Pulsating Stars - RR Lyrae

RR Lyrae in M3 cluster
RR Lyrae in M3 cluster

Orientation - Cepheids and RR Lyrae - 

Classical cepheids

  • Period   1-50 days
  • Population I
  • Spectral Type  F5 - G2

RR - Lyrae

  • Period   0,2 - <1 day
  • Population II
  • Spectral Type  A2 - F6

History

  • First discovered 1595
    o Ceti given the name Mira, 11 month period
  • Second discovered 1784
    δ Cephei, period  5d 8h 58min → classical Cepheid
  • Early 20th Century
    Cepheids (Long Period), Henrietta Leavit discovered 2400 classical,
    RR-Lyrae (Short Period)

Properties of RR Lyrae

population II age            ~109 years
mass            ~0,5 - 0,7 sun radius        ~4 - 6x sun
temperature     6000 - 7500K variation    ~10-20% of radius
abs. brghtness  ~0,5 - 1 Mag luminosity  ~45x sun
spectral class     A - F metallicity  -2,5 > [Fe/H] < 0

RR-Lyrae Example SY Ari

Occurence

  • Globular clusters (see age)
  • Milky Way: halo - bulge (see age) 
  • Extra galactic systems

 

  • RRab type stars are easier to find than RRc stars
  • RR-Lyrae stars are very common in globular clusters