12997( 2) - 10-Jul-2012 23:51:18 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12997 Version: 2 Check-in Time: 10-Jul-2012 23:51:18 STScI Edit Number: 0 Title The Blue Horizontal Branch as a Reliable Tracer of Galaxy Stellar Halos ------------------------------------------------------------------------------------ Type Cycle GO 20 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Benjamin F. Williams University of Washington Y CoI: Dr. Julianne Dalcanton University of Washington N CoI: Prof. Puragra Guhathakurta University of California - Santa Cruz N CoI: Dr. Karoline Gilbert University of Washington N CoI: Dr. Tod R. Lauer National Optical Astronomy Observatory, N AURA CoI: Dr. Anil C. Seth University of Utah N CoI: Dr. Jason S. Kalirai Space Telescope Science Institute N CoI: Dr. Dustin Lang Carnegie Mellon University N CoI: Dr. Leo Girardi Osservatorio Astronomico di Padova N ------------------------------------------------------------------------------------ Abstract We propose ACS and WFC3 F475W and F814W imaging in two fields between 5 and 10 kpc along the minor axis of M31. These locations sample the transition between the bulge/disk-dominated and halo-dominated regions. The images would cover a total of 19 square arcminutes and would be used to characterize the complete blue horizontal branch (BHB) populations within the halo/bulge transition zone. The observations will test model predictions of the density of BHB stars and the ratio of BHB to red giant branch stars at these radii. Our present halo model is based on HST measurements of BHB stars from 2 to 35 kpc, but has a large gap in coverage from 5 kpc to 10 kpc. The proposed observations will result in the first reliable M31 halo profile covering such a large radial baseline, breaking degeneracies in current attempts to decompose M31 into bulge, disk, and halo components. Furthermore, this test will validate the use of the BHB to measure halo profiles in other systems, potentially making it possible to characterize galaxy halo populations with photometry that reaches only the horizontal branch. Our proposed observations will bridge the current gap between the large amounts of HST data available in the M31 halo and the excellent HST coverage of the M31 disk. Ultimately, these data will complete the most reliable profile ever measured of the inner regions of the M31 stellar halo, which yields an accurate total stellar halo mass and represents an historical record of how the halo formed. ------------------------------------------------------------------------------------ Observations Description ------------------------ We are performing ACS/WFC and WFC3/UVIS observations in parallel, orienting the telescope so that the fields are aligned with the M31 minor axis. Both cameras will observe for one orbit through the F475W filter and one orbit through the F814W filter. Real Time Justification ----------------------- 12997( 2) - 10-Jul-2012 23:51:18 - [ 2] Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 12997( 2) - 10-Jul-2012 23:51:18 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 M31-MINOR-AX GALAXY, HALO RA=00H44M46.6541S +/- 0.1", J2000 V = 26.5 IS-30 DEC=+40D56'50.08" +/- 0.1" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 2 M31-MINOR-AX GALAXY, HALO RA=00H44M46.6541S +/- 0.1", J2000 V = 26.5 IS-36 DEC=+40D56'50.08" +/- 0.1" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 12997( 2) - 10-Jul-2012 23:51:18 - [ 4] Visit: 01 Visit Requirements: SCHED 100%; ORIENT 79D TO 79 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| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 M31-MINOR-A ACS/WFC ACCUM WFC F475W 1 300 S PAR 2 WITH 1 XIS-30 ------------------------------------------------------------------------------------------------------------------------------------ 2 M31-MINOR-A WFC3/UVI ACCUM UVIS F475W 1 370 S XIS-36 S see below ------------------------------------------------------------------------------------------------------------------------------------ 3 M31-MINOR-A ACS/WFC ACCUM WFC F475W 1 340 S POS TARG 0.125, null; XIS-30 PAR 4 WITH 3 ------------------------------------------------------------------------------------------------------------------------------------ 4 M31-MINOR-A WFC3/UVI ACCUM UVIS F475W 1 360 S XIS-36 S see below ------------------------------------------------------------------------------------------------------------------------------------ 5 M31-MINOR-A ACS/WFC ACCUM WFC F475W 1 1000 S POS TARG 0.125, -0.125; XIS-30 PAR 6 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 M31-MINOR-A WFC3/UVI ACCUM UVIS F475W 1 1020 S XIS-36 S see below ------------------------------------------------------------------------------------------------------------------------------------ 7 M31-MINOR-A ACS/WFC ACCUM WFC F475W 1 340 S POS TARG 0.0 , -0.125; XIS-30 PAR 8 WITH 7 ------------------------------------------------------------------------------------------------------------------------------------ 8 M31-MINOR-A WFC3/UVI ACCUM UVIS F475W 1 390 S XIS-36 S see below ------------------------------------------------------------------------------------------------------------------------------------ 9 M31-MINOR-A ACS/WFC ACCUM WFC F814W 1 300 S PAR 10 WITH 9 XIS-30 see below ------------------------------------------------------------------------------------------------------------------------------------ 10 M31-MINOR-A WFC3/UVI ACCUM UVIS F814W 1 370 S XIS-36 S see below ------------------------------------------------------------------------------------------------------------------------------------ 11 M31-MINOR-A ACS/WFC ACCUM WFC F814W 1 340 S POS TARG 0.125, null; XIS-30 see below PAR 12 WITH 11 ------------------------------------------------------------------------------------------------------------------------------------ 12 M31-MINOR-A WFC3/UVI ACCUM UVIS F814W 1 360 S XIS-36 S see below ------------------------------------------------------------------------------------------------------------------------------------ 13 M31-MINOR-A ACS/WFC ACCUM WFC F814W 1 1000 S POS TARG 0.125, -0.125; XIS-30 see below PAR 14 WITH 13 ------------------------------------------------------------------------------------------------------------------------------------ 14 M31-MINOR-A WFC3/UVI ACCUM UVIS F814W 1 1020 S XIS-36 S see below ------------------------------------------------------------------------------------------------------------------------------------ 12997( 2) - 10-Jul-2012 23:51:18 - [ 5] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 15 M31-MINOR-A ACS/WFC ACCUM WFC F814W 1 340 S POS TARG 0.0 , -0.125; XIS-30 see below PAR 16 WITH 15 ------------------------------------------------------------------------------------------------------------------------------------ 16 M31-MINOR-A WFC3/UVI ACCUM UVIS F814W 1 390 S XIS-36 S see below ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ M31-MINOR-AXIS-30 1 ACS/WFC ACCUM WFC F475W none none none none 1 N/A M31-MINOR-AXIS-36 2 WFC3/UVI ACCUM UVIS F475W none none none none 1 380.0 S S M31-MINOR-AXIS-30 3 ACS/WFC ACCUM WFC F475W none none none none 1 N/A M31-MINOR-AXIS-36 4 WFC3/UVI ACCUM UVIS F475W none none none none 1 370.0 S S M31-MINOR-AXIS-30 5 ACS/WFC ACCUM WFC F475W none none none none 1 N/A M31-MINOR-AXIS-36 6 WFC3/UVI ACCUM UVIS F475W none none none none 1 1030.0 S S M31-MINOR-AXIS-30 7 ACS/WFC ACCUM WFC F475W none none none none 1 N/A M31-MINOR-AXIS-36 8 WFC3/UVI ACCUM UVIS F475W none none none none 1 390.0 S S M31-MINOR-AXIS-30 9 ACS/WFC ACCUM WFC F814W none none none none 2 339.0 S M31-MINOR-AXIS-36 10 WFC3/UVI ACCUM UVIS F814W none none none none 2 380.0 S S M31-MINOR-AXIS-30 11 ACS/WFC ACCUM WFC F814W none none none none 2 379.0 S M31-MINOR-AXIS-36 12 WFC3/UVI ACCUM UVIS F814W none none none none 2 360.0 S S M31-MINOR-AXIS-30 13 ACS/WFC ACCUM WFC F814W none none none none 2 1039.0 S M31-MINOR-AXIS-36 14 WFC3/UVI ACCUM UVIS F814W none none none none 2 1020.0 S S M31-MINOR-AXIS-30 15 ACS/WFC ACCUM WFC F814W none none none none 2 379.0 S M31-MINOR-AXIS-36 16 WFC3/UVI ACCUM UVIS F814W none none none none 2 390.0 S S 12997( 2) - 10-Jul-2012 23:51:18 - [ 6] Summary Form for Proposal 12997 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS, WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 79D TO 79 D, PAR 10 WITH 9, PAR 12 WITH 11, PAR 14 WITH 13, PAR 16 WITH 15, PAR 2 WITH 1, PAR 4 WITH 3, PAR 6 WITH 5, PAR 8 WITH 7, POS TARG 0.0 , -0.125, POS TARG 0.125, -0.125, POS TARG 0.125, null, SCHED 100% ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F475W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names M31-MINOR-AXIS-30, M31-MINOR-AXIS-36 ------------------------------------------------------------------------------------------------------------------------------------