GRW +70 8247

GRW +70 8247 is a white dwarf star 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.

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 mas[1]
Distance	42.00 ± 0.02 ly (12.878 ± 0.005 pc)
Details[5]
Mass	1.029 M☉
Radius	5,960[a] km
Luminosity	0.013182 L☉
Surface gravity (log g)	8.67 cgs
Temperature	12540±143 K
Age	(as white dwarf) 1.138 Gyr
Other designations
GJ 742, AC +70 8247, G 260-15, LFT 1446, LHS 3424, LTT 15585, Grw+70 8247, WD 1900+705[2][6]
Database references
SIMBAD	data
ARICNS	data

Properties

Although photographed in the 19th century as part of the Carte du Ciel project, the star was not determined to be a white dwarf until G. P. Kuiper observed it in 1934.^[7] This makes it the fifth or sixth white dwarf discovered.^[b] At first, its spectrum was thought to be almost featureless,^[7] but later observation showed it to have unusual broad, shallow absorption bands.^[11][12] In 1970, when light that it emitted was observed to be circularly polarized, it became the first white dwarf known to have a magnetic field.^[13][14] In the 1980s, it was realized that the unusual absorption bands could be explained as hydrogen absorption lines shifted by the Zeeman effect.^[6][15][16]

Notes

1. Applying the Stefan–Boltzmann law with a nominal solar effective temperature of 5,772 K:

   ${\displaystyle {\sqrt {{\biggl (}{\frac {5,772}{11,880}}{\biggr )}^{4}\cdot 10^{-2.88}}}=0.00857\ R_{\odot }}$.

2. The star EGGR 37 was suspected to be a white dwarf by April 1934,^[8] but this was not confirmed until 1938.^[9][10]