Special Talk

• Special Talks

  Speaker: Qier An (JHU)
  Title: Unveiling Massive Substellar Companions: A Multi-Method Approach
  Abstract: This talk presents a multi-technique framework for detecting and precisely characterizing massive substellar companions by combining complementary orbital constraints from astrometry, radial velocities, and direct imaging. I use precision absolute astrometry from the Hipparcos and Gaia missions to measure long-term accelerations from reflex motion, RV time series to anchor the line-of-sight dynamics, and high-contrast direct-imaging relative astrometry from Keck and Subaru to resolve relative positions and break key geometric degeneracies. By jointly modeling these datasets, we recover full three-dimensional orbits and true dynamical masses for companions spanning the giant planet to brown dwarf regime. The resulting orbit-and-mass determinations provide benchmark substellar objects and a scalable approach for interpreting the growing set of Gaia-identified accelerators with targeted RV and imaging follow-up.

  Speaker: Nick Indriolo (STScI)
  Title: Mapping the Cosmic-Ray Ionization Rate in the Solar Neighborhood
  Abstract: Chemical complexity in the molecular interstellar medium (ISM) is driven by fast ion-molecule reactions. This network of chemical reactions requires a source of ionization, and as molecular gas is generally well shielded from ionizing UV photons, cosmic rays provide the dominant source of ionization in such environments. The impact of cosmic rays on atomic and molecular hydrogen is parameterized as the cosmic-ray ionization rate (CRIR; number of ionizations per atom/molecule per unit time), which serves as an important input variable in astrochemical modeling. We use observations of H3+, a molecule with very simple formation and destruction pathways, in combination with advanced 3D chemical modeling to infer the CRIR in diffuse molecular gas along sight lines toward bright, early type stars. Until recently, it was impossible to constrain the location of the absorbing gas along a sight line, but with Gaia extinction maps we can now link molecular absorption features to physical complexes of dust and gas in the local (1 kpc) ISM. This has allowed us to begin creating the first 3D map of CRIRs in the solar neighborhood, and to investigate correlations with properties such as location, gas density, distance from proposed cosmic-ray acceleration sites, and more. Here, I will present the results of our recent H3+ survey using IRTF/iSHELL, which has more than doubled the number of sight lines where we have precision estimates of the CRIR, and enabled the investigation of spatial variations in the cosmic-ray flux.