14213( 7) - 26-Oct-2015 11:11:42 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 14213 Version: 7 Check-in Time: 26-Oct-2015 11:11:42 STScI Edit Number: 3 Title Defining New IR-Bright Flux Standards for Cosmology Applications ------------------------------------------------------------------------------------ Type Cycle GO 23 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Pier-Emmanuel Tremblay Space Telescope Science Institute Y CoI: Dr. Ralph C. Bohlin Space Telescope Science Institute N CoI: Dr. Jason S. Kalirai Space Telescope Science Institute N CoI: Dr. Susana E. Deustua Space Telescope Science Institute N CoI: Dr. Adam Riess The Johns Hopkins University N ------------------------------------------------------------------------------------ Abstract 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. ------------------------------------------------------------------------------------ Observations Description ------------------------ 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 14213( 7) - 26-Oct-2015 11:11:42 - [ 2] < 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. ------------------------------------------------------------------------------------ 14213( 7) - 26-Oct-2015 11:11:42 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 WD1327-083 STAR, DA RA=13H30M13.6402S +/- 0.04", J2000 V = 12.34 +/- 0.05 DEC=-08D34'29.50" +/- 0.04" Reference Frame: ICRS Comments: Coordinates and proper motions from Hipparcos. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 -0.0745870754601794 -0.47597 0.05755 ------------------------------------------------------------------------------------------------------------------------------------ 2 WD2341+322 STAR, DA RA=23H43M50.7202S +/- 0.2", J2000 V = 12.95 +/- 0.05 DEC=+32D32'46.76" +/- 0.2" Reference Frame: ICRS Comments: Coordinates and proper motions from Hipparcos. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 -0.01653465561242007 -0.06908 0.05839 ------------------------------------------------------------------------------------------------------------------------------------ 14213( 7) - 26-Oct-2015 11:11:42 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-IR-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.636 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 41.788 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 14213( 7) - 26-Oct-2015 11:11:42 - [ 5] Visit: 01 Visit Requirements: SCHED 80%; ORIENT 130D TO 210 D; ORIENT 310D TO 30 D 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 WD1327-083 WFC3/IR MULTIAC GRISM512 G141 NSAMP=11, SAMP-SEQ=SPARS5 1 DEF GS ACQ SCENARIO ONEB1B3; CUM (60.136 S) PATTERN 2 1 Comments: 2 point dither in both x and y direction to mitigate against bad pixels and avoid saturation ------------------------------------------------------------------------------------------------------------------------------------ 2 WD1327-083 WFC3/IR MULTIAC GRISM512 G102 NSAMP=15, SAMP-SEQ=SPARS5 1 DEF PATTERN 2 2 CUM (83.508 S) Comments: 2 point dither in both x and y direction to mitigate against bad pixels and avoid saturation ------------------------------------------------------------------------------------------------------------------------------------ 3 WD1327-083 STIS/CCD ACQ F28X50LP MIRROR 1 1 S (1 S) GS ACQ SCENARIO BASE1B3 ------------------------------------------------------------------------------------------------------------------------------------ 4 WD1327-083 STIS/CCD ACCUM 52X2 G750L 7751 CR-SPLIT=3, GAIN=4, WAVECAL=NO 1 936 S (936 S) Comments: Manual fringe flat used instead of default to get higher S/N. ------------------------------------------------------------------------------------------------------------------------------------ 5 WAVE STIS/CCD ACCUM 52X0.1 G750L 7751 1 DEF (0 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 NONE STIS/CCD ACCUM 0.3X0.09 G750L 7751 LAMP=TUNGSTEN, GAIN=4 4 120 S (480 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 WAVE STIS/CCD ACCUM 52X0.1 G430L 4300 1 DEF (0 S) ------------------------------------------------------------------------------------------------------------------------------------ 8 WD1327-083 STIS/CCD ACCUM 52X2E1 G430L 4300 CR-SPLIT=2, GAIN=4, WAVECAL=NO 1 200 S (200 S) ------------------------------------------------------------------------------------------------------------------------------------ 9 WAVE STIS/NUV ACCUM 31X0.05ND G230L 2376 1 DEF (0 S) -MAMA C ------------------------------------------------------------------------------------------------------------------------------------ 10 WD1327-083 STIS/NUV ACCUM 52X2 G230L 2376 WAVECAL=NO 1 605 S (605 -MAMA S) ------------------------------------------------------------------------------------------------------------------------------------ 11 WD1327-083 STIS/FUV ACCUM 52X2 G140L 1425 WAVECAL=NO 1 1244 S -MAMA (1244 S) Comments: BOT has a safety warning but it comes from our target, and the ETC information above confirms the safety of the observations. ------------------------------------------------------------------------------------------------------------------------------------ 14213( 7) - 26-Oct-2015 11:11:42 - [ 6] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 12 WAVE STIS/FUV ACCUM 52X0.05 G140L 1425 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 | ------------------------------------------------------------------------------------------------------------------------------------ WD1327-083 1 WFC3/IR MULTIAC GRISM512 G141 1 none none none 1 N/A CUM WD1327-083 1 WFC3/IR MULTIAC GRISM512 G141 2 none none none 1 N/A CUM WD1327-083 2 WFC3/IR MULTIAC GRISM512 G102 1 none none none 1 N/A CUM WD1327-083 2 WFC3/IR MULTIAC GRISM512 G102 2 none none none 1 N/A CUM WD1327-083 3 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A WD1327-083 4 STIS/CCD ACCUM 52X2 G750L 7751 none none none 1 1 N/A WD1327-083 4 STIS/CCD ACCUM 52X2 G750L 7751 none none none 2 1 N/A WD1327-083 4 STIS/CCD ACCUM 52X2 G750L 7751 none none none 3 1 N/A WAVE 5 STIS/CCD ACCUM 52X0.1 G750L 7751 none none none none 1 N/A NONE 6 STIS/CCD ACCUM 0.3X0.09 G750L 7751 none none 1 none 1 N/A NONE 6 STIS/CCD ACCUM 0.3X0.09 G750L 7751 none none 2 none 1 N/A NONE 6 STIS/CCD ACCUM 0.3X0.09 G750L 7751 none none 3 none 1 N/A NONE 6 STIS/CCD ACCUM 0.3X0.09 G750L 7751 none none 4 none 1 N/A WAVE 7 STIS/CCD ACCUM 52X0.1 G430L 4300 none none none none 2 N/A WD1327-083 8 STIS/CCD ACCUM 52X2E1 G430L 4300 none none none 1 2 N/A WD1327-083 8 STIS/CCD ACCUM 52X2E1 G430L 4300 none none none 2 2 N/A WAVE 9 STIS/NUV ACCUM 31X0.05N G230L 2376 none none none none 2 N/A -MAMA DC WD1327-083 10 STIS/NUV ACCUM 52X2 G230L 2376 none none none none 2 N/A -MAMA WD1327-083 11 STIS/FUV ACCUM 52X2 G140L 1425 none none none none 2 N/A -MAMA WAVE 12 STIS/FUV ACCUM 52X0.05 G140L 1425 none none none none 2 N/A -MAMA 14213( 7) - 26-Oct-2015 11:11:42 - [ 7] Visit: 02 Visit Requirements: 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 WD2341+322 WFC3/IR MULTIAC GRISM512 G141 NSAMP=9, SAMP-SEQ=SPARS10 1 DEF PATTERN 2 1 CUM (128.453 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 WD2341+322 WFC3/IR MULTIAC GRISM512 G102 NSAMP=12, SAMP-SEQ=SPARS10 1 DEF PATTERN 2 2 CUM (175.983 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 WD2341+322 STIS/CCD ACQ F28X50LP MIRROR 1 1 S (1 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 WD2341+322 STIS/CCD ACCUM 52X2 G750L 7751 CR-SPLIT=3, GAIN=4, WAVECAL=NO 1 939.0 S (939 S) Comments: Manual fringe flat used instead of default to get higher S/N. ------------------------------------------------------------------------------------------------------------------------------------ 5 WAVE STIS/CCD ACCUM 52X0.1 G750L 7751 1 DEF (0 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 NONE STIS/CCD ACCUM 0.3X0.09 G750L 7751 LAMP=TUNGSTEN, GAIN=4 4 120 S (480 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 WAVE STIS/CCD ACCUM 52X0.1 G430L 4300 1 DEF (0 S) ------------------------------------------------------------------------------------------------------------------------------------ 8 WD2341+322 STIS/CCD ACCUM 52X2E1 G430L 4300 CR-SPLIT=2, GAIN=4, WAVECAL=NO 1 240.0 S (240 S) ------------------------------------------------------------------------------------------------------------------------------------ 9 WAVE STIS/NUV ACCUM 31X0.05ND G230L 2376 1 DEF (0 S) -MAMA C ------------------------------------------------------------------------------------------------------------------------------------ 10 WD2341+322 STIS/NUV ACCUM 52X2 G230L 2376 WAVECAL=NO 1 650 S (650 -MAMA S) ------------------------------------------------------------------------------------------------------------------------------------ 11 WD2341+322 STIS/FUV ACCUM 52X2 G140L 1425 WAVECAL=NO 1 1370 S -MAMA (1370 S) ------------------------------------------------------------------------------------------------------------------------------------ 12 WAVE STIS/FUV ACCUM 52X0.05 G140L 1425 1 DEF (0 S) -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 14213( 7) - 26-Oct-2015 11:11:42 - [ 8] 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 | ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ WD2341+322 1 WFC3/IR MULTIAC GRISM512 G141 1 none none none 1 N/A CUM WD2341+322 1 WFC3/IR MULTIAC GRISM512 G141 2 none none none 1 N/A CUM WD2341+322 2 WFC3/IR MULTIAC GRISM512 G102 1 none none none 1 N/A CUM WD2341+322 2 WFC3/IR MULTIAC GRISM512 G102 2 none none none 1 N/A CUM WD2341+322 3 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A WD2341+322 4 STIS/CCD ACCUM 52X2 G750L 7751 none none none 1 1 N/A WD2341+322 4 STIS/CCD ACCUM 52X2 G750L 7751 none none none 2 1 N/A WD2341+322 4 STIS/CCD ACCUM 52X2 G750L 7751 none none none 3 1 N/A WAVE 5 STIS/CCD ACCUM 52X0.1 G750L 7751 none none none none 1 N/A NONE 6 STIS/CCD ACCUM 0.3X0.09 G750L 7751 none none 1 none 1 N/A NONE 6 STIS/CCD ACCUM 0.3X0.09 G750L 7751 none none 2 none 1 N/A NONE 6 STIS/CCD ACCUM 0.3X0.09 G750L 7751 none none 3 none 1 N/A NONE 6 STIS/CCD ACCUM 0.3X0.09 G750L 7751 none none 4 none 1 N/A WAVE 7 STIS/CCD ACCUM 52X0.1 G430L 4300 none none none none 2 N/A WD2341+322 8 STIS/CCD ACCUM 52X2E1 G430L 4300 none none none 1 2 N/A WD2341+322 8 STIS/CCD ACCUM 52X2E1 G430L 4300 none none none 2 2 N/A WAVE 9 STIS/NUV ACCUM 31X0.05N G230L 2376 none none none none 2 N/A -MAMA DC WD2341+322 10 STIS/NUV ACCUM 52X2 G230L 2376 none none none none 2 N/A -MAMA WD2341+322 11 STIS/FUV ACCUM 52X2 G140L 1425 none none none none 2 N/A -MAMA WAVE 12 STIS/FUV ACCUM 52X0.05 G140L 1425 none none none none 2 N/A -MAMA 14213( 7) - 26-Oct-2015 11:11:42 - [ 9] Summary Form for Proposal 14213 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 0.3X0.09, 31X0.05NDC, 52X0.05, 52X0.1, 52X2, 52X2E1, F28X50LP, GRISM512 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA, STIS/NUV-MAMA, WFC3/IR ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ, MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=2, CR-SPLIT=3, GAIN=4, LAMP=TUNGSTEN, NSAMP=11, NSAMP=12, NSAMP=15, NSAMP=9, SAMP-SEQ=SPARS10, SAMP-SEQ=SPARS5, WAVECAL=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GS ACQ SCENARIO BASE1B3, GS ACQ SCENARIO ONEB1B3, ORIENT 130D TO 210 D, ORIENT 310D TO 30 D, PATTERN 2 1, PATTERN 2 2, SCHED 80% ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G102, G140L, G141, G230L, G430L, G750L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names NONE, WAVE, WD1327-083, WD2341+322 ------------------------------------------------------------------------------------------------------------------------------------