A spectroscopic hunt for binary RR Lyrae pulsators

Transcription

1 A spectroscopic hunt for binary RR Lyrae pulsators Elisabeth Guggenberger Max Planck Institute for Solar System Research, Göttingen In collaboration with Thomas G. Barnes and Katrien Kolenberg

2 Some Background on RR Lyraes Magnitude D mag Pulsating stars (κ-mechanism in He II, predominantly radial mode) Large amplitudes: mag Periods: approx. 0.5 d Evolved stars (He core burning) 6000 K < T < 7500 K M Some are modulated Time (d) Time (d)

3 Many RR Lyraes known, for example from the OGLE experiment: in the Galactic Bulge (Soszynski et al. 2014) 7612 in the LMC 2475 in the SMC (Soszynski 2010) Credit: J. Hartman (Harcard CfA) & K. Stanek (Ohio State Univ.)

4 Any Binaries? Very few known! Would be good to get mass (independently from pulsation/evolution models) OGLE-BLG-RRLYR-02792: + TU Uma and some of other candidates that still await confirmation Question: Are they really rare or just hard to find?

5 How to find them? O-C technique: Use the pulsation as a clock Light time effect Assume constant period Magnitude Observed - expected Sharp maximum Time (d) Wrong period. Too short. time

6 How to find them? O-C technique: Use the pulsation as a clock Light time effect Assume constant period Magnitude Observed - expected Sharp maximum Time (d) Wrong period. Too long. time

7 How to find them? O-C technique: Use the pulsation as a clock Light time effect Assume constant period Magnitude Observed - expected Sharp maximum Time (d) Nothing going on. Correct period. time

8 How to find them? O-C technique: Use the pulsation as a clock Light time effect Assume constant period Magnitude Observed - expected Sharp maximum Time (d) Changing period. Evolution? time

9 How to find them? O-C technique: Use the pulsation as a clock Light time effect Assume constant period Magnitude Observed - expected Sharp maximum Time (d) Changing period. Evolution? time

10 How to find them? O-C technique: Use the pulsation as a clock Light time effect Assume constant period Magnitude Observed - expected Sharp maximum Time (d) Binary or time

11 brightness Modulation? We do not fully understand the Blazhko effect What shapes can the curve have? Cannot differentiate it from a light time effect without additional information..

12 other intrinsic variations sudden jumps, irregular changes, (e.g. LeBorgne et al. 2007) Studies systematically searching for O-C variations: Li & Qian (2014) Guggenberger & Steixner (2014) Hajdu et al. (2015): 1952 analyzed > initially 29 candidates -> reduced to 12 Liska et al (2016) Radial velocities are more reliable indicators

13 Target selection TU Uma:

14 Target selection Other stars: Follow up on candidates that have either: discordant velocities in the past Suspicious O-C variations Cover RV curve well to prevent phasing errors Create individual templates if possible Lay a solid foundation for future studies (we expect long orbits!)

15 Target selection III Too south Solano et al Fernley and Barnes 1997

16 Challenge: High RV amplitude of pulsation!

17 Challenges Incomplete phase coverage is pernicious Often templates are used (e.g. Liu 1991, Sesar et al. 2012), but: Amplitude needs to be known (from spectra or photometry) Phases need to be correct Template does not fit every star equally well

18

19 McDonald Observatory 2.1m Otto Struve telescope 22 nights awarded (15 useful with good weather) Sandiford Echelle Spectrometer R=60000, λ= Å Spring ? (new proposal sent in) Image credit: Tim Jones/McDonald observatory

20 Techniques Integration times < 5% of P Several radial velocity standard stars/night ThAr spectra after each exposure Cross correlation with iraf/fxcor Metal lines only! Orders analyzed separately for consistency check

21 TU UMa

22 TU UMa

23 Finding the center of mass velocity

24 Individual template RVc,2014=92.6km/s

25 Comparison to orbit model

26 CN Lyr

27 CN Lyr

28 Z CVn

29 BX Leo

30 Targets observed so far Target # of velocity measurements Target # of velocity measurements TU Uma 47+5 ST Leo 7 CN Lyr 11 BK And 6 DM Cyg 11 XX Hya 5 Z CVn 9 RR Gem 4 BK Dra 9 RV UMa 4 AO Peg 8 CI And 3 BX Leo 7 U Tri 2 SZ Leo 7 TT Lyn 1 AV Vir 7 SS Leo 1 Hopefully more to come

31 Conclusions Campaign ongoing Extraction of systemic RVs from spectra in progress Detailed comparison with literature values and photometry upcoming New individual TU Uma template future measurements easier and more accurate Individual as well as center of mass velocities will be published for further use