Pi1 Ursae Majoris

For other stars with this name, see Pi Ursae Majoris.

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 46.8 light years from Earth,^[1] 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]

Pi¹ Ursae Majoris

Location of π¹ Ursae Majoris (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Ursa Major
Right ascension	08h 39m 11.70440s[1]
Declination	+65° 01′ 15.2667″[1]
Apparent magnitude (V)	5.63
Characteristics
Spectral type	G1.5Vb[2]
U−B color index	+0.07[3]
B−V color index	+0.62[3]
Variable type	BY Draconis
Astrometry
Radial velocity (Rv)	–13.88 ± 0.47[4] km/s
Proper motion (μ)	RA: -27.44 ± 0.31[1] mas/yr Dec.: +88.13 ± 0.26[1] mas/yr
Parallax (π)	69.66±0.37 mas[1]
Distance	46.8 ± 0.2 ly (14.36 ± 0.08 pc)
Absolute magnitude (MV)	4.86[5]
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[4] 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

A light curve for pi¹ Ursae Majoris, plotted from TESS data.^[13] The main plot shows the variation over several weeks, and the inset plot shows the same data folded, assuming a 4.9 day period,^[14] and averaged into 250 phase bins.

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]