Pi1 Ursae Majoris
Star in the constellation Ursa Major
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Pi1 Ursae Majoris (Pi1 UMa, π1 Ursae Majoris, π1 UMa) is a yellow G-type main sequence dwarf with a mean apparent magnitude of +5.63. It is approximately 47.1 light years from Earth,[2] and is a relatively young star with an age of about 200 million years.[11] It is classified as a BY Draconis type variable star and its brightness varies by 0.08 magnitudes. In 1986, it became the first solar-type star to have the emission from an X-ray flare observed.[15] Based upon its space velocity components, this star is a member of the Ursa Major moving group of stars that share a common motion through space.[7][10]
 Location of π¹ Ursae Majoris (circled) | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Ursa Major[1] |
| Right ascension | 08h 39m 11.70461s[2] |
| Declination | +65° 01′ 15.2631″[2] |
| Apparent magnitude (V) | 5.63[1] |
| Characteristics | |
| Evolutionary stage | main sequence[2] |
| Spectral type | G1.5Vb[3] |
| U−B color index | +0.07[4] |
| B−V color index | +0.62[4] |
| Variable type | BY Draconis |
| Astrometry | |
| Radial velocity (Rv) | −13.88±0.47[5] km/s |
| Proper motion (μ) | RA: −27.274±0.024[2] mas/yr Dec.: +88.881±0.049[2] mas/yr |
| Parallax (π) | 69.2576±0.0485 mas[2] |
| Distance | 47.09 ± 0.03 ly (14.44 ± 0.01 pc) |
| Absolute magnitude (MV) | 4.84 |
| Details | |
| Mass | 0.90[6] M☉ |
| Luminosity | 0.97[7] L☉ |
| Surface gravity (log g) | 4.48[8] cgs |
| Temperature | 5,884±6.8[9] K |
| Metallicity [Fe/H] | –0.04[8] dex |
| Rotation | 5 days[10] |
| Rotational velocity (v sin i) | 14.27[5] km/s |
| Age | 200[11] Myr |
| Other designations | |
| π1 UMa, 3 UMa, BD+65 643, GC 11817, GJ 311, HD 72905, HIP 42438, HR 3391, SAO 14609, PPM 16705[12] | |
| Database references | |
| SIMBAD | data |
An excess of infrared radiation has been detected from this system, which suggests the presence of a debris disk. The best fit to the data indicates that there is a ring of fine debris out to a radius of about 0.4 AU, consisting of 0.25 μm grains of amorphous silicates or crystalline forsterite. There may also be a wider ring of larger (10 μm) grains out to a distance of 16 AU.[16]
Naming and etymology
With π2, σ1, σ2, ρ, A and d, it composed the Arabic asterism Al Ṭhibā᾽, the Gazelle.[17] According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al Ṭhibā were the title for seven stars : A as Althiba I, this star (π1) as Althiba II, π2 as Althiba III, ρ as Althiba IV, σ1 as Althiba V, σ2 as Althiba VI, and d as Althiba VII.[18]