| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Fornax[1] |
| Right ascension | 03h20m 02.94286s[2] |
| Declination | −28° 47′ 01.7905″[2] |
| Apparent magnitude (V) | 8.48[3] |
| Characteristics | |
| Spectral type | K0V[3] |
| B−V color index | 0.82[3] |
| Astrometry | |
| Radial velocity (Rv) | 40.27±0.12[2] km/s |
| Proper motion (μ) | RA: 348.869±0.015 mas/yr[2] Dec.: −66.614±0.019 mas/yr[2] |
| Parallax (π) | 27.8123 ± 0.0239 mas[2] |
| Distance | 117.3 ± 0.1 ly (35.96 ± 0.03 pc) |
| Absolute magnitude (MV) | 5.70[3] |
| Details[3] | |
| Mass | 0.7 M☉ |
| Luminosity | 0.49±0.04 L☉ |
| Surface gravity (log g) | 4.37±0.05 cgs |
| Temperature | 5256±29 K |
| Metallicity [Fe/H] | −0.11±0.02 dex |
| Rotation | 46.8±4.4 d |
| Rotational velocity (v sin i) | 1.1 km/s |
| Other designations | |
CD–29° 1229, HIP 15526, LTT 1581, SAO 168468, 2MASS J03200291-2847016, Gaia DR1 5060105892897388288[4] | |
| Database references | |
| SIMBAD | data |
HD 20781 is a star which is part of a wide binary system with HD 20782. The companion star has a very large angular separation of 252 arcsec, corresponding to 9080 AU at the distance of HD 20782.[5] Both stars possess their own planetary systemsinS type orbits, with a total of five known planets around both stars.[3][6] This is the first known example of planets being found orbiting both components of a wide binary system.[5][7] HD 20781 has no noticeable starspot activity.[3]
In 2011, a pair of Neptune-mass gas giants were detected with the radial velocity method.[7] In 2017, these planets were confirmed and an additional two inner super-Earths were detected, with periods of 5.3 and 13.9 days respectively.[3]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | ≥1.93+0.39 −0.36 M🜨 |
0.0529+0.0024 −0.0027 |
5.3135±0.0010 | 0.10+0.11 −0.07 |
— | — |
| c | ≥5.33+0.70 −0.67 M🜨 |
0.1004+0.0046 −0.0051 |
13.8905+0.0033 −0.0034 |
0.09+0.09 −0.06 |
— | — |
| d | ≥10.61+1.20 −1.19 M🜨 |
0.1647+0.0076 −0.0083 |
29.1580+0.0102 −0.0100 |
0.11+0.05 −0.06 |
— | — |
| e | ≥14.03±1.56 M🜨 | 0.3374+0.0155 −0.0170 |
85.5073+0.0983 −0.0947 |
0.06+0.06 −0.04 |
— | — |
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