12:00–1:00 pm Zoom
Host: Vikram Dwarkadas
Kayla Owens "Current Challenges in Cepheid Distance Calibrations Using Gaia EDR3"
Gaia’s early third data release provided parallaxes to nearly 1.5 billion stars in the Milky Way. These parallaxes have been widely used to anchor local distance indicators in the pursuit of obtaining a more precise measurement of the Hubble Constant. In this talk, I will discuss calibrating the Cepheid period-luminosity relation from optical to mid-infrared wavelengths using the Gaia EDR3 distances. I will particularly focus on the challenges of obtaining precise and accurate distances to these bright stars, including how the potential for an additional parallax offset leads to a degeneracy with metallicity effects. At this time, Gaia-based Cepheid distance measurements appear to have a systematic error floor of approximately 3%, precluding a measurement of the Hubble Constant to 1% precision.
Siddhartha Gupta "Lepton-driven Non-resonant Streaming Instability"
Streaming instabilities driven by energetic charged particles are crucial for understanding the self-confinement of these particles near the sources in astrophysical environments. Using kinetic plasma simulations, we investigate non-resonant (Bell) streaming instability driven by energetic leptons. We identify the conditions to drive the instability, characterise the linear and saturated stages and compare the results with the proton-driven case. Our results are important for understanding the phenomenology of astrophysical environments where leptons are accelerated (e.g., oblique shocks and around pulsar wind nebulae), and in laboratory experiments.