| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Eridanus[1] |
| Right ascension | 04h 26m 26.323s[2] |
| Declination | −10° 33′ 02.95″[2] |
| Apparent magnitude (V) | +7.80[1] |
| Characteristics | |
| Evolutionary stage | Main sequence/subgiant |
| Spectral type | G6.5IV-V[3] |
| B−Vcolor index | 0.750±0.010[1] |
| Astrometry | |
| Radial velocity (Rv) | 50.40±0.14[2] km/s |
| Proper motion (μ) | RA: 84.070(18)mas/yr[2] Dec.: −59.637(16)mas/yr[2] |
| Parallax (π) | 25.4868±0.0207 mas[2] |
| Distance | 128.0 ± 0.1 ly (39.24 ± 0.03 pc) |
| Absolute magnitude (MV) | 4.67[1] |
| Details | |
| Mass | 0.974±0.018[4] M☉ |
| Radius | 1.048±0.015[4] R☉ |
| Luminosity | 0.970±0.019[4] L☉ |
| Surface gravity (log g) | 4.386±0.015[4] cgs |
| Temperature | 5,602±36[4] K |
| Metallicity[Fe/H] | 0.19±0.01[1] dex |
| Rotation | 30 days[5] |
| Age | 8.3±1.0[4] Gyr |
| Other designations | |
| BD–10°919,HD 28185,HIP 20723,SAO 149631,GSC 05317-00733[6] | |
| Database references | |
| SIMBAD | data |
HD 28185 is a single[4]yellow dwarf star similar to theSun, located 128light-years away from Earth in theconstellationEridanus. The designation HD 28185 refers to its entry in theHenry Draper catalogue. The star is known to possess two long-periodextrasolar planets.[4]
According to measurements from theGaia spacecraft, HD 28185 has aparallax of 25.4868milliarcseconds,[2] which corresponds to a distance of 39.24parsecs (128.0light-years). Since the star is located further than 25 parsecs from Earth, it is not listed in theGliese Catalogue of Nearby Stars. With anapparent magnitude of 7.81, the star is almost never visible with thenaked eye, though it can be seen usingbinoculars.
HD 28185 is similar to the Sun in terms ofmass,radius, andluminosity. Thespectral type of G6.5IV-V[3] implies HD 28185 is cooler than the Sun, and that the star is on themain sequence and is generatingenergy byfusinghydrogen in its core. Like the majority of extrasolar planet host stars, HD 28185 ismetal-rich relative to the Sun, containing around 173% of the solar abundance ofiron. The star rotates slower than the Sun, with a period of around 30 days,[5] compared to 25.4 days for the Sun.
Based on the star'schromospheric activity, HD 28185 is estimated to have an age of around 2,900 million years. On the other hand,evolutionary models give an age of around 7,500 million years and a mass 0.99 times that of the Sun.[5] The higher luminosity and longer rotation period favour an older age for the star. As of 2024[update], the most recent estimate is about 8,300 million years, based on the star's observed physical properties.[4]
In 2001, anextrasolar planet more massive thanJupiter, designatedHD 28185 b, was discovered in orbit around the star with a period of 1.04 years.[5][7] Unlike many long-period extrasolar planets, it has a loworbital eccentricity.[8] The planet experiences similarinsolation toEarth, which has led to speculations about the possibilities forhabitablemoons.[9][10] In addition, numerical simulations suggest that low-mass planets located in the gas giant'sTrojan points would be stable for long periods.[11] The planet's existence was independently confirmed by theMagellan Planet Search Program in 2008.[12]
The star also shows evidence of a long-term radial velocity trend, which may indicate the presence of an additional outer companion.[13] In 2022, the presence of an outer companion (HD 28185 c) was confirmed using a combination ofradial velocity andastrometry, with the proposed mass of nearly 20 times that of Jupiter being in the range ofbrown dwarfs.[14] However, this was revised by a 2024 follow-up study which found HD 28185 c to be a planet with a mass 6 times that of Jupiter, comparable to HD 28185 b.[4] Also in 2024, the inclination and true mass of HD 28185 b were measured viaastrometry.[15]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (years) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | 13.3+5.0 −3.9 MJ | 1.0282+0.0063 −0.0064 | 1.05642(15) | 0.0634±0.0030 | 156.5+6.1 −9.5° | — |
| c | 5.68+0.44 −0.36 MJ | 8.54+0.21 −0.14 | 25.27+0.91 −0.61 | 0.15±0.04 | 73+10.0 −8.4 or109.5+9.1 −12.0° | — |
