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Kepler/K2 and IGRINS constrain starspot filling factors and temperatures.

January 09, 2019

Kepler/K2 and IGRINS constrain starspot filling factors and temperatures.

In this contribution I highlight how large starspot coverage fractions alter the interpretation of existing data: age biases and spreads in young clusters and spectral-type mismatches in the optical and infrared. I showcase results of probabilistic spectral decomposition using custom extensions to the Starfish inference framework. High spectral resolution, high bandwidth near-infrared spectra from IGRINS are shown to detect the collective emission from large starspots and/or spot groups. I demonstrate these precision measurements on the most conspicuously spotted benchmarks, Weak Line T-Tauri Stars in nearby young star forming clusters. I report their starspot coverage fractions and photospheric temperatures. These measurements indicate large biases in isochrone-derived ages of young stars.


January 09, 2019

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  1. Kepler/K2 and IGRINS constrain starspot filling factors and temperatures. Michael

    Gully-Santiago Kepler/K2 Guest Observer Office NASA Ames Research Center & baeri.org AAS233 "YSOs and friends" Seattle, WA January 2019
  2. Claim: Starspots confound isochronal ages. How? 1. Inhibit convective efficiency,

    puffing up the star 2. Bias observations (nontrivial SpT - Teff mapping)
  3. What can you measure? = + to first order, starspots

    are photospheres indexed by cooler temperatures. area & temperature
  4. ghtcurve ghtcurve fspot = 23.5% spot free! black spot is

    face-on Coverage fractions smaller than 23.5% would not block enough flux. Kepler/K2 lightcurves offer lower limits to starspot area.
  5. IGRINS can directly see the collective starspot emission from stars.

    ^Gully-Santiago et al. 2015 silicon immersion gratings <Park et al. 2014 R = 45,000 spectrograph Huge bandwidth: 1.5 - 2.5 μm (all H & K) McDonald 2.7m, DCT, Gemini South
  6. Probabilistic Spectral Decomposition Starfish is an open source spectral inference

    framework for stellar spectra. = + Composite Ambient Starspot Tspot = 2800 K Tamb = 4100 K Czekala et al. 2015 github.com/iancze/Starfish Gully-Santiago et al. 2017 github.com/gully/Starfish
  7. Constraints from K2 and IGRINS measurements. Each point is an

    independent estimate from different IGRINS spectral orders.
  8. IGRINS affirms huge coverage fractions of spots on WTTS's. Model-dependent

    isochronal ages are likely biased if some/most young stars go through a heavily spotted phase Observations are biased (consistently wrong visible spectral types) Suppressed convection efficiency changes isochrones in pre-MS HRD Also contributes to age scatter (apparent age spreads) What are the consequences?