Winter Parts
Title:  Rotationally Modulated Zeeman Spectral Signatures in Two Slowly Rotating M Dwarfs
Abstract:  The focus on M dwarfs as planet hosts has led to a number of high-precision spectroscopic surveys monitoring M dwarfs to detect the Doppler radial-velocity signature of planets, including with the near-infrared Habitable Zone Planet Finder (HPF) instrument. In this work, we studied the variability of the K I 12435.67Å line in spectra of two M dwarfs–GJ 699 (Barnard's Star) and Teegarden's Star–and we attribute these changes to Zeeman splitting. Using the Non-LTE Inversion COde using the Lorien Engine (NICOLE), we modeled the shape of the K I line under the influence of the Zeeman effect for various configurations of the magnetic field on the surfaces of Barnard's star and Teegarden's star. Comparing measurements of the K I line's equivalent width and full width at half maximum in our NICOLE simulations to measurements of the same line in Habitable zone Planet Finder (HPF) spectra of the two stars over multiple years, we find that our models encompassed the range of variation seen in the data. The temporal behavior of these variations matches line width changes across the spectrum, as would be expected with rotationally modulated photospheric magnetic field changes. Our results demonstrate that detailed line profile measurements and modeling the Zeeman effect in near infrared lines are useful for analyzing stellar magnetic variability even for some of the slowest rotating stars. The techniques demonstrated here hold promise for future efforts to separate exoplanet radial velocity signals from noise introduced by magnetic activity of their host stars.
 

Nick Tusay
Title:  A Search for Radio Technosignatures at the Solar Gravitational Lens Targeting Alpha Centauri
Abstract:  Stars provide an enormous gain for interstellar communications at their gravitational focus, perhaps as part of an interstellar network. If the Sun is part of such a network, there should be probes at the gravitational foci of nearby stars. If there are probes within the solar system connected to such a network, we might detect them via transmissions to them from relays at these foci. In our paper, we demonstrate a search across a wide bandwidth for interstellar communication relays beyond the Sun's innermost gravitational focus at 550 AU using the Green Bank Telescope (GBT) and Breakthrough Listen (BL) backend. As a first target, we searched for a relay at the focus of the Alpha Centauri AB system while correcting for the parallax due to Earth's orbit around the Sun. We searched for radio signals directed at the inner solar system from such a source in the L and S bands. Our analysis, utilizing the turboSETI software developed by BL, did not detect any signal indicative of a non-human-made artificial origin. Further analysis was done to exclude false negatives and signals from the nearby target HD 13908. Assuming a conservative gain of 103 in L-band and roughly 4 times that in S-band, a ~1 meter transmitter would be detectable by our search above 7 W at 550 AU or 23 W at 1000 AU in L-band, and above 2 W at 550 AU or 7 W at 1000 AU in S-band. Finally, we discuss the application of this method to other frequencies and targets.

Seminar starts at 12:00 pm and will be held in 538 Davey and virtually via Zoom:  https://psu.zoom.us/j/92637070419