RR Lyrae (rrlyr)

RR Lyrae are pulsating horizontal branch dA/dF stars with a mass 0.5 of Solar masses. They are part of the main ‘instability strip’ in the HR-diagram, where stars pulsate due to the double ionisation of He. The two main subtypes are ab and c,

Classification and numbers

  • Supertypes

    • variable

    • periodic

    • pulsator

  • Subtypes

    • RR Lyrae ab

    • RR Lyrae c

  • Occurrence rate: very common, about 105 expected in ZTF data

ZTF light curves

ZTF rrlyr ab ZTF rrlyr c

Description

RR Lyrae (ab) are easy to recognise by their distinctive light curve shape and high amplitude variability. RR Lyrae (c) are a bit more of a challenge since their light curve shape is more sinusoidal. For low-SNR cases they can sometimes be confused with contact binaries (EW), which occur at similar periods and have sinusoidal-like light curves.

Light curve characteristics

  • periodic variable

  • period range: 0.2-1 days

  • amplitude: up to 1 mag (subtype ab), or 0.5 mag (subtype c)

  • light curve shape:

    • sawtooth; steep rise and slow decay (subtype ab)

    • periodic sinusoidal (subtype c)

  • can show modulation of the light curve shape on timescales of ~100 days (Blazhko effect)

Other characteristics and selection methods

  • intrinsic RR Lyrae colors: blue, that of A/F type main sequence stars (g-r = -0.1 – 0.5). Reddening can be significant since these stars can be detected at large distances.

  • absolute magnitude: -1<G<1

HR diagram of RRlyrae

RA/Dec diagram of RRlyrae

References and further reading:

  • Sterken & Jasschek: Light curves of variable stars