HD 202206
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| Observation data Epoch J2000.0 |
|
|---|---|
| Constellation (pronunciation) |
Capricornus |
| Right ascension | 21h 14m 57.79s |
| Declination | -20° 47′ 20.1″ |
| Apparent magnitude (V) | +8.08 |
| Characteristics | |
| Spectral type | G6V |
| U-B color index | ? |
| B-V color index | 0.714 |
| Variable type | none |
| Astrometry | |
| Radial velocity (Rv) | ? km/s |
| Proper motion (μ) | RA: -38.23 mas/yr Dec.: -119.77 mas/yr |
| Parallax (π) | 21.58 ± 1.14 mas |
| Distance | 151.14 ly (46.3 pc) |
| Absolute magnitude (MV) | +4.75 |
| Details | |
| Mass | 1.15 M☉ |
| Radius | 1.02 R☉ |
| Luminosity | 1.07 L☉ |
| Temperature | 5765 ± 40 K |
| Metallicity | 234% |
| Rotation | ? |
| Age | (5.6 ± 1.2) × 109 years |
| Other designations | |
|
HIP 104903
|
|
| Database references | |
| SIMBAD | data |
HD 202206 is a yellow dwarf star approximately 151 light-years away in the constellation Capricornus. The star is orbited by two companions with substellar masses in a near-resonant configuration.
Contents |
[edit] Distance, age and metallicity
Measurements by the Hipparcos astrometric satellite give a parallax of 21.58 milliarcseconds, which corresponds to a distance of 46.3 parsecs[1]. It is similar in mass, radius, and luminosity to the Sun, though estimated to be older at around 5.6 Gyr old[2]. It is also more metal-rich than our Sun based on the amount of iron relative to hydrogen.
[edit] Planetary system
In 2002, analysis of radial velocity measurements of the star revealed the existence of a substellar companion (designated HD 202206 b) with at least 17 times the mass of Jupiter around the star in an eccentric orbit with a period of around 256 days[2]. This mass exceeds the 13 Jupiter mass limit above which an object can undergo deuterium fusion in its core, which some take to be the dividing line between planets and brown dwarfs. The classification of this object as a brown dwarf or "superplanet" is currently unclear.
Even after HD 202206 b was accounted for, the star still showed a drift in the radial velocity measurements, indicating another companion in a longer-period orbit. In 2004 after further observations, the parameters of a companion was announced[3]. This companion has a planetary mass, at least 2.44 times that of Jupiter, and has an eccentric orbit taking around 1384 days to complete. The planet is located in a 5:1 orbital resonance with the brown dwarf.
The formation history of this planetary system is interesting: depending on the method of formation of the inner companion, the system can either be regarded as consisting of a superplanet and a planet, or alternatively a planet revolving in a circumbinary orbit.
| Planet (in order from star) |
Mass (MJ) |
Orbital period (days) |
Semimajor axis (AU) |
Eccentricity |
|---|---|---|---|---|
| b | >17.4 | 255.87 ± 0.06 | 0.83 | 0.435 ± 0.001 |
| c | >2.44 | 1383.4 ± 18.4 | 2.55 | 0.267 ± 0.021 |
[edit] See also
[edit] References
- ^ HIP 104903. The Hipparcos and Tycho Catalogues. ESA (1997). Retrieved on 26 June, 2006.
- ^ a b Udry, S. et al. (2002). "The CORALIE survey for southern extra-solar planets VIII. The very low-mass companions of HD 141937, HD 162020, HD 168443, HD 202206: Brown dwarfs or "superplanets"?" (abstract). Astronomy and Astrophysics 390: 267 – 279. doi:.
- ^ Correia, A. et al. (2005). "The CORALIE survey for southern extra-solar planets. XIII. A pair of planets around HD202206 or a circumbinary planet?" (abstract). Astronomy and Astrophysics 440: 751 – 758. doi:.
