Bisector analysis of RR Lyrae

1. Bisector analysis of RR Lyrae atmosphere dynamics at different pulsation and Blazhko phases Work in progress… Elisabeth Guggenberger – IAU Symposium 301, August 2013

2. Basics I We are not only seeing a velocity versus intensity. We are seeing into the atmosphere. What we need to do is match the bisector points with the corresponding depth of formation. This can be used e.g. as a tool to study granulation (Gray 2002, 2005) Usually a spectral line bisector is plotted as velocity versus normalized intensity. Used e.g. for planet hunting to exclude false positives that are caused by stellar pulsation (MartínezFiorenzano et al 2005).

3. Why are we doing this? • See the atmosphere in motion • RR Lyrae stars have very violent atmospheres with strong velocity gradients, shock waves, and phase lags between layers (Van Hoof effect) • Watch different layers by studying different parts of the line profile Fokin & Gillet 1997 • Finally compare to pulsation models • See how motion at the same pulsation phase changes when the Blazhko phase is different Fokin 1992

4. The spectra and the analysis of the “quiet” phase • Kolenberg et al (2010) • 55 Spectra (45 around Blazhko phase of 0.3 and 10 at Blazhko phase 0.8) • Obtained with Robert G. TullCoudé Spectrograph on the 2.7-m telescope of McDonald Observatory • R=60000 • 120 < S/N < 360 • Integration time 16 min • Wavelength range 3633−10849 Å (with several gaps) • Simultaneous photometry to accurately determine the phase • For the most quiescent phase, an abundance analysis was performed • A depth-dependence of v_mic was found Kolenberg et al. 2010

5. RR Lyrae • Temperature change of 1000K (between 6000K and 7000K) • Brightness change of up to 1 mag • Radial velocity amplitude of about 60 km/s • Shock waves, line doubling • V Magnitude 7-8

6. Before the bisector analysis: • Consistent analysis of ALL phases • Teff and the depth-dependent vmic function determined in an iterative process for each spectrum/pulsation phase (Fossati et al 2013, in prep) • Models: LLModels (Shulyak et al. 2004), Syntheses: SYNTHV (by VadimTsymbal), Abundances: WIDTHV

7. The process on each spectrum Based on the T_eff found in the iterative analysis, and based on the abundances from the quiet phase: get line list from VALD database (Piskunov et al, 1995) Select set of unblended lines suitable for analysis. Strong as well as weak lines. Use SynthV (Tsymbal, 1996) to compute synthetic alspectrum Calculate bisector for each line in the list and get velocity as function of intensity Map points on the line wings to profile in tau obtained from the synthesis. Calculate average bisector from all selected lines Obtain “tau bisector”, i.e. velocity as a function of depth in the star

8. Used lines • 114 lines in total, of those: • 47 Fe1 lines in the range 4060-5510A • 17 Fe2 lines in the range 4170-5430A • 24 Ti2 lines in the range 4310-5420A • 9 Cr2 lines in the range 4250-5240A • 13 Ca2 lines in the range 4310-6500A • 4 Mg1 lines in the range 4160-5190A

9. Bisector motion during the pulsation 4491.577 Fe2

10. Bisector motion during the pulsation 5197.577 Fe2

11. Bisector motion during the pulsation 4383.545 Fe2

12. Example Bisectors (for the “quiet” phase)

13. Another result of the analysis: velocity curves for each selected line

14. The next steps • Compute pulsational acceleration • Compare to models of RR Lyrae atmospheres Work in progress …