February 16, 2024

Talk announcement by Fuda Nguyen and Garrett Levine

The ExoExplorer Science Series presents talks by cohort members Fuda Nguyen (U. Arizona) & Garrett Levine (Yale) on February 16, 2024, from 11 AM - 12 PM Pacific Standard / 2 PM - 3 PM Eastern Standard. Connection information is below.

Speaker: Fuda Nguyen (U. Arizona)

Title: Latitude-dependent Atmospheric Waves and Long-period Modulations in Luhman 16 B from the Longest Lightcurve of an Extrasolar World

Abstract: We present the longest photometric monitoring of up to 1200-hours of the brown-dwarf binaries Luhman 16AB, documenting ±5% variability with periods under 10-hours. We show that short-period rotational modulation around 5-hour (k=1) and 2.5-hour (k=2) dominate the variability, where the planetary-scale waves model of k=1 and k=2 waves fit the lightcurve extremely well. We explain the difference in the narrowed range of k=2 periods compared to k=1 periods using models of zonal banding in Solar System giants (Jupiter and Saturn) and suggest that this difference arises from higher wind speed distribution at low latitudes compared to mid-to-high latitudes. Lastly, we show that Luhman 16 AB exhibits long-period ±5% variability with periods up to 100-hour - potentially coming from polar regions in the atmospheres? Our results are consistent with past GCMs, demonstrating that zonal-banding, latitude-dependent waves, and slowly varying atmospheric features could be present in Luhman 16 AB.

Speaker: Garrett Levine (Yale)

Title: Atmospheric Outflow Variability of Extrasolar Planets

Abstract: XUV-driven photoevaporation is a leading hypothesis on the astrophysical processes that sculpt the observed distribution of short-period planetary radii. In recent years, direct evidence of atmospheric escape has been detected via in-transit transmission of the metastable He triplet near 10830 Å. Dozens of planets have been probed with this tracer, mostly as single-epoch snapshots. Since the stellar XUV that underlies planetary mass-loss is time-variable, it is necessary to understand the outflows’ responses to changes in the incident flux. Here, we report results from an ongoing longitudinal study to characterize the time-variability of WASP-69b’s atmospheric outflow. In August and September 2023, we obtained contemporaneous metastable He data from Palomar/WIRC along with X-ray and mid-UV data from the Swift Observatory. Together, these data lead to a comprehensive characterization of WASP-69b’s hydrodynamical state in the epoch of observation. By comparison to archival metastable He data and archival high-energy data from XMM-Newton, we assess the time variability of WASP-69b’s mass-loss rate on timescales commensurate with typical stellar activity cycles.

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