Groombridge 1830

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**Groombridge 1830**
Observation data Equinox J2000
Constellation	Ursa Major
Right ascension	11^h 52^m 58.8^s
Declination	+37° 43′ 07″
Apparent magnitude (V)	6.42
Characteristics
Spectral type	G8 VIp
U-B color index	0.17
B-V color index	0.75
Variable type	Suspected
Astrometry
Radial velocity (R_v)	-98.8 km/s
Proper motion (μ)	RA: 4,003.69 mas/yr Dec.: -5,813.00 mas/yr
Parallax (π)	109.78 ± 0.70 mas
Distance	29.7 ± 0.2 ly (9.11 ± 0.06 pc)
Absolute magnitude (M_V)	6.62
Details
Mass	0.6 M_☉
Radius	0.64 R_☉
Luminosity	0.19 L_☉
Temperature	5,030 K
Metallicity	3-10%
Rotation	?
Age	5.4 × 10⁹ years
Other designations
GJ 451, HR 4550, BD +38°2285, HD 103095, LHS 44, LTT 13276, GCTP 2745.00, SAO 62738, FK5 1307, Giclas 122-51, G 148-18, LFT 855, Gmb 1830, HIP 57939.

Groombridge 1830 is a star in the constellation Ursa Major.

It is a yellow-orange class G8 subdwarf catalogued by Stephen Groombridge in the 1830s. Its high proper motion was noted by Friedrich Wilhelm Argelander in 1842.

It is 29.7 light years from Earth's Solar System, which means its absolute magnitude is almost equal to its apparent magnitude. It is a halo star; such stars account for only 0.1 to 0.2 percent of the stars near the Sun.

Once suspected of being a binary star with a period of 175 days, current consensus is that it is single.

When discovered, it had the highest proper motion of any star known, replacing 61 Cygni in that department. Later it dropped to second place after the discovery of Kapteyn's Star, and still later to third place after the discovery of Barnard's Star. It is considerably farther away than either of those stars, however, which means its transverse velocity is greater.

Actually, it is the Sun which is following the motion of galaxy rotation by revolving around the center of the Milky Way; halo stars like Groombridge 1830 do not follow this galaxy rotation and thus are "standing still" and appear to be moving in "retrograde direction" at high speed.

1 References
2 See also
3 External links
- 3.1 Discovery of high proper motion

[edit] References

Garik Israelian et al, 1998, "Oxygen Abundances in Unevolved Metal-poor Stars from Near-Ultraviolet OH Lines", Astrophysical Journal, 507, November.