0 Assigned ID: 1241 ----- Attempting Submission 1 (Mon Sep 12 09:57:44 GMT 2016) ----- Re-submission after splitting into 2 visits (with GROUP WITHIN 5 orbits) 76707251 ----- Attempting Submission 1 (Wed Oct 12 09:35:23 GMT 2016) ----- ----- Attempting Submission 2 (Mon Apr 03 14:30:25 GMT 2017) ----- ----- Attempting Submission 3 (Wed May 10 13:19:39 GMT 2017) ----- HST Phase II Proposal 14860 (STIS_setup_0.2_slit_no_PEAK.apt) successfully submitted. Receipt: # 14860-3 ----- Attempting Submission 4 (Wed May 10 16:39:07 GMT 2017) ----- Proxima Centauri b is the nearest exoplanet to the Sun. It orbits an M5.5 dwarf and is potentially habitable. The latter statement, however, depends sensitively on the high-energy irradiation on the planet. Ribas et al. (2016) estimated the high-energy flux of the host star by collecting archival data from the X-ray to the FUV regime, but explicitly state that one "unavoidable complication of estimating XUV fluxes is [...] intrinsic [stellar] variability". Here, we propose to greatly improve upon this "unavoidable complication" by obtaining simultaneous X-ray and UV observations to measure a high-resolution irradiation spectrum and, thus, to assess the habitability of Proxima b. Our upcoming, very deep Chandra grating observation of Proxima Cen (175 ks, LETGS, PI: P. Predehl) provides a great opportunity to obtain simultaneous coverage at X-ray and UV wavelengths, i.e., to measure most of the stellar high-energy flux in a coherent way. The reason for proposing a HST DDT is that the Chandra observation is a GTO and, thus, could not be augmented by simultaneous HST observations directly as we would have proposed for in a regular GO. Combining Chandra X-ray and HST UV data allows us to reconstruct a high-resolution spectral energy distribution (SED) including the EUV regime and, thus, a reference irradiation spectrum using the methods developed by us for the MUSCLES project. Our observing strategy is inspired by our experience from the MUSCLES project and modified to obtain a broad number of lines simultaneous with Chandra by using the STIS E140M grating instead of switching between COS G130M and G160M. The total exposure time of the Chandra observation (175 ks) will be split into two up to a few sub-exposures and we propose that HST covers one of these observations with simultaneous UV data. We will use STIS to cover the FUV range and to resolve individual lines. Similar to the MUSCLES observations, we will append a STIS G230LB exposure to cover the wavelength range beyond ~2000 Angstrom, which allows us to cover the NUV continuum, Fe II lines at 2400 and 2600 Angstrom, and Mg II lines at 2800 Angstrom. Lastly, a short optical observation with the STIS G430L grating will calibrate the UV data to visible/IR photospheric models. We will use the photon-counting mode to relate line fluxes (and consequently chromospheric plasma) with X-ray fluxes. Employing this strategy in APT, we find that Proxima Cen has several observing windows in May/early June2017 that allow simultaneous scheduling with Chandra. Details of the Chandra observation are: ObsID 19708, PropNo 18200754. Detector safety: We follow ISR STIS 2017-02 to determine the instrument safety. Proxima Cen is classified as M5.5. However, its effective temperature of 2927 K places the star closer to M6 than M5 (Passegger, Wende-von Berg, Reiners, A&A, 2016). In addition, its radius of ~0.15 Rsun (as in Demory et al., A&A, 2009) is about that of M6. Thus, one should rather use the values for M6 than M5. Given that Proxima Cen is between both limits and that stellar properties do not follow step functions, we consider delta U = -5.4 as a reasonable and physically appropriate value. Attenuating the Lya with the observed interstellar absorption towards Proxima Cen (Wood et al., ApJ, 2001), we find that the brightest pixel has 12.5 cts/s and the global detector count rate is ~3,700 cts/s. Both values are well below the limit. Detailed calculation: Assuming delta U = -5.4 Flare = U + delta U = 14.21 - 5.4 = 8.81 fU = 1.26e-12, log fU = -11.90 log f(C IV) = -10.63, f(C IV) = 2.3e-11 log f(S IV) = -10.69, f(Si IV) = 2e-11 f(Lya) ~ 1e-10 (from scaling relations) f(Lya) ~ 8.5e-10 (from 37 * f(C IV)) These values are 6.2, 7.8, and 7.1 magnitudes below the mean fluxes that already include flares (for C IV, S IV, and Lya, resp.). BOT: The source reported to possibly violate the bright object limits has the GSC II ID S7Q6372147 at coordinates 14:29:33.02 -62:40:39.12 at a V magntiude of 15.66. The nearest source known to Simbad is our target Proxima Cen although its V magnitude is V=11.13, i.e., significantly brighter in the optical. Galex has observed this field and the nearest (and brightest) source is at 14:29:36.66 -62:40:37.6, which is consistent with the position of our target Proxima Cen during the epoch of the Galex observation (2011.5). The next nearest UV bright source is about two arcmin from our target (14:29:26.313 - 62:40:45.5, Galex objID 6387417244251458407, IAU Name: GALEX J142926.3-624045). Therefore, we consider the field to be safe. Extrasolar Planets and Planet Formation Stellar Physics 0 SUPPORTED STAR CORONA EXTRA-SOLAR PLANET M V-IV NO This object was generated by the targetselector and retrieved from the SIMBAD database. Coordinates are from Hipparcos. Thus, have an accuracy better than about 1 mas for the observing date. Due to large proper motion of Proxima Cen, we adopt a larger uncertainty. Typically, the pm error is about 1 mas/yr from Hipparcos so that the formal uncertainty is still well below 0.1 arcsec for the position. J2000 COS/FUV Spectroscopic No No G140L 1280 STIS/CCD Spectroscopic No No G230LB 2375 STIS/CCD Spectroscopic No No G430L 4300 1494434116260 Timing link suitability includes constraints ([Group (01 02) Within 0.3 days]) The scheduling data was generated by CASM 25.0. CASM was run in Phase II mode. /data/hspc13/stgh325/proposals/HST/Prox_Cen/OP-cache/STIS_setup_0-v01.xml To be excecuted simultaneous with (one of) our Chandra LETGS observations (PI Predehl). Details for the Chandra observation are: ObsID 19708, PropNo 18200754. No timing contraints have been entered, because the dates of the Chandra observations are not fixed yet. (Tic-Visit :proposal-id 14860 :visit-id "01" :proposal-version -1 :trans-version "20170109" :date "10-May-2017 18:35:15.0" :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 1966112 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 14860 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 14860 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3145 :al-overhead-at-end 0 :internal-dur-at-end 316 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3478 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14860 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3256 :al-overhead-at-end 0 :internal-dur-at-end 316 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3478 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14860 :visit-id "01" :orbit-number 3 :pcs-time 222 :si-vis-utilization 3256 :al-overhead-at-end 0 :internal-dur-at-end 316 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3478 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14860 :visit-id "01" :orbit-number 4 :pcs-time 222 :si-vis-utilization 3256 :al-overhead-at-end 0 :internal-dur-at-end 578 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3478 :pcs-gap 0 ) true 4 0 We chose to use the [O III] filter, because the 28x50LP filter would result in saturation within 0.16 s. Exposure time reflects the time based on the flux around [O III] while most of the flux is likely due to the red leak. Still saturation occurs only for texp>200 s. The buffer time is chosen based on the mean observed spectrum. 1494434158664 /data/hspc13/stgh325/proposals/HST/Prox_Cen/OP-cache/STIS_setup_0-v02.xml Timing link suitability includes constraints ([Group (01 02) Within 0.3 days]) The scheduling data was generated by CASM 25.0. CASM was run in Phase II mode. (Tic-Visit :proposal-id 14860 :visit-id "02" :proposal-version -1 :trans-version "20170109" :date "10-May-2017 18:35:58.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 110256 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 14860 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 14860 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3143 :al-overhead-at-end 0 :internal-dur-at-end 419 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3478 :pcs-gap 0 ) true 1 0 We chose to use the [O III] filter, because the 28x50LP filter would result in saturation within 0.16 s. Exposure time reflects the time based on the flux around [O III] while most of the flux is likely due to the red leak. Still saturation occurs only for texp>200 s. The exposure time is about double the value of archival data. We expect S/N > 5 in the continuum for wavelengths longwards of 2500 Angstrom. We use a subarray mode to minimize readout times and use CR-SPLIT=8 to obtain some time resolution.