GJ 229B was the first T dwarf to be discovered in 1995, and its spectrum has been more thoroughly... more GJ 229B was the first T dwarf to be discovered in 1995, and its spectrum has been more thoroughly observed than that of most other brown dwarfs. Yet a full spectroscopic analysis of its atmosphere has not been done with modern techniques. This spectrum has several peculiar features, and recent dynamical estimates of GJ 229B’s mass and orbit have disagreed widely, both of which warrant closer investigation. With a separation of tens of astronomical units from its host star, GJ 229B falls near the border of the planet and stellar population formation regimes, so its atmosphere could provide clues to formation processes for intermediate objects of this type. In an effort to resolve these questions, we performed retrievals on published spectra of GJ 229B over a wide range of wavelengths (0.5–5.1 μm) using the open-source APOLLO code. Based on these retrievals, we present a more precise mass estimate of 41.6 ± 3.3 M J and an effective temperature estimate of 869 − 7 + 5 K, which are more...
We present retrieved atmospheric properties for the very low mass companion, HD 106906b, which is... more We present retrieved atmospheric properties for the very low mass companion, HD 106906b, which is spatially resolved from its host star, using APOLLO, a spectral retrieval code designed for flexibility of atmosphere models. APOLLO allows retrieval on both transit and emission spectra of planets to determine molecular abundances as well as comparison of different parameterizations of the thermal structure and cloud properties. We compare fits of our models to high signal-to-noise spectra of HD 106906b, a 10-20 Jupiter mass early L-type companion orbiting a 10-15 Myr old binary system at 730 AU projected separation, obtained with SINFONI on the ESO VLT (Daemgen et al. 2017). Using these models, we measure molecular abundances and present constraints on cloud properties. Comparing the retrieved abundances of volatile species (e.g. C/O) to those of the host star, we can speculate on whether this object may have formed much closer to its host star through a core accretion-like mechanism ...
We present new calculations of transit spectra of super-Earths that allow for atmospheres with ar... more We present new calculations of transit spectra of super-Earths that allow for atmospheres with arbitrary proportions of common molecular species and haze. We test this method with generic spectra, reproducing the expected systematics and absorption features, then apply it to the nearby super-Earth GJ 1214b, which has produced conflicting observational data, leaving the questions of a hydrogen-rich versus hydrogen-poor atmosphere and the water content of the atmosphere ambiguous. We present representative transit spectra for a range of classes of atmosphere models for GJ 1214b. Our analysis supports a hydrogen-rich atmosphere with a cloud or haze layer, although a hydrogen-poor model with .10% water is not ruled out. Several classes of models are ruled out, however, including hydrogen-rich atmospheres with no haze, hydrogen-rich atmospheres with a haze of ∼0.01-micron tholin particles, and hydrogen-poor atmospheres with major sources of absorption other than water. We propose an obse...
GJ 229B was the first T dwarf to be discovered in 1995, and its spectrum has been more thoroughly... more GJ 229B was the first T dwarf to be discovered in 1995, and its spectrum has been more thoroughly observed than that of most other brown dwarfs. Yet a full spectroscopic analysis of its atmosphere has not been done with modern techniques. This spectrum has several peculiar features, and recent dynamical estimates of GJ 229B’s mass and orbit have disagreed widely, both of which warrant closer investigation. With a separation of tens of astronomical units from its host star, GJ 229B falls near the border of the planet and stellar population formation regimes, so its atmosphere could provide clues to formation processes for intermediate objects of this type. In an effort to resolve these questions, we performed retrievals on published spectra of GJ 229B over a wide range of wavelengths (0.5–5.1 μm) using the open-source APOLLO code. Based on these retrievals, we present a more precise mass estimate of 41.6 ± 3.3 M J and an effective temperature estimate of 869 − 7 + 5 K, which are more...
We present retrieved atmospheric properties for the very low mass companion, HD 106906b, which is... more We present retrieved atmospheric properties for the very low mass companion, HD 106906b, which is spatially resolved from its host star, using APOLLO, a spectral retrieval code designed for flexibility of atmosphere models. APOLLO allows retrieval on both transit and emission spectra of planets to determine molecular abundances as well as comparison of different parameterizations of the thermal structure and cloud properties. We compare fits of our models to high signal-to-noise spectra of HD 106906b, a 10-20 Jupiter mass early L-type companion orbiting a 10-15 Myr old binary system at 730 AU projected separation, obtained with SINFONI on the ESO VLT (Daemgen et al. 2017). Using these models, we measure molecular abundances and present constraints on cloud properties. Comparing the retrieved abundances of volatile species (e.g. C/O) to those of the host star, we can speculate on whether this object may have formed much closer to its host star through a core accretion-like mechanism ...
We present new calculations of transit spectra of super-Earths that allow for atmospheres with ar... more We present new calculations of transit spectra of super-Earths that allow for atmospheres with arbitrary proportions of common molecular species and haze. We test this method with generic spectra, reproducing the expected systematics and absorption features, then apply it to the nearby super-Earth GJ 1214b, which has produced conflicting observational data, leaving the questions of a hydrogen-rich versus hydrogen-poor atmosphere and the water content of the atmosphere ambiguous. We present representative transit spectra for a range of classes of atmosphere models for GJ 1214b. Our analysis supports a hydrogen-rich atmosphere with a cloud or haze layer, although a hydrogen-poor model with .10% water is not ruled out. Several classes of models are ruled out, however, including hydrogen-rich atmospheres with no haze, hydrogen-rich atmospheres with a haze of ∼0.01-micron tholin particles, and hydrogen-poor atmospheres with major sources of absorption other than water. We propose an obse...
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