A Planet is Born: Leveraging the Keck Telescopes to Catch Planet Formation in the Act

Accretion processes in forming stars and exoplanets produce observable signatures in their spectral energy distributions in the form of UV continuum excess and emission lines. The relationship converting measured line fluxes to absolute accretion rates for T Tauri stars has been determined empirically down to substellar masses, but a robust relationship calibrated for objects of planetary mass is yet to be determined. In this presentation, I will discuss preliminary results from a Keck pilot study to measure the accretion rates of planetary-mass objects using UV/optical and IR spectroscopy. The spectra of the planetary-mass objects in our sample are obtained near-simultaneously with both Keck-I/LRIS and Keck-II/NIRSPEC to ensure our L_acc-L_line relationships are robust to variability in accretion. I will also discuss the first detections of Paβ and Brα in FU Tau A, a ~50 M_Jup brown dwarf host of a ~15 M_Jup planetary-mass companion, and their implications for accretion variability and brown dwarf formation scenarios in this benchmark system. Our Keck campaign will calibrate and extend empirical relationships between hydrogen recombination line fluxes and accretion luminosity down to planetary masses. These observations will place the first UV-calibrated constraints on Brα emission in accreting substellar objects, and I will conclude my presentation with discussion of the outlook for using infrared hydrogen emission lines as a protoplanet search strategy in the era of JWST.