55 Cancri

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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
Exoplanet Archive data
ARICNS data
Extrasolar Planets
Encyclopaedia		 data

55 Cancri (play /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 G-type star and a smaller red dwarf, separated by over 1,000 AUs (one thousand times the distance from the Earth to the Sun).

As of 2011, five extrasolar planets have been confirmed to be orbiting the primary, 55 Cancri A (the yellow dwarf). The 55 Cancri system is one of only six planetary systems (the others being our own Solar System, Gliese 581, HD 10180, Kepler-11 and KOI-500) known to have at least five planets,[5] and may possibly have more. The innermost planet, 55 Cancri e, transits 55 Cancri A as viewed from Earth.[6] The innermost planet is thought to be a terrestrial "super-Earth" planet, with a mass similar to Neptune but without the massive gas atmosphere that Neptune has, although signs of a smaller atmosphere may have been detected. The outermost planets in the system are thought to be Jovian planets with masses similar to Jupiter.

Contents

[edit] 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.

[edit] 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.[7]

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.[7] 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 5.5 billion years.[8] Other studies yield age estimates of 7.4 and 8.7 billion 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.[9]

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.[10]

55 Cancri B is a red dwarf star located at an estimated distance of 1065 AU from the primary star,[11] 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.[7] There are indications that component B may itself be a double star, though this is uncertain.[12]

[edit] Planetary system

Comparison of the orbits of the inner planets of 55 Cancri A (black) with the planets of the 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.[13] 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. These 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.

This planet was designated HR 3522b by its discoverers (HR 3522 is an alternative designation for 55 Cancri),[13] though it is more commonly referred to as 55 Cancri b.[14] Under the rules for naming objects in binary star systems it should be named 55 Cancri Ab[15] and this more formal form is occasionally used to avoid confusion with the secondary star 55 Cancri B.

In 1998 the discovery of a possible dust disk around 55 Cancri A was announced.[16] 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.[17]

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.[7] 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), but 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

A planet designated 55 Cancri e orbits 55 Cnc A with a 0.78-day period (while the 2004 discovery claimed a 2.8-day orbit),[18] observations of e transiting show a 0.78-day period and indicate that the initial period measurement was aliased.[6] At 8.3 Earth masses (1/2 Neptune mass), it is a super-Earth. The measurements that led to the discovery of this planet also confirmed the existence of 55 Cancri c.

Jack Wisdom has suggested[19] that 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, in 55 Cancri A's habitable zone.[20][21] 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.[21] Assuming that the astrometric determination of the orbit (with an inclination of 53°) of the outer planet made by the Hubble Space Telescope is correct, the true masses of the planets are around 25% greater than the lower limits measured by the radial velocity method. However, this conflicts with the observed transits of e, which show that its orbit is inclined to within 9° of normal to the line-of-light, placing its mass only slightly above the minimum. Assuming coplanarity, the same applies for the rest of the planets.

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.[21]

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.[22]

A METI message was 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.[23]

The 55 Cancri A system[24]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity
e 0.027 MJ 0.016 0.74 0.17 ± 0.04
b ≥0.83 MJ 0.11 14.65 0.010 ± 0.003
c ≥0.17 MJ 0.24 44.36 0.005 ± 0.003
f ≥0.16 MJ 0.78 259.8 ± 0.5 0.30 ± 0.05
d ≥3.82 ± 0.04 MJ 5.74 ± 0.04 5169 ± 53 0.014 ± 0.009

[edit] See also

Book icon Book: 55 Cancri
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[edit] References

  1. ^ a b c d e f 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. ^ van Belle, Gerard T.; von Braun, Kaspar (2009). "Directly Determined Linear Radii and Effective Temperatures of Exoplanet Host Stars". The Astrophysical Journal 694 (2): 1085–1098. arXiv:0901.1206. Bibcode 2009ApJ...694.1085V. doi:10.1088/0004-637X/694/2/1085. http://iopscience.iop.org/0004-637X/694/2/1085/fulltext/. 
  3. ^ Kovtyukh, V. V. et al. (2003). "High precision effective temperatures for 181 F-K dwarfs from line-depth ratios". Astronomy and Astrophysics 411 (3): 559–564. arXiv:astro-ph/0308429. Bibcode 2003A&A...411..559K. doi:10.1051/0004-6361:20031378. http://www.aanda.org/articles/aa/full/2003/46/aa3944/aa3944.html. 
  4. ^ a b 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. Bibcode 2008ApJ...687.1264M. doi:10.1086/591785. 
  5. ^ Schneider, Jean (8 October 2011). "Interactive Extra-solar Planets Catalog". The Extrasolar Planets Encyclopedia. http://exoplanet.eu/catalog.php. Retrieved 8 October 2011. 
  6. ^ a b Winn, Joshua N. et al. (2011). "A Super-Earth Transiting a Naked-Eye Star". The Astrophysical Journal Letters 737 (1): article number L18. arXiv:1104.5230. Bibcode 2011ApJ...737L..18W. doi:10.1088/2041-8205/737/1/L18. 
  7. ^ a b c d Marcy, Geoffrey W. et al. (2002). "A planet at 5 AU Around 55 Cancri". The Astrophysical Journal 581 (2): 1375–1388. arXiv:astro-ph/0207294. Bibcode 2002ApJ...581.1375M. doi:10.1086/344298. http://iopscience.iop.org/0004-637X/581/2/1375/fulltext/. 
  8. ^ Saffe, C. et al. (2005). "On the Ages of Exoplanet Host Stars". Astronomy and Astrophysics 443 (2): 609–626. arXiv:astro-ph/0510092. Bibcode 2005A&A...443..609S. doi:10.1051/0004-6361:20053452. http://www.aanda.org/articles/aa/full/2005/44/aa3452-05/aa3452-05.html. 
  9. ^ 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. 
  10. ^ Jayawardhana, Ray et al. (2002). "New Submillimeter Limits on Dust in the 55 Cancri Planetary System". The Astrophysical Journal Letters 570 (2): L93–L96. arXiv:astro-ph/0204140. Bibcode 2002ApJ...570L..93J. doi:10.1086/341101. http://iopscience.iop.org/1538-4357/570/2/L93/fulltext/. 
  11. ^ Eggenberger, A. et al. (2003). "Planets in Binaries". Scientific Frontiers in Research on Extrasolar Planets 294: 43–46. Bibcode 2003ASPC..294...43E. http://adsabs.harvard.edu/full/2003ASPC..294...43E. 
  12. ^ Raghavan, Deepak et al. (2006). "Two Suns in The Sky: Stellar Multiplicity in Exoplanet Systems". The Astrophysical Journal 646 (1): 523–542. arXiv:astro-ph/0603836. Bibcode 2006ApJ...646..523R. doi:10.1086/504823. http://iopscience.iop.org/0004-637X/646/1/523/fulltext/. 
  13. ^ a b Butler, R. Paul et al. (1997). "Three New 51 Pegasi Type Planets". The Astrophysical Journal Letters 474 (2): L115–L118. Bibcode 1997ApJ...474L.115B. doi:10.1086/310444. http://iopscience.iop.org/1538-4357/474/2/L115/fulltext/. 
  14. ^ Jean Schneider (2011). "Notes for Planet 55 Cnc b". Extrasolar Planets Encyclopaedia. http://exoplanet.eu/planet.php?p1=55+Cnc&p2=b. Retrieved 8 October 2011. 
  15. ^ William I. Hartkopf & Brian D. Mason. "Addressing confusion in double star nomenclature: The Washington Multiplicity Catalog". United States Naval Observatory. http://ad.usno.navy.mil/wds/wmc/wmc_post191.html. Retrieved 2011-10-08. 
  16. ^ Trilling, David E.; Brown, Robert H. (1998). "A circumstellar dust disk around a star with a known planetary companion" (PDF). Nature 395 (6704): 775–777. Bibcode 1998Natur.395..775T. doi:10.1038/27389. http://astro.berkeley.edu/~kalas/disksite/library/trilling98a.pdf. 
  17. ^ Schneider, G. et al. (2001). "NICMOS Coronagraphic Observations of 55 Cancri". The Astronomical Journal 121 (1): 525–537. arXiv:astro-ph/0010175. Bibcode 2001AJ....121..525S. doi:10.1086/318050. http://iopscience.iop.org/1538-3881/121/1/525/fulltext/. 
  18. ^ McArthur, Barbara E. et al. (2004). "Detection of a NEPTUNE-mass planet in the ρ1 Cnc system using the Hobby-Eberly Telescope". The Astrophysical Journal Letters 614 (1): L81–L84. arXiv:astro-ph/0408585. Bibcode 2004ApJ...614L..81M. doi:10.1086/425561. http://iopscience.iop.org/1538-4357/614/1/L81/fulltext/. 
  19. ^ 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. 
  20. ^ "Astronomers Discover Record Fifth Planet Around Nearby Star 55 Cancri". Sciencedaily.com. November 6, 2007. http://www.sciencedaily.com/releases/2007/11/071106133058.htm. Retrieved 2008-09-14. 
  21. ^ a b c Fischer, Debra A. et al. (2008). "Five Planets Orbiting 55 Cancri". The Astrophysical Journal 675 (1): 790–801. arXiv:0712.3917. Bibcode 2008ApJ...675..790F. doi:10.1086/525512. http://iopscience.iop.org/0004-637X/675/1/790/fulltext/. 
  22. ^ Raymond, Sean N. et al. (2008). "A dynamical perspective on additional planets in 55 Cancri". The Astrophysical Journal 689: 478–491. arXiv:0808.3295. Bibcode 2008ApJ...689..478R. doi:10.1086/592772. http://iopscience.iop.org/0004-637X/689/1/478/fulltext/. 
  23. ^ "Передача и поиски разумных сигналов во Вселенной". Cplire.ru. http://www.cplire.ru/rus/ra&sr/VAK-2004.html. Retrieved 2008-09-14. 
  24. ^ Dawson, Rebekah I.; Fabrycky, Daniel C.. "Radial velocity planets de-aliased. A new, short period for Super-Earth 55 Cnc e". The Astrophysical Journal 722: 937–953. arXiv:1005.4050. Bibcode 2010ApJ...722..937D. doi:10.1088/0004-637X/722/1/937. http://iopscience.iop.org/0004-637X/722/1/937/fulltext/. 

[edit] External links

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

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