the end , we saw a faint trace after our first two-hour observation block , and two months later , we had a reasonable spectrum ( Figures 1 and 2 ).
This observation could not have been done anywhere else . The combination of Gemini ’ s low-emissivity silver primary coating , queue-mode scheduling ( that provided two hours per night over 14 nights ), dry Maunakea weather , and a fantastic observing staff were all necessary to obtain such a faint spectrum . Before our Gemini observation , there had never been an M-band spectrum of a brown dwarf or extrasolar planet colder than 700 K .
As theoretical work suggested , WISE 0855 should have a spectrum dominated by water vapor . When we fit the Wise 0855 data to our initial cloud-free model , all of the wiggles in the spectrum were indeed the result of water vapor but their signature appeared more muted . Borrowing a wellestablished technique from our friends who study Jupiter , we inserted an optically thick water cloud deep in the photosphere of our model atmosphere , to see if it would produce the muting seen in our spectrum . The cloudy model fit significantly better than the cloud-free … one ( Figure 3 , upper left ). However , water clouds are notoriously difficult to model . WISE 0855 is just our first chance to apply these models to an extrasolar object .
Measuring Up
By far the closest analog to WISE 0855 is Jupiter , which has a temperature of ~ 130 K . We compared our WISE 0855 spectrum to one of Jupiter ’ s and noticed striking similarities from 4.8-5.15 microns ( Figure 3 , upper right ), wherewhere water vapor absorption features dominate both objects . Shortward of 4.8 microns , the spectra diverge . Jupiter shows phosphine absorption , while WISE 0855 does not ( Figure 3 , lower left ).
Figure 3 . Upper Left : Water cloud models fit better than cloud-free models . Upper Right : WISE 0855 looks strikingly similar to Jupiter from 4.8-5.15 microns . Shortward of 4.8 microns , the spectra diverge as Jupiter is dominated by phosphine , while WISE 0855 is dominated by water vapor . Lower Left : Our WISE 0855 spectrum is sensitive to a Jupiter abundance of phosphine , but none is seen . Lower Right : Our WISE 0855 spectrum is marginally sensitive to deuterated methane , but the feature is blended with water vapor features that are not well understood .
January 2017 | 2016 Year in Review GeminiFocus
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