G 240-72

G 240-72 (or WD 1748+708, or LHS 455, or GJ 1221) is a nearby degenerate star (white dwarf) of spectral class DQP9.0,^[2] located 20.3 light-years away in the constellation Draco.

G 240-72

G 240-72 Location of G 240-72 in the constellation Draco
Observation data Epoch J2000      Equinox J2000
Constellation	Draco
Right ascension	17h 48m 07.99282s[1]
Declination	+70° 52′ 35.9221″[1]
Apparent magnitude (V)	14.15[2]
Characteristics
Spectral type	DQP9.0[2]
Apparent magnitude (B)	14.55[3]
Apparent magnitude (V)	14.15[3]
Apparent magnitude (R)	13.5[3]
Apparent magnitude (I)	13.1[3]
Apparent magnitude (J)	12.709 ± 0.021[3]
Apparent magnitude (H)	12.528 ± 0.023[3]
Apparent magnitude (K)	12.507 ± 0.023[3]
Astrometry
Proper motion (μ)	RA: -1266.387 mas/yr[1] Dec.: 1108.801 mas/yr[1]
Parallax (π)	160.9952±0.0119 mas[1]
Distance	20.259 ± 0.001 ly (6.2114 ± 0.0005 pc)
Absolute magnitude (MV)	15.23[2][4][note 1]
Details
Mass	0.81 ± 0.01[2] M☉
Radius	0.00984[2][note 2] R☉
Luminosity	0.000085[5] L☉
Surface gravity (log g)	8.36 ± 0.02[2] cgs
Temperature	5590 ± 90[2] K
Rotation	>100 years[6]
Age	5.69[note 3][7] Gyr
Other designations
GJ 1221, EGGR 372, G 240-72, LHS 455, LP 44-113, NLTT 45565, WD 1748+708, 2MASS J17480817+7052353[3]
Database references
SIMBAD	data

Distance

G 240-72 is the seventh closest white dwarf (after Sirius B, Procyon B, van Maanen's star, Gliese 440, 40 Eridani B and Stein 2051 B). Its trigonometric parallax, as measured by the Gaia space telescope, is 160.9952±0.0119 mas,^[1] corresponding to a distance of 6.2114 parsecs (20.259 light-years).

Properties

G 240-72 has a mass of 0.81 Solar masses^[2] and surface gravity 10^8.36 (2.29 · 10⁸) cm·s⁻²,^[2] or approximately 234 000 of Earth's, corresponding to a radius 6850 km, or 107% of Earth's.

This white dwarf has a relatively low temperature of 5590 K^[2] (slightly cooler than the Sun), and an old cooling age, i.e. the age as a degenerate star (not counting the duration of its previous existence as a main sequence and giant star) of 5.69 Gyr.^[7] It has a white appearance, due to its similar temperature to the Sun. It has a pure helium atmosphere and rotates very slowly, with period of possibly over 100 years.^[6]