Phi1 Lupi

Phi¹ Lupi is a solitary^[13] star in the southern constellation of Lupus. It is visible to the naked eye with an apparent visual magnitude of 3.58.^[3] Based upon an annual parallax shift of 11.86 mas as seen from Earth, it is located around 275 light years from the Sun. The star is drifting closer with a radial velocity of −29 km/s.^[6] It has an absolute magnitude of −1.55.^[7]

For other stars with this Bayer designation, see φ Lupi.

φ¹ Lupi

Location of φ1 Lupi (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Lupus[1]
Right ascension	15h 21m 48.36967s[2]
Declination	−36° 15′ 40.9525″[2]
Apparent magnitude (V)	3.58[3]
Characteristics
Spectral type	K5 III[4]
U−B color index	+1.85[3]
B−V color index	+1.534±0.005[5]
Astrometry
Radial velocity (Rv)	−29.4±0.7[6] km/s
Proper motion (μ)	RA: −92.33[2] mas/yr Dec.: −85.67[2] mas/yr
Parallax (π)	11.86±0.16 mas[2]
Distance	275 ± 4 ly (84 ± 1 pc)
Absolute magnitude (MV)	−1.55[7]
Details
Mass	1.78[8] M☉
Radius	40[9] R☉
Luminosity	1,413[8] L☉
Surface gravity (log g)	1.93[10] cgs
Temperature	3,800[8] K
Metallicity [Fe/H]	−0.40[8] dex
Other designations
φ1 Lup, CD−35°10236, FK5 566, HD 136422, HIP 75177, HR 5705, SAO 206552[11]
Database references
SIMBAD	data

A light curve for Phi¹ Lupi, plotted from Hipparcos data^[12]

This is an evolved K-type giant star with a stellar classification of K5 III,^[4] which means it has used up its core hydrogen and has expanded. At present it has 40 times the radius of the Sun.^[9] It is a variable star of unknown type, with an amplitude of 0.008 in visual magnitude and a period of 4.82 days.^[14] The star is radiating 1,413 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 3,800 K.^[8]