ExoExplorers

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.

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.

Abstract: The present-day orbital architecture of planetary systems is a fossil record of the system's formation history. While transit surveys have provided us with numerous planetary systems, it is unable to determine the mass of a planet, its orbital eccentricity, and whether the system harbors planets with inclinations large enough to preclude them from transiting. Where the transit method falls short, radial velocity follow-up demonstrates its strength. In this presentation, I will share the system architectures revealed by the TESS-Keck Survey: a significant radial velocity follow-up effort aimed at measuring the masses and orbital properties of 86 TESS Objects of Interest. My work represents the largest uniform analysis of TESS-discovered planets to date, resulting in mass and orbital constraints for 127 planets. This includes 12 non-transiting companions and precise constraints on orbital eccentricity, which are crucial for accurate dynamical modeling of these systems. Additionally, I will highlight the importance of complimenting primary survey instruments, such as Keck/HIRES, with instruments of comparatively lower precision. This synergy leads to fuller phase space coverage, resulting in more precise measurements of critical orbital parameters, such as eccentricity.The present-day orbital architecture of planetary systems is a fossil record of the system's formation history. While transit surveys have provided us with numerous planetary systems, it is unable to determine the mass of a planet, its orbital eccentricity, and whether the system harbors planets with inclinations large enough to preclude them from transiting. Where the transit method falls short, radial velocity follow-up demonstrates its strength.

Abstract: The last decade of exoplanet exploration has a population of 1-3 RE short-period planets, with peaks in the population at sub-Neptune and super-Earth radii, and a “radius valley” in between. Based on bulk composition alone, the nature of these planets has remained elusive, but atmospheric observations offer a new window to explore their compositional diversity. The JWST COMPASS survey (Compositions of Mini-Planet Atmospheres for Statistical Study) will obtain transmission spectra of 11 such planets using JWST NIRSpec/G395H, building a critical link between atmospheric characterisation and planetary demographics. In this talk, I will present results from the first multi-planet system observed by the COMPASS program, with the 2.8–5.2μm transmission spectrum of the ~870K, 1.7RE super-Earth TOI-836b. We find that transmission spectra from two visits are consistent with one another, and that by combining both visits, we can narrow in on the potential metallicity and cloud properties of the planet. I will also compare TOI-836b to its exterior sibling planet, the sub-Neptune TOI-836c, and the wider implications for this radius valley straddling system. This work provides insight into planning future observations of high metallicity planets around bright host stars, given the noise properties of our data.