Iota Ursae Majoris

From Wikipedia, the free encyclopedia

**Iota Ursae Majoris A/B/C**
Observation data Epoch J2000
Constellation	Ursa Major
Right ascension	08^h 59^m 12.4^s
Declination	+48° 02′ 30″
Apparent magnitude (V)	3.12/10.1/10.3
Spectral Characteristics
Spectral type	A7 IV/dM1 J/?
U-B color index	0.07
B-V color index	0.19
Variable type	Suspected
Astrometry
Radial velocity (R_v)	7.6 km/s
Proper motion (μ)	RA: -441.12 mas/yr Dec.: -215.21 mas/yr
Parallax (π)	68.32 ± 0.79 mas
Distance	47.7 ± 0.6 ly (14.6 ± 0.2 pc)
Absolute magnitude (M_V)	2.29
Physical Characteristics
Mass	1.7 M_☉
Radius	1.5 R_☉
Luminosity	9 L_☉
Temperature	8165 K
Metallicity	?
Rotation	151 km/s.
Age	? years
Other designations
Talitha Borealis, Alphikra Borealis, 9 Ursae Majoris, Gl 331, HR 3569, BD +48°1707, HD 76644, LHS 2084/2083, LTT 12347, GCTP 2143.00, SAO 42630, FK5 335, GC 12407, ADS 7114, CCDM 08592+4803, HIP 44127.

Iota Ursae Majoris (ι UMa / ι Ursae Majoris) is a star system in the constellation Ursa Major. It is approximately 47.7 light years from Earth. It has the traditional names Talitha Borealis and Alphikra Borealis, and was also named Dnoces ("Second," backwards) after Edward H. White II, an Apollo 1 astronaut. The name was invented by his fellow astronaut Gus Grissom as a practical joke.

The Iota Ursae Majoris system is composed of two binary stars. The brightest component, Iota Ursae Majoris A, is a white A-type subgiant with an apparent magnitude of +3.12. It is a spectroscopic binary whose components have an orbital period of 4028 days.

The companion binary is composed of the 9th magnitude Iota Ursae Majoris B and the 10th magnitude Iota Ursae Majoris C. These two stars orbit around each other with a period of 39.7 years, and are separated by roughly 0.7 arcseconds, or at least 10 Astronomical Units (AU). The two binary systems orbit around each other once every 818 years. The separation between the two binaries is rapidly decreasing as they follow their orbits. In 1841 when the B component was first discovered, they had a separation of 10.7 arcseconds, or at least 156 AU. By 1971 their separation had decreased to 4.5 arcseconds, or at least 66 AU.