10891( 3) - 06/12/06 09:11 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 10891 Version: 3 Check-in Time: 12-Jun-2006 13:11:11 STScI Edit Number: Title The Dynamical Mass of the Bright Cepheid Polaris ------------------------------------------------------------------------------------ Type Cycle Parallel Pointing Tolerance GO 15 ------------------------------------------------------------------------------------ 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 Space Telescope Science Institute N ------------------------------------------------------------------------------------ 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 imaging proposed here will thus provide extremely valuable astrophysical information from a very modest additional investment of observing time. ------------------------------------------------------------------------------------ 10891( 3) - 06/12/06 09:11 - [ 2] Observations Description ------------------------ The observations with ACS/HRC will consist of a series of 0.3-sec exposures in F220W, with dithering to improve the astrometric accuracy. At each of 4 dither positions we will obtain 5x0.3 sec exposures, for a grand total of 20 frames. The aim is to resolve the close companion of Polaris, and measure the separation and position angle. The target will be positioned in the HRC field of view so as to also show the wide companion, Polaris B, which will serve as a check on the position angle measurement. We will then move the telescope so as to place the companion Polaris B at the SAME set of 4 dither positions used for Polaris A. At each of the 4 positions we will take 4x20 sec, for a grand total of 16 frames. The purpose of these exposures is for Polaris B to provide a PSF of a single star at the same positions in the field of view used for the very close binary Polaris A, and exposed to the same count level as for Polaris A (since the flux ratio between B and A is 0.015). Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 10891( 3) - 06/12/06 09:11 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 POLARIS STAR, F3-F9, CEPHEID, 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 HRC 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 10891( 3) - 06/12/06 09:11 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-HRC-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 1.9 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 5.85 Angle_Between_Sides Center_Pattern YES ------------------------------------------------------------------------------------------------------------------------------------ 10891( 3) - 06/12/06 09:11 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENT 253.43965D TO 253.43965 D; BETWEEN 01-AUG-2006:00:00:00 AND 15-OCT- 2006:00:00:00 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| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 POLARIS ACS/HRC ACCUM HRC-FIX F220W CR-SPLIT=NO,GAIN=4 5 0.3 S PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 POLARIS-B ACS/HRC ACCUM HRC-FIX F220W CR-SPLIT=NO,GAIN=4 4 20 S PATTERN 1 2 ------------------------------------------------------------------------------------------------------------------------------------ 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 ACS/HRC ACCUM HRC-FIX F220W 1 none 1 none 1 N/A POLARIS 1 ACS/HRC ACCUM HRC-FIX F220W 1 none 2 none 1 N/A POLARIS 1 ACS/HRC ACCUM HRC-FIX F220W 1 none 3 none 1 N/A POLARIS 1 ACS/HRC ACCUM HRC-FIX F220W 1 none 4 none 1 N/A POLARIS 1 ACS/HRC ACCUM HRC-FIX F220W 1 none 5 none 1 N/A POLARIS 1 ACS/HRC ACCUM HRC-FIX F220W 2 none 1 none 1 N/A POLARIS 1 ACS/HRC ACCUM HRC-FIX F220W 2 none 2 none 1 N/A POLARIS 1 ACS/HRC ACCUM HRC-FIX F220W 2 none 3 none 1 N/A POLARIS 1 ACS/HRC ACCUM HRC-FIX F220W 2 none 4 none 1 N/A POLARIS 1 ACS/HRC ACCUM HRC-FIX F220W 2 none 5 none 1 N/A POLARIS 1 ACS/HRC ACCUM HRC-FIX F220W 3 none 1 none 1 N/A POLARIS 1 ACS/HRC ACCUM HRC-FIX F220W 3 none 2 none 1 N/A POLARIS 1 ACS/HRC ACCUM HRC-FIX F220W 3 none 3 none 1 N/A POLARIS 1 ACS/HRC ACCUM HRC-FIX F220W 3 none 4 none 1 N/A POLARIS 1 ACS/HRC ACCUM HRC-FIX F220W 3 none 5 none 1 N/A POLARIS 1 ACS/HRC ACCUM HRC-FIX F220W 4 none 1 none 1 N/A POLARIS 1 ACS/HRC ACCUM HRC-FIX F220W 4 none 2 none 1 N/A POLARIS 1 ACS/HRC ACCUM HRC-FIX F220W 4 none 3 none 1 N/A POLARIS 1 ACS/HRC ACCUM HRC-FIX F220W 4 none 4 none 1 N/A POLARIS 1 ACS/HRC ACCUM HRC-FIX F220W 4 none 5 none 1 N/A POLARIS-B 2 ACS/HRC ACCUM HRC-FIX F220W 1 none 1 none 1 N/A POLARIS-B 2 ACS/HRC ACCUM HRC-FIX F220W 1 none 2 none 1 N/A POLARIS-B 2 ACS/HRC ACCUM HRC-FIX F220W 1 none 3 none 1 N/A POLARIS-B 2 ACS/HRC ACCUM HRC-FIX F220W 1 none 4 none 1 N/A POLARIS-B 2 ACS/HRC ACCUM HRC-FIX F220W 2 none 1 none 1 N/A POLARIS-B 2 ACS/HRC ACCUM HRC-FIX F220W 2 none 2 none 1 N/A POLARIS-B 2 ACS/HRC ACCUM HRC-FIX F220W 2 none 3 none 1 N/A POLARIS-B 2 ACS/HRC ACCUM HRC-FIX F220W 2 none 4 none 1 N/A POLARIS-B 2 ACS/HRC ACCUM HRC-FIX F220W 3 none 1 none 1 N/A POLARIS-B 2 ACS/HRC ACCUM HRC-FIX F220W 3 none 2 none 1 N/A 10891( 3) - 06/12/06 09:11 - [ 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 2 ACS/HRC ACCUM HRC-FIX F220W 3 none 3 none 1 N/A POLARIS-B 2 ACS/HRC ACCUM HRC-FIX F220W 3 none 4 none 1 N/A POLARIS-B 2 ACS/HRC ACCUM HRC-FIX F220W 4 none 1 none 1 N/A POLARIS-B 2 ACS/HRC ACCUM HRC-FIX F220W 4 none 2 none 1 N/A POLARIS-B 2 ACS/HRC ACCUM HRC-FIX F220W 4 none 3 none 1 N/A POLARIS-B 2 ACS/HRC ACCUM HRC-FIX F220W 4 none 4 none 1 N/A 10891( 3) - 06/12/06 09:11 - [ 7] Summary Form for Proposal 10891 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures HRC-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/HRC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO GAIN=4 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 253.43965D TO 253.43965 D; BETWEEN 01-AUG-2006 00 00 00 AND 15-OCT-2006 00 00 00; PATTERN 1 1; PATTERN 1 2; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F220W ------------------------------------------------------------------------------------------------------------------------------------ Target Names POLARIS POLARIS-B ------------------------------------------------------------------------------------------------------------------------------------