Convection in Cool Stars, as Seen through Kepler's Eyes

Convection in Cool Stars, as Seen through Kepler's Eyes Fabienne A. Bastien (Hubble Fellow, Penn State) Keivan G. Stassun (Vanderbilt), Gibor Basri (Berkeley), Jason Wright (Penn State), Joshua Pepper (Lehigh), David Kipping (Columbia), John A. Johnson (Harvard), Andrew Vanderburg (Harvard), Steven Cranmer (U. Colorado) K2 Science Conference Tuesday, 3 November, 2015

Motivation planets flares spots pulsations http://en.wikipedia.org/wiki/sun

Motivation planets flares How can we remove stellar variability, a major impediment to planet detection? spots pulsations http://en.wikipedia.org/wiki/sun

Motivation planets flares Can we use stellar variations to enhance exoplanet science? spots pulsations http://en.wikipedia.org/wiki/sun

Guiding Questions

Guiding Questions Can we use discovery light curves to provide accurate estimates of stellar (and planet) properties?

Guiding Questions Can we use discovery light curves to provide accurate estimates of stellar (and planet) properties? Can we use stellar brightness variations to predict which stars will be amenable to RV follow-up? Can stellar brightness variations provide insight into the nature of granulation and its relationship with magnetic activity?

Approach Photometric Variations Radial Velocity Variations Archival (Keck, Lick) Kepler Magnetic Activity WIYN 3.5m (NOAO time)

CoRoT PLATO TESS Kepler, K2

Kepler: A Stellar Astrophysics Mission

Kepler: A Stellar Astrophysics Mission Basri et al. 2010

Kepler: A Stellar Astrophysics Mission Space-based surveys like Kepler allow us to redefine stellar variability Basri et al. 2010

The Sample Sun-like stars (F,G,K) Only long (30 min) cadence data Simple variability measures Basri et al. (2011)

Range: measure of surface spot coverage Number of Zero Crossings: measure of light curve complexity Flicker: measure of short-timescale variability (< 8 hrs)

Results 1. Kepler Light Curves Encode Fundamental Stellar Parameters

A Simple Photometric Measurement of log(g) log10(range) [ppt; Kepmag corrected] Point size: Number of Zero Crossings Discovery: a tight photometric variability sequence extending from low to high flicker 8-hr Flicker [ppt; Kepmag corrected] Bastien et al. 2013, Nature

A Simple Photometric Measurement of log(g) Asteroseismic log10(g) [cgs] log10(range) [ppt; Kepmag corrected] Point size: Number of Zero Crossings 8-hr Flicker [ppt; Kepmag corrected] Bastien et al. 2013, Nature Result: Stellar surface gravity manifests in Kepler long-cadence light curves, even for dwarfs

A Simple Photometric Measurement of log(g) Result: Stellar surface gravity manifests in Kepler long-cadence light curves, even for dwarfs Bastien et al. 2013, Nature

A Simple Photometric Measurement of log(g) Precision: Flicker: ~0.1 dex KIC: 0.4-0.75 dex Spectroscopy: 0.1-0.2 dex Asteroseismology: 0.01 dex Bastien et al. 2013, Nature

A Simple Photometric Measurement of log(g) log10(range) [ppt; Kepmag corrected] Point size: Number of Zero Crossings 8-hr Flicker [ppt; Kepmag corrected] Bastien et al. 2013, Nature

A Simple Photometric Measurement of log(g) log10(range) [ppt; Kepmag corrected] Point size: Number of Zero Crossings Solar flicker invariant over magnetic cycle 8-hr Flicker [ppt; Kepmag corrected] Bastien et al. 2013, Nature

A Simple Photometric Measurement of log(g) log10(range) [ppt; Kepmag corrected] Point size: Number of Zero Crossings Recover solar gravity to 0.05 dex 8-hr Flicker [ppt; Kepmag corrected] Bastien et al. 2013, Nature

A Simple Photometric Measurement of log(g) Asteroseismic log10(g) [cgs] log10(range) [ppt; Kepmag corrected] Point size: Number of Zero Crossings 8-hr Flicker [ppt; Kepmag corrected] Bastien et al. 2013, Nature Interpretation: - Flicker traces granulation Kjeldsen & Bedding (2011) Mathur et al. (2011) Cranmer et al. (2014) Kallinger et al. (2014)

A Simple Photometric Measurement of log(g) Interpretation: - Flicker traces granulation Bastien et al. 2013, Nature Trampedach et al. (2013)

A Simple Photometric Measurement of log(g) Asteroseismic log10(g) [cgs] log10(range) [ppt; Kepmag corrected] Point size: Number of Zero Crossings 8-hr Flicker [ppt; Kepmag corrected] Bastien et al. 2013, Nature Interpretation: - Flicker traces granulation - Flicker floor sequence tied to relative absence of spots? García et al. (2010) Chaplin et al. (2011) Huber et al. (2011)

The Photometric Evolution of Sun-Like Stars log10(range) [ppt; Kepmag corrected] Point size: Number of Zero Crossings 8-hr Flicker [ppt; Kepmag corrected] Bastien et al. 2013, Nature

log10(range) [ppt; Kepmag corrected] The Photometric Evolution of Sun-Like Stars 8-hr Flicker [ppt; Kepmag corrected]

A Simple Photometric Measurement of log(g) Red Clump stars Results: Red Giants Bastien, Stassun et al., submitted log(g) for ~ 29 000 Kepler stars Update error bar treatment (magnitude dependent) Extension to ~ 7000K Distinguish Red Giants from Clump stars

A Simple Photometric Measurement of Stellar Density Uncertainty: ~30% Kipping et al. 2014

Results 2. Kepler light curves suggest that granulation in F stars is magnetically suppressed

Light Curves Suggest F Star Granulation is Magnetically Suppressed Cranmer et al. 2014

Light Curves Suggest F Star Granulation is Magnetically Suppressed Result: Granulation in F stars must be magnetically suppressed to fit observations Cranmer et al. 2014

Light Curves Suggest F Star Granulation is Magnetically Suppressed Gray: stars without seismic detections Black: stars with seismic detections Range [ppt] Result: Activity appears to suppress p-modes (which are excited by near surface convection) Effective Temperature (K) Chaplin et al. 2011 Ca II H&K survey with WIYN 3.5m + Hydra (F. Bastien [PI], W. Chaplin, D. Huber, K. Stassun)

Results 3. K2 Light Curves May Encode Fundamental Stellar Parameters

K2 Light Curves Yield a Simple Measure of log(g) Vanderburg & Johnson (2014)

K2 Light Curves Yield a Simple Measure of log(g) Approach: Bastien, Vanderburg et al., in prep

K2 Light Curves Yield a Simple Measure of log(g) Approach: Bastien, Vanderburg et al., in prep Degrade Kepler light curves to K2 precision

K2 Light Curves Yield a Simple Measure of log(g) Approach: Bastien, Vanderburg et al., in prep Degrade Kepler light curves to K2 precision Inject K2-like instrumental noise

K2 Light Curves Yield a Simple Measure of log(g) Approach: Bastien, Vanderburg et al., in prep Degrade Kepler light curves to K2 precision Inject K2-like instrumental noise Apply Vanderburg & Johnson (2014)

K2 Light Curves Yield a Simple Measure of log(g) Preliminary Prediction: Flicker, as currently defined, cannot be measured with K2, even for evolved stars. Bastien, Vanderburg et al., in prep

K2 Light Curves Yield a Simple Measure of log(g) Preliminary Result: We can measure log(g) from K2 light curves by redefining Flicker. Preliminary Precision: <0.2 dex Bastien, Vanderburg et al., in prep

K2 Light Curves Yield a Simple Measure of log(g) Implication: Pointing jitter greatest impediment to Flicker measurement (Applies through Campaign 2) Bastien, Vanderburg et al., in prep

Approach Photometric Variations Radial Velocity Variations Magnetic Activity

Results 4. Discovery Light Curves Can Be Used To Prioritize RV Follow-Up of Transiting Planets RV Noise/RV Jitter/RV RMS: stellar processes that induce RV variations

Results 4. Discovery Light Curves Can Be Used To Prioritize RV Follow-Up of Transiting Planets All Kepler stars with long-term RV monitoring from California Planet Search (Keck, Lick)

Kepler Insights into RV Noise Result: RV noise visible in Kepler light curves of magnetically inactive stars Bastien et al. 2014a

Kepler Insights into RV Noise Model 1 Model 2 Bastien et al. 2014a Model 1 Model 2 Result: Spot models systematically underpredict RV jitter in inactive stars by factors of 2 1000

Kepler Insights into RV Noise Model 1 Model 2 Bastien et al. 2014a Model 1 Model 2 Result: presumably because underestimate granulation contribution

Kepler Insights into RV Noise Results: RV noise of inactive stars linked to flicker, granulation (97% confidence) Wright (2005) Dumusque et al. (2011) Cegla et al. (2014) Bastien et al. 2014a

Kepler Insights into RV Noise Results: Bastien et al. 2014a RV noise of inactive stars linked to flicker, granulation (97% confidence) Discovery light curves may be used as predictors of good RV follow-up targets Wright (2005) Dumusque et al. (2011) Cegla et al. (2014) Aigrain et al. (2012)

Approaching the Stellar Astrophysical Limits of Exoplanet Detection: Getting to 10 cm/s...aug 28 to Sept 18 Organizers: F. Bastien, G. Basri, X. Dumusque, S. Sigurdsson, J. Wright

Summary of Core Results

Summary of Core Results Light curves encode fundamental stellar parameters (surface gravity, density)

Summary of Core Results Light curves encode fundamental stellar parameters (surface gravity, density) Light curves suggest that granulation in F stars is magnetically suppressed

Summary of Core Results Light curves encode fundamental stellar parameters (surface gravity, density) Light curves suggest that granulation in F stars is magnetically suppressed RV jitter in magnetically inactive stars may be linked to high frequency power revealed by light curves