About

Ian Weaver, Ph.D.

Hi, I'm Ian, a recent PhD from the Center for Astrophysics | Harvard & Smithsonian. I focused on studying large exoplanets with large telescopes and writing software to analyze them. I worked on all stages of the process, including extraction and reduction of the raw time series spectral data, detrending of potential signals via different Gaussian Process (GP) and Principal Component Analysis (PCA) techniques, and the applications of a range of statistical Bayesian inference frameworks including Markov chain Monte Carlo (MCMC) and nested sampling to study the atmospheres of these other worlds.

In my free time, I love rowing, participating in STEM outreach in underrepresented communities, and learning more about Julia with other folks!

Resume: | CV: | NASA ADS:

Projects

Exoplanets

Data wrangling/visualization of publicly available exoplanet data, with Julia and Pluto.jl.

Exoplanet locator
A groovy exoplanet sky chart created with data queried from the exoplanet archive, bright star locations from the Hipparcos, Yale Bright Star, Gliese (HYG) database, and asterisms from the Stellarium public repo.
A groovy exoplanet sky chart created with data queried from the exoplanet archive, bright star locations from the Hipparcos, Yale Bright Star, Gliese (HYG) database, and asterisms from the Stellarium public repo.

System parameters calculator
Self-consistent computations of exoplanet parameters from stellar and orbital observations. Useful for
    estimating the potential observability of an exoplanet's atmopshere.
Self-consistent computations of exoplanet parameters from stellar and orbital observations. Useful for estimating the potential observability of an exoplanet's atmopshere.

spacejam

Python package for numerical integration, powered by automatic differentiation.

Orbital trajectories

Integrated orbit of a hypothetical three-body star-planet-moon system via s=2 Adams-Moulton method. This is motivated by the first potential discovery of an exomoon made not too long ago.

Population dynamics

The same integration method applied to the Lotka–Volterra system of differential equations describing population growth.


Accretion stream toy model

Orbital dynamics code written in Fortran, visualized in Python.

Artificial energy loss
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Particle stream trajectory in a binary Roche Potential with artificial energy loss every time step to mimic the energy that is lost to shocks and other collisions in real fluid interactions. This was done by having the test particle lose energy while maintaining its angular momentum. I also added a little kick in the z component of the particle's initial velocity to make it a little more fun to watch.

WASP-12/b system
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Top-down view of the same code applied to WASP-12/b (to scale). I waited until a full orbit to turn on the artificial energy loss to mimic one full lap of the accretion stream before colliding with itself. The corners due to the Coriolis force are clearly seen and the orbit settles down into its circularization radius (in green), as predicted from angular momentum conservation.


Accretion disk fluid simulations

Hydrodynamical simulations of planetary cannibalism made with FLASH.

WASP-12/b 2D

An analog to the toy-model from the particle trajectory code above. I replaced the massless test particle in that code with a fluid outflow boundary, following properties adopted from Lai et al. (2010). I then added an artificial ramp up in density at around the 5 day mark to effectively fast-forward the disk to a more evolved state.

WASP-12/b 3D
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I adapted the hydro simulation to 3D to create the image above. This is an isodensity contour plot taken partway through the simulation. The location of L1 can be seen as the orange-yellow sphere towards the bottom left. These simulations were used to create virtual light curves to compare with observations from HST's Cosmic Origins Spectrograph.

Research

WASP-50b (Weaver et al. submitted)

We present a new ground-based visual transmission spectrum of the hot Jupiter WASP-43b, obtained as part of ACCESS. We collected four transits observed between 2015 and 2018, with a combined wavelength coverage between 5300 and 9000 Å and an average photometric precision of 708 ppm in 230 Å bins. We perform an atmospheric retrieval of our transmission spectrum combined with literature Hubble Space Telescope/WFC3 observations to search for the presence of clouds/hazes as well as Na, K, Hα, and H₂O planetary absorption and stellar spot contamination. We do not detect a statistically significant presence of Na I or K I alkali lines, or Hα in the atmosphere of WASP-43b. We find that the observed transmission spectrum can be best explained by a combination of heterogeneities on the photosphere of the host star and a clear planetary atmosphere with water.

HAT-P-23b (Weaver et al. 2021)

We present a new <b>ground-based visible transmission spectrum</b> of the <b>high-gravity, hot
    Jupiter</b> HAT-P-23b, obtained as part of the <b>ACCESS</b> project. We derive the spectrum from five transits
    observed between 2016 and 2018, with combined wavelength coverage between 5200 Å - 9269 Å in 200 Å bins, and with a
    median precision of 247 ppm per bin. HAT-P-23b's relatively high surface gravity (g ~ 30 m/s²), combined with
    updated stellar and planetary parameters from Gaia DR2, gives a 5-scale-height signal of 384 ppm for a
    hydrogen-dominated atmosphere. Bayesian models favor a <b>clear atmosphere for the planet with the tentative
    presence of TiO</b>, after simultaneously modeling stellar contamination, using spots parameter constraints from
    photometry. <b>If confirmed, HAT-P-23b would be the first example of a high-gravity gas giant with a clear
    atmosphere observed in transmission at optical/NIR wavelengths</b>; therefore, we recommend expanding observations
    to the UV and IR to confirm our results and further characterize this planet. This result demonstrates how combining
    transmission spectroscopy of exoplanet atmospheres with long-term photometric monitoring of the host stars can help
    disentangle the exoplanet and <b>stellar activity signals</b>.
We present a new ground-based visible transmission spectrum of the high-gravity, hot Jupiter HAT-P-23b, obtained as part of the ACCESS project. We derive the spectrum from five transits observed between 2016 and 2018, with combined wavelength coverage between 5200 Å - 9269 Å in 200 Å bins, and with a median precision of 247 ppm per bin. HAT-P-23b's relatively high surface gravity (g ~ 30 m/s²), combined with updated stellar and planetary parameters from Gaia DR2, gives a 5-scale-height signal of 384 ppm for a hydrogen-dominated atmosphere. Bayesian models favor a clear atmosphere for the planet with the tentative presence of TiO, after simultaneously modeling stellar contamination, using spots parameter constraints from photometry. If confirmed, HAT-P-23b would be the first example of a high-gravity gas giant with a clear atmosphere observed in transmission at optical/NIR wavelengths; therefore, we recommend expanding observations to the UV and IR to confirm our results and further characterize this planet. This result demonstrates how combining transmission spectroscopy of exoplanet atmospheres with long-term photometric monitoring of the host stars can help disentangle the exoplanet and stellar activity signals.

WASP-43b (Weaver et al. 2020)

We present a new <b>ground-based visual transmission spectrum</b> of the hot Jupiter WASP-43b, obtained as
    part of <b>ACCESS</b>. We collected four transits observed between 2015 and 2018, with a combined wavelength coverage
    between 5300 and 9000 Å and an average photometric precision of 708 ppm in 230 Å bins. We perform an <b>atmospheric
    retrieval</b> of our transmission spectrum combined with literature Hubble Space Telescope/WFC3 observations to search
    for the presence of clouds/hazes as well as Na, K, Hα, and H₂O planetary absorption and stellar spot contamination.
    <b>We do not detect a statistically significant presence of Na I or K I alkali lines, or Hα in the atmosphere of
    WASP-43b</b>. We find that the observed transmission spectrum can be best explained by a combination of
    heterogeneities on the photosphere of the host star and a <b>clear planetary atmosphere</b> with water.
We present a new ground-based visual transmission spectrum of the hot Jupiter WASP-43b, obtained as part of ACCESS. We collected four transits observed between 2015 and 2018, with a combined wavelength coverage between 5300 and 9000 Å and an average photometric precision of 708 ppm in 230 Å bins. We perform an atmospheric retrieval of our transmission spectrum combined with literature Hubble Space Telescope/WFC3 observations to search for the presence of clouds/hazes as well as Na, K, Hα, and H₂O planetary absorption and stellar spot contamination. We do not detect a statistically significant presence of Na I or K I alkali lines, or Hα in the atmosphere of WASP-43b. We find that the observed transmission spectrum can be best explained by a combination of heterogeneities on the photosphere of the host star and a clear planetary atmosphere with water.
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