Resolve the nature of the cold component in UNCOVER-A2744-20698

Determine whether the cold, water-absorbing component of UNCOVER-A2744-20698 is a dense outflow-confined cloud or a magnetically induced starspot by obtaining sufficiently high-resolution spectra to resolve its individual water absorption lines and measure their velocity relative to the photosphere.

Background

UNCOVER-A2744-20698 requires a two-component spectral fit. Its cold component has a surface gravity, and therefore an inferred pressure, roughly two orders of magnitude higher than expected for a smooth extended atmosphere that conserves the Eddington ratio of the hot component.

The authors interpret this component either as a dense cloud formed by ram pressure in shocked wind ejecta or as a cool starspot. These alternatives make different observational predictions: a cloud moving with the outflow should produce blueshifted molecular lines, whereas a starspot should retain the stellar systemic velocity.

References

Higher resolution spectra may thus be able to deduce whether or not we are seeing clouds in the atmosphere of a quasi-star by resolving the water band into its individual lines, since a cloud moving with the outflow would shift those lines blueward of the photospheric absorption while a starspot would keep them at the stellar velocity.

— A Spectral Framework for Testing the Quasi-Star Hypothesis in Little Red Dots I: Weighing LRDs by Their Super-Eddington Luminosity Ratios---No Signs of Overmassive Black Holes  (2609.09265 - Curtis et al., 8 Sep 2026) in Section 4.1, “Photospheric Fits and Eddington Ratios” (Section \ref{sec:res_fits})