Mapping Clouds on a Variable Planetary-Mass Companion
Abstract
Time-series observations of rotational modulations in brown dwarfs and planetary-mass companions are a powerful tool to characterize ultra-cool atmospheres. In particular, the chromatic variations in variability amplitudes place strong constraints on the properties of heterogeneous clouds, and the temporal evolution of the lightcurve directly probes the physical processes that drive atmospheric circulation. We recently discovered that a planetary-mass companion has a J-band variability of more than 22%. This is so far the largest variability amplitude discovered for a PMC and offers the best opportunity for a detailed characterization of an ultra-cool, very low surface gravity atmosphere. We propose fifteen orbits HST/WFC3/IR G141 time-series observations of this companion. We have developed a seven-visit strategy to establish a time baseline of ~60 hrs, which will continuously monitor our target for two rotation periods. These spectrally-resolved rotational modulated variability measurements will provide a measure to distinguish and characterize multiple aspects of atmospheric heterogeneity. This precise light curve will determine this object's circulation patterns. This object will also be monitored by Spitzer at 4.5-micron band in the near future through a compleetary program. This proposal and the Spitzer observations together will determine this object's mid- to long-term atmospheric evolution. Importantly, this object is also a JWST ERS program target which will result in a high-quality 2 to 28 micron JWST spectrum. The atmospheric structures and their temporal evolution revealed in these observations will provide crucial context for interpreting its JWST spectrum.
- Publication:
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HST Proposal
- Pub Date:
- October 2019
- Bibcode:
- 2019hst..prop16036Z