12985( 9) - 13-Nov-2012 19:45:02 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12985 Version: 9 Check-in Time: 13-Nov-2012 19:45:02 STScI Edit Number: 2 Title Determining the Mass of Proxima Centauri through Astrometric Microlensing ------------------------------------------------------------------------------------ Type Cycle GO 20 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Kailash C. Sahu Space Telescope Science Institute Y CoI: Dr. Howard E. Bond Space Telescope Science Institute N CoI: Dr. Jay Anderson Space Telescope Science Institute N CoI: Dr. Martin Dominik University of St. Andrews N ------------------------------------------------------------------------------------ Abstract We propose to determine the mass of our nearest neighbor, Proxima Centauri, using the novel technique of astrometric microlensing. Proxima is a dM6e star, with an estimated mass of about 0.12 Msun, lying at a distance of 1.3 pc and having a large proper motion of 3.8 arcsec/yr. In a reprise of the famous 1919 solar eclipse that verified general relativity, Proxima will pass in front of a pair of 18th-magnitude background stars in 2015, affording us two independent opportunities to measure the relativistic deflection. The first passage will occur in May 2015 (impact parameter 1.5 arcsec), and the second in June 2015 (impact parameter 1.4 arcsec). As Proxima passes in front, it will cause a relativistic deflection of the background stars' images by ~0.5 milliarcsec, an amount readily detectable with HST/WFC3. The gravitational deflection angle depends only upon the distances and relative positions of the stars, and the mass of the lens (Proxima). Since the distance to Proxima is well known from accurate parallax measurements, and the relative stellar positions can be determined precisely before the event, the astrometric measurement offers a unique and direct method to measure the mass of a single, isolated star. We anticipate better than 10% accuracy for the mass determination. The mass of Proxima is of special interest because it is the nearest M dwarf, representing the most common type of star in the Galaxy, for which the mass-luminosity relation is still uncertain at present. ------------------------------------------------------------------------------------ Observations Description ------------------------ The first epoch observations will be taken in a few different filters (F475W, F555W, F606W, F814W) to better characterize the spectral type of the source. Subsequent observations will be taken mainly in 2 filters (F606W and F814W). We will obtain one short (0.5 sec) exposure to get an unsaturated image of Proxima, in order to register its position. The other exposures will be of 90 to 200 sec durations, so that the source stars will have a S/N & 300 in each exposure. We can obtain about 10 such exposures in each orbit, at 2 dither positions, which would be adequate to achieve the astrometric accuracy required for the project. Real Time Justification ----------------------- 12985( 9) - 13-Nov-2012 19:45:02 - [ 2] Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 12985( 9) - 13-Nov-2012 19:45:02 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PROXIMA-CEN- STAR, K V-IV RA=14H29M34.3300S +/- 0.1", J2000 V = 18.4 +/- 0.2 SOURCE DEC=-62D40'33.98" +/- 0.1" Reference Frame: ICRS Comments: This object was updated to the SOURCE that Proxima-Cen is going to lens. At present, the source and proxima-cen are separated by about 10.5 arcsec, and this separation will slowly decrease to 1.5 arcsec in 2015. ------------------------------------------------------------------------------------------------------------------------------------ 12985( 9) - 13-Nov-2012 19:45:02 - [ 4] Visit: 01 Visit Requirements: ORIENT 140.0D TO 152.0 D; BETWEEN 25-AUG-2012 AND 15-OCT-2012 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 PROXIMA-CEN WFC3/UVI ACCUM UVIS2-2K2 F814W FLASH=12 1 0.5 S POS TARG 10.4, 9 -SOURCE S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 2 PROXIMA-CEN WFC3/UVI ACCUM UVIS2-2K2 F814W FLASH=10 1 70 S SAME POS AS 1 -SOURCE S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 3 PROXIMA-CEN WFC3/UVI ACCUM UVIS2-2K2 F606W FLASH=8 1 100 S POS TARG 14.35, 9 -SOURCE S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 4 PROXIMA-CEN WFC3/UVI ACCUM UVIS2-2K2 F606W FLASH=12 1 0.5 S POS TARG 14.35, 9 -SOURCE S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 5 PROXIMA-CEN WFC3/UVI ACCUM UVIS2-2K2 F555W FLASH=12 1 0.5 S POS TARG 10.39, 12.95 -SOURCE S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 6 PROXIMA-CEN WFC3/UVI ACCUM UVIS2-2K2 F555W FLASH=5 1 200 S SAME POS AS 5 -SOURCE S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 7 PROXIMA-CEN WFC3/UVI ACCUM UVIS2-2K2 F475W FLASH=8 1 200 S POS TARG 6.45, 8.98 -SOURCE S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 8 PROXIMA-CEN WFC3/UVI ACCUM UVIS2-2K2 F475W FLASH=12 1 0.5 S POS TARG 6.45, 8.98 -SOURCE S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 9 PROXIMA-CEN WFC3/UVI ACCUM UVIS2-2K2 F555W FLASH=6 1 175 S POS TARG 10.43, 5.05 -SOURCE S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 10 PROXIMA-CEN WFC3/UVI ACCUM UVIS2-2K2 F555W FLASH=12 1 0.5 S POS TARG 10.43, 5.05 -SOURCE S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ PROXIMA-CEN-SOURCE 1 WFC3/UVI ACCUM UVIS2-2K F814W none none none none 1 N/A S 2C-SUB PROXIMA-CEN-SOURCE 2 WFC3/UVI ACCUM UVIS2-2K F814W none none none none 1 N/A S 2C-SUB PROXIMA-CEN-SOURCE 3 WFC3/UVI ACCUM UVIS2-2K F606W none none none none 1 N/A S 2C-SUB 12985( 9) - 13-Nov-2012 19:45:02 - [ 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 | ------------------------------------------------------------------------------------------------------------------------------------ PROXIMA-CEN-SOURCE 4 WFC3/UVI ACCUM UVIS2-2K F606W none none none none 1 N/A S 2C-SUB PROXIMA-CEN-SOURCE 5 WFC3/UVI ACCUM UVIS2-2K F555W none none none none 1 N/A S 2C-SUB PROXIMA-CEN-SOURCE 6 WFC3/UVI ACCUM UVIS2-2K F555W none none none none 1 N/A S 2C-SUB PROXIMA-CEN-SOURCE 7 WFC3/UVI ACCUM UVIS2-2K F475W none none none none 1 N/A S 2C-SUB PROXIMA-CEN-SOURCE 8 WFC3/UVI ACCUM UVIS2-2K F475W none none none none 1 N/A S 2C-SUB PROXIMA-CEN-SOURCE 9 WFC3/UVI ACCUM UVIS2-2K F555W none none none none 1 N/A S 2C-SUB PROXIMA-CEN-SOURCE 10 WFC3/UVI ACCUM UVIS2-2K F555W none none none none 1 N/A S 2C-SUB 12985( 9) - 13-Nov-2012 19:45:02 - [ 6] Visit: 02 Visit Requirements: ORIENT 326.12D TO 326.12 D; BETWEEN 25-MAR-2013 AND 01-APR-2013 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 PROXIMA-CEN WFC3/UVI ACCUM UVIS2-2K2 F814W FLASH=12 1 0.5 S POS TARG 10.4, 9 -SOURCE S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 2 PROXIMA-CEN WFC3/UVI ACCUM UVIS2-2K2 F814W FLASH=10 1 70 S SAME POS AS 1 -SOURCE S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 3 PROXIMA-CEN WFC3/UVI ACCUM UVIS2-2K2 F606W FLASH=8 1 100 S POS TARG 14.35, 9 -SOURCE S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 4 PROXIMA-CEN WFC3/UVI ACCUM UVIS2-2K2 F606W FLASH=12 1 0.5 S POS TARG 14.35, 9 -SOURCE S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 5 PROXIMA-CEN WFC3/UVI ACCUM UVIS2-2K2 F555W FLASH=12 1 0.5 S POS TARG 10.39, 12.95 -SOURCE S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 6 PROXIMA-CEN WFC3/UVI ACCUM UVIS2-2K2 F555W FLASH=5 1 200 S SAME POS AS 5 -SOURCE S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 7 PROXIMA-CEN WFC3/UVI ACCUM UVIS2-2K2 F475W FLASH=8 1 200 S POS TARG 6.45, 8.98 -SOURCE S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 8 PROXIMA-CEN WFC3/UVI ACCUM UVIS2-2K2 F475W FLASH=12 1 0.5 S POS TARG 6.45, 8.98 -SOURCE S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 9 PROXIMA-CEN WFC3/UVI ACCUM UVIS2-2K2 F555W FLASH=8 1 150 S POS TARG 10.43, 5.05 -SOURCE S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 10 PROXIMA-CEN WFC3/UVI ACCUM UVIS2-2K2 F555W FLASH=12 1 0.5 S POS TARG 10.43, 5.05 -SOURCE S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ PROXIMA-CEN-SOURCE 1 WFC3/UVI ACCUM UVIS2-2K F814W none none none none 1 N/A S 2C-SUB PROXIMA-CEN-SOURCE 2 WFC3/UVI ACCUM UVIS2-2K F814W none none none none 1 N/A S 2C-SUB PROXIMA-CEN-SOURCE 3 WFC3/UVI ACCUM UVIS2-2K F606W none none none none 1 N/A S 2C-SUB 12985( 9) - 13-Nov-2012 19:45:02 - [ 7] 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 | ------------------------------------------------------------------------------------------------------------------------------------ PROXIMA-CEN-SOURCE 4 WFC3/UVI ACCUM UVIS2-2K F606W none none none none 1 N/A S 2C-SUB PROXIMA-CEN-SOURCE 5 WFC3/UVI ACCUM UVIS2-2K F555W none none none none 1 N/A S 2C-SUB PROXIMA-CEN-SOURCE 6 WFC3/UVI ACCUM UVIS2-2K F555W none none none none 1 N/A S 2C-SUB PROXIMA-CEN-SOURCE 7 WFC3/UVI ACCUM UVIS2-2K F475W none none none none 1 N/A S 2C-SUB PROXIMA-CEN-SOURCE 8 WFC3/UVI ACCUM UVIS2-2K F475W none none none none 1 N/A S 2C-SUB PROXIMA-CEN-SOURCE 9 WFC3/UVI ACCUM UVIS2-2K F555W none none none none 1 N/A S 2C-SUB PROXIMA-CEN-SOURCE 10 WFC3/UVI ACCUM UVIS2-2K F555W none none none none 1 N/A S 2C-SUB 12985( 9) - 13-Nov-2012 19:45:02 - [ 8] Summary Form for Proposal 12985 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2-2K2C-SUB ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=10, FLASH=12, FLASH=5, FLASH=6, FLASH=8 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 25-AUG-2012 AND 15-OCT-2012, BETWEEN 25-MAR-2013 AND 01-APR-2013, ORIENT 140.0D TO 152.0 D, ORIENT 326.12D TO 326.12 D, POS TARG 10.39, 12.95, POS TARG 10.4, 9, POS TARG 10.43, 5.05, POS TARG 14.35, 9, POS TARG 6.45, 8.98, SAME POS AS 1, SAME POS AS 5 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F475W, F555W, F606W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names PROXIMA-CEN-SOURCE ------------------------------------------------------------------------------------------------------------------------------------