TY - JOUR
T1 - Spitzer Phase Curves of KELT-1b and the Signatures of Nightside Clouds in Thermal Phase Observations
AU - Beatty, Thomas G.
AU - Marley, Mark S.
AU - Gaudi, B. Scott
AU - Colón, Knicole D.
AU - Fortney, Jonathan J.
AU - Showman, Adam
N1 - Publisher Copyright:
© 2019. The American Astronomical Society. All rights reserved..
PY - 2019
Y1 - 2019
N2 - We observed two full orbital phase curves of the transiting brown dwarf KELT-1b, at 3.6 and 4.5 μm, using the Spitzer Space Telescope. Combined with previous eclipse data from Beatty et al., we strongly detect KELT-1b's phase variation as a single sinusoid in both bands, with amplitudes of 964 ± 36 ppm at 3.6 μm and 979 ± 54 ppm at 4.5 μm, and confirm the secondary eclipse depths measured by Beatty et al. We also measure noticeable eastward hotspot offsets of 28.°4 ± 3.°5 at 3.6 μm and 18.°6 ± 5.°2 at 4.5 μm. Both the day-night temperature contrasts and the hotspot offsets we measure are in line with the trends seen in hot Jupiters, though we disagree with the recent suggestion of an offset trend by Zhang et al. Using an ensemble analysis of Spitzer phase curves, we argue that nightside clouds are playing a noticeable role in modulating the thermal emission from these objects, based on: (1) the lack of a clear trend in phase offsets with equilibrium temperature, (2) the sharp day-night transitions required to have non-negative intensity maps, which also resolves the inversion issues raised by Keating & Cowan, (3) the fact that all the nightsides of these objects appear to be at roughly the same temperature of 1000 K, while the dayside temperatures increase linearly with equilibrium temperature, and (4) the trajectories of these objects on a Spitzer color-magnitude diagram, which suggest colors only explainable via nightside clouds.
AB - We observed two full orbital phase curves of the transiting brown dwarf KELT-1b, at 3.6 and 4.5 μm, using the Spitzer Space Telescope. Combined with previous eclipse data from Beatty et al., we strongly detect KELT-1b's phase variation as a single sinusoid in both bands, with amplitudes of 964 ± 36 ppm at 3.6 μm and 979 ± 54 ppm at 4.5 μm, and confirm the secondary eclipse depths measured by Beatty et al. We also measure noticeable eastward hotspot offsets of 28.°4 ± 3.°5 at 3.6 μm and 18.°6 ± 5.°2 at 4.5 μm. Both the day-night temperature contrasts and the hotspot offsets we measure are in line with the trends seen in hot Jupiters, though we disagree with the recent suggestion of an offset trend by Zhang et al. Using an ensemble analysis of Spitzer phase curves, we argue that nightside clouds are playing a noticeable role in modulating the thermal emission from these objects, based on: (1) the lack of a clear trend in phase offsets with equilibrium temperature, (2) the sharp day-night transitions required to have non-negative intensity maps, which also resolves the inversion issues raised by Keating & Cowan, (3) the fact that all the nightsides of these objects appear to be at roughly the same temperature of 1000 K, while the dayside temperatures increase linearly with equilibrium temperature, and (4) the trajectories of these objects on a Spitzer color-magnitude diagram, which suggest colors only explainable via nightside clouds.
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U2 - 10.3847/1538-3881/ab33fc
DO - 10.3847/1538-3881/ab33fc
M3 - Article
AN - SCOPUS:85081229445
SN - 0004-6256
VL - 158
JO - Astronomical Journal
JF - Astronomical Journal
IS - 4
M1 - 166
ER -