11783( 4) - 13-Jul-2009 20:00:46 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 11783 Version: 4 Check-in Time: 13-Jul-2009 20:00:46 STScI Edit Number: 1 Title The Dynamical Mass of the Bright Cepheid Polaris ------------------------------------------------------------------------------------ Type Cycle GO 17 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Nancy R. Evans Smithsonian Institution Astrophysical Observatory CoI: Dr. Howard E. Bond Space Telescope Science Institute N CoI: Dr. Giuseppe Bono INAF, Osservatorio Astronomico di Roma N CoI: Dr. Margarita Karovska Smithsonian Institution Astrophysical N Observatory CoI: Dr. Edmund Nelan Space Telescope Science Institute N CoI: Dr. Dimitar D. Sasselov Harvard University N CoI: Dr. Gail Schaefer Georgia State University Research N Foundation ------------------------------------------------------------------------------------ Abstract Cepheid variables are of central importance in Galactic and extragalactic astronomy. They are the primary standard candles for measuring extragalactic distances, and they provide critical tests of stellar-evolution theory. Surprisingly, however, until now there was not a single Cepheid with a purely dynamical measurement of its mass. Polaris (alpha UMi) is the nearest and brightest of all Cepheids. It offers the unique opportunity to measure the dynamical mass of a Cepheid, because it is in a binary system for which a single-lined spectroscopic orbit is already available. In Cycle 14, we resolved the system in the UV using ACS/HRC, thus providing the first direct detection of the companion, as well as a first approximation to the dynamical mass. In the present proposal we request one HST orbit per year for the next 3 Cycles, in order to refine the visual orbit. Combined with the HST/FGS parallax (see below), this program will provide an accurate mass for the Cepheid (the error should be about 0.5 Msun by Cycle 17), and the only one based purely on dynamical information. Only HST's combination of high spatial resolution and UV sensitivity can achieve this result. The parallax is a key ingredient in the mass determination. In an ongoing multi-year program (GO-9888, GO-10113, GO-10482), we are using the FGS to improve significantly upon the Hipparcos parallax of Polaris. The continued ACS/HRC imaging proposed here (updated to WFC3 following SM4) will thus provide extremely valuable astrophysical information from a very modest additional investment of observing time. ------------------------------------------------------------------------------------ Observations Description ------------------------ The observations, originally planned for ACS/HRC, will be made with WFC3/UVIS. We will use the FQ232N quad filter, which suppresses the light of Polaris Aa so that it will not saturate. We will take a series of 4-point dithered exposures. 11783( 4) - 13-Jul-2009 20:00:46 - [ 2] One set will be on Polaris A, 0.5 sec each, and a second set also on Polaris A at 0.7 sec each. One extra 0.7-sec exposure is also made, to fill the orbit. According to the WFC3 ETC, even the 0.7 sec exposures should not saturate. We will then move the single star Polaris B to the same chip position and take a 4-point dither set of 45-sec exposures, for the purpose of providing a PSF reference image. We will fill the orbit by taking one more 45-sec exposure on Polaris B. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 11783( 4) - 13-Jul-2009 20:00:46 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 POLARIS STAR, CEPHEID, F3-F9, RA=02H31M29.2000S +/- 0.1", J2000 V = 1.98 +/- 0.1 PULSATING VARIABLE DEC=+89D15'45.90" +/- 0.1" Reference Frame: ICRS Comments: Coordinates are from Hipparcos, but are adjusted so as to place the center of the field of view one-third of the way between Polaris A and Polaris B (which are separated by 18"). This will place both stars within the WFC3 quad filter field of view, as desired, with Polaris A about 6" from the center. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1991.25 0.230315 -0.01175 0.00756 ------------------------------------------------------------------------------------------------------------------------------------ 2 POLARIS-B STAR, F3-F9 RA=02H30M16.6500S +/- 0.1", J2000 V = 8.5 +/- 0.2 DEC=+89D15'34.30" +/- 0.1" Reference Frame: ICRS Comments: These coordinates will place Polaris B at the same location in the FOV as Polaris A, as desired. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1991.25 0.230315 -0.01175 0.00756 ------------------------------------------------------------------------------------------------------------------------------------ 11783( 4) - 13-Jul-2009 20:00:46 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.173 Line_Spacing 0.112 Coordinate_Frame POS-TARG Pattern_Orient 23.884 Angle_Between_Sides 81.785 Center_Pattern YES ------------------------------------------------------------------------------------------------------------------------------------ 11783( 4) - 13-Jul-2009 20:00:46 - [ 5] Visit: 01 Visit Requirements: ORIENT 240D TO 280 D; ORIENT 330D TO 10 D; ORIENT 60D TO 100 D; ORIENT 150D TO 190 D; BETWEEN 01-AUG-2009:00:00:00 AND 01-APR-2010:00:00:00 On Hold Comments: Additional Comments: ORIENT is chosen to place Polaris Ab at 45 +/- 20 deg relative to the diffraction spikes of Polaris Aa. BETWEEN dates added to assure observation is completed by middle of Cycle 17, to maintain proper cadence for this long-term monitoring program. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 POLARIS WFC3/UVI ACCUM UVIS-QUAD FQ232N CR-SPLIT=NO 1 0.5 S GS ACQ SCENARIO BASE1B3; S -SUB PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 POLARIS WFC3/UVI ACCUM UVIS-QUAD FQ232N CR-SPLIT=NO 1 0.7 S PATTERN 1 2 S -SUB ------------------------------------------------------------------------------------------------------------------------------------ 3 POLARIS WFC3/UVI ACCUM UVIS-QUAD FQ232N CR-SPLIT=NO 1 0.7 S POS TARG 0, 0 S -SUB ------------------------------------------------------------------------------------------------------------------------------------ 4 POLARIS-B WFC3/UVI ACCUM UVIS-QUAD FQ232N CR-SPLIT=NO 1 45 S PATTERN 1 4 S -SUB ------------------------------------------------------------------------------------------------------------------------------------ 5 POLARIS-B WFC3/UVI ACCUM UVIS-QUAD FQ232N CR-SPLIT=NO 1 45 S POS TARG 0, 0 S -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 | ------------------------------------------------------------------------------------------------------------------------------------ POLARIS 1 WFC3/UVI ACCUM UVIS-QUA FQ232N 1 none none none 1 N/A S D-SUB POLARIS 1 WFC3/UVI ACCUM UVIS-QUA FQ232N 2 none none none 1 N/A S D-SUB POLARIS 1 WFC3/UVI ACCUM UVIS-QUA FQ232N 3 none none none 1 N/A S D-SUB POLARIS 1 WFC3/UVI ACCUM UVIS-QUA FQ232N 4 none none none 1 N/A S D-SUB POLARIS 2 WFC3/UVI ACCUM UVIS-QUA FQ232N 1 none none none 1 N/A S D-SUB POLARIS 2 WFC3/UVI ACCUM UVIS-QUA FQ232N 2 none none none 1 N/A S D-SUB POLARIS 2 WFC3/UVI ACCUM UVIS-QUA FQ232N 3 none none none 1 N/A S D-SUB POLARIS 2 WFC3/UVI ACCUM UVIS-QUA FQ232N 4 none none none 1 N/A S D-SUB POLARIS 3 WFC3/UVI ACCUM UVIS-QUA FQ232N none none none none 1 N/A S D-SUB 11783( 4) - 13-Jul-2009 20:00:46 - [ 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 | ------------------------------------------------------------------------------------------------------------------------------------ POLARIS-B 4 WFC3/UVI ACCUM UVIS-QUA FQ232N 1 none none none 1 N/A S D-SUB POLARIS-B 4 WFC3/UVI ACCUM UVIS-QUA FQ232N 2 none none none 1 N/A S D-SUB POLARIS-B 4 WFC3/UVI ACCUM UVIS-QUA FQ232N 3 none none none 1 N/A S D-SUB POLARIS-B 4 WFC3/UVI ACCUM UVIS-QUA FQ232N 4 none none none 1 N/A S D-SUB POLARIS-B 5 WFC3/UVI ACCUM UVIS-QUA FQ232N none none none none 1 N/A S D-SUB 11783( 4) - 13-Jul-2009 20:00:46 - [ 7] Summary Form for Proposal 11783 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS-QUAD-SUB ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 01-AUG-2009:00:00:00 AND 01-APR-2010:00:00:00, GS ACQ SCENARIO BASE1B3, ORIENT 150D TO 190 D, ORIENT 240D TO 280 D, ORIENT 330D TO 10 D, ORIENT 60D TO 100 D, PATTERN 1 1, PATTERN 1 2, PATTERN 1 4, POS TARG 0, 0 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements FQ232N ------------------------------------------------------------------------------------------------------------------------------------ Target Names POLARIS, POLARIS-B ------------------------------------------------------------------------------------------------------------------------------------