GJ 3991

Gliese 3991

Observation data Epoch J2000.0      Equinox 2015.5
Constellation	Hercules
GJ 3991 A
Right ascension	17^h 09^m 32.018^s[1]
Declination	+43° 40′ 48.52″
Apparent magnitude (V)	13.671
GJ 3991 B
Right ascension	17^h 09^m 32.018^s
Declination	+43° 40′ 48.52″
Apparent magnitude (V)	>15
Characteristics
GJ 3991 A
Spectral type	M3.5V
Apparent magnitude (B)	13.46
Apparent magnitude (R)	11.511
Apparent magnitude (J)	7.380
Apparent magnitude (H)	6.76
Apparent magnitude (K)	6.485
GJ 3991 B
Evolutionary stage	White dwarf
Spectral type	D?12
Astrometry
Radial velocity (Rv)	−9.7±0.2 km/s
Total velocity	17.971±0.199 km/s
Proper motion (μ)	RA: 332.59±1.01[1] mas/yr Dec.: −271.83±1.11 mas/yr
Parallax (π)	131.5996 ± 0.4285 mas[2]
Distance	24.78 ± 0.08 ly (7.60 ± 0.02 pc)
Absolute magnitude (MV)	14.316
Orbit[3]
Primary	GJ 3991 B
Companion	GJ 3991 A
Period (P)	14.7136±0.0005 days (0.0402836±0.0000014 yr)
Semi-major axis (a)	0.015+0.01 −0.05" (0.1102 AU)
Eccentricity (e)	0.068±0.004
Argument of periastron (ω) (primary)	175.0±3.0°
Semi-amplitude (K1) (primary)	50.6±0.2 km/s
Details
GJ 3991 A
Mass	0.20 M☉
Temperature	3250±50 K
Metallicity	1.584+0.235 −0.205 Fe/☉
Metallicity [Fe/H]	0.20±0.06 dex
GJ 3991 B
Mass	0.50 M☉
Temperature	~4900 K
Age	>6? Gyr
Other designations
G 203-47, Gliese 3991, HIP 83945, USNO 752
GJ 3991 A: G 203-47 A
GJ 3991 B: G 203-47 B, WD 1708+437
Database references
SIMBAD	data

GJ 3991 (also known as Gliese 3991 and G 203-47) is a binary star system located 24.2 light-years away in the constellation Hercules. It consists of a Red dwarf star with 20-30% the mass of the Sun, and a White dwarf star roughly 50% the mass of the sun. The two components orbit each other in a tight orbit only 0.11 astronomical units from each other, with an orbital period of only 14.71 days. Due to their small separation, the two objects have never been visually resolved and are merely predicted from the radial velocity changes of GJ 3991 A, making the system a spectroscopic binary.

White dwarf

GJ 3991 B was first identified in 1997 by astronomers I. N. Reid and J. E. Gizis through significant radial velocity variations visible through GJ 3991 A, although were unable to identify the nature of the secondary object.^[4] In 1998, another group of astronomers was able to determine the secondary as a cold white dwarf star, the compact remnant that remains after a low-mass star such as the Sun is no longer able to fuse elements for energy. GJ 3991 B is the 9th nearest white dwarf, after Sirius B, Procyon B, Van Maanen 2, LP 145-141, 40 Eridani B, Stein 2051 B, G 240-72, and Gliese 223.2. Among these, GJ 3991 B is not only the coldest, but the only one in a short-period orbit with another star. GJ 3991 B is probably over 6 billion years old, making it the oldest among these objects as well.^[5]

See also

• List of star systems within 20–25 light-years

References

1. Lindegren, L.; et al. (25 April 2018). "Gaia Data Release 2: The astrometric solution". Astronomy & Astrophysics. A2: 616. arXiv:1804.09366. Bibcode:2018A&A...616A...2L. doi:10.1051/0004-6361/201832727. S2CID 54497421.
2. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
3. Delfosse, Xavier; et al. (April 1999), "New neighbours. I. 13 new companions to nearby M dwarfs", Astronomy and Astrophysics, 344: 897–910, arXiv:astro-ph/9812008, Bibcode:1999A&A...344..897D.
4. Reid, I. Neill; Gizis, John E. (June 1997). "Low-Mass Binaries and the Stellar Luminosity Function". The Astronomical Journal. 113: 2246. Bibcode:1997AJ....113.2246R. doi:10.1086/118436. ISSN 0004-6256.
5. Bergeron, Pierre. "Synthetic Colors and Evolutionary Sequences of Hydrogen- and Helium-Atmosphere White Dwarfs". Retrieved 22 June 2018.