Bisector analysis of RR Lyrae

atmosphere dynamics at different pulsation and Blazhko phases

Elisabeth Guggenberger – IAU Symposium 301, August 2013

Work in progress…

Basics

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 (Martínez Fiorenzano et al 2005).

I

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 1992

• Finally compare to pulsation models

• See how motion at the same pulsation phase changes when the Blazhko phase is different

Fokin & Gillet 1997

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. Tull Coudé 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

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

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 Vadim Tsymbal), Abundances: WIDTHV

The process on each spectrumBased 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)

Use SynthV (Tsymbal, 1996) to compute synthetic alspectrum

Select set of unblended lines suitable for analysis. Strong as well as weak lines.

Calculate bisector for each line in the list and get velocity as function of intensity

Obtain “tau bisector”, i.e. velocity as a function of depth in the star

Map points on the line wings to profile in tau obtained from the synthesis.

Calculate average bisector from all selected lines

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

Bisector motion during the pulsation

4491.577 Fe2

Bisector motion during the pulsation

5197.577 Fe2

Bisector motion during the pulsation

4383.545 Fe2

Example Bisectors (for the “quiet” phase)

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

The next steps

• Compute pulsational acceleration• Compare to models of RR Lyrae atmospheres

Work in progress…