0 Assigned ID: 668 ----- Attempting Submission 1 (Fri Apr 10 18:50:52 GMT 2015) ----- HST Phase I Proposal 668 (APT_template_proposal2.apt) successfully submitted. Receipt: # 668-1 ----- Attempting Submission 2 (Fri Apr 10 23:06:33 GMT 2015) ----- HST Phase I Proposal 668 (APT_template_proposal2.apt) successfully submitted. Receipt: # 668-2 MISSING FRINGE FLAT CALIBRATION MISSING FRINGE FLAT CALIBRATION Update 1 (10/20/15): We have added ORIENT constraints for the WD1327 visit in order to prevent overlapping grism spectra of our target and a faint companion. Update 2 (10/26/15): In order to schedule Visit 1 given Update 1, we have added Schedulability = 80 and changed exposure times accordingly. -1924040378 ----- Attempting Submission 1 (Tue Jul 21 16:41:53 GMT 2015) ----- ----- Attempting Submission 2 (Wed Oct 21 10:29:19 GMT 2015) ----- HST Phase II Proposal 14213 (proposal2_phase2_resubmitted.apt) successfully submitted. Receipt: # 14213-2 ----- Attempting Submission 3 (Mon Oct 26 11:08:14 GMT 2015) ----- Manual fringe flat used instead of default to get higher S/N. The uncertainties on the determination of the nature of the dark energy, that is driving the observed accelerating cosmic expansion, depend critically on the stellar flux standards that are used to calibrate the relative flux of redshifted type Ia supernovae. Currently, the most precise and internally consistent set of fluxes are HST spectrophotometry which are based on computed models atmospheres for three hot pure-hydrogen white dwarfs. Our proposal will directly address the accuracy of this calibration, one of the current current barriers to understand the nature of dark energy. We request 4 orbits to observe two nearby pure-hydrogen atmosphere white dwarfs with significantly cooler temperatures than the current hot white dwarf HST standards. These cooler objects are now accurately modeled by our state-of-the-art 3D model atmospheres and do not suffer from the known shortcomings in models of hot white dwarfs and main-sequence stars. In addition to providing the first robust external confirmation of the HST flux scale in the optical, these new flux standards will be especially useful in the JWST era as standards for the near-IR and IR regions, and their colors will be more similar to those of high-redshift supernovae and galaxies. Furthermore, the parallax of such close stars can be measured with higher precision, so that the absolute flux level can be established as well as the relative flux vs. wavelength. We request to observe two cool, bright, and close WDs to compare directly with STIS data for the current three hot primary WDs (Teff = 30,000-60,000 K). These cool WDs will confirm the internal consistency of the HST flux vs. wavelength scale and they will be employed to calibrate future IR-surveys such as JWST. We have scanned the White Dwarf Catalog (McCook & Sion 1999) for targets, requesting objects with Teff < 20,000 K so that the SEDs are significantly different to those of the current hot WD stars. We further impose that the atmosphere is pure-hydrogen with no evidence of accretion from evolved planetary systems, which would lead to a metal contamination (Zuckerman et al. 2010). The new standards should have no magnetic field, no companion or close bright object, and no pulsations, the latter excluding most WDs in the 11,000 < Teff (K) < 13,000 range (Gianninas et al. 2011). The targets should also have well constrained atmospheric parameters from optical ground based observations. We have selected the brightest objects that satisfied these requirements to minimize the number of HST orbits. Our first target is WD 1327-083 with with V = 12.34, Teff = 14,571 +/- 235 K, log g = 7.99 +/- 0.04, and pi = 55.5 +/- 3.77 mas. The second target is WD 2341+322 with V = 12.95, Teff = 13,128 +/- 198 K, log g = 7.92 +/- 0.04, and pi = 56.8 +/- 1.8 mas. The atmospheric parameters are constrained from fits of the Balmer lines (Giammichele et al. 2012), and the error is the sum in quadrature of the internal uncertainty from the fitting procedure and the external uncertainty obtained by repeating the procedure with spectra secured from different ground based facilities. We note that Gaia will increase by a factor of ten the precision of the current parallax measurements. Both targets have been confirmed multiple times to be photometrically constant, i.e. non-pulsating (Gianninas et al. 2005). We have compared the observed 2MASS JHK colors to predicted colors using the published atmospheric parameters and it agrees within 1-sigma for both targets, which corresponds to a constraint at the 4% level on the near-IR flux, still well above our 1% precision goal. It nevertheless confirms that our targets have no unresolved companions, even though they are both in very wide binaries with main-sequence companions, with separations of 174.7 and 503.3 arcsec, respectively (Farihi et al. 2005). Ground based spectroscopy (0.36-0.6 micron) with a rough flux calibration is sufficient to extract the atmospheric parameters from the Balmer lines of our targets. As a consequence, the precise spectrophotometric observations that are necessary to establish the model SEDs as flux standards do not exist. We therefore require STIS low-resolution observations covering the range 0.115-1 micron, which implies exposures with the STIS/G140L, G230L, G430L, and G750L filters for each target. This is a sufficient resolution for flux calibration since the only spectral features are broad Balmer lines. We also request to observe our targets with the WFC3 grisms G141 and G102 that will extend the coverage to 1.7 microns, an important aspect of establishing new standards for the near-IR and comparing their accuracies to hot WDs. We require a signal-to-noise ratio of >100, in broad delta lambda = 50-100 A bands, which is necessary to constrain the flux calibration at the 1% level. We computed model SEDs on the effective temperatures, surface gravities, and V-band magnitudes from Giammichele et al. (2012), and fed them into the STIS and WFC3 Exposure Time Calculator (ETC). Given the brightness of our targets, the four STIS exposures fit in 1.5 orbits. Only a partial orbit is required for WFC3 to reach S/N > 100, hence we have a strong requirement to change instrument mid-orbit to acheive our science goals. The best compromise is to use WFC3 first and then STIS, allowing STIS wave calibrations and fringe flat in the occultation at the ends of the orbits. We therefore request 1 visit and 2 orbits for each of the 2 targets. COSMOLOGY 12 false true false false AVAILABLE STAR DA Coordinates and proper motions from Hipparcos. J2000 J2000 STAR DA Coordinates and proper motions from Hipparcos. J2000 J2000 STIS/FUV-MAMA Spectroscopic No No G140L 1425 STIS/NUV-MAMA Spectroscopic No No G230L 2376 STIS/CCD Spectroscopic No No G430L 4300 STIS/CCD Spectroscopic No No G750L 7751 WFC3/IR Spectroscopic No No G102 WFC3/IR Spectroscopic No No G141 STIS/FUV-MAMA Spectroscopic No No G140L 1425 STIS/NUV-MAMA Spectroscopic No No G230L 2376 STIS/CCD Spectroscopic No No G430L 4300 STIS/CCD Spectroscopic No No G750L 7751 WFC3/IR Spectroscopic No No G102 WFC3/IR Spectroscopic No No G141 POS-TARG DITHER 0.636 LINE false false 2 41.788 WFC3-IR-DITHER-LINE 2 false The scheduling data was generated by CASM 23.2. CASM was run in Phase II mode. 1445856437155 C:\Users\Pier-Emmanuel\AppData\Local\Temp\OPVisit1101004726524482280.xml (Tic-Visit :proposal-id 14213 :visit-id "01" :proposal-version -1 :trans-version "20150609" :date "26-Oct-2015 10:47:16.0" :trans-errors '(:WARNINGS 1 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 631360 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 14213 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 14213 :visit-id "01" :obset-id "A1" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 14213 :visit-id "01" :orbit-number 1 :pcs-time 241 :si-vis-utilization 2791 :al-overhead-at-end 116 :internal-dur-at-end 825 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3034 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14213 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2811 :al-overhead-at-end 132 :internal-dur-at-end 394 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3034 :pcs-gap 0 ) true 2 0 2 point dither in both x and y direction to mitigate against bad pixels and avoid saturation 2 point dither in both x and y direction to mitigate against bad pixels and avoid saturation Manual fringe flat used instead of default to get higher S/N. BOT has a safety warning but it comes from our target, and the ETC information above confirms the safety of the observations. 1445422292345 The scheduling data was generated by CASM 23.2. CASM was run in Phase II mode. C:\Travail\Back\APT Phase 2\OP-cache\proposal2_phase2_resubmitted-v02.xml (Tic-Visit :proposal-id 14213 :visit-id "02" :proposal-version -1 :trans-version "20150609" :date "21-Oct-2015 11:11:28.0" :trans-errors '(:WARNINGS 1 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 585904 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 14213 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 14213 :visit-id "02" :obset-id "A2" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 14213 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2911 :al-overhead-at-end 116 :internal-dur-at-end 825 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3245 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14213 :visit-id "02" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3022 :al-overhead-at-end 132 :internal-dur-at-end 394 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3245 :pcs-gap 0 ) true 2 0 Manual fringe flat used instead of default to get higher S/N.