R Horologii

R Horologii is a red giant star approximately 760 light-years away in the southern constellation of Horologium.^[13] It is a Mira variable with a period of 404.83 days,^[14] ranging from apparent magnitude 4.7 to 14.3—one of the largest ranges in brightness known of stars in the night sky visible to the unaided eye.^[2] The star is losing mass at the rate of 5.9×10⁻⁷ M_☉·y⁻¹.^[10]

R Horologii

Location of R Horologii (R) in Horologium
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Horologium
Right ascension	02h 53m 52.77010s[1]
Declination	−49° 53′ 22.7305″[1]
Apparent magnitude (V)	4.7 – 14.3[2]
Characteristics
Spectral type	M5-7e[3]
B−V color index	1.044±0.011[4]
Variable type	Mira[5]
Astrometry
Radial velocity (Rv)	+60.0±4.4[6] km/s
Proper motion (μ)	RA: +128.567 mas/yr[1] Dec.: +35.766 mas/yr[1]
Parallax (π)	4.3236±0.1524 mas[1]
Distance	756.0+31.6 −30.3 ly (231.8+9.7 −9.3 pc)[7]
Details
Mass	0.89[8] M☉
Radius	630[9][a] R☉
Luminosity	8,500[9] L☉
Surface gravity (log g)	−0.44[8] cgs
Temperature	2,200[10][9] K
Metallicity [Fe/H]	+0.545[8] dex
Other designations
R Hor, AAVSO 0250-50, CD−50° 860, HD 18242, HIP 13502, HR 868[11]
Database references
SIMBAD	data

The light curve of R Horologii from AAVSO V band data^[12]

Notes

1. Applying the Stefan–Boltzmann law with a nominal solar effective temperature of 5,772 K:

   ${\displaystyle {\sqrt {{\biggl (}{\frac {5,772}{2,200}}{\biggr )}^{4}\cdot 8,500}}=630\ R_{\odot }}$.