Gliese 318

Gliese 318 is a white dwarf in the constellation Pyxis. Its spectral type is DA5.5 and it has a visual magnitude of 11.85,^[2] and lies 27.8 light-years (8.5 parsecs) away.^[6]

Gliese 318

Observation data Epoch J2000      Equinox J2000
Constellation	Pyxis
Right ascension	08h 41m 32.42908s[1]
Declination	–32° 56′ 32.9158″[1]
Apparent magnitude (V)	11.85[2]
Characteristics
Spectral type	DA5.5
U−B color index	−0.59[3]
B−V color index	+0.25[4]
Astrometry
Radial velocity (Rv)	+29.3 ± 2.9 km/s
Proper motion (μ)	RA: –1061.158 mas/yr[1] Dec.: 1345.900 mas/yr[1]
Parallax (π)	117.3961±0.0205 mas[1]
Distance	27.783 ± 0.005 ly (8.518 ± 0.001 pc)
Absolute magnitude (MV)	12.22±0.04[5]
Details[5]
Mass	0.47±0.02 M☉
Radius	0.0148 ± 0.00092[a] R☉
Luminosity	1.32+0.13 −0.12×10−3 L☉
Surface gravity (log g)	7.77±0.03 cgs
Temperature	9,040±190 K
Age	590±40[b] Myr
Other designations
GJ 318, CD−32° 5613, LHS 253, L 532-81, LTT 3218, WD 0839-327
Database references
SIMBAD	data
ARICNS	data

The star was too faint to have had its parallax measured by the Hipparcos satellite. Earth-based measurement in 2009 gave its parallax as 113.63±1.97 milliarcseconds, yielding a distance of 28.7±0.5 light-years;^[7] this parallax measurement has since been substantially improved by Gaia.

Gliese 318 is a rather young white dwarf with an age estimated to be 590 million years. Its temperature is around 9,000 K and it shines with 0.13 percent of the luminosity of the Sun. Like all white dwarfs, Gliese 318 is small, with just 1.5 percent the Sun's radius (1.6 R_🜨),^[a] but has around half the Sun's mass.^[5]

Bragaglia et al. suspect this star to be a double white dwarf due to strong spectral line variations.^[8] From Gaia DR2 it was not possible to confirm this claim. It is still possible that Gliese 318 is a double white dwarf and additional spectroscopic observations are needed in order to confirm this claim.^[9] Gliese 318 could be the closest double white dwarf to earth.^[10][11]

Notes

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

   ${\displaystyle {\sqrt {{\biggl (}{\frac {5,772}{9,040}}{\biggr )}^{4}\cdot 10^{-2.88}}}=0.0148\ R_{\odot }}$.

2. This is just the cooling age