G 240-72

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Coordinates: Sky map 17h 48m 08.17s, +70° 52′ 35.3″

G 240-72
Observation data
Epoch J2000[1]      Equinox J2000[1]
Constellation Draco
Right ascension 17h 48m 08.17s[1]
Declination +70° 52′ 35.3″[1]
Apparent magnitude (V) 14.15[2]
Characteristics
Spectral type DQP9.0[2]
Apparent magnitude (B) 14.55[1]
Apparent magnitude (V) 14.15[1]
Apparent magnitude (R) 13.5[1]
Apparent magnitude (I) 13.1[1]
Apparent magnitude (J) 12.709 ± 0.021[1]
Apparent magnitude (H) 12.528 ± 0.023[1]
Apparent magnitude (K) 12.507 ± 0.023[1]
Astrometry
Proper motion (μ) RA: -1261[3] mas/yr
Dec.: 1112[3] mas/yr
Parallax (π) 164.7 ± 2.4[4] mas
Distance 19.8 ± 0.3 ly
(6.07 ± 0.09 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
Age 5.69[note 3][3] Gyr
Other designations
WD 1748+708,[2][3] LHS 455,[2] LP 44-113,[1] NLTT 45565,[1] GJ 1221,[4] EGGR 372,[1] 2MASS J17480817+7052353[1]
Database references
SIMBAD data

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 in constellation Draco. It 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 is 0.1647 ± 0.0024 arcsec,[4] corresponding to a distance 6.07 ± 0.09 pc, or 19.80 ± 0.30 ly.

G 240-72 has mass 0.81 Solar masses[2] and surface gravity 108.36 (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 relatively low temperature 5590 K[2] (slightly cooler than Sun), and old cooling age, i. e. age as degenerate star (not counting duration of previous existence as main sequence star and as giant star) 5.69 Gyr.[3] Despite it is classified as "white dwarf", it should appear yellow, not white, due low temperature.

External links[edit]

Notes[edit]

  1. ^ From apparent magnitude and parallax.
  2. ^ From surface gravity and mass.
  3. ^ Cooling age, i. e. age as degenerate star (not counting duration of previous existence as main sequence star and as giant star)

References[edit]

  1. ^ a b c d e f g h i j k l m n o "GJ 1221 -- White Dwarf". Centre de Données astronomiques de Strasbourg. Retrieved 2011-10-23. 
  2. ^ a b c d e f g h i j k l m Holberg, J. B.; Sion; Oswalt; McCook; Foran; Subasavage (2008). "A NEW LOOK AT THE LOCAL WHITE DWARF POPULATION". The Astronomical Journal 135: 1225–1238. Bibcode:2008AJ....135.1225H. doi:10.1088/0004-6256/135/4/1225. 
  3. ^ a b c d e Sion, Edward M.; Holberg; Oswalt; McCook; Wasatonic (2009). "THE WHITE DWARFS WITHIN 20 PARSECS OF THE SUN: KINEMATICS AND STATISTICS". The Astronomical Journal 138: 1681–1689. arXiv:0910.1288. Bibcode:2009AJ....138.1681S. doi:10.1088/0004-6256/138/6/1681. 
  4. ^ a b c d Yale Trigonometric Parallaxes, Fourth Edition (van Altena+ 1995)
  5. ^ Giammichele, N.; Bergeron, P.; Dufour, P. (April 2012), "Know Your Neighborhood: A Detailed Model Atmosphere Analysis of Nearby White Dwarfs", The Astrophysical Journal Supplement 199 (2): 29, arXiv:1202.5581, Bibcode:2012ApJS..199...29G, doi:10.1088/0067-0049/199/2/29.