55 Cancri
  | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cancer |
| Pronunciation | /ˈkæŋkraɪ/ or /ˈkæŋkriː/ |
| 55 Cancri A | |
| Right ascension | 08h 52m 35.8111s[1] |
| Declination | +28° 19′ 50.955″[1] |
| Apparent magnitude (V) | 5.95[2] |
| 55 Cancri B | |
| Right ascension | 08h 52m 40.8627s[3] |
| Declination | +28° 19′ 58.821″[3] |
| Apparent magnitude (V) | 13.15[4] |
| Characteristics | |
| 55 Cancri A | |
| Evolutionary stage | Main sequence or subgiant |
| Spectral type | K0IV–V[5] |
| U−B color index | 0.63[6] |
| B−V color index | 0.87[6] |
| 55 Cancri B | |
| Evolutionary stage | Main sequence (red dwarf) |
| Spectral type | M4.5V[7] |
| B−V color index | 1.7[4] |
| Astrometry | |
| 55 Cancri A | |
| Radial velocity (Rv) | 27.51[1] km/s |
| Proper motion (μ) | RA: −485.681±0.040[1] mas/yr Dec.: −233.517±0.037[1] mas/yr |
| Parallax (π) | 79.4482 ± 0.0429[1] mas |
| Distance | 41.05 ± 0.02 ly (12.587 ± 0.007 pc) |
| Absolute magnitude (MV) | +5.50[8] |
| 55 Cancri B | |
| Proper motion (μ) | RA: −481.176±0.041[3] mas/yr Dec.: −244.544±0.032[3] mas/yr |
| Parallax (π) | 79.6560 ± 0.0475[3] mas |
| Distance | 40.95 ± 0.02 ly (12.554 ± 0.007 pc) |
| Absolute magnitude (MV) | 12.58[9] |
| Details | |
| 55 Cnc A | |
| Mass | 0.960±0.067[10] M☉ |
| Radius | 0.960±0.018[10] R☉ |
| Luminosity | 0.589±0.014[10] L☉ |
| Surface gravity (log g) | 4.37[5] cgs |
| Temperature | 5,165±46[10] K |
| Metallicity [Fe/H] | −0.09[5] dex |
| Rotation | 42.2 d |
| Age | 10.2 ± 2.5[11] Gyr |
| 55 Cnc B | |
| Mass | 0.255[12] M☉ |
| Radius | 0.273[12] R☉ |
| Luminosity | 0.003[13] L☉ |
| Temperature | 3,233[9] K |
| Metallicity [Fe/H] | 0.360[14] dex |
| Rotational velocity (v sin i) | 6.110[9] km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
| 55 Cnc B | |
| Exoplanet Archive | data |
| ARICNS | data |
| Extrasolar Planets Encyclopaedia | data |
55 Cancri is a binary star system located 41[1] light-years away from the Sun in the zodiac constellation of Cancer. It has the Bayer designation Rho1 Cancri (ρ1 Cancri); 55 Cancri is the Flamsteed designation (abbreviated 55 Cnc). The system consists of a K-type star (designated 55 Cancri A, also named Copernicus /koʊˈpɜːrnɪkəs/)[15] and a smaller red dwarf (55 Cancri B).
As of 2015, five extrasolar planets (designated 55 Cancri b, c, d, e and f; named Galileo, Brahe, Lipperhey, Janssen and Harriot, respectively) are believed to orbit 55 Cancri A.
Nomenclature[]
55 Cancri is the system's Flamsteed designation. It also bears the Bayer designation ρ1 Cancri (Latinised to Rho1 Cancri) and the Bright Star Catalogue designation HR 3522. The two components are designated A and B,[16] though A is itself sometimes referred to as 55 Cancri.[17] The first planet discovered orbiting 55 Cancri A was designated HR 3522b by its discoverers,[18] though it is more commonly referred to as 55 Cancri b.[19] Under the rules for naming objects in binary star systems it should be named 55 Cancri Ab[20] and this more formal form is occasionally used to avoid confusion with the secondary star 55 Cancri B. The other planets discovered were designated 55 Cancri c, d, e and f, in order of their discovery.
In July 2014 the International Astronomical Union launched NameExoWorlds, a process for giving proper names to certain exoplanets and their host stars.[21] The process involved public nomination and voting for the new names.[22] In December 2015, the IAU announced the winning names were Copernicus for 55 Cancri A and Galileo, Brahe, Lipperhey, Janssen and Harriot for its planets (b, c, d, e and f, respectively).[23]
The winning names were those submitted by the Royal Netherlands Association for Meteorology and Astronomy of the Netherlands. They honor the astronomers Nicolaus Copernicus, Galileo Galilei, Tycho Brahe and Thomas Harriot and the spectacle makers and telescope pioneers Hans Lipperhey and Jacharias Janssen.[24] (The IAU originally announced the winning name was Lippershey for 55 Cancri d. In January 2016, in recognition that his actual name was Lipperhey (with Lippershey an error introduced in the 19th century), the exoplanet name was corrected to Lipperhey by the IAU and that name was submitted to the official sites that keep track of astronomical information).[23][24]
In 2016, the IAU organized a Working Group on Star Names (WGSN)[25] to catalog and standardize proper names for stars. In its first bulletin of July 2016,[26] the WGSN explicitly recognized the names of exoplanets and their host stars approved by the Executive Committee Working Group Public Naming of Planets and Planetary Satellites, including the names of stars adopted during the 2015 NameExoWorlds campaign. This star is now so entered in the IAU Catalog of Star Names.[15]
Stellar system[]
The 55 Cancri system is located fairly close to the Solar System: the Gaia astrometry satellite measured the parallax of 55 Cancri A as 79.45 milliarcseconds, corresponding to a distance of 12.6 parsecs (41 light-years).[1] 55 Cancri A has an apparent magnitude of 5.95, making it 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. The two components are separated by an estimated distance of 1,065 AU[27] (6.15 light-days). Despite their wide separation, the two stars appear to be gravitationally bound, as they share a common proper motion.[17]
The primary star, 55 Cancri A, has a spectral type of K0IV-V, indicating a main-sequence or subgiant star. It is smaller in radius and slightly less massive than the Sun, and so is cooler and less luminous. The star has only low emission from its chromosphere, and is not variable in the visible spectrum;[17] but it is variable in X-rays.[28] It is more enriched than the 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.[17] This abundance of metal makes estimating the star's age and mass difficult, as evolutionary models are less well defined for such stars.[citation needed] 55 Cancri A also has more carbon than the Sun, with a C/O ratio of 0.78,[29] compared to solar value of 0.55. Age estimates for 55 Cancri A include 7.4–8.7 billion years[30] and 10.2 ± 2.5 billion years.[11]
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.[31]
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.[32]
The secondary, 55 Cancri B, is a red dwarf star much less massive and luminous than the Sun. There are indications that component B may itself be a double star, though this is uncertain.[16]
Planetary system[]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity[34][35] | Inclination[33] | Radius |
|---|---|---|---|---|---|---|
| e (Janssen) | 7.99+0.32 −0.33 M |