15694( 3) - 12-Apr-2019 11:41:14 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15694 Version: 3 Check-in Time: 12-Apr-2019 11:41:14 STScI Edit Number: 1 Title UV reconnaissance of the evaporating super-Neptune WASP-107b ------------------------------------------------------------------------------------ Type Cycle GO 26 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Vincent Bourrier Observatoire de Geneve Y CoI: Prof. David Ehrenreich Observatoire de Geneve N CoI: Dr. Christophe Lovis Observatoire de Geneve N CoI: Mr. Romain Allart Observatoire de Geneve N CoI: Prof. David K. Sing The Johns Hopkins University N CoI: Jessica Spake The Johns Hopkins University N ------------------------------------------------------------------------------------ Abstract The population of close-in exoplanets features a desert of hot Neptunes thought to have lost their atmosphere under strong stellar irradiation. Direct observations of extended atmospheres and mass loss are essential to constrain this scenario. Exoplanets surviving at the border of the desert are ideal targets to determine the conditions that lead from stable atmospheres to dramatic mass loss. Recently, the near-infrared helium triplet (10833 A) was revealed as a probe of extended thermospheres, complementing traditional observations of the exosphere at UV wavelengths. Combining the two tracers for the same exoplanet would bring much more detailed information about its upper atmospheric structure and better constrain its mass loss. Here we propose a reconnaissance program of WASP-107b with HST/STIS in the Lyman-alpha line. The first exoplanet where helium was detected, this warm super-Neptune stands at the border of the desert and at the transition between stable Jupiter-mass planets and hot Neptunes that fully lost their atmosphere. The age and UV emission of WASP-107, as well as the interstellar medium density toward this star, are uncertain. Two HST orbits scheduled out- and in- of the transit will allow us to determine if a) the stellar Lyman-alpha line is measurable, and b) the giant neutral hydrogen exosphere expected to surround the planet is detectable. A mid-cycle program is the perfect opportunity to justify the investment required to fully characterize WASP-107b in the UV, and to best plan the use of HST UV capabilities in next cycles. ------------------------------------------------------------------------------------ Observations Description ------------------------ We will use the two allocated HST orbits to observe the star WASP-107, which hosts a transiting exoplanet WASP-107b. Observations will make use of the STIS/FUV-MAMA and the G140M grism centered on a wavelength of 1222 A to observe the Ly-alpha line. - Visit #01: One HST orbit will be performed before the transit of WASP-107b (when its orbital phase is within 0.5 to 0.85), to try and measure the intrinsic stellar line while avoiding potential absorption by a hydrogen trail trailing the planet (which would occult the star after the planet transit). - Visit #02: One HST orbit will be performed during the planet transit, when absorption by the putative exosphere of neutral hydrogen is expected to be 15694( 3) - 12-Apr-2019 11:41:14 - [ 2] maximal. The comparison between the out- and in-transit HST exposures will allow detecting the signature of the exosphere if the Ly-alpha line is bright enough. We would like the two visits to be scheduled as close as possible from one another, ideally within one orbital period of the planet (5.7 days). We defined visits constraints accordingly. If this constraint makes the visits too difficult to schedule, we will relax them. As in past programs from our team (GO#13820 and #12681, PI: D. Ehrenreich; GO#14143, PI: V. Bourrier) we moved the AUTO-WAVECAL to GO-WAVECAL during Earth occultation. The time gained for the scientific exposures would be very useful, in particular because the star is faint, and the ACQ-PEAK takes a relatively long time to perform. ------------------------------------------------------------------------------------ 15694( 3) - 12-Apr-2019 11:41:14 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 WASP-107 STAR, EXTRA-SOLAR RA=12H33M32.8441S +/- J2000 V = V = 11.47 B 14.62, G 11.1740, J 9.378, PLANETARY SYSTEM 0.0000536", DEC=-10D08'46.22" 13.74 H 8.777, K 8.637 +/- 0.0000349" Reference Frame: ICRS Comments: All target properties come from the SIMBAD and GAIA databases. We used the confirmation charts to check that the coordinates and proper motion were correct. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 -0.006545480993297018 -0.009482605647713256 0.015417519178256992 ------------------------------------------------------------------------------------------------------------------------------------ 15694( 3) - 12-Apr-2019 11:41:14 - [ 4] Visit: 01 (Out-of-Transit) Visit Requirements: Period 5.721474 D AND ZERO-PHASE HJD2457584.329897; GROUP 01, 02 WITHIN 6D On Hold Comments: Additional Comments: This visit must be obtained far from the time of transit of planet WASP-107b, to provide a clean estimate of the baseline UV flux from the star. Experience from GJ436b (GO #12965) suggests that, in an extreme case, it might be possible for Ly-alpha to be absorbed from the phase of transit all the way to anti-transit. We thus request in the timing requirements that the planet is between orbital phases 0.5 to 0.85. We further request that Visit #02 is scheduled within 6 days (one orbital period of the planet) after Visit#01. This constraint can be relaxed if it makes the scheduling of the program too difficult. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 WASP-107 STIS/CCD ACQ F28X50OII MIRROR 1 20 S (20 PHASE 0.5 TO 0.85; SEQ S) 1-4 NON-INT Comments: The target is too bright for the longpass filter, and the F28X50OII was selected instead. Time to reach signal to noise ratio of 40 is estimated at 16s, with time to saturation 1660s. We set exposure time to 20s ------------------------------------------------------------------------------------------------------------------------------------ 2 WASP-107 STIS/CCD ACQ/PEA 52X0.05D1 G430L 4300 1 10 S (10 K S) Comments: 10s allows to reach over S/N=43 with STIS/CCD/G430L at 4300 Angstroms, and is well below the time to saturation (325s). The Spectroscopic ETC yields a warning about the issue with charge transfer eff iciency for low background, but we are just using the CCD for the target acquisition, after which we switch to the MAMA. ------------------------------------------------------------------------------------------------------------------------------------ 3 WASP-107 STIS/FUV TIME-TA 52X0.05D1 G140M 1222 BUFFER-TIME=900, WAVECAL=NO 1 1500 S -MAMA G see below (1722 S) Comments: We are basically photon-starved and set the exposure time to the maximum possible value. The star is later-type (K6) than the K0 stars HD189733 (see above ETC run) and HD97658, observed with the same settings in previous programs, and it is farther away and fainter. We thus expect lower count rates, and set the buffer-time as Texp/2. ------------------------------------------------------------------------------------------------------------------------------------ 4 WAVE STIS/FUV ACCUM 52X0.05 G140M 1222 1 DEF (0 S) -MAMA 15694( 3) - 12-Apr-2019 11:41:14 - [ 5] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ WASP-107 1 STIS/CCD ACQ F28X50OI MIRROR none none none none 1 N/A I WASP-107 2 STIS/CCD ACQ/PEA 52X0.05D G430L 4300 none none none none 1 N/A K 1 WASP-107 3 STIS/FUV TIME-TA 52X0.05D G140M 1222 none none none none 1 1722.0 S -MAMA G 1 WAVE 4 STIS/FUV ACCUM 52X0.05 G140M 1222 none none none none 1 N/A -MAMA 15694( 3) - 12-Apr-2019 11:41:14 - [ 6] Visit: 02 (In-Transit) Visit Requirements: Period 5.721474 D AND ZERO-PHASE HJD2457584.329897 On Hold Comments: Additional Comments: This visit targets the transit of planet WASP-107b, and we indicate relevant lower/upper phase constraints in the ACQ subexposure. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 WASP-107 STIS/CCD ACQ F28X50OII MIRROR 1 20 S (20 PHASE 0.993 TO 0.002; S) SEQ 1-4 NON-INT Comments: The target is too bright for the longpass filter, and the F28X50OII was selected instead. Time to reach signal to noise ratio of 40 is estimated at 16s, with time to saturation 1660s. We set exposure time to 20s ------------------------------------------------------------------------------------------------------------------------------------ 2 WASP-107 STIS/CCD ACQ/PEA 52X0.05D1 G430L 4300 1 10 S (10 K S) Comments: 10s allows to reach over S/N=43 with STIS/CCD/G430L at 4300 Angstroms, and is well below the time to saturation (325s). The Spectroscopic ETC yields a warning about the issue with charge transfer eff iciency for low background, but we are just using the CCD for the target acquisition, after which we switch to the MAMA. ------------------------------------------------------------------------------------------------------------------------------------ 3 WASP-107 STIS/FUV TIME-TA 52X0.05D1 G140M 1222 BUFFER-TIME=900, WAVECAL=NO 1 1500 S -MAMA G see below (1722 S) Comments: We are basically photon-starved and set the exposure time to the maximum possible value. The star is later-type (K6) than the K0 stars HD189733 (see above ETC run) and HD97658, observed with the same settings in previous programs, and it is farther away and fainter. We thus expect lower count rates, and set the buffer-time as Texp/2 for the orbits of all visits. ------------------------------------------------------------------------------------------------------------------------------------ 4 WAVE STIS/FUV ACCUM 52X0.05 G140M 1222 1 DEF (0 S) -MAMA ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ 15694( 3) - 12-Apr-2019 11:41:14 - [ 7] Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ WASP-107 1 STIS/CCD ACQ F28X50OI MIRROR none none none none 1 N/A I WASP-107 2 STIS/CCD ACQ/PEA 52X0.05D G430L 4300 none none none none 1 N/A K 1 WASP-107 3 STIS/FUV TIME-TA 52X0.05D G140M 1222 none none none none 1 1722.0 S -MAMA G 1 WAVE 4 STIS/FUV ACCUM 52X0.05 G140M 1222 none none none none 1 N/A -MAMA 15694( 3) - 12-Apr-2019 11:41:14 - [ 8] Summary Form for Proposal 15694 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X0.05, 52X0.05D1, F28X50OII ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ, ACQ/PEAK, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=900, WAVECAL=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GROUP 01, 02 WITHIN 6D, PHASE 0.5 TO 0.85, PHASE 0.993 TO 0.002, Period 5.721474 D AND ZERO-PHASE HJD2457584.329897, SEQ 1-4 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140M, G430L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names WASP-107, WAVE ------------------------------------------------------------------------------------------------------------------------------------