 Position of HR 858 in Fornax | |
| Observation data Epoch J2000.00 Equinox J2000.00 | |
|---|---|
| Constellation | Fornax |
| Right ascension | 02h 51m 56.246s[1] |
| Declination | −30° 48′ 52.26″[1] |
| Apparent magnitude (V) | 6.382[2] |
| Characteristics | |
| Evolutionary stage | F6V[3] + M[4] |
| Spectral type | Main sequence |
| B−Vcolor index | +0.484[5] |
| Astrometry | |
| Radial velocity (Rv) | +9.77±0.12[1] km/s |
| Proper motion (μ) | RA: 123.435(25)mas/yr[1] Dec.: 105.996(37)mas/yr[1] |
| Parallax (π) | 31.5418±0.0352 mas[1] |
| Distance | 103.4 ± 0.1 ly (31.70 ± 0.04 pc) |
| Absolute magnitude (MV) | +3.82[5] |
| Details[6] | |
| A | |
| Mass | 1.204±0.052 M☉ |
| Radius | 1.258±0.019 R☉ |
| Luminosity | 2.31±0.12 L☉ |
| Surface gravity (log g) | 4.30±0.06 cgs |
| Temperature | 6,354±70 K |
| Metallicity[Fe/H] | 0.025±0.050 dex |
| Rotation | 6.7±1.3 d |
| Rotational velocity (v sin i) | 7.5±0.2 km/s |
| Age | 2.0±0.6 Gyr |
| B | |
| Radius | 0.17±0.04[4] R☉ |
| Temperature | 2,800±300[4] K |
| Other designations | |
| CD−31°1148,GC 3443,HD 17926,HIP 13363,HR 858,SAO 193951,TOI-396,TIC 178155732[7] | |
| Database references | |
| SIMBAD | data |
| Exoplanet Archive | data |
HR 858 (also known asHD 17926 orTOI-396) is astar with aplanetary system located 103 light-years from theSun in the southernconstellation ofFornax. It has a yellow-white hue and is visible to the naked eye, but it is a challenge to see with anapparent visual magnitude of 6.4.[2] The star is drifting further away with aradial velocity of 10 km/s.[1] It has anabsolute magnitude of +3.82.[5]
This object is a slightly-evolvedF-type main-sequence star with astellar classification of F6V,[3] which indicates it is generating energy throughcorehydrogen fusion. It is roughly two[8] billion years old and is spinning with aprojected rotational velocity of 8.3 km/s. The star has 1.1 times themass of the Sun and 1.3 times theSun's radius. It is radiating 2.3 times theluminosity of the Sun from itsphotosphere at aneffective temperature of 6,201 K.[4]
A faint co-moving stellar companion, designated component B, at an angular separation of8.4″. This corresponds to a projected separation of270 AU. It is ared dwarf star.[4]
In May 2019, HR 858 was announced to have at least 3exoplanets as observed by thetransit method with theTransiting Exoplanet Survey Satellite. All three are orbiting close to the host star and are close in size, each about twice the radius of the Earth. Described assuper-Earths by their discovery paper,[4] measurements of their masses suggest that in terms of composition they may be better described assub-Neptunes.[6] Planets 'b' and 'c' may be in a 3:5mean-motion resonance.[4]
Further research measured the masses of the planets b and d using accurateradial velocities, giving masses of3.55 and 7.1 M🜨 as well as planetary densities of 2.44 and 4.9g/cm3. The system displays significanttransit timing variations. The mass of planet c could not be measured using radial velocities, but it is constrained to be less than3.8 M🜨, and a not very reliable value of2.24 M🜨 was measured using TTVs.[6]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | 3.55+0.94 −0.96 M🜨 | 0.04888±0.00066 | 3.585287+0.000009 −0.000012 | 0 | 85.98+0.26 −0.25° | 2.004+0.045 −0.047 R🜨 |
| c | <3.8 M🜨 | 0.06870±0.00092 | 5.973865+0.000015 −0.000016 | 0 | 86.59+0.15 −0.14° | 1.979+0.054 −0.051 R🜨 |
| d | 7.1±1.6 M🜨 | 0.1046±0.0014 | 11.230511+0.000043 −0.000045 | 0 | 87.72+0.10 −0.11° | 2.001+0.063 −0.064 R🜨 |
