| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Draco |
| Right ascension | 16h 40m 57.16s[1] |
| Declination | +53° 41′ 09.6″[1] |
| Apparent magnitude (V) | 15.06[1] |
| Characteristics | |
| Spectral type | DC7[1] |
| Apparent magnitude (B) | ~15.39[1] |
| Apparent magnitude (V) | ~15.06[1] |
| Apparent magnitude (R) | ~15.1[1] |
| Apparent magnitude (I) | ~14.0[1] |
| Apparent magnitude (J) | ~14.493[1] |
| Apparent magnitude (H) | ~14.479[1] |
| Apparent magnitude (K) | ~14.369[1] |
| U−B color index | -0.52[1] |
| B−V color index | +0.33[1] |
| Variable type | 0.2% over 115 minutes |
| Astrometry | |
| Radial velocity (Rv) | 25 km/s |
| Proper motion (μ) | RA: -0.125[2] mas/yr Dec.: -0.200[2] mas/yr |
| Parallax (π) | 545.4[1] ± 3.5 mas |
| Distance | 65 ly (21.1 pc) |
| Absolute magnitude (MV) | 13.43 |
| Details | |
| Mass | 0.67 M☉ |
| Surface gravity (log g) | 8 cgs |
| Temperature | 7510 K |
| Rotation | 115 minutes |
| Age | About 2.1 Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
| ARICNS | data |
GD 356 is a white dwarf in the constellation of Draco showing an unusual emission of circular polarised light. The star is 65 light years from earth.[3] The class of this white dwarf is DAe meaning that it has a cool helium rich atmosphere.[4] This star exhibits emission lines showing the Zeeman effect in the hydrogen Balmer spectrum.[4] GD 356 belongs to a class of high field magnetic white dwarfs (HFMWD), but it is unique in that the split lines are purely emission lines with no absorption. The emission region appears to be due to a heated upper layer in the photosphere in which the magnetic field is uniform to within 10%.[4] The emission can be produced by an atmosphere at 7500K in a gravity field of 106 ms−2 and a magnetic field of 13 megaGauss. The magnetically split emission lines, Hα and Hβ, are circularly polarised.[5] One explanation is that it is caused by a large electric current flowing between the poles of the star and a highly conducting planet.[3] Other explanations such as being due to Bondi-Hoyle accretion or due to a corona are ruled out by the lack of radio and X-ray emissions. Accretion of gas at a low rate over a broad area of the star, only results in heating at levels high in the atmosphere and not down to the opacity depth of 1.0 as observed with these lines.
The spectrum does not vary over periods of hours or days. This indicates that the rotation axis must match the magnetic dipole axis. The power radiated by the emission lines is 1027 erg s−1. Overall light from the white dwarf varies by 0.2% smoothly over a period of 117 minutes.[4] Explanations given for the variation are a dark spot rotating with the star. This could be near the rotation pole when viewed nearly edge on, or could be on the equator with the pole pointing roughly towards Earth.[6]
Other catalog names for this are LP 137-43, EGGR 329 and WD 1639+537.[5]