R Lyrae

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R Lyrae
Lyra constellation map.svg
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] [lower-alpha 1]   R
Luminosity 4,130 [6] [lower-alpha 2]   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, 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 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 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) RLyrLightCurve.png
Visual band light curves for R Lyrae, adapted from Percy et al. (2001)

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] [11]

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:
    .
  2. Calculated using the absolute bolometric magnitude of R lyrae, with respect to the Sun's absolute bolometric magnitude of 4.83:
    100.4(4.74+(4.3) = 4130.48.

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References

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