Astronomy Tea Talk

Speaker 1: Jack Dinsmore (PhD candidate; Stanford University)

Title: Mysterious Pulsar X-ray Filaments: Observational and Theoretical Advances

Abstract: Pulsar X-ray filaments or "misaligned outflows" are a long and narrow stream of ultrarelativistic particles, emitted by some high velocity pulsars which have escaped their natal supernova remnant. Unlike normal pulsar wind nebulae, these filaments extend into the undisturbed interstellar medium, with no supernova remnant or pulsar bow shock between them and interstellar space. Thus they present a rare opportunity to study particle cosmic ray interaction with the ISM, and they may function as probes of local ISM properties. Filaments may also leak positrons and electrons into the Galactic cosmic ray population and could help to explain the positron excess detected at Earth. I will discuss my work expanding and characterizing the population of X-ray filaments and describe the theoretical models I and others have developed. The objects remain not fully understood and are the targets of several future X-ray observations and numerical simulations, which should help uncover the physical processes responsible for these mysterious objects.

Speaker 2: Dom Rowan (Postdoctoral Fellow; UC Berkeley)

Title: Precise Masses and Radii for Metal-Poor Eclipsing Binaries

Abstract: Detached eclipsing binaries (EBs) offer the most effective method to measure model-independent stellar masses and radii. These fundamental stellar parameters are key benchmarks for stellar models, but current catalogs of detached EBs are dominated by stars at solar metallicity, leaving models poorly tested in the metal-poor regime. We characterize 15 detached eclipsing binaries with metallicity ([M/H] ≲ −0.5) using TESS photometry and ground-based spectroscopy and measure masses and radii with fractional uncertainties of <3%. We disentangle the binary component spectra and use spectral synthesis to measure the metallicities and alpha-abundances of the binaries. Three systems have [M/H] < −2.0, making them the most metal-poor EBs characterized to date. We find that the alpha-abundance generally correlates with Galactic kinematics, with the most alpha-enhanced stars being part of the thick disk or halo. By comparing the stellar parameters to theoretical isochrones, we derive ages with uncertainties of < 0.5 Gyr, with three binaries older than 10 Gyr (up to ~13.8 Gyr). Finally, we use a sample of 623 stars to update empirical mass and radius relations for main-sequence stars.