| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cygnus |
| Right ascension | 21h23m 48.38864s[1] |
| Declination | +37° 21′ 05.3177″[1] |
| Apparent magnitude (V) | 6.46[2] |
| Characteristics | |
| Spectral type | K5[3] |
| B−V color index | 1.472±0.006[2] |
| Astrometry | |
| Radial velocity (Rv) | −6.26±0.16[1] km/s |
| Proper motion (μ) | RA: −5.999[1] mas/yr Dec.: −8.364[1] mas/yr |
| Parallax (π) | 2.6601 ± 0.0417 mas[1] |
| Distance | 1,230 ± 20 ly (376 ± 6 pc) |
| Absolute magnitude (MV) | −0.75[2] |
| Details[4] | |
| Mass | 1.7 M☉ |
| Radius | 46-50 R☉ |
| Luminosity | 513 L☉ |
| Temperature | 4,080 K |
| Other designations | |
BD+36°4543, HD 203857, HIP 105637, HR 8193, SAO 71280, CCDM J21237+3722A[5] | |
| Database references | |
| SIMBAD | data |
HD 203857 is a double star in the constellation Cygnus. It is near the lower limit of visibility to the naked eye, having a combined apparent visual magnitude of 6.46.[2] The distance to the primary component is approsimatly 1,230 light years based on parallax, and it has an absolute magnitude of −0.75.[2] The star is drifting closer to the Sun with a radial velocity of −6.3 km/s.[1] It has a stellar classification of K5[3] and is known to be evolved. The star likely hosts an extrasolar planet, though yet unconfirmed.
HD 203857 is listed in the Washington Double Star Catalogue as having five visual companions. It is separated by six arc-minutes from HD 203784, an F-type subgiant, though it is likely they are actually not gravitationally–bound.[4] HD 203784 is thought to be closer to us and less luminous than HD 203857.[6] There are also fainter stars at 23″ and 178″. HD 203784 has a 13th-magnitude star and a 14th-magnitude star within 20″.[7]
Okayama Planet Search team has published a paper in late 2008 reporting investigations on radial velocity variations observed for a set of evolved stars, announcing possible detection of a substellar companion orbiting the giant star HD 203857.[4] Orbital period is estimated 2.3 years, but planet has still to be confirmed.
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b (unconfirmed) | ≥8.1 MJ | 2.1 | 836.8 | 0.3 | — | — |
