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Time Series Photometry; S ome M usings

Time Series Photometry; S ome M usings. Steve B. Howell, NASA Ames Research Center. Photometric, Time-Series Surveys. Surveys and variable objects are great ! Discovery (vs. detailed study) & Large Samples (vs. single objects) Detected transients and variables vary with Filter / color

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Time Series Photometry; S ome M usings

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  1. Time Series Photometry; Some Musings Steve B. Howell, NASA Ames Research Center

  2. Photometric, Time-Series Surveys • Surveys and variable objects are great ! • Discovery (vs. detailed study) & Large Samples (vs. single objects) • Detected transients and variables vary with • Filter / color • Galactic location • Etc. • Detected sources also “vary”, and become more or less interesting, with our ability to understand them • What about classification & follow-up?

  3. Three items considered • Time sampling • Allow additional science: e.g., Seismology, accretion physics, exoplanet transit models • Time coverage • Long term changes • Transient discovery and behavior • Photometric precision • New types of variable sources discovered • Better details and fitting of light curves

  4. Good Time Sampling: DataSampling is Important Sample: 7.5 hrs       

  5. Good Time Sampling: DataSampling is Important Sample: 0.5 hrs

  6. Long Time Coverage Some objects appear to be boring, non-periodic and non-variable, but it is often a matter of time…..

  7. Long Time Coverage:BOKS 45906 – IB w/56.6 min period

  8. %Variability vs. Phot. Precision(σ) • Periodic variables make up ~10% of all variables. • %Var (Kepler) ~72% Still not at edge of variable universe %Var = -23.95 (log σ) - 39.52

  9. Non-Periodic variables • Non-periodic sources dominate variability • Some non-periodic sources are well known • Flares, CV outbursts, granulation noise , SN • Most are not • Two examples – fooled and hopeful

  10. Variable stars greatest hits V344 Lyr 1 minute Kepler observations Discovery of asymmetric rise/fall shape at start/end of cycle.

  11. Variable stars greatest hits KIC 11390659 Quasi-periodic source. Examining ΔE, Δt at start of quasi-periods

  12. (Non) Periodic Variables: Kepler data Variability across the H-R Diagram - Stars brighter than 13, one month of observation, 30 minute sampling Top: χ2 >2 Middle: χ2 >10 Bottom: χ2>100

  13. Variability of giants and dwarfs Standard deviations of 30 minute sampled light curves. These data span 33 days of time.

  14. Variability of giants and dwarfs Standard deviations of 30 minute sampled light curves. These data span 33 days of time. Histogram cuts of previous diagrams

  15. Solar-like Exoplanet host stars H-R Diagram of a sample of Solar-like stars Note distribution of subgiants- lower gravity, RV jitter stars Larger convective cells, more variable

  16. Solar-like Exoplanet host stars M-R relation for the sample of Solar-like stars Note distribution of subgiants- lower gravity, RV jitter stars. Jitter ~5-10 m/sec Spectroscopic variables

  17. Solar-like Exoplanet host stars Variability of the sample of quiet Solar-like stars Red: sigma > 0.002 Blue: 0.001 to 0.002 Green: < 0.001 Note random distribution of variability; not all subgiants ~10 m/sec RV jitter = 0.001 mag

  18. Conclusions • Our expectations are sometimes wrong • Surveys all have biases, keep them in mind • Spectroscopy may not always provide an answer • Spectroscopic variable subgiants are (mostly) not photometric variables • Traditional analysis techniques tend to find traditional results • Sonification of variability & other new research tools may reveal new insights • Non-Periodic variables form ~90% of all variables • Yet we know little about most of them

  19. The End??Stayed Tuned for K2 !!Coming to a galaxy near you in 2014 • K2 will be a repurposed Kepler mission • K2 will point to 4-5 fields/year in the plane of the ecliptic • K2 will stare at each ~100 sq. degree field for 75-85 days • K2 will observe at least 10,000 to 20,000 targets in each pointing • K2 will use 30 minute cadence with limited targets at 1 minute • K2 will achieve better than 300 ppm (6 hr avg) at 12th mag • K2 will be a community mission, selecting targets based on guest observer input. No exclusive use period.

  20. Good Time Sampling: DataSampling is Important Sample: 5 hrs                 

  21. Good Time Sampling: DataSampling is Important Sample: 0.5 hrs RR Lyrae star Observed during K2 science verification

  22. Kep Mag brighter than 12 Top: chi^2 >2 Middle: chi^2 >10 Bottom: chi^2>100

  23. Kep Mag brighter than 14 Top: chi^2 >2 Middle: chi^2 >10 Bottom: chi^2>100

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