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The RR Lyrae of w Centauri: a theoretical route (progress report)

The RR Lyrae of w Centauri: a theoretical route (progress report). Castellani V. 1 , Degl’Innocenti S. 1 , Marconi M. 2 1 Physics Department, University of Pisa, Italy 2 Capodimonte Astronomical Observatory, Naples, Italy.

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The RR Lyrae of w Centauri: a theoretical route (progress report)

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  1. The RR Lyrae of w Centauri: a theoretical route(progress report) Castellani V.1,Degl’Innocenti S.1, Marconi M.2 1 Physics Department, University of Pisa, Italy 2 Capodimonte Astronomical Observatory, Naples, Italy Omega Centauri, Cambridge 2001

  2. w Cen RR Lyrae Rich sample by Kaluzny et al. (1997) Metallicity by Rey et al. (2000) <V> ? An exciting possibility……However : [Fe/H]? Omega Centauri, Cambridge 2001

  3. wCen RR Lyrae Sub-sample of the Kaluzny et al. RR Lyrae for which the metallicity evaluation from Rey et al. is available Bearing inmind sucha “warning” let us try to move along a theoretical route…. Omega Centauri, Cambridge 2001

  4. Is theory consistent with observations? Z peaked at  0.0004 (Rey et al. 2000, Suntzeff & Kraft 1996) Omega Centauri, Cambridge 2001

  5. Visual magnitude distribution Kaluzny et al. sample The bulk of RR Lyrae has a mean visual magnitude in the range 14.4514.60 mag. By adopting: (mv-Mv )=14.050.11 (Thompson et al. 2001) <Mv> approximately in the range 0.40.55 mag Omega Centauri, Cambridge 2001

  6. Evolutionary theory Consistent with observations…nothing more until more precise [Fe/H] and <V> will be available Omega Centauri, Cambridge 2001

  7. Pulsational theory The strongest constraint: Light curve (P,31, A are only a partial parametrization of the light curve) Let us recall the scenario: UComae : a field RRc  observations: P=0.29 days, E(B-V)  0 Omega Centauri, Cambridge 2001

  8. by assuming the mass in the range predicted by evolutionary theory for the observed P the fitting exists  L, Te* (in agreement with independent evaluations available in the literature) Comparison between theory and observation for UComae light curve (Bono, Castellani, Marconi, 2000, ApJ 532, L129) *We recall the Bono et al. (1997) relations: LogPF =11.627 +0.823 LogL -0.582 LogM -3.506 LogTe LogPFO=10.789 +0.800 LogL -0.594 LogM -3.309 LogTe ________________________ (see Bono & Stellingwerf, 1994, for a description of the adopted non linear, convective, hydrodinamical code) Omega Centauri, Cambridge 2001

  9. To appreciate the sensitivity of the method: varying the temperature by 50 oK and <Mbol> by  0.03 mag. Omega Centauri, Cambridge 2001

  10. w Centauri: a different approach Given the period, for each Te, one finds a mass and a light curve morphology RR ab type  light curve 99B P=0.627 days, [Fe/H]= -1.740.05 (however the results are barely sensitive to the metallicity value within the metal poor range*)  Let us assume a distance modulus (DM=14.050.11) and thus <Mv> for RR Lyrae *see e.g. Bono, Incerpi & Marconi 1996, Bono et al. 1997 Omega Centauri, Cambridge 2001

  11. For the givenDM (DM=14.05  <Mv>=0.38)the temperature is fixed mainly by therequired amplitude, in fact: Te  A  : For RRab the amplitude increases by increasing the effective temperature (at fixed period) Light curves at fixed period and <Mv> but with different Te One obtains the pulsator mass Omega Centauri, Cambridge 2001

  12. The amplitude is almost constant What happens if DM is changed? ..but the light curve shape changes Light curves at fixed period and Te but with different <Mv> A different distance modulus has been applied to each light curve to obtain the observed <V>14.43 for the light curve 99 Omega Centauri, Cambridge 2001

  13. Summarising: By fitting Av One finds Te Best fit Best fit of the light curve DM mass DM=14.05 (In agreement with the DM estimate by Thompson et al. 2001) …. The fit is not perfect, but satisfactory.. ...at least to characterize a method In this case pulsational theory is consistent with observations and stellar evolution Note that the estimated stellar mass agrees with the one predicted by stellar evolution! Omega Centauri, Cambridge 2001

  14. If one changes the DM by about 0.1 mag. the light curve fit appears less satisfactory upper limit for a DM variation Omega Centauri, Cambridge 2001

  15. A variation of the distance modulus by  0.15 mag. can be definitely ruled out Omega Centauri, Cambridge 2001

  16. This is the “theoretical truth”… ….how true is this truth? Pulsational computations are quite sophisticated: one has to account for difficult mechanisms as eddy viscosity, overshooting and so on.... The true truth: we were already surprised of the rather beautiful agreement…. We would like to test deeper the theory:  Firmer Te Better [Fe/H]  Velocity curve A strong test! Details of LC depend on Z a further prediction Goal*: a well tested and well calibrated theory promises to provide reliable distance modulus from just one (or few) RR! …the work is in progress... ________ *These results confirm a similar analysis on a LMC bump Cepheid by Wood et al. (1997) Omega Centauri, Cambridge 2001

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