GD 356

GD 356
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 DAHe[2]
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: -119.425 ±0.031 mas/yr[3]
Dec.: -190.438 ±0.031 mas/yr[3]
Parallax (π)49.6501 ± 0.0207 mas[3]
Distance65.69 ± 0.03 ly
(20.141 ± 0.008 pc)
Absolute magnitude (MV)13.43
Details
Mass0.67 M☉
Surface gravity (log g)8 cgs
Temperature7510 K
Rotation115 minutes
AgeAbout 2.1 Gyr
Other designations
Gliese 1205, LP 137-43, EGGR 329, WD 1639+537
Database references
SIMBADdata
ARICNSdata

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.[4] The class of this white dwarf is DAe meaning that it has a cool helium rich atmosphere.[5] This star exhibits emission lines showing the Zeeman effect in the hydrogen Balmer spectrum.[5] 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%.[5] 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.[6] One explanation is that it is caused by a large electric current flowing between the poles of the star and a highly conducting planet.[4] This planet was not detected in a later, more detailed analysis with new data. Rejecting the idea of an orbiting planet.[2] 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.[5] 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.[7]

Other catalog names for this are LP 137-43, EGGR 329 and WD 1639+537.[6]

  1. ^ a b c d e f g h i j k l "SIMBAD Query Result: GD 356". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 13 June 2012.
  2. ^ a b Cite error: The named reference Walters2021 was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference Gaia EDR3 was invoked but never defined (see the help page).
  4. ^ a b Muir, Hazel (1 August 1998). "The Earth could be in for an electrifying time". New Scientist (2145): 7.
  5. ^ a b c d Wickramasinghe, Dayal T.; Farihi, Jay; Tout, Christopher A.; Ferrario, Lilia; Stancliffe, Richard J. (9 February 2010). "Does GD356 have a Terrestrial Planetary Companion?". Monthly Notices of the Royal Astronomical Society. 404 (4): 1984–1991. arXiv:1002.1761. Bibcode:2010MNRAS.404.1984W. doi:10.1111/j.1365-2966.2010.16417.x. S2CID 119255099.
  6. ^ a b Ferrario, Lilia; Wickramasinghe, Dayal T.; Liebert, James; Schmidt, Gary D.; Bieging, John H. (1997). "The Magnetic Field and Emission-Line Spectrum of the Remarkable White Dwarf GD 356". Monthly Notices of the Royal Astronomical Society. 289 (1): 105–116. Bibcode:1997MNRAS.289..105F. doi:10.1093/mnras/289.1.105.
  7. ^ Brinkworth, C. S.; M. R. Burleigh; G. A. Wynn; T. R. Marsh (2004). "Photometric variability of the unique magnetic white dwarf GD 356". Monthly Notices of the Royal Astronomical Society. 384 (3): L33–L37. arXiv:astro-ph/0312311. Bibcode:2004MNRAS.348L..33B. doi:10.1111/j.1365-2966.2004.07538.x. S2CID 15677179.