HD 203857
Double star in the constellation Cygnus
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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. The distance to the primary component is approximately 1,223 light years based on parallax, and it has an absolute magnitude of −0.75. The star is drifting closer to the Sun with a radial velocity of −6.3 km/s. It has a stellar classification of K5 and is known to be evolved. The star likely hosts an extrasolar planet, though not yet confirmed.
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cygnus[1] |
| Right ascension | 21h 23m 48.38841s[2] |
| Declination | +37° 21′ 05.3216″[2] |
| Apparent magnitude (V) | 6.46[1] |
| Characteristics | |
| Evolutionary stage | red giant branch[2] |
| Spectral type | K5[3] |
| B−V color index | 1.472±0.006[1] |
| Astrometry | |
| Radial velocity (Rv) | −6.26±0.16[4] km/s |
| Proper motion (μ) | RA: −5.825[2] mas/yr Dec.: −8.629[2] mas/yr |
| Parallax (π) | 2.6676±0.0184 mas[2] |
| Distance | 1,223 ± 8 ly (375 ± 3 pc) |
| Absolute magnitude (MV) | −0.75[1] |
| Details[5] | |
| 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[6] | |
| Database references | |
| SIMBAD | data |
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.[5] HD 203784 is thought to be closer to us and less luminous than HD 203857.[7] There are also fainter stars at 23″ and 178″. HD 203784 has a 13th-magnitude star and a 14th-magnitude star within 20″.[8]
Substellar companion
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.[5] 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 | — | — |