Characterizing a new prototype Saturn-mass exoplanet with the clearest atmosphere yet

0 Assigned ID: 1663 ----- Attempting Submission 1 (Tue Mar 20 21:19:24 GMT 2018) ----- Dear Colleagues, Here is the updated version of my phase II, following your recommendations for reducing the scan rates and scan lengths. I have chosen not to change the phase windows and clarify this in a separate e-mail with a plot. Thanks so much for your help! Best wishes, Nikolay 284974165 ----- Attempting Submission 1 (Thu May 31 08:38:20 GMT 2018) ----- ----- Attempting Submission 2 (Sun Aug 12 22:06:29 GMT 2018) ----- Characterizing a new prototype Saturn-mass exoplanet with the clearest atmosphere yet Rarely in astrophysics does one have the chance to characterize an exoplanet atmosphere free of clouds. Transmission spectra of such exoplanets are the only way to constrain elemental abundances (e.g. Na, K, and water) and metallicity objectively, as clouds and hazes obscure the amplitudes of absorption features. Cloud-free exoplanet atmospheres are therefore of very high value for the field. Our team has recently published the optical transmission spectrum of the hot Saturn WASP-96b (~1300K) obtained with VLT FORS2. Unlike the optical transmission spectrum of any other hot-Jupiter observed to date, the spectrum of WASP-96b shows very clear pressure-broadened wings of the sodium line, evidence of potassium and a near-UV Rayleigh scattering slope; the latter defining the hydrogen continuum level and proving the planet has a clear atmosphere at the limb. The clear atmosphere of WASP-96b rivals the top three currently known such planets: WASP-39b, HD209458b and WASP-17b, each of which show narrow absorption features and non-negligible haze in their optical spectra. We propose to use WFC3+G102 and WFC3+G142 to measure the near-infrared transmission spectrum of WASP-96b, which will allow us to retrieve precise absolute water and metallicity abundance constraints. Even today, few such constraints exist with well-measured Na and water abundances. The spectrum of WASP-96b can become a standard benchmark for the theory of irradiated gas-giants and an outstanding target for abundance measurements with the James Webb Space Telescope. Our WFC3 observations will provide infrared transmission spectrum for the 'hot Saturn' exoplanet WASP-96b, covering the wavelength range from 0.9 to 1.6 microns. **Observing strategy: To measure the planet's transmission spectrum we will observe one transit of WASP-96b with WFC3 G102 and one transit with WFC3 G141. Each of the observations will be made in slitless spectroscopic mode. Our observing setup is very similar to that used in previous successful programs, such as Prog 15135, 14468 (PI Evans; G102 secondary eclipses and G141 primary transit of WASP-121b), Prog 14767 (PI Sing; G141 secondary eclipse of WASP-121b ), and Prog 13467 (PI Bean; G102 transits for WASP-12b). Each visit starts with a standard phase-constrained acquisition image. Then each visit continues with repeated exposures covering the transit plus time before and after the transit to establish the out-of-transit baseline flux. We provide similar phase constrains of the acquisition image of each visit. These observations use the forward spatial scanning mode with rates optimised for the individual grisms. Table 1 lists the scan rates, sequences, NSAMP and the resulting exposure times and scan lengths. Table 1 ............................................................................................................................................... .Grism......Scan.rate.........SPARS........NSAMP........Exp.time........Scan.length......N.rows.......... ..................arcsec/sec..................................................sec.................arcsec.............px......... ............................................................................................................................................... .G102...........0.013...............25...............9..................179..................2.33................47........... .G141...........0.022...............25...............8..................156..................3.45................69........... ............................................................................................................................................... We will read out a subarray size of 256 pixels to reduce overheads. We apply no offsets to the position of the spectra on the detector, because there is enough space above and below the scan to estimate the background flux. The transit of WASP-96b lasts for 146 minutes. We therefore require 5 consecutive HST orbits for each visit. The first orbit serves to allow the telescope to thermally relax into its new pointing position and for the detector charge-traps to fill, which is a standard procedure adopted by all HST WFC3 transiting exoplanet observations. The remaining orbits will provide good phase coverage during the transit, and allow for sufficient time (2 HST orbits - one before transit, one after transit) to establish the baseline stellar flux necessary to accurately measure the transit depth. We will obtain 11 science exposures per HST orbit, coming to a total of 16 in-transit and 28 out-of-transit science exposures per visit. We choose not to use bi-directional spatial scanning, e.g. as has been done for WASP-12b in Program 13467 (PI Bean). This is because although bi-directional spatial scanning would allow an additional 1 exposure to be acquired per HST orbit (i.e. 12 per orbit), the instrumental systematics are different for each scan direction, which is likely more of a disadvantage. **Signal-to-noise estimates: WASP-96b is moderately bright target (J=11.27). We used the HST Exposure Time Calculator with the observational setup described above to calculate a SNR of ~1057 and ~1260 per resolution element per exposure for G102 and G141, respectively. Note that this flux will be spread over ~47 and ~69 pixel columns due to the spatial scan (see above), so there is no risk of saturation. According to the HST Exposure Time Calculator, with this setup the brightest pixel per exposure will reach around 31,000 electrons (see linked ETC Run #'s in the observing sequences). Planets and Planet Formation 0 false false false false false false false SUPPORTED EXT-STAR EXTRA-SOLAR PLANET This object was generated by the targetselector and retrieved from the SIMBAD database. WASP-96 J2000 J2000 WFC3/IR Spectroscopic No No G102 WFC3/IR Spectroscopic No No G141 1534111305990 The scheduling data was generated by CASM 26.0. CASM was run in Phase II mode. Observation of transiting exoplanet WASP-96b with WFC3 G102. It is essential that the 5 HST orbits are scheduled in a continuous block to cover a transit event. Each of the 5 HST orbits contain a non-interruptible sequence. 1536217665000 335.8709111781984 (Tic-Visit :proposal-id 15469 :visit-id "01" :proposal-version -1 :trans-version "20180409" :date "12-Aug-2018 23:01:44.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 5 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 654064 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15469 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15469 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2447 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2993 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15469 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2628 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2993 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15469 :visit-id "01" :orbit-number 3 :pcs-time 222 :si-vis-utilization 2628 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2993 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15469 :visit-id "01" :orbit-number 4 :pcs-time 222 :si-vis-utilization 2628 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2993 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15469 :visit-id "01" :orbit-number 5 :pcs-time 222 :si-vis-utilization 2628 :al-overhead-at-end 0 :internal-dur-at-end 370 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2993 :pcs-gap 0 ) false 5 0 1534111305990 Observation of transiting exoplanet WASP-96b with WFC3 G102. It is essential that the 5 HST orbits are scheduled in a continuous block to cover a transit event. Each of the 5 HST orbits contain a non-interruptible sequence. (Tic-Visit :proposal-id 15469 :visit-id "01" :proposal-version -1 :trans-version "20180409" :date "12-Aug-2018 23:01:44.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 5 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 654064 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15469 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15469 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2447 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2993 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15469 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2628 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2993 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15469 :visit-id "01" :orbit-number 3 :pcs-time 222 :si-vis-utilization 2628 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2993 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15469 :visit-id "01" :orbit-number 4 :pcs-time 222 :si-vis-utilization 2628 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2993 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15469 :visit-id "01" :orbit-number 5 :pcs-time 222 :si-vis-utilization 2628 :al-overhead-at-end 0 :internal-dur-at-end 370 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2993 :pcs-gap 0 ) false 5 0 1534111316369 The scheduling data was generated by CASM 26.0. CASM was run in Phase II mode. Observation of transiting exoplanet WASP-96b with WFC3 G141. It is essential that the 5 HST orbits are scheduled in a continuous block to cover a transit event. Each of the 5 HST orbits contain a non-interruptible sequence. (Tic-Visit :proposal-id 15469 :visit-id "02" :proposal-version -1 :trans-version "20180409" :date "12-Aug-2018 23:01:54.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 5 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 644464 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15469 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15469 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2467 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2993 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15469 :visit-id "02" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2627 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2993 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15469 :visit-id "02" :orbit-number 3 :pcs-time 222 :si-vis-utilization 2627 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2993 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15469 :visit-id "02" :orbit-number 4 :pcs-time 222 :si-vis-utilization 2627 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2993 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15469 :visit-id "02" :orbit-number 5 :pcs-time 222 :si-vis-utilization 2627 :al-overhead-at-end 0 :internal-dur-at-end 421 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2993 :pcs-gap 0 ) false 5 0