Mapping out the time-evolution of exoplanet processes

There are many competing theories and models describing the formation, migration and evolution of exoplanet systems. As both the precision with which we can characterize exoplanets and their host stars, and the number of systems for which we can make such a characterization increase, we begin to see pathways forward for validating these theories. In this white paper we identify predicted, observable correlations that are accessible in the near future, particularly trends in exoplanet populations, radii, orbits and atmospheres with host star age. By compiling a statistically significant sample of well-characterized exoplanets with precisely measured ages, we should be able to begin identifying the dominant processes governing the time-evolution of exoplanet systems.Comment: Astro2020 white pape

Forward and Inverse Modeling of the Emission and Transmission Spectrum of GJ 436b: Investigating Metal Enrichment, Tidal Heating, and Clouds

The Neptune-mass GJ 436b is one of the most-studied transiting exoplanets with repeated measurements of both its thermal emission and transmission spectra. We build on previous studies to answer outstanding questions about this planet, including its potentially high metallicity and tidal heating of its interior. We present new observations of GJ 436b's thermal emission at 3.6 and 4.5 micron, which reduce uncertainties in estimates of GJ 436b's flux at those wavelengths and demonstrate consistency between Spitzer observations spanning more than 7 years. We analyze the Spitzer thermal emission photometry and Hubble WFC3 transmission spectrum in tandem. We use a powerful dual-pronged modeling approach, comparing these data to both self-consistent and retrieval models. We vary the metallicity, intrinsic luminosity from tidal heating, disequilibrium chemistry, and heat redistribution. We also study the effect of clouds and photochemical hazes on the spectra, but do not find strong evidence for either. The self-consistent and retrieval modeling combine to suggest that GJ 436b has a high atmospheric metallicity, with best fits at or above several hundred times solar metallicity, tidal heating warming its interior with best-fit intrinsic effective effective temperatures around 300--350 K, and disequilibrium chemistry. High metal-enrichments (>600x solar) can only occur from the accretion of rocky, rather than icy, material. Assuming Tint~300--350 K, we find that Q'~2x10^5--10^6, larger than Neptune's Q', and implying a long tidal circularization timescale for the planet's orbit. We suggest that Neptune-mass planets may be a more diverse class than previously imagined, with metal-enhancements potentially spanning several orders of magnitude, to perhaps over 1000x solar metallicity. High fidelity observations with instruments like JWST will be critical for characterizing this diversity.Comment: 15 pages, 18 figures. Revised for publication in Ap

Searches for Pair Production of a Heavy Vector-Like Quarks in pp Collisions at s=13 TeV with the ATLAS Detector

A summary of two orthogonal and complementary searches for pair production of heavy vector-like quarks is presented. The first analysis considers final states with 1-lepton and hadronic jets that can be used to reconstruct the vector-like quark system after identifying the boosted decay of W bosons and building the neutrino from the missing transverse momentum. Control and signal regions constrain the uncertainties associated with top quark production that most negatively impact this analysis. The second analysis searches in the fully-hadronic final state where no leptons are considered. An explicit veto on the lepton number ensures orthogonality between the analyses. The analysis uses a deep neural network to reconstruct the decays of heavy objects and a data-driven technique to estimate the dominant multi-jet background. Data were recorded by the ATLAS experiment in sqrt(s)=13 TeV proton-proton collisions delivered by the Large Hadron Collider in 2015 and 2016. No excess above the Standard Model background is observed in either analysis. The results from the 1-lepton analysis are interpreted assuming vector-like quarks decay TT->Wb+X. The 0-lepton analysis assumes both types of pair produced vector-like quarks TT and BB that decay to T->Wb,Ht,Zt and B->Wt,Hb,Zb. The 1-lepton analysis observes a 95% CL lower limit on the T mass of 1090 (810) GeV assuming the scenario BR(T->Wb)=1 (SU(2) singlet). The strongest observed 95% CL lower limits in the 0-lepton analysis are 850 GeV and 903 GeV in the BR(T->Ht)=1 and BR(B->Hb)=1 decays, respectively.PHDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138552/1/demarley_1.pd

Vertical Atmospheric Structure in a Variable Brown Dwarf: Pressure-dependent Phase Shifts in Simultaneous Hubble Space Telescope-Spitzer Light Curves

Heterogeneous clouds or temperature perturbations in rotating brown dwarfs produce variability in the observed flux. We report time-resolved simultaneous observations of the variable T6.5 brown dwarf 2MASSJ22282889-431026 over the wavelength ranges 1.1-1.7 microns and broadband 4.5 microns. Spectroscopic observations were taken with Wide Field Camera 3 on board the Hubble Space Telescope and photometry with the Spitzer Space Telescope. The object shows sinusoidal infrared variability with a period of 1.4 hr at most wavelengths with peak-to-peak amplitudes between 1.45% and 5.3% of the mean flux. While the light curve shapes are similar at all wavelengths, their phases differ from wavelength to wavelength with a maximum difference of more than half of a rotational period. We compare the spectra with atmospheric models of different cloud prescriptions, from which we determine the pressure levels probed at different wavelengths. We find that the phase lag increases with decreasing pressure level, or higher altitude. We discuss a number of plausible scenarios that could cause this trend of light curve phase with probed pressure level. These observations are the first to probe heterogeneity in an ultracool atmosphere in both horizontal and vertical directions, and thus are an ideal test case for realistic three dimensional simulations of the atmospheric structure with clouds in brown dwarfs and extrasolar planets.Comment: Accepted to ApJL, 6 pages, 3 figures. Minor language updates from v1 to match published versio