• CART Astrophysics Seminar Series

April 10, 2025 2:00 PM
PAIS 3205

Host:

Greg Taylor

Presenter:

Lucas Hunt (NRAO)

Astrometry, the study of precise positions of celestial bodies, plays a critical role in understanding our Universe. It helps determine positions and motion of stars and pulsars within our galaxy,  tests General Relativity, and our understanding of Active Galactic Nuclei. All of these studies are dependent on a grid of sources, that allow us to measure the position of our target relative to an inertial reference frame. This reference frame, the International Celestial Reference Frame (ICRF), was first defined in 1998 from Very Long Baseline Interferometry observations of 608 quasars that began in 1986. It was originally defined at frequencies of 2.3 (S-band) and 8.4 GHz (X-band). Since this first iteration, the ICRF has grown to include observations over 5,000 sources at S and X-band, and observations of a subset of these sources at 24 (K-Band) and 32 GHz (Ka-Band). The higher frequencies were originally pursued because of the improved spatial resolution, but also because the jets that are often seen near the core of the AGN have a steep negative spectral index and are less likely to be seen at higher frequencies. These jets can cause confusion in source positions and increase error.

Inspired by the success of the K and Ka-band reference frames, we have taken observations exploring the feasibility of a 43 GHz (Q-band) reference frame. This talk will discuss our initial Very Long Baseline Array observations of 458 sources selected from the K-band reference frame. We observed these sources in 3 separate observations over 3 months, including observations at S, X, and K bands for comparison. We find that the VLBA is able to detect over 80% of the target sources at Q-band, and images generally show fewer extended components at Q-band than at the lower frequencies. This implies a Q-band reference frame would have higher precision due to improved resolution and fewer confusing components within the field of view.

If time allows, I will also provide information on the VLBA New Digital Architecture (VNDA) project. VNDA will replace and improve upon the aging Roach Digital Backend (RDBE) on the VLBA. VNDA will provide more options for bit-depth, number of available channels, and remove tuning restrictions set by the RDBE. I will highlight VNDA's capabilities and show some preliminary testing results with VNDA installed at two VLBA stations.