The MACHO Project Large Magellanic Cloud Variable Star Inventory. XIII. Fourier Parameters for the First Overtone RR Lyrae Variables and the LMC Distance
Shapes of RR Lyrae light curves can be described in terms of Fourier coefficients which past research has linked with physical characteristics such as luminosity, mass and temperature. Fourier coefficients 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. In general, the Fourier phase differences {phi}{sub 21}, {phi}{sub 31} and {phi}{sub 41} increase and the amplitude ratio R{sub 21} decreases with increasing period. The coefficients for both the V and R magnitudes follow these patterns, but the phase differences for the R curves are on average slightly greater, and their amplitudes are about 20% smaller, than the ones for the V curves. The {phi}{sub 31} and R{sub 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 L{sub {center_dot}} and log T{sub 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}{sub 31} - log P plot) are used to determine an LMC distance. After correcting for the effects of extinction and crowding, a mean apparent magnitude < V{sub 0} > = 18.99 {+-} 0.02 (statistical) {+-} 0.16 (systematic) has been estimated for these 80 stars. Combining this with a mean absolute magnitude M{sub V} = 0.56 {+-} 0.06 for M5-like stars derived from Baade-Wesselink analyses, main sequence fitting, Fourier parameters and the trigonometric parallax of RR Lyrae, they derive an LMC distance modulus {mu} = 18.43 {+-} 0.06 (statistical) {+-} (systematic) mag. The large systematic error arises from the difficulties of correcting for interstellar extinction and for crowding.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15011534
- Report Number(s):
- UCRL-JRNL-201664; TRN: US200507%%517
- Journal Information:
- The Astronomical Journal, Vol. 127
- Country of Publication:
- United States
- Language:
- English
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