The 55 Cancri system is one of only three planetary systems (including our own Solar System and the HD 10180 system) known to have at least five planets,[5][6] and may possibly have more. 55 Cancri A is ranked 63rd in the list of top 100 target stars for the NASA Terrestrial Planet Finder mission.[7]

Contents

Name

The term 55 Cancri (the star's Flamsteed designation) is seen more often used for the system, rather than its Bayer designation Rho1 Cancri. The latter is used by those who feel that it should be preferred to the Flamsteed number – as is usually done (e.g., Tau Boötis is almost never called "4 Boötis"). But in this case the superscript in "Rho1" makes the Bayer designation rather cumbersome, so that 55 Cancri is the more commonly used name for this star.

Distance and visibility

The 55 Cancri system is located fairly close to our solar system: the Hipparcos astrometry satellite measured the parallax of 55 Cancri A as 81.03 Milliarcseconds, corresponding to a distance of 12.3 parsecs (40.3 light years).[1] 55 Cancri A has an apparent magnitude of 5.95, making it visible through binoculars. It is just visible to the naked eye under very dark skies. The red dwarf 55 Cancri B is of the 13th magnitude and only visible through a telescope.

System components

The primary star 55 Cancri A is a yellow dwarf star of main sequence spectral type G8V. It is smaller in radius and slightly less massive than our Sun, and so is cooler and less luminous. The star has little or no variability and only low emission from its chromosphere.[8]

55 Cancri A is more enriched than our sun in elements heavier than helium, with 186% the solar abundance of iron; it is therefore classified as a rare "super metal-rich" (SMR) star.[8] This abundance of metal makes estimating the star's age and mass difficult, as evolutionary models are less well defined for such stars. One estimate based on chromospheric activity suggests an age of around 5,500 million years.[9] Other studies yield age estimates of 7,400 and 8,700 million years.[4]

A hypothesis for the high metal content in SMR dwarf stars is that material enriched in heavy elements fell into the atmosphere from a protoplanetary disk. This would pollute the star's external layers, resulting in a higher than normal metallicity. The lack of a deep convection zone would mean that the outer layers would retain higher abundance ratios of these heavy elements.[10]

Observations of 55 Cancri A in the submillimeter region of the spectrum have thus far failed to detect any associated dust. The upper limit on emissions within 100 AU of this star is about 850 mJy, at a wavelength of 850 μm. This limits the total mass of fine dust around the star to less than 0.01% of the Earth's mass. However, this does not exclude the presence of an asteroid belt or a Kuiper belt equivalent.[11]

55 Cancri B is a red dwarf star located at an estimated distance of 1065 AU from the primary star,[12] and is much less massive and luminous than our Sun. Despite their wide separation, the two stars appear to be gravitationally bound, as they share a common proper motion.[8] There are indications that component B may itself be a double star, though this is uncertain.[13]

Planetary system

Comparison of the orbits of the inner planets of 55 Cancri A (black) with the planets of our solar system.

In 1997, the discovery of a 51 Pegasi-like planet orbiting 55 Cancri A was announced, together with the planet of Tau Boötis and the inner planet of Upsilon Andromedae.[14] The planet was discovered by measuring the star's radial velocity, which showed a periodicity of around 14.7 days corresponding to a planet at least 78% of the mass of Jupiter. This planet was designated 55 Cancri b, though to distinguish it from the star 55 Cancri B it is occasionally referred to as 55 Cancri Ab. The radial velocity measurements still showed a drift unaccounted-for by this planet, which could be explained by the gravitational influence of a more distant object.

In 1998 the discovery of a possible dust disk around 55 Cancri A was announced.[15] Calculations gave the disk radius at least 40 AU, similar to the Kuiper belt in our solar system, with an inclination of 25° with respect to the plane of the sky. However, the discovery could not be verified and was later deemed to be spurious, caused instead by background radiation.[16]

Our solar system compared with the solar system of 55 Cancri. (Note: this depiction was made before planets e and f were discovered.)

After making further radial velocity measurements, a planet orbiting at a distance of around 5 AU was announced in 2002.[8] This planet received the designation 55 Cancri d. At the time of discovery, the planet was thought to be in an orbit of mild eccentricity (close to 0.1), however this value was increased by later measurements. Even after accounting for these two planets, a periodicity at 43 days remained, possibly due to a third planet. Measurements of the star suggested that this was close to the star's rotation period, which raised the possibility that the 43-day signal was caused by stellar activity. This possible planet received the designation 55 Cancri c.

Artist's Rendition of 55 Cnc's planets

In 2004 a Neptune-mass planet designated 55 Cancri e was announced in a 2.8-day orbit.[17] This planet may either be a small gas giant or a large terrestrial planet. The measurements that led to the discovery of this planet also confirmed the existence of 55 Cancri c. In addition, astrometric measurements made by the Hubble Space Telescope led to an estimate of the inclination of the orbit of the outer planet: around 53° with respect to the plane of the sky.

In 2005 the existence of planet e was questioned by Jack Wisdom in a reanalysis of the data.[18] According to him, instead of the 2.8-day planet there is a planet with a mass similar to that of Neptune in a 261-day orbit (corresponding to 0.77 AU in distance). This analysis has been partially confirmed in November 2007 – a planet designated 55 Cancri f with half the mass of Saturn was announced in a 260-day orbit, right in 55 Cancri A's habitable zone.[19][20] The planet itself is not thought to be conducive to life, but hypothetical moons in principle could maintain at least microbial life.

With five planets, the system cannot deviate far from coplanar in order to maintain stability.[20] Assuming the astrometric determination of the orbit of the outer planet is correct, this means the true masses of the planets are around 25% greater than the lower limits measured by the radial velocity method.

The approximate ratios of periods of adjacent orbits are (proceeding outward): 1:20, 1:3, 1:6, 1:20. The nearly 1:3 ratio between 55 Cancri b and c is apparently a near resonance, rather than a genuine mean motion resonance.[20]

More planets are possible within the stable zone, between f and d at 0.9 to 3.8 AU with eccentricities below 0.4. Given hypothetical planet g of up to 50 Earth masses, stable mean motion resonance regions lie at 3f:2g, 2g:1d, and 3g:2d. As for the space outside d's orbit, its stability zone begins beyond 10 AU.[21]

There was a METI message sent to 55 Cancri. It was transmitted from Eurasia's largest radar – 70-meter (230-foot) Eupatoria Planetary Radar. The message was named Cosmic Call 2, it was sent on July 6, 2003, and it will arrive at 55 Cancri in May 2044.[22]

The 55 Cancri A system[23]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity
e >0.0260 ± 0.0010 MJ 0.01560 ± 0.00011 0.736537 ± 0.000013 0.17 ± 0.04
b >0.825 ± 0.003 MJ 0.1148 ± 0.0008 14.6507 ± 0.0004 0.010 ± 0.003
c >0.171 ± 0.004 MJ 0.2403 ± 0.0017 44.364 ± 0.007 0.005 ± 0.003
f >0.155 ± 0.008 MJ 0.781 ± 0.006 259.8 ± 0.5 0.30 ± 0.05
d >3.82 ± 0.04 MJ 5.74 ± 0.04 5169 ± 53 0.014 ± 0.009

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 van Leeuwen, F. (2007). "HIP 43587". Hipparcos, the New Reduction. http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=I/311/hip2&recno=43452. Retrieved 2009-12-08. 
  2. ↑ Gerard T. van Belle and Kaspar von Braun (2009). "Directly Determined Linear Radii and Effective Temperatures of Exoplanet Host Stars" (abstract). The Astrophysical Journal 694 (2): 1085–1098. doi:10.1088/0004-637X/694/2/1085. http://www.iop.org/EJ/abstract/0004-637X/694/2/1085/. (web Preprint)
  3. ↑ Kovtyukh et al.; Soubiran, C.; Belik, S. I.; Gorlova, N. I. (2003). "High precision effective temperatures for 181 F-K dwarfs from line-depth ratios". Astronomy and Astrophysics 411 (3): 559–564. doi:10.1051/0004-6361:20031378. http://www.aanda.org/articles/aa/full/2003/46/aa3944/aa3944.html. 
  4. ↑ 4.0 4.1 Mamajek, Eric E.; Hillenbrand, Lynne A. (November 2008). "Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics". The Astrophysical Journal 687 (2): 1264–1293. doi:10.1086/591785. Bibcode: 2008ApJ...687.1264M. 
  5. ↑ "The Extrasolar Planets Encyclopaedia". Exoplanet.eu. http://exoplanet.eu/catalog-all.php. Retrieved 2008-09-14. 
  6. ↑ "The Extrasolar Planets Encyclopaedia". Exoplanet.eu. http://exoplanet.eu/star.php?st=HD+10180. Retrieved 2010-08-25. 
  7. ↑ "TPF-C Top 100". http://sco.stsci.edu/tpf_top100/index.php. Retrieved 4 July 2006. 
  8. ↑ 8.0 8.1 8.2 8.3 Marcy et al.; Butler, R. Paul; Fischer, Debra A.; Laughlin, Greg; Vogt, Steven S.; Henry, Gregory W.; Pourbaix, Dimitri (2002). "A planet at 5 AU Around 55 Cancri". The Astrophysical Journal 581 (2): 1375–1388. doi:10.1086/344298. http://www.iop.org/EJ/article/0004-637X/581/2/1375/56220.html. 
  9. ↑ Saffe, C. et al. (2005). "On the Ages of Exoplanet Host Stars". Astronomy and Astrophysics 443 (2): 609 – 626. doi:10.1051/0004-6361:20053452. http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2005A%26A...443..609S&db_key=AST&nosetcookie=1. 
  10. ↑ Pasquini, Luca; Hatzes, Artie (2007-07-06). "Star Surface Polluted by Planetary Debris". ESO. http://www.eso.org/public/outreach/press-rel/pr-2007/pr-29-07.html. Retrieved 2007-11-08. 
  11. ↑ Jayawardhana et al.; Holland, Wayne S.; Kalas, Paul; Greaves, Jane S.; Dent, William R. F.; Wyatt, Mark C.; Marcy, Geoffrey W. (2002). "New Submillimeter Limits on Dust in the 55 Cancri Planetary System". The Astrophysical Journal Letters 570 (2): L93–L96. doi:10.1086/341101. http://www.iop.org/EJ/article/1538-4357/570/2/L93/16185.html. 
  12. ↑ Eggenberger, A. et al. (2003). "Planets in Binaries" (PostScript). Scientific Frontiers in Research on Extrasolar Planets 294: 43 – 46. http://www-lep.gsfc.nasa.gov/code693/esp_papers/web/ps2/eggenberger_43.ps. 
  13. ↑ Raghavan et al.; Henry, Todd J.; Mason, Brian D.; Subasavage, John P.; Jao, Wei‐Chun; Beaulieu, Thom D.; Hambly, Nigel C. (2006). "Two Suns in The Sky: Stellar Multiplicity in Exoplanet Systems". The Astrophysical Journal 646 (1): 523–542. doi:10.1086/504823. http://www.iop.org/EJ/article/0004-637X/646/1/523/64035.html. 
  14. ↑ Butler et al.; Marcy, Geoffrey W.; Williams, Eric; Hauser, Heather; Shirts, Phil (1997). "Three New 51 Pegasi-Type Planets". The Astrophysical Journal 474 (2): L115–L118. doi:10.1086/310444. http://www.iop.org/EJ/article/1538-4357/474/2/L115/5590.html. 
  15. ↑ Trilling, D., Brown. R (1998). "A circumstellar dust disk around a star with a known planetary companion". Nature 395: 775 – 777. doi:10.1038/27389. http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v395/n6704/abs/395775a0_fs.html. 
  16. ↑ Schneider, G. et al. (2001). "NICMOS Coronagraphic Observations of 55 Cancri". The Astronomical Journal 121 (1): 525 – 537. doi:10.1086/318050. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001AJ....121..525S&db_key=AST&high=3cab10bb0320924. 
  17. ↑ McArthur, B. et al. (2004). "Detection of a NEPTUNE-mass planet in the ρ1 Cnc system using the Hobby-Eberly Telescope". The Astrophysical Journal 614: L81 – L84. doi:10.1086/425561. http://xxx.lanl.gov/abs/astro-ph/0408585. 
  18. ↑ Wisdom, J. (2005). "Evidence of a Neptune-Sized Planet in the ρ1 Cancri System" (PostScript). The Astrophysical Journal Letters (submitted). http://swiss.csail.mit.edu/users/wisdom/planet.ps. 
  19. ↑ "Astronomers Discover Record Fifth Planet Around Nearby Star 55 Cancri". Sciencedaily.com. ScienceDaily (November 6, 2007). http://www.sciencedaily.com/releases/2007/11/071106133058.htm. Retrieved 2008-09-14. 
  20. ↑ 20.0 20.1 20.2 Fischer, D. A. et al. (2008). "Five Planets Orbiting 55 Cancri". The Astrophysical Journal 675 (1): 790–801. doi:10.1086/525512. http://www.iop.org/EJ/article/0004-637X/675/1/790/72072.html. 
  21. ↑ Raymond, Sean N.; Rory Barnes; Noel Gorelick (2008). "A dynamical perspective on additional planets in 55 Cancri". arΧiv:0808.3295v1 [astro-ph]. 
  22. ↑ "Передача и поиски разумных сигналов во Вселенной". Cplire.ru. http://www.cplire.ru/rus/ra&sr/VAK-2004.html. Retrieved 2008-09-14. 
  23. ↑ Rebekah et al.; Fabrycky (2010-05-21). "Radial velocity planets de-aliased. A new, short period for Super-Earth 55 Cnc e". The Astrophysical Journal. arXiv:1005.4050. 

External links

Coordinates: Sky map 08h 52m 35.8s, +28° 19′ 51″

Stars of Cancer
Bayer
α (Acubens / Sertan) • β (Tarf) • γ (Asellus Borealis) • δ (Asellus Australis) • ε • ζ (Tegmen) • η • θ • ι • κ • λ • μ¹ • μ² • ν • ξ • ο¹ • ο² • π • ρ¹ • ρ² • σ¹ • σ² • σ³ • τ • υ¹ • υ² • φ¹ • φ² • χ • ψ¹ • ψ² • ω • b • c • d¹ • d² • A¹ • A²
Flamsteed
1 • 2 (ω) • 3 • 4 • 5 • 7 • 8 • 9 (μ¹) • 10 (μ²) • 11 • 12 • 13 (ψ¹) • 14 (ψ²) • 15 • 16 (ζ, Tegmen) • 17 (β, Tarf) • 18 (χ) • 19 (λ) • 20 (d¹) • 21 • 22 (φ¹) • 23 (φ²) • 24 • 25 (d²) • 27 • 28 • 29 • 30 (υ¹) • 31 (θ) • 32 (υ²) • 33 (η) • 34 • 35 • 36 (c) • 37 • 38 • 39 • 40 • 41 (ε) • 42 • 43 (γ, Asellus Borealis) • 45 (A¹) • 46 • 47 (δ, Asellus Australis) • 48 (ι) • 49 (b) • 50 (A²) • 51 (σ¹) • 52 • 53 • 54 • 55 (ρ¹) • 57 • 58 (ρ²) • 59 (σ²) • 60 • 61 • 62 (ο¹) • 63 (ο²) • 64 (σ³) • 65 (α, Acubens / Sertan) • 66 • 67 • 68 • 69 (ν) • 70 • 72 (τ) • 74 • 75 • 76 (κ) • 77 (ξ) • 78 • 79 • 80 • 81 • 82 (π) • 83
Nearby
DX • EI • LHS 2090 • Gliese 299
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