| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Hydra |
| Right ascension | 08h 42m 25.12195s [1] |
| Declination | +04° 34′ 41.1457″ [1] |
| Apparent magnitude (V) | +7.614 [2] |
| Characteristics | |
| Spectral type | G0V |
| U−B color index | ? |
| B−V color index | 0.581 [2] |
| V−R color index | 0.4 |
| R−I color index | 0.2 |
| Variable type | “None” |
| Astrometry | |
| Radial velocity (Rv) | 3.90±0.13 [1] km/s |
| Proper motion (μ) | RA: 24.666±0.025 mas/yr [1] Dec.: −200.238±0.019 mas/yr [1] |
| Parallax (π) | 17.4242±0.0247 mas [1] |
| Distance | 187.2 ± 0.3 ly (57.39 ± 0.08 pc) |
| Absolute magnitude (MV) | +3.57 ± 0.15 |
| Details | |
| Mass | 1.24 [2] M☉ |
| Radius | 1.64 ± 0.19 [2] R☉ |
| Luminosity (bolometric) | 3.037 ± 0.485 [2] L☉ |
| Surface gravity (log g) | 4.4 ± 0.15 [2] cgs |
| Temperature | 5960 ± 100 [2] K |
| Metallicity [Fe/H] | +0.13 [2] dex |
| Rotational velocity (v sin i) | 4.3 [2] km/s |
| Age | 3.7 ± 0.4 [2] Gyr |
| Other designations | |
| HIP 42723, SAO 117040, BD+05 2035, 2MASS J08422511+0434411 | |
| Database references | |
| SIMBAD | data |
HD 74156 is a yellow dwarf star (spectral type G0V) in the constellation of Hydra, 187 light years from the Solar System. [1] It is known to be orbited by two giant planets.
This star is 24% more massive and 64% larger than the Sun. The total luminosity is 2.96 times that of the Sun and its temperature 5960 K. [2] The age of the star is estimated at 3.7 billion years, [2] 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. [3] [4] The first planet HD 74156 b orbits the star at a distance closer than Mercury is to the 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. [2] In 2022, the inclination and true mass of HD 74156 c were measured via astrometry. [5]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | ≥1.778±0.020 MJ | 0.2916±0.0033 | 51.6385±0.0015 | 0.6380±0.0061 | — | — |
| c | 8.665+1.385 −0.470 MJ | 3.678+0.145 −0.159 | 2448.5±4.2 | 0.377±0.006 | 120.162+7.601 −66.225 ° | — |
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. [7] 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. [8] 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. [9] However, Roman V. Baluev has cast doubt on this discovery, suggesting that the observed variations may be due to annual errors in the data. [10] A subsequent search using the Hobby-Eberly Telescope also failed to confirm the planet, [11] and further data obtained using HIRES instrument strongly contradicts its existence. [2]
