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.

Transcript

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. Starspots cause both scatter and bias in the pre-MS HR diagram. spot-free models
4. Starspots cause both scatter and bias in the pre-MS HR diagram. observed
5. Starspots cause both scatter and bias in the pre-MS HR diagram. observed
6. Starspots cause both scatter and bias in the pre-MS HR diagram. observed reality?
7. We need to measure starspots to quantify their role in age bias and scatter.
8. What can you measure?
9. What can you measure? = + to first order, starspots are photospheres indexed by cooler temperatures. area & temperature
10. How to measure starspot area and temperature?
11. Kepler/K2 lightcurves offer lower limits to starspot area.
12. flux deficit at minimum Kepler/K2 lightcurves offer lower limits to starspot area.
13. 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.
14. 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
15. 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
16. wavelength (A) Starfish, Czekala et al. 2015, Gully-Santiago et al. 2017 We see spectral lines from spots.
17. Constraints from K2.
18. Constraints from K2 and IGRINS measurements. Each point is an independent estimate from different IGRINS spectral orders.
19. Is a ~70% coverage fraction of starspots realistic?
20. Ask to see the 30+ year lightcurve in question time
21. 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?