The MACHO Project Large Magellanic Cloud Variable-Star Inventory. XIII. Fourier Parameters for the First-Overtone RR Lyrae Variables and the LMC Distance Academic Article uri icon

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abstract

  • Fourier coefficents have been derived for the $V$ and $R$ light curves of 785 overtone RR Lyrae variables in 16 MACHO fields near the bar of the LMC. The $\phi_{31}$ and $R_{21}$ coefficients have been compared with those of the first overtone RR Lyrae variables in the Galactic globular clusters NGC 6441, M107, M5, M3, M2, $\omega$ Centauri and M68. The results indicate that many of the LMC variables have properties similar to the ones in M2, M3, M5 and the Oosterhoff type I variables in $\omega$ Cen, but they are different from the Oosterhoff type II variables in $\omega$ Cen. Equations derived from hydrodynamic pulsation models have been used to calculate the luminosity and temperature for the 330 bona fide first-overtone variables. The results indicate that they have $\log L$ in the range 1.6 to $1.8\lsun$ and $\log T_{eff}$ between 3.85 and 3.87. Based on these temperatures, a mean color excess $E(V-R) =0.08$ mag, equivalent to $E(B-V)=0.14$ mag, has been estimated for these 330 stars. The 80 M5-like variables (selected according to their location in the $\phi_{31}-\log P$ plot) are used to determine a LMC distance. After correcting for the effects of extinction and crowding, a mean apparent magnitude $=18.99 \pm 0.02$ (statistical) $\pm 0.16$ (systematic) has been estimated for these 80 stars. Combining this with a mean absolute magnitude $M_V=0.56\pm 0.06$ for M5-like stars derived from Baade-Wesselink analyses, main sequence fitting, Fourier parameters and the trigonometric parallax of RR Lyrae, we derive an LMC distance modulus $\mu=18.43\pm 0.06$ (statistical) $\pm 0.16$ (systematic) mag. The large systematic error arises from the difficulties of correcting for interstellar extinction and for crowding.

authors

  • Alcock, C
  • Alves, DR
  • Axelrod, TS
  • Becker, AC
  • Bennett, DP
  • Clement, CM
  • Cook, KH
  • Drake, AJ
  • Freeman, KC
  • Geha, M
  • Griest, K
  • Lehner, MJ
  • Marshall, SL
  • Minniti, D
  • Muzzin, A
  • Nelson, CA
  • Peterson, BA
  • Popowski, P
  • Quinn, PJ
  • Rodgers, AW
  • Rowe, JF
  • Sutherland, W
  • Vandehei, T
  • Welch, Douglas L

publication date

  • January 2004