15498( 2) - 06-Dec-2018 13:28:17 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15498 Version: 2 Check-in Time: 06-Dec-2018 13:28:17 STScI Edit Number: 0 Title Building an astrometric reference frame for tests of General Relativity with stellar orbits at the Galactic center with HST and GAIA ------------------------------------------------------------------------------------ Type Cycle GO 26 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Tuan Do University of California - Los Angeles Y CoI: Dr. Andrea M. Ghez University of California - Los Angeles N CoI: Dr. Shoko Sakai University of California - Los Angeles N CoI: Dr. Jessica Ryan Lu University of California - Berkeley N CoI: Dr. Aurelien Hees University of California - Los Angeles N CoI: Dr. Mark R. Morris University of California - Los Angeles N CoI: Matthew Hosek Jr. University of Hawaii N CoI: Dr. Jay Anderson Space Telescope Science Institute N CoI: Dr. Eric E. Becklin University of California - Los Angeles N CoI: Dr. Gunther Witzel University of California - Los Angeles N CoI: Dr. Keith Matthews California Institute of Technology N ------------------------------------------------------------------------------------ Abstract The short-period star S0-2 will reach its closest approach to the supermassive black hole at the Galactic center in 2018 at a separation of < 120 AU. This event will offer the first of a series of tests of General Relativity with stellar orbits around a supermassive black hole, an unexplored regime for tests of gravity. While S0-2 has been monitored for over 20 years with high angular resolution measurements from the ground, the astrometric reference frame is currently not stable enough for GR tests. The current reference frame is constructed using observations of 7 radio masers with narrow-field adaptive optics imaging from the ground. While this method provides a reference frame that is stable enough to measure the Keplerian orbits, it does not meet the more stringent requirements needed to measure post-Newtonian effects such as the precession of the periapse of the orbit. The small number of reference stars and the systematic errors associated with using large mosaics to observe these stars limit the accuracy of this method. We propose to construct a new reference frame for tests of gravity with WFC3-IR observations in Cycles 25, 26, & 27. When combined with absolute positions and proper motions from GAIA, these observations will provide the required precision in the reference frame. The WFC3-IR field of view has over 1000 times greater areal coverage than the narrow-field AO observations, providing 3 times the number of absolute reference sources from GAIA. The proposed observations build on a legacy of HST, GAIA, and adaptive optics data to open an era of gravitational science with orbits at the Galactic center. ------------------------------------------------------------------------------------ Observations Description ------------------------ This is an astrometric program to measure precise astrometry for a sample of stars in common with GAIA at the Galactic center in order to build a stable reference frame for the measurements of orbits around the supermassive black hole at the Galactic center. The stability of the reference frame is driven by the goal of measuring the effect of General Relativity on the orbit of the star 15498( 2) - 06-Dec-2018 13:28:17 - [ 2] S0-2. As such, this program requires very high astrometric precision and minimal systematic errors. We have designed the Phase II observations to achieve these goals. We request that observations in Cycle 25 to have an ORIENT=270 deg, the same as GO-13770, in order to optimize the astrometric performance and minize the effect of residual optical distortions. We request that the observations be made between 2018-02-01 and 2018-05-31 in order to be close in time to GAIA observations of this region. This time range will also allow us to observe near the closest approach of the star S0-2 to the supermassive black hole in 2018. We request observations in the F153M filter with a spiral dither pattern for astrometry. We also plan to observe with the F127M filter to check against the astrometry at F153M, since the stellar crowding is much higher at F153M. Since the GAIA sources are very blue compared to the background Galactic center sources, we will be able to use the F127M astrometry instead of F153M for confused sources at F153M. ------------------------------------------------------------------------------------ 15498( 2) - 06-Dec-2018 13:28:17 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SGR-A STELLAR CLUSTER, RA=17H45M40.0360S, J2000 V = 14 NUCLEUS DEC=-29D00'28.17" Reference Frame: Other: SIMBAD Extended: NO Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. ------------------------------------------------------------------------------------------------------------------------------------ 15498( 2) - 06-Dec-2018 13:28:17 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 6 Primary_Pattern Secondary_Pattern Pattern_Type SPIRAL Pattern_Purpose DITHER Number_Of_Points 15 Point_Spacing 0.42 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 11.0 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 7 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-IR-DITHER-BOX-MIN Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.572 Line_Spacing 0.365 Coordinate_Frame POS-TARG Pattern_Orient 18.528 Angle_Between_Sides 74.653 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 15498( 2) - 06-Dec-2018 13:28:17 - [ 5] Visit: 01 Visit Requirements: ORIENT 270D TO 270 D; BETWEEN 01-FEB-2019:00:00:00 AND 06-JUN-2019:00:00:00 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 SGR-A WFC3/IR MULTIAC IR-FIX F153M SAMP-SEQ=STEP50, NSAMP=12 1 DEF PATTERN 6 1 CUM (5238.494 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SGR-A WFC3/IR MULTIAC IR-FIX F127M NSAMP=11, SAMP-SEQ=STEP100 1 DEF PATTERN 7 2 CUM (1996.928 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SGR-A WFC3/IR MULTIAC IR-FIX F153M NSAMP=11, SAMP-SEQ=STEP50 1 DEF CUM (299.232 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 | ------------------------------------------------------------------------------------------------------------------------------------ SGR-A 1 WFC3/IR MULTIAC IR-FIX F153M 1 none none none 1 N/A CUM SGR-A 1 WFC3/IR MULTIAC IR-FIX F153M 2 none none none 1 N/A CUM SGR-A 1 WFC3/IR MULTIAC IR-FIX F153M 3 none none none 1 N/A CUM SGR-A 1 WFC3/IR MULTIAC IR-FIX F153M 4 none none none 1 N/A CUM SGR-A 1 WFC3/IR MULTIAC IR-FIX F153M 5 none none none 1 N/A CUM SGR-A 1 WFC3/IR MULTIAC IR-FIX F153M 6 none none none 1 N/A CUM SGR-A 1 WFC3/IR MULTIAC IR-FIX F153M 7 none none none 1 N/A CUM SGR-A 1 WFC3/IR MULTIAC IR-FIX F153M 8 none none none 2 N/A CUM SGR-A 1 WFC3/IR MULTIAC IR-FIX F153M 9 none none none 2 N/A CUM SGR-A 1 WFC3/IR MULTIAC IR-FIX F153M 10 none none none 2 N/A CUM SGR-A 1 WFC3/IR MULTIAC IR-FIX F153M 11 none none none 2 N/A CUM SGR-A 1 WFC3/IR MULTIAC IR-FIX F153M 12 none none none 2 N/A CUM 15498( 2) - 06-Dec-2018 13:28:17 - [ 6] 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 | ------------------------------------------------------------------------------------------------------------------------------------ SGR-A 1 WFC3/IR MULTIAC IR-FIX F153M 13 none none none 2 N/A CUM SGR-A 1 WFC3/IR MULTIAC IR-FIX F153M 14 none none none 2 N/A CUM SGR-A 1 WFC3/IR MULTIAC IR-FIX F153M 15 none none none 3 N/A CUM SGR-A 2 WFC3/IR MULTIAC IR-FIX F127M 1 none none none 3 N/A CUM SGR-A 2 WFC3/IR MULTIAC IR-FIX F127M 2 none none none 3 N/A CUM SGR-A 2 WFC3/IR MULTIAC IR-FIX F127M 3 none none none 3 N/A CUM SGR-A 2 WFC3/IR MULTIAC IR-FIX F127M 4 none none none 3 N/A CUM SGR-A 3 WFC3/IR MULTIAC IR-FIX F153M none none none none 3 N/A CUM 15498( 2) - 06-Dec-2018 13:28:17 - [ 7] Summary Form for Proposal 15498 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/IR ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters NSAMP=11, NSAMP=12, SAMP-SEQ=STEP100, SAMP-SEQ=STEP50 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 01-FEB-2019:00:00:00 AND 06-JUN-2019:00:00:00, ORIENT 270D TO 270 D, PATTERN 6 1, PATTERN 7 2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F127M, F153M ------------------------------------------------------------------------------------------------------------------------------------ Target Names SGR-A ------------------------------------------------------------------------------------------------------------------------------------