Introduction to Stellar Pulsations RR Lyrae Stars and the Blazhko Effect Part I of the Thesis Work: Temporal Behaviour of the RR Lyrae Data Part II of the Thesis Work: Trying to Unravel the Blazhko Effect Conclusions and Future Prospects Stars: General Properties Stellar Spectra... and what they learn us Variable Stars } Pulsating Stars Asteroseismology Apparent magnitude m ~luminosity Brightness Colour ~surface temperature Absolute magnitude M 1 Photometry and Spectroscopy The Spectroscopic Principle Absorption Lines Plotting a Spectrum Spectral Line Shapes "Line Profiles" velocity of the vehicle REDSHIFTED BLUESHIFTED radial velocity Naked eye: 3% variable stars We studied intrinsic variables, more precisely... 1 Pulsation Cycle 1 Pulsation Phase : 01 Accurately 1 "Pulsation Modes"... the Study of Stellar Pulsations n = radial order number of node surfaces between center and surface l = degree m = azimuthal number -l < m < l l = degree m = azimuthal number number of node lines on the stellar surface l = degree m = azimuthal number number of node lines on the stellar surface |m|= number of meridian lines l = degree m = azimuthal number number of node lines on the stellar surface |m|= number of meridian lines (l,m) = (3,2) tesseral (l,m) = (3,3) sectoral Blue } Moving towards Observer Red } Moving away from Observer (l,m) = (3,0) axisymmetri c [ m=0] l] [|m|= l] 1. Period or Frequency Analysis which pulsation frequencies are present?... the Study of Stellar Pulsations Periodogram or Frequency Spectrum highest peaks ~ most prominent frequencies in the signal 1. Period or Frequency Analysis which pulsation frequencies are present?... the Study of Stellar Pulsations 2. Mode Identification which pulsation modes (l,m) are related to those frequencies? Pulsation 1 Periodically Moving Spectral Lines "Line Profile Variations" 1 Information on Pulsation Modes (l,m)... the Study of Stellar Pulsations What's the use??? Stellar Pulsations 1 Inner Structure of the Star 1 Stellar Models 1 Stellar & Galactic Evolution 1 Understanding the Universe the Study of Stellar Pulsations General Properties The Blazhko Effect Explanations for the Blazhko Effect Objectives of our Research " Cluster Type Variables " short periods (< 1 day) variations of ~ 1 mag Also in the Galactic Field RR Lyrae Standard Candles Witnesses of the Universe at Young Age "Pure Radial Pulsators" : Blazhko Amplitude Modulation 20-30% RR ab 2 % RR c Resonance between Radial Modes? Resonance between the Radial Mode and a Nonradial Mode of low degree l [ l=2 ] 1958: Babcock 1994: Romanov et al. controversial... Magnetic Field of ~1 kGauss required... " Up to now: Photometric Data " Better diagnostic: High-Resolution Spectra Detect and Identify Nonradial Components in the Line Profile Variations of RR Lyrae Part I: Temporal Behaviour ~ Period Analysis Part II: Mode Identification 1 Crucial Test for the Models 1 l < 3 ? Brightest RR Lyrae and Blazhko star m v = P 0 = 13 h 36 mn ~ f 0 = c/d P B = 40.8 d ~ f B = c/d High-Resolution Spectrograph Attached to 1.93m telescope at the Observatoire de Haute-Provence (France) Collaboration with Dr. M. Chadid and Dr. D. Gillet (France) 669 spectra - 16 nights 1996 &1997 Time Resolution 5 % Coverage of the Pulsation Cycle (13h36mn) (km/s) Coverage of the Blazhko Cycle (40.8 days) (km/s) Data Reduction by Dr. M. Chadid First Line Profile Study of a Blazhko Star! Main Frequency... Nonlinearity of the Radial Mode up to 8 th order Multiplet Structure... Nonradial Modes! Nonlinearity & Multiplet RR Lyrae: multiperiodic... for the special case of RR Lyrae Radial Mode (0,0) : well known! Very prominent Nonlinear behaviour Nonradial Mode(s) (l,m) : to be identified Much less prominent Mode Identification from Nonadiabatic Observables A Nonlinear Model for the Radial Mode Idea: 1 Program for Theoretical Line Profiles Velocity Profile Intrinsic Profile Nonlinear Velocity Expression Temperature Variations due to Pulsation Influence of a Nonradial Mode upon the Line Profile Variations: Idea: 1 Program for Theoretical Line Profiles Nonlinear Velocity Expression Temperature Variations due to Pulsation Compare with Observational Profiles 1 Nonradial Modes Velocity Profile Intrinsic Profile Ingredients: Velocity Profile Intrinsic Profile Values derived from Literature 1 Intrinsic profiles from Static Atmosphere Models Ingredients: Velocity Profile Intrinsic Profile First Step: 3 rd Order Velocity Expression Nonlinear Pulsation Theory (Van Hoolst 1996) ARGUMENTS: Period Analysis: f 0 f B appears right after f 0, 2 f 0 and 3 f 0 Nonlinear Theory only exists up to 3 rd Order Observations Theory Second Step: 8 th Order Velocity Expression Pragmatic "ad hoc" Approach of the Radial Mode REMARKS: Based on the Observations Contains no Physics... Ingredients: Velocity Profile Intrinsic Profile Line Doubling ~ Shock Wave ~ Hydrodynamical Models Observations Theory Observations Theory (km/s) (km/s) 2 First Moment Second Moment Observations Theory (km/s) (km/s) 2 First Moment Second Moment ARGUMENT: Contains the Physics ! QUESTION: Can these Models yield good correspondance in the Profiles? Ingredients: Velocity Profile Intrinsic Profile (Fokin & Gillet 1997) Collaboration with Dr. A. Fokin (Russia) Observations Theory Results Eighth Order Model: good agreement, but not physical Hydrodynamical Models: further development is the best way to proceed! For Now: Turn to the Moment Variations Mode Identification from Nonadiabatic Observables A Nonlinear Model for the Radial Mode An Adapted Version of the Moment Method Idea: (Aerts 1993) Observed Moments & Theoretical Moments Which (l,|m|) gives the best agreement? Based on Linear Pulsation Theory Succesful in Identifying Linear Nonradial Modes in Main Sequence Stars ... to the special case of RR Lyrae Amplitudes of "Blazhko Terms" from First and Second Moment Coupling with Radial Mode Nonradial Modes have Small Amplitudes 1 Linear Treatment Applicable to each Nonradial Mode separately Ingredients: On Artificial data Radial Mode: Eighth Order Model Nonradial Mode ~ Conclusions: Accurate Determination of l and |m| Some (l,|m|) Configurations are hard to distinguish (1,1) (2,1) (2,2) Conclusion: l < 3 and 0 (l,|m|) =... (1,1) (2,1) (2,2) :i = 0 deg :i = 40 deg :i = 90 deg Inclination angle (km/s) 2 Time (days) Discriminant works well! Evidence for a Triplet Structure in our Frequency Spectra Evidence for Nonradial Modes (l,m) Adapted Version of the Moment Method: l < 3 and Evaluation through Line Profile Calculations: Dipole Modes (1,1) are most probable First Line Profile Study of a Blazhko Star Nonradial Modes which Effects vary through the Blazhko Cycle More Spectroscopic Observations better spread over the Blazhko Cycle Include all Nonradial Components in the Identification Exclude Quintuplet Structure? Further Development of the Hydrodynamical Models Refinement of the Identification Techniques ...