14860( 7) - 10-May-2017 16:48:20 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 14860 Version: 7 Check-in Time: 10-May-2017 16:48:20 STScI Edit Number: 2 Title The most detailed high-energy picture of Proxima Centauri, our nearest extrasolar neighbor ------------------------------------------------------------------------------------ Type Cycle GO/DD 24 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Christian Schneider Universitat Hamburg, Hamburger Sternwarte Y CoI: Dr. Kevin France University of Colorado at Boulder N CoI: Prof. Jurgen H.M.M. Schmitt Universitat Hamburg, Hamburger Sternwarte N CoI: Parke Loyd University of Colorado at Boulder N CoI: Dr. Jan Robrade Universitat Hamburg, Hamburger Sternwarte N CoI: Dr. Antonio Garcia Munoz Technische Universitat Berlin N CoI: Dr. Peter Predehl Max-Planck-Institut fur extraterrestrische N Physik ------------------------------------------------------------------------------------ Abstract 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. ------------------------------------------------------------------------------------ Observations Description ------------------------ 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. 14860( 7) - 10-May-2017 16:48:20 - [ 2] 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. ------------------------------------------------------------------------------------ 14860( 7) - 10-May-2017 16:48:20 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 V-V645-CEN STAR, CORONA, RA=14H29M42.9485S +/- 0.1", J2000 V = 11.13 EXTRA-SOLAR PLANET, M DEC=-62D40'46.16" +/- 0.1" V-IV Reference Frame: ICRS Extended: NO Comments: 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. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 -0.5484409919787686 0.76554 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 14860( 7) - 10-May-2017 16:48:20 - [ 4] Visit: 01 (FUV) Visit Requirements: GROUP 01, 02 WITHIN 5 Orbits On Hold Comments: Additional Comments: 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. 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 V-V645-CEN STIS/CCD ACQ F28X50OII MIRROR ACQTYPE=POINT 1 10 S (10 I S) Comments: 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. ------------------------------------------------------------------------------------------------------------------------------------ 2 V-V645-CEN STIS/FUV TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=500 1 2500 S -MAMA G see below (2579 S) Comments: The buffer time is chosen based on the mean observed spectrum. ------------------------------------------------------------------------------------------------------------------------------------ 3 V-V645-CEN STIS/FUV TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=500 1 200 S -MAMA G see below (3226 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 V-V645-CEN STIS/FUV TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=500 1 2500 S -MAMA G see below (3226 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 V-V645-CEN STIS/FUV TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=500 1 2500 S -MAMA G see below (3226 S) ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ V-V645-CEN 1 STIS/CCD ACQ F28X50OI MIRROR none none none none 1 N/A II V-V645-CEN 2 STIS/FUV TIME-TA 0.2X0.2 E140M 1425 none none none none 1 2579.0 S -MAMA G V-V645-CEN 3 STIS/FUV TIME-TA 0.2X0.2 E140M 1425 none none none none 2 3226.0 S -MAMA G 14860( 7) - 10-May-2017 16:48:20 - [ 5] 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 | ------------------------------------------------------------------------------------------------------------------------------------ V-V645-CEN 4 STIS/FUV TIME-TA 0.2X0.2 E140M 1425 none none none none 3 3226.0 S -MAMA G V-V645-CEN 5 STIS/FUV TIME-TA 0.2X0.2 E140M 1425 none none none none 4 3226.0 S -MAMA G 14860( 7) - 10-May-2017 16:48:20 - [ 6] Visit: 02 (NUV/optical (CCD)) Visit Requirements: GROUP 02, 01 WITHIN 5 Orbits On Hold Comments: Additional Comments: 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 V-V645-CEN STIS/CCD ACQ F28X50OII MIRROR ACQTYPE=POINT 1 10 S (10 I S) Comments: 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. ------------------------------------------------------------------------------------------------------------------------------------ 2 V-V645-CEN STIS/CCD ACCUM 52X0.2 G230LB 2375 CR-SPLIT=8, SIZEAXIS2=256 1 2048 S see below (2128 S) Comments: 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. ------------------------------------------------------------------------------------------------------------------------------------ 3 V-V645-CEN STIS/CCD ACCUM 52X0.2 G430L 4300 CR-SPLIT=2 1 33 S (33 S) ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ V-V645-CEN 1 STIS/CCD ACQ F28X50OI MIRROR none none none none 1 N/A II V-V645-CEN 2 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 1 1 266.0 S V-V645-CEN 2 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 2 1 266.0 S V-V645-CEN 2 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 3 1 266.0 S V-V645-CEN 2 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 4 1 266.0 S V-V645-CEN 2 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 5 1 266.0 S V-V645-CEN 2 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 6 1 266.0 S V-V645-CEN 2 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 7 1 266.0 S V-V645-CEN 2 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 8 1 266.0 S V-V645-CEN 3 STIS/CCD ACCUM 52X0.2 G430L 4300 none none none 1 1 N/A V-V645-CEN 3 STIS/CCD ACCUM 52X0.2 G430L 4300 none none none 2 1 N/A 14860( 7) - 10-May-2017 16:48:20 - [ 7] Summary Form for Proposal 14860 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 0.2X0.2, 52X0.2, F28X50OIII ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT, BUFFER-TIME=500, CR-SPLIT=2, CR-SPLIT=8, SIZEAXIS2=256 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GROUP 01, 02 WITHIN 5 Orbits, GROUP 02, 01 WITHIN 5 Orbits ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements E140M, G230LB, G430L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names V-V645-CEN ------------------------------------------------------------------------------------------------------------------------------------