| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Pisces[1] |
| Right ascension | 00h 34m 57.524s[2] |
| Declination | +04° 22′ 53.28″[2] |
| Apparent magnitude (V) | 8.97[1] |
| Characteristics | |
| Evolutionary stage | Main sequence[2] |
| Spectral type | K0 V[3] |
| B−Vcolor index | 0.827±0.021 |
| Variable type | Constant[1] |
| Astrometry | |
| Radial velocity (Rv) | +19.5±0.1[4] km/s |
| Proper motion (μ) | RA: +107.569mas/yr[2] Dec.: −173.334mas/yr[2] |
| Parallax (π) | 21.1363±0.0187 mas[2] |
| Distance | 154.3 ± 0.1 ly (47.31 ± 0.04 pc) |
| Absolute magnitude (MV) | 5.67[1] |
| Details[5][6] | |
| Mass | 0.837+0.053 −0.043 M☉ |
| Radius | 0.880+0.012 −0.013 R☉ |
| Luminosity | 0.56[1] L☉ |
| Surface gravity (log g) | 4.47±0.05 cgs |
| Temperature | 5,261±60 K |
| Metallicity[Fe/H] | 0.04±0.05 dex |
| Rotational velocity (v sin i) | 1.7±1.1 km/s |
| Age | 7.8±4.3 Gyr |
| Other designations | |
| K2-96,BD+03°68,HD 3167,HIP 2736,LTT 10198,EPIC 220383386,2MASS J00345752+0422531[7] | |
| Database references | |
| SIMBAD | data |
HD 3167 is a single,[4] orange-hued star in thezodiacconstellation ofPisces that hosts asystem with threeexoplanets.[8][9] The star is too faint to be seen with the naked eye, having anapparent visual magnitude of 8.97.[1] The distance to HD 3167 can be determined from its annualparallax shift of21.1363 mas as measured by theGaiaspace observatory,[2] yielding a range of 154 light years. It has a relatively highproper motion, traversing thecelestial sphere at the rate of0.204″ per year.[10] Since it was first photographed during thePalomar observatory sky survey in 1953, it had moved over12.5″ by 2017.[5] The star is moving away from the Earth with an average heliocentricradial velocity of +19.5 km/s.[4]
This is an ordinaryK-type main-sequence star with astellar classification of K0 V[3] and no significantvariability.[1] The star has 86% of themass of the Sun and 86% of theSun's radius.[5] It is achromospherically inactive[4] star and is radiating 56%[1] of theSun's luminosity from itsphotosphere at aneffective temperature of 5,261 K. The spin of the star displays a relatively lowprojected rotational velocity of around 1.7 km/s. It has a near solarmetallicity – a term astronomers use for the proportion of elements other than hydrogen and helium in astellar atmosphere.[5]
In 2019, a group of astronomers first reported that the orbits of the detected exoplanets hosted by the star are oddly unusual: two planets (HD 3167 c; HD 3167 d) revolve around the star onpolar orbits, i.e. orbits that pass over thepoles of the star.[11] Later, in October 2021, the third planet (HD 3167 b) was found to orbit around theequator of the star instead, while confirming the other planets' orbital inclinations from the 2019 study.[12][13]
In 2016, data collected during the extended K2 mission of theKepler space telescope was used to identify twotransiting exoplanet candidates orbiting this star, designated HD 3167 b and HD 3167 c. This made it one of the closest and brightest such multi-transiting stars known at the time. The lack of chromospheric activity makes it ideal for the preciseradial velocity (RV) measurements needed to estimate the masses of its planets.[4] Follow-up RV observations showed additionalperturbation signals beyond the two planets already identified.[14] This led to the discovery in 2017 of a third, non-transiting planet, designated HD 3167 d.[5]
The close-orbiting body HD 3167 b has a mass of5.02 M🜨 and radius 1.70 R🜨. It most likely has had its atmosphere stripped away by the host star, leaving arocky planet with about 15% iron by mass. HD 3167 b is orbiting HD 3167 with a period of 23.03 hours, anorbital inclination of 83.4°, and an assumedorbital eccentricity of zero – a circular orbit. Thesemimajor axis of its orbit is0.01815 AU, or just four times the star's radius.[5]
The second planet, HD 3167 c, has an orbital period of 29.8454 days and an eccentricity of less than 0.267. The semimajor axis is0.1795 AU. It has9.80 M🜨 and 3.01 R🜨, giving it a low bulk density of1.97+0.94
−0.59 g/cm3.[5] This suggests either a mini-Neptune[14] with a gaseous envelope consisting mainly of hydrogen and helium, or a planet consisting of mostly water. In 2020,transmission spectroscopy measurements of its atmosphere strongly favored a model with a high (>700 × Solar) metallicity atmosphere, due to discovered molecular absorption bands which cannot be attributed to hydrogen or helium.[15] The incidentflux from the host star is around 16 times the amount the Earth receives from the Sun, and it is less susceptible toatmospheric stripping than HD 3167 b.
The orbital inclination of HD 3167 d is inclined at least 1.3° away from theorbital planes of the other two exoplanets. Its orbit is expected to remain stable for periods longer than 100 million years only if this inclination is less than 40°. It has an orbital period of8.509±0.045 d, placing it in between the other two orbits, and shows a minimum mass of6.90 M🜨. The true mass is most likely less than Neptune.[5]
A fourth planet, HD 3167 e, first suggested as a candidate in 2019,[11] was discovered in 2022 by the radial-velocity method.[16]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | 4.97+0.24 −0.23 M🜨 | 0.01796+0.00037 −0.00031 | 0.959641±0.000011 | 0 (fixed) | 83.4+4.6 −7.7° | 1.67+0.17 −0.10 R🜨 |
| d | ≥4.33±0.45 M🜨 | 0.0763±0.0015 | 8.4112±0.0052 | <0.12 | — | — |
| c | 11.13+0.78 −0.74 M🜨 | 0.1776+0.0037 −0.0031 | 29.8454±0.0012 | <0.060 | 89.3+0.5 −1.0° | 3.00+0.45 −0.21 R🜨 |
| e | ≥8.41±1.02 M🜨 | 0.3885±0.0079 | 96.63±0.29 | <0.15 | — | — |
