60 research outputs found
Rotational Spectral Unmixing of Exoplanets: Degeneracies between Surface Colors and Geography
Unmixing the disk-integrated spectra of exoplanets provides hints about
heterogeneous surfaces that we cannot directly resolve in the foreseeable
future. It is particularly important for terrestrial planets with diverse
surface compositions like Earth. Although previous work on unmixing the spectra
of Earth from disk-integrated multi-band light curves appeared successful, we
point out a mathematical degeneracy between the surface colors and their
spatial distributions. Nevertheless, useful constraints on the spectral shape
of individual surface types may be obtained from the premise that albedo is
everywhere between 0 and 1. We demonstrate the degeneracy and the possible
constraints using both mock data based on a toy model of Earth, as well as real
observations of Earth. Despite the severe degeneracy, we are still able to
recover an approximate albedo spectrum for an ocean. In general, we find that
surfaces are easier to identify when they cover a large fraction of the planet
and when their spectra approach zero or unity in certain bands.Comment: 11 pages, 7 figures, published in AJ. Minor text updates from
previous versio
STARRY: Analytic Occultation Light Curves
We derive analytic, closed form, numerically stable solutions for the total
flux received from a spherical planet, moon or star during an occultation if
the specific intensity map of the body is expressed as a sum of spherical
harmonics. Our expressions are valid to arbitrary degree and may be computed
recursively for speed. The formalism we develop here applies to the computation
of stellar transit light curves, planetary secondary eclipse light curves, and
planet-planet/planet-moon occultation light curves, as well as thermal
(rotational) phase curves. In this paper we also introduce STARRY, an
open-source package written in C++ and wrapped in Python that computes these
light curves. The algorithm in STARRY is six orders of magnitude faster than
direct numerical integration and several orders of magnitude more precise.
STARRY also computes analytic derivatives of the light curves with respect to
all input parameters for use in gradient-based optimization and inference, such
as Hamiltonian Monte Carlo (HMC), allowing users to quickly and efficiently fit
observed light curves to infer properties of a celestial body's surface map.Comment: 55 pages, 20 figures. Accepted to the Astronomical Journal. Check out
the code at https://github.com/rodluger/starr
Surface pressure impact on nitrogen-dominated USP super-Earth atmospheres
In this paper, we compare the chemistry and the emission spectra of
nitrogen-dominated cool, warm, and hot ultra-short-period (USP) super-Earth
atmospheres in and out of chemical equilibrium at various surface pressure
scenarios ranging from 0.1 to 10 bar. We link the one-dimensional VULCAN
chemical kinetic code, in which thermochemical kinetic and vertical transport
and photochemistry are taken into account, to the one-dimensional radiative
transfer model, PETITRADTRANS, to predict the emission spectra of these
planets. The radiative-convective temperature-pressure profiles were computed
with the HELIOS code. Then, using PANDEXO noise simulator, we explore the
observability of the differences produced by disequilibrium processes with the
JWST. Our grids show how different surface pressures can significantly affect
the temperature profiles, the atmospheric abundances, and consequently the
emission spectra of these planets. We find that the divergences due to
disequilibrium processes would be possible to observe in cooler planets by
targeting HCN, C2H4, and CO, and in warmer planets by targeting CH4 with HCN,
using the NIRSpec and MIRI LRS JWST instruments. These species are also found
to be sensitive indicators of the existence of surfaces on nitrogen-dominated
USP super-Earths, providing information regarding the thickness of these
atmospheres.Comment: 12 page
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