RR Lyrae

This article is about the star. For the variable star class, see RR Lyrae variable.
RR Lyrae

Illustration of the typical light curve for RR Lyrae.
Observation data
Epoch J2000      Equinox J2000
Constellation Lyra
Right ascension 19h 25m 27.91285s[1]
Declination +42° 47′ 03.6942″[1]
Apparent magnitude (V) 7.195[2] (7.06–8.12)[3]
Characteristics
Spectral type A7III - F8III
U−B color index +0.172[2]
B−V color index +0.181[2]
Variable type RR Lyr[4]
Astrometry
Radial velocity (Rv)-72.4[5] km/s
Proper motion (μ) RA: -109.68[1] mas/yr
Dec.: -195.75[1] mas/yr
Parallax (π)3.64 ± 0.23 mas[6]
Distance900 ± 60 ly
(270 ± 20 pc)
Absolute magnitude (MV)0.600 ± 0.126[7]
Details
Mass0.65[8] M☉
Radius5.1 to 5.6[8] R☉
Luminosity49 ± 5[8] L☉
Surface gravity (log g)2.4 ± 0.2[8] cgs
Temperature6,125 ± 50[8] K
Metallicity [Fe/H]–1.16[7] dex
Other designations
RR Lyr, 2MASS J19252793+4247040, NLTT 47799, HD 182989, BD+42°3338, HIP 95497, SAO 48421, LTT 15677[9]
Database references
SIMBADdata

RR Lyrae is a variable star in the Lyra constellation, figuring in its west near to Cygnus.[10] As the brightest star in its class,[11] it became the eponym for the RR Lyrae variable class of stars[3] and it has been extensively studied by astronomers.[7] RR Lyrae variables serve as important standard candles that are used to measure astronomical distances. The period of pulsation of an RR Lyrae variable depends on its mass, luminosity and temperature, while the difference between the measured luminosity and the actual luminosity allows its distance to be determined via the inverse-square law. Hence, understanding the period-luminosity relation for a local set of such stars allows the distance of more distant stars of this type to be determined.[12]

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