ORCID Profile
0000-0002-9807-5435
Current Organisation
University of California, San Diego
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Publisher: American Astronomical Society
Date: 02-08-2023
Abstract: The carbon-to-oxygen (C/O) ratio in an exoplanet atmosphere has been suggested as a potential diagnostic of planet formation. Now that a number of exoplanets have measured C/O ratios, it is possible to examine this diagnostic at a population level. Here, we present an analysis of currently measured C/O ratios of directly imaged and transit/eclipse planets. First, we derive atmospheric parameters for the substellar companion HD 284149 AB b using data taken with the OSIRIS integral field spectrograph at the W.M. Keck Observatory and report two non-detections from our ongoing imaging spectroscopy survey with Keck/OSIRIS. We find an effective temperature of T eff = 2502 K, with a range of 2291–2624 K, log g = 4.52 , with a range of 4.38–4.91, and [M/H] = 0.37, with a range of 0.10–0.55. We derive a C/O of 0.59 − 0.30 + 0.15 for HD 284149 AB b. We add this measurement to the list of C/O ratios for directly imaged planets and compare them with those from a s le of transit/eclipse planets. We also derive the first dynamical mass estimate for HD 284149 AB b, finding a mass of ∼28 M Jup . There is a trend in C/O ratio with companion mass ( M Jup ), with a break seen around 4 M Jup . We run a Kolmogorov–Smirnov and an Anderson–Darling test on planets above and below this mass boundary, and find that they are two distinct populations. This could be additional evidence of two distinct populations possibly having two different formation pathways, with companion mass as an indicator of most likely formation scenario.
Publisher: American Astronomical Society
Date: 02-2022
Abstract: The kinematics and dynamics of stellar and substellar populations within young, still-forming clusters provide valuable information for constraining theories of formation mechanisms. Using Keck II NIRSPEC+AO data, we have measured radial velocities for 56 low-mass sources within 4′ of the core of the Orion Nebula Cluster (ONC). We also remeasure radial velocities for 172 sources observed with SDSS/APOGEE. These data are combined with proper motions measured using HST ACS/WFPC2/WFC3IR and Keck II NIRC2, creating a s le of 135 sources with all three velocity components. The velocities measured are consistent with a normal distribution in all three components. We measure intrinsic velocity dispersions of ( σ v α , σ v δ , σ v r ) = (1.64 ± 0.12, 2.03 ± 0.13, 2.56 − 0.17 + 0.16 ) km s −1 . Our computed intrinsic velocity dispersion profiles are consistent with the dynamical equilibrium models from Da Rio et al. (2014) in the tangential direction but not in the line-of-sight direction, possibly indicating that the core of the ONC is not yet virialized, and may require a nonspherical potential to explain the observed velocity dispersion profiles. We also observe a slight elongation along the north–south direction following the filament, which has been well studied in previous literature, and an elongation in the line-of-sight to tangential velocity direction. These 3D kinematics will help in the development of realistic models of the formation and early evolution of massive clusters.
Publisher: Oxford University Press (OUP)
Date: 30-05-2022
Abstract: We present the discovery of TOI-2136 b, a sub-Neptune planet transiting a nearby M4.5V-type star every 7.85 d, identified through photometric measurements from the Transiting Exoplanet Survey Satellite (TESS) mission. The host star is located 33 pc away with a radius of R* = 0.34 ± 0.02 R⊙, a mass of $0.34\\pm 0.02 \\, \\mathrm{M}_{\\odot }$, and an effective temperature of 3342 ± 100 K. We estimate its stellar rotation period to be 75 ± 5 d based on archival long-term photometry. We confirm and characterize the planet based on a series of ground-based multiwavelength photometry, high-angular-resolution imaging observations, and precise radial velocities from Canada–France–Hawaii Telescope (CFHT)/SpectroPolarimètre InfraROUge (SPIRou). Our joint analysis reveals that the planet has a radius of 2.20 ± 0.17 R⊕ and a mass of 6.4 ± 2.4 M⊕. The mass and radius of TOI-2136 b are consistent with a broad range of compositions, from water-ice to gas-dominated worlds. TOI-2136 b falls close to the radius valley for M dwarfs predicted by thermally driven atmospheric mass-loss models, making it an interesting target for future studies of its interior structure and atmospheric properties.
Publisher: American Astronomical Society
Date: 11-02-2019
Location: United States of America
No related grants have been discovered for Christopher Theissen.