Testing the Hypothesis of a Low Metallicity Atmosphere for the Extremely Inflated Sub-Saturn-Mass Planet KELT-11b

0 Assigned ID: 769 ----- Attempting Submission 1 (Fri Apr 05 21:09:48 GMT 2019) ----- HST Phase I Proposal 769 (kelt-11-cycle27.apt) successfully submitted. Receipt: # 769-1 ----- Attempting Submission 2 (Fri Apr 05 21:15:19 GMT 2019) ----- HST Phase I Proposal 769 (kelt-11-cycle27.apt) successfully submitted. Receipt: # 769-2 ----- Attempting Submission 3 (Fri Apr 05 22:26:22 GMT 2019) ----- HST Phase I Proposal 769 (kelt-11-cycle27.apt) successfully submitted. Receipt: # 769-3 ----- Attempting Submission 4 (Fri Apr 05 23:17:37 GMT 2019) ----- HST Phase I Proposal 769 (kelt-11-cycle27.apt) successfully submitted. Receipt: # 769-4 We are submitting our Phase 2 file for our program to observe a single transit of KELT-11b with WFC3/G102. This program is designed to be extremely similar to program 15255 where we successfully obtained a single transit of KELT-11b with WFC3/G141. We are resubmitting our Phase 2 file to include a "Same Orient As" requirement for all visits within the sequence and also using the Non-Int Sequence parameter. -621709795 ----- Attempting Submission 1 (Wed Jul 24 17:24:53 GMT 2019) ----- ----- Attempting Submission 2 (Fri Aug 09 20:15:03 GMT 2019) ----- Testing the Hypothesis of a Low Metallicity Atmosphere for the Extremely Inflated Sub-Saturn-Mass Planet KELT-11b We are now in an era of exoplanet characterization. Exoplanets are being intensively studied to measure the abundances of water and other metals in their atmospheres in order to place constraints on the location of their origin within a disk. Inflated sub-Saturn-mass planets bridge the divide between super-Earths and Jupiters, so constraints on their atmospheric composition and metallicities are particularly important for informing planet formation models. Here, we propose to perform a detailed investigation of the atmosphere of the hot and extremely inflated sub-Saturn-mass planet KELT-11b. This is one of the best planets to study thanks to its very bright host, low mass and surface gravity, and high equilibrium temperature. An HST/WFC3 G141 transmission spectrum indicates that KELT-11b has a clearly sub-solar metallicity atmosphere, but additional data are needed to determine just how metal-poor the atmosphere is. The proposed observations to measure KELT-11b's transmission spectrum in the G102 band will not only lead to more precise metallicity constraints but will also reveal whether KELT-11b followed a rare planet formation pathway if the planet's metallicity is indeed ultra-low. In addition, with precise atmospheric metallicity constraints for the sub-Saturn-mass KELT-11b, we will be able to empirically test correlations between planet mass-planet metallicity and between stellar metallicity-planet metallicity. The proposed observations of KELT-11b will ultimately add to a comparative study with the other inflated sub-Saturns discovered to date that can be used to better inform planet formation and evolution models as well as future observations with JWST. We will obtain time series spectroscopy of the KELT-11b planetary system with the WFC3 instrument during one transit of the planet. We will use the G102 grism and the 512x512 subarray. The observation will consist of 9 sequential HST orbits to obtain quasi-continuous coverage of the planet's transit. Nine orbits are required to observe the transit and measure the out-of-transit baseline flux level. The observation duration is longer than usual for exoplanet transit spectroscopy because the transit duration is over 7.0 hours thanks to the slightly evolved host star. The 9 orbits have been defined as separate visits in APT, which forces WFC3 to do a complete buffer dump during occultation. This strategy follows that applied in program 15698 and allows us to ensure that we do not lose any observing time to buffer dumps that could occur during the middle of a traditional observing plan (i.e. containing a single visit with 9 orbits defined as non-interruptible sequences). We have sequenced the visits (orbits) so that all orbits should occur immediately after the first one, so we can obtain a "continuous" observation of 9 consecutive orbits to observe a transit of KELT-11b. We will obtain a direct image of the target star with the F130N filter at the beginning of each orbit for wavelength calibration. The remainder of each orbit will consist of 46.696 s exposures with the NSAMP = 3, SPARS25 readout pattern. To keep the fluence below saturation, we will use spatial scan mode with a 0.96 arcsec/sec scan rate (yielding a total scan height of 345 pixels). Using past WFC3 observations of similar targets as a benchmark, we estimate the maximum expected per pixel counts to be below 40k electrons. To maximize the duty cycle of the observations, we will alternate between forward and reverse scanning along the detector. This is the same observational strategy we used extensively for transit/eclipse observations in our programs in previous cycles, including in our Cycle 25 Program 15255 for this same target, which yielded photon-noise limited light curves. We have left at least 2 min of time unused in each orbit to allow for any pointing resets that may be necessary. We left approximately 5 min of time unused in orbits (visits) 4 and 8 to allow for gyro bias updates that may be necessary. The proposed observations are time-critical and must be centered on the transit of the planet. Transits occur often (every 4.7 days), so there are many opportunities to observe the planet. The observations should also be scheduled to minimize impacts of crossing the South Atlantic Anomaly if possible. The observations will not need to be coordinated with other observatories. When the HST observations are scheduled, we will arrange for simultaneous ground-based optical and IR photometry in order to trace the intrinsic variability of the system. These observations will be performed with small-to-mid-sized telescopes which are easily accessible to the world-wide KELT network of collaborators of the proposers. In the case of reduced-gyro operations, the schedulability of our observations will likely be impacted by having few observing windows available for our target. Our spatial scan mode uses a rate of 0.96 arcsec/sec so would not be impacted by a limit placed on spatial scan speeds to be less than 5 arcsec/sec. We conclude that the greatest impact to our program in reduced gyro-observations would be the schedulability of our observations. The proposed investigation relies on the precise planning of exoplanet transit observations with HST and the careful reduction and analysis of WFC3 data. Dr. Thomas Beatty, Dr. Knicole Colon, Dr. Laura Kreidberg, Dr. Avi Mandell, Dr. Kevin Stevenson have expertise in these tasks. These investigators have all been PIs of successful HST observing campaigns in past cycles, which have in turn led to numerous publications based on the HST data collected (e.g., Beatty et al. 2017b; Kreidberg et al. 2014a,b, 2015, 2018a,b; Mandell et al. 2013; Stevenson et al. 2014a,b,c,d). Drs. Colon and Kreidberg were the PI and Co-PI on HST GO-15255 and led the planning and implementation of WFC3 transit observations of KELT-11b, which this proposal is building on. Drs. Kreidberg and Stevenson led the reduction and analysis of those WFC3 transit observations. PI Colon is leading a paper presenting the results from HST GO-15255. Dr. Daniel Angerhausen, Dr. Thomas Barclay, Dr. David James, Dr. Joseph Rodriguez, Dr. Keivan Stassun have expertise in stellar and exoplanet characterization using a variety of photometric and spectroscopic tools. Dr. Rodriguez specifically was a lead author on the original discovery paper on KELT-11b. Dr. Jonathan Fortney, Dr. Michael Line, Dr. Nikku Madhusudhan have expertise in interpreting exoplanet transmission and emission spectroscopy, including with the retrieval tools required to measure the atmospheric metallicity from exoplanet spectra as we propose to do in this investigation. Drs. Line and Madhusudhan led the retrievals of the WFC3 transmission spectrum from HST GO-15255, results from which were used to develop the proposed investigation. Dr. Thomas Beatty, Dr. Avi Mandell, Dr. Kevin Stevenson, Mr. Patrick Tamburo have expertise in the reduction and analysis of Spitzer data. This team contributed to the analysis of existing Spitzer transit and eclipse data that provided critical constraints on the orbital and atmospheric properties of KELT-11b that were used to help interpret the HST GO-15255 data and will be used to complement the proposed investigation. Dr. Eric Lopez is an expert in formation, evolution, and interior models of exoplanets, which will be applied to this investigation to interpret findings from the HST observations of KELT-11b. Planets and Planet Formation 6 false false false false false false false SUPPORTED STAR EXTRA-SOLAR PLANET EXTRA-SOLAR PLANETARY SYSTEM NO This object was generated by the targetselector and retrieved from the SIMBAD database. The proper motions and parallax come from Gaia DR2. 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