R Boötis

Not to be confused with Rho Boötis.

R Boötis is a variable star in the northern constellation of Boötes. The star's brightness varies tremendously, ranging from apparent magnitude 6.0, when it might be faintly visible to the naked eye under very good observing conditions, to 13.3, when a fairly large telescope would be required to see it.^[3] The distance to this star is approximately 2,150 light years based on parallax measurements.^[2] It is drifting closer with a radial velocity of about −58 km/s.^[8]

R Boötis

The visual band light curve of R Boötis, from AAVSO data[1]
Observation data Epoch J2000      Equinox J2000
Constellation	Boötes
Right ascension	14h 37m 11.57616s[2]
Declination	26° 44′ 11.6562″[2]
Apparent magnitude (V)	6.0 - 13.3[3]
Characteristics
Evolutionary stage	AGB[4]
Spectral type	M4-8e[5]
B−V color index	1.50±0.51[6]
Variable type	Mira variable[3][7]
Astrometry
Radial velocity (Rv)	−58.0±4.7[8] km/s
Proper motion (μ)	RA: –25.537[2] mas/yr Dec.: 11.968[2] mas/yr
Parallax (π)	1.5204±0.0586 mas[2]
Distance	2,150 ± 80 ly (660 ± 30 pc)
Details
Mass	1.492[9] M☉
Radius	241 – 268[10] R☉
Luminosity	4,255+1,009 −821[10] L☉
Surface gravity (log g)	−0.33 or −0.25[10] cgs
Temperature	3,029 – 3,061[10] K
Metallicity [Fe/H]	+0.512[9] dex
Other designations
R Boo, BD+27°2400, GC 19706, HD 128609, HIP 71490, SAO 83440[11]
Database references
SIMBAD	data

The variability of this star was discovered by German astronomer F. W. Argelander in 1857.^[12] It is classified as a Mira-type pulsating variable that ranges in brightness from magnitude 6.0 down to 13.3 with a period of 223.11 days.^[3][7] The stellar classification of the star ranges from M4e to M8e,^[5] where the 'e' indicates emission features in the spectrum.

R Boötis is much larger and luminous than the Sun, at 4,000 solar luminosities and a size 250 times that of the Sun. It has cooled to an effective temperature of 3,000 Kelvins,^[10] giving it a reddish hue.^[13]