Stars from Kepler. Courtney Dressing

Transcription

1 Images: Pale Blue Dots (K. Mora) & KOI 961 (NASA/JPL Caltech) The Prevalence of Small Planets Around Small Stars from Kepler Courtney Dressing & David Charbonneau Harvard Smithsonian Center for Astrophysics Porto, Portugal Funding provided by NSF GRFP awarded to CD & NASA Kepler PSP awarded to DC 15 September 2014

2 K2 TESS PLATO CHEOPS ExoplanetSat SPECULOOS Current & Future Missions Targeting Planets Around Small Stars CARMENES SPIRou HPF MEarth & MEarth South ExTrA

3 The M Dwarf Advantage 1 Transit Per Year 0.008% Deep 0.47% Probability

4 The M Dwarf Advantage 1 Transit Per Year 0.008% Deep 0.47% Probability 12 Transits Per Year 0.13% Deep 1.4% Probability

5 The M Dwarf Advantage 75% of nearby stars are M dwarfs 1 Transit Per Year 0.008% Deep 0.47% Probability 12 Transits Per Year 0.13% Deep 1.4% Probability

6 Computing the Planet Occurrence Rate Occurrence Actual Number of Planets Number of Stars Important Corrections: We are not sensitive to all planets. Some ``planets might be false positives. Searched

7 Revised Stellar Parameters for Kepler M Dwarfs Dressing & Charbonneau 2013 Fit KIC photometry (Brown+ 2011) to Dartmouth stellar models (Dotter+ 2008, Feiden+ 2011) using priors on [Fe/H] and galactic height (Casagrande+ 2008)

8 Our 2013 Planet Occurrence Estimate Dressing & Charbonneau planets perstar with P<50 days and 05< 0.5 Rp < 4 R Earth 0.15 (+0.13/ 0.06) Earth size planets per HZ

9 Improvement 1: More Data Comparison of January 2013 and February 2012 KOI lists Image Credit: NASA

10 Improvement 2: Refined Small Star Sample lar Radiu us (R Sun ) Stel Possible Stars: 4915 Selected Stars: 2622 Selection Criteria: >1000 days coverage Well behaved bh dlight curve Stellar Effective Temperature (K) Data from Kepler Stellar Properties Table at the NASA Exoplanet Archive (Huber et al. 2014)

11 Improvement 3: MEASURED PIPELINE COMPLETENESS

12 Our Planet Detection Pipeline Detrend & clean Kepler light curves Generate Box-fitting Least Squares power spectrum for each star (Scott Fleming s Fortran implementation of Kovacs et al. 2002) Identify highest peaks & fit simple transit models Excise data near accepted transits Repeat until no new signals are detected

13 Pipeline Performance Versus Insolation

14 Smoothed Search Completeness

15 Search Completeness Versus Period

16 We Recover Most KOIs

17 Normalize ed Flux + Offset 1.05 nded Flux Detre Folded Time (Days) Detrended Flux De etrended Flux Detrended Flux KID (1 Candidate), P = Days, t0 = Days Possible New Mars sized Planet Obiti Orbiting a Star without t Known Planets Time (Days) P = 11.9 Days Zoom Folded Time (Days) Phase = 0.5 rp/rstar: a/rstar: inc: Rp: Rs: Delta Chi Sq: Dur (Hr): Dur / Max Dur: Odd/Even: Dep Sig: Rat 2/1: Phase 2: Odd Folded Time (Days) Even Folded Time (Days) Detrended Flux Folded Time (Days) De etrended Flux Folded Time (Days) Time (Days) Folded Time (Days) Count Depth

18 Detren nded Flux KID (4 Candidates), P = Days, t0 = Days Possible New Earth sized Planet in a M lti Pl t System Multi Planet S t Time (Days) Detrended Flux D P = 21.9 Days Zoom 15 Folded Time (Days) De etrended Flux Folded Time (Days) Folded Time (Days) Folded Time (Days) Detrended Flux D 16.5 Odd Even Folded Time (Days) Folded Time (Days) 20 rp/rstar: a/rstar: inc: Rp: Rs: Delta Chi Sq: Dur (Hr): Dur / Max Dur: Odd/Even: Dep Sig: Rat 2/1: Phase 2: Count Phase = Time (Days) De etrended Flux 1.04 Detrended Flux D Normalize ed Flux + Offset Folded Time (Days) Depth

19 Improvement 4: Inspected Follow up Observations of Planet Candidates KOI 2626 KOI 1422 Keck NIRC2 AO HST WFC3 K band Ciardi F555W Gilliland Revised System Properties in Star et al. (2014)

20 Improvement 5: False Positive Correction Class Radius (R Earth ) False Positive Rate Earths % ±3.0% Super Earths %± 8.8% ± 1.9% Small Neptunes % ±1.1% Large Neptunes % ±3.5% Giants % ±2.9% Rates from Fressin et al. (2013)

21 Smoothed Population of Planet Candidates

22 Improvement 6: More Sophisticated HZ Boundaries Moist & Maximum greenhouse limits from Kopparapu et al Desert worlds (Zsom et al. 2013) Clouds (Yang et al. 2013)

23 Interim Summary: List of Changes 1) Used all four years of Kepler data 2) Refined stellarsamplesample 3) Measured pipeline completeness 4) Inspected follow up observations 5) Applied a false positive correction 6) Used more sophisticated habitable zone boundaries

24 Resulting Occurrence Rate

25 Estimated Planet Occurrence Rate (%) 0.5 Earths per star with P < 50 days

26 Planet Occurrence Versus Period See P3.16 by Mulders for connection to planet formation

27 Smoothed Planet Occurrence Rate

28 Planet Occurrence (%) versus Flux 0.2 Earths per Habitable Zone HZ from Kopparapu et al. 2013

29 Alternative HZ Choices R Earth in Mars Venus HZ: R Earth in Petigura et al. (2013) HZ: 0.71 > 1 Planet Per Star for Pierrehumbert & Gaidos HZ Nominal insolation boundaries from Kopparapu et al. 2014

30 Summary & Conclusions We refined our estimate of M dwarf planet occurrence by: Using all four years of Kepler data Refining stellar sample Explicitly measuring pipeline completeness Inspecting follow up observations & accounting for dilution Applying a false positive correction Incorporating updated habitable zone boundaries Radius (R Earth ) Period (Days) Estimated Number per Star (+0.06/ 0.05) (+0.07/ 0.06) Narrow HZ 0.2 (+0.2/ 0.1) 1 2 Venus Mars HZ 0.4 ±0.1

31 ADDITIONAL SLIDES

32 Pipeline Sensitivity 5.0 Detected: Not Detected: Radius (R R REarth) Only 25% of injections shown 10 Period (Days) 100

33 Smaller Planets Are More Common

34 Potentially Habitable Worlds are Common HZ from Kopparapu et al. 2014