TESS Sci Con 2021

Joel Ong, et al.

August 2021 | Slides at http://hyad.es/talks

How are the **initial helium abundances** of stars

related to their **metallicities**?

T_\text{eff}/\mathrm{K}

M_0 = 1.0 M_\odot; Z_0 = 0.019

T_\text{MS} = 8.6\ \mathrm{Gyr}

T_\text{MS} = 13\ \mathrm{Gyr}

T_\text{eff}/\mathrm{K}

Y_0 = 0.27; Z_0 = 0.019

grey lines: models from previous slide

Power spectra of MDI dopplergrams

Individual mode frequencies exhibit

detailed structure on an échelle diagram.

\underbrace{\color{red}\Delta\nu, \nu_\text{max}}_{\mathclap{\text{Global properties only}}}, \overbrace{\color{blue}\left\{\nu_{nl}\right\}}^{\mathclap{\text{interior structure}}}

Second frequency differences/\mu\mathrm{Hz}

“Acoustic glitches” as indicator of surface helium abundances

Main-sequence *Kepler* sample consistent with broad range of \Delta Y / \Delta Z.

T_\text{eff}/\mathrm{K}

only l=1, pure p-modes: subtle changes

only l=1, mixed modes: pretty sensitive

(some missing metallicities)

- Inputs:
- Classical constraints (L, [\mathrm{Fe/H}], T_\text{eff})
- Detailed seismic constraints (individual mode frequencies \nu_{nl})

- Inference:
- Grids of evolutionary models (MESA; YREC)
- Computation of mixed-mode frequencies (GYRE; ADIPLS)
- Different inference schemes (glitches vs. avoided crossings)

- Outputs:
**Initial mass fractions Y_0 and Z_0**

Avoided crossings appear to constrain Y_0

better than glitches.

(main-sequence *Kepler* stars, for comparison)

(*TESS* subgiant sample, two ways)

Suspiciously small/asymmetric

posterior errors?

Caustics in posterior distribution:

low-metallicity results prior-dominated

(we’re already fixing this)

(including *Kepler/K2* subgiants)

Main-sequence results analysed differently — possible methodological offset?

- Inference of Y_0 from mixed-mode pattern is feasible, yielding
**stronger constraints**on Y_0 than from pure p-modes - Constraints may be placed on \Delta Y / \Delta Z given large enough subgiant sample (so far only have processed Southern CVZ)
- Bigger sample from Northern CVZ and 20-second data may help

- May be a need for a homogenous reanalysis of all available asteroseismic targets (including
*Kepler*/*K2*, MS and RG stars)