Confirmation of water emission in the dayside spectrum of the ultrahot Jupiter WASP-121b
Abstract
We present four new secondary eclipse observations for the ultrahot Jupiter WASP-121b acquired using the Hubble Space Telescope Wide Field Camera 3. The eclipse depth is measured to a median precision of 60 ppm across 28 spectroscopic channels spanning the 1.12- $1.64\, \mu {\rm m}$ wavelength range. This is a considerable improvement to the 90 ppm precision we achieved previously for a single eclipse observation using the same observing set-up. Combining these data with those reported at other wavelengths, a blackbody spectrum for WASP-121b is ruled out at >6σ confidence and we confirm the interpretation of previous retrieval analyses that found the data are best explained by a dayside thermal inversion. The updated spectrum clearly resolves the water emission band at 1.3- $1.6\, \mu {\rm m}$ , with higher signal-to-noise than before. It also fails to reproduce a bump in the spectrum at $1.25\, \mu {\rm m}$ derived from the first eclipse observation, which had tentatively been attributed to VO emission. We conclude that the latter was either a statistical fluctuation or a systematic artefact specific to the first eclipse data set.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- August 2020
- DOI:
- 10.1093/mnras/staa1628
- arXiv:
- arXiv:2005.09631
- Bibcode:
- 2020MNRAS.496.1638M
- Keywords:
-
- techniques: spectroscopic;
- planets and satellites: atmospheres;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- Accepted in MNRAS