R Lyrae

Not to be confused with RR Lyrae.

R Lyrae, also known as its Flamsteed designation 13 Lyrae, is a 4th magnitude semiregular variable star in the constellation Lyra, approximately 350 light years away from Earth. It is visible to the naked eye. It is a red giant star of the spectral type M5III, currently at the last stages of evolution. It is much larger and brighter, yet cooler, than the Sun. In the near-infrared J band, it is brighter than the nearby Vega.

R Lyrae

R Lyrae (labelled as 13)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Lyra
Right ascension	18h 55m 20.101223s[1]
Declination	+43° 56′ 45.9215″[1]
Apparent magnitude (V)	4.00[2] (3.9 - 5.0[3])
Characteristics
Spectral type	M5 III[4]
Apparent magnitude (J)	−0.90[2]
U−B color index	+1.41[2]
B−V color index	+1.59[2]
Variable type	SRb[3]
Astrometry
Radial velocity (Rv)	−27.15[5] km/s
Proper motion (μ)	RA: 21.05[1] mas/yr Dec.: 82.06[1] mas/yr
Parallax (π)	10.94±0.12 mas[1]
Distance	298 ± 3 ly (91 ± 1 pc)
Absolute magnitude (MV)	−1.1[4]
Details
Mass	1.8±0.2[6] M☉
Radius	195[6][a] R☉
Luminosity	4,130[6][b] L☉
Surface gravity (log g)	0.47[7] cgs
Temperature	3,313[6] K
Other designations
R Lyrae, 13 Lyrae, HR 7157, BD+43°3117, HD 175865, SAO 47919, HIP 92862, GC 25996, GSC 03131-02155
Database references
SIMBAD	data

R Lyrae is unusual in that it is a red star with a high proper motion, greater than 50 milliarcseconds a year.^[8] It is one of the brightest stars at the K band, having an apparent magnitude of −2.08, only 14 stars are brighter.^[9]

Visual band light curves for R Lyrae, adapted from Percy et al. (2001)^[10]

In 1856, Joseph Baxendell announced that the star, then called 13 Lyrae, is a variable star.^[11] In 1907 it appeared with its variable star designation, R Lyrae, in Annie Jump Cannon's Second Catalog of Variable Stars.^[12] The variability is not consistent and regular, but periods of 46, 64, 378, and 1,000 days have been reported, with the 46-day period being the strongest.^[4][13]

It is calculated that R Lyrae was a 2.0 M_☉ star on the main sequence, similar to Sirius A today. It is now an oxygen-rich asymptotic giant branch star, with both hydrogen and helium shells fusing. Due to stellar mass loss, R Lyrae now has a mass of 1.8 M_☉.^[6]

Notes

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

   ${\displaystyle {\sqrt {{\biggl (}{\frac {5,772}{3,313}}{\biggr )}^{4}\cdot 4,130}}=195\ R_{\odot }}$.

2. Calculated using the absolute bolometric magnitude of R lyrae, with respect to the Sun's absolute bolometric magnitude of 4.83:
   10^{0.4(4.74+(−4.3)} = 4130.48.