Cruz: The First Billion Years in Seconds: An Effective Model for the 21-cm Signal with Population III Stars / Phillips: Atmospheric Characterization of the Dusty Planetary-Mass Companion BD+60 1417B

Speaker: Hector Cruz ( Johns Hopkins University) / Caprice Phillips (OSU) zoom 

Zoom info: https://stanford.zoom.us/j/98604058568

Cruz: In the next few years, observations of the 21-cm signal will open a window to the cosmic dawn epoch, when the first stars formed. It is conventional to interpret these observations through semi-numerical or hydrodynamical simulations, which are often computationally intensive and inflexible to exotic cosmological or astrophysical effects. I will present a new approach to predict the 21-cm global signal and fluctuations in the presence of PopIII stars in seconds. PopIII stars, residing in low-mass molecular-cooling halos, are highly sensitive to feedback, especially from H2-dissociating Lyman-Werner radiation and dark matter-baryon relative velocities. To bypass expensive numerical simulations, we develop an effective prescription of the star formation rate density in the presence of PopIII stars. Our method recovers the full nonlinear distributions of radiative fields that determine the 21-cm signal including anisotropic feedback. I will show how PopIII stars impact the 21-cm global signal and power spectrum across cosmic time and at different distance scales. I will also highlight how the spatial modulation of the relative velocities induces Velocity Acoustic Oscillations in 21-cm power spectra, providing us with a new and robust cosmological standard ruler. Our public code, Zeus21, can predict 21-cm observables in seconds, presenting a meaningful first step towards rapid precision astrophysics and cosmology in the first billion years.

Phillips: In this talk, I will present a detailed characterization of the BD+60 1417 system that incorporates an atmospheric retrieval and spectroscopic variability monitoring of BD+60 1417B, elemental abundance measurements of BD+60 1417, and a spin-alignment measurement of both components.  The recently discovered, L6-L8γ planetary-mass companion, BD+60 1417 B (15± 5 MJup), lies at a separation of >1000 AU from its K0 host star and has an age of 50 – 150 Myr. I used the Brewster retrieval code to test thermal profile parameterizations and ultimately detail the atmospheric composition.  The retrieval results presented in this work demonstrate that the emergence of condensate cloud species complicates retrieval analysis, most notably when only near-infrared spectra are available.  We also present new spectroscopic monitoring observations of BD+60 1417B obtained with HST/WFC3. We detect significant variability across the full 1.1-1.7 micron region probed by HST that is likely driven by inhomogeneous atmospheric features such as non-uniform clouds. Our observations allow us to measure the rotation rate and viewing angle of the companion BD+60 1417B and thus test the spin axis alignment of the BD+60 1417 system. Finally, I will present the first elemental abundance measurements of the young K-dwarf, BD+60 1417. We find a relatively high Mg/Si value and a near solar C/O ratio, which allows us to predict the cloud conditions likely present in the secondary.