10267( 4) - 12/01/04 09:21 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 10267 Version: 4 Check-in Date: 01-Dec-2004 14:20:12 1.Proposal Title: The Shadow Echoes of the Unique R Coronae Borealis Star, UW Cen ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle 4. Parallel Pointing Tolerance GO 13 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Prof. Geoffrey C. Clayton Louisiana State University & Agricultural & Mechanical College CoI: Dr. W. A. Lawson Australian Defence Force Academy N CoI: Dr. Orsola De Marco American Museum of Natural History N CoI: Dr. Don Pollacco The Queen's University of Belfast N CoI: Dr. Tracy L. Smith Space Science Institute N CoI: Dr. Florian Kerber Space Telescope - European Coordinating N Facility CoI: Dr. Ben Sugerman Space Telescope Science Institute - GC AO N CoI: Dr. Karl D. Gordon University of Arizona N CoI: Dr. Howard E. Bond Space Telescope Science Institute N ------------------------------------------------------------------------------------ 6. Abstract Understanding the R Coronae Borealis (RCB) stars is a key test for any theory aiming to explain hydrogen deficiency in post-AGB stars. The RCB stars are rare hydrogen- deficient carbon-rich supergiants that undergo very spectacular declines in brightness of up to 8 magnitudes at irregular intervals as dust forms near the star along the line of sight. UW Cen is unique among the cool RCB stars in having a visible circumstellar shell. The morphology of the nebula appears to change as different parts are illuminated by light from the central star modulated by shifting, thick dust clouds near its surface. The central star acts like a "lighthouse, " shining through gaps between the near-star dust clouds, and lighting up different portions of the outer nebula. We propose a scientific program in which a small number of observations using ACS/HRC will exploit UW Cen's unique circumstellar shell to address two critical elements in understanding RCB stars: determining an accurate distance to the star, and studying the otherwise unobservable dust clouds forming near the star's surface. We will model the images using Monte Carlo techniques to calculate the radiative transfer through arbitrary distributions of dust viewed from any angle. ------------------------------------------------------------------------------------ 10267( 4) - 12/01/04 09:21 - [ 2] Observations Description ------------------------ We propose a hybrid target-of-opportunity program with ACS/HRC. The nebula surrounding UW Cen is approximately 15" in diameter, an ideal size for the HRC. We will make good use of the smaller pixels for examining the small scale structure of the nebula, and for PSF-matching the data. The ACS/HRC will give a two pixel resolution of about 0.05". We need to use the coronographic mode to prevent excessive saturation because the central star will be V=15 or brighter during the observations. We plan to use one filter setting, F606W. The visibility of UW Cen is a maximum of 57 minutes per orbit. For our exposures we include the guide star acquisition (6.1 min), on-board target acquisition for the coronograph (3.7 min), exposure overhead including filter change, camera set-up and readout (2.5 min), and CR-SPLIT=2. The UW Cen nebula is very tenuous. The maximum surface brightness is 21-22 mag per square arcsec. We can expose for up to 45 minutes in one orbit and get a S/N per resolution element of ~14 for a surface brightness of 21mag per square arcsec. Using the coronograph with the 1.8" spot, the fraction of the central star's brightness in the PSF wings will be less than 1E-5 at 4" from the star and 2 orders of magnitude better with star subtraction. Therefore, the surface brightness of the PSF will be significantly less than the surface brightness of the nebula. We will use observations of other stars in the archive to help characterize the PSF of the coronograph. The small instabilities in the ACS coronograph will not affect this program. One visit will be made at the beginning of Cycle 13, to establish a reference image of the nebula for difference imaging. If UW Cen enters a decline up to two months prior to the end of the cycle, we will initiate a series of 4 observations, each separated by two weeks. Otherwise, that series will be taken during the last 2 months of the cycle. As noted above, this temporal spacing will constrain the distance to within a few hundred pc. Repeated imaging is also necessary to model the geometry and formation mechanisms of the inner dust clouds. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 10267( 4) - 12/01/04 09:21 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 UW-CEN STAR, IRREGULAR RA=12H43M17.1500S +/- 0.6", J2000 V = 9.5+/-6.0 VARIABLE DEC=-54D31'40.30" +/- 0.6", nebula is 21 mag per square arcsec PLATE-ID=03DP Coordinate Source: GUIDE_STAR_CATALOG Comments: V=9.5 is the maximum brightness. The declines in brightness are quite irregular. 10267( 4) - 12/01/04 09:21 - [ 4] Visit: 01 Visit Priority: Visit Requirements: BETWEEN 07-AUG-2004:12:00:00 AND 26-AUG-2004:11:59:00 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 UW-CEN ACS/HRC ACQ HRC-ACQ F555W 1 0.1 S ------------------------------------------------------------------------------------------------------------------------------------ 2 UW-CEN ACS/HRC ACCUM HRC-CORON F606W CR-SPLIT=2 1 2600 S USE OFFSET 10267A 1.8 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ UW-CEN 1 ACS/HRC ACQ HRC-ACQ F555W none none none none 1 N/A UW-CEN 2 ACS/HRC ACCUM HRC-CORO F606W none none none 1 1 N/A N1.8 UW-CEN 2 ACS/HRC ACCUM HRC-CORO F606W none none none 2 1 N/A N1.8 10267( 4) - 12/01/04 09:21 - [ 5] Visit: 02 Visit Priority: Visit Requirements: SCHED 100%; AFTER 01; ON HOLD ; ON HOLD FOR 01 On Hold Comments: TOO will be activated sometime after Visit 01 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 UW-CEN ACS/HRC ACQ HRC-ACQ F555W 1 0.1 S ------------------------------------------------------------------------------------------------------------------------------------ 2 UW-CEN ACS/HRC ACCUM HRC-CORON F606W CR-SPLIT=2 1 2300 S USE OFFSET 10267B 1.8 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ UW-CEN 1 ACS/HRC ACQ HRC-ACQ F555W none none none none 1 N/A UW-CEN 2 ACS/HRC ACCUM HRC-CORO F606W none none none 1 1 N/A N1.8 UW-CEN 2 ACS/HRC ACCUM HRC-CORO F606W none none none 2 1 N/A N1.8 10267( 4) - 12/01/04 09:21 - [ 6] Visit: 03 Visit Priority: Visit Requirements: SCHED 100%; AFTER 02; ON HOLD ; ON HOLD FOR 01 On Hold Comments: TOO will be activated sometime after Visit 01 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 UW-CEN ACS/HRC ACQ HRC-ACQ F555W 1 120 S ------------------------------------------------------------------------------------------------------------------------------------ 2 UW-CEN ACS/HRC ACCUM HRC-CORON F606W CR-SPLIT=2 1 2300 S USE OFFSET 10267C 1.8 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ UW-CEN 1 ACS/HRC ACQ HRC-ACQ F555W none none none none 1 N/A UW-CEN 2 ACS/HRC ACCUM HRC-CORO F606W none none none 1 1 N/A N1.8 UW-CEN 2 ACS/HRC ACCUM HRC-CORO F606W none none none 2 1 N/A N1.8 10267( 4) - 12/01/04 09:21 - [ 7] Visit: 04 Visit Priority: Visit Requirements: SCHED 100%; AFTER 03; ON HOLD ; ON HOLD FOR 01 On Hold Comments: TOO will be activated sometime after Visit 01 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 UW-CEN ACS/HRC ACQ HRC-ACQ F555W 1 120 S ------------------------------------------------------------------------------------------------------------------------------------ 2 UW-CEN ACS/HRC ACCUM HRC-CORON F606W CR-SPLIT=2 1 2300 S USE OFFSET 10267D 1.8 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ UW-CEN 1 ACS/HRC ACQ HRC-ACQ F555W none none none none 1 N/A UW-CEN 2 ACS/HRC ACCUM HRC-CORO F606W none none none 1 1 N/A N1.8 UW-CEN 2 ACS/HRC ACCUM HRC-CORO F606W none none none 2 1 N/A N1.8 10267( 4) - 12/01/04 09:21 - [ 8] Visit: 05 Visit Priority: Visit Requirements: SCHED 100%; AFTER 04; ON HOLD ; ON HOLD FOR 01 On Hold Comments: TOO will be activated sometime after Visit 01 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 UW-CEN ACS/HRC ACQ HRC-ACQ F555W 1 120 S ------------------------------------------------------------------------------------------------------------------------------------ 2 UW-CEN ACS/HRC ACCUM HRC-CORON F606W CR-SPLIT=2 1 2300 S USE OFFSET 10267E 1.8 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ UW-CEN 1 ACS/HRC ACQ HRC-ACQ F555W none none none none 1 N/A UW-CEN 2 ACS/HRC ACCUM HRC-CORO F606W none none none 1 1 N/A N1.8 UW-CEN 2 ACS/HRC ACCUM HRC-CORO F606W none none none 2 1 N/A N1.8 10267( 4) - 12/01/04 09:21 - [ 9] Summary Form for Proposal 10267 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures HRC-ACQ HRC-CORON1.8 ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/HRC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=2 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 07-AUG-2004 12 00 00 AND 26-AUG-2004 11 59 00 USE OFFSET 10267A SCHED 100%; AFTER 01; ON HOLD ; ON HOLD FOR 01 USE OFFSET 10267B SCHED 100%; AFTER 02; ON HOLD ; ON HOLD FOR 01 USE OFFSET 10267C SCHED 100%; AFTER 03; ON HOLD ; ON HOLD FOR 01 USE OFFSET 10267D SCHED 100%; AFTER 04; ON HOLD ; ON HOLD FOR 01 USE OFFSET 10267E ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F606W ------------------------------------------------------------------------------------------------------------------------------------ Target Names UW-CEN ------------------------------------------------------------------------------------------------------------------------------------