Physical properties of starspots - Speaker Deck

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Physical properties of starspots and their effects on young stellar ages Michael Gully-Santiago Kepler/K2 Guest Observer Office Thursday, June 22, 2017 at NASA Ames Kepler/K2 Science Conference Collaborators: Greg Herczeg (KIAA), Ian Czekala (CfA/KICAP), Garrett Somers (OSU/Vanderbilt), J.F. Donati (CNRS), Konstantin Grankin (CrAO), Kevin Covey (WWU), G. Mace (UTexas), MATYSSE team, ASASSN team, ++

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Disk fraction as a function of age gives us the disk lifetime. Haisch et al. 2001

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Disk fraction as a function of age gives us the disk lifetime. The disk lifetime limits the planet formation timescale. Haisch et al. 2001, Alexander & Armitage 2009, Kraus et al. 2012

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The disk lifetime limits the planet formation timescale. Haisch et al. 2001, Alexander & Armitage 2009, Kraus et al. 2012 How accurate are cluster ages?

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How accurate are cluster ages? ? ? ? ?

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We want to know the ages and masses of young stars so that we can understand how star and planet formation proceed in time.

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We want to know the ages and masses of young stars so that we can understand how star and planet formation proceed in time. Age is not a direct observable. Mass is sometimes a direct observable, but only in rare eclipsing binary systems or resolved gas disk systems.

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We want to know the ages and masses of young stars so that we can understand how star and planet formation proceed in time. Age is not a direct observable. Mass is sometimes a direct observable, but only in rare eclipsing binary systems or resolved gas disk systems.

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Ages are estimated by placing a young star on a pre-main sequence HR diagram.

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Ages are estimated by placing a young star on a pre-main sequence HR diagram.

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Ages are estimated by placing a young star on a pre-main sequence HR diagram.

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Ages are estimated by placing a young star on a pre-main sequence HR diagram.

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Ages are estimated by placing a young star on a pre-main sequence HR diagram.

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Ages are estimated by placing a young star on a pre-main sequence HR diagram.

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Observed star clusters (~1 Myr) show large age spreads of 1-10 Myr. Why?

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Observed star clusters (~1 Myr) show large age spreads of 1-10 Myr. Why? - Observational uncertainties - True age spreads - Episodic accretion - Physics beyond the standard evolutionary models - Magnetic fields - Starspots

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Observed star clusters (~1 Myr) show large age spreads of 1-10 Myr. Why? - Observational uncertainties - True age spreads - Episodic accretion - Physics beyond the standard evolutionary models - Magnetic fields - Starspots Herczeg & Hillenbrand 2014 Spectral types map imprecisely to Teff

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Observed star clusters (~1 Myr) show large age spreads of 1-10 Myr. Why? - Observational uncertainties - True age spreads - Episodic accretion - Physics beyond the standard evolutionary models - Magnetic fields - Starspots APOGEE spectra of thousands of young stars show large disagreement Cottaar et al. 2014

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Observed star clusters (~1 Myr) show large age spreads of 1-10 Myr. Why? - Observational uncertainties - True age spreads - Episodic accretion - Physics beyond the standard evolutionary models - Magnetic fields - Starspots

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Observed star clusters (~1 Myr) show large age spreads of 1-10 Myr. Why? - Observational uncertainties - True age spreads - Episodic accretion - Physics beyond the standard evolutionary models - Magnetic fields - Starspots 290 300 310 320 330 340 350 360 l 10 5 0 5 10 15 20 25 30 b ⇢ Oph Lup I Lup II Lup III Lup IV F/G/K/M Pre-MS Accretors Turnoff B-type Other B1-B5 24 Myr 20 Myr 16 Myr 13 Myr 11 Myr 9 Myr 7 Myr Age Pecaut & Mamajek 2016

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Observed star clusters (~1 Myr) show large age spreads of 1-10 Myr. Why? - Observational uncertainties - True age spreads - Episodic accretion - Physics beyond the standard evolutionary models - Magnetic fields - Starspots

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Observed star clusters (~1 Myr) show large age spreads of 1-10 Myr. Why? - Observational uncertainties - True age spreads - Episodic accretion - Physics beyond the standard evolutionary models - Magnetic fields - Starspots

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Observed star clusters (~1 Myr) show large age spreads of 1-10 Myr. Why? - Observational uncertainties - True age spreads - Episodic accretion - Physics beyond the standard evolutionary models - Magnetic fields - Starspots

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Conspicuous starspot transits have been relatively rare. Little/no enhanced in-transit variance has been observed. - B. Morris & E. Krause from discussions at this conference

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Starspots imbue periodic flux diminution as they enter-and-exit the unresolved stellar disk. Spots have been taken for granted for measuring rotation periods. Spot amplitudes encode information about longitudinally asymmetric spots. Notsu et al. 2013

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Starspots have both theoretical and observational consequences.

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Starspots inhibit convective efficiency. Somers & Pinnsoneault 2015 Less efficient energy transport means stars get larger (R increases) but cooler (T decreases) Postdoc at Vanderbilt

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Starspots confound measurements of L and Teff. Tamb=Teff 0th order assumption No starspots Tamb

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Starspots confound measurements of L and Teff. Tamb=Teff 0th order assumption No starspots 1st order correction Non-emitting starspots Tamb Tspot = 0 K fspot Tamb

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Starspots confound measurements of L and Teff. Tamb=Teff 0th order assumption No starspots 1st order correction Non-emitting starspots Tamb Tspot > 0 K fspot Tamb Tspot = 0 K fspot Tamb 2nd order correction Emitting starspots

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Starspots confound measurements of L and Teff. Tamb=Teff 0th order assumption No starspots 1st order correction Non-emitting starspots Tamb Tspot > 0 K fspot Tamb Tspot = 0 K fspot Tamb 2nd order correction Emitting starspots Teff < Tamb

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Photometric modulation probes longitudinally asymmetric spots. ΔV LkCa 4 ΔV 2015: 0.5 2004: 0.8 1986: 0.2 LkCa 4 light curve

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You can find a minimum coverage of starspots for LkCa 4 ΔV LkCa 4 ΔV 2015: 0.5 2004: 0.8 1986: 0.2 Spot-free Spotted, non-emitting spots

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You can find a minimum coverage of starspots for LkCa 4 ΔV LkCa 4 ΔV 2015: 0.5 2004: 0.8 1986: 0.2 Spot-free Spotted, emitting spots Tspot

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Expected range of starspot properties

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"any photometric modula2ons due to starspots is the asymmetric component of the starspot coverage" Neﬀ et al. 1995, Harrison et al 2011 Smith 1994 Uniformly distributed spots; pole-on star spots circumpolar spots Differential rotation confounding periods Geometrical effects hinder interpretation of lightcurve amplitudes.

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K2 Campaign 2 Observed the ~few Myr Oph and Upper Sco. What can be learned from periodic lightcurve amplitudes in K2?

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Young stars have larger amplitude of periodic variability than typical stars (we already knew that). K2 Cycle 2 light curves for 1658 candidate or conﬁrmed young stars towards Oph/Sco. compared to everything else in that Cycle. Uncorrected Vanderburg and Johnson lightcurves

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Caveats: non-members non-periodic structures Vanderburg and Johnson lightcurves Periods < 10 days K2 C2 lightcurve amplitudes: ~0.5-5% peak to valley

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How to resolve geometric degeneracies to assess total starspot coverage fraction?

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Directly detect the spectrum arising from starspots. Tamb Tspot fspot 1-fspot My Research - This has historically been challenging due to low flux ratio of spots. - My strategy leverages new high resolution near-IR spectrographs.

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Starspot emission Tamb Tspot fspot 1-fspot Tspot = 2800 K Tamb = 4100 K fspot = 0.5 (!) Example Key insight: - In the visible, starspot flux is 5-20x weaker than the ambient photosphere. - In the near-IR, starspot flux is only 2.5-4x weaker than ambient

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Starspot emission Tamb Tspot fspot 1-fspot Tspot = 2800 K Tamb = 4100 K fspot = 0.5 (!) Example Key insight: - In the visible, starspot flux is 5-20x weaker than the ambient photosphere. - In the near-IR, starspot flux is only 2.5-4x weaker than ambient IGRINS ESPaDOnS

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How to figure out which lines are attributable to starspots or ambient photosphere? portion of LkCa 4 IGRINS spectrum from November 2015

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We forward model the IGRINS spectra. Starfish is an open source spectral inference framework for stellar spectra. Czekala et al. 2015 github.com/iancze/Starfish Starfish parameters: 1. Tamb 2. logg 3. [Fe/H] 4. v sini 5. vz 6. Ω 7-9. c0, c1, c2... 10. GP scale 11. GP amplitude 12. σ scale 13. Tspot 14. fspot Intrinsic Starspots = + Composite Ambient Starspot Tspot = 2800 K Tamb = 4100 K **Lots of assump,ons embedded here

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The spectrum has features from both ambient photosphere and starspots. λ (Angstrom) The constraint on filling factor comes from the range of flux ratios.

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Expected range of starspot properties

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LkCa 4 looks younger and less massive in *unspotted* tracks.

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Unspotted tracks from G. Somers

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Spotted tracks from G. Somers

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Take aways 1. Stars are probably more spotted than we previously thought 2. Polar spots would have evaded most conventional methods of detecting and characterizing starspots, since they induce zero photometric modulation. 3. If LkCa 4 is representative of other young stars, the masses and ages of all young stars are considerably biased. 4. The stellar age biases change timescale available for planet formation. 5. What matters is the starspot coverage history, which is generally unobservable. 6. Teff measurement is hindered for highly inclined young spotted stars.

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1. Stars are probably more spotted than we previously thought 2. Polar spots would have evaded most conventional methods of detecting and characterizing starspots, since they induce zero photometric modulation. 3. If LkCa 4 is representative of other young stars, the masses and ages of all young stars are considerably biased. 4. The stellar age biases change timescale available for planet formation. 5. What matters is the starspot coverage history, which is generally unobservable. 6. Teff measurement is hindered for highly inclined young spotted stars. Take aways

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1. Stars are probably more spotted than we previously thought 2. Polar spots would have evaded most conventional methods of detecting and characterizing starspots, since they induce zero photometric modulation. 3. If LkCa 4 is representative of other young stars, the masses and ages of all young stars are considerably biased. 4. The stellar age biases change timescale available for planet formation. 5. What matters is the starspot coverage history, which is generally unobservable. 6. Teff measurement is hindered for highly inclined young spotted stars. Take aways

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LkCa 4 has photometric monitoring going back 31 years. May 6, 1985 June 22, 2017

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1. Stars are probably more spotted than we previously thought 2. Polar spots would have evaded most conventional methods of detecting and characterizing starspots, since they induce zero photometric modulation. 3. If LkCa 4 is representative of other young stars, the masses and ages of all young stars are considerably biased. 4. The stellar age biases change timescale available for planet formation. 5. What matters is the starspot coverage history, which is generally unobservable. 6. Need spectroscopy to assess full spot coverage fraction. Take aways

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1. Stars are probably more spotted than we previously thought 2. Polar spots would have evaded most conventional methods of detecting and characterizing starspots, since they induce zero photometric modulation. 3. If LkCa 4 is representative of other young stars, the masses and ages of all young stars are considerably biased. 4. The stellar age biases change timescale available for planet formation. 5. What matters is the starspot coverage history, which is generally unobservable. 6. Need spectroscopy to assess full spot coverage fraction. Take aways

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Recent evidence for large spot coverage in Pleiades 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 2600 3000 3500 4000 4500 5000 5500 6000 6500 TiO2n Teff (K) Inactive dwarfs PHOENIX(4.5) PHOENIX(5.0) Cubic splines fits Estimate of Tamb, Tspot, fspot in 304 LAMOST spectra 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 3000 3500 3800 4000 4500 5000 5500 6000 6500 fs Teff (K) Pleiades? Pleiades

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Thanks!