Pi1 Orionis

For other stars with this Bayer designation, see Pi Orionis.

Pi¹ Orionis (π¹ Ori, π¹ Orionis) is a star in the equatorial constellation of Orion. It is faintly visible to the naked eye with an apparent visual magnitude of 4.74.^[2] Based upon an annual parallax shift of 28.04 mas,^[1] it is located about 116 light-years from the Sun.

π¹ Orionis

Location of π1 Orionis (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Orion
Right ascension	04h 54m 53.72877s[1]
Declination	+10° 09′ 02.9952″[1]
Apparent magnitude (V)	4.74[2]
Characteristics
Spectral type	A3 Va[3]
U−B color index	+0.09[2]
B−V color index	+0.08[2]
Astrometry
Proper motion (μ)	RA: +41.49[1] mas/yr Dec.: −128.73[1] mas/yr
Parallax (π)	28.04±0.25 mas[1]
Distance	116 ± 1 ly (35.7 ± 0.3 pc)
Absolute magnitude (MV)	1.71±0.09[4]
Details[4]
Mass	1.90+0.08 −0.09 M☉
Radius	1.73±0.13 R☉
Luminosity	16.91+1.42 −1.29 L☉
Surface gravity (log g)	4.22+0.04 −0.05 cgs
Temperature	8,900±131 K
Metallicity [Fe/H]	−0.12+0.14 −0.16 dex
Rotational velocity (v sin i)	120[5] km/s
Age	100[6] Myr
Other designations
π1 Ori, 7 Orionis, BD+09°683, HD 31295, HIP 22845, HR 1570, SAO 94201[7]
Database references
SIMBAD	data

This is an A-type main-sequence star with a stellar classification of A3 Va.^[3] It is a Lambda Boötis star,^[8] which means the spectrum shows lower-than-expected abundances for heavier elements.^[9] Pi¹ Orionis is a relatively young star, just 100 million years old,^[6] and is spinning fairly rapidly with a projected rotational velocity of 120 km/s.^[5] It has nearly double the mass of the Sun and 173% of the Sun's radius. The star radiates 16.9 times the solar luminosity from its outer atmosphere at an effective temperature of 8,900 K.^[4]

An infrared excess indicates there is a debris disk with a temperature of 80 K orbiting 49 AU from the star. The dust has a combined mass 2.2% that of the Earth.^[6]