Asteroseismic Signatures of Planetary Engulfment

NHFP Symposium | Slides at http://hyad.es/talks

Joel Ong, Marc Hon, Melinda Soares-Furtado, et al.

September 19, 2023

Introduction:
Solar-like Oscillations

\(\ell = 0\) MDI Doppler velocities

Power spectra of MDI dopplergrams

\[ \begin{aligned} {\Delta\nu_\odot} &\sim 135\ \mathrm{\mu Hz} \\ {\nu_{\text{max},\odot}} &\sim 3090\ \mathrm{\mu Hz} \end{aligned} \]

(roughly 5-minute oscillations)

p-mode frequencies satisfy \(\nu_{n\ell} \sim \Delta\nu\left(n + {\ell \over 2} + \epsilon_\ell(\nu)\right) + \mathcal{O}(1/\nu)\)

Stochastic,
broad-band
excitation

\(\implies\) equipartition
between different \(m\)

Key Application: Global Parameter Estimation

Hare “Zebedee”, Cunha+ (incl. Ong, 2021)

Precise measurements of field stars: \[ {\sigma_R \over R} \lesssim 2 \%; {\sigma_M \over M} \lesssim 5 \% \]

A Rapidly Rotating Red Giant

Very high \(\mathrm{A(Li)}\),
but otherwise innocuous

Mode Identification

\[\ell = 0,2?\]

But Kepler says \(\ell = 0\) have to live here!
(and theory says so too…)

Asteroseismology Happens…

Rotational splittings from seismology:

\(\ell = 1\): \(\delta\nu_{\text{rot},1} \sim 0.09\ \mu\mathrm{Hz}\)
\(\ell = 2\): \(\delta\nu_{\text{rot},2} \sim 0.10\ \mu\mathrm{Hz}\)

\(\implies P_\text{rot} \sim 115\ \mathrm{d}?\)

Rotational signal probably got
detrended away
by systematic corrections…

TESS w/ Pixel-Level Decorrelation + Stitching

Very suggestive…
but is this real?

Probably yes!

Observational Overview

Asteroseismology:

\(M \sim 1.14 \pm 0.04\ M_\odot\)
\(R \sim 23.5 \pm 0.03\ R_\odot\)
\(P_\text{rot,bulk} \sim 115 \pm 10\ \mathrm{d}\)
(Weak evidence for rotational shear)

Photometry:

\(P_\text{rot,surf} \sim 99 \pm 3\ \mathrm{d}\)

Spectroscopy:

\(V\sin i \implies \sim 110 \pm 8\ \mathrm{d}\)
\(\mathrm{A(Li)} = 3.16 \pm 0.08\ \mathrm{dex}\)
\(^{14}\mathrm{N}\)-deficient relative to APOGEE sample

Gaia DR3:

RUWE of 1.06
\(\sigma_V = 0.16\ \mathrm{km/s}\)
over 2.2 years

How did this happen??

Gaia RV scatter rules out
large RV semiamplitudes…

\(P_\text{orb} \gg 99\ \mathrm{d}\) cannot spin star
up to 99-day rotational period…

Remaining permissible orbits are
unstable to tidal dissipation!

\(\implies\) ENGULFMENT?

Conclusion

A Rapidly-Rotating Red Giant

TESS finds a lithium-rich, rapidly rotating,
and likely standalone red giant, with rotation
confirmed independently using ASAS-SN, seismology, \(V \sin i\).

Other constraints from spectroscopy and Gaia
strongly suggest an engulfment scenario.

If engulfment, \(< 5\ \mathrm{Mya}\), with mass about \(6\)-\(10\ M_J\).

\[\mathrm{j}\mathrm{o}\mathrm{e}\mathrm{l}\mathrm{o}\mathrm{n}\mathrm{g}\ \text{@}\ \text{hawaii}.\text{edu}\]

Extras

Magnetorotational Braking

Could it be a T Tauri Star?

V501 Aur: a red giant accidentally misclassified as a WTT!
(Vaňko et al. 2017: spectroscopic binary with \(K = 27\ \mathrm{km/s}, P \sim 69\ \mathrm{d}\))

Other Observational Constraints

Orbits of Engulfed Companions