0 Assigned ID: 855 ----- Attempting Submission 1 (Fri Apr 08 21:24:05 GMT 2016) ----- 0 ----- Attempting Submission 1 (Wed Jul 20 17:28:36 GMT 2016) ----- In the past months we have obtained evidence that an unusual phenomenon is happening in the atmosphere of one of the Hot Jupiters with shortest period. High-resolution spectroscopy from the ground reveals a transit spectrum where the sodium absorption signal from the planet peaks at 2-3%, which is larger than the planet transit depth in white light and 100 times larger than the well HST-established detection of sodium in HD 209458b (Charbonneau et al. 2002). Only in the UV have such large signatures been observed, for lighter hydrogen, carbon and oxygen atoms being blown-off by hydrodynamical atmospheric escape. So far, sodium atoms have never been observed higher than the thermosphere, where they should get promptly ionized. Analysis of ground-based data is challenging because the spectroscopic signatures can be mimicked by the Earth atmosphere, and a sophisticated removal of telluric contamination is necessary. Our observations show that an efficient telluric correction for this target, particularly faint in the sodium region, is impossible, making a space-based confirmation necessary. In a single transit, HST/STIS could obtain a 5-sigma confirmation of the signal. This detection would unambiguously show that the planetary atmosphere is in a state of extreme blow-off, with large exospheric densities allowing for a high recombination rate able to maintain sodium in a neutral state even high up in the atmosphere. This would represent the first constraint on atmospheric evaporation obtained in the optical, and would thus open a new, UV-independent path to the characterization of evaporating atmospheres, crucial in the post-HST era. We are going to collect STIS spectra during one transit of WASP-43b. In order to have enough out-of-transit and in-transit data 4 orbits are required. Two orbits will be collected before the transit of the planet to establish the baseline flux, one during and one after the transit. This strategy allows to measure the drop in stellar flux due to the transit of the planet. Key to the success of the program is extremely precise photometry, of which HST/STIS has already demonstrated to be capable. We are going to use the STIS CCD G750M observing mode centred at 6094 A to observe sodium at R ~ 5000, and with the 52'' x 2'' slit to minimize flux losses. The duration of the transit is of 2200 s excluding ingress and egress, thus it is possible to completely cover it with the third orbit. Each orbit is split in ~ 270 s exposures with sub-array reading (efficiency > 90 %), to sample the transit of the planet finely enough while keeping a high duty cycle. Additional comments: Experience gained from past proposals by several groups (14461, 14410, 12473, 11572 among others) has shown that maximized photometric precision and efficient thermal breathing trends removal is key to the success of HST transit observations. This is achieved with three main precautions: - We set WAVECAL=NO for the visit and perform manual wavelength calibrations during Earth occultation to acquire a consevutive time series in each orbit. - A short exposure (1 sec) is performed before the scientific time series, following the method indicated in Sing et al., 2015, MNRAS, 446, 2428. This is to minimize the impact of possible systematics in the first exposure. - Again following past proposals, we set the other STIS settings in order to maximize counts and reduce readout time overheads: CR-SPLIT=NO, GAIN=4, SIZEAXIS2=128. Extrasolar Planets and Planet Formation 12 false false false false false false AVAILABLE STAR EXTRA-SOLAR PLANET K V-IV This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 APASS r = 11.9 STIS/CCD Spectroscopic No No G750M 6094 1469035312788 Phase windows are not calculated when the gap between schedulable intervals is less than 1 days, assuming no scheduling restrictions for constraint Phase 0.806/0.816. The scheduling data was generated by CASM 24.2. CASM was run in Phase II mode. For this proposal it is necessary to have a visit of four orbits in a continuous block, because the transit of the planet has to be fully sampled. (Tic-Visit :proposal-id 14782 :visit-id "01" :proposal-version -1 :trans-version "20160601" :date "20-Jul-2016 19:21:49.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 169472 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 14782 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 14782 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2869 :al-overhead-at-end 120 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3213 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14782 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2976 :al-overhead-at-end 120 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3213 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14782 :visit-id "01" :orbit-number 3 :pcs-time 222 :si-vis-utilization 2976 :al-overhead-at-end 120 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3213 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14782 :visit-id "01" :orbit-number 4 :pcs-time 222 :si-vis-utilization 2976 :al-overhead-at-end 123 :internal-dur-at-end 335 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3213 :pcs-gap 0 ) false 4 0 Short exposure to minimize instrument systematic of first exposure in each orbit (e.g. HST proposal 12473). Explicit WAVECAL, auto-wave disabled Short exposure to minimize instrument systematic of first exposure in each orbit (e.g. HST proposal 12473). Short exposure to minimize instrument systematic of first exposure in each orbit (e.g. HST proposal 12473). Short exposure to minimize instrument systematic of first exposure in each orbit (e.g. HST proposal 12473).