| Observation data Epoch J2000.0 Equinox J2000.0 |
|
|---|---|
| Constellation | Hydra |
| Right ascension | 08h 42m 25.1222s |
| Declination | +04° 34′ 41.151″ |
| Apparent magnitude (V) | +7.614[1] |
| Characteristics | |
| Spectral type | G0V |
| U−B color index | ? |
| B−V color index | 0.581[1] |
| V−R color index | 0.4 |
| R−I color index | 0.2 |
| Variable type | “None” |
| Astrometry | |
| Radial velocity (Rv) | +3.7 km/s |
| Proper motion (μ) | RA: 24.96 mas/yr Dec.: –200.48 mas/yr |
| Parallax (π) | 15.49 ± 1.10 mas |
| Distance | 210 ± 10 ly (65 ± 5 pc) |
| Absolute magnitude (MV) | +3.57±0.15 |
| Details | |
| Mass | 1.24[1] M☉ |
| Radius | 1.64 ± 0.19[1] R☉ |
| Surface gravity (log g) | 4.4 ± 0.15[1] |
| Luminosity (bolometric) | 3.037 ± 0.485[1] L☉ |
| Temperature | 5960 ± 100[1] K |
| Metallicity | [Fe/H] = +0.13[1] |
| Rotation | 4.3 km/s[1] |
| Age | (3.7 ± 0.4) × 109[1] years |
| Other designations | |
| Database references | |
| SIMBAD | data |
HD 74156 is a yellow dwarf star (spectral type G0V) in the constellation of Hydra, 211 light years from our solar system. It is known to be orbited by two giant planets.
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This star is 24% more massive and 64% larger than our Sun. The total luminosity is 2.96 times that of our Sun and its temperature 5960 K.[1] The age of the star is estimated at approximately 3.7 billion years[1], with metallicity 1.35 times that of the Sun based on its abundance of iron.
In April 2001, two giant planets were announced orbiting the star.[2] The first planet HD 74156 b orbits the star at a distance closer than Mercury is to our Sun, in an extremely eccentric orbit. The second planet HD 74156 c is a long-period, massive planet (at least 8 times the mass of Jupiter), which orbits the star in an elliptical orbit with a semimajor axis of 3.90 astronomical units.[1]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity |
|---|---|---|---|---|
| b | >1.78 ± 0.04 MJ | 0.29169 ± 0.00001 | 51.638 ± 0.004 | 0.63 ± 0.01 |
| c | >8.2 ± 0.2 MJ | 3.90 ± 0.02 | 2520 ± 15 | 0.38 ± 0.02 |
Given the two-planet configuration of the system under the assumption that the orbits are coplanar and have masses equal to their minimum masses, an additional Saturn-mass planet would be stable in a region between 0.9 and 1.4 AU between the orbits of the two known planets.[3] Under the "packed planetary systems" hypothesis, which predicts that planetary systems form in such a way that the system could not support additional planets between the orbits of the existing ones, the gap would be expected to host a planet.
In September 2007, a third planet with a mass at least 0.396 Jupiter masses was announced to be orbiting between planets b and c with an eccentric orbit.[4] The planet, orbiting in a region of the planetary system previously known to be stable for additional planets, was seen as a confirmation of the "packed planetary systems" hypothesis.[5] However, Roman V. Baluev has cast doubt on this discovery, suggesting that the observed variations may be due to annual errors in the data.[6] A subsequent search using the Hobby-Eberly Telescope also failed to confirm the planet,[7] and further data obtained using HIRES instrument strongly contradicts its existence.[1]