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55 Cancri c

Coordinates:Sky map08h52m35.8s,+28° 19′ 51″
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55 Cancri c / Brahe
The planet 55 Cnc c (min mass ~0.17 MJ) in MPL3D
Discovery
Discovered byMarcyet al.
Discovery siteCalifornia, USA
Discovery dateJune 13, 2002
Radial velocity
Orbital characteristics
Apastron0.260 AU (38,900,000 km)
Periastron0.219 AU (32,800,000 km)
0.240 ± 0.00005 AU (35,903,500 ± 7,500 km)[1]
Eccentricity0.086 ± 0.052[1]
44.3446 ± 0.007[1]d
0.121407y
2,449,989.3385 ± 3.3[1]
77.9 ± 29[1]
Semi-amplitude10.18 ± 0.43[1]
Star55 Cancri A
Radial velocity changes over time of 55 Cancri caused by the orbit of 55 Cancri c.

55 Cancri c(abbreviated55 Cnc c), formally namedBrahe(pronounced/ˈbrɑːhiː/or/ˈbrɑː/), is anextrasolar planetin aneccentricorbit around theSun-likestar55 Cancri A,making onerevolutionevery 44.34days.It is the third known planet in order of distance from its star. 55 Cancri c was discovered on June 13, 2002, and has amassroughly half ofSaturn.

In July 2014 theInternational Astronomical UnionlaunchedNameExoWorlds,a process for giving proper names to certain exoplanets and their host stars.[2]The process involved public nomination and voting for the new names.[3]In December 2015, the IAU announced the winning name was Brahe for this planet.[4]The winning name was submitted by the Royal Netherlands Association for Meteorology and Astronomy of theNetherlands.It honors the astronomerTycho Brahe.[5]

Discovery[edit]

Like the majority of known extrasolar planets, 55 Cancri c was detected by observing changes in its star'sradial velocity.This was achieved by making sensitive measurements of theDoppler shiftof the star'sspectrum.At the time of discovery, 55 Cancri A was already known to possess one planet (55 Cancri b); however, there was still a drift in the radial velocity measurements which was unaccounted for.[6]

In 2002, further measurements revealed the presence of a long-period planet in an orbit at around 5AUfrom the star. Even when both of the two planets were accounted for, there was still a periodicity at around 43 days. However, this period is close to the rotation period of 55 Cancri A, which led to the possibility that the 43-day period was caused by stellar rotation rather than a planet. Both the 43-day planet (designated 55 Cancri c) and the 5 AU planet (designated55 Cancri d) were announced in the same paper, labeled in order of increasing distance from the star.[7]

Further measurements which led to the discovery of the inner planet55 Cancri ein 2004 lent support to the planet hypothesis.[8]Photometricmeasurements of the star over 11 years show no activity with the same period as 55 Cancri c's radial velocity variations, and furthermore the period is stable over long timescales, which is inconsistent with the hypothesis of stellar activity causing the radial velocity variations. The amplitude of the radial velocity signal is inconsistent with stellar variations on stars with 55 Cancri A's low level ofchromosphericactivity.[1]

Orbit and mass[edit]

In the 5-planet solution for the 55 Cancri system, the orbit of 55 Cancri c is mildly eccentric: atapoastronthe planet is about 19% further from the star than it is atperiastron.It is located closer to 55 Cancri A thanMercuryis to the Sun, though it has a longer orbital period than thehot Jupiters.The planet is located close to a 3:1resonancewith the inner planet 55 Cancri b; however, simulations indicate that the two planets are not actually in this resonance.[1]

A limitation of the radial velocity method used to discover the planet is that only a lower limit on themasscan be obtained. Further astrometric observations with theHubble Space Telescopeon the outer planet 55 Cancri d suggest that planet is inclined at 53° to the plane of the sky;[8]but innermost b and e are inclined at 85°. Planet c's inclination is unknown.

Characteristics[edit]

Since the planet was detected indirectly through observations of its star, properties such as itsradius,composition, andtemperatureare unknown. With a mass similar to that of Saturn, 55 Cancri c is likely to be agas giantwithout a solid surface.

See also[edit]

References[edit]

  1. ^abcdefghFischer, D.A.; et al. (March 2008). "Five Planets Orbiting 55 Cancri".Astrophysical Journal.675(675): 790–801.arXiv:0712.3917.Bibcode:2008ApJ...675..790F.doi:10.1086/525512.S2CID17083836.
  2. ^NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars.IAU.org. 9 July 2014
  3. ^"NameExoWorlds The Process".Archived fromthe originalon 2015-08-15.Retrieved2015-09-05.
  4. ^Final Results of NameExoWorlds Public Vote Released,International Astronomical Union, 15 December 2015.
  5. ^"NameExoWorlds The Approved Names".Archived fromthe originalon 2018-02-01.Retrieved2015-12-27.
  6. ^Butler; et al. (1997). "Three New 51 Pegasi-Type Planets".The Astrophysical Journal.474(2): L115–L118.Bibcode:1997ApJ...474L.115B.doi:10.1086/310444.
  7. ^Marcy, G.; 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.S2CID16170184.
  8. ^abMcArthur, B.; et al. (2004). "Detection of a NEPTUNE-mass planet in the ρ1Cnc system using the Hobby-Eberly Telescope ".The Astrophysical Journal.614(1): L81–L84.arXiv:astro-ph/0408585.Bibcode:2004ApJ...614L..81M.doi:10.1086/425561.S2CID119085463.

External links[edit]

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