Detecting Water In the atmosphere of HR 8799 c with L-band High Dispersion Spectroscopy Aided By Adaptive Optics

Reducing L-band raw data (left) into rectified 2-d spectra (right). On the left side of the detector, the noise pattern is repeated every 8th row. In raw data, the height of each order is 130 pixels on the left side and 120 pixels on the right side. The spectral trace of HR 8799 is clearly visible along with sky emission lines. In contrast, the spectral trace of HR 8799 c is buried in noise and thus not visible from either raw data or reduced 2-d spectra. The grey box indicates the region used for subsequent data analyses.

High dispersion spectroscopy of brown dwarfs and exoplanets enables exciting science cases, e.g., mapping surface inhomogeneity and measuring spin rate.

Here, we present L band observations of HR 8799 c using Keck NIRSPEC (R=15,000) in adaptive optics (AO) mode (NIRSPAO). We search for molecular species (H2O and CH4) in the atmosphere of HR 8799 c with a template matching method, which involves cross correlation between reduced spec- trum and a template spectrum. We detect H2O but not CH4, which suggests disequilibrium chemistry in the atmosphere of HR 8799 c, and this is consistent with previous findings. We conduct planet signal injection simulations to estimate the sensitivity of our AO-aided high dispersion spectroscopy observations. We conclude that 10−4 contrast can be reached in L band. The sensitivity is mainly limited by the accuracy of line list used in modeling spectra and detector noise. The latter will be alleviated by the NIRSPEC upgrade.

Ji Wang, Dimitri Mawet Jonathan J. Fortney, Callie Hood, Caroline V. Morley, Bjorn Benneke
(Submitted on 24 Sep 2018)

Comments: 14 pages, 5 figures, 5 tables, accepted for publication on AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:1809.09080 [astro-ph.EP] (or arXiv:1809.09080v1 [astro-ph.EP] for this version)
Submission history
From: Ji Wang
[v1] Mon, 24 Sep 2018 17:48:14 GMT (3965kb,D)
https://arxiv.org/abs/1809.09080
Astrobiology

Please follow Astrobiology on Twitter.


  • submit to reddit