GRW +70 8247

GRW +70 8247 is a white dwarf located 42 light-years from Earth[1] in the constellation Draco. With a magnitude of about 13 it is visible only through a large telescope. It is the smallest star known at this date at just under 2 kilometers diameter.

GRW +70 8247
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Draco
Right ascension  19h 00m 10.2534s[1]
Declination +70° 39′ 51.418″[1]
Apparent magnitude (V) 13.19[2]
Characteristics
Spectral type DAP4.5[3]
U−B color index -0.85[4]
B−V color index +0.05[4]
Astrometry
Proper motion (μ) RA: +85.774[1] mas/yr
Dec.: +505.050[1] mas/yr
Parallax (π)77.6525 ± 0.0317[1] mas
Distance42.00 ± 0.02 ly
(12.878 ± 0.005 pc)
Other designations
GJ 742, AC +70 8247, G 260-15, LFT 1446, LHS 3424, LTT 15585, Grw+70 8247, WD 1900+705[2][5]
Database references
SIMBADdata
ARICNSdata

Properties

Although photographed in the 19th century as part of the Carte du Ciel project, it was not determined to be a white dwarf until observed in 1934 by G. P. Kuiper.[6] This makes it the fifth or sixth white dwarf discovered.[7] At first, its spectrum was thought to be almost featureless,[6] but later observation showed it to have unusual broad, shallow absorption bands.[8], p. 28; [9] In 1970, when light it emitted was observed to be circularly polarized, it became the first white dwarf known to have a magnetic field.[10][11] In the 1980s it was realized that the unusual absorption bands could be explained as hydrogen absorption lines shifted by the Zeeman effect.[5][12][13]

Notes and references
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. "LAWD 73". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved November 5, 2007.
  3. Wesemael, F.; Greenstein, J. L.; Liebert, James; Lamontagne, R.; Fontaine, G.; Bergeron, P.; Glaspey, J. W. (1993). "An atlas of optical spectra of white-dwarf stars". Publications of the Astronomical Society of the Pacific. 105: 761. Bibcode:1993PASP..105..761W. doi:10.1086/133228.
  4. Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
  5. Further identifications of hydrogen in Grw +70°8247, Jesse L. Greenstein, Ronald J. W. Henry, and R. F. O'Connell, Astrophysical Journal 289 (February 15, 1985), pp. L25–L29.
  6. Two New White Dwarfs of Large Parallax, G. P. Kuiper, Publications of the Astronomical Society of the Pacific 46, #273 (October 1934), pp. 287–290.
  7. The star EGGR 37 was suspected to be a white dwarf by April 1934 (Some new members of the Hyades cluster, P. J. van Rhijn and J. J. Raimond, Monthly Notices of the Royal Astronomical Society 94 (April 1934), pp. 508–518, at p. 517) but this was not confirmed until 1938 (Zwei weiße Zwerge unter den physischen Hyadenmigliedern, Jöran M. Ramberg, Astronomische Nachrichten 265 (May 1938), pp. 111–112; see also List of Known White Dwarfs, Gerard P. Kuiper, Publications of the Astronomical Society of the Pacific 53, #314 (August 1941), pp. 248–252).
  8. Annual Report of the Director of the Mount Wilson Observatory (1937-1938), Walter S. Adams and Frederick H. Seahes, Mount Wilson Observatory Annual Report 10 (1938), pp. 1–40.
  9. Studies of the White Dwarfs. I. Broad Features in White Dwarf Spectra, Jesse L. Greenstein and Mildred S. Matthews, Astrophysical Journal 126 (July 1957), pp. 14–18.
  10. Discovery of Circularly Polarized Light from a White Dwarf, James C. Kemp, John B. Swedlund, J. D. Landstreet, and J. R. P. Angel, Astrophysical Journal 161 (August 1970), pp. L77–L79.
  11. Angel, J.R.P.; Landstreet, J.D.; Oke, J.B. (1972). "The Spectral Dependence of Circular Polarization in Grw+70°8247". Astrophysical Journal. 171: L11–L15. Bibcode:1972ApJ...171L..11A. doi:10.1086/180857.
  12. The optical spectrum of hydrogen at 160-350 million gauss in the white dwarf Grw +70°8247, J. R. P. Angel, James Liebert, and H. S. Stockman, Astrophysical Journal 292 (May 1, 1985), pp. 260–266.
  13. A centered dipole model for the high field magnetic white dwarf GRW +70°8247, D. T. Wickramasinghe and Lilia Ferrario, Astrophysical Journal 327 (April 1, 1988), pp. 222–233.
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