10593( 2) - 05/09/05 07:37 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 10593 Version: 2 Check-in Date: 09-May-2005 11:36:55 1.Proposal Title: The Dynamical Mass of the Bright Cepheid Polaris ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle 4. Parallel Pointing Tolerance GO 14 ------------------------------------------------------------------------------------ 5. 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 ------------------------------------------------------------------------------------ 6. 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, there is 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. We show that the binary should be easily resolved in the UV using ACS/HRC, thus providing the first direct detection of the companion. In the present proposal we request one HST orbit in order to make this detection and measure the separation. We show that this initial detection, combined with the HST/FGS parallax (see below), will provide a mass accurate to 0.9 Msun. Only HST's combination of high spatial resolution and UV sensitivity can achieve this result. We plan to continue the program in future cycles, leading to rapid refinement of the dynamical mass measurement of the Cepheid. The parallax is a key ingredient in the mass determination. In an ongoing multi-year program (GO-9888, GO-10113), we are using the FGS to improve significantly upon the Hipparcos parallax of Polaris. The ACS imaging proposed here will thus provide extremely valuable astrophysical information from a very modest additional investment of observing time. ------------------------------------------------------------------------------------ 10593( 2) - 05/09/05 07:37 - [ 2] Observations Description ------------------------ The observations with ACS/HRC will consist of a series of 0.5-sec exposures in F220W, with dithering to improve the astrometric accuracy. 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. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 10593( 2) - 05/09/05 07:37 - [ 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" Coordinate Source: HIPPARCOS/TYCHO_CATALOGUE 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 10593( 2) - 05/09/05 07:37 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 10593( 2) - 05/09/05 07:37 - [ 5] Visit: 01 Visit Priority: Visit Requirements: SCHED 30%; BEFORE 01-SEP-2005:00:00:00 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 3 0.1 S PATTERN 1 1-4 ------------------------------------------------------------------------------------------------------------------------------------ 2 POLARIS ACS/HRC ACCUM HRC-FIX F220W CR-SPLIT=NO,GAIN=4 3 0.2 S ------------------------------------------------------------------------------------------------------------------------------------ 3 POLARIS ACS/HRC ACCUM HRC-FIX F220W CR-SPLIT=NO,GAIN=4 3 0.3 S ------------------------------------------------------------------------------------------------------------------------------------ 4 POLARIS ACS/HRC ACCUM HRC-FIX F220W CR-SPLIT=NO,GAIN=4 2 0.4 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 | ------------------------------------------------------------------------------------------------------------------------------------ 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 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 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 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 2 ACS/HRC ACCUM HRC-FIX F220W 1 none 1 none 1 N/A POLARIS 2 ACS/HRC ACCUM HRC-FIX F220W 1 none 2 none 1 N/A POLARIS 2 ACS/HRC ACCUM HRC-FIX F220W 1 none 3 none 1 N/A POLARIS 2 ACS/HRC ACCUM HRC-FIX F220W 2 none 1 none 1 N/A POLARIS 2 ACS/HRC ACCUM HRC-FIX F220W 2 none 2 none 1 N/A POLARIS 2 ACS/HRC ACCUM HRC-FIX F220W 2 none 3 none 1 N/A POLARIS 2 ACS/HRC ACCUM HRC-FIX F220W 3 none 1 none 1 N/A POLARIS 2 ACS/HRC ACCUM HRC-FIX F220W 3 none 2 none 1 N/A POLARIS 2 ACS/HRC ACCUM HRC-FIX F220W 3 none 3 none 1 N/A POLARIS 2 ACS/HRC ACCUM HRC-FIX F220W 4 none 1 none 1 N/A POLARIS 2 ACS/HRC ACCUM HRC-FIX F220W 4 none 2 none 1 N/A POLARIS 2 ACS/HRC ACCUM HRC-FIX F220W 4 none 3 none 1 N/A POLARIS 3 ACS/HRC ACCUM HRC-FIX F220W 1 none 1 none 1 N/A POLARIS 3 ACS/HRC ACCUM HRC-FIX F220W 1 none 2 none 1 N/A POLARIS 3 ACS/HRC ACCUM HRC-FIX F220W 1 none 3 none 1 N/A 10593( 2) - 05/09/05 07:37 - [ 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 3 ACS/HRC ACCUM HRC-FIX F220W 2 none 1 none 1 N/A POLARIS 3 ACS/HRC ACCUM HRC-FIX F220W 2 none 2 none 1 N/A POLARIS 3 ACS/HRC ACCUM HRC-FIX F220W 2 none 3 none 1 N/A POLARIS 3 ACS/HRC ACCUM HRC-FIX F220W 3 none 1 none 1 N/A POLARIS 3 ACS/HRC ACCUM HRC-FIX F220W 3 none 2 none 1 N/A POLARIS 3 ACS/HRC ACCUM HRC-FIX F220W 3 none 3 none 1 N/A POLARIS 3 ACS/HRC ACCUM HRC-FIX F220W 4 none 1 none 1 N/A POLARIS 3 ACS/HRC ACCUM HRC-FIX F220W 4 none 2 none 1 N/A POLARIS 3 ACS/HRC ACCUM HRC-FIX F220W 4 none 3 none 1 N/A POLARIS 4 ACS/HRC ACCUM HRC-FIX F220W 1 none 1 none 1 N/A POLARIS 4 ACS/HRC ACCUM HRC-FIX F220W 1 none 2 none 1 N/A POLARIS 4 ACS/HRC ACCUM HRC-FIX F220W 2 none 1 none 1 N/A POLARIS 4 ACS/HRC ACCUM HRC-FIX F220W 2 none 2 none 1 N/A POLARIS 4 ACS/HRC ACCUM HRC-FIX F220W 3 none 1 none 1 N/A POLARIS 4 ACS/HRC ACCUM HRC-FIX F220W 3 none 2 none 1 N/A POLARIS 4 ACS/HRC ACCUM HRC-FIX F220W 4 none 1 none 1 N/A POLARIS 4 ACS/HRC ACCUM HRC-FIX F220W 4 none 2 none 1 N/A 10593( 2) - 05/09/05 07:37 - [ 7] Summary Form for Proposal 10593 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures HRC-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/HRC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO GAIN=4 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements SCHED 30%; BEFORE 01-SEP-2005 00 00 00 PATTERN 1 1-4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F220W ------------------------------------------------------------------------------------------------------------------------------------ Target Names POLARIS ------------------------------------------------------------------------------------------------------------------------------------